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Sample records for perovskite transition-metal oxides

  1. Influence of transition metal electronegativity on the oxygen storage capacity of perovskite oxides.

    PubMed

    Liu, Lu; Taylor, Daniel D; Rodriguez, Efrain E; Zachariah, Michael R

    2016-08-16

    The selection of highly efficient oxygen carriers (OCs) is a key step necessary for the practical development of chemical looping combustion (CLC). In this study, a series of ABO3 perovskites, where A = La, Ba, Sr, Ca and B = Cr, Mn, Fe, Co, Ni, Cu, are synthesized and tested in a fixed bed reactor for reactivity and stability as OCs with CH4 as the fuel. We find that the electronegativity of the transition metal on the B-site (λB), is a convenient descriptor for oxygen storage capacity (OSC) of our perovskite samples. By plotting OSC for total methane oxidation against λB, we observe an inverted volcano plot relationship. These results could provide useful guidelines for perovskite OC design and their other energy related applications. PMID:27478888

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

    DOE PAGES

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

    2015-02-19

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

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

    SciTech Connect

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

    2015-02-19

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

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

    SciTech Connect

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

    2014-05-15

    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.

  5. Transition Metal-Oxide Free Perovskite Solar Cells Enabled by a New Organic Charge Transport Layer.

    PubMed

    Chang, Sehoon; Han, Ggoch Ddeul; Weis, Jonathan G; Park, Hyoungwon; Hentz, Olivia; Zhao, Zhibo; Swager, Timothy M; Gradečak, Silvija

    2016-04-01

    Various electron and hole transport layers have been used to develop high-efficiency perovskite solar cells. To achieve low-temperature solution processing of perovskite solar cells, organic n-type materials are employed to replace the metal oxide electron transport layer (ETL). Although PCBM (phenyl-C61-butyric acid methyl ester) has been widely used for this application, its morphological instability in films (i.e., aggregation) is detrimental. Herein, we demonstrate the synthesis of a new fullerene derivative (isobenzofulvene-C60-epoxide, IBF-Ep) that serves as an electron transporting material for methylammonium mixed lead halide-based perovskite (CH3NH3PbI(3-x)Cl(x)) solar cells, both in the normal and inverted device configurations. We demonstrate that IBF-Ep has superior morphological stability compared to the conventional acceptor, PCBM. IBF-Ep provides higher photovoltaic device performance as compared to PCBM (6.9% vs 2.5% in the normal and 9.0% vs 5.3% in the inverted device configuration). Moreover, IBF-Ep devices show superior tolerance to high humidity (90%) in air. By reaching power conversion efficiencies up to 9.0% for the inverted devices with IBF-Ep as the ETL, we demonstrate the potential of this new material as an alternative to metal oxides for perovskite solar cells processed in air.

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

    PubMed

    Okamoto, Satoshi

    2013-02-01

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

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

    SciTech Connect

    Okamoto, Satoshi

    2013-01-01

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

  8. Extraction of exchange parameters in transition-metal perovskites

    DOE PAGES

    Furrer, A.; Podlesnyak, A.; Krämer, K. W.

    2015-09-15

    When extracting exchange parameters from measured spin-wave dispersion relations there are severe limitations particularly for magnetic compounds such as the transition-metal perovskites, where the nearest-neighbor exchange parameter usually dominates the couplings between the further-distant-neighbor spins. Very precise exchange parameters beyond the nearest-neighbor spins can be obtained by neutron spectroscopic investigations of the magnetic excitation spectra of isolated multimers in magnetically diluted compounds. Moreover, this is exemplified for manganese trimers in the mixed three-and two-dimensional perovskite compounds KMnxZn1-xF3 and K2MnxZn1-xF4, respectively. We show that the small exchange couplings between the second-nearest-neighbor and the third-nearest-neighbor spins can be determined unambiguously and withmore » equal precision as the dominating nearest-neighbor exchange coupling.« less

  9. Extraction of exchange parameters in transition-metal perovskites

    SciTech Connect

    Furrer, A.; Podlesnyak, A.; Krämer, K. W.

    2015-09-15

    When extracting exchange parameters from measured spin-wave dispersion relations there are severe limitations particularly for magnetic compounds such as the transition-metal perovskites, where the nearest-neighbor exchange parameter usually dominates the couplings between the further-distant-neighbor spins. Very precise exchange parameters beyond the nearest-neighbor spins can be obtained by neutron spectroscopic investigations of the magnetic excitation spectra of isolated multimers in magnetically diluted compounds. Moreover, this is exemplified for manganese trimers in the mixed three-and two-dimensional perovskite compounds KMnxZn1-xF3 and K2MnxZn1-xF4, respectively. We show that the small exchange couplings between the second-nearest-neighbor and the third-nearest-neighbor spins can be determined unambiguously and with equal precision as the dominating nearest-neighbor exchange coupling.

  10. Nanostructured transition metal oxides useful for water oxidation catalysis

    DOEpatents

    Frei, Heinz M; Jiao, Feng

    2013-12-24

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

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

    DOEpatents

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

    2013-12-24

    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.

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

    NASA Astrophysics Data System (ADS)

    Chi, Miaofang

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

  13. On the behavior of Brønsted-Evans-Polanyi relations for transition metal oxides.

    PubMed

    Vojvodic, A; Calle-Vallejo, F; Guo, W; Wang, S; Toftelund, A; Studt, F; Martínez, J I; Shen, J; Man, I C; Rossmeisl, J; Bligaard, T; Noørskov, J K; Abild-Pedersen, F

    2011-06-28

    Versatile Brønsted-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. PMID:21721645

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

    SciTech Connect

    Vojvodic, Aleksandra

    2011-08-22

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

  15. Electrolytic separation of crystals of transition-metal oxides

    NASA Technical Reports Server (NTRS)

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

    1969-01-01

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

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

    PubMed

    Oleś, Andrzej M

    2012-08-01

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

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

    SciTech Connect

    Fiete, Gregory A.; Rüegg, Andreas

    2015-05-07

    Using a combination of density functional theory, tight-binding models, and Hartree-Fock theory, we predict topological phases with and without time-reversal symmetry breaking in oxide heterostructures. We consider both heterostructures containing light transition metal ions and those containing heavy transition metal ions. We find that the (111) growth direction naturally leads to favorable conditions for topological phases in both perovskite structures and pyrochlore structures. For the case of light transition metal elements, Hartree-Fock theory predicts the spin-orbit coupling is effectively enhanced by on-site multiple-orbital interactions and may drive the system through a topological phase transition, while heavy elements with intrinsically large spin-orbit coupling require much weaker or even vanishing electron interactions to bring about a topological phase.

  18. Electrocatalytic Activity of Transition Metal Oxide-Carbon Composites for Oxygen Reduction in Alkaline Batteries and Fuel Cells

    SciTech Connect

    Malkhandi, S; Trinh, P; Manohar, AK; Jayachandrababu, KC; Kindler, A; Prakash, GKS; Narayanan, SR

    2013-06-07

    Conductive transition metal oxides (perovskites, spinels and pyrochlores) are attractive as catalysts for the air electrode in alkaline rechargeable metal-air batteries and fuel cells. We have found that conductive carbon materials when added to transition metal oxides such as calcium-doped lanthanum cobalt oxide, nickel cobalt oxide and calcium-doped lanthanum manganese cobalt oxide increase the electrocatalytic activity of the oxide for oxygen reduction by a factor of five to ten. We have studied rotating ring-disk electrodes coated with (a) various mass ratios of carbon and transition metal oxide, (b) different types of carbon additives and (c) different types of transition metal oxides. Our experiments and analysis establish that in such composite catalysts, carbon is the primary electro- catalyst for the two-electron electro-reduction of oxygen to hydroperoxide while the transition metal oxide decomposes the hydroperoxide to generate additional oxygen that enhances the observed current resulting in an apparent four-electron process. These findings are significant in that they change the way we interpret previous reports in the scientific literature on the electrocatalytic activity of various transition metal oxide- carbon composites for oxygen reduction, especially where carbon is assumed to be an additive that just enhances the electronic conductivity of the oxide catalyst. (C) 2013 The Electrochemical Society. All rights reserved.

  19. Electronic entanglement in late transition metal oxides.

    PubMed

    Thunström, Patrik; Di Marco, Igor; Eriksson, Olle

    2012-11-01

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

  20. Impurity diffusion in transition-metal oxides

    SciTech Connect

    Peterson, N.L.

    1982-06-01

    Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe/sub 3/O/sub 4/. Tracer impurity diffusion in these materials and TiO/sub 2/, together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate size impurity) diffuse rapidly along the open channels parallel to the c-axis in TiO/sub 2/ whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures.

  1. Optical properties of transition metal oxide quantum wells

    SciTech Connect

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

    2015-01-21

    Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO{sub 3}/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

  2. Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

    DOE PAGES

    Krogel, Jaron T.; Santana Palacio, Juan A.; Reboredo, Fernando A.

    2016-02-22

    Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentialsmore » to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.« less

  3. Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Krogel, Jaron T.; Santana, Juan A.; Reboredo, Fernando A.

    2016-02-01

    Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentials to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results also compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.

  4. Electrocatalysis using transition metal carbide and oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Regmi, Yagya N.

    Carbides are one of the several families of transition metal compounds that are considered economic alternatives to catalysts based on noble metals and their compounds. Phase pure transition metal carbides of group 4-6 metals, in the first three periods, were synthesized using a common eutectic salt flux synthesis method, and their electrocatalytic activities compared under uniform electrochemical conditions. Mo2C showed highest hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) activities among the nine metal carbides investigated, but all other metal carbides also showed substantial activities. All the metal carbides showed remarkable enhancement in catalytic activities as supports, when compared to traditional graphitic carbon as platinum support. Mo2C, the most active transition metal carbide electrocatalyst, was prepared using four different synthesis routes, and the synthesis route dependent activities compared. Bifunctional Mo 2C that is HER as well as oxygen evolution reaction (OER) active, was achieved when the carbide was templated on a multiwalled carbon nanotube using carbothermic reduction method. Bimetallic carbides of Fe, Co, and Ni with Mo or W were prepared using a common carbothermic reduction method. Two different stoichiometries of bimetallic carbides were obtained for each system within a 60 °C temperature window. While the bimetallic carbides showed relatively lower electrocatalytic activities towards HER and ORR in comparison to Mo2C and WC, they revealed remarkably higher OER activities than IrO2 and RuO2, the state-of-the-art OER catalysts. Bimetallic oxides of Fe, Co, and Ni with Mo and W were also prepared using a hydrothermal synthesis method and they also revealed OER activities that are much higher than RuO2 and IrO2. Additionally, the OER activities were dependent on the degree and nature of hydration in the bimetallic oxide crystal lattice, with the completely hydrated, as synthesized, cobalt molybdate and nickel

  5. Tuning the work function in transition metal oxides and their heterostructures

    NASA Astrophysics Data System (ADS)

    Zhong, Z.; Hansmann, P.

    2016-06-01

    The development of novel functional materials in experimental labs combined with computer-based compound simulation brings the vision of materials design on a microscopic scale continuously closer to reality. For many applications interface and surface phenomena rather than bulk properties are key. One of the most fundamental qualities of a material-vacuum interface is the energy required to transfer an electron across this boundary, i.e., the work function. It is a crucial parameter for numerous applications, including organic electronics, field electron emitters, and thermionic energy converters. Being generally very resistant to degradation at high temperatures, transition metal oxides present a promising materials class for such devices. We have performed a systematic study for perovskite oxides that provides reference values and, equally important, reports on materials trends and the tunability of work functions. Our results identify and classify dependencies of the work function on several parameters including specific surface termination, surface reconstructions, oxygen vacancies, and heterostructuring.

  6. Transition metal oxide as anode interface buffer for impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Hui; Tang, Chao; Wang, Xu-Liang; Zhai, Wen-Juan; Liu, Rui-Lan; Rong, Zhou; Pang, Zong-Qiang; Jiang, Bing; Fan, Qu-Li; Huang, Wei

    2015-12-01

    Impedance spectroscopy is a strong method in electric measurement, which also shows powerful function in research of carrier dynamics in organic semiconductors when suitable mathematical physical models are used. Apart from this, another requirement is that the contact interface between the electrode and materials should at least be quasi-ohmic contact. So in this report, three different transitional metal oxides, V2O5, MoO3 and WO3 were used as hole injection buffer for interface of ITO/NPB. Through the impedance spectroscopy and PSO algorithm, the carrier mobilities and I-V characteristics of the NPB in different devices were measured. Then the data curves were compared with the single layer device without the interface layer in order to investigate the influence of transitional metal oxides on the carrier mobility. The careful research showed that when the work function (WF) of the buffer material was just between the work function of anode and the HOMO of the organic material, such interface material could work as a good bridge for carrier injection. Under such condition, the carrier mobility measured through impedance spectroscopy should be close to the intrinsic value. Considering that the HOMO (or LUMO) of most organic semiconductors did not match with the work function of the electrode, this report also provides a method for wide application of impedance spectroscopy to the research of carrier dynamics.

  7. Nanostructured transition metal oxides for energy storage and conversion

    NASA Astrophysics Data System (ADS)

    Li, Qiang

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

  8. Interface of transition metal oxides at the atomic scale

    NASA Astrophysics Data System (ADS)

    Shang, Tong-Tong; Liu, Xin-Yu; Gu, Lin

    2016-09-01

    Remarkable phenomena arise at well-defined heterostructures, composed of transition metal oxides, which is absent in the bulk counterpart, providing us a paradigm for exploring the various electron correlation effects. The functional properties of such heterostructures have attracted much attention in the microelectronic and renewable energy fields. Exotic and unexpected states of matter could arise from the reconstruction and coupling among lattice, charge, orbital and spin at the interfaces. Aberration-corrected scanning transmission electron microscopy (STEM) is a powerful tool to visualize the lattice structure and electronic structure at the atomic scale. In the present study some novel phenomena of oxide heterostructures at the atomic scale are summarized and pointed out from the perspective of electron microscopy.

  9. Transition Metal Oxide Alloys as Potential Solar Energy Conversion Materials

    SciTech Connect

    Toroker, Maytal; Carter, Emily A.

    2013-02-21

    First-row transition metal oxides (TMOs) are inexpensive potentia alternative materials for solar energy conversion devices. However, some TMOs, such as manganese(II) oxide, have band gaps that are too large for efficiently absorbing solar energy. Other TMOs, such as iron(II) oxide, have conduction and valence band edges with the same orbital character that may lead to unfavorably high electron–hole recombination rates. Another limitation of iron(II) oxide is that the calculated valence band edge is not positioned well for oxidizing water. We predict that key properties, including band gaps, band edge positions, and possibly electron–hole recombination rates, may be improved by alloying TMOs that have different band alignments. A new metric, the band gap center offset, is introduced for simple screening of potential parent materials. The concept is illustrated by calculating the electronic structure of binary oxide alloys that contain manganese, nickel, iron, zinc, and/or magnesium, within density functional theory (DFT)+U and hybrid DFT theories. We conclude that alloys of iron(II) oxide are worth evaluating further as solar energy conversion materials.

  10. Resonant Ultrasound Studies of Complex Transition Metal Oxides

    SciTech Connect

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

    2008-08-18

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

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

    SciTech Connect

    Xiao, Di; Zhu, Wenguang; Ran, Ying; Nagaosa, Naoto; Okamoto, Satoshi

    2011-01-01

    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.

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

    PubMed

    Xiao, Di; Zhu, Wenguang; Ran, Ying; Nagaosa, Naoto; Okamoto, Satoshi

    2011-01-01

    Topological insulators are characterized by a non-trivial band topology driven by the spin-orbit coupling. To fully explore the fundamental science and application of topological insulators, material realization is indispensable. Here we predict, based on tight-binding modelling and first-principles calculations, that bilayers of perovskite-type transition-metal oxides grown along the [111] crystallographic axis are potential candidates for two-dimensional topological insulators. 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.

  13. Ionically-mediated electromechanical hysteresis in transition metal oxides.

    PubMed

    Kim, Yunseok; Morozovska, Anna N; Kumar, Amit; Jesse, Stephen; Eliseev, Eugene A; Alibart, Fabien; Strukov, Dmitri; Kalinin, Sergei V

    2012-08-28

    Nanoscale electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO(2) and SrTiO(3) thin films are observed using scanning probe microscopy. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Landau-Ginzburg-Devonshire (LGD) 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 LGD expansion coefficient, rendering material effectively ferroelectric. The lifetime of these ionically induced ferroelectric states is then controlled by the transport time of the mobile ionic species and well above that of polarization switching. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.

  14. Are Magnetically Doped Transition-metal Oxides Spin-glasses?

    NASA Astrophysics Data System (ADS)

    Lussier, A.; Dvorak, J.; Idzerda, Y. U.; Ogale, S. B.; Shinde, S. R.; Venkatesan, T.; Lofland, S. E.

    2004-03-01

    Many magnetic impurity doped transition-metal oxides exhibit ferromagnetism at room temperature. Some also exhibit strange magnetic aging behavior. One such material is Co-doped SnO2 which displays a saturation magnetization decrease over time, as well as with successive field applications. From the theoretical perspective, there are two prerequisites for spin-glass behavior which are both satisfied for these samples: disorder and frustration. Disorder is readily satisfied because the dilute magnetic impurities are randomly scattered. Additionally, the suggested RKKY interaction between magnetic impurities, coupled with their random spacing, likely results in frustration. Magnetometry, XAS, and XMCD measurements, with temperature, measurement time, and history dependence help elucidate the magnetic order in these materials, and are consistent with spin-glass character. We would like to acknowledge the support of NSF (MSU), the Office of Naval Research (MSU), DARPA SpinS (UMD) and NSF-MRSEC (UMD).

  15. Topological and unconventional magnetic states in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Fiete, Gregory

    In this talk I describe some recent work on unusual correlated phases that may be found in bulk transition metal oxides with strong spin-orbit coupling. I will focus on model Hamiltonian studies that are motivated by the pyrocholore iridates, though the correlated topological phases described may appear in a much broader class of materials. I will describe a variety of fractionalized topological phases protected by time-reversal and crystalline symmetries: The weak topological Mott insulator (WTMI), the TI* phase, and the topological crystalline Mott insulator (TCMI). If time permits, I will also discuss closely related heterostructures of pyrochlore iridates in a bilayer and trilayer film geometry. These quasi-two dimensional systems may exhibit a number of interesting topological and magnetic phases. This work is generously funded by the ARO, DARPA, and the NSF.

  16. Transition metal oxide hierarchical nanotubes for energy applications.

    PubMed

    Wei, Wei; Wang, Yongcheng; Wu, Hao; Al-Enizi, Abdullah M; Zhang, Lijuan; Zheng, Gengfeng

    2016-01-15

    We report a general synthetic method for transition metal oxide (TMO) hierarchical nanotube (HNT) structures by a solution-phase cation exchange method from Cu2O nanowire templates. This method leads to the formation of hollow, tubular backbones with secondary, thin nanostructures on the tube surface, which substantially increases the surface reactive sites for electrolyte contacts and electrochemical reactions. As proofs-of-concept, several representative first-row TMO HNTs have been synthesized, including CoOx, NiOx, MnOx, ZnOx and FeOx, with specific surface areas much larger than nanotubes or nanoparticles of corresponding materials. An example of the potential energy storage applications of CoOx HNTs as supercapacitors is also demonstrated. PMID:26629880

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

    NASA Astrophysics Data System (ADS)

    Quan, Yundi; Pickett, Warren

    2015-03-01

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

  18. Electronic, magnetic and topological properties of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Quan, Yundi

    Transition metal oxides have been the ideal platform for designing materials with exotic properties due to the complex interplay between spin, charge, and orbital degrees of freedom which can be fine-tuned by varying pressure, temperature, and external magnetic field to give rise to novel phases. Transition metal oxides are also a challenge from the theoretical point of view. The (semi)local density approximation for the exchange correlation functional that is often used in density functional calculations fails to adequately describe the many-body effects of 3d and 4f electrons thereby leading to underestimated band gaps. Several techniques, such as hybrid functionals, dynamical mean field theory, and DFT+U, have been developed over the past few decades to account for the many-body effects of 3d and 4f electrons. The DFT+U method, which will be used extensively throughout this thesis, has proved to be very successful in modeling gap opening, structure optimization and predicting transport properties. Rare earth nickelates have attracted a lot of attention in recent years due to their complex phase diagram that arises from the competition between spin, charge, and orbital degrees of freedom. Of particular interest is the metal-insulator transition that occurs upon cooling for RNiO3 (R=rare earth, except for La) which was found to be accompanied by symmetry lowering, later theorized as the evidence for charge ordering. By using first principles calculations, we found that the charge difference between Ni ions in the "charge-ordered" phase is negligibly small, while various aspects such as core energy levels, spectral weight immediately above and below the Fermi level, and magnetic moments do differ. Using Wannier function analysis, the charge states of Ni ions in the lower symmetry structure are systematically studied and found to correlated to the number of Wannier charge centers at the Ni site. The same approach was applied to study the charge states of Ag I and Ag

  19. APCVD Transition Metal Oxides - Functional Layers in "Smart windows"

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  20. Transition-Metal Oxides in Warm Circumstellar Environments

    NASA Astrophysics Data System (ADS)

    Schmidt, Mirosław R.; Kaminski, Tomasz; Tylenda, Romuald

    2013-06-01

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

  1. Resistance switching memory in perovskite oxides

    SciTech Connect

    Yan, Z.B. Liu, J.-M.

    2015-07-15

    The resistance switching behavior has recently attracted great attentions for its application as resistive random access memories (RRAMs) due to a variety of advantages such as simple structure, high-density, high-speed and low-power. As a leading storage media, the transition metal perovskite oxide owns the strong correlation of electrons and the stable crystal structure, which brings out multifunctionality such as ferroelectric, multiferroic, superconductor, and colossal magnetoresistance/electroresistance effect, etc. The existence of rich electronic phases, metal–insulator transition and the nonstoichiometric oxygen in perovskite oxide provides good platforms to insight into the resistive switching mechanisms. In this review, we first introduce the general characteristics of the resistance switching effects, the operation methods and the storage media. Then, the experimental evidences of conductive filaments, the transport and switching mechanisms, and the memory performances and enhancing methods of perovskite oxide based filamentary RRAM cells have been summarized and discussed. Subsequently, the switching mechanisms and the performances of the uniform RRAM cells associating with the carrier trapping/detrapping and the ferroelectric polarization switching have been discussed. Finally, the advices and outlook for further investigating the resistance switching and enhancing the memory performances are given.

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

    PubMed

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

    2001-10-21

    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.

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

    NASA Astrophysics Data System (ADS)

    Vaugier, Loïg; Jiang, Hong; Biermann, Silke

    2012-10-01

    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.

  4. Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems.

    PubMed

    Park, Min-Sik; Kim, Jeonghun; Kim, Ki Jae; Lee, Jong-Won; Kim, Jung Ho; Yamauchi, Yusuke

    2015-12-14

    Transition metal oxides possessing two kinds of metals (denoted as AxB3-xO4, which is generally defined as a spinel structure; A, B = Co, Ni, Zn, Mn, Fe, etc.), with stoichiometric or even non-stoichiometric compositions, have recently attracted great interest in electrochemical energy storage systems (ESSs). The spinel-type transition metal oxides exhibit outstanding electrochemical activity and stability, and thus, they can play a key role in realising cost-effective and environmentally friendly ESSs. Moreover, porous nanoarchitectures can offer a large number of electrochemically active sites and, at the same time, facilitate transport of charge carriers (electrons and ions) during energy storage reactions. In the design of spinel-type transition metal oxides for energy storage applications, therefore, nanostructural engineering is one of the most essential approaches to achieving high electrochemical performance in ESSs. In this perspective, we introduce spinel-type transition metal oxides with various transition metals and present recent research advances in material design of spinel-type transition metal oxides with tunable architectures (shape, porosity, and size) and compositions on the micro- and nano-scale. Furthermore, their technological applications as electrode materials for next-generation ESSs, including metal-air batteries, lithium-ion batteries, and supercapacitors, are discussed.

  5. Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems.

    PubMed

    Park, Min-Sik; Kim, Jeonghun; Kim, Ki Jae; Lee, Jong-Won; Kim, Jung Ho; Yamauchi, Yusuke

    2015-12-14

    Transition metal oxides possessing two kinds of metals (denoted as AxB3-xO4, which is generally defined as a spinel structure; A, B = Co, Ni, Zn, Mn, Fe, etc.), with stoichiometric or even non-stoichiometric compositions, have recently attracted great interest in electrochemical energy storage systems (ESSs). The spinel-type transition metal oxides exhibit outstanding electrochemical activity and stability, and thus, they can play a key role in realising cost-effective and environmentally friendly ESSs. Moreover, porous nanoarchitectures can offer a large number of electrochemically active sites and, at the same time, facilitate transport of charge carriers (electrons and ions) during energy storage reactions. In the design of spinel-type transition metal oxides for energy storage applications, therefore, nanostructural engineering is one of the most essential approaches to achieving high electrochemical performance in ESSs. In this perspective, we introduce spinel-type transition metal oxides with various transition metals and present recent research advances in material design of spinel-type transition metal oxides with tunable architectures (shape, porosity, and size) and compositions on the micro- and nano-scale. Furthermore, their technological applications as electrode materials for next-generation ESSs, including metal-air batteries, lithium-ion batteries, and supercapacitors, are discussed. PMID:26549729

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

    SciTech Connect

    Ogihara, Hitoshi; Masahiro, Sadakane; Nodasaka, Yoshinobu; Ueda, Wataru

    2009-06-15

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

  7. A-site ordered quadruple perovskite oxides

    NASA Astrophysics Data System (ADS)

    Youwen, Long

    2016-07-01

    The A-site ordered perovskite oxides with chemical formula display many intriguing physical properties due to the introduction of transition metals at both A‧ and B sites. Here, research on the recently discovered intermetallic charge transfer occurring between A‧-site Cu and B-site Fe ions in LaCu3Fe4O12 and its analogues is reviewed, along with work on the magnetoelectric multiferroicity observed in LaMn3Cr4O12 with cubic perovskite structure. The Cu-Fe intermetallic charge transfer leads to a first-order isostructural phase transition accompanied by drastic variations in magnetism and electrical transport properties. The LaMn3Cr4O12 is a novel spin-driven multiferroic system with strong magnetoelectric coupling effects. The compound is the first example of cubic perovskite multiferroics to be found. It opens up a new arena for studying unexpected multiferroic mechanisms. Project supported by the National Basic Research Program of China (Grant No. 2014CB921500), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB07030300), and the National Natural Science Foundation of China (Grant No. 11574378).

  8. Aberration-corrected scanning transmission electron microscopy for complex transition metal oxides

    NASA Astrophysics Data System (ADS)

    Qing-Hua, Zhang; Dong-Dong, Xiao; Lin, Gu

    2016-06-01

    Lattice, charge, orbital, and spin are the four fundamental degrees of freedom in condensed matter, of which the interactive coupling derives tremendous novel physical phenomena, such as high-temperature superconductivity (high-T c SC) and colossal magnetoresistance (CMR) in strongly correlated electronic system. Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it, and also indispensable for designing new materials and devices. Scanning transmission electron microscopy (STEM) integrating multiple techniques of structure imaging and spectrum analysis, is a comprehensive platform for providing structural, chemical and electronic information of materials with a high spatial resolution. Benefiting from the development of aberration correctors, STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization; many improvements have been achieved in recent years, thereby giving an in-depth insight into material research. Here, we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides; atomic-scale mapping of ferroelectric polarization, octahedral distortions and rotations, valence state, coordination and spin ordering are presented. We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides. Project supported by the National Key Basic Research Project, China (Grant No. 2014CB921002), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB07030200), and the National Natural Science Foundation of China (Grant Nos. 51522212 and 51421002).

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  10. Compositional dependence of elastic moduli for transition-metal oxide spinels

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

  11. In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation.

    PubMed

    Chen, Wei; Wang, Haotian; Li, Yuzhang; Liu, Yayuan; Sun, Jie; Lee, Sanghan; Lee, Jang-Soo; Cui, Yi

    2015-08-26

    The development of catalysts with earth-abundant elements for efficient oxygen evolution reactions is of paramount significance for clean and sustainable energy storage and conversion devices. Our group demonstrated recently that the electrochemical tuning of catalysts via lithium insertion and extraction has emerged as a powerful approach to improve catalytic activity. Here we report a novel in situ electrochemical oxidation tuning approach to develop a series of binary, ternary, and quaternary transition metal (e.g., Co, Ni, Fe) oxides from their corresponding sulfides as highly active catalysts for much enhanced water oxidation. The electrochemically tuned cobalt-nickel-iron oxides grown directly on the three-dimensional carbon fiber electrodes exhibit a low overpotential of 232 mV at current density of 10 mA cm(-2), small Tafel slope of 37.6 mV dec(-1), and exceptional long-term stability of electrolysis for over 100 h in 1 M KOH alkaline medium, superior to most non-noble oxygen evolution catalysts reported so far. The materials evolution associated with the electrochemical oxidation tuning is systematically investigated by various characterizations, manifesting that the improved activities are attributed to the significant grain size reduction and increase of surface area and electroactive sites. This work provides a promising strategy to develop electrocatalysts for large-scale water-splitting systems and many other applications. PMID:27162978

  12. In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation

    PubMed Central

    2015-01-01

    The development of catalysts with earth-abundant elements for efficient oxygen evolution reactions is of paramount significance for clean and sustainable energy storage and conversion devices. Our group demonstrated recently that the electrochemical tuning of catalysts via lithium insertion and extraction has emerged as a powerful approach to improve catalytic activity. Here we report a novel in situ electrochemical oxidation tuning approach to develop a series of binary, ternary, and quaternary transition metal (e.g., Co, Ni, Fe) oxides from their corresponding sulfides as highly active catalysts for much enhanced water oxidation. The electrochemically tuned cobalt–nickel–iron oxides grown directly on the three-dimensional carbon fiber electrodes exhibit a low overpotential of 232 mV at current density of 10 mA cm–2, small Tafel slope of 37.6 mV dec–1, and exceptional long-term stability of electrolysis for over 100 h in 1 M KOH alkaline medium, superior to most non-noble oxygen evolution catalysts reported so far. The materials evolution associated with the electrochemical oxidation tuning is systematically investigated by various characterizations, manifesting that the improved activities are attributed to the significant grain size reduction and increase of surface area and electroactive sites. This work provides a promising strategy to develop electrocatalysts for large-scale water-splitting systems and many other applications. PMID:27162978

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

    SciTech Connect

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

    2008-06-01

    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.

  14. An Ultrahigh-Performance Photodetector based on a Perovskite-Transition-Metal-Dichalcogenide Hybrid Structure.

    PubMed

    Kang, Dong-Ho; Pae, Seong Ryul; Shim, Jaewoo; Yoo, Gwangwe; Jeon, Jaeho; Leem, Jung Woo; Yu, Jae Su; Lee, Sungjoo; Shin, Byungha; Park, Jin-Hong

    2016-09-01

    An ultrahigh performance MoS2 photodetector with high photoresponsivity (1.94 × 10(6) A W(-1) ) and detectivity (1.29 × 10(12) Jones) under 520 nm and 4.63 pW laser exposure is demonstrated. This photodetector is based on a methyl-ammonium lead halide perovskite/MoS2 hybrid structure with (3-aminopropyl)triethoxysilane doping. The performance degradation caused by moisture is also minimized down to 20% by adopting a new encapsulation bilayer of octadecyltrichlorosilane/polymethyl methacrylate.

  15. Perovskite oxides: Oxygen electrocatalysis and bulk structure

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    SciTech Connect

    S.E. Ziemniak

    2000-05-18

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

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

    PubMed Central

    2015-01-01

    The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the σ and π bonds of the graphene oxide and graphene oxide–metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graphene oxide with the metal oxide nanostructures has not altered the electronic structure of either of them. As the restoration of the π network is important for good electrical conductivity, the C K edge NEXAFS spectra of reduced graphene oxide nanocomposites confirms the same through increased intensity of the sp2-derived unoccupied states π* band. A pronounced angular dependency of the reduced sample and the formation of excitonic peaks confirmed the formation of extended conjugated network. PMID:25152800

  18. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation

    PubMed Central

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-01-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation. PMID:27030159

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

    NASA Astrophysics Data System (ADS)

    Sithambaram, Shanthakumar

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

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

    SciTech Connect

    Ngaruiya, J.M.; Kappertz, O.; Mohamed, S.H.; Wuttig, M.

    2004-08-02

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

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

    PubMed

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

    2014-04-01

    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

  2. Perovskite catalysts for oxidative coupling

    DOEpatents

    Campbell, K.D.

    1991-06-25

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

  3. Perovskite catalysts for oxidative coupling

    DOEpatents

    Campbell, Kenneth D.

    1991-01-01

    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.

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

    PubMed Central

    2012-01-01

    Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 − ySry)0.45MnO3 (y = 0.25), SrTiO3, and Ti1 − xCoxO2 (x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons. PMID:23092248

  5. Coupling between crystal structure and magnetism in transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Barton, Phillip Thomas

    Transition-metal oxides exhibit a fascinating array of phenomena ranging from superconductivity to negative thermal expansion to catalysis. This dissertation focuses on magnetism, which is integral to engineering applications such as data storage, electric motors/generators, and transformers. The investigative approach follows structure-property relationships from materials science and draws on intuition from solid-state chemistry. The interplay between crystal structure and magnetic properties is studied experimentally in order to enhance the understanding of magnetostructural coupling mechanisms and provide insight into avenues for tuning behavior. A combination of diffraction and physical property measurements were used to study structural and magnetic phase transitions as a function of chemical composition, temperature, and magnetic field. The systems examined are of importance in Li-ion battery electrochemistry, condensed-matter physics, solid-state chemistry, and p-type transparent conducting oxides. The materials were prepared by solid-state reaction of powder reagents at high temperatures for periods lasting tens of hours. The first project discussed is of a solid solution between NiO, a correlated insulator, and LiNiO2, a layered battery cathode. Despite the deceptive structural and compositional simplicity of this system, a complete understanding of its complex magnetic properties has remained elusive. This study shows that nanoscale domains of chemical order form at intermediate compositions, creating interfaces between antiferromagnetism and ferrimagnetism that give rise to magnetic exchange bias. A simple model of the magnetism is presented along with a comprehensive phase diagram. The second set of investigations focus on the Ge-Co-O system where the spin-orbit coupling of Co(II) plays a significant role. GeCo2O 4 is reported to exhibit unusual magnetic behavior that arises from Ising spin in its spinel crystal structure. Studies by variable

  6. Optical properties of transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

    Demkov, Alexander; Choi, Miri; Butcher, Matthew; Rodriguez, Cesar; He, Qian; Posadas, Agham; Borisevich, Albina; Zollner, Stefan; Lin, Chungwei; Ortmann, Elliott

    2015-03-01

    We report on the investigation of SrTiO3/LaAlO3 quantum wells (QWs) grown by molecular beam epitaxy (MBE) on LaAlO3 substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized using x-ray photoemission spectroscopy, reflection high-energy electron diffraction (RHEED), scanning transmission electron microscopy (STEM). Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry (SE) in the range of 1.0 eV to 6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells (uc). Density functional theory and tight-binding are used to model the optical response of these heterostructures. Our results demonstrate that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material. We acknowledge support from Air Force Office of Scientific Research (FA9550-12-10494).

  7. Influence of Surface Morphology on the Antimicrobial Effect of Transition Metal Oxides in Polymer Surface.

    PubMed

    Oh, Yoo Jin; Hubauer-Brenner, Michael; Hinterdorfer, Peter

    2015-10-01

    In this study, the physical properties of transition metal oxide surfaces were examined using scanning probe microscopic (SPM) techniques for elucidating the antimicrobial activity of molybdenum trioxide (MoO3), tungsten trioxide (WO3), and zinc oxide (ZnO) embedded into the polymers thermoplastic polyurethane (TPU) and polypropylene (PP). We utilized atomic force microscopy (AFM) in the contact imaging mode and its derivative single-pass Kelvin probe force microscopy for investigating samples that were presumably identical in their compositions, but showed different antimicrobial activity in bacterial adhesion tests. Our results revealed that surfaces with larger roughness and higher surface potential variation showed stronger antimicrobial activities compared to smoother and homogeneously charge-distributed surfaces. In addition, capacitance gradient (dC/dZ) measurements were performed to elucidate the antimicrobial activity arising from the different dielectric behavior of the transition metal oxides in this heterogeneous polymer surface. We found that the nano-scale exposure of transition metal oxides on polymer surfaces provided strong antimicrobial effects. Applications arising from our studies will be useful for public and healthcare environments.

  8. Influence of Surface Morphology on the Antimicrobial Effect of Transition Metal Oxides in Polymer Surface.

    PubMed

    Oh, Yoo Jin; Hubauer-Brenner, Michael; Hinterdorfer, Peter

    2015-10-01

    In this study, the physical properties of transition metal oxide surfaces were examined using scanning probe microscopic (SPM) techniques for elucidating the antimicrobial activity of molybdenum trioxide (MoO3), tungsten trioxide (WO3), and zinc oxide (ZnO) embedded into the polymers thermoplastic polyurethane (TPU) and polypropylene (PP). We utilized atomic force microscopy (AFM) in the contact imaging mode and its derivative single-pass Kelvin probe force microscopy for investigating samples that were presumably identical in their compositions, but showed different antimicrobial activity in bacterial adhesion tests. Our results revealed that surfaces with larger roughness and higher surface potential variation showed stronger antimicrobial activities compared to smoother and homogeneously charge-distributed surfaces. In addition, capacitance gradient (dC/dZ) measurements were performed to elucidate the antimicrobial activity arising from the different dielectric behavior of the transition metal oxides in this heterogeneous polymer surface. We found that the nano-scale exposure of transition metal oxides on polymer surfaces provided strong antimicrobial effects. Applications arising from our studies will be useful for public and healthcare environments. PMID:26726428

  9. Nanostructure sensitization of transition metal oxides for visible-light photocatalysis

    PubMed Central

    Chen, Hongjun

    2014-01-01

    Summary To better utilize the sunlight for efficient solar energy conversion, the research on visible-light active photocatalysts has recently attracted a lot of interest. The photosensitization of transition metal oxides is a promising approach for achieving effective visible-light photocatalysis. This review article primarily discusses the recent progress in the realm of a variety of nanostructured photosensitizers such as quantum dots, plasmonic metal nanostructures, and carbon nanostructures for coupling with wide-bandgap transition metal oxides to design better visible-light active photocatalysts. The underlying mechanisms of the composite photocatalysts, e.g., the light-induced charge separation and the subsequent visible-light photocatalytic reaction processes in environmental remediation and solar fuel generation fields, are also introduced. A brief outlook on the nanostructure photosensitization is also given. PMID:24991507

  10. Transition-metal-free direct alkylation of aryl tetrazoles via intermolecular oxidative C-N formation.

    PubMed

    Wang, Liang; Zhu, Kaiqiang; Chen, Qun; He, Mingyang

    2014-12-01

    A transition-metal-free synthetic approach for constructing alkylated aryl tetrazoles has been developed using n-Bu4NI as the catalyst and t-BuOOH as the oxidant. It involves the direct C-N bond formation through sp(3) C-H activation. A wide range of benzylic C-H substrates (or alkyl ethers) and aryl tetrazoles undergo this reaction smoothly to deliver the corresponding products in good yields.

  11. Evaluation of transition metal oxide as carrier-selective contacts for silicon heterojunction solar cells

    SciTech Connect

    Ding, L.; Boccard, Matthieu; Holman, Zachary; Bertoni, M.

    2015-04-06

    "Reducing light absorption in the non-active solar cell layers, while enabling the extraction of the photogenerated minority carriers at quasi-Fermi levels are two key factors to improve current generation and voltage, and therefore efficiency of silicon heterojunction solar devices. To address these two critical aspects, transition metal oxide materials have been proposed as alternative to the n- and p-type amorphous silicon used as electron and hole selective contacts, respectively. Indeed, transition metal oxides such as molybdenum oxide, titanium oxide, nickel oxide or tungsten oxide combine a wide band gap typically over 3 eV with a band structure and theoretical band alignment with silicon that results in high transparency to the solar spectrum and in selectivity for the transport of only one carrier type. Improving carrier extraction or injection using transition metal oxide has been a topic of investigation in the field of organic solar cells and organic LEDs; from these pioneering works a lot of knowledge has been gained on materials properties, ways to control these during synthesis and deposition, and their impact on device performance. Recently, the transfer of some of this knowledge to silicon solar cells and the successful application of some metal oxide to contact heterojunction devices have gained much attention. In this contribution, we investigate the suitability of various transition metal oxide films (molybdenum oxide, titanium oxide, and tungsten oxide) deposited either by thermal evaporation or sputtering as transparent hole or electron selective transport layer for silicon solar cells. In addition to systematically characterize their optical and structural properties, we use photoemission spectroscopy to relate compound stoichiometry to band structure and characterize band alignment to silicon. The direct silicon/metal oxide interface is further analyzed by quasi-steady state photoconductance decay method to assess the quality of surface

  12. Which orbital and charge ordering in transition metal oxides can resonant X-ray diffraction detect?

    NASA Astrophysics Data System (ADS)

    Di Matteo, Sergio

    2009-11-01

    The present article is a brief critical review about the possibility of detecting charge and/or orbital order in transition-metal oxides by means of resonant x-ray diffraction. Many recent models of transition-metal oxides are based on charge and/or orbitally ordered ground-states and it has been claimed in the past that resonant x-ray diffraction is able to confirm or reject them. However, in spite of the many merits of this technique, such claims are ambiguous, because the interpretative frameworks used to analyze such results in transition-metal oxides, where structural distortions are always associated to the claimed charged/orbitally ordered transition, strongly influence (not to say suggest) the answer. In order to clarify this point, I discuss the two different definitions of orbital and charge orderings which are often used in the literature without a clear distinction. My conclusion is that the answer to the question of the title depends on which definition is adopted.

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

    SciTech Connect

    Guan Jie; Wang Yao; Qin Minglei; Yang Ying; Li Xiang; Wang Anjie

    2009-06-15

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

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

    SciTech Connect

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

    1996-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  16. Effect of UV exposure on photochromic glasses doped with transition metal oxides

    NASA Astrophysics Data System (ADS)

    El-Zaiat, S. Y.; Medhat, M.; Omar, Mona F.; Shirif, Marwa A.

    2016-07-01

    Silver halide photochromic glasses doped with one of the transition metal oxides, (Ti O2), (CoO),(Cr2 O3) are prepared using the melt quench technique. Glass samples are exposed to a UV source for 20 min. Spectral reflectance and transmittance at normal incidence of the prepared glasses are recorded before and after UV exposure with a double beam spectrophotometer in the spectral range 200-2500 nm. Dispersion parameters such as: single oscillator energy, dispersion energy and Abbe's number are deduced and compared. Absorption dispersion parameters, like optical energy gap for direct and indirect transitions, Urbach energy and steepness parameter, are deduced for the different glass prepared. Reflection loss, molar refractivity and electronic polarizability are deduced and compared. The effect of UV light exposure of these glasses on transmittance, reflectance, the linear and the predicted nonlinear optical parameters are investigated and discussed for the three transition metals. Nonlinear parameters increase in the three glass samples after UV exposure.

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

    DOEpatents

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

    1985-08-16

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

  18. Structure-Reactivity Relationships in Multi-Component Transition Metal Oxide Catalysts FINAL Report

    SciTech Connect

    Altman, Eric I.

    2015-10-06

    The focus of the project was on developing an atomic-level understanding of how transition metal oxide catalysts function. Over the course of several renewals the specific emphases shifted from understanding how local structure and oxidation state affect how molecules adsorb and react on the surfaces of binary oxide crystals to more complex systems where interactions between different transition metal oxide cations in an oxide catalyst can affect reactivity, and finally to the impact of cluster size on oxide stability and reactivity. Hallmarks of the work were the use of epitaxial growth methods to create surfaces relevant to catalysis yet tractable for fundamental surface science approaches, and the use of scanning tunneling microscopy to follow structural changes induced by reactions and to pinpoint adsorption sites. Key early findings included the identification of oxidation and reduction mechanisms on a tungsten oxide catalyst surface that determine the sites available for reaction, identification of C-O bond cleavage as the rate limiting step in alcohol dehydration reactions on the tungsten oxide surface, and demonstration that reduction does not change the favored reaction pathway but rather eases C-O bond cleavage and thus reduces the reaction barrier. Subsequently, a new reconstruction on the anatase phase of TiO2 relevant to catalysis was discovered and shown to create sites with distinct reactivity compared to other TiO2 surfaces. Building on this work on anatase, the mechanism by which TiO2 enhances the reactivity of vanadium oxide layers was characterized and it was found that the TiO2 substrate can force thin vanadia layers to adopt structures they would not ordinarily form in the bulk which in turn creates differences in reactivity between supported layers and bulk samples. From there, the work progressed to studying well-defined ternary oxides where synergistic effects between the two cations can induce

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

    SciTech Connect

    Boffa, A B

    1994-07-01

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

  20. Recent advances of transition-metal catalyzed radical oxidative cross-couplings.

    PubMed

    Liu, Chao; Liu, Dong; Lei, Aiwen

    2014-12-16

    CONSPECTUS: Oxidative cross-coupling reactions between two nucleophiles are a powerful synthetic strategy to synthesize various kinds of functional molecules. Along with the development of transition-metal-catalyzed oxidative cross-coupling reactions, chemists are applying more and more first-row transition metal salts (Fe, Co, etc.) as catalysts. Since first-row transition metals often can go through multiple chemical valence changes, those oxidative cross-couplings can involve single electron transfer processes. In the meantime, chemists have developed diverse mechanistic hypotheses of these types of reactions. However, none of these hypotheses have led to conclusive reaction pathways until now. From studying both our own work and that of others in this field, we believe that radical oxidative cross-coupling reactions can be classified into four models based on the final bond formations. In this Account, we categorize and summarize these models. In model I, one of the starting nucleophiles initially loses one electron to generate its corresponding radical under oxidative conditions. Then, bond formations between this radical and another nucleophile create a new radical, [Nu(1)-Nu(2)](•), followed by a further radical oxidation step to generate the cross-coupling product. The radical oxidative alkenylation with olefin, radical oxidative arylative-annulation, and radical oxidative amidation are examples of this model. In model II, one of the starting nucleophiles loses its two electrons via two steps of single-electron-transfer to generate an electrophilic intermediate, followed by a direct bond formation with the other nucleophile. For example, the oxidative C-O coupling of benzylic sp(3) C-H bonds with carboxylic acids and oxidative C-N coupling of aldehydes with amides are members of this model group. For model III, both nucleophiles are oxidized to their corresponding radicals. Then, the radicals combine to form the final coupling product. The dioxygen

  1. Development of new transition metal oxide catalysts for the destruction of PCDD/Fs.

    PubMed

    Yu, Ming-Feng; Li, Wen-Wei; Li, Xiao-Dong; Lin, Xiao-Qing; Chen, Tong; Yan, Jian-Hua

    2016-08-01

    Various transition metal oxide and vanadium-containing multi-metallic oxide catalysts were developed for the destruction of PCDD/Fs (polychlorinated dibenzo-p-dioxins and furans). A stable PCDD/Fs generating system was installed to support the catalytic destruction tests in this study. Nano-titania supported vanadium catalyst (VOx/TiO2) showed the highest activity, followed by CeOx, MnOx, WOx and finally MoOx. Multi-metallic oxide catalysts, prepared by doping WOx, MoOx, MnOx and CeOx into VOx/TiO2 catalysts, showed different activities on the decomposition of PCDD/Fs. The highest destruction efficiency of 92.5% was observed from the destruction test over VOxCeOx/TiO2 catalyst. However, the addition of WOx and MoOx even played a negative role in multi-metallic VOx/TiO2 catalysts. Characterizations of transition metal oxides and multi-metallic VOx/TiO2 catalysts were also investigated with XRD and TPR. After the catalysts were used, the conversion from high valent metals to low valence states was observed by XPS.

  2. Development of new transition metal oxide catalysts for the destruction of PCDD/Fs.

    PubMed

    Yu, Ming-Feng; Li, Wen-Wei; Li, Xiao-Dong; Lin, Xiao-Qing; Chen, Tong; Yan, Jian-Hua

    2016-08-01

    Various transition metal oxide and vanadium-containing multi-metallic oxide catalysts were developed for the destruction of PCDD/Fs (polychlorinated dibenzo-p-dioxins and furans). A stable PCDD/Fs generating system was installed to support the catalytic destruction tests in this study. Nano-titania supported vanadium catalyst (VOx/TiO2) showed the highest activity, followed by CeOx, MnOx, WOx and finally MoOx. Multi-metallic oxide catalysts, prepared by doping WOx, MoOx, MnOx and CeOx into VOx/TiO2 catalysts, showed different activities on the decomposition of PCDD/Fs. The highest destruction efficiency of 92.5% was observed from the destruction test over VOxCeOx/TiO2 catalyst. However, the addition of WOx and MoOx even played a negative role in multi-metallic VOx/TiO2 catalysts. Characterizations of transition metal oxides and multi-metallic VOx/TiO2 catalysts were also investigated with XRD and TPR. After the catalysts were used, the conversion from high valent metals to low valence states was observed by XPS. PMID:27186687

  3. Scalable salt-templated synthesis of two-dimensional transition metal oxides

    PubMed Central

    Xiao, Xu; Song, Huaibing; Lin, Shizhe; Zhou, Ying; Zhan, Xiaojun; Hu, Zhimi; Zhang, Qi; Sun, Jiyu; Yang, Bo; Li, Tianqi; Jiao, Liying; Zhou, Jun; Tang, Jiang; Gogotsi, Yury

    2016-01-01

    Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm−3 in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications. PMID:27103200

  4. Scalable salt-templated synthesis of two-dimensional transition metal oxides

    NASA Astrophysics Data System (ADS)

    Xiao, Xu; Song, Huaibing; Lin, Shizhe; Zhou, Ying; Zhan, Xiaojun; Hu, Zhimi; Zhang, Qi; Sun, Jiyu; Yang, Bo; Li, Tianqi; Jiao, Liying; Zhou, Jun; Tang, Jiang; Gogotsi, Yury

    2016-04-01

    Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm-3 in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications.

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

    USGS Publications Warehouse

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

    1996-01-01

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

  6. Generation of highly N-type, defect passivated transition metal oxides using plasma fluorine insertion

    DOEpatents

    Baker, L. Robert; Seo, Hyungtak; Hervier, Antoine; Somorjai, Gabor A.

    2016-04-12

    A new composition of matter is disclosed wherein oxygen vacancies in a semiconducting transition metal oxide such as titanium dioxide are filled with a halogen such as Fluorine, whereby the conductivity of the composition is greatly enhanced, while at the same time the chemical stability of the composition is greatly improved. Stoichiometric titanium dioxide having less than 3 % oxygen vacancies is subject to fluorine insertion such that oxygen vacancies are filled, limited amounts of fluorine replace additional oxygen atoms and fluorine interstitially inserts into the body of the TiO.sub.2 composition.

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

    SciTech Connect

    Shitade, Atsuo

    2010-05-26

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

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

    SciTech Connect

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

    2010-07-08

    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.

  10. Multiferroic crossover in perovskite oxides

    NASA Astrophysics Data System (ADS)

    Weston, L.; Cui, X. Y.; Ringer, S. P.; Stampfl, C.

    2016-04-01

    The coexistence of ferroelectricity and magnetism in A B O3 perovskite oxides is rare, a phenomenon that has become known as the ferroelectric "d0 rule." Recently, the perovskite BiCoO3 has been shown experimentally to be isostructural with PbTiO3, while simultaneously the d6Co3 + ion has a high-spin ground state with C -type antiferromagnetic ordering. It has been suggested that the hybridization of Bi 6 s states with the O 2 p valence band stabilizes the polar phase, however, we have recently demonstrated that Co3 + ions in the perovskite structure can facilitate a ferroelectric distortion via the Co 3 d -O 2 p covalent interaction [L. Weston, et al., Phys. Rev. Lett. 114, 247601 (2015), 10.1103/PhysRevLett.114.247601]. In this paper, using accurate hybrid density functional calculations, we investigate the atomic, electronic, and magnetic structure of BiCoO3 to elucidate the origin of the multiferroic state. To begin with, we perform a more general first-principles investigation of the role of d electrons in affecting the tendency for perovskite materials to exhibit a ferroelectric distortion; this is achieved via a qualitative trend study in artificial cubic and tetragonal La B O3 perovskites. We choose La as the A cation so as to remove the effects of Bi 6 s hybridization. The lattice instability is identified by the softening of phonon modes in the cubic phase, as well as by the energy lowering associated with a ferroelectric distortion. For the La B O3 series, where B is a d0-d8 cation from the 3 d block, the trend study reveals that increasing the d orbital occupation initially removes the tendency for a polar distortion, as expected. However, for high-spin d5-d7 and d8 cations a strong ferroelectric instability is recovered. This effect is explained in terms of increased pseudo-Jahn-Teller (PJT) p -d vibronic coupling. The PJT effect is described by the competition between a stabilizing force (K0) that favors the cubic phase, and a vibronic term that

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

    PubMed

    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

    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.

  12. Direct Oxidation of Aliphatic C-H Bonds in Amino-Containing Molecules under Transition-Metal-Free Conditions.

    PubMed

    Li, Xin; Che, Xing; Chen, Gui-Hua; Zhang, Jun; Yan, Jia-Lei; Zhang, Yun-Fei; Zhang, Li-Sheng; Hsu, Chao-Ping; Gao, Yi Qin; Shi, Zhang-Jie

    2016-03-18

    By employing a simple, inexpensive, and transition-metal-free oxidation system, secondary C-H bonds in a series of phthaloyl protected primary amines and amino acid derivatives were oxidized to carbonyls with good regioselectivities. This method could also be applied to oxidize tertiary C-H bonds and modify synthetic dipeptides.

  13. Enhanced role of transition metal ion catalysis during in-cloud oxidation of SO2.

    PubMed

    Harris, Eliza; Sinha, Bärbel; van Pinxteren, Dominik; Tilgner, Andreas; Fomba, Khanneh Wadinga; Schneider, Johannes; Roth, Anja; Gnauk, Thomas; Fahlbusch, Benjamin; Mertes, Stephan; Lee, Taehyoung; Collett, Jeffrey; Foley, Stephen; Borrmann, Stephan; Hoppe, Peter; Herrmann, Hartmut

    2013-05-10

    Global sulfate production plays a key role in aerosol radiative forcing; more than half of this production occurs in clouds. We found that sulfur dioxide oxidation catalyzed by natural transition metal ions is the dominant in-cloud oxidation pathway. The pathway was observed to occur primarily on coarse mineral dust, so the sulfate produced will have a short lifetime and little direct or indirect climatic effect. Taking this into account will lead to large changes in estimates of the magnitude and spatial distribution of aerosol forcing. Therefore, this oxidation pathway-which is currently included in only one of the 12 major global climate models-will have a significant impact on assessments of current and future climate.

  14. Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains.

    PubMed

    Ferstl, Pascal; Hammer, Lutz; Sobel, Christopher; Gubo, Matthias; Heinz, Klaus; Schneider, M Alexander; Mittendorfer, Florian; Redinger, Josef

    2016-07-22

    We report on the self-organized growth of monatomic transition-metal oxide chains of (3×1) periodicity and unusual MO_{2} stoichiometry (M=Ni, Co, Fe, Mn) on Ir(100). We analyze their structural and magnetic properties by means of quantitative LEED, STM, and density functional theory (DFT) calculations. LEED analyses reveal a fascinating common atomic structure in which the transition-metal atoms sit above a missing-row structure of the surface and are coupled to the substrate only via oxygen atoms. This structure is confirmed by DFT calculations with structural parameters deviating by less than 1.7 pm. The DFT calculations predict that the NiO_{2} chains are nonmagnetic, CoO_{2} chains are ferromagnetic, while FeO_{2} and MnO_{2} are antiferromagnetic. All structures show only weak magnetic interchain coupling. Further, we demonstrate the growth of oxide chains of binary alloys of Co and Ni or Fe on Ir(100), which allows us to produce well-controlled ensembles of ferromagnetic chains of different lengths separated by nonmagnetic or antiferromagnetic segments. PMID:27494483

  15. Transition metal-modified zinc oxides for UV and visible light photocatalysis.

    PubMed

    Bloh, J Z; Dillert, R; Bahnemann, D W

    2012-11-01

    In order to use photocatalysis with solar light, finding more active and especially visible light active photocatalysts is a very important challenge. Also, studies of these photocatalysts should employ a standardized test procedure so that their results can be accurately compared and evaluated with one another. A systematic study of transition metal-modified zinc oxide was conducted to determine whether they are suitable as visible light photocatalysts. The photocatalytic activity of ZnO modified with eight different transition metals (Cu, Co, Fe, Mn, Ni, Ru, Ti, Zr) in three different concentrations (0.01, 0.1, and 1 at.%) was investigated under irradiation with UV as well as with visible light. The employed activity test is the gas-phase degradation of acetaldehyde as described by the ISO standard 22197-2. The results suggest that the UV activity can be improved with almost any modification element and that there exists an optimal modification ratio at about 0.1 at.%. Additionally, Mn- and Ru-modified ZnO display visible light activity. Especially the Ru-modified ZnO is highly active and surpasses the visible light activity of all studied titania standards. These findings suggest that modified zinc oxides may be a viable alternative to titanium dioxide-based catalysts for visible light photocatalysis. Eventually, possible underlying mechanisms are proposed and discussed.

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

    SciTech Connect

    Hu, Shu-jun; Yan, Shi-shen Zhang, Yun-peng; Zhao, Ming-wen; Kang, Shi-shou; Mei, Liang-mo

    2014-07-28

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

  17. Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains

    NASA Astrophysics Data System (ADS)

    Ferstl, Pascal; Hammer, Lutz; Sobel, Christopher; Gubo, Matthias; Heinz, Klaus; Schneider, M. Alexander; Mittendorfer, Florian; Redinger, Josef

    2016-07-01

    We report on the self-organized growth of monatomic transition-metal oxide chains of (3 ×1 ) periodicity and unusual M O2 stoichiometry (M =Ni , Co, Fe, Mn) on Ir(100). We analyze their structural and magnetic properties by means of quantitative LEED, STM, and density functional theory (DFT) calculations. LEED analyses reveal a fascinating common atomic structure in which the transition-metal atoms sit above a missing-row structure of the surface and are coupled to the substrate only via oxygen atoms. This structure is confirmed by DFT calculations with structural parameters deviating by less than 1.7 pm. The DFT calculations predict that the NiO2 chains are nonmagnetic, CoO2 chains are ferromagnetic, while FeO2 and MnO2 are antiferromagnetic. All structures show only weak magnetic interchain coupling. Further, we demonstrate the growth of oxide chains of binary alloys of Co and Ni or Fe on Ir(100), which allows us to produce well-controlled ensembles of ferromagnetic chains of different lengths separated by nonmagnetic or antiferromagnetic segments.

  18. First-principles analysis of X-ray magnetic circular dichroism for transition metal complex oxides

    NASA Astrophysics Data System (ADS)

    Ikeno, Hidekazu

    2016-10-01

    X-ray magnetic circular dichroism (XMCD) is widely used for the characterization of magnetism of materials. However, information from XMCD related to the atomic, electronic, and magnetic structures is not fully utilized due to the lack of reliable theoretical tools for spectral analysis. In this work, the first-principles configuration interaction (CI) calculations for X-ray absorption spectra developed by the author were extended for the calculation of XMCD, where the Zeeman energy was taken into the Hamiltonian of the CI to mimic magnetic polarization in the solid state. This technique was applied to interpret the L2,3 XMCD from 3d transition metal complex oxides, such as NiFe2O4 and FeTiO3. The experimental XMCD spectra were quantitatively reproduced using this method. The oxidation states as well as the magnetic ordering between transition metal ions on crystallographically different sites in NiFe2O4 can be unambiguously determined. A first-principles analysis of XMCD in FeTiO3 revealed the presence of Fe3+ and Ti3+ ions, which indicates that the charge transfer from Fe to Ti ions occurs. The origin of magnetic polarization of Ti ions in FeTiO3 was also discussed.

  19. Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains.

    PubMed

    Ferstl, Pascal; Hammer, Lutz; Sobel, Christopher; Gubo, Matthias; Heinz, Klaus; Schneider, M Alexander; Mittendorfer, Florian; Redinger, Josef

    2016-07-22

    We report on the self-organized growth of monatomic transition-metal oxide chains of (3×1) periodicity and unusual MO_{2} stoichiometry (M=Ni, Co, Fe, Mn) on Ir(100). We analyze their structural and magnetic properties by means of quantitative LEED, STM, and density functional theory (DFT) calculations. LEED analyses reveal a fascinating common atomic structure in which the transition-metal atoms sit above a missing-row structure of the surface and are coupled to the substrate only via oxygen atoms. This structure is confirmed by DFT calculations with structural parameters deviating by less than 1.7 pm. The DFT calculations predict that the NiO_{2} chains are nonmagnetic, CoO_{2} chains are ferromagnetic, while FeO_{2} and MnO_{2} are antiferromagnetic. All structures show only weak magnetic interchain coupling. Further, we demonstrate the growth of oxide chains of binary alloys of Co and Ni or Fe on Ir(100), which allows us to produce well-controlled ensembles of ferromagnetic chains of different lengths separated by nonmagnetic or antiferromagnetic segments.

  20. First Principles Study of Effect of 3d Transition Metal-Doped Zinc Oxide on Gas Sensitivity

    NASA Astrophysics Data System (ADS)

    Qiu, Zhiyong; Murakami, Ri-Ichi

    Two series models were developed in order to investigate the gas sensitivity of 3d transition metal-doped zinc oxide (ZnO) materials. Software based on a discrete variation method (DVM) within the framework of density functional theory was used to calculate the electronic structures of the models. It was possible to determine gas sensitivity using the calculated results, from which a relationship between electronic properties and gas sensitivity was formed. The results showed that doping the transition metals greatly affected the gas sensitivity of ZnO-based materials. The main effect was attributed to the change in carrier concentration. On the contrary, the doping of transition metals had a negligible effect on the mobility of ZnO-based materials. Titanium or iron doped-ZnO is thus expected to have the best gas sensitivity of all of the 3d transition metal-doped ZnO materials.

  1. Synthesis and control of morphology, stoichiometry, and composition of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Brier, Matthew Isaac

    Transition metal oxides (TMOs) are an important class of materials that have found uses in diverse applications, such as heterogeneous catalysts, sensors, and high temperature superconductors, due to their complex surface chemistry and high mobility of lattice oxygen atoms. Point defects such as oxygen and metal atom vacancies significantly perturb the electronic structure of TMOs and profoundly impact their electrical, optical, ferroelectric, photocatalytic, and other functional properties. As a result, significant research is being done to develop synthesis techniques that can produce metal oxides with controllable material properties. In this thesis, the use of hot wire chemical vapor deposition (HWCVD) was studied with the aim of precisely controlling the morphology, stoichiometry, and composition of TMOs. With molybdenum oxide as the model system, the control of morphology and stoichiometry was achieved by modulation of deposition parameters, such as filament power and gas phase composition. The study of HWCVD of MoOx led to the development of phase diagrams for the dependence of morphology and stoichiometry on deposition parameters. The knowledge gained studying the HWCVD of MoOx was then shown to translate to the deposition of other binary metal oxides by using tungsten, nickel, and vanadium metal filaments to synthesize their respective transition metal oxides. Additionally, NiMoO4 was synthesized as a proof-of-concept to show that HWCVD can be used to make ternary oxides. Nitridation of samples in an ammonia atmosphere was conducted to explore the potential for conversion of HWCVD grown TMOs to their respective metal nitrides, which are also reported to have catalytic properties. To examine the quality of TMOs grown by HWCVD, samples were electrochemically tested for their electrochromic properties and photoactivity with respect to splitting of water.

  2. Synthesis and characterization of transition metal-mullite catalysts for nitric oxide (NO) oxidation

    NASA Astrophysics Data System (ADS)

    Thampy, Sampreetha

    AMn2O5 (A = Pr, Sm, Gd, Y, Bi), and (Y, Bi)FeMnO5 mullite prepared by coprecipitation-calcination method are investigated as catalysts for NO oxidation. The effect of precursor stoichiometry, calcination temperature, and coprecipitation pH on phase, specific surface area (SSA) and NO chemisorption are studied. The precursor stoichiometry controlled the oxide phase (mullite vs. perovskite) obtained. In comparison, when the calcination temperature is increased from 750 ºC to 1000 ºC, a tradeoff is observed, where purity of mullite phase increased from 73 % to 100 % but SSA decreased from 30 m2/g to 5 m2/g. Formation of crystalline SmMn2O5 is found to be weakly dependent on pH whereas SSA monotonically increased from 13 m2/g at pH 8.1 to 27 m2/g at pH 13. A strong correlation between NO uptake volume and SSA is found. The highest SSA value (27 m2/g) being associated to a sample showing the highest NO uptake (104 micromol/g). These results suggest that the SSA is the key contributor to higher catalytic performance of TM-mullites.

  3. The Oxidation of Sulfur-Containing Compounds Using Heterogeneous Catalysts of Transition Metal Oxides Deposited on the Polymeric Matrix

    NASA Astrophysics Data System (ADS)

    Dinh Vu, Ngo; Dinh Bui, Nhi; Thi Minh, Thao; Thi Thanh Dam, Huong; Thi Tran, Hang

    2016-05-01

    We investigate the activity of heterogeneous catalysts of transition metal oxides deposited on the polymeric matrix in the oxidation of sulfur-containing compounds. It is shown that MnO2-10/CuO-10 has the highest catalytic activity. The physicomechanical properties of polymeric heterogeneous catalysts of transition-metal oxides, including the specific surface area, elongation at break and breaking strength, specific electrical resistance, and volume resistivity were studied by using an Inspekt mini 3 kN universal tensile machine in accordance with TCVN 4509:2006 at a temperature of 20 ± 2°C. Results show that heterogeneous polymeric catalysts were stable under severe reaction conditions. Scanning electron microscopy, and energy-dispersive analysis are used to study the surfaces of the catalysts. Microstructural characterization of the catalysts is performed by using x-ray computed tomography. We demonstrate the potential application of polymeric heterogeneous catalysts of transition-metal oxides in industrial wastewater treatment.

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

    We have investigated the effect of gamma irradiation on the optical properties of Li 2O-B 2O 3 containing two concentrations (0.2 or 0.5 g) of each one of the following transition metals, V, Mn, Fe or Ni oxide glass samples. We studied the impacts of gamma irradiation in terms of the mechanism by which radiation-induced defects are generated. A resolution of the observed absorption spectra showed several bands which were induced by photo-reduction or photo-oxidation assumed to take place by photo-chemical reaction according to the type of transition metal oxide (TMO). Small deviations of these induced bands characteristic of the glass constituents were observed and explained in terms of the physical properties, in relation to different oxidation states of TMO in the glass matrix. The series Mn 2+, Fe 2+ and Ni 2+ ions shows a trend of increased photo-oxidation with increasing electronegativity or decreasing mass of the ions. The prepared samples were studied in terms of their dosimetric characteristics: calibration curves from 1.0524 to 42.096 kGy and fading at (25 and 50 °C). Thermal bleaching of irradiated glass was found to permit the reduction of the larger part of TMO ions in Li 2O-B 2O 3. Also, the results showed that the degeneration of the induced bands was faster at 50 than at 25 °C. The optical energy gap Eg was found to decrease with the increase of the radiation dose, and it is suggested that the mechanism of optical transition is forbidden by indirect transition.

  5. Charge Transfer Stabilization of Late Transition Metal Oxide Nanoparticles on a Layered Niobate Support.

    PubMed

    Strayer, Megan E; Senftle, Thomas P; Winterstein, Jonathan P; Vargas-Barbosa, Nella M; Sharma, Renu; Rioux, Robert M; Janik, Michael J; Mallouk, Thomas E

    2015-12-30

    Interfacial interactions between late transition metal/metal oxide nanoparticles and oxide supports impact catalytic activity and stability. Here, we report the use of isothermal titration calorimetry (ITC), electron microscopy and density functional theory (DFT) to explore periodic trends in the heats of nanoparticle-support interactions for late transition metal and metal oxide nanoparticles on layered niobate and silicate supports. Data for Co(OH)2, hydroxyiridate-capped IrOx·nH2O, Ni(OH)2, CuO, and Ag2O nanoparticles were added to previously reported data for Rh(OH)3 grown on nanosheets of TBA0.24H0.76Ca2Nb3O10 and a layered silicate. ITC measurements showed stronger bonding energies in the order Ag < Cu ≈ Ni ≈ Co < Rh < Ir on the niobate support, as expected from trends in M-O bond energies. Nanoparticles with exothermic heats of interaction were stabilized against sintering. In contrast, ITC measurements showed endothermic interactions of Cu, Ni, and Rh oxide/hydroxide nanoparticles with the silicate and poor resistance to sintering. These trends in interfacial energies were corroborated by DFT calculations using single-atom and four-atom cluster models of metal/metal oxide nanoparticles. Density of states and charge density difference calculations reveal that strongly bonded metals (Rh, Ir) transfer d-electron density from the adsorbed cluster to niobium atoms in the support; this mixing is absent in weakly binding metals, such as Ag and Au, and in all metals on the layered silicate support. The large differences between the behavior of nanoparticles on niobate and silicate supports highlight the importance of d-orbital interactions between the nanoparticle and support in controlling the nanoparticles' stability. PMID:26651875

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

    SciTech Connect

    Meyer, Jens; Kröger, M.; Hamwi, S.; Gnam, F.; Riedl, T.; Kowalsky, W.; Kahn, Antoine

    2010-01-01

    The energetics of an archetype charge generation layer (CGL) architecture comprising of 4,4' ,4 '' -tris(N -carbazolyl)triphenylamine (TCTA), tungsten oxide (WO3 ) , and bathophenanthroline (BPhen) n-doped with cesium carbonate (Cs2 CO3 ) are determined by ultraviolet and inverse photoemissionspectroscopy. We show that the charge generation process occurs at the interface between the hole-transport material (TCTA) and WO3 and not, as commonly assumed, at the interface between WO3 and the n-doped electron-transport material (BPhen:Cs2 CO3 ) . However, the n-doped layer is also essential to the realization of an efficient CGL structure. The charge generation mechanism occurs via electron transfer from the TCTA highest occupied molecular orbital level to the transition metal-oxide conduction band.

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

    SciTech Connect

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

    2015-03-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  9. Growth of Hollow Transition Metal (Fe, Co, Ni) Oxide Nanoparticles on Graphene Sheets through Kirkendall Effect as Anodes for High-Performance Lithium-Ion Batteries.

    PubMed

    Yu, Xianbo; Qu, Bin; Zhao, Yang; Li, Chunyan; Chen, Yujin; Sun, Chunwen; Gao, Peng; Zhu, Chunling

    2016-01-26

    A general strategy based on the nanoscale Kirkendall effect has been developed to grow hollow transition metal (Fe, Co or Ni) oxide nanoparticles on graphene sheets. When applied as lithium-ion battery anodes, these hollow transition metal oxide-based composites exhibit excellent electrochemical performance, with high reversible capacities and long-term stabilities at a high current density, superior to most transition metal oxides reported to date.

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

    PubMed

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

    2011-10-01

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

  11. Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

    2016-02-01

    Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge.

  12. Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy.

    PubMed

    Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

    2016-02-24

    Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge.

  13. Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy

    PubMed Central

    Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

    2016-01-01

    Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge. PMID:26908198

  14. A comparison of the bonding in the second-row transition-metal oxides and carbenes

    NASA Astrophysics Data System (ADS)

    Siegbahn, Per E. M.

    1993-01-01

    Calculations including electron correlation of all valence electrons have been performed for the sequence of second-row transition-metal oxides and carbenes. For the atoms to the right the bond strengths of the carbenes and the oxides are similar while for the atoms to the left the oxide bond strengths are much larger. The origin of this difference is the interaction between the oxygen lone pairs and empty 4d orbitals on the metal. With the large donation of electrons from the oxygen lone pair to the metal for the atoms to the left, the bonding can almost be described as triple bond formation for YO, ZrO and NbO. For MoO, where a 4d π orbital is singly occupied on the metal, the bond strength is much smaller than for the oxides to the left. For the metal carbenes two covalent bonds are formed. The ground state spin for the oxides to the right is higher than for the corresponding carbenes, which can be explained by the presence of the π degeneracy for the oxides. The relevance of the present results for the epoxidation and the olefin metathesis reactions are discussed.

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

    PubMed

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

    2014-02-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    SciTech Connect

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

    2013-09-01

    Density-functional theory calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula are applied to predict electrical conductivity in Ta2Ox (0 x 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (VOn; n=0,1+,2+). Our calculations of DC conductivity at 300K agree well with experimental measurements taken on Ta2Ox thin films and bulk Ta2O5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta2O5 electronic structure provide further theoretical basis to substantiate VO0 as a donor dopant in Ta2O5 and other metal oxides. Furthermore, this dopant-like behavior appears specific to neutral VO cases in both Ta2O5 and TiO2 and was not observed in other oxidation states. This suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for VO0 in transition metal oxides.

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

    PubMed

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

    2014-09-15

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

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

    PubMed

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

    2012-10-23

    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.

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

    PubMed

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

    2012-10-23

    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

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

    DOEpatents

    Tracy, C. Edwin; Benson, David K.; Ruth, Marta R.

    1987-01-01

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

  2. CeO2 nanorods-supported transition metal catalysts for CO oxidation.

    PubMed

    Mock, Samantha A; Sharp, Shannon E; Stoner, Thomas R; Radetic, Michael J; Zell, Elizabeth T; Wang, Ruigang

    2016-03-15

    A catalytically active oxide support in combination with metal catalysts is required in order to achieve better low temperature activity and selectivity. Here, we report that CeO2 nanorods with a superior surface oxygen release/storage capability were used as an active support of transition metal (TM) catalysts (Mn, Fe, Co, Ni, Cu) for CO oxidation reaction. The as-prepared CeO2 nanorods supported 10 wt% TM catalysts were highly active for CO oxidation at low temperature, except for the Fe sample. It is found that the 10%Cu-CeO2 catalyst performed best, and it provided a lower light-off temperature with T50 (50% conversion) at 75 °C and T100 (100% conversion) of CO to CO2 at 194 °C. The atomic level surface structure of CeO2 nanorods was investigated in order to understand the improved low temperature catalytic activity. The richness of surface roughness and various defects (voids, lattice distortion, bending, steps, twinning) on CeO2 nanorods could facilitate oxygen release and storage. According to XRD and Raman analysis, copper species migrate into the bulk CeO2 nanorods to a greater degree. Since CO adsorbed over the surface of the catalyst/support is detrimental to its catalytic activity, the surface defects on the CeO2 nanorods and CeO2-TM interactions were critical to the enhanced activity.

  3. CeO2 nanorods-supported transition metal catalysts for CO oxidation.

    PubMed

    Mock, Samantha A; Sharp, Shannon E; Stoner, Thomas R; Radetic, Michael J; Zell, Elizabeth T; Wang, Ruigang

    2016-03-15

    A catalytically active oxide support in combination with metal catalysts is required in order to achieve better low temperature activity and selectivity. Here, we report that CeO2 nanorods with a superior surface oxygen release/storage capability were used as an active support of transition metal (TM) catalysts (Mn, Fe, Co, Ni, Cu) for CO oxidation reaction. The as-prepared CeO2 nanorods supported 10 wt% TM catalysts were highly active for CO oxidation at low temperature, except for the Fe sample. It is found that the 10%Cu-CeO2 catalyst performed best, and it provided a lower light-off temperature with T50 (50% conversion) at 75 °C and T100 (100% conversion) of CO to CO2 at 194 °C. The atomic level surface structure of CeO2 nanorods was investigated in order to understand the improved low temperature catalytic activity. The richness of surface roughness and various defects (voids, lattice distortion, bending, steps, twinning) on CeO2 nanorods could facilitate oxygen release and storage. According to XRD and Raman analysis, copper species migrate into the bulk CeO2 nanorods to a greater degree. Since CO adsorbed over the surface of the catalyst/support is detrimental to its catalytic activity, the surface defects on the CeO2 nanorods and CeO2-TM interactions were critical to the enhanced activity. PMID:26745742

  4. Raman microscopy of lithium-manganese-rich transition metal oxide cathodes

    DOE PAGES

    Ruther, Rose E.; Callender, Andrew F.; Zhou, Hui; Martha, Surendra K.; Nanda, Jagjit

    2014-11-15

    Lithium-rich and manganese-rich (LMR) layered transition metal (TM) oxide composites with general formula xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, Mn) are promising cathode candidates for high energy density lithium ion batteries. Lithium-manganese-rich TM oxides crystallize as a nanocomposite layered phase whose structure further evolves with electrochemical cycling. Raman spectroscopy is a powerful tool to monitor the crystal chemistry and correlate phase changes with electrochemical behavior. While several groups have reported Raman spectra of lithium rich TM oxides, the data show considerable variability in terms of both the vibrational features observed and their interpretation. In this paper, Raman microscopy is used tomore » investigate lithium-rich and manganese-rich TM cathodes as a function of voltage and electrochemical cycling at various temperatures. No growth of a spinel phase is observed within the cycling conditions. However, analysis of the Raman spectra does indicate the structure of LMR-NMC deviates significantly from an ideal layered phase. Finally, the results also highlight the importance of using low laser power and large sample sizes to obtain consistent data sets.« less

  5. Raman microscopy of lithium-manganese-rich transition metal oxide cathodes

    SciTech Connect

    Ruther, Rose E.; Callender, Andrew F.; Zhou, Hui; Martha, Surendra K.; Nanda, Jagjit

    2014-11-15

    Lithium-rich and manganese-rich (LMR) layered transition metal (TM) oxide composites with general formula xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, Mn) are promising cathode candidates for high energy density lithium ion batteries. Lithium-manganese-rich TM oxides crystallize as a nanocomposite layered phase whose structure further evolves with electrochemical cycling. Raman spectroscopy is a powerful tool to monitor the crystal chemistry and correlate phase changes with electrochemical behavior. While several groups have reported Raman spectra of lithium rich TM oxides, the data show considerable variability in terms of both the vibrational features observed and their interpretation. In this paper, Raman microscopy is used to investigate lithium-rich and manganese-rich TM cathodes as a function of voltage and electrochemical cycling at various temperatures. No growth of a spinel phase is observed within the cycling conditions. However, analysis of the Raman spectra does indicate the structure of LMR-NMC deviates significantly from an ideal layered phase. Finally, the results also highlight the importance of using low laser power and large sample sizes to obtain consistent data sets.

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

    PubMed

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

    2006-11-01

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

  7. Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides

    PubMed Central

    Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying

    2015-01-01

    Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects. PMID:26510508

  8. Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides

    DOE PAGES

    Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying

    2015-10-29

    Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and amore » thin surface layer on certain crystallographic facets. Finally and more specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.« less

  9. Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides

    SciTech Connect

    Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying

    2015-10-29

    Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. Finally and more specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.

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

    SciTech Connect

    Kellar, S.A. |

    1997-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Lam, Ching Yee

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

  12. Mesoporous transition metal oxides quasi-nanospheres with enhanced electrochemical properties for supercapacitor applications.

    PubMed

    Wang, Lu; Duan, Guorong; Zhu, Junwu; Chen, Shen-Ming; Liu, Xiao-Heng; Palanisamy, Selvakumar

    2016-12-01

    In this report, we obtain mesoporous transition metal oxides quasi-nanospheres (includes MnO2, NiO, and Co3O4) by utilizing mesoporous silica nanospheres as a template for high-performance supercapacitor electrodes. All samples have a large specific surface area of approximately 254-325m(2)g(-1) and a relatively narrow pore size distribution in the region of 7nm. Utilization of a nanosized template resulted in a product with a relative uniform morphology and a small particle diameter in the region of 50-100nm. As supercapacitor electrodes, MnO2, NiO, and Co3O4 exhibit an outstanding capacity as high as 838-1185Fg(-1) at 0.5Ag(-1) and a superior long-term stability with minimal loss of 3-7% after 6000 cycles at 1Ag(-1). Their excellent electrochemical performances are attributed to favorable morphologies with a large surface area and a uniform architecture with abundant pores. The associated enhancement of electrolyte ion circulation within the electrode facilitates a significant increase in availability of Faradic reaction electroactive sites.

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

    NASA Astrophysics Data System (ADS)

    Zhang, Bo; Duan, Yuhua; Johnson, Karl

    2012-02-01

    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.

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

    SciTech Connect

    Deng, Yan-Hong; Chen, Xiang-Yu E-mail: xychen@suda.edu.cn; Ou, Qing-Dong; Wang, Qian-Kun; Jiang, Xiao-Cheng; Zhang, Dan-Dan; Li, Yan-Qing E-mail: xychen@suda.edu.cn

    2014-06-02

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

  15. Transition metal decorated graphene-like zinc oxide monolayer: A first-principles investigation

    SciTech Connect

    Lei, Jie; Xu, Ming-Chun; Hu, Shu-Jun

    2015-09-14

    Transition metal (TM) atoms have been extensively employed to decorate the two-dimensional materials, endowing them with promising physical properties. Here, we have studied the adsorption of TM atoms (V, Cr, Mn, Fe, and Co) on graphene-like zinc oxide monolayer (g-ZnO) and the substitution of Zn by TM using first-principles calculations to search for the most likely configurations when TM atoms are deposited on g-ZnO. We found that when a V atom is initially placed on the top of Zn atom, V will squeeze out Zn from the two-dimensional plane then substitute it, which is a no barrier substitution process. For heavier elements (Cr to Co), although the substitution configurations are more stable than the adsorption ones, there is an energy barrier for the adsorption-substitution transition with the height of tens to hundreds meV. Therefore, Cr to Co prefers to be adsorbed on the hollow site or the top of oxygen, which is further verified by the molecular dynamics simulations. The decoration of TM is revealed to be a promising approach in terms of tuning the work function of g-ZnO in a large energy range.

  16. Identification of Surface Reactivity Descriptor for Transition Metal Oxides in Oxygen Evolution Reaction.

    PubMed

    Tao, Hua Bing; Fang, Liwen; Chen, Jiazang; Yang, Hong Bin; Gao, Jiajian; Miao, Jianwei; Chen, Shengli; Liu, Bin

    2016-08-10

    A number of important reactions such as the oxygen evolution reaction (OER) are catalyzed by transition metal oxides (TMOs), the surface reactivity of which is rather elusive. Therefore, rationally tailoring adsorption energy of intermediates on TMOs to achieve desirable catalytic performance still remains a great challenge. Here we show the identification of a general and tunable surface structure, coordinatively unsaturated metal cation (MCUS), as a good surface reactivity descriptor for TMOs in OER. Surface reactivity of a given TMO increases monotonically with the density of MCUS, and thus the increase in MCUS improves the catalytic activity for weak-binding TMOs but impairs that for strong-binding ones. The electronic origin of the surface reactivity can be well explained by a new model proposed in this work, wherein the energy of the highest-occupied d-states relative to the Fermi level determines the intermediates' bonding strength by affecting the filling of the antibonding states. Our model for the first time well describes the reactivity trends among TMOs, and would initiate viable design principles for, but not limited to, OER catalysts. PMID:27441842

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

    SciTech Connect

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

    2010-03-05

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

  18. Rovibronically Selected and Resolved Laser Photoionization and Photoelectron Studies of Transition Metal Carbides, Nitrides, and Oxides.

    NASA Astrophysics Data System (ADS)

    Luo, Zhihong; Chang, Yih-Chung; Huang, Huang; Ng, Cheuk-Yiu

    2014-06-01

    Transition metal (M) carbides, nitrides, and oxides (MX, X = C, N, and O) are important molecules in astrophysics, catalysis, and organometallic chemistry. The measurements of the ionization energies (IEs), bond energies, and spectroscopic constants for MX/MX+ in the gas phase by high-resolution photoelectron methods represent challenging but profitable approaches to gain fundamental understandings of the electronic structures and bonding properties of these compounds and their cations. We have developed a two-color laser excitation scheme for high-resolution pulse field ionization photoelectron (PFI-PE) measurements of MX species. By exciting the neutral MX species to a single rovibronic state using a visible laser prior to photoionization by a UV laser, we have obtained fully rotational resolved PFI-PE spectra for TiC+, TiO+, VCH+, VN+, CoC+, ZrO+, and NbC+. The unambiguous rotational assignments of these spectra have provided highly accurate IE values for TiC, TiO, VCH, VN, CoC, ZrO, and NbC, and spectroscopic constants for their cations.

  19. Mesoporous transition metal oxides quasi-nanospheres with enhanced electrochemical properties for supercapacitor applications.

    PubMed

    Wang, Lu; Duan, Guorong; Zhu, Junwu; Chen, Shen-Ming; Liu, Xiao-Heng; Palanisamy, Selvakumar

    2016-12-01

    In this report, we obtain mesoporous transition metal oxides quasi-nanospheres (includes MnO2, NiO, and Co3O4) by utilizing mesoporous silica nanospheres as a template for high-performance supercapacitor electrodes. All samples have a large specific surface area of approximately 254-325m(2)g(-1) and a relatively narrow pore size distribution in the region of 7nm. Utilization of a nanosized template resulted in a product with a relative uniform morphology and a small particle diameter in the region of 50-100nm. As supercapacitor electrodes, MnO2, NiO, and Co3O4 exhibit an outstanding capacity as high as 838-1185Fg(-1) at 0.5Ag(-1) and a superior long-term stability with minimal loss of 3-7% after 6000 cycles at 1Ag(-1). Their excellent electrochemical performances are attributed to favorable morphologies with a large surface area and a uniform architecture with abundant pores. The associated enhancement of electrolyte ion circulation within the electrode facilitates a significant increase in availability of Faradic reaction electroactive sites. PMID:27552415

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

    Das, Supriyo

    2010-01-01

    Oxide compounds containing the transition metal vanadium (V) have attracted a lot of attention in the field of condensed matter physics owing to their exhibition of interesting properties including metal-insulator transitons, structural transitions, ferromagnetic and an- tiferromagnetic orderings, and heavy fermion behavior. Binary vanadium oxides VnO2n-1 where 2 ≤ n ≤ 9 have triclinic structures and exhibit metal-insulator and antiferromagnetic transitions.[1–6] The only exception is V7O13 which remains metallic down to 4 K.[7] The ternary vanadium oxide LiV2O4 has the normal spinel structure, is metallic, does not un- dergo magnetic ordering and exhibits heavy fermion behavior below 10 K.[8] CaV2O4 has an orthorhombic structure[9, 10] with the vanadium spins forming zigzag chains and has been suggested to be a model system to study the gapless chiral phase.[11, 12] These provide great motivation for further investigation of some known vanadium compounds as well as to ex- plore new vanadium compounds in search of new physics. This thesis consists, in part, of experimental studies involving sample preparation and magnetic, transport, thermal, and x- ray measurements on some strongly correlated eletron systems containing the transition metal vanadium. The compounds studied are LiV2O4, YV4O8, and YbV4O8. The recent discovery of superconductivity in RFeAsO1-xFx (R = La, Ce, Pr, Gd, Tb, Dy, Sm, and Nd), and AFe2As2 (A = Ba, Sr, Ca, and Eu) doped with K, Na, or Cs at the A site with relatively high Tc has sparked tremendous activities in the condensed matter physics community and a renewed interest in the area of superconductivity as occurred following the discovery of the layered cuprate high Tc superconductors in 1986. To discover more supercon- ductors

  2. First-principles data-driven discovery of transition metal oxides for artificial photosynthesis

    NASA Astrophysics Data System (ADS)

    Yan, Qimin

    We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.

  3. Experimental bandstructure of the 5 d transition metal oxide IrO2

    NASA Astrophysics Data System (ADS)

    Kawasaki, Jason; Nie, Yuefeng; Uchida, Masaki; Schlom, Darrell; Shen, Kyle

    2015-03-01

    In the 5 d iridium oxides the close energy scales of spin-orbit coupling and electron-electron correlations lead to emergent quantum phenomena. Much research has focused on the ternary iridium oxides, e.g. the Ruddlesden-Poppers An + 1BnO3 n + 1 , which exhibit behavior from metal to antiferromagnetic insulator ground states, share common features with the cuprates, and may host a number of topological phases. The binary rutile IrO2 is another important 5 d oxide, which has technological importance for spintronics due to its large spin Hall effect and also applications in catalysis. IrO2 is expected to share similar physics as its perovskite-based cousins; however, due to bond-length distortions of the IrO6 octahedra in the rutile structure, the extent of similarities remains an open question. Here we use angle-resolved photoemission spectroscopy to perform momentum-resolved measurements of the electronic structure of IrO2 . IrO2 thin films were grown by molecular beam epitaxy on TiO2 (110) substrates using an Ir e-beam source and distilled ozone. Films were subsequently transferred through ultrahigh vacuum to a connected ARPES system. Combined with first-principles calculations we explore the interplay of spin-orbit coupling and correlations in IrO2 .

  4. Electrocatalytic reduction of carbon dioxide on post-transition metal and metal oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    White, James L.

    The electroreduction of carbon dioxide to liquid products is an important component in the utilization of CO2 and in the high-density storage of intermittent renewable energy in the form of chemical bonds. Materials based on indium and tin, which yield predominantly formic acid, have been investigated in order to gain a greater understanding of the electrochemically active species and the mechanism of CO2 reduction on these heavy post-transition metals, since prior studies on the bulk metals did not provide thermodynamically sensible reaction pathways. Nanoparticles of the oxides and hydroxides of tin and indium have been prepared and characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and various electrochemical methods in order to obtain structural information and analyze the role of various surface species on the CO2 reduction pathway. On both indium and tin, metastable surface-bound hydroxides bound CO2 and formed metal carbonates, which can then be reduced electrochemically. The relevant oxidation state of tin was suggested to be SnII rather than SnIV, necessitating a pre reduction to generate the CO2-binding species. Metallic indium nanoparticles partially oxidized in air and became highly efficient CO2 reduction electrocatalysts. Unit Faradaic efficiencies for formate, much higher than on bulk indium, were achieved with only 300 mV of overpotential on these particles, which possessed an oxyhydroxide shell surrounding a conductive metallic core. Alloys and mixed-metal oxide and hydroxide particles of tin and indium have also been studied for their carbon dioxide electrocatalytic capabilities, especially in comparison to the pure metal species. Additionally, a solar-driven indium-based CO2 electrolyzer was developed to investigate the overall efficiency for intermittent energy storage. The three flow cells were powered by a commercial photovoltaic array and had a maximum conversion efficiency of incident

  5. Oxidatively Electrodeposited Thin-Film Transition Metal (Oxy)hydroxides as Oxygen Evolution Catalysts.

    PubMed

    Morales-Guio, Carlos G; Liardet, Laurent; Hu, Xile

    2016-07-20

    The electrolysis of water to produce hydrogen and oxygen is a simple and attractive approach to store renewable energies in the form of chemical fuels. The oxygen evolution reaction (OER) is a complex four-electron process that constitutes the most energy-inefficient step in water electrolysis. Here we describe a novel electrochemical method for the deposition of a family of thin-film transition metal (oxy)hydroxides as OER catalysts. The thin films have nanodomains of crystallinity with lattice spacing similar to those of double-layered hydroxides. The loadings of these thin-film catalysts were accurately determined with a resolution of below 1 μg cm(-2) using an electrochemical quartz microcrystal balance. The loading-activity relations for various catalysts were established using voltammetry and impedance spectroscopy. The thin-film catalysts have up to four types of loading-activity dependence due to film nucleation and growth as well as the resistance of the films. A zone of intrinsic activity has been identified for all of the catalysts where the mass-averaged activity remains constant while the loading is increased. According to their intrinsic activities, the metal oxides can be classified into three categories: NiOx, MnOx, and FeOx belong to category I, which is the least active; CoOx and CoNiOx belong to category II, which has medium activity; and FeNiOx, CoFeOx, and CoFeNiOx belong to category III, which is the most active. The high turnover frequencies of CoFeOx and CoFeNiOx at low overpotentials and the simple deposition method allow the fabrication of high-performance anode electrodes coated with these catalysts. In 1 M KOH and with the most active electrode, overpotentials as low as 240 and 270 mV are required to reach 10 and 100 mA cm(-2), respectively.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Wang, Xin

    2012-02-01

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

  8. Transition-metal catalyzed oxidative cross-coupling reactions to form C-C bonds involving organometallic reagents as nucleophiles.

    PubMed

    Shi, Wei; Liu, Chao; Lei, Aiwen

    2011-05-01

    Transition-metal-catalyzed coupling reactions have become a versatile tool for chemical bond formation. From the variation of the coupling partners, coupling reactions can be classified into three models: traditional coupling, reductive coupling and oxidative coupling. The oxidative coupling, which is different from the traditional coupling, occurs between two nucleophiles. This critical review focuses on transition-metal-catalyzed oxidative coupling reactions involving organometallic reagents as nucleophiles. Since the scope of the oxidative coupling is highly diversified, this paper only reviews the oxidative coupling reactions concerning C-C bond formation, including the coupling between organometal reagents and hydrocarbons as well as coupling between two organometal reagents. Since terminal alkynes are normally activated by metal salts and in situ form the alkynyl metal reagents in coupling reactions, they are directly considered as organometal reagents in this review. Intramolecular oxidative couplings and oxidative cyclizations are not included in this critical review. Moreover, there are many examples of oxidative coupling leading to the formation of functional materials, such as the oxidative polymerization of thiophenes. Since several reviews in these areas have been published they are not included in this review either (99 references).

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

    SciTech Connect

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

    2008-09-04

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

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

    NASA Astrophysics Data System (ADS)

    Cheng, Jihong

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

  11. First-principles study of nitric oxide oxidation on Pt(111) versus Pt overlayer on 3d transition metals

    SciTech Connect

    Arevalo, Ryan Lacdao; Escaño, Mary Clare Sison; Kasai, Hideaki

    2015-03-15

    Catalytic oxidation of NO to NO{sub 2} is a significant research interest for improving the quality of air through exhaust gas purification systems. In this paper, the authors studied this reaction on pure Pt and Pt overlayer on 3d transition metals using kinetic Monte Carlo simulations coupled with density functional theory based first principles calculations. The authors found that on the Pt(111) surface, NO oxidation proceeds via the Eley–Rideal mechanism, with O{sub 2} dissociative adsorption as the rate-determining step. The oxidation path via the Langmuir–Hinshelwood mechanism is very slow and does not significantly contribute to the overall reaction. However, in the Pt overlayer systems, the oxidation of NO on the surface is more thermodynamically and kinetically favorable compared to pure Pt. These findings are attributed to the weaker binding of O and NO on the Pt overlayer systems and the binding configuration of NO{sub 2} that promotes easier N-O bond formation. These results present insights for designing affordable and efficient catalysts for NO oxidation.

  12. Transition Metal-Free Selective Double sp(3) C-H Oxidation of Cyclic Amines to 3-Alkoxyamine Lactams.

    PubMed

    Osorio-Nieto, Urbano; Chamorro-Arenas, Delfino; Quintero, Leticia; Höpfl, Herbert; Sartillo-Piscil, Fernando

    2016-09-16

    The first chemical method for selective dual sp(3) C-H functionalization at the alpha-and beta positions of cyclic amines to their corresponding 3-alkoxyamine lactams is reported. Unlike traditional Cα-H oxidation of amines to amides mediated by transition metals, the present protocol, which involves the use of NaClO2/TEMPO/NaClO in either aqueous or organic solvent, not only allows the Cα-H oxidation but also the subsequent functionalization of the unreactive β-methylene group in an unprecedented tandem fashion and using environmentally friendly reactants.

  13. Transition Metal-Free Selective Double sp(3) C-H Oxidation of Cyclic Amines to 3-Alkoxyamine Lactams.

    PubMed

    Osorio-Nieto, Urbano; Chamorro-Arenas, Delfino; Quintero, Leticia; Höpfl, Herbert; Sartillo-Piscil, Fernando

    2016-09-16

    The first chemical method for selective dual sp(3) C-H functionalization at the alpha-and beta positions of cyclic amines to their corresponding 3-alkoxyamine lactams is reported. Unlike traditional Cα-H oxidation of amines to amides mediated by transition metals, the present protocol, which involves the use of NaClO2/TEMPO/NaClO in either aqueous or organic solvent, not only allows the Cα-H oxidation but also the subsequent functionalization of the unreactive β-methylene group in an unprecedented tandem fashion and using environmentally friendly reactants. PMID:27564379

  14. Electron-phonon coupling and structural phase transitions in early transition metal oxides and chalcogenides

    NASA Astrophysics Data System (ADS)

    Farley, Katie Elizabeth

    Pronounced nonlinear variation of electrical transport characteristics as a function of applied voltage, temperature, magnetic field, strain, or photo-excitation is usually underpinned by electronic instabilities that originate from the complex interplay of spin, orbital, and lattice degrees of freedom. This dissertation focuses on two canonical materials that show pronounced discontinuities in their temperature-dependent resistivity as a result of electron---phonon and electron---electron correlations: orthorhombic TaS3 and monoclinic VO2. Strong electron-phonon interactions in transition metal oxides and chalcogenides results in interesting structural and electronic phase transitions. The properties of the material can be changed drastically in response to external stimuli such as temperature, voltage, or light. Understanding the influence these interactions have on the electronic structure and ultimately transport characteristics is of utmost importance in order to take these materials from a fundamental aspect to prospective applications such as low-energy interconnects, steep-slope transistors, and synaptic neural networks. This dissertation describes synthetic routes to nanoscale TaS3 and VO2, develops mechanistic understanding of their electronic instabilities, and in the case of the latter system explores modulation of the electronic and structural phase transition via the incorporation of substitutional dopant atoms. We start in chapter 2 with a detailed study of the synthesis and electronic transport properties of TaS3, which undergoes a Peierls' distortion to form a charge density wave. Scaling this material down to the nanometer-sized regime allows for interrogation of single or discrete phase coherent domains. Using electrical transport and broad band noise measurements, the dynamics of pinning/depinning of the charge density wave is investigated. Chapter 3 provides a novel synthetic approach to produce high-edge-density MoS2 nanorods. MoS2 is a

  15. General Self-Template Synthesis of Transition-Metal Oxide and Chalcogenide Mesoporous Nanotubes with Enhanced Electrochemical Performances.

    PubMed

    Wang, Huan; Zhuo, Sifei; Liang, Yu; Han, Xiling; Zhang, Bin

    2016-07-25

    The development of a general strategy for synthesizing hierarchical porous transition-metal oxide and chalcogenide mesoporous nanotubes, is still highly challenging. Herein we present a facile self-template strategy to synthesize Co3 O4 mesoporous nanotubes with outstanding performances in both the electrocatalytic oxygen-evolution reaction (OER) and Li-ion battery via the thermal-oxidation-induced transformation of cheap and easily-prepared Co-Asp(cobalt-aspartic acid) nanowires. The initially formed thin layers on the precursor surfaces, oxygen-induced outward diffusion of interior precursors, the gas release of organic oxidation, and subsequent Kirkendall effect are important for the appearance of the mesoporous nanotubes. This self-template strategy of low-cost precursors is found to be a versatile method to prepare other functional mesoporous nanotubes of transition-metal oxides and chalcogenides, such as NiO, NiCo2 O4 , Mn5 O8 , CoS2 and CoSe2 . PMID:27239778

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

    PubMed Central

    Vejerano, Eric; Dellinger, Barry

    2014-01-01

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

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

    PubMed Central

    Charrier, J. G.; Anastasio, C.

    2013-01-01

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

  18. Catalytic combustion of methane by perovskite-type oxide nanoparticles as pollution prevention strategy

    NASA Astrophysics Data System (ADS)

    Zaza, F.; Luisetto, I.; Serra, E.; Tuti, S.; Pasquali, M.

    2016-06-01

    The transition from the existing brown economy towards the desired green economy drives the research efforts to the development of advanced technologies promoting the efficient utilization of energy sources. Catalysis science offers to combustion technology significant opportunity to increase the fuel efficiency by lowering the internal temperature gradients and reduce the environmental impact by lowering local peak temperature and, consequently, thermodynamically inhibiting the nitrogen oxides formation. Alternative catalytic materials are transition metals oxide, including complex oxides with perovskite crystalline structure. The aim of this work is to synthetize lanthanum ferrite perovskites with lanthanum ions partially substituted by strontium ions in order to study the substitution effects on structural properties and redox activity of the original oxide. Lanthanum ferrite oxides partially substituted with different Strontium amount were synthesized by solution combustion method. The perovskite nanopowders obtained were characterized by XRD, SEM, TPR analyses for defining crystalline structure, morphology and redox properties. Finally, the catalytic activity for methane combustion was tested. The most performing catalysts was La0.6Sr0.4FeO3 having the highest oxygen vacancy concentration as revealed by TPR analysis.

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

    PubMed

    Muthuswamy, Elayaraja; Brock, Stephanie L

    2010-11-17

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

  20. Relative stability of normal vs. inverse spinel for 3d transition metal oxides as lithium intercalation cathodes.

    PubMed

    Bhattacharya, Jishnu; Wolverton, C

    2013-05-01

    Spinel oxides represent an important class of cathode materials for Li-ion batteries. Two major variants of the spinel crystal structure are normal and inverse. The relative stability of normal and inverse ordering at different stages of lithiation has important consequences in lithium diffusivity, voltage, capacity retention and battery life. In this paper, we investigate the relative structural stability of normal and inverse structures of the 3d transition metal oxide spinels with first-principles DFT calculations. We have considered ternary spinel oxides LixM2O4 with M = Ti, V, Cr, Mn, Fe, Co and Ni in both lithiated (x = 1) and delithiated (x = 0) conditions. We find that for all lithiated spinels, the normal structure is preferred regardless of the metal. We observe that the normal structure for all these oxides has a lower size mismatch between octahedral cations compared to the inverse structure. With delithiation, many of the oxides undergo a change in stability with vanadium in particular, showing a tendency to occupy tetrahedral sites. We find that in the delithiated oxide, only vanadium ions can access a +5 oxidation state which prefers tetrahedral coordination. We have also calculated the average voltage of lithiation for these spinels. The calculated voltages agree well with the previously measured and calculated values, wherever available. For the yet to be characterized spinels, our calculation provides voltage values which can motivate further experimental attention. Lastly, we observe that all the normal spinel oxides of the 3d transition metal series have a driving force for a transformation to the non-spinel structure upon delithiation.

  1. Parasitic Absorption Reduction in Metal Oxide-Based Transparent Electrodes: Application in Perovskite Solar Cells.

    PubMed

    Werner, Jérémie; Geissbühler, Jonas; Dabirian, Ali; Nicolay, Sylvain; Morales-Masis, Monica; Wolf, Stefaan De; Niesen, Bjoern; Ballif, Christophe

    2016-07-13

    Transition metal oxides (TMOs) are commonly used in a wide spectrum of device applications, thanks to their interesting electronic, photochromic, and electrochromic properties. Their environmental sensitivity, exploited for gas and chemical sensors, is however undesirable for application in optoelectronic devices, where TMOs are used as charge injection or extraction layers. In this work, we first study the coloration of molybdenum and tungsten oxide layers, induced by thermal annealing, Ar plasma exposure, or transparent conducting oxide overlayer deposition, typically used in solar cell fabrication. We then propose a discoloration method based on an oxidizing CO2 plasma treatment, which allows for a complete bleaching of colored TMO films and prevents any subsequent recoloration during following cell processing steps. Then, we show that tungsten oxide is intrinsically more resilient to damage induced by Ar plasma exposure as compared to the commonly used molybdenum oxide. Finally, we show that parasitic absorption in TMO-based transparent electrodes, as used for semitransparent perovskite solar cells, silicon heterojunction solar cells, or perovskite/silicon tandem solar cells, can be drastically reduced by replacing molybdenum oxide with tungsten oxide and by applying a CO2 plasma pretreatment prior to the transparent conductive oxide overlayer deposition. PMID:27338079

  2. Parasitic Absorption Reduction in Metal Oxide-Based Transparent Electrodes: Application in Perovskite Solar Cells.

    PubMed

    Werner, Jérémie; Geissbühler, Jonas; Dabirian, Ali; Nicolay, Sylvain; Morales-Masis, Monica; Wolf, Stefaan De; Niesen, Bjoern; Ballif, Christophe

    2016-07-13

    Transition metal oxides (TMOs) are commonly used in a wide spectrum of device applications, thanks to their interesting electronic, photochromic, and electrochromic properties. Their environmental sensitivity, exploited for gas and chemical sensors, is however undesirable for application in optoelectronic devices, where TMOs are used as charge injection or extraction layers. In this work, we first study the coloration of molybdenum and tungsten oxide layers, induced by thermal annealing, Ar plasma exposure, or transparent conducting oxide overlayer deposition, typically used in solar cell fabrication. We then propose a discoloration method based on an oxidizing CO2 plasma treatment, which allows for a complete bleaching of colored TMO films and prevents any subsequent recoloration during following cell processing steps. Then, we show that tungsten oxide is intrinsically more resilient to damage induced by Ar plasma exposure as compared to the commonly used molybdenum oxide. Finally, we show that parasitic absorption in TMO-based transparent electrodes, as used for semitransparent perovskite solar cells, silicon heterojunction solar cells, or perovskite/silicon tandem solar cells, can be drastically reduced by replacing molybdenum oxide with tungsten oxide and by applying a CO2 plasma pretreatment prior to the transparent conductive oxide overlayer deposition.

  3. High-temperature desulfurization of gasifier effluents with rare earth and rare earth/transition metal oxides

    SciTech Connect

    Dooley, Kerry M.; Kalakota, Vikram; Adusumilli, Sumana

    2011-02-11

    We have improved the application of mixed rare-earth oxides (REOs) as hot gas desulfurization adsorbents by impregnating them on stable high surface area supports and by the inclusion of certain transition metal oxides. We report comparative desulfurization experiments at high temperature (900 K) using a synthetic biomass gasifier effluent containing 0.1 vol % H2S, along with H2, CO2, and water. More complex REO sorbents outperform the simpler CeO2/La2O3 mixtures, in some cases significantly. Supporting REOs on Al2O3 (~20 wt % REO) or ZrO2 actually increased the sulfur capacities found after several cycles on a total weight basis. Another major increase in sulfur capacity took place when MnOx or FeOx is incorporated. Apparently most of the Mn or Fe is dispersed on or near the surface of the mixed REOs because the capacities with REOs greatly exceeded those of Al2O3-supported MnOx or FeOx alone at these conditions. In contrast, incorporating Cu has little effect on sulfur adsorption capacities. Both the REO and transition metal/REO adsorbents could be regenerated completely using air for at least five repetitive cycles.

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

    SciTech Connect

    Daene, Markus W; Lueders, Martin; Ernst, Arthur; Diemo, Koedderitzsch; Temmerman, Walter M; Szotek, Zdzislawa; Wolfam, Hergert

    2009-01-01

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

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

    PubMed

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

    2003-09-01

    Near-edge fine structures of the metal L(2,3) and O K-edges in transition metal-oxides have been studied with a transmission electron microscope equipped with a monochromator and a high-resolution imaging filter. This system enables the recording of EELS spectra with an energy resolution of 0.1eV thus providing new near-edge fine structure details which could not be observed previously by EELS in conventional TEM instruments. EELS-spectra from well-defined oxides like titanium oxide (TiO(2)), vanadium oxide (V(2)O(5)), chromium oxide (Cr(2)O(3)), iron oxide (Fe(2)O(3)), cobalt oxide (CoO) and nickel oxide (NiO) have been measured with the new system. These spectra are compared with EELS data obtained from a conventional microscope and the main spectral features are interpreted. Additionally, the use of monochromised TEMs is discussed in view of the natural line widths of K and L(2,3) edges. PMID:12871809

  6. Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

    SciTech Connect

    Yan, Pengfei; Zheng, Jianming; Lv, Dongping; Wei, Yi; Zheng, Jiaxin; Wang, Zhiguo; Kuppan, Saravanan; Yu, Jianguo; Luo, Langli; Edwards, Danny J.; Olszta, Matthew J.; Amine, Khalil; Liu, Jun; Xiao, Jie; Pan, Feng; Chen, Guoying; Zhang, Jiguang; Wang, Chong M.

    2015-07-06

    Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions. However, it is scarcely clear about the behavior of each of these transition metal ions. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

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

    PubMed

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

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Erten, Onur

    Transition metal oxides exhibit a wide range of fascinating phenomena ranging from high Tc superconductivity to colossal magnetoresistance. In this thesis, we examine the novel electronic and magnetic properties of double perovskites and oxide interfaces. First we focus on Sr2FeMoO6 which has a half-metallic ground state and a ferrimagnetic Tc=420 K, well above the room temperature. There are very few half-metals in nature and along with its high Tc, Sr2FeMoO6 has enormous potential in spintronics applications. We develop a minimal model that couples the conduction electrons on Mo (4d1) to the core spins of Fe (3d5). Delocalization of conduction electrons and maximizing the kinetic energy drives the long-range magnetic order. "Integrating out" the conduction electrons, we derive a new effective Hamiltonian, H eff, only for the localized spins. Heff is unique to double perovskites, and with its peculiar double square root form, it is different from standard Heisenberg or Anderson-Hasegawa Hamiltonians. Using Heff, we perform the first 3D, finite temperature calculations of double perovskites, going well beyond previous mean field or small cluster calculations. Next we consider Sr2CrOsO6 which has the highest Tc among all perovskites with a net moment. Its insulating behavior is puzzling given that Cr and Os are in the 3d3 and 5d3 configurations, half filled in t2g orbitals. The net moment at low temperature is M(0)=0.75 muB and non-monotonic magnetization as a function of temperature are quite unusual. To address these questions, we organize the problem through the hierarchy of its energy scales. To deal with the highest energy scale, the charge sector, we develop a multi-band Hubbard model that has different on-site Coulomb correlations on the Cr and Os sites. We solve this model using slave-rotor mean field theory which captures the essentials of the metal-Mott insulator transition and goes well beyond Hartree-Fock. We find a new criterion for the Mott transition

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

    NASA Astrophysics Data System (ADS)

    Chiu, Tien-Lung; Chuang, Ya-Ting

    2015-02-01

    Transition metal oxides, such as molybdenum trioxide (MoO3), tungsten trioxide (WO3) and vanadium pent-oxide (V2O5), are well-known hole injection materials used for organic electronic devices. These materials promote work functions of anodes, reduce energy barriers, and facilitate hole transport at the interface between the inorganic anode and organic hole-transporting layer (HTL). In this study, we characterized the transmittance spectra and work function of these materials. Furthermore, we employed a hole-injection layer (HIL) in a blue phosphorescent organic light-emitting diode (OLED) to evaluate their hole-injection capacity by detecting the variation in the emission spectra. Thus, we utilized an OLED structure that has fast electron transporting dynamics to establish the recombination zone located at emitting layer and a partial HTL close to the anode. We used these three transition metal oxides individually as HILs sandwiched between the ITO anode and HTL and concluded that the strength of emissive light from the HTL was determined by their hole-injection capacity, depending on work function. The small amount of HTL emission light of the V2O5 OLED was explained by the high work function of 5.8 eV for the V2O5 film. However, the V2O5 OLED demonstrated the least favorable optoelectrical performance because of its low transmittance and high resistance of the V2O5 film. Ultimately, the 5 nm-MoO3 OLED exhibited the highest device performance because of its high material conductivity and transparency in the visible band.

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

    PubMed

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

    2014-02-14

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

  11. Investigation of the Spatially Resolved Electronic Structure of Single Layer WS2 on Transition Metal Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Katoch, Jyoti; Ulstrup, Søren; Koch, Roland; Schwarz, Daniel; Singh, Simranjeet; McCreary, Kathy; Keun Yoo, Hyang; Xu, Jinsong; Jonker, Berry; Kawakami, Roland; Bostwick, Aaron; Rotenberg, Eli; Jozwiak, Chris

    The family of semiconducting single layer (SL) transition metal dichalcogenides (TMDs) have lately been intensely studied, owing to the strong coupling between spin and valley degrees of freedom as well as the presence of strongly bound excitons. The choice of supporting substrate is known to strongly influence these properties. We set out to investigate the electronic properties of CVD grown SL WS2 transferred onto the dielectric oxide materials SrTiO3 and TiO2. By using a combination of photoemission electron microscopy (PEEM) and angle-resolved photoemission (ARPES) with micrometer focus we obtain simultaneous spatial, momentum and energy-resolved information about SL WS2 on a polar (SrTiO3) and a nonpolar (TiO2) surface for the first time.

  12. Synthesis and characterization of new ternary transition metal sulfide anodes for H 2S-powered solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Vorontsov, V.; Luo, J. L.; Sanger, A. R.; Chuang, K. T.

    A number of ternary transition metal sulfides with general composition AB 2S 4 (where A and B are different transition metal atoms) have been prepared and investigated as potential anode catalysts for use in H 2S-powered solid oxide fuel cells (SOFCs). For the initial screening, polarization resistance of the materials was measured in a two electrode symmetrical cell at 700-850 °C. Vanadium-based materials showed the lowest polarization resistance, and so were chosen for subsequent full cell tests using the configuration [H 2S, AV 2S 4/YSZ/Pt, air] (where A = Ni, Cr, Mo). MoV 2S 4 anode had superior activity and performance in the full cell setup, consistent with results from symmetrical cell tests. Polarization curves showed MoV 2S 4 had the lowest potential drop, with up to a 200 mA cm -2 current density at 800 °C. The highest power density of ca. 275 mW cm -2 at 800 °C was obtained with a pure H 2S stream. Polarization resistance of materials was a strong function of current density, and showed a sharp change of slope attributable to a change in the rate-limiting step of the anode reaction mechanism. MoV 2S 4 was chemically stable during prolonged (10 days) exposure to H 2S at 850 °C, and fuel cell performance was stable during continuous 3-day operation at 370 mA cm -2 current density.

  13. Generalized trends in the formation energies of perovskite oxides.

    PubMed

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

    2013-05-28

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

  14. Generalized trends in the formation energies of perovskite oxides.

    PubMed

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

    2013-05-28

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

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

    NASA Astrophysics Data System (ADS)

    Hwang, Jungmin

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

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

    PubMed

    Xu, Yi-Jun; Fu, Xianzhi

    2009-09-01

    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

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

    PubMed

    Murahashi, Shun-Ichi

    2011-01-01

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

  18. n-Type Transition Metal Oxide as a Hole Extraction Layer in PbS Quantum Dot Solar Cells

    SciTech Connect

    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

    The n-type transition metal oxides (TMO) consisting of molybdenum oxide (MoO{sub x}) and vanadium oxide (V₂O{sub 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{sub 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{sub x} and PbS interface enhancing band bending to allow efficient hole extraction from the valence band of the PbS layer by MoO{sub x}. The carrier transport to the metal anode is likely enhanced through shallow gap states in the MoO{sub x} layer.

  19. [Deactivation by SO2 of transition metal oxides modified low-temperature SCR catalyst for NOx reduction with NH3].

    PubMed

    Shen, Bo-xiong; Liu, Ting; Yang, Ting-ting; Xiong, Li-xian; Wang, Jing

    2009-08-15

    MnOx-CeOx/ACF catalyst was prepared by impregnation method, which exhibited high activity for low-temperature selective catalytic reduction of NOx over the temperature range 110-230 degrees C. Experiments results indicated that the catalyst yielded 80% NO conversion at 150 degrees C and 90% at 230 degrees C. The Oxides of Fe,Cu and V were added to the catalysts based on MnOx-CeOx/ACF. The additions of these transition metal oxides had a negative effect on the activity of the catalysts. Compared with MnOx-CeOx/ACF and Cu and V modified catalysts, NO conversion for Fe-MnOx-CeOx/ACF catalyst leveled off at nearly 75% in the first 6 h in the presence of SO2. Two mechanisms of catalyst deactivation by SO2 were discovered by the methods of X-ray photoelectron spectrum (XPS) and Fourier transform infrared spectra (FTIR), indicating that the catalysts were covered by ammonium sulfates and the metal oxides, acting as active components, were also sulfated by SO2 to form metal sulfates.

  20. Recent advances of lanthanum-based perovskite oxides for catalysis

    SciTech Connect

    Zhu, Huiyuan; Zhang, Pengfei; Dai, Sheng

    2015-09-21

    There is a need to reduce the use of noble metal elements especially in the field of catalysis, where noble metals are ubiquitously applied. To this end, perovskite oxides, an important class of mixed oxide, have been attracting increasing attention for decades as potential replacements. Benefiting from the extraordinary tunability of their compositions and structures, perovskite oxides can be rationally tailored and equipped with targeted physical and chemical properties e.g. redox behavior, oxygen mobility, and ion conductivity for enhanced catalysis. Recently, the development of highly efficient perovskite oxide catalysts has been extensively studied. This review article summarizes the recent development of lanthanum-based perovskite oxides as advanced catalysts for both energy conversion applications and traditional heterogeneous reactions.

  1. Recent advances of lanthanum-based perovskite oxides for catalysis

    DOE PAGES

    Zhu, Huiyuan; Zhang, Pengfei; Dai, Sheng

    2015-09-21

    There is a need to reduce the use of noble metal elements especially in the field of catalysis, where noble metals are ubiquitously applied. To this end, perovskite oxides, an important class of mixed oxide, have been attracting increasing attention for decades as potential replacements. Benefiting from the extraordinary tunability of their compositions and structures, perovskite oxides can be rationally tailored and equipped with targeted physical and chemical properties e.g. redox behavior, oxygen mobility, and ion conductivity for enhanced catalysis. Recently, the development of highly efficient perovskite oxide catalysts has been extensively studied. This review article summarizes the recent developmentmore » of lanthanum-based perovskite oxides as advanced catalysts for both energy conversion applications and traditional heterogeneous reactions.« less

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

    SciTech Connect

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

    2012-07-13

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

  3. Water oxidation using earth-abundant transition metal catalysts: opportunities and challenges.

    PubMed

    Kärkäs, Markus D; Åkermark, Björn

    2016-10-01

    Catalysts for the oxidation of H2O are an integral component of solar energy to fuel conversion technologies. Although catalysts based on scarce and precious metals have been recognized as efficient catalysts for H2O oxidation, catalysts composed of inexpensive and earth-abundant element(s) are essential for realizing economically viable energy conversion technologies. This Perspective summarizes recent advances in the field of designing homogeneous water oxidation catalysts (WOCs) based on Mn, Fe, Co and Cu. It reviews the state of the art catalysts, provides insight into their catalytic mechanisms and discusses future challenges in designing bioinspired catalysts based on earth-abundant metals for the oxidation of H2O.

  4. Storage capacity and oxygen mobility in mixed oxides from transition metals promoted by cerium

    NASA Astrophysics Data System (ADS)

    Perdomo, Camilo; Pérez, Alejandro; Molina, Rafael; Moreno, Sonia

    2016-10-01

    The oxygen mobility and storage capacity of Ce-Co/Cu-MgAl or Ce-MgAl mixed oxides, obtained by hydrotalcite precursors, were evaluated using Toluene-temperature-programmed-reaction, 18O2 isotopic exchange and O2-H2 titration. The presence of oxygen vacancies-related species was evaluated by means of Electron Paramagnetic Resonance. A correlation was found between the studied properties and the catalytic activity of the oxides in total oxidation processes. It was evidenced that catalytic activity depends on two related processes: the facility with which the solid can be reduced and its ability to regenerate itself in the presence of molecular oxygen in the gas phase. These processes are enhanced by Cu-Co cooperative effect in the mixed oxides. Additionally, the incorporation of Ce in the Co-Cu catalysts improved their oxygen transport properties.

  5. Recent Advances in Modeling Transition Metal Oxides for Photo-electrochemistry

    NASA Astrophysics Data System (ADS)

    Caspary Toroker, Maytal

    Computational research offers a wide range of opportunities for materials science and engineering, especially in the energy arena where there is a need for understanding how material composition and structure control energy conversion, and for designing materials that could improve conversion efficiency. Potential inexpensive materials for energy conversion devices are metal oxides. However, their conversion efficiency is limited by at least one of several factors: a too large band gap for efficiently absorbing solar energy, similar conduction and valence band edge characters that may lead to unfavorably high electron-hole recombination rates, a valence band edge that is not positioned well for oxidizing water, low stability, low electronic conductivity, and low surface reactivity. I will show how we model metal oxides with ab-initio methods, primarily DFT +U. Our previous results show that doping with lithium, sodium, or hydrogen could improve iron (II) oxide's electronic properties, and alloying with zinc or nickel could improve iron (II) oxide's optical properties. Furthermore, doping nickel (II) oxide with lithium could improve several key properties including solar energy absorption. In this talk I will highlight new results on our understanding of the mechanism of iron (III) oxide's surface reactivity. Our theoretical insights bring us a step closer towards understanding how to design better materials for photo-electrochemistry. References: 1. O. Neufeld and M. Caspary Toroker, ``Pt-doped Fe2O3 for enhanced water splitting efficiency: a DFT +U study'', J. Phys. Chem. C 119, 5836 (2015). 2. M. Caspary Toroker, ``Theoretical Insights into the Mechanism of Water Oxidation on Non-stoichiometric and Ti - doped Fe2O3 (0001)'', J. Phys. Chem. C, 118, 23162 (2014). This research was supported by the Morantz Energy Research Fund, the Nancy and Stephen Grand Technion Energy Program, the I-CORE Program of the Planning and Budgeting Committee, and The Israel Science

  6. Tetravalent dysprosium in a perovskite-type oxide.

    PubMed

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

    2012-04-17

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  8. NIS-catalyzed oxidative cyclization of alcohols with amidines: a simple and efficient transition-metal free method for the synthesis of 1,3,5-triazines.

    PubMed

    Tiwari, Abhishek R; T, Akash; Bhanage, Bhalchandra M

    2015-12-01

    An efficient method for the synthesis of 1,3,5-triazines by NIS-catalyzed oxidative cyclization of alcohols with amidines has been developed. The reaction works smoothly under transition-metal free and phosphine-free conditions to afford a wide range of 1,3,5-triazine derivatives in moderate to good yields. The synthetic methodology was achieved via in situ oxidation of alcohols to aldehydes. PMID:26477749

  9. Syntheses of [1,2,4]triazolo[1,5-a]benzazoles enabled by the transition-metal-free oxidative N-N bond formation.

    PubMed

    Shang, Erchang; Zhang, Junzhi; Bai, Jinyi; Wang, Zhan; Li, Xiang; Zhu, Bing; Lei, Xiaoguang

    2016-05-19

    A transition-metal-free oxidative N-N bond formation strategy was developed to generate various structurally interesting [1,2,4]triazolo[1,5-a]benzazoles efficiently. The mechanism of the key oxidative N-N bond formation was investigated by using an intramolecular competition reaction. Notably, the first single crystal structure was also obtained to confirm the structure of 2-aryl[1,2,4]triazolo[1,5-a]benzimidazole. PMID:27161847

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

    PubMed Central

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Held, Karsten

    2015-03-01

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

  12. Electronic and Magnetic Properties of Transition-Metal Oxide Nanocomposites: A Tight-Binding Modeling at Mesoscale

    NASA Astrophysics Data System (ADS)

    Tai, Yuan-Yen; Zhu, Jian-Xin

    Transition metal oxides (TMOs) exhibit many emergent phenomena ranging from high-temperature superconductivity and giant magnetoresistance to magnetism and ferroelectricity. In addition, when TMOs are interfaced with each other, new functionalities can arise, which are absent in individual components. In this talk, I will present an overview on our recent efforts in theoretical understanding of the electronic and magnetic properties TMO nanocomposites. In particular, I will introduce our recently developed tight-binding modeling of these properties arising from the interplay of competing interactions at the interfaces of planar and pillar nanocomposites. Our theoretical tool package will provide a unique capability to address the emergent phenomena in TMO nanocomposites and their mesoscale response to such effects like strain and microstructures at the interfaces, and ultimately help establish design principles of new multifunctionality with TMOs. This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at LANL under Contract No. DE-AC52-06NA25396, and was supported by the LANL LDRD Program.

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

    NASA Astrophysics Data System (ADS)

    Caudle, Sean; Tao, Meng; Peng, Xihong

    2012-10-01

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

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

    PubMed

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

    2004-08-01

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

  15. Single crystal growth from separated educts and its application to lithium transition-metal oxides

    PubMed Central

    Freund, F.; Williams, S. C.; Johnson, R. D.; Coldea, R.; Gegenwart, P.; Jesche, A.

    2016-01-01

    Thorough mixing of the starting materials is the first step of a crystal growth procedure. This holds true for almost any standard technique, whereas the intentional separation of educts is considered to be restricted to a very limited number of cases. Here we show that single crystals of α-Li2IrO3 can be grown from separated educts in an open crucible in air. Elemental lithium and iridium are oxidized and transported over a distance of typically one centimeter. In contrast to classical vapor transport, the process is essentially isothermal and a temperature gradient of minor importance. Single crystals grow from an exposed condensation point placed in between the educts. The method has also been applied to the growth of Li2RuO3, Li2PtO3 and β-Li2IrO3. A successful use of this simple and low cost technique for various other materials is anticipated. PMID:27748402

  16. Single crystal growth from separated educts and its application to lithium transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Freund, F.; Williams, S. C.; Johnson, R. D.; Coldea, R.; Gegenwart, P.; Jesche, A.

    2016-10-01

    Thorough mixing of the starting materials is the first step of a crystal growth procedure. This holds true for almost any standard technique, whereas the intentional separation of educts is considered to be restricted to a very limited number of cases. Here we show that single crystals of α-Li2IrO3 can be grown from separated educts in an open crucible in air. Elemental lithium and iridium are oxidized and transported over a distance of typically one centimeter. In contrast to classical vapor transport, the process is essentially isothermal and a temperature gradient of minor importance. Single crystals grow from an exposed condensation point placed in between the educts. The method has also been applied to the growth of Li2RuO3, Li2PtO3 and β-Li2IrO3. A successful use of this simple and low cost technique for various other materials is anticipated.

  17. Enhancing capacitance behaviour of CoOOH nanostructures using transition metal dopants by ambient oxidation

    PubMed Central

    Chen, Yanhui; Zhou, Junfeng; Maguire, Pierce; O’Connell, Robert; Schmitt, Wolfgang; Li, Yonghe; Yan, Zhengguang; Zhang, Yuefei; Zhang, Hongzhou

    2016-01-01

    Cobalt hydrate and doped binary Co0.9M0.1OOH (M = Ni, Mn, Fe) nanorings of 100–300 nm were fabricated in solution through a facile ambient oxidation method. A transformation from Co0.9Ni0.1(OH)2 nanodiscs to hollow Co0.9Ni0.1OOH nanorings was observed with prolonged reaction time. Core-shell nanodiscs have elemental segregation with a Co(OH)2 core and Ni(OH)2 shell. Co0.9Ni0.1OOH nanorings displayed a higher electrochemical capacitance than Mn and Fe doped nanorings materials or materials with disc-like geometries. PMID:26853105

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

    NASA Astrophysics Data System (ADS)

    Xu, Linping

    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

  19. Synthesis and characterisation of polyol-capped transition metal oxide nanoparticles.

    PubMed

    Varadwaj, K S K; Ghose, J

    2005-04-01

    In-situ capped nanocrystalline gamma-Fe2O3, Co3O4, and Cu2O were prepared in 1,4-butanediol in aerobic conditions. X-ray diffraction (XRD) patterns show that the synthesised samples are nanocrystalline cubic oxides with crystallite sizes 9.5 nm, 13.4 nm, and 11 nm, respectively. Raman spectroscopy shows peaks at 350 cm(-1), 500 cm(-1), and 700 cm(-1), indicating that the iron oxide is gamma-Fe2O3; Mössbauer spectroscopy shows the presence of two Fe3(3+) sites. Transmission electron microscopy images show that the particle sizes of gamma-Fe2O3 and Co3O4 samples are 8.9 nm and 7 nm, respectively. The absence of agglomeration indicates that the synthesised nanoparticles are capped. FT-IR spectra show the presence of an organic moiety in the sample which acts as a capping agent. Thermogravimetry shows that the capping is stable up to 873 K in gamma-Fe2O3, and up to 400 K in Co3O4. The samples are soluble in water to form stable hydrosols. During synthesis of gamma-Fe2O3 a 6-line ferrihydrite is formed as an intermediate, which is stable in solution up to 473 K, and transforms to gamma-Fe2O3 at 483 K, by rapid dissolution-reprecipitation. In the syntheses of Co3O4 and Cu2O, no intermediates are formed.

  20. Synthesis and characterisation of polyol-capped transition metal oxide nanoparticles.

    PubMed

    Varadwaj, K S K; Ghose, J

    2005-04-01

    In-situ capped nanocrystalline gamma-Fe2O3, Co3O4, and Cu2O were prepared in 1,4-butanediol in aerobic conditions. X-ray diffraction (XRD) patterns show that the synthesised samples are nanocrystalline cubic oxides with crystallite sizes 9.5 nm, 13.4 nm, and 11 nm, respectively. Raman spectroscopy shows peaks at 350 cm(-1), 500 cm(-1), and 700 cm(-1), indicating that the iron oxide is gamma-Fe2O3; Mössbauer spectroscopy shows the presence of two Fe3(3+) sites. Transmission electron microscopy images show that the particle sizes of gamma-Fe2O3 and Co3O4 samples are 8.9 nm and 7 nm, respectively. The absence of agglomeration indicates that the synthesised nanoparticles are capped. FT-IR spectra show the presence of an organic moiety in the sample which acts as a capping agent. Thermogravimetry shows that the capping is stable up to 873 K in gamma-Fe2O3, and up to 400 K in Co3O4. The samples are soluble in water to form stable hydrosols. During synthesis of gamma-Fe2O3 a 6-line ferrihydrite is formed as an intermediate, which is stable in solution up to 473 K, and transforms to gamma-Fe2O3 at 483 K, by rapid dissolution-reprecipitation. In the syntheses of Co3O4 and Cu2O, no intermediates are formed. PMID:16004130

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

    NASA Astrophysics Data System (ADS)

    Jin, Lei

    2011-12-01

    This thesis contains two parts: 1) Studies of novel synthesis methods and characterization of advanced functional manganese oxide octahedral molecular sieves (OMS) and their applications in Li/Air batteries, solvent free toluene oxidations, and ethane oxydehydrogenation (ODH) in the presence of CO2, recycling the green house gas. 2) Development of unique Ln2O2CO3 (Ln = rare earth) layered materials and ZnO/La2O2CO3 composites as clean energy biofuel catalysts. These parts are separated into five different focused topics included in this thesis. The first topic presents studies of catalytic activities of a single step synthesized gamma-MnO2 octahedral molecular sieve nano fiber in solvent free atmospheric oxidation of toluene with molecular oxygen. Solvent free atmospheric oxidation of toluene is a notoriously difficult liquid phase oxidation process due to the challenge of oxidizing sp³ hybridized carbon in inactive hydrocarbons. The synthesized gamma-MnO2 showed excellent catalytic activity and good selectivity under the mild atmospheric reflux system. Under optimized conditions, a 47.8% conversion of toluene, along with 57% selectivity of benzoic acid and 15% of benzaldehyde were obtained. The effects of reaction time, amount of catalyst and initiator, and the reusability of the catalyst were investigated. The second topic involves developing titanium containing gamma-MnO 2 (TM) hollow spheres as electrocatalysts in Li/Air Batteries. Li/air batteries have recently attracted interest because they have the largest theoretical specific energy (11,972 Wh.kg-1) among all practical electrochemical couples. In this study, unique hollow aspheric materials were prepared for the first time using a one-step synthesis method and fully characterized by various techniques. These prepared materials were found to have excellent electrocatalytic activation as cathode materials in lithium-air batteries with a very high specific capacity (up to 2.3 A.h/g of carbon). The third

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

    NASA Astrophysics Data System (ADS)

    Jin, Lei

    2011-12-01

    This thesis contains two parts: 1) Studies of novel synthesis methods and characterization of advanced functional manganese oxide octahedral molecular sieves (OMS) and their applications in Li/Air batteries, solvent free toluene oxidations, and ethane oxydehydrogenation (ODH) in the presence of CO2, recycling the green house gas. 2) Development of unique Ln2O2CO3 (Ln = rare earth) layered materials and ZnO/La2O2CO3 composites as clean energy biofuel catalysts. These parts are separated into five different focused topics included in this thesis. The first topic presents studies of catalytic activities of a single step synthesized gamma-MnO2 octahedral molecular sieve nano fiber in solvent free atmospheric oxidation of toluene with molecular oxygen. Solvent free atmospheric oxidation of toluene is a notoriously difficult liquid phase oxidation process due to the challenge of oxidizing sp³ hybridized carbon in inactive hydrocarbons. The synthesized gamma-MnO2 showed excellent catalytic activity and good selectivity under the mild atmospheric reflux system. Under optimized conditions, a 47.8% conversion of toluene, along with 57% selectivity of benzoic acid and 15% of benzaldehyde were obtained. The effects of reaction time, amount of catalyst and initiator, and the reusability of the catalyst were investigated. The second topic involves developing titanium containing gamma-MnO 2 (TM) hollow spheres as electrocatalysts in Li/Air Batteries. Li/air batteries have recently attracted interest because they have the largest theoretical specific energy (11,972 Wh.kg-1) among all practical electrochemical couples. In this study, unique hollow aspheric materials were prepared for the first time using a one-step synthesis method and fully characterized by various techniques. These prepared materials were found to have excellent electrocatalytic activation as cathode materials in lithium-air batteries with a very high specific capacity (up to 2.3 A.h/g of carbon). The third

  3. Approach to multifunctional device platform with epitaxial graphene on transition metal oxide

    PubMed Central

    Park, Jeongho; Back, Tyson; Mitchel, William C.; Kim, Steve S.; Elhamri, Said; Boeckl, John; Fairchild, Steven B.; Naik, Rajesh; Voevodin, Andrey A.

    2015-01-01

    Heterostructures consisting of two-dimensional materials have shown new physical phenomena, novel electronic and optical properties, and new device concepts not observed in bulk material systems or purely three dimensional heterostructures. These new effects originated mostly from the van der Waals interaction between the different layers. Here we report that a new optical and electronic device platform can be provided by heterostructures of 2D graphene with a metal oxide (TiO2). Our novel direct synthesis of graphene/TiO2 heterostructure is achieved by C60 deposition on transition Ti metal surface using a molecular beam epitaxy approach and O2 intercalation method, which is compatible with wafer scale growth of heterostructures. As-grown heterostructures exhibit inherent photosensitivity in the visible light spectrum with high photo responsivity. The photo sensitivity is 25 times higher than that of reported graphene photo detectors. The improved responsivity is attributed to optical transitions between O 2p orbitals in the valence band of TiO2 and C 2p orbitals in the conduction band of graphene enabled by Coulomb interactions at the interface. In addition, this heterostructure provides a platform for realization of bottom gated graphene field effect devices with graphene and TiO2 playing the roles of channel and gate dielectric layers, respectively. PMID:26395160

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

    PubMed Central

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

    2013-01-01

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

  5. Synthesis and characterization of nanostructured transition metal oxides for energy storage devices

    NASA Astrophysics Data System (ADS)

    Kim, Jong Woung

    Finding a promising material and constructing a new method to have both high energy and power are key issues for future energy storage systems. This dissertation addresses three different materials systems to resolve those issues. Pseudocapacitive materials such as RuO2 and MnO2 display high capacitance but Nb2O5, displays a different charge storage mechanism, one highly dependent on its crystal phase rather than its surface area. Various sol-gel techniques were used to synthesize the different phases of Nb2O5 and electrochemical testing was used to study their charge storage with some phases displaying comparable charge storage to MnO2. To overcome the electrical limitations of using an insulating material, the core-shell structure (Nb2O 5/C) was also examined and the method could be generalized to improve other pseudocapacitors. Besides electronic conductivity, the diffusion of the electrolyte ions through the shell material is a critical factor for fast charging/discharging in the core-shell structure. This dissertation also involves another topic, a reconfigurable electrode, that displays both high energy and power density. By constructing a reconfigurable electrode which has different electrical properties (metallic or insulating state) depending on the amount of intercalated `guest' ions into `host' material, it can be used as a battery or electrochemical capacitor material in the insulating or metallic state respectively. Metal oxide bronzes having metal-insulator transition were investigated in this study.

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

    SciTech Connect

    Dai, Pengcheng

    2014-02-18

    Understanding the interplay between magnetism and superconductivity continues to be a “hot” topic in modern condensed matter physics. The discovery of high-temperature superconductivity in iron-based materials in 2008 provided an unique opportunity to compare and contrast these materials with traditional high-Tc copper oxide superconductors. Neutron scattering plays an important role in determining the dynamical spin properties in these materials. This proposal is a continuation of previous DOE supported proposal. This report summarizes the final progress we have made over from May 2005 till Aug. 2013. Overall, we continue to carry out extensive neutron scattering experiments on Fe-based materials, focusing on understanding their magnetic properties. In addition, we have established a materials laboratory at UT that has allowed us to grow these superconductors. Because neutron scattering typically demands a large amount of samples, by growing these materials in our own laboratory, we can now pursuit neutron scattering experiments over the entire electronic phase diagram, focusing on regions of interests. The material synthesis laboratory at UT was established entirely with the support of DOE funding. This not only allowed us to carry out neutron scattering experiments, but also permit us to provide samples to other US/International collaborators for studying these materials.

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

    PubMed

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

    2014-07-04

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

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

    SciTech Connect

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

    2011-10-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

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

    PubMed

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

    2015-06-21

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

  11. Transition metal sulfide loaded catalyst

    DOEpatents

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

    1994-04-26

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

  12. Transition metal sulfide loaded catalyst

    DOEpatents

    Maroni, Victor A.; Iton, Lennox E.; Pasterczyk, James W.; Winterer, Markus; Krause, Theodore R.

    1994-01-01

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

  13. Activation of Methane and Carbon Dioxide Mediated by Transition-Metal Doped Magnesium Oxide Clusters [MMgO](+/0/-) (M=Sc-Zn).

    PubMed

    Li, Jilai; González-Navarrete, Patricio; Schlangen, Maria; Schwarz, Helmut

    2015-05-18

    Mission: impossible? DFT calculations show that the trends in the thermochemistry are very different for the activation of CO2 and CH4 mediated by transition-metal doped magnesium oxide clusters [MMgO](+/0/-) (M=Sc-Zn). Thus, seeking a "simple" reagent to simultaneously mediate activation and coupling of CH4 and CO2 with high efficiency seems extremely daunting, if not impossible. PMID:25867011

  14. Technologies for deposition of transition metal oxide thin films: application as functional layers in “Smart windows” and photocatalytic systems

    NASA Astrophysics Data System (ADS)

    Gesheva, K.; Ivanova, T.; Bodurov, G.; Szilágyi, I. M.; Justh, N.; Kéri, O.; Boyadjiev, S.; Nagy, D.; Aleksandrova, M.

    2016-02-01

    “Smart windows” are envisaged for future low-energy, high-efficient architectural buildings, as well as for the car industry. By switching from coloured to fully bleached state, these windows regulate the energy of solar flux entering the interior. Functional layers in these devices are the transition metals oxides. The materials (transitional metal oxides) used in smart windows can be also applied as photoelectrodes in water splitting photocells for hydrogen production or as photocatalytic materials for self-cleaning surfaces, waste water treatment and pollution removal. Solar energy utilization is recently in the main scope of numerous world research laboratories and energy organizations, working on protection against conventional fuel exhaustion. The paper presents results from research on transition metal oxide thin films, fabricated by different methods - atomic layer deposition, atmospheric pressure chemical vapour deposition, physical vapour deposition, and wet chemical methods, suitable for flowthrough production process. The lower price of the chemical deposition processes is especially important when the method is related to large-scale glazing applications. Conclusions are derived about which processes are recently considered as most prospective, related to electrochromic materials and devices manufacturing.

  15. Benchmark Calculations of Energetic Properties of Groups 4 and 6 Transition Metal Oxide Nanoclusters Including Comparison to Density Functional Theory.

    PubMed

    Fang, Zongtang; Both, Johan; Li, Shenggang; Yue, Shuwen; Aprà, Edoardo; Keçeli, Murat; Wagner, Albert F; Dixon, David A

    2016-08-01

    The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller-Peterson-Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n (M = Ti, Zr, Hf, n = 1-4) and (MO3)n (M = Cr, Mo, W, n = 1-3) clusters have been benchmarked with 55 exchange-correlation density functional theory (DFT) functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors, and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer. PMID:27384926

  16. Benchmark Calculations of Energetic Properties of Groups 4 and 6 Transition Metal Oxide Nanoclusters Including Comparison to Density Functional Theory.

    PubMed

    Fang, Zongtang; Both, Johan; Li, Shenggang; Yue, Shuwen; Aprà, Edoardo; Keçeli, Murat; Wagner, Albert F; Dixon, David A

    2016-08-01

    The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller-Peterson-Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n (M = Ti, Zr, Hf, n = 1-4) and (MO3)n (M = Cr, Mo, W, n = 1-3) clusters have been benchmarked with 55 exchange-correlation density functional theory (DFT) functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors, and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer.

  17. Perovskite LaRhO{sub 3} as a p-type active layer in oxide photovoltaics

    SciTech Connect

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

    2015-02-16

    Perovskite-type transition-metal oxides have a wide variety of physical properties and triggered intensive research on functional devices in the form of heteroepitaxial junctions. However, there is a missing component that is a p-type conventional band semiconductor. LaRhO{sub 3} (LRO) is one of very few promising candidates having its bandgap between filled t{sub 2g} and empty e{sub g} of Rh in low-spin state, but there has been no report on the synthesis of large-size single crystals or thin films. Here, we report on the junction properties of single-crystalline thin films of LRO grown on (110) oriented Nb-doped SrTiO{sub 3} substrates. The external quantum efficiency of the photo-electron conversion exceeds 1% in the visible-light region due to the wide depletion layer and long diffusion length of minority carriers in LRO. Clear indication of p-type band semiconducting character in a perovskite oxide of LRO will pave a way to explore oxide electronics of perovskite heterostructures.

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

    PubMed

    Ma, Jing-jing; Yi, Wen-bin; Lu, Guo-ping; Cai, Chun

    2015-03-14

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

  19. Transition metals activate TFEB in overexpressing cells.

    PubMed

    Peña, Karina A; Kiselyov, Kirill

    2015-08-15

    Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach. PMID:26251447

  20. Transition metals activate TFEB in overexpressing cells

    PubMed Central

    Peña, Karina A.; Kiselyov, Kirill

    2015-01-01

    Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach. PMID:26251447

  1. Method for dry etching of transition metals

    DOEpatents

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

    1998-09-29

    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.

  2. Method for dry etching of transition metals

    DOEpatents

    Ashby, Carol I. H.; Baca, Albert G.; Esherick, Peter; Parmeter, John E.; Rieger, Dennis J.; Shul, Randy J.

    1998-01-01

    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.

  3. Accurate electronic and chemical properties of 3d transition metal oxides using a calculated linear response U and a DFT + U(V) method

    SciTech Connect

    Xu, Zhongnan; Kitchin, John R.; Joshi, Yogesh V.; Raman, Sumathy

    2015-04-14

    We validate the usage of the calculated, linear response Hubbard U for evaluating accurate electronic and chemical properties of bulk 3d transition metal oxides. We find calculated values of U lead to improved band gaps. For the evaluation of accurate reaction energies, we first identify and eliminate contributions to the reaction energies of bulk systems due only to changes in U and construct a thermodynamic cycle that references the total energies of unique U systems to a common point using a DFT + U(V ) method, which we recast from a recently introduced DFT + U(R) method for molecular systems. We then introduce a semi-empirical method based on weighted DFT/DFT + U cohesive energies to calculate bulk oxidation energies of transition metal oxides using density functional theory and linear response calculated U values. We validate this method by calculating 14 reactions energies involving V, Cr, Mn, Fe, and Co oxides. We find up to an 85% reduction of the mean average error (MAE) compared to energies calculated with the Perdew-Burke-Ernzerhof functional. When our method is compared with DFT + U with empirically derived U values and the HSE06 hybrid functional, we find up to 65% and 39% reductions in the MAE, respectively.

  4. Transparent conducting oxide free backside illuminated perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Li, Jia; Yao, Jiexiong; Xia, Huarong; Sun, Wentao; Liu, Jian; Peng, Lianmao

    2015-07-01

    Recently, hybrid perovskites have attracted great attention because of their promising applications in solar cells. However, perovskite solar devices reported till now are mostly based on transparent conducting oxide (TCO) substrates which account for a large proportion in the total cost. Herein, TCO-free perovskite solar cells are fabricated. A photo-electricity conversion efficiency of 5.27% is obtained with short circuit current density (Jsc) of 10.7 mA/cm2, open circuit voltage (Voc) of 0.837 V, and fill factor of 0.588. This study points a feasible way of replacing TCO substrate by low cost substrates, indicating promising potentials in solar energy conversion applications.

  5. Calculated transport and magnetic properties of some perovskite metallic oxides AMO{sub 3}

    SciTech Connect

    Santi, G.; Jarlborg, T.

    1998-12-31

    The authors study some compounds of the perovskite (or pseudo-cubic perovskite) series AMO{sub 3}, where M is a transition metal and A is Ca, Sr, or Nd, by LSDA self-consistent electronic structure calculations with the LMTO method. Transport and magnetic properties, as well as Fermi surfaces are calculated. These materials exhibit sharp density of states features in the vicinity of the Fermi level that strongly affect their transport and magnetic properties and make them very sensitive to structural deformation and stoichiometry. Calculated total energies are very close for anti-ferromagnetic and ferromagnetic solutions. This explains qualitatively the magnetoresistive anomalies shown by this family of compounds.

  6. Synthesis-Microstructure-Performance Relationship of Layered Transition Metal Oxides as Cathode for Rechargeable Sodium Batteries Prepared by High-Temperature Calcination

    SciTech Connect

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

    2014-09-05

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

  7. Topological Phases in Perovskite Oxide Heterostructures

    NASA Astrophysics Data System (ADS)

    Kim, Rokyeon; Yu, Jaejun; Jin, Hosub

    Quantum spin Hall (QSH) insulator is a new state of matter characterized by gapless edge states and insulating bulk states. Because the edge states are topologically protected and therefore robust against non-magnetic perturbations, it has a potential to be utilized in spintronics devices. Quauntum vally Hall (QVH) phase, on the other hand, is another class of topological state exhibiting valley-contrasting Berry curvature and spin splitting, which could yield novel transport properties, such as valley Hall effect and valley spin Hall effect. We propose a new kind of perovskite (111) heterostructures which can host both QSH and QVH phases with appropriate choices of composing elements. By carrying out first-principles calculations, we demonstrate that a Dirac cone emerges in a particular choice of heterostructure, and a sizable spin-orbit coupling turns the system into the QSH phase. In addition, the QVH phase with different Berry phases and spin textures in each valley is shown to be realized in the heterostructure with broken inversion symmetry. We porpose that these perovskite heterostructures can provide a feasible platform for spintronics, valleytronics, and topological engineering of the two-dimensional electron system.

  8. Rapid Microwave Synthesis of Perovskite Oxide Nanostructures with Enhanced Functionality

    NASA Astrophysics Data System (ADS)

    Salazar, Gregory; Datta, Anuja; Mukherjee, Pritish

    2015-03-01

    Perovskite oxides are an important class of materials having high dielectric and piezoelectric coefficients, switchable ferroelectric (FE) polarization and interesting optical and electrical properties. Realization of functional devices based on classic perovskite oxides such as Pb(Zr0.52Ti0.48) O3 (PZT), and emerging Pb-free noncentrosymmetric (NCS) oxides, such as, ZnSnO3, ZnTiO3 and CaTiO3 have reinforced the investigation of these materials in multiple dimensions and length scales. However, large-scale synthesis and integration of ordered low-dimensional structures is a challenge, due to their complicated methodologies, high-cost and difficulties with phase stability. We discuss a generalized, cost-effective, rapid microwave synthesis route for size and shape selective nanostructure growth of these functional perovskite oxides on industrially viable flexible and hard substrates, stabilized by an enhanced ionic covalence. The rational synthesis approach allowed improved tunability of the size, shape, and orientation of the structures with improved electrical and FE properties. The facile fabrication route of these nanostructures may expand the outreach of probes for understanding the structure-property relationships in these hitherto unexplored and technologically important materials.

  9. Temperature-independent sensors based on perovskite-type oxides

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  10. Temperature-independent sensors based on perovskite-type oxides

    SciTech Connect

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

    2014-06-19

    The need of energy security and environment sustainability drives toward the development of energy technology in order to enhance the performance of internal combustion engines. Gas sensors play a key role for controlling the fuel oxygen ratio and monitoring the pollution emissions. The perovskite-type oxides can be synthesized for an extremely wide variety of combinations of chemical elements, allowing to design materials with suitable properties for sensing application. Lanthanum strontium ferrites, such as La{sub 0.7}Sr{sub 0.3}FeO{sub 3}, are suitable oxygen sensing materials with temperature-independence conductivity, but they have low chemical stability under reducing conditions. The addition of aluminum into the perovskite structure improves the material properties in order to develop suitable oxygen sensing probes for lean burn engine control systems. Perovskite-type oxides with formula (La{sub 0.7}Sr{sub 0.3})(Al{sub x}Fe{sub 1−x})O{sub 3} was synthesized by the citrate-nitrate combustion synthesis method. XRD analyses, show that it was synthesized a phase-pure powder belonging to the perovskite structure. Aluminum affects both the unit cell parameters, by shrinking the unit cell, and the powder morphology, by promoting the synthesis of particles with small crystallite size and large specific surface area. The partial substitution of iron with aluminum improves the chemical stability under reducing gas conditions and modulates the oxygen sensitivity by affecting the relative amount of Fe{sup 4+} and Fe{sup 3+}, as confirmed from TPR profiles. In the same time, the addition of aluminum does not affects the temperature-independent properties of lanthanum strontium ferrites. Indeed, the electrical measurements show that (La{sub 0.7}Sr{sub 0.3})(Al{sub x}Fe{sub 1−x})O{sub 3} perovskites have temperature-independence conductivity from 900 K.

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

    PubMed

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

    2015-04-01

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

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

    SciTech Connect

    Nekrasov, I. A. Pavlov, N. S.; Sadovskii, M. V.

    2013-04-15

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

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

    NASA Astrophysics Data System (ADS)

    Nekrasov, I. A.; Pavlov, N. S.; Sadovskii, M. V.

    2013-04-01

    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 (SrVO3 and Sr2RuO4). 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 4 s-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.

  14. General facile approach to transition-metal oxides with highly uniform mesoporosity and their application as adsorbents for heavy-metal-ion sequestration.

    PubMed

    Seisenbaeva, Gulaim A; Daniel, Geoffrey; Kessler, Vadim G; Nedelec, Jean-Marie

    2014-08-18

    Mesoporous powders of transition-metal oxides, TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5, pure from organic impurities were produced by a rapid single-step thermohydrolytic approach. The obtained materials display an impressively large active surface area and sharp pore-size distribution, being composed of partially coalesced uniform nanoparticles with crystalline cores and amorphous shells. They reveal extremely high adsorption capacity in removal of Cr(VI) anions from solutions (25.8 for TiO2, 73.0 for ZrO2, and 74.7 mg g(-1) for Nb2O5 in relation to the Cr2O7(2-) anion), making them very attractive as adsorbents in water remediation applications. The difference in adsorption capacities for the studied oxides may be explained by variation in surface hydration and surface-charge distribution.

  15. Position-sensitive change in the transition metal L-edge fine structures

    SciTech Connect

    Gulec, Ahmet; Phillips, Patrick J.; Klie, Robert F.

    2015-10-05

    Studying the structure and composition of solid-state materials on the atomic scale has become nearly routine in transmission electron microscopy with the development of novel electron optics and electron sources. In particular, with spatial resolutions better than 0.1 nm and energy resolution smaller than 100 meV, the stoichiometry, bonding, and coordination can now be examined on similar scales. Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) have played a crucial role in identifying charge ordering, valence, and as spin state transitions in transition metal perovskite oxides. In this letter, we investigate the effects of ever-decreasing electron-probe sizes on the measured near-edge fine-structure of the transition metal core-loss edge using EELS. We find that for certain transition metal perovskites, the position of the electron probe with respect to the atomic column is crucial in determining the correct valence state. Several reasons for the observed position-sensitive EELS fine-structure are discussed.

  16. Oxide perovskite crystals for HTSC film substrates microwave applications

    NASA Technical Reports Server (NTRS)

    Bhalla, A. S.; Guo, Ruyan

    1995-01-01

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

  17. Charge-compensation in 3d-transition-metal-oxide intercalation cathodes through the generation of localized electron holes on oxygen.

    PubMed

    Luo, Kun; Roberts, Matthew R; Hao, Rong; Guerrini, Niccoló; Pickup, David M; Liu, Yi-Sheng; Edström, Kristina; Guo, Jinghua; Chadwick, Alan V; Duda, Laurent C; Bruce, Peter G

    2016-07-01

    During the charging and discharging of lithium-ion-battery cathodes through the de- and reintercalation of lithium ions, electroneutrality is maintained by transition-metal redox chemistry, which limits the charge that can be stored. However, for some transition-metal oxides this limit can be broken and oxygen loss and/or oxygen redox reactions have been proposed to explain the phenomenon. We present operando mass spectrometry of (18)O-labelled Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+)]O2, which demonstrates that oxygen is extracted from the lattice on charging a Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+)]O2 cathode, although we detected no O2 evolution. Combined soft X-ray absorption spectroscopy, resonant inelastic X-ray scattering spectroscopy, X-ray absorption near edge structure spectroscopy and Raman spectroscopy demonstrates that, in addition to oxygen loss, Li(+) removal is charge compensated by the formation of localized electron holes on O atoms coordinated by Mn(4+) and Li(+) ions, which serve to promote the localization, and not the formation, of true O2(2-) (peroxide, O-O ~1.45 Å) species. The quantity of charge compensated by oxygen removal and by the formation of electron holes on the O atoms is estimated, and for the case described here the latter dominates. PMID:27325095

  18. Charge-compensation in 3d-transition-metal-oxide intercalation cathodes through the generation of localized electron holes on oxygen.

    PubMed

    Luo, Kun; Roberts, Matthew R; Hao, Rong; Guerrini, Niccoló; Pickup, David M; Liu, Yi-Sheng; Edström, Kristina; Guo, Jinghua; Chadwick, Alan V; Duda, Laurent C; Bruce, Peter G

    2016-07-01

    During the charging and discharging of lithium-ion-battery cathodes through the de- and reintercalation of lithium ions, electroneutrality is maintained by transition-metal redox chemistry, which limits the charge that can be stored. However, for some transition-metal oxides this limit can be broken and oxygen loss and/or oxygen redox reactions have been proposed to explain the phenomenon. We present operando mass spectrometry of (18)O-labelled Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+)]O2, which demonstrates that oxygen is extracted from the lattice on charging a Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+)]O2 cathode, although we detected no O2 evolution. Combined soft X-ray absorption spectroscopy, resonant inelastic X-ray scattering spectroscopy, X-ray absorption near edge structure spectroscopy and Raman spectroscopy demonstrates that, in addition to oxygen loss, Li(+) removal is charge compensated by the formation of localized electron holes on O atoms coordinated by Mn(4+) and Li(+) ions, which serve to promote the localization, and not the formation, of true O2(2-) (peroxide, O-O ~1.45 Å) species. The quantity of charge compensated by oxygen removal and by the formation of electron holes on the O atoms is estimated, and for the case described here the latter dominates.

  19. Effect of Transition Metal Ions on the B Ring Oxidation of Sterols and their Kinetics in Oil-in-Water Emulsions

    PubMed Central

    Lu, Baiyi; Hu, Yinzhou; Huang, Weisu; Wang, Mengmeng; Jiang, Yuan; Lou, Tiantian

    2016-01-01

    This study investigated the effect of metal ions on the oxidation of sterols and their kinetics in oil-in-water emulsions. Sterol substrates were added with different metal ions (Cu2+, Fe2+, Mn2+, Zn2+, Na+, and Mg2+) of five concentrations and investigated after 2 h of heating at 90 °C. The substrates added with Fe2+ and Cu2+ were heated continuously to evaluate the kinetics of four sterols and their corresponding sterol oxidation products (SOPs). Sterol oxidation increased as the metal ion concentration increased and the heating time was prolonged. The capability of the metal ions oxidizing sterols ranked as followed: Fe2+ > Cu2+ > Mn2+ > Zn2+ > Mg2+ ≈ Na+. 7-Ketosterol, 7β/7α-Hydroxysterol, 5β,6β/5α,6α-Epoxysterol, and Triols were the main oxides on the B ring, whereas 6β-Hydroxysterol was not or only slightly influenced. The acceleration of sterol degradation induced by Fe2+ and Cu2+, as well as the formation of oxidation products, followed first-order formation/elimination kinetics. The acceleration effect may be partly ascribed to the increase in elimination rate constant and formation rate constant. Transition metal ions can significantly induce sterol oxidation, which reduces food nutritional quality and triggers the formation of undesirable compounds, such as SOPs. PMID:27328709

  20. Effect of Transition Metal Ions on the B Ring Oxidation of Sterols and their Kinetics in Oil-in-Water Emulsions.

    PubMed

    Lu, Baiyi; Hu, Yinzhou; Huang, Weisu; Wang, Mengmeng; Jiang, Yuan; Lou, Tiantian

    2016-01-01

    This study investigated the effect of metal ions on the oxidation of sterols and their kinetics in oil-in-water emulsions. Sterol substrates were added with different metal ions (Cu(2+), Fe(2+), Mn(2+), Zn(2+), Na(+), and Mg(2+)) of five concentrations and investigated after 2 h of heating at 90 °C. The substrates added with Fe(2+) and Cu(2+) were heated continuously to evaluate the kinetics of four sterols and their corresponding sterol oxidation products (SOPs). Sterol oxidation increased as the metal ion concentration increased and the heating time was prolonged. The capability of the metal ions oxidizing sterols ranked as followed: Fe(2+) > Cu(2+) > Mn(2+) > Zn(2+) > Mg(2+) ≈ Na(+). 7-Ketosterol, 7β/7α-Hydroxysterol, 5β,6β/5α,6α-Epoxysterol, and Triols were the main oxides on the B ring, whereas 6β-Hydroxysterol was not or only slightly influenced. The acceleration of sterol degradation induced by Fe(2+) and Cu(2+), as well as the formation of oxidation products, followed first-order formation/elimination kinetics. The acceleration effect may be partly ascribed to the increase in elimination rate constant and formation rate constant. Transition metal ions can significantly induce sterol oxidation, which reduces food nutritional quality and triggers the formation of undesirable compounds, such as SOPs. PMID:27328709

  1. 3s- and 3p-core level excitations in 3d-transition metal oxides from electron-energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Steiner, P.; Zimmermann, R.; Reinert, F.; Engel, Th.; Hüfner, S.

    1995-03-01

    3s- and 3p-core level excitations for a large number of 3d-transition metal oxides, with a formal 3d occupation from 3d0 to 3d10, have been measured by electron energy loss spectroscopy in reflection geometry (REELS) with primary energies 200 eV≤ E 0≤1600 eV. Their intensities decrease systematically with the formal 3d-count, classifying them as transitions to empty 3d-states. The structure of the 3s excitations is analysed in detail and is compared to the 3s-XPS photoemission spectra of the samples. This 3s-REELS structure and its change with the 3d occupation can be explained by the assumption that the excitation arises mainly from a 3s23dn→3s13dn+1 quadrupole transition.

  2. Perovskite Oxide Thin Film Growth, Characterization, and Stability

    NASA Astrophysics Data System (ADS)

    Izumi, Andrew

    Studies into a class of materials known as complex oxides have evoked a great deal of interest due to their unique magnetic, ferroelectric, and superconducting properties. In particular, materials with the ABO3 perovskite structure have highly tunable properties because of the high stability of the structure, which allows for large scale doping and strain. This also allows for a large selection of A and B cations and valences, which can further modify the material's electronic structure. Additionally, deposition of these materials as thin films and superlattices through techniques such as pulsed laser deposition (PLD) results in novel properties due to the reduced dimensionality of the material. The novel properties of perovskite oxide heterostructures can be traced to a several sources, including chemical intermixing, strain and defect formation, and electronic reconstruction. The correlations between microstructure and physical properties must be investigated by examining the physical and electronic structure of perovskites in order to understand this class of materials. Some perovskites can undergo phase changes due to temperature, electrical fields, and magnetic fields. In this work we investigated Nd0.5Sr 0.5MnO3 (NSMO), which undergoes a first order magnetic and electronic transition at T=158K in bulk form. Above this temperature NSMO is a ferromagnetic metal, but transitions into an antiferromagnetic insulator as the temperature is decreased. This rapid transition has interesting potential in memory devices. However, when NSMO is deposited on (001)-oriented SrTiO 3 (STO) or (001)-oriented (LaAlO3)0.3-(Sr 2AlTaO6)0.7 (LSAT) substrates, this transition is lost. It has been reported in the literature that depositing NSMO on (110)-oriented STO allows for the transition to reemerge due to the partial epitaxial growth, where the NSMO film is strained along the [001] surface axis and partially relaxed along the [11¯0] surface axis. This allows the NSMO film enough

  3. Transition metals in superheat melts

    NASA Technical Reports Server (NTRS)

    Jakes, Petr; Wolfbauer, Michael-Patrick

    1993-01-01

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

  4. Artificial layered perovskite oxides A(B{sub 0.5}B′{sub 0.5})O{sub 3} as potential solar energy conversion materials

    SciTech Connect

    Chen, Hungru; Umezawa, Naoto

    2015-02-07

    Perovskite oxides with a d{sup 0} electronic configuration are promising photocatalysts and exhibit high electron mobilities. However, their band gaps are too large for efficient solar energy conversion. On the other hand, transition metal cations with partially filled d{sup n} electronic configurations give rise to visible light absorption. In this study, by using hybrid density functional theory calculations, it is demonstrated that the virtues of the two categories of materials can be combined in perovskite oxide A(B{sub 0.5}B′{sub 0.5})O{sub 3} with a layered B-site ordering along the [001] direction. The electronic structures of the four selected perovskite oxide compounds, La(Ti{sub 0.5}Ni{sub 0.5})O{sub 3}, La(Ti{sub 0.5}Zn{sub 0.5})O{sub 3}, Sr(Nb{sub 0.5}Cr{sub 0.5})O{sub 3}, and Sr(Nb{sub 0.5}Fe{sub 0.5})O{sub 3} are calculated and discussed.

  5. Superconductivity in transition metals.

    PubMed

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified.

  6. Superconductivity in transition metals.

    PubMed

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. PMID:25666075

  7. Autothermal reforming catalyst having perovskite structure

    DOEpatents

    Krumpel, Michael; Liu, Di-Jia

    2009-03-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    A facile and novel preparation strategy based on electrochemical techniques for the fabrication of electrodeposited graphene (EGR) and zinc oxide (ZnO) nanocomposite was developed. The morphology and structure of the EGR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (XPS) and Raman spectroscopy. Meanwhile, the electrochemical performance of the nanocomposite was demonstrated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect of EGR and ZnO nanoparticles, an ultrasensitive electrochemical sensor for acetaminophen (AC) and phenacetin (PCT) was successfully fabricated. The linearity ranged from 0.02 to 10 μM for AC and 0.06 to 10 μM for PCT with high sensitivities of 54 295.82 μA mM-1 cm2 for AC and 21 344.66 μA 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 μM for AC and 0.06 to 10

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

    PubMed

    Khaleel, Abbas; Nawaz, Muhammad

    2015-03-01

    High-surface-area mesoprous powders of γ-Al2O3 doped with Cu2+, Cr3+, and V3+ ions were prepared via a modified sol-gel method and were investigated as catalysts for the oxidation of chlorinated organic compounds. The composites retained high surface areas and pore volumes comparable with those of undoped γ-Al2O3 and the presence of the transition metal ions enhanced their surface acidic properties. The catalytic activity of the prepared catalysts in the oxidation of 1,2-dichloroethane (DCE) was studied in the temperature range of 250-400°C. The catalytic activity and product selectivity were strongly dependent on the presence and the type of dopant ion. While Cu2+- and Cr3+-containing catalysts showed 100% conversion at 300°C and 350°C, V3+-containing catalyst showed considerably lower conversion. Furthermore, while the major products of the reactions over γ-alumina were vinyl chloride (C2H3Cl) and hydrogen chloride (HCl) at all temperatures, Cu- and Cr-doped catalysts showed significantly stronger capability for deep oxidation to CO2. PMID:25766029

  10. Beyond Metal-Hydrides: Non-Transition-Metal and Metal-Free Ligand-Centered Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation.

    PubMed

    Haddad, Andrew Z; Garabato, Brady D; Kozlowski, Pawel M; Buchanan, Robert M; Grapperhaus, Craig A

    2016-06-29

    A new pathway for homogeneous electrocatalytic H2 evolution and H2 oxidation has been developed using a redox active thiosemicarbazone and its zinc complex as seminal metal-free and transition-metal-free examples. Diacetyl-bis(N-4-methyl-3-thiosemicarbazone) and zinc diacetyl-bis(N-4-methyl-3-thiosemicarbazide) display the highest reported TOFs of any homogeneous ligand-centered H2 evolution catalyst, 1320 and 1170 s(-1), respectively, while the zinc complex also displays one of the highest reported TOF values for H2 oxidation, 72 s(-1), of any homogeneous catalyst. Catalysis proceeds via ligand-centered proton-transfer and electron-transfer events while avoiding traditional metal-hydride intermediates. The unique mechanism is consistent with electrochemical results and is further supported by density functional theory. The results identify a new direction for the design of electrocatalysts for H2 evolution and H2 oxidation that are not reliant on metal-hydride intermediates. PMID:27326672

  11. Transition-Metal-Free Regioselective Alkylation of Pyridine N-Oxides Using 1,1-Diborylalkanes as Alkylating Reagents.

    PubMed

    Jo, Woohyun; Kim, Junghoon; Choi, Seoyoung; Cho, Seung Hwan

    2016-08-01

    Reported herein is an unprecedented base-promoted deborylative alkylation of pyridine N-oxides using 1,1-diborylalkanes as alkyl sources. The reaction proceeds efficiently for a wide range of pyridine N-oxides and 1,1-diborylalkanes with excellent regioselectivity. The utility of the developed method is demonstrated by the sequential C-H arylation and methylation of pyridine N-oxides. The reaction also can be applied for the direct introduction of a methyl group to 9-O-methylquinine N-oxide, thus it can serve as a powerful method for late-stage functionalization. PMID:27351367

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

    PubMed

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

    2014-11-18

    oxygen vacancy formation energy is a robust descriptor for evaluating oxide ion transport properties. We also find it has a direct relationship with (i) the transition metal-oxygen bond strength and (ii) the extent to which electrons left behind by the departing oxygen delocalize onto the oxygen sublattice. Design principles from our QM results may guide further development of perovskite-based MIEC materials for SOFC applications.

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

    SciTech Connect

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

    1996-12-01

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

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

    DOEpatents

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

    2001-01-01

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

  15. Transition Metal Switchable Mirror

    SciTech Connect

    2009-08-21

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

  16. Transition Metal Switchable Mirror

    ScienceCinema

    None

    2016-07-12

    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

  17. Transition Metal Switchable Mirror

    ScienceCinema

    None

    2016-07-12

    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.

  18. Oxidation of methanol on 2nd and 3rd row group VIII transition metals (Pt, Ir, Os, Pd, Rh, and Ru): Application to direct methanol fuel cells

    SciTech Connect

    Kua, J.; Goddard, W.A. III

    1999-12-01

    Using first principles quantum mechanics [nonlocal density functional theory (B3LYP)], the authors calculated the 13 most likely intermediate species for methanol oxidation on clusters of all 2nd and 3rd row Group VIII transition metals for all three likely binding sites (top, bridge, and cap). This comprehensive set of binding energies and structures allows a detailed analysis of possible reaction mechanisms and how they change for different metals. This illustrates the role in which modern quantum chemical methods can be used to provide data for combinatorial strategies for discovering and designing new catalysts. Methanol dehydrogenation is most facile on Pt, with the hydrogens preferentially stripped off the carbon end. However, water dehydrogenation is most facile on Ru. These results support the bifunctional mechanism for methanol oxidation on Pt-Ru alloys in direct methanol fuel cells (DMFCs). Pure Os is capable of performing both functionalities without cocatalyst. It is suggested that pure Os be examined as a potential catalyst for low overpotential, highly dispersed catalyst DMFCs. Pathways to form the second C-O bond differ between the pure metals (Pt and Os) in which (CO){sub ads} is probably activated by (OH){sub ads} and the Pt-Ru binary system in which (COH){sub ads} is probably activated by O{sub ads}. For all cases formation of (COOH){sub ads} is an important precursor to the final dehydrogenation to desorb CO{sub 2} from the surface.

  19. Oxide-Ion Conduction in Anion-Deficient Perovskites.

    NASA Astrophysics Data System (ADS)

    Feng, Man

    1995-01-01

    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 of the motional enthalpy of the disordered vacancy. Substitution of both aliovalent and isovalent cations were investigated as a means of suppressing the long-range ordering. Substitution of Nb^{5+}, Ti ^{4+}, Sn^{4+ } could be made for In^{3+ } at the B sites of the ABO_ {3-delta} perovskite structure, and this strategy did suppress long-range ordering of the oxygen vacancies for more than 10 mole % dopant. However, it was found that these dopants have a sufficient preference for octahedral anion coordination that water is introduced into the vacancies below 400^circ C; the protons introduced with the water became dominant conductive species below 400^circ C. At high temperature, the oxide-ion conduction is dominant and, below 930^circC, is enhanced by two orders of magnitude for about 20% dopant whether quadravalent or pentavalent dopants are used. Substitution of La^{3+} for Ba ^{2+} suppressed the introduction of water at low temperature, and the best oxide-ion conduction was achieved in rm Ba_{0.6}La _{0.4}InO_{2.7} isovalent doping of Y for In in rm Ba_2In _2O_5<=ad to the discovery of an extremely high ionic conduction in rm Ba _3Y_4O_9 stabilized at room temperature by quenching from above 1200^ circC. On heating in air, it first decomposes into rm Y_2O_3 and a Ba(OH)_2-BaO_2 mix that becomes an immobilized melt and a fast ionic conductor above 370^circC. With time in air, the melt is transformed to BaCO_3 , which is not conductive. Superior oxide-ion conduction was discovered in the Sr and Mg doped perovskite La

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

    SciTech Connect

    Vasbinder, Michael John

    2006-01-01

    Chapters 1 and 2 dealt with the chemistry of superoxo-, hydroperoxo-, and oxo- complexes of chromium, rhodium and cobalt. Chapter 3 dealt with the mechanism of oxygen-atom transfer catalyzed by an oxo-complex of rhenium. In Chapter 1, it was shown that hydroperoxometal complexes of cobalt and rhodium react with superoxochromium and chromyl ions, generating reduced chromium species while oxidizing the hydroperoxometal ions to their corresponding superoxometal ions. It was shown that the chromyl and superoxochromium ions are the more powerful oxidants. Evidence supports hydrogen atom transfer from the hydroperoxometal ion to the oxidizing superoxochromium or chromyl ion as the reaction mechanism. There is a significant H/D kinetic isotope effect. Comparisons to the rate constants of other known hydrogen atom transfer reactions show the expected correlation with bond dissociation energies. In Chapter 2, it was found that the superoxometal complexes Cr{sub aq}OO2+ and Rh(NH3)4(H2O)OO2+ oxidize stable nitroxyl radicals of the TEMPO series with rate constants that correlate with the redox potentials of both the oxidant and reductant. These reactions fit the Marcus equation for electron transfer near the theoretical value. Acid catalysis is important to the reaction, especially the thermodynamically limited cases involving Rh(NH3)4(H2O)OO2+ as the oxidant. The rate constants are notably less than those measured in the reaction between the same nitroxyl radicals and other strong free-radical oxidants, an illustration of the delocalized and stabilized nature of the superoxometal ions. Chapter 3 showed that oxo-rhenium catalysts needed a nucleophile to complete the catalytic oxygen-atom transfer from substituted pyridine-N-oxides to triphenylphosphine. The reaction was studied by introducing various pyridine-derived nucleophiles and monitoring their effect on the rate, then

  1. Tuning ferromagnetism at interfaces between insulating perovskite oxides.

    PubMed

    Ganguli, Nirmal; Kelly, Paul J

    2014-09-19

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

  2. Strategies to curb structural changes of lithium/transition metal oxide cathode materials & the changes’ effects on thermal & cycling stability

    NASA Astrophysics Data System (ADS)

    Xiqian, Yu; Enyuan, Hu; Seongmin, Bak; Yong-Ning, Zhou; Xiao-Qing, Yang

    2016-01-01

    Structural transformation behaviors of several typical oxide cathode materials during a heating process are reviewed in detail to provide in-depth understanding of the key factors governing the thermal stability of these materials. We also discuss applying the information about heat induced structural evolution in the study of electrochemically induced structural changes. All these discussions are expected to provide valuable insights for designing oxide cathode materials with significantly improved structural stability for safe, long-life lithium ion batteries, as the safety of lithium-ion batteries is a critical issue; it is widely accepted that the thermal instability of the cathodes is one of the most critical factors in thermal runaway and related safety problems. Project supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies (Grant No. DE-SC0012704).

  3. Strategies to curb structural changes of lithium/transition metal oxide cathode materials & the changes' effects on thermal & cycling stability

    DOE PAGES

    Yu, Xiqian; Hu, Enyuan; Bak, Seongmin; Zhou, Yong -Ning; Yang, Xiao -Qing

    2015-12-07

    Structural transformation behaviors of several typical oxide cathode materials during a heating process are reviewed in detail to provide in-depth understanding of the key factors governing the thermal stability of these materials. Furthermore, we also discuss applying the information about heat induced structural evolution in the study of electrochemically induced structural changes. All these discussions are expected to provide valuable insights for designing oxide cathode materials with significantly improved structural stability for safe, long-life lithium ion batteries, as the safety of lithium-ion batteries is a critical issue. As a result, it is widely accepted that the thermal instability of themore » cathodes is one of the most critical factors in thermal runaway and related safety problems.« less

  4. Strategies to curb structural changes of lithium/transition metal oxide cathode materials & the changes' effects on thermal & cycling stability

    SciTech Connect

    Yu, Xiqian; Hu, Enyuan; Bak, Seongmin; Zhou, Yong -Ning; Yang, Xiao -Qing

    2015-12-07

    Structural transformation behaviors of several typical oxide cathode materials during a heating process are reviewed in detail to provide in-depth understanding of the key factors governing the thermal stability of these materials. Furthermore, we also discuss applying the information about heat induced structural evolution in the study of electrochemically induced structural changes. All these discussions are expected to provide valuable insights for designing oxide cathode materials with significantly improved structural stability for safe, long-life lithium ion batteries, as the safety of lithium-ion batteries is a critical issue. As a result, it is widely accepted that the thermal instability of the cathodes is one of the most critical factors in thermal runaway and related safety problems.

  5. Degradation of vulcanized and nonvulcanized polyisoprene rubbers by lipid peroxidation catalyzed by oxidative enzymes and transition metals.

    PubMed

    Sato, Shin; Honda, Yoichi; Kuwahara, Masaaki; Watanabe, Takashi

    2003-01-01

    Despite numerous reports concerning the biodegradation of rubber materials, there has been no report of rubber degradation by fully characterized enzymes. In the present paper, we presented a new method to decompose nonvulcanized and vulcanized polyisoprene rubbers by controlling the free radical chain reactions of lipids using oxidative enzymes, manganese peroxidase (MnP), laccase (Lac), and horseradish peroxidase (HRP). Nonvulcanized synthetic polyisoprene (IR) was degraded by the free radicals from unsaturated fatty acids produced by MnP, HRP, and a combination of Lac/1-hydroxybenzotriazole. In contrast, lipoxygenase caused no apparent degradation. Degradation of IR was also observed in lipid peroxidation initiated by the Fenton reaction (FR) and Mn(III), an oxidation product produced by MnP. Vulcanized polyisoprene rubber sheets were degraded by the lipid peroxidation initiated by HRP, MnP, Mn(III), and FR. Pyrolysis GC-MS analysis demonstrated that the lipid peroxidation liberated isoprenoid fragments from the vulcanized rubbers. PMID:12625727

  6. Cooperative tin oxide fullerene electron selective layers for high-performance planar perovskite solar cells

    SciTech Connect

    Ke, Weijun; Zhao, Dewei; Xiao, Chuanxiao; Wang, Changlei; Cimaroli, Alexander J.; Grice, Corey R.; Yang, Mengjin; Li, Zhen; Jiang, Chun-Sheng; Al-Jassim, Mowafak; Zhu, Kai; Kanatzidis, Mercouri G.; Fang, Guojia; Yan, Yanfa

    2016-01-01

    Both tin oxide (SnO2) and fullerenes have been reported as electron selective layers (ESLs) for producing efficient lead halide perovskite solar cells. Here, we report that SnO2 and fullerenes can work cooperatively to further boost the performance of perovskite solar cells. We find that fullerenes can be redissolved during perovskite deposition, allowing ultra-thin fullerenes to be retained at the interface and some dissolved fullerenes infiltrate into perovskite grain boundaries. The SnO2 layer blocks holes effectively; whereas, the fullerenes promote electron transfer and passivate both the SnO2/perovskite interface and perovskite grain boundaries. With careful device optimization, the best-performing planar perovskite solar cell using a fullerene passivated SnO2 ESL has achieved a steady-state efficiency of 17.75% and a power conversion efficiency of 19.12% with an open circuit voltage of 1.12 V, a short-circuit current density of 22.61 mA cm-2, and a fill factor of 75.8% when measured under reverse voltage scanning. We find that the partial dissolving of fullerenes during perovskite deposition is the key for fabricating high-performance perovskite solar cells based on metal oxide/fullerene ESLs.

  7. 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)

    Tang, Yu Ming

    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.

  8. GW approximation study of late transition metal oxides: Spectral function clusters around Fermi energy as the mechanism behind smearing in momentum density

    NASA Astrophysics Data System (ADS)

    Khidzir, S. M.; Ibrahim, K. N.; Wan Abdullah, W. A. T.

    2016-05-01

    Momentum density studies are the key tool in Fermiology in which electronic structure calculations have proven to be the integral underlying methodology. Agreements between experimental techniques such as Compton scattering experiments and conventional density functional calculations for late transition metal oxides (TMOs) prove elusive. In this work, we report improved momentum densities of late TMOs using the GW approximation (GWA) which appears to smear the momentum density creating occupancy above the Fermi break. The smearing is found to be largest for NiO and we will show that it is due to more spectra surrounding the NiO Fermi energy compared to the spectra around the Fermi energies of FeO and CoO. This highlights the importance of the positioning of the Fermi energy and the role played by the self-energy term to broaden the spectra and we elaborate on this point by comparing the GWA momentum densities to their LDA counterparts and conclude that the larger difference at the intermediate level shows that the self-energy has its largest effect in this region. We finally analyzed the quasiparticle renormalization factor and conclude that an increase of electrons in the d-orbital from FeO to NiO plays a vital role in changing the magnitude of electron correlation via the self-energy.

  9. Resistive switching mechanism in delafossite-transition metal oxide (CuInO2-CuO) bilayer structure

    NASA Astrophysics Data System (ADS)

    Varandani, Deepak; Singh, Bharti; Mehta, Bodh R.; Singh, Mandeep; Singh, Vidya Nand; Gupta, Dasees

    2010-05-01

    This study reports reversible and unipolar resistive switching in oxide bilayer structure due to the conversion of rectifying CuInO2-CuO semiconductor heterojunction to metal-semiconductor CuInO2-Cu Ohmic contact. High resolution transmission electron microscopy and conducting atomic force microscopy studies establish that switching occurs due to formation of conducting Cu filaments in CuO layer with CuInO2 layer remaining unaffected. The bilayer structure, with CuO layer acting as the switching element and CuInO2 layer as the resistance controlling element, exhibits improved switching parameters in comparison to single CuO layer.

  10. Mechanical mixtures of metal oxides and phosphorus pentoxide as novel precursors for the synthesis of transition-metal phosphides.

    PubMed

    Guo, Lijuan; Zhao, Yu; Yao, Zhiwei

    2016-01-21

    This study presents a new type of precursor, mechanical mixtures of metal oxides (MOs) and phosphorus pentoxide (P2O5) are used to synthesize Ni2P, Co2P and MoP phosphides by the H2 reduction method. In addition, this is first report of common solid-state P2O5 being used as a P source for the synthesis of metal phosphides. The traditional precursors are usually prepared via a complicated preparation procedure involving dissolution, drying and calcination steps. However, these novel MOs/P2O5 precursors can be obtained only by simple mechanical mixing of the starting materials. Furthermore, unlike the direct transformation from amorphous phases to phosphides, various specific intermediates were involved in the transformation from MOs/P2O5 to phosphides. It is worthy to note that the dispersions of Ni2P, Co2P and MoP obtained from MOs/P2O5 precursors were superior to those of the corresponding phosphides prepared from the abovementioned traditional precursors. It is suggested that the morphology of the as-prepared metal phosphides might be inherited from the corresponding MOs. Based on the results of XRD, XPS, SEM and TEM, the formation pathway of phosphides can be defined as MOs/P2O5 precursors → complex intermediates (metals, metal phosphates and metal oxide-phosphates) → metal phosphides.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  12. Melting of Transition Metals

    SciTech Connect

    Ross, M; Japel, S; Boehler, R

    2005-04-11

    We review the transition melting studies carried out at Mainz, and describe a recently developed model used to explain that the relatively low melting slopes are due to the partially filled d-bands, and the persistence of the pressure induced s-d transition. The basic tenets of the model have now been reconfirmed by new measurements for Cu and Ni. The measurements show that Cu which has a filled 3d-band, has a melt slope that is about 2.5 greater than its neighbor Ni. In the case of Mo, the apparent discrepancy of DAC melting measurements with shock melting can be explained by accounting for the change in melt slope due to the bcc-cp transition observed in the shock studies. The Fe melt curve is revisited. The possible relevance of the Jahn-Teller effect and recently observed transition metal melts with Icosahedral Short-Range Order (ISRO) is discussed.

  13. Transition metal-mediated donor-acceptor coordination of low-oxidation state Group 14 element halides.

    PubMed

    Swarnakar, Anindya K; Ferguson, Michael J; McDonald, Robert; Rivard, Eric

    2016-04-14

    The reactivity of tungsten carbonyl adducts of Group 14 element (Ge, Sn and Pb) dihalides towards the metal-based donors (η(5)-C5H5)Rh(PMe2Ph)2 and Pt(PCy3)2 was examined. When (η(5)-C5H5)Rh(PMe2Ph)2 was treated with the Lewis acid supported Ge(ii) complex, THF·GeCl2·W(CO)5, cyclopentadienyl ring activation occurred, whereas the analogous Lewis acidic units SnCl2·W(CO)5 and PbCl2 form direct adducts with the Rh complex to yield Rh-Sn and Rh-Pb dative bonds. Attempts to prepare metal coordinated element(ii) hydrides by adding hydride sources to the above mentioned rhodium-E(ii) halide complexes were unsuccessful; in each case insoluble products were formed along with regeneration of free (η(5)-C5H5)Rh(PMe2Ph)2. In a parallel study, ECl2·W(CO)5 (E = Ge or Sn) groups were shown to participate in E-Cl oxidation addition chemistry with (Cy3P)2Pt to give the formal Pt(ii) complexes ClPt(PCy3)2ECl·W(CO)5.

  14. Dimethylaminoborane (H2BNMe2) coordination to late transition metal centers: snapshots of the B-H oxidative addition process.

    PubMed

    Bénac-Lestrille, Gaëtan; Helmstedt, Ulrike; Vendier, Laure; Alcaraz, Gilles; Clot, Eric; Sabo-Etienne, Sylviane

    2011-11-01

    The reaction of cyclodiborazane [Me(2)N-BH(2)](2) with the chloro(dihydrogen) ruthenium complex RuHCl(η(2)-H(2))(P(i)Pr(3))(2) (1) led to the formation of the unsymmetricaly coordinated dimethylaminoborane complex RuHCl(H(2)BNMe(2))(P(i)Pr(3))(2) (2). The dimethylaminoborane coordination (H(2)BNMe(2)) to the ruthenium center in 2 was carefully studied by combining X-ray, multinuclear NMR, and density functional theory (DFT) techniques, and compared with the recently reported osmium analogue which was originally formulated as a σ-B-H borinium complex [OsH(2)Cl(HBNMe(2))(P(i)Pr(3))(2)] (4). All our data are in favor of a bis(σ-B-H) coordination mode at a very activated stage in the case of the ruthenium complex 2, whereas in the osmium complex 4, full oxidative addition is favored leading to a complex better formulated as an osmium(IV) boryl species with an α-agostic B-H interaction. The synthesis and characterization of the symmetrical dihydride complex RuH(2)(H(2)BNMe(2))(P(i)Pr(3))(2) (3) from addition of the lithium dimethylaminoborohydride to 1 is reported for comparison. PMID:21954867

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

    NASA Astrophysics Data System (ADS)

    Carraher, Jack McCaslin

    Reactive species like high-valent metal-oxo complexes and carbon and oxygen centered radicals are important intermediates in enzymatic systems, atmospheric chemistry, and industrial processes. Understanding the pathways by which these intermediates form, their relative reactivity, and their fate after reactions is of the utmost importance. Herein are described the mechanistic detail for the generation of several reactive intermediates, synthesis of precursors, characterization of precursors, and methods to direct the chemistry to more desirable outcomes yielding 'greener' sources of commodity chemicals and fuels. High-valent Chromium from Hydroperoxido-Chromium(III). The decomposition of pentaaquahydroperoxido chromium(III) ion (hereafter Cr aqOOH2+) in acidic aqueous solutions is kinetically complex and generates mixtures of products (Craq3+, HCrO 4-, H2O2, and O2). The yield of high-valent chromium products (known carcinogens) increased from a few percent at pH 1 to 70 % at pH 5.5 (near biological pH). Yields of H 2O2 increased with acid concentration. The reproducibility of the kinetic data was poor, but became simplified in the presence of H2O2 or 2,2‧-azinobis(3-ethylbenzothiazoline-6-sulfonate) dianion (ABTS2-). Both are capable of scavenging strongly oxidizing intermediates). The observed rate constants (pH 1, [O2] ≤ 0.03 mM) in the presence of these scavengers are independent of [scavenger] and within the error are the same (k,ABTS2- = (4.9 +/- 0.2) x 10-4 s-1 and kH2O2 = (5.3 +/- 0.7) x 10-4 s-1); indicating involvement of the scavengers in post-rate determining steps. In the presence of either scavenger, decomposition of CrOOH2+ obeyed a two-term rate law, k obs / s-1 = (6.7 +/- 0.7) x 10-4 + (7.6 +/- 1.1) x 10-4 [H+]. Effect of [H+] on the kinetics and the product distribution, cleaner kinetics in the presence of scavengers, and independence of kobs on [scavenger] suggest a dual-pathway mechanism for the decay of Craq OOH2+. The H+-catalyzed path

  16. Transition Metal Homeostasis.

    PubMed

    Nies, Dietrich H; Grass, Gregor

    2009-08-01

    This chapter focuses on transition metals. All transition metal cations are toxic-those that are essential for Escherichia coli and belong to the first transition period of the periodic system of the element and also the "toxic-only" metals with higher atomic numbers. Common themes are visible in the metabolism of these ions. First, there is transport. High-rate but low-affinity uptake systems provide a variety of cations and anions to the cells. Control of the respective systems seems to be mainly through regulation of transport activity (flux control), with control of gene expression playing only a minor role. If these systems do not provide sufficient amounts of a needed ion to the cell, genes for ATP-hydrolyzing high-affinity but low-rate uptake systems are induced, e.g., ABC transport systems or P-type ATPases. On the other hand, if the amount of an ion is in surplus, genes for efflux systems are induced. By combining different kinds of uptake and efflux systems with regulation at the levels of gene expression and transport activity, the concentration of a single ion in the cytoplasm and the composition of the cellular ion "bouquet" can be rapidly adjusted and carefully controlled. The toxicity threshold of an ion is defined by its ability to produce radicals (copper, iron, chromate), to bind to sulfide and thiol groups (copper, zinc, all cations of the second and third transition period), or to interfere with the metabolism of other ions. Iron poses an exceptional metabolic problem due its metabolic importance and the low solubility of Fe(III) compounds, combined with the ability to cause dangerous Fenton reactions. This dilemma for the cells led to the evolution of sophisticated multi-channel iron uptake and storage pathways to prevent the occurrence of unbound iron in the cytoplasm. Toxic metals like Cd2+ bind to thiols and sulfide, preventing assembly of iron complexes and releasing the metal from iron-sulfur clusters. In the unique case of mercury, the

  17. Aluminum-Doped Zinc Oxide as Highly Stable Electron Collection Layer for Perovskite Solar Cells.

    PubMed

    Zhao, Xingyue; Shen, Heping; Zhang, Ye; Li, Xin; Zhao, Xiaochong; Tai, Meiqian; Li, Jingfeng; Li, Jianbao; Li, Xin; Lin, Hong

    2016-03-01

    Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid-base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (Voc) of 0.94 V, a short-circuit current (Jsc) of 20.2 mA cm(-2), a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material. PMID:26960451

  18. Aluminum-Doped Zinc Oxide as Highly Stable Electron Collection Layer for Perovskite Solar Cells.

    PubMed

    Zhao, Xingyue; Shen, Heping; Zhang, Ye; Li, Xin; Zhao, Xiaochong; Tai, Meiqian; Li, Jingfeng; Li, Jianbao; Li, Xin; Lin, Hong

    2016-03-01

    Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid-base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (Voc) of 0.94 V, a short-circuit current (Jsc) of 20.2 mA cm(-2), a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material.

  19. Selenophene transition metal complexes

    SciTech Connect

    White, C.J.

    1994-07-27

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

  20. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

    2013-04-01

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding

  1. New pathways for organic synthesis. Practical applications of transition metals

    SciTech Connect

    Colquhoun, H.M.; Holton, J.; Thompson, D.J.; Twigg, M.V.

    1984-01-01

    This book contains a considerable number of transition-metal-based procedures that have genuine applications in synthesis, and which are arranged according to the nature of the organic product or synthetic transformation being carried out. The objective is to provide those engaged in the preparation of pharmaceuticals, natural products, herbicides, dyestuffs, and other organic chemicals with a practical guide to the application of transition metals in organic synthesis. Topics considered include the formation of carbon-carbon bonds, the formation of carbocyclic compounds, the formation of heterocyclic compounds, the isomerization of alkenes, the direct introduction and removal of carbonyl groups, reduction, oxidation, and preparing and handling transition metal catalysts.

  2. Design Insights for Tuning the Electrocatalytic Activity of Perovskite Oxides for the Oxygen Evolution Reaction

    SciTech Connect

    Malkhandi, S; Trinh, P; Manohar, AK; Manivannan, A; Balasubramanian, M; Prakash, GKS; Narayanan, SR

    2015-04-16

    Rechargeable metal-air batteries and water electrolyzers based on aqueous alkaline electrolytes hold the potential to be sustainable solutions to address the challenge of storing large amounts of electrical energy generated from solar and wind resources. For these batteries and electrolyzers to be economically viable, it is essential to have efficient, durable, and inexpensive electrocatalysts for the oxygen evolution reaction. In this article, we describe new insights for predicting and tuning the activity of inexpensive transition metal oxides for designing efficient and inexpensive electrocatalysts. We have focused on understanding the factors determining the electrocatalytic activity for oxygen evolution in a strong alkaline medium. To this end, we have conducted a systematic investigation of nanophase calcium-doped lanthanum cobalt manganese oxide, an example of a mixed metal oxide that can be tuned for its electrocatalytic activity by varying the transition metal composition. Using X-ray absorption spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS), electrochemical polarization experiments, and analysis of mechanisms, we have identified the key determinants of electrocatalytic activity. We have found that the Tafel slopes are determined by the oxidation states and the bond energy of the surface intermediates of Mn-OH and Co-OH bonds while the catalytic activity increased with the average d-electron occupancy of the sigma* orbital of the M-OH bond. We anticipate that such understanding will be very useful in predicting the behavior of other transition metal oxide catalysts.

  3. Low-temperature solution-processed p-type vanadium oxide for perovskite solar cells.

    PubMed

    Sun, Haocheng; Hou, Xiaomeng; Wei, Qiulong; Liu, Huawei; Yang, Kecheng; Wang, Wei; An, Qinyou; Rong, Yaoguang

    2016-06-21

    A low-temperature solution-processed inorganic p-type contact material of vanadium oxide (VOx) was developed to fabricate planar-heterojunction perovskite solar cells. Using a solvent-assisted process, high-quality uniform and compact perovskite (CH3NH3PbI3) films were deposited on VOx coated substrates. Due to the high transmittance and quenching efficiency of VOx layers, a power conversion efficiency of over 14% was achieved.

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

    PubMed Central

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

    2015-01-01

    Cross-sections of a hole-conductor-free CH3NH3PbI3 perovskite solar cell were characterized with Kelvin probe force microscopy. A depletion region width of about 45 nm was determined from the measured potential profiles at the interface between CH3NH3PbI3 and nanocrystalline TiO2, whereas a negligible depletion was measured at the CH3NH3PbI3/Al2O3 interface. A complete solar cell can be realized with the CH3NH3PbI3 that functions both as light harvester and hole conductor in combination with a metal oxide. The band diagrams were estimated from the measured potential profile at the interfaces, and are critical findings for a better understanding and further improvement of perovskite based solar cells. PMID:25731963

  5. Significant enhancement of photovoltage in artificially designed perovskite oxide structures

    NASA Astrophysics Data System (ADS)

    Zhou, Wen-jia; Jin, Kui-juan; Guo, Hai-zhong; He, Xu; He, Meng; Xu, Xiu-lai; Lu, Hui-bin; Yang, Guo-zhen

    2015-03-01

    La0.9Sr0.1MnO3/insulator/SrNb0.007Ti0.993O3 multilayer and La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3/In2O3:SnO2(ITO)/La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3 multilayer structures were designed to enhance the photovoltage. The photovoltages of these two structures under an illumination of 308 nm laser are 410 and 600 mV, respectively. The latter is 20 times larger than that (30 mV) observed in La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3 single junction. The origin of such significant enhancement of photovoltage is discussed in this letter. These results suggest that the photoelectric property of perovskite oxides could be much improved by artificial structure designing. The enhanced photovoltaic effects have potential applications in the ultraviolet photodetection and solar cells.

  6. Modeling of thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode

    NASA Astrophysics Data System (ADS)

    Heydari, F.; Maghsoudipour, A.; Alizadeh, M.; Khakpour, Z.; Javaheri, M.

    2015-09-01

    Artificial intelligence models have the capacity to eliminate the need for expensive experimental investigation in various areas of manufacturing processes, including the material science. This study investigates the applicability of adaptive neuro-fuzzy inference system (ANFIS) approach for modeling the performance parameters of thermal expansion coefficient (TEC) of perovskite oxide for solid oxide fuel cell cathode. Oxides (Ln = La, Nd, Sm and M = Fe, Ni, Mn) have been prepared and characterized to study the influence of the different cations on TEC. Experimental results have shown TEC decreases favorably with substitution of Nd3+ and Mn3+ ions in the lattice. Structural parameters of compounds have been determined by X-ray diffraction, and field emission scanning electron microscopy has been used for the morphological study. Comparison results indicated that the ANFIS technique could be employed successfully in modeling thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode, and considerable savings in terms of cost and time could be obtained by using ANFIS technique.

  7. Atomic layer deposition of perovskite oxides and their epitaxial integration with Si, Ge, and other semiconductors

    SciTech Connect

    McDaniel, Martin D.; Ngo, Thong Q.; Hu, Shen; Ekerdt, John G.; Posadas, Agham; Demkov, Alexander A.

    2015-12-15

    Atomic layer deposition (ALD) is a proven technique for the conformal deposition of oxide thin films with nanoscale thickness control. Most successful industrial applications have been with binary oxides, such as Al{sub 2}O{sub 3} and HfO{sub 2}. However, there has been much effort to deposit ternary oxides, such as perovskites (ABO{sub 3}), with desirable properties for advanced thin film applications. Distinct challenges are presented by the deposition of multi-component oxides using ALD. This review is intended to highlight the research of the many groups that have deposited perovskite oxides by ALD methods. Several commonalities between the studies are discussed. Special emphasis is put on precursor selection, deposition temperatures, and specific property performance (high-k, ferroelectric, ferromagnetic, etc.). Finally, the monolithic integration of perovskite oxides with semiconductors by ALD is reviewed. High-quality epitaxial growth of oxide thin films has traditionally been limited to physical vapor deposition techniques (e.g., molecular beam epitaxy). However, recent studies have demonstrated that epitaxial oxide thin films may be deposited on semiconductor substrates using ALD. This presents an exciting opportunity to integrate functional perovskite oxides for advanced semiconductor applications in a process that is economical and scalable.

  8. Transition Metal Oxides for the Oxygen Reduction Reaction: Influence of the Oxidation States of the Metal and its Position on the Periodic Table.

    PubMed

    Toh, Rou Jun; Sofer, Zdeněk; Pumera, Martin

    2015-11-16

    Electrocatalysts have been developed to meet the needs and requirements of renewable energy applications. Metal oxides have been well explored and are promising for this purpose, however, many reports focus on only one or a few metal oxides at once. Herein, thirty metal oxides, which were either commercially available or synthesized by a simple and scalable method, were screened for comparison with regards to their electrocatalytic activity towards the oxygen reduction reaction (ORR). We show that although manganese, iron, cobalt, and nickel oxides generally displayed the ability to enhance the kinetics of oxygen reduction under alkaline conditions compared with bare glassy carbon, there is no significant correlation between the position of a metal on the periodic table and the electrocatalytic performance of its respective metal oxides. Moreover, it was also observed that mixed valent (+2, +3) oxides performed the poorest, compared with their respective pure metal oxides. These findings may be of paramount importance in the field of renewable energy. PMID:26351175

  9. Transition Metal Oxides for the Oxygen Reduction Reaction: Influence of the Oxidation States of the Metal and its Position on the Periodic Table.

    PubMed

    Toh, Rou Jun; Sofer, Zdeněk; Pumera, Martin

    2015-11-16

    Electrocatalysts have been developed to meet the needs and requirements of renewable energy applications. Metal oxides have been well explored and are promising for this purpose, however, many reports focus on only one or a few metal oxides at once. Herein, thirty metal oxides, which were either commercially available or synthesized by a simple and scalable method, were screened for comparison with regards to their electrocatalytic activity towards the oxygen reduction reaction (ORR). We show that although manganese, iron, cobalt, and nickel oxides generally displayed the ability to enhance the kinetics of oxygen reduction under alkaline conditions compared with bare glassy carbon, there is no significant correlation between the position of a metal on the periodic table and the electrocatalytic performance of its respective metal oxides. Moreover, it was also observed that mixed valent (+2, +3) oxides performed the poorest, compared with their respective pure metal oxides. These findings may be of paramount importance in the field of renewable energy.

  10. Aging of Transition Metal Dichalcogenide Monolayers.

    PubMed

    Gao, Jian; Li, Baichang; Tan, Jiawei; Chow, Phil; Lu, Toh-Ming; Koratkar, Nikhil

    2016-02-23

    Two-dimensional sheets of transition metal dichalcogenides are an emerging class of atomically thin semiconductors that are considered to be "air-stable", similar to graphene. Here we report that, contrary to current understanding, chemical vapor deposited transition metal dichalcogenide monolayers exhibit poor long-term stability in air. After room-temperature exposure to the environment for several months, monolayers of molybdenum disulfide and tungsten disulfide undergo dramatic aging effects including extensive cracking, changes in morphology, and severe quenching of the direct gap photoluminescence. X-ray photoelectron and Auger electron spectroscopy reveal that this effect is related to gradual oxidation along the grain boundaries and the adsorption of organic contaminants. These results highlight important challenges associated with the utilization of transition metal dichalcogenide monolayers in electronic and optoelectronic devices. We also demonstrate a potential solution to this problem, featuring encapsulation of the monolayer sheet by a 10-20 nm thick optically transparent polymer (parylene C). This strategy is shown to successfully prevent the degradation of the monolayer material under accelerated aging (i.e., high-temperature, oxygen-rich) conditions.

  11. Aging of Transition Metal Dichalcogenide Monolayers.

    PubMed

    Gao, Jian; Li, Baichang; Tan, Jiawei; Chow, Phil; Lu, Toh-Ming; Koratkar, Nikhil

    2016-02-23

    Two-dimensional sheets of transition metal dichalcogenides are an emerging class of atomically thin semiconductors that are considered to be "air-stable", similar to graphene. Here we report that, contrary to current understanding, chemical vapor deposited transition metal dichalcogenide monolayers exhibit poor long-term stability in air. After room-temperature exposure to the environment for several months, monolayers of molybdenum disulfide and tungsten disulfide undergo dramatic aging effects including extensive cracking, changes in morphology, and severe quenching of the direct gap photoluminescence. X-ray photoelectron and Auger electron spectroscopy reveal that this effect is related to gradual oxidation along the grain boundaries and the adsorption of organic contaminants. These results highlight important challenges associated with the utilization of transition metal dichalcogenide monolayers in electronic and optoelectronic devices. We also demonstrate a potential solution to this problem, featuring encapsulation of the monolayer sheet by a 10-20 nm thick optically transparent polymer (parylene C). This strategy is shown to successfully prevent the degradation of the monolayer material under accelerated aging (i.e., high-temperature, oxygen-rich) conditions. PMID:26808328

  12. A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles.

    PubMed

    Suntivich, Jin; May, Kevin J; Gasteiger, Hubert A; Goodenough, John B; Shao-Horn, Yang

    2011-12-01

    The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an e(g) symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an e(g) occupancy close to unity, with high covalency of transition metal-oxygen bonds.

  13. An aqueous preoxidation method for monolithic perovskite electrocatalysts with enhanced water oxidation performance

    PubMed Central

    Li, Bo-Quan; Tang, Cheng; Wang, Hao-Fan; Zhu, Xiao-Lin; Zhang, Qiang

    2016-01-01

    Perovskite oxides with poor conductivity call for three-dimensional (3D) conductive scaffolds to demonstrate their superb reactivities for oxygen evolution reaction (OER). However, perovskite formation usually requires high-temperature annealing at 600° to 900°C in air, under which most of the used conductive frameworks (for example, carbon and metal current collectors) are reductive and cannot survive. We propose a preoxidization coupled electrodeposition strategy in which Co2+ is preoxidized to Co3+ through cobalt Fenton reaction in aqueous solution, whereas the reductive nickel framework is well maintained during the sequential annealing under nonoxidative atmosphere. The in situ–generated Co3+ is inherited into oxidized perovskites deposited on 3D nickel foam, rendering the monolithic perovskite electrocatalysts with extraordinary OER performance with an ultralow overpotential of 350 mV required for 10 mA cm−2, a very small Tafel slope of 59 mV dec−1, and superb stability in 0.10 M KOH. Therefore, we inaugurate a unique strategy for in situ hybridization of oxidative active phase with reductive framework, affording superb reactivity of perovskite electrocatalyst for efficient water oxidation.

  14. Transition Metal Free Intermolecular Direct Oxidative C-N Bond Formation to Polysubstituted Pyrimidines Using Molecular Oxygen as the Sole Oxidant.

    PubMed

    Guo, Wei; Li, Chunsheng; Liao, Jianhua; Ji, Fanghua; Liu, Dongqing; Wu, Wanqing; Jiang, Huanfeng

    2016-07-01

    Various polysubstituted pyrimidines are smoothly formed via a base-promoted intermolecular oxidation C-N bond formation of allylic C(sp(3))-H and vinylic C(sp(2))-H of allyllic compounds with amidines using O2 as the sole oxidant. This protocol features protecting group free nitrogen sources, good functional group tolerance, high atom economy, and environmental advantages.

  15. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen–Popper, Dion–Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  16. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen-Popper, Dion-Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  17. 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)

    Rogado, Nyrissa S.

    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

  18. First-principles calculations of the OH- adsorption energy on perovskite oxide

    NASA Astrophysics Data System (ADS)

    Ohzuku, Hideo; Ikeno, Hidekazu; Yamada, Ikuya; Yagi, Shunsuke

    2016-08-01

    The oxygen evolution reaction (OER) that occurs during water oxidation is of considerable importance as an essential energy conversion reaction for rechargeable metal-air batteries and direct solar water splitting. ABO3 perovskite oxides have been extensively studied because of their high catalytic OER activity. In the present study, the OH- adsorption process on the perovskite surface about different B site cations was investigated by the first-principles calculations. We concluded that the adsorption energy of SrFeO3 surface is larger than that of SrTiO3.

  19. Activity and stability trends of perovskite oxides for oxygen evolution catalysis at neutral pH.

    PubMed

    Han, Binghong; Risch, Marcel; Lee, Yueh-Lin; Ling, Chen; Jia, Hongfei; Shao-Horn, Yang

    2015-09-21

    Perovskite oxides (ABO3) have been studied extensively to promote the kinetics of the oxygen evolution reaction (OER) in alkaline electrolytes. However, developing highly active catalysts for OER at near-neutral pH is desirable for many photoelectrochemical/electrochemical devices. In this paper, we systematically studied the activity and stability of well-known perovskite oxides for OER at pH 7. Previous activity descriptors established for perovskite oxides at pH 13, such as having an eg occupancy close to unity or having an O p-band center close to Fermi level, were shown to scale with OER activity at pH 7. Stability was a greater challenge at pH 7 than at pH 13, where two different modes of instability were identified from combined transmission electron microscopy and density functional theory analyses. Perovskites with O p-band close to Fermi level showed leaching of A-site atoms and surface amorphization under all overpotentials examined at pH 7, while those with O p-band far from Fermi level were stable under low OER current/potential but became unstable at high current/potential accompanied by leaching of B-site atoms. Therefore, efforts are needed to enhance the activity and stability of perovskites against A-site or B-site loss if used at neutral pH. PMID:26271910

  20. Activity and stability trends of perovskite oxides for oxygen evolution catalysis at neutral pH.

    PubMed

    Han, Binghong; Risch, Marcel; Lee, Yueh-Lin; Ling, Chen; Jia, Hongfei; Shao-Horn, Yang

    2015-09-21

    Perovskite oxides (ABO3) have been studied extensively to promote the kinetics of the oxygen evolution reaction (OER) in alkaline electrolytes. However, developing highly active catalysts for OER at near-neutral pH is desirable for many photoelectrochemical/electrochemical devices. In this paper, we systematically studied the activity and stability of well-known perovskite oxides for OER at pH 7. Previous activity descriptors established for perovskite oxides at pH 13, such as having an eg occupancy close to unity or having an O p-band center close to Fermi level, were shown to scale with OER activity at pH 7. Stability was a greater challenge at pH 7 than at pH 13, where two different modes of instability were identified from combined transmission electron microscopy and density functional theory analyses. Perovskites with O p-band close to Fermi level showed leaching of A-site atoms and surface amorphization under all overpotentials examined at pH 7, while those with O p-band far from Fermi level were stable under low OER current/potential but became unstable at high current/potential accompanied by leaching of B-site atoms. Therefore, efforts are needed to enhance the activity and stability of perovskites against A-site or B-site loss if used at neutral pH.

  1. Electronically conductive perovskite-based oxide nanoparticles and films for optical sensing applications

    DOEpatents

    Ohodnicki, Jr., Paul R; Schultz, Andrew M

    2015-04-28

    The disclosure relates to a method of detecting a change in a chemical composition by contacting a electronically conducting perovskite-based metal oxide material with a monitored stream, illuminating the electronically conducting perovskite-based metal oxide with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The electronically conducting perovskite-based metal oxide has a perovskite-based crystal structure and an electronic conductivity of at least 10.sup.-1 S/cm, where parameters are specified at the gas stream temperature. The electronically conducting perovskite-based metal oxide has an empirical formula A.sub.xB.sub.yO.sub.3-.delta., where A is at least a first element at the A-site, B is at least a second element at the B-site, and where 0.8perovskite-based oxides include but are not limited to La.sub.1-xSr.sub.xCoO.sub.3, La.sub.1-xSr.sub.xMnO.sub.3, LaCrO.sub.3, LaNiO.sub.3, La.sub.1-xSr.sub.xMn.sub.1-yCr.sub.yO.sub.3, SrFeO.sub.3, SrVO.sub.3, La-doped SrTiO.sub.3, Nb-doped SrTiO.sub.3, and SrTiO.sub.3-.delta..

  2. Electrical Conductivity in Transition Metals

    ERIC Educational Resources Information Center

    Talbot, Christopher; Vickneson, Kishanda

    2013-01-01

    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…

  3. Alkali and transition metal phospholides

    NASA Astrophysics Data System (ADS)

    Bezkishko, I. A.; Zagidullin, A. A.; Milyukov, V. A.; Sinyashin, O. G.

    2014-06-01

    Major tendencies in modern chemistry of alkali and transition metal phospholides (phosphacyclopentadienides) are systematized, analyzed and generalized. Basic methods of synthesis of these compounds are presented. Their chemical properties are considered with a special focus on their complexing ability. Potential applications of phospholides and their derivatives are discussed. The bibliography includes 184 references.

  4. The preparation of large surface area lanthanum based perovskite supports for AuPt nanoparticles: tuning the glycerol oxidation reaction pathway by switching the perovskite B site

    PubMed Central

    Evans, Christopher D.; Smith, Paul J.; Manning, Troy D.; Miedziak, Peter J.; Brett, Gemma L.; Armstrong, Robert D.; Bartley, Jonathan K.; Taylor, Stuart H.; Rosseinsky, Matthew J.; Hutchings, Graham J.

    2016-01-01

    Gold and gold alloys, in the form of supported nanoparticles, have been shown over the last three decades to be highly effective oxidation catalysts. Mixed metal oxide perovskites, with their high structural tolerance, are ideal for investigating how changes in the chemical composition of supports affect the catalysts' properties, while retaining similar surface areas, morphologies and metal co-ordinations. However, a significant disadvantage of using perovskites as supports is their high crystallinity and small surface area. We report the use of a supercritical carbon dioxide anti-solvent precipitation methodology to prepare large surface area lanthanum based perovskites, making the deposition of 1 wt% AuPt nanoparticles feasible. These catalysts were used for the selective oxidation of glycerol. By changing the elemental composition of the perovskite B site, we dramatically altered the reaction pathway between a sequential oxidation route to glyceric or tartronic acid and a dehydration reaction pathway to lactic acid. Selectivity profiles were correlated to reported oxygen adsorption capacities of the perovskite supports and also to changes in the AuPt nanoparticle morphologies. Extended time on line analysis using the best oxidation catalyst (AuPt/LaMnO3) produced an exceptionally high tartronic acid yield. LaMnO3 produced from alternative preparation methods was found to have lower activities, but gave comparable selectivity profiles to that produced using the supercritical carbon dioxide anti-solvent precipitation methodology. PMID:27074316

  5. The preparation of large surface area lanthanum based perovskite supports for AuPt nanoparticles: tuning the glycerol oxidation reaction pathway by switching the perovskite B site.

    PubMed

    Evans, Christopher D; Kondrat, Simon A; Smith, Paul J; Manning, Troy D; Miedziak, Peter J; Brett, Gemma L; Armstrong, Robert D; Bartley, Jonathan K; Taylor, Stuart H; Rosseinsky, Matthew J; Hutchings, Graham J

    2016-07-01

    Gold and gold alloys, in the form of supported nanoparticles, have been shown over the last three decades to be highly effective oxidation catalysts. Mixed metal oxide perovskites, with their high structural tolerance, are ideal for investigating how changes in the chemical composition of supports affect the catalysts' properties, while retaining similar surface areas, morphologies and metal co-ordinations. However, a significant disadvantage of using perovskites as supports is their high crystallinity and small surface area. We report the use of a supercritical carbon dioxide anti-solvent precipitation methodology to prepare large surface area lanthanum based perovskites, making the deposition of 1 wt% AuPt nanoparticles feasible. These catalysts were used for the selective oxidation of glycerol. By changing the elemental composition of the perovskite B site, we dramatically altered the reaction pathway between a sequential oxidation route to glyceric or tartronic acid and a dehydration reaction pathway to lactic acid. Selectivity profiles were correlated to reported oxygen adsorption capacities of the perovskite supports and also to changes in the AuPt nanoparticle morphologies. Extended time on line analysis using the best oxidation catalyst (AuPt/LaMnO3) produced an exceptionally high tartronic acid yield. LaMnO3 produced from alternative preparation methods was found to have lower activities, but gave comparable selectivity profiles to that produced using the supercritical carbon dioxide anti-solvent precipitation methodology. PMID:27074316

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

    SciTech Connect

    Djerdj, Igor Arcon, Denis; Jaglicic, Zvonko; Niederberger, Markus

    2008-07-15

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

  7. Development of new layered selenide oxides with perovskite-type oxide layers

    NASA Astrophysics Data System (ADS)

    Ushiyama, Koichi; Ogino, Hiraku; Kishio, Kohji; Shimoyama, Jun-Ichi

    2010-03-01

    Several Fe-based superconductors with perovskite-type oxide layers, such as Sr2ScFePO3 (Tc ˜ 17 K)^[1], were discovered in our previous study. These compounds are composed of alternate stacking of superconducting layers with antifluorite structure and perovskite-type blocking layers. Since both layers are flexible in terms of chemical composition, development of various new functional materials can be expected from this family. In the present study, we have attempted to synthesize new layered selenide oxides with CuSe layers and discovered more than ten compounds, such as Sr2MCu2Se2O2 (M = Mn, Co, Ni, Cu, Zn) and Sr2MCuSeO3 (M = Sc, Cr, Mn, Fe, Ga, In), thus far. These indicated that the CuSe layer can accommodate various types of blocking layers, which may lead various functions. Among them, Sr2Cu3Se2O2 has a potential as for the mother compound of superconductor, if appropriate concentration of carrier is introduced to the CuO2 layer. Crystal structure and physical properties of these newly found compounds will be reported. [1] H. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008

  8. Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers.

    PubMed

    You, Jingbi; Meng, Lei; Song, Tze-Bin; Guo, Tzung-Fang; Yang, Yang Michael; Chang, Wei-Hsuan; Hong, Ziruo; Chen, Huajun; Zhou, Huanping; Chen, Qi; Liu, Yongsheng; De Marco, Nicholas; Yang, Yang

    2016-01-01

    Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiO(x) and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p-i-n structure (glass/indium tin oxide/NiO(x)/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%.

  9. Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers

    NASA Astrophysics Data System (ADS)

    You, Jingbi; Meng, Lei; Song, Tze-Bin; Guo, Tzung-Fang; Yang, Yang (Michael); Chang, Wei-Hsuan; Hong, Ziruo; Chen, Huajun; Zhou, Huanping; Chen, Qi; Liu, Yongsheng; De Marco, Nicholas; Yang, Yang

    2016-01-01

    Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiOx and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p-i-n structure (glass/indium tin oxide/NiOx/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%.

  10. Towards printed perovskite solar cells with cuprous oxide hole transporting layers: a theoretical design

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Xia, Zhonggao; Liang, Jun; Wang, Xinwei; Liu, Yiming; Liu, Chuan; Zhang, Shengdong; Zhou, Hang

    2015-05-01

    Solution-processed p-type metal oxide materials have shown great promise in improving the stability of perovskite-based solar cells and offering the feasibility for a low cost printing fabrication process. Herein, we performed a device modeling study on planar perovskite solar cells with cuprous oxide (Cu2O) hole transporting layers (HTLs) by using a solar cell simulation program, wxAMPS. The performance of a Cu2O/perovskite solar cell was correlated to the material properties of the Cu2O HTL, such as thickness, carrier mobility, mid-gap defect, and doping concentrations. The effect of interfacial defect densities on the solar cell performance was also investigated. Our simulation indicates that, with an optimized Cu2O HTL, high performance perovskite solar cells with efficiencies above 13% could be achieved, which shows the potential of using Cu2O as an alternative HTL over other inorganic materials, such as NiOx and MoOx. This study provides theoretical guidance for developing perovskite solar cells with inorganic hole transporting materials via a printing process.

  11. PREFACE: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. Parallel session of the 18th International School on Condensed Matter Physics

    NASA Astrophysics Data System (ADS)

    2014-11-01

    The Special issue presents the papers for the INERA Workshop entitled "Transition Metal Oxides as Functional Layers in Smart windows and Water Splitting Devices", which was held in Varna, St. Konstantin and Elena, Bulgaria, from the 4th-6th September 2014. The Workshop is organized within the context of the INERA "Research and Innovation Capacity Strengthening of ISSP-BAS in Multifunctional Nanostructures", FP7 Project REGPOT 316309 program, European project of the Institute of Solid State Physics at the Bulgarian Academy of Sciences. There were 42 participants at the workshop, 16 from Sweden, Germany, Romania and Hungary, 11 invited lecturers, and 28 young participants. There were researchers present from prestigious European laboratories which are leaders in the field of transition metal oxide thin film technologies. The event contributed to training young researchers in innovative thin film technologies, as well as thin films characterization techniques. The topics of the Workshop cover the field of technology and investigation of thin oxide films as functional layers in "Smart windows" and "Water splitting" devices. The topics are related to the application of novel technologies for the preparation of transition metal oxide films and the modification of chromogenic properties towards the improvement of electrochromic and termochromic device parameters for possible industrial deployment. The Workshop addressed the following topics: Metal oxide films-functional layers in energy efficient devices; Photocatalysts and chemical sensing; Novel thin film technologies and applications; Methods of thin films characterizations; From the 37 abstracts sent, 21 manuscripts were written and later refereed. We appreciate the comments from all the referees, and we are grateful for their valuable contributions. Guest Editors: Assoc. Prof. Dr.Tatyana Ivanova Prof. DSc Kostadinka Gesheva Prof. DSc Hassan Chamatti Assoc. Prof. Dr. Georgi Popkirov Workshop Organizing Committee Prof

  12. Oxidative Cleavage of the β-O-4 Linkage of Lignin by Transition Metals: Catalytic Properties and the Performance of Density Functionals.

    PubMed

    Wang, Jiaqi; Liu, Lily; Wilson, Angela K

    2016-02-11

    The catalytic degradation of lignin is of considerable interest because the depolymerization of lignin to small molecules is the initial step for the conversion of lignin to biofuels and other useful chemicals. Because of the complex structure of lignin, methoxyethane was used in this study as a representative model of the most common linkage within lignin, the β-O-4 linkage. The completely renormalized coupled cluster with singles, doubles, and perturbative triples [CR-CCSD(T)] method was used to calculate the energetics of the C-O bond cleavage in methoxyethane by late 3d, 4d, and 5d transition metal atoms and to evaluate the performance of a set of density functionals (BLYP, B97D, TPSS, M06L, B3LYP, PBE0, M06, TPSSh, and B2PLYP) in predicting the reaction energetics. PMID:26735613

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

    SciTech Connect

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

    2001-06-11

    Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial ZnO thin films doped with all the 3d transition metal (TM) ions in a high throughput fashion. The solubility behavior of TM ions was discussed from the viewpoints of the ionic radius and valence state. The magneto-optical responses coincident with absorption spectra were observed for Mn- and Co-doped samples. Cathodoluminescence spectra were studied for Cr-, Mn-, Fe-, and Co-doped samples, among which Cr-doped ZnO showed two sharp peaks at 2.97 eV and 3.71 eV, respectively, at the expense of the exciton emission peak of pure ZnO at 3.25 eV. Different magnetoresistance behavior was observed for the samples codoped with n-type carriers. Ferromagnetism was not observed for Cr- to Cu-doped samples down to 3 K. {copyright} 2001 American Institute of Physics.

  14. Transition-Metal-Mediated Release of Nitric Oxide (NO) from S-Nitroso-N-acetyl-d-penicillamine (SNAP): Potential Applications for Endogenous Release of NO at the Surface of Stents Via Corrosion Products.

    PubMed

    McCarthy, Connor W; Guillory, Roger J; Goldman, Jeremy; Frost, Megan C

    2016-04-27

    Nitric oxide (NO), identified over the last several decades in many physiological processes and pathways as both a beneficial and detrimental signaling molecule, has been the subject of extensive research. Physiologically, NO is transported by a class of donors known as S-nitrosothiols. Both endogenous and synthetic S-nitrosothiols have been reported to release NO during interactions with certain transition metals, primarily Cu(2+) and Fe(2+). Ag(+) and Hg(2+) have also been identified, although these metals are not abundantly present in physiological systems. Here, we evaluate Pt(2+), Fe(2+), Fe(3+), Mg(2+), Zn(2+), Mn(2+), Co(2+), Ni(2+), and Cu(2+) for their ability to generate NO from S-nitroso-N-acetyl-d-penicillamine (SNAP) under physiological pH conditions. Specifically, we report NO generation from RSNOs initiated by three transition metal ions; Co(2+), Ni(2+), and Zn(2+), which have not been previously reported to generate NO. Additionally, preliminary in vivo evidence of zinc wires implanted in the rat arterial wall and circulating blood is presented which demonstrated inhibited thrombus formation after 6 months. One potentially useful application of these metal ions capable of generating NO from RSNOs is their use in the fabrication of biodegradable metallic stents capable of generating NO at the stent-blood interface, thereby reducing stent-related thrombosis and restenosis.

  15. Iron-based perovskite cathodes for solid oxide fuel cells

    DOEpatents

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

    2007-01-02

    An A and/or A' site deficient perovskite of general formula of (A.sub.1-xA'.sub.x).sub.1-yFeO.sub.3-.delta. or of general formula A.sub.1-x-yA'.sub.xFeO.sub.3-67, wherein A is La alone or with one or more of the rare earth metals or a rare earth metal other than Ce alone or a combination of rare earth metals and X is in the range of from 0 to about 1; A' is Sr or Ca or mixtures thereof and Y is in the range of from about 0.01 to about 0.3; .delta. represents the amount of compensating oxygen loss. If either A or A' is zero the remaining A or A' is deficient. A fuel cell incorporating the inventive perovskite as a cathode is disclosed as well as an oxygen separation membrane. The inventive perovskite is preferably single phase.

  16. Bifunctional Perovskite Oxide Catalysts for Oxygen Reduction and Evolution in Alkaline Media.

    PubMed

    Gupta, Shiva; Kellogg, William; Xu, Hui; Liu, Xien; Cho, Jaephil; Wu, Gang

    2016-01-01

    Oxygen electrocatalysis, namely of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), governs the performance of numerous electrochemical energy systems such as reversible fuel cells, metal-air batteries, and water electrolyzers. However, the sluggish kinetics of these two reactions and their dependency on expensive noble metal catalysts (e.g, Pt or Ir) prohibit the sustainable commercialization of these highly innovative and in-demand technologies. Bifunctional perovskite oxides have emerged as a new class of highly efficient non-precious metal catalysts (NPMC) for oxygen electrocatalysis in alkaline media. In this review, we discuss the state-of-the-art understanding of bifunctional properties of perovskites with regards to their OER/ORR activity in alkaline media and review the associated reaction mechanisms on the oxides surface and the related activity descriptors developed in the recent literature. We also summarize the present strategies to modify their electronic structure and to further improve their performance for the ORR/OER through highlighting the new concepts relating to the role of surface redox chemistry and oxygen deficiency of perovskite oxides for the ORR/OER activity. In addition, we provide a brief account of recently developed advanced perovskite-nanocarbon hybrid bifunctional catalysts with much improved performances. PMID:26247625

  17. Bifunctional Perovskite Oxide Catalysts for Oxygen Reduction and Evolution in Alkaline Media.

    PubMed

    Gupta, Shiva; Kellogg, William; Xu, Hui; Liu, Xien; Cho, Jaephil; Wu, Gang

    2016-01-01

    Oxygen electrocatalysis, namely of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), governs the performance of numerous electrochemical energy systems such as reversible fuel cells, metal-air batteries, and water electrolyzers. However, the sluggish kinetics of these two reactions and their dependency on expensive noble metal catalysts (e.g, Pt or Ir) prohibit the sustainable commercialization of these highly innovative and in-demand technologies. Bifunctional perovskite oxides have emerged as a new class of highly efficient non-precious metal catalysts (NPMC) for oxygen electrocatalysis in alkaline media. In this review, we discuss the state-of-the-art understanding of bifunctional properties of perovskites with regards to their OER/ORR activity in alkaline media and review the associated reaction mechanisms on the oxides surface and the related activity descriptors developed in the recent literature. We also summarize the present strategies to modify their electronic structure and to further improve their performance for the ORR/OER through highlighting the new concepts relating to the role of surface redox chemistry and oxygen deficiency of perovskite oxides for the ORR/OER activity. In addition, we provide a brief account of recently developed advanced perovskite-nanocarbon hybrid bifunctional catalysts with much improved performances.

  18. Transition Metal Diborides as Electrode Material for MHD Direct Power Extraction: High-temperature Oxidation of ZrB2-HfB2 Solid Solution with LaB6 Addition

    NASA Astrophysics Data System (ADS)

    Sitler, Steven; Hill, Cody; Raja, Krishnan S.; Charit, Indrajit

    2016-06-01

    Transition metal borides are being considered for use as potential electrode coating materials in magnetohydrodynamic direct power extraction plants from coal-fired plasma. These electrode materials will be exposed to aggressive service conditions at high temperatures. Therefore, high-temperature oxidation resistance is an important property. Consolidated samples containing an equimolar solid solution of ZrB2-HfB2 with and without the addition of 1.8 mol pct LaB6 were prepared by ball milling of commercial boride material followed by spark plasma sintering. These samples were oxidized at 1773 K (1500 °C) in two different conditions: (1) as-sintered and (2) anodized (10 V in 0.1 M KOH electrolyte). Oxidation studies were carried out in 0.3 × 105 and 0.1 Pa oxygen partial pressures. The anodic oxide layers showed hafnium enrichment on the surface of the samples, whereas the high-temperature oxides showed zirconium enrichment. The anodized samples without LaB6 addition showed about 2.5 times higher oxidation resistance in high-oxygen partial pressures than the as-sintered samples. Addition of LaB6 improved the oxidation resistance in the as-sintered condition by about 30 pct in the high-oxygen partial pressure tests.

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

    PubMed

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

    2008-05-16

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

  20. Thermodynamic Hydricity of Transition Metal Hydrides.

    PubMed

    Wiedner, Eric S; Chambers, Matthew B; Pitman, Catherine L; Bullock, R Morris; Miller, Alexander J M; Appel, Aaron M

    2016-08-10

    Transition metal hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen. PMID:27483171

  1. Comparisons between intrinsic bonding defects in d 0 transition metal oxide such as HfO 2, and impurity atom defects in d 0 complex oxides such as GdScO 3

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerald; Chung, Kwun-Bum; Miotti, Leonardi; Bastos, Karen Pas; Amado, Carolina; Schlom, Darrell

    2009-12-01

    This article addresses O-atom vacancy defects in the d 0 transition metal (TM) oxides HfO 2 and TiO 2, and Ti substitutions for Sc in the d 0 complex oxide GdScO 3. In each instance this results in occupied TM atoms with d 1 state representations. These are important for different aspects of the ultimate scaling limits for performance and functionality in nano-scale Si devices. The occupancy of d 1 states is cast in terms of many-electron theory in order to determine the effects of correlation on device performance and functionality. The first section of this article identifies equivalent d-state representations using on an ionic model for the effective valence states of Ti and Hf atoms bordering on O-atom vacancy defects. Removal of an O atom to create a neutral vacancy; this is equivalent to the bonding of two electrons to each vacancy site. This give rise to two coupled d 1 states for a mono-vacancy defect. Transitions from these occupied states generate spectroscopic features in the (i) pre-edge shake-up, and (ii) virtual bound state (VBS) shake-off energy regimes in O K edge XAS spectra. The number of states confirm that these are mono-vacancy defects. The second section addresses incorporation of Ti tetravalent impurities into trivalent GdScO 3, forcing Ti into a Ti 3+ state and generating a d 1 electronic structure. Vacancy defect concentrations in HfO 2 are generally <10 19 cm -3. However, the Ti solubility in GdScO 3 is higher, and relative concentrations in excess of 16-17% lead to an insulator to metal transition with a ferri-magnetic electronic structure.

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

    SciTech Connect

    Not Available

    1993-05-01

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

  3. [Non-empirical interatomic potentials for transition metals

    SciTech Connect

    Not Available

    1993-01-01

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

  4. Topotactic synthesis of strontium cobalt oxyhydride thin film with perovskite structure

    SciTech Connect

    Katayama, Tsukasa; Chikamatsu, Akira Kamisaka, Hideyuki; Yokoyama, Yuichi; Hirata, Yasuyuki; Wadati, Hiroki; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2015-10-15

    The substitution of hydride anions (H{sup −}) into transition metal oxides has recently become possible through topotactic reactions or high-pressure synthesis methods. However, the fabrication of oxyhydrides is still difficult because of their inherently less-stable frameworks. In this study, we successfully fabricated perovskite SrCoO{sub x}H{sub y} thin films via the topotactic hydride doping of brownmillerite SrCoO{sub 2.5} epitaxial thin films with CaH{sub 2}. The perovskite-type cation framework was maintained during the topotactic treatment owing to epitaxial stabilization. Structural and chemical analyses accompanied by X-ray absorption spectroscopy measurements revealed that the doped hydride ions form a two-dimensional network of Co-H{sup −}-Co bonds, in contrast to other reported perovskite oxyhydrides, SrMO{sub 3−x}H{sub x} (M = Cr, Ti, V). The SrCoO{sub x}H{sub y} thin film exhibited insulating behavior and had a direct band gap of 2.1 eV. Thus, topotactic hydride doping of transition-metal-oxide thin films on suitable substrates is a promising method for the synthesis of new transition metal oxyhydrides.

  5. Photochemistry of Transition Metal Hydrides.

    PubMed

    Perutz, Robin N; Procacci, Barbara

    2016-08-10

    Photochemical reactivity associated with metal-hydrogen bonds is widespread among metal hydride complexes and has played a critical part in opening up C-H bond activation. It has been exploited to design different types of photocatalytic reactions and to obtain NMR spectra of dilute solutions with a single pulse of an NMR spectrometer. Because photolysis can be performed on fast time scales and at low temperature, metal-hydride photochemistry has enabled determination of the molecular structure and rates of reaction of highly reactive intermediates. We identify five characteristic photoprocesses of metal monohydride complexes associated with the M-H bond, of which the most widespread are M-H homolysis and R-H reductive elimination. For metal dihydride complexes, the dominant photoprocess is reductive elimination of H2. Dihydrogen complexes typically lose H2 photochemically. The majority of photochemical reactions are likely to be dissociative, but hydride complexes may be designed with equilibrated excited states that undergo different photochemical reactions, including proton transfer or hydride transfer. The photochemical mechanisms of a few reactions have been analyzed by computational methods, including quantum dynamics. A section on specialist methods (time-resolved spectroscopy, matrix isolation, NMR, and computational methods) and a survey of transition metal hydride photochemistry organized by transition metal group complete the Review.

  6. Fluorination of epitaxial oxides: synthesis of perovskite oxyfluoride thin films.

    PubMed

    Moon, Eun Ju; Xie, Yujun; Laird, Eric D; Keavney, David J; Li, Christopher Y; May, Steven J

    2014-02-12

    While the synthesis of ABO3 perovskite films has enabled new strategies to control the functionality of this material class, the chemistries that have been realized in thin film form constitute only a fraction of those accessible to bulk chemists. Here, we report the synthesis of oxyfluoride films, where the incorporation of F may provide a new means to tune physical properties in thin films by modifying electronic structure. Fluorination is achieved by spin coating a poly(vinylidene fluoride) (PVDF) solution onto oxygen-deficient films. The film/polymer bilayer is then annealed, promoting the diffusion of F into the film. We have used this method to synthesize SrFeO(3-α)Fγ films, as confirmed by X-ray photoemission spectroscopy and X-ray absorption spectroscopy. PMID:24443775

  7. Anion Redox Chemistry in the Cobalt Free 3d Transition Metal Oxide Intercalation Electrode Li[Li0.2Ni0.2Mn0.6]O2.

    PubMed

    Luo, Kun; Roberts, Matthew R; Guerrini, Niccoló; Tapia-Ruiz, Nuria; Hao, Rong; Massel, Felix; Pickup, David M; Ramos, Silvia; Liu, Yi-Sheng; Guo, Jinghua; Chadwick, Alan V; Duda, Laurent C; Bruce, Peter G

    2016-09-01

    Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g., Mn(3+/4+) in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V versus Li(+)/Li. The capacity at 4.5 V is dominated by oxidation of the O(2-) anions accounting for ∼0.43 e(-)/formula unit, with an additional 0.06 e(-)/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V is mainly O loss, ∼0.08 e(-)/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn(4+)/Li(+)). The results have been obtained by combining operando electrochemical mass spec on (18)O labeled Li[Li0.2Ni0.2Mn0.6]O2 with XANES, soft X-ray spectroscopy, resonant inelastic X-ray spectroscopy, and Raman spectroscopy. Finally the general features of O redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials. PMID:27498756

  8. Anion Redox Chemistry in the Cobalt Free 3d Transition Metal Oxide Intercalation Electrode Li[Li0.2Ni0.2Mn0.6]O2.

    PubMed

    Luo, Kun; Roberts, Matthew R; Guerrini, Niccoló; Tapia-Ruiz, Nuria; Hao, Rong; Massel, Felix; Pickup, David M; Ramos, Silvia; Liu, Yi-Sheng; Guo, Jinghua; Chadwick, Alan V; Duda, Laurent C; Bruce, Peter G

    2016-09-01

    Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g., Mn(3+/4+) in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V versus Li(+)/Li. The capacity at 4.5 V is dominated by oxidation of the O(2-) anions accounting for ∼0.43 e(-)/formula unit, with an additional 0.06 e(-)/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V is mainly O loss, ∼0.08 e(-)/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn(4+)/Li(+)). The results have been obtained by combining operando electrochemical mass spec on (18)O labeled Li[Li0.2Ni0.2Mn0.6]O2 with XANES, soft X-ray spectroscopy, resonant inelastic X-ray spectroscopy, and Raman spectroscopy. Finally the general features of O redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials.

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

    NASA Astrophysics Data System (ADS)

    Vajifdar, Kayzad Jimmy

    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

  10. Synthesis of transition metal carbonitrides

    DOEpatents

    Munir, Zuhair A. R.; Eslamloo-Grami, Maryam

    1994-01-01

    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.

  11. Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface.

    PubMed

    Tsvetkov, Nikolai; Lu, Qiyang; Sun, Lixin; Crumlin, Ethan J; Yildiz, Bilge

    2016-09-01

    Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces are detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (for example, ) by the positively charged oxygen vacancies () enriched at the surface. Here we show that reducing the surface concentration improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while reducing the concentration of and making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 °C achieved by Hf addition onto LSC. Finally, the results revealed a 'volcano' relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss. PMID:27295099

  12. Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface

    NASA Astrophysics Data System (ADS)

    Tsvetkov, Nikolai; Lu, Qiyang; Sun, Lixin; Crumlin, Ethan J.; Yildiz, Bilge

    2016-09-01

    Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces are detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (for example, ) by the positively charged oxygen vacancies () enriched at the surface. Here we show that reducing the surface concentration improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while reducing the concentration of and making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 °C achieved by Hf addition onto LSC. Finally, the results revealed a `volcano' relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss.

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

    PubMed

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

    2014-07-23

    Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La(0.8-x)Bi(x)Sr0.2FeO(3-δ) (0 ≤ x ≤ 0.8) as novel cathode material for intermediate-temperature solid oxide fuel cells. The perovskite properties including oxygen nonstoichiometry coefficient (δ), average valence of Fe, sinterability, thermal expansion coefficient, electrical conductivity (σ), oxygen chemical surface exchange coefficient (K(chem)), and chemical diffusion coefficient (D(chem)) are explored as a function of bismuth content. While σ decreases with x due to the reduced Fe(4+) content, D(chem) and K(chem) increase since the oxygen vacancy concentration is increased by Bi doping. Consequently, the electrochemical performance is substantially improved and the interfacial polarization resistance is reduced from 1.0 to 0.10 Ω 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.

  14. Time-resolved XAFS spectroscopic studies of B-H and N-H oxidative addition to transition metal catalysts relevant to hydrogen storage

    SciTech Connect

    Bitterwolf, Thomas E.

    2014-12-09

    Successful catalytic dehydrogenation of aminoborane, H3NBH3, prompted questions as to the potential role of N-H oxidative addition in the mechanisms of these processes. N-H oxidative addition reactions are rare, and in all cases appear to involve initial dative bonding to the metal by the amine lone pairs followed by transfer of a proton to the basic metal. Aminoborane and its trimethylborane derivative block this mechanism and, in principle, should permit authentic N-H oxidative attrition to occur. Extensive experimental work failed to confirm this hypothesis. In all cases either B-H complexation or oxidative addition of solvent C-H bonds dominate the chemistry.

  15. Iridium-based double perovskites for efficient water oxidation in acid media

    NASA Astrophysics Data System (ADS)

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-08-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.

  16. Iridium-based double perovskites for efficient water oxidation in acid media

    PubMed Central

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-01-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2. PMID:27498694

  17. Reduced Graphene Oxide/Mesoporous TiO2 Nanocomposite Based Perovskite Solar Cells.

    PubMed

    Han, Gill Sang; Song, Young Hyun; Jin, Young Un; Lee, Jin-Wook; Park, Nam-Gyu; Kang, Bong Kyun; Lee, Jung-Kun; Cho, In Sun; Yoon, Dae Ho; Jung, Hyun Suk

    2015-10-28

    We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO2 nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO2 nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO2 nanocomposite film reduces interfacial resistance when compared to the mp-TiO2 film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO2 nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO2 nanoparticles based perovskite solar cells.

  18. Iridium-based double perovskites for efficient water oxidation in acid media.

    PubMed

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J; Wezendonk, Tim; Gascon, Jorge; Fu, W T; Koper, Marc T M

    2016-01-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2. PMID:27498694

  19. Direct synthesis of 2-aryl-4-quinolones via transition-metal-free intramolecular oxidative C(sp(3))-H/C(sp(3))-H coupling.

    PubMed

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

    2015-03-01

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

  20. High valence transition metal doped strontium ferrites for electrode materials in symmetrical SOFCs

    NASA Astrophysics Data System (ADS)

    Fernández-Ropero, A. J.; Porras-Vázquez, J. M.; Cabeza, A.; Slater, P. R.; Marrero-López, D.; Losilla, E. R.

    2014-03-01

    In this paper we report the successful incorporation of high valence transition metals, i.e. Cr, Mo, W, V, Nb, Ti, Zr into SrFeO3-δ perovskite materials, for potential applications as symmetric electrode materials for Solid Oxide Fuel Cells. It is observed that the doping leads to a change from an orthorhombic structure (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). These electrodes are chemically compatibles with Ce0.9Gd0.1O1.95 (CGO) and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolytes at least up to 1100 °C. Thermal annealing experiments in 5% H2-Ar at 800 °C also show the stability of the doped samples in reducing conditions, suggesting that they may be suitable for both cathode and anode applications. In contrast, reduction of undoped SrFeO3-δ leads to the observation of extra peaks indicating the formation of the brownmillerite structure with the associated oxygen vacancy ordering. The performance of these electrodes was examined on dense electrolyte pellets of CGO and LSGM in air and 5% H2-Ar. In both atmospheres an improvement in the area specific resistances (ASR) values is observed for the doped samples with respect to the parent compound. Thus, the results show that high valence transition metals can be incorporated into SrFeO3-δ-based materials and can have a beneficial effect on the electrochemical performance, making them potentially suitable for use as cathode and anode materials in symmetrical SOFC.

  1. Water-Gas Shift and Methane Reactivity on Reducible Perovskite-Type Oxides

    PubMed Central

    2015-01-01

    Comparative (electro)catalytic, structural, and spectroscopic studies in hydrogen electro-oxidation, the (inverse) water-gas shift reaction, and methane conversion on two representative mixed ionic–electronic conducting perovskite-type materials La0.6Sr0.4FeO3−δ (LSF) and SrTi0.7Fe0.3O3−δ (STF) were performed with the aim of eventually correlating (electro)catalytic activity and associated structural changes and to highlight intrinsic reactivity characteristics as a function of the reduction state. Starting from a strongly prereduced (vacancy-rich) initial state, only (inverse) water-gas shift activity has been observed on both materials beyond ca. 450 °C but no catalytic methane reforming or methane decomposition reactivity up to 600 °C. In contrast, when starting from the fully oxidized state, total methane oxidation to CO2 was observed on both materials. The catalytic performance of both perovskite-type oxides is thus strongly dependent on the degree/depth of reduction, on the associated reactivity of the remaining lattice oxygen, and on the reduction-induced oxygen vacancies. The latter are clearly more reactive toward water on LSF, and this higher reactivity is linked to the superior electrocatalytic performance of LSF in hydrogen oxidation. Combined electron microscopy, X-ray diffraction, and Raman measurements in turn also revealed altered surface and bulk structures and reactivities. PMID:26045733

  2. 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

    Valavanidis, Athanasios; Vlahoyianni, Thomais; Fiotakis, Konstantinos

    2005-10-01

    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).

  3. Fabrication of (110)-one-axis-oriented perovskite-type oxide thin films and their application to buffer layer

    NASA Astrophysics Data System (ADS)

    Sato, Tomoya; Ichinose, Daichi; Kimura, Junichi; Inoue, Takaaki; Mimura, Takanori; Funakubo, Hiroshi; Uchiyama, Kiyoshi

    2016-10-01

    BaCe0.9Y0.1O3-δ (BCYO) and SrZr0.8Y0.2O3-δ (SZYO) thin films of perovskite-type oxides were deposited on (111)Pt/TiO x /SiO2/(100)Si substrates. X-ray diffraction patterns showed that the (110)-oriented BCYO and SZYO thin films were grown on (111)Pt/Si substrates directly without using any buffer layers. Thin films of SrRuO3 (SRO), a conductive perovskite-type oxide, were also deposited on those films and highly (110)-oriented SRO thin films were obtained. We believe that this (110)-oriented SRO works as a buffer layer to deposit (110)-oriented perovskite-type ferroelectric oxide thin films as well as a bottom electrode and can modify the ferroelectric properties of the oxide thin films by controlling their crystallographic orientations.

  4. Self-assembly and crystallization behavior of mesoporous, crystalline HfO2 thin films: a model system for the generation of mesostructured transition-metal oxides.

    PubMed

    Brezesinski, Torsten; Smarsly, Bernd; Iimura, Ken-ichi; Grosso, David; Boissière, Cédric; Amenitsch, Heinz; Antonietti, Markus; Sanchez, Clément

    2005-08-01

    Mesoporous thin films of crystalline hafnium oxide were fabricated by evaporation-induced self-assembly in combination with sol-gel processing, followed by a suitable post heat-treatment procedure to initiate the crystallization. A novel type of block-copolymer template was used as structure-directing agent, which generated a distorted cubic arrangement of spherical mesopores, the size of which could be quantified by suitable techniques, such as ellipsometry-porosimetry, small-angle X-ray scattering, and atomic force microscopy. Detailed insights into the nature of the crystallization process of mesostructured hafnium oxide were obtained by temperature-dependent, in situ X-ray scattering experiments. These investigations revealed that crystallization takes place, within the confinement of the mesostructure, as a solid-solid transition from a dehydrated, amorphous form of hafnium oxide. The study suggests that one main benefit of the novel template results from the ability of the polymer to stabilize the mesostructure of amorphous hafnium oxide up to 400-450 degrees C.

  5. Self-assembly and crystallization behavior of mesoporous, crystalline HfO2 thin films: a model system for the generation of mesostructured transition-metal oxides.

    PubMed

    Brezesinski, Torsten; Smarsly, Bernd; Iimura, Ken-ichi; Grosso, David; Boissière, Cédric; Amenitsch, Heinz; Antonietti, Markus; Sanchez, Clément

    2005-08-01

    Mesoporous thin films of crystalline hafnium oxide were fabricated by evaporation-induced self-assembly in combination with sol-gel processing, followed by a suitable post heat-treatment procedure to initiate the crystallization. A novel type of block-copolymer template was used as structure-directing agent, which generated a distorted cubic arrangement of spherical mesopores, the size of which could be quantified by suitable techniques, such as ellipsometry-porosimetry, small-angle X-ray scattering, and atomic force microscopy. Detailed insights into the nature of the crystallization process of mesostructured hafnium oxide were obtained by temperature-dependent, in situ X-ray scattering experiments. These investigations revealed that crystallization takes place, within the confinement of the mesostructure, as a solid-solid transition from a dehydrated, amorphous form of hafnium oxide. The study suggests that one main benefit of the novel template results from the ability of the polymer to stabilize the mesostructure of amorphous hafnium oxide up to 400-450 degrees C. PMID:17193544

  6. Piperazine pivoted transition metal dithiocarbamates

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  7. Syntheses, structures, and ionic conductivities of perovskite-structured lithium–strontium–aluminum/gallium–tantalum-oxides

    SciTech Connect

    Phraewphiphat, Thanya; Iqbal, Muhammad; Suzuki, Kota; Matsuda, Yasuaki; Yonemura, Masao; Hirayama, Masaaki; Kanno, Ryoji

    2015-05-15

    The ionic conductivities of new perovskite-structured lithium–strontium–aluminum/gallium–tantalum oxides were investigated. Solid solutions of the new perovskite oxides, (Li{sub x}Sr{sub 1−x})(Al{sub (1−x)/2}Ta{sub (1+x)/2})O{sub 3} and (Li{sub x}Sr{sub 1−x})(Ga{sub (1−x)/2}Ta{sub (1+x)/2})O{sub 3}, were synthesized using a ball-milled-assisted solid-state method. The partial substitution of the smaller Ga{sup +3} for Ta{sup +5} resulted in new compositions, the structures of which were determined by neutron diffraction measurements using a cubic perovskite structural model with the Pm−3m space group. Vacancies were introduced into the Sr(Li) sites by the formation of solid solutions with compositions (Li{sub x}Sr{sub 1−x−y}☐{sub y})(Ga{sub [(1−x)/2]−y}Ta{sub [(1+x)/2]+y})O{sub 3}, where the composition range of 0≤y≤0.20 was examined for x=0.2 and 0.25. The highest conductivity, 1.85×10{sup −3} S cm{sup −1} at 250 °C, was obtained for (Li{sub 0.25}Sr{sub 0.625}☐{sub 0.125})(Ga{sub 0.25}Ta{sub 0.75})O{sub 3} (x=0.25, y=0.125). Enhanced ionic conductivities were achieved by the introduction of vacancies at the A-sites. - Graphical abstract: Novel lithium-conducting oxides with the cubic perovskite structure (Li{sub x}Sr{sub 1−x−y}☐{sub y})(Ga{sub [(1−x)/2]−y}Ta{sub [(1+x)/2]+y})O{sub 3} provide a specific solid-solution region with various x and y values, exhibiting the highest ionic conductivity (1.85 S cm{sup −1} at 250 °C) for (Li{sub 0.25}Sr{sub 0.625}☐{sub 0.125})(Ga{sub 0.25}Ta{sub 0.75})O{sub 3} (x=0.25, y=0.125 in (Li{sub x}Sr{sub 1−x−y}☐{sub y})(Ga{sub [(1−x)/2]−y}Ta{sub [(1+x)/2]+y})O{sub 3}). The vacancies (☐) introduced into the A-sites contribute to the enhancement of lithium diffusion in the perovskite structure because of the enlargement of the bottleneck size and suppression of the interaction between lithium and oxygen. - Highlights: • The perovskite-structured novel Li

  8. Platinum nanoparticles decorated robust binary transition metal nitride-carbon nanotubes hybrid as an efficient electrocatalyst for the methanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Zhan, Guohe; Fu, Zhenggao; Sun, Dalei; Pan, Zhanchang; Xiao, Chumin; Wu, Shoukun; Chen, Chun; Hu, Guanghui; Wei, Zhigang

    2016-09-01

    Titanium cobalt nitride (TiCoN)-CNTs hybrid support is prepared by a facile and efficient method, including a one-pot solvothermal process followed by a nitriding process, and this hybrid support is further decorated with Pt nanoparticles to catalyze the oxidation of methanol. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. Notably, Pt/CNTs@TiCoN catalyst exhibits a much higher mass activity and durability than that of the conventional Pt/C (JM) for methanol oxidation. The experimental data indicates that the CNTs@TiCoN hybrid support combines the merits of the CNTs's high conductivity and the superb corrosion resistance of external TiCoN coating.

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

    NASA Astrophysics Data System (ADS)

    Balachandran, Prasanna V.; Rondinelli, James M.

    2013-08-01

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

  10. Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brahlek, Matthew; Zhang, Lei; Zhang, Hai-Tian; Lapano, Jason; Dedon, Liv R.; Martin, Lane W.; Engel-Herbert, Roman

    2016-09-01

    Requisite to growing stoichiometric perovskite thin films of the solid-solution A'1-xAxBO3 by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'BO3 and ABO3, which can be grown in a self-regulated fashion, but under different conditions. Using the example of La1-xSrxVO3, the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x, was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x. This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A'1-xAxBO3.

  11. Research Update: Interface-engineered oxygen octahedral tilts in perovskite oxide heterostructures

    SciTech Connect

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

    2015-06-01

    Interface engineering of structural distortions is a key for exploring the functional properties of oxide heterostructures and superlattices. In this paper, we report on our comprehensive investigations of oxygen octahedral distortions at the heterointerface between perovskite oxides SrRuO{sub 3} and BaTiO{sub 3} on GdScO{sub 3} substrates and of the influences of the interfacially engineered distortions on the magneto-transport properties of the SrRuO{sub 3} layer. Our state-of-the-art annular bright-field imaging in aberration-corrected scanning transmission electron microscopy revealed that the RuO{sub 6} octahedral distortions in the SrRuO{sub 3} layer have strong dependence on the stacking order of the SrRuO{sub 3} and BaTiO{sub 3} layers on the substrate. This can be attributed to the difference in the interfacial octahedral connections. We also found that the stacking order of the oxide layers has a strong impact on the magneto-transport properties, allowing for control of the magnetic anisotropy of the SrRuO{sub 3} layer through interface engineering. Our results demonstrate the significance of the interface engineering of the octahedral distortions on the structural and physical properties of perovskite oxides.

  12. New class of single-source precursors for the synthesis of main group-transition metal oxides: heterobimetallic Pb-Mn beta-diketonates.

    PubMed

    Zhang, Haitao; Yang, Jen-Hsien; Shpanchenko, Roman V; Abakumov, Artem M; Hadermann, Joke; Clérac, Rodolphe; Dikarev, Evgeny V

    2009-09-01

    Heterometallic lead-manganese beta-diketonates have been isolated in pure form by several synthetic methods that include solid-state and solution techniques. Two compounds with different Pb/Mn ratios, PbMn(2)(hfac)(6) (1) and PbMn(hfac)(4) (2) (hfac = hexafluoroacetylacetonate), can be obtained in quantitative yield by using different starting materials. Single crystal X-ray investigation revealed that the solid-state structure of 1 contains trinuclear molecules in which lead metal center is sandwiched between two [Mn(hfac)(3)] units, while 2 consists of infinite chains of alternating [Pb(hfac)(2)] and [Mn(hfac)(2)] fragments. The heterometallic structures are held together by strong Lewis acid-base interactions between metal atoms and diketonate ligands acting in chelating-bridging fashion. Spectroscopic investigation confirmed the retention of heterometallic structures in solutions of non-coordinating solvents as well as upon sublimation-deposition procedure. Thermal decomposition of heterometallic diketonates has been systematically investigated in a wide range of temperatures and annealing times. For the first time, it has been shown that thermal decomposition of heterometallic diketonates results in mixed-metal oxides, while both the structure of precursors and the thermolysis conditions have a significant influence on the nature of the resulting oxides. Five different Pb-Mn oxides have been detected by X-ray powder diffraction when studying the decomposition of 1 and 2 in the temperature range 500-800 degrees C. The phase that has been previously reported as "Pb(0.43)MnO(2.18)" was synthesized in the pure form by decomposition of 1, and crystallographically characterized. The orthorhombic unit cell parameters of this oxide, obtained by electron diffraction technique, have been subsequently refined using X-ray powder diffraction data. Besides that, a previously unknown lead-manganese oxide has been obtained at low temperature decomposition and short annealing

  13. Impact Electrochemistry of Layered Transition Metal Dichalcogenides.

    PubMed

    Lim, Chee Shan; Tan, Shu Min; Sofer, Zdeněk; Pumera, Martin

    2015-08-25

    Layered transition metal dichalcogenides (TMDs) exhibit paramount importance in the electrocatalysis of the hydrogen evolution reaction. It is crucial to determine the size of the electrocatalytic particles as well as to establish their electrocatalytic activity, which occurs at the edges of these particles. Here, we show that individual TMD (MoS2, MoSe2, WS2, or WSe2; in general MX2) nanoparticles impacting an electrode surface provide well-defined current "spikes" in both the cathodic and anodic regions. These spikes originate from direct oxidation of the nanoparticles (from M(4+) to M(6+)) at the anodic region and from the electrocatalytic currents generated upon hydrogen evolution in the cathodic region. The positive correlation between the frequency of the impacts and the concentration of TMD nanoparticles is also demonstrated here, enabling determination of the concentration of TMD nanoparticles in colloidal form. In addition, the size of individual TMD nanoparticles can be evaluated using the charge passed during every spike. The capability of detecting both the "indirect" catalytic effect of an impacting TMD nanoparticle as well as "direct" oxidation indicates that the frequency of impacts in both the "indirect" and "direct" scenarios are comparable. This suggests that all TMD nanoparticles, which are electrochemically oxidizable (thus capable of donating electrons to electrodes), are also capable of catalyzing the hydrogen reduction reaction.

  14. High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Polar/Nonpolar Perovskite Oxide Heterostructures

    NASA Astrophysics Data System (ADS)

    Yang, Kesong; Nazir, Safdar; Behtash, Maziar; Cheng, Jianli

    2016-10-01

    The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO3 and SrTiO3 (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO3-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests. Of these, Al-, Ga-, Sc-, and Ta-based compounds can form a 2DEG with STO, while In-based compounds exhibit a strain-induced strong polarization when deposited on STO substrate. In particular, the Ta-based compounds can form 2DEG with potentially high electron mobility at (TaO2)+/(SrO)0 interface. Our approach, by defining materials descriptors solely based on the bulk materials properties, and by relying on the perovskite-oriented quantum materials repository, opens new avenues for the discovery of perovskite-oxide-based functional interface materials in a HT fashion.

  15. High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Polar/Nonpolar Perovskite Oxide Heterostructures

    PubMed Central

    Yang, Kesong; Nazir, Safdar; Behtash, Maziar; Cheng, Jianli

    2016-01-01

    The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO3 and SrTiO3 (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO3-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests. Of these, Al-, Ga-, Sc-, and Ta-based compounds can form a 2DEG with STO, while In-based compounds exhibit a strain-induced strong polarization when deposited on STO substrate. In particular, the Ta-based compounds can form 2DEG with potentially high electron mobility at (TaO2)+/(SrO)0 interface. Our approach, by defining materials descriptors solely based on the bulk materials properties, and by relying on the perovskite-oriented quantum materials repository, opens new avenues for the discovery of perovskite-oxide-based functional interface materials in a HT fashion. PMID:27708415

  16. O3-type layered transition metal oxide Na(NiCoFeTi)1/4O2 as a high rate and long cycle life cathode material for sodium ion batteries

    DOE PAGES

    Yue, Ji -Li; Yang, Xiao -Qing; Zhou, Yong -Ning; Yu, Xiqian; Bak, Seong -Min; Fu, Zheng -Wen

    2015-10-09

    High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mA h g–1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be retained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterizationmore » revealed reversible phase transformations and electronic structural changes during the Na+ deintercalation/intercalation process. Ni, Co and Fe ions contribute to charge compensation during charge and discharge. Although Ti ions do not contribute to the charge transfer, they play a very important role in stabilizing the structure during charge and discharge by suppressing the Fe migration. Additionally, Ti substitution can also smooth the charge–discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.« less

  17. O3-type layered transition metal oxide Na(NiCoFeTi)1/4O2 as a high rate and long cycle life cathode material for sodium ion batteries

    SciTech Connect

    Yue, Ji -Li; Yang, Xiao -Qing; Zhou, Yong -Ning; Yu, Xiqian; Bak, Seong -Min; Fu, Zheng -Wen

    2015-10-09

    High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mA h g–1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be retained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterization revealed reversible phase transformations and electronic structural changes during the Na+ deintercalation/intercalation process. Ni, Co and Fe ions contribute to charge compensation during charge and discharge. Although Ti ions do not contribute to the charge transfer, they play a very important role in stabilizing the structure during charge and discharge by suppressing the Fe migration. Additionally, Ti substitution can also smooth the charge–discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.

  18. Molecular precursor routes to transition metal sulfides

    NASA Astrophysics Data System (ADS)

    Dinnage, Christopher Walker

    This thesis is primarily concerned with the synthesis of homoleptic early transition meta thiolates and the subsequent preparation of bulk and thin-film metal disulfides from these compounds. Chapter 1 gives an introduction into the properties, preparation procedures and uses of bulk and thin-film transition metal disulfides as well as giving an overview of early transition metal thiolates synthesied so far in the literature (for titanium, zirconium, tantalum and niobium). Chapter 2 is concerned with the synthesis of a number of ionic and neutral transition metal thiolates. The main synthetic methodologies discussed in this chapter include substitution reactions of transition metal amides and alkyls with thiols, salt metathesis reactions of transition metal chlorides with alkali metal thiolates or with a base / thiol and the use of Grignard reagents. Chapter 3 discusses the preparation of bulk transition metal disulfides using the thiolates prepared in the previous chapter via a thio "sol-gel" route. The preparation of a range of bulk metal and mixed-metal disulfides using transition metal chlorides and hexamethyldisilathiane is also discussed in this chapter. Finally, chapter 4 is concerned with the attempted preparation of thin-films of some transition metal disulfides. Decomposition studies of some of the thiolates prepared in chapter 2 are discussed using thermal gravimetric analysis. Vapour-phase deposition studies are also explored in order to test the potential of the transition metal thiolates as precursors to the disulfides. Experiments using low-pressure chemical vapour deposition and aerosol-assisted chemical vapour deposition are also described.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

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

    PubMed

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

    2009-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ardo, Shane

    Photovoltaics provide a direct means of converting photons into useful, electric power; however traditional silicon-based technologies are too expensive for global commercialization. Dye-sensitized mesoporous semiconducting thin films, when utilized in regenerative photoelectrochemical cells, are one category of next generation photovoltaics that could eventually circumvent this issue. In fact, their architecture also affords a clear platform for implementation of a direct, solar fuel-forming system. The mechanisms involved in the myriad of molecular processes that occur in these molecular--solid-state hybrid materials are poorly understood. Thus, the overriding goal of this dissertation was to evaluate sensitized mesoporous, nanocrystalline metal-oxide thin films critically so as to elucidate mechanistic phenomena. Using transient and steady-state absorption and emission spectroscopies as well as (photo)electrochemistry, various previously unobserved processes have been identified. Chapter 2 demonstrates for the first time that the electric fields emanating from these charged thin films affect surface-anchored molecular sensitizers via a Stark effect. In most cases, further, but incomplete, ionic screening of the charged nanoparticles from the sensitizers, as non-Faradaic electrolyte redistribution, was spectroscopically inferred after rapid semiconductor charging. Chapter 3 highlights the reactivity of Co(I) coordination-compound catalysts anchored to anatase TiO2 thin-film electrodes. Visible-light excitation resulted in prompt excited-state electron injection into TiO2 while introduction of benzylbromide into the fluid solution surrounding the thin film led to a 2e--transfer, oxidative-addition reaction to Co1 forming a stable Co--benzyl product. Subsequent visible-light excitation initiated a photocatalytic cycle for C--C bond formation. Unique to the nanocrystalline thin films employed here, Chapter 4 demonstrates that traditional time-resolved polarization

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

    SciTech Connect

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

    2011-09-15

    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).

  3. Transition metal oxide pillared clay. 1: A comparative study of textural and acidic properties of Fe(III) pillared montmorillonite and pillared acid activated montmorillonite

    SciTech Connect

    Mishra, T.; Parida, K.M.; Rao, S.B.

    1996-10-15

    Fe(III) pillared montmorillonite samples have been prepared by intercalating trinuclear acetato hydroxy-iron (III) nitrate [Fe(COOCH{sub 3}){sub 7}OH 2H{sub 2}O]{sup +} NO{sub 3}{sup {minus}} between the layers of both Na-exchanged and acid-activated montmorillonite, followed by calcination and characterized by various techniques. The multistep ion exchange process gave better complex loading than the single step process. FTIR and Moessbauer spectral analysis showed the presence of the complex inside the silicate layers. Materials prepared from the two starting materials are thermally stable up to 500 C, having basal spacings of 18.0 and 17.6 {angstrom} and high surface areas of 284 and 276 m{sup 2}/g, respectively. The acid-activated pillared montmorillonite shows somewhat low complex intake, but has high acidity in comparison to the Na-exchanged material. Iron oxide pillared clay has gained considerable importance as it can be used in demetalization, reduction of NO by NH{sub 3}, and Fischer-Tropsch reactions.

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

    PubMed

    Oyedepo, Gbenga A; Wilson, Angela K

    2011-12-01

    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(α)-C(β) bond in an archetypal arylglycerol β-aryl ether (β-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 (ΔH°(298)) and activation energies (ΔH-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(α)-C(β) bond of β-O-4, the use of platinum metal catalysts will lead to the most thermodynamically favored reaction with the lowest activation barrier. PMID:22144374

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

    PubMed

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

    2013-01-01

    For the development of highly active and robust catalysts for dehydrogenation of ethylbenzene (EBDH) to produce styrene; an important monomer for polystyrene production, perovskite-type oxides were applied to the reaction. Controlling the mobility of lattice oxygen by changing the structure of Ba1 - x SrxFe y Mn1 - y O3 - δ (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 - δ catalyst with that of an industrial potassium promoted iron (Fe-K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ catalyst showed higher initial activity than the industrial Fe-K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ 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 - δ 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 - δ catalyst while the Fe-K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ 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 - δ was superior to that of Fe-K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ perovskite oxide.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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-d(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-d catalyst with that of an industrial potassium promoted iron (Fe-K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst showed higher initial activity than the industrial Fe-K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3-d 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-d and the Fe-K catalysts in aH2O/H2 atmosphere, reduction was suppressed by the presence of H2O over the Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst while the Fe-K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3-d 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-d was superior to that of Fe-K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3-d perovskite oxide.

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

    PubMed Central

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

    2013-01-01

    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 − δ (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 − δ catalyst with that of an industrial potassium promoted iron (Fe–K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst showed higher initial activity than the industrial Fe–K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ 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 − δ 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 − δ catalyst while the Fe–K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ 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 − δ was superior to that of Fe–K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ perovskite oxide. PMID:24790949

  8. Understanding the spin-driven polarizations in Bi MO3 (M = 3 d transition metals) multiferroics

    NASA Astrophysics Data System (ADS)

    Kc, Santosh; Lee, Jun Hee; Cooper, Valentino R.

    Bismuth ferrite (BiFeO3) , a promising multiferroic, stabilizes in a perovskite type rhombohedral crystal structure (space group R3c) at room temperature. Recently, it has been reported that in its ground state it possess a huge spin-driven polarization. To probe the underlying mechanism of this large spin-phonon response, we examine these couplings within other Bi based 3 d transition metal oxides Bi MO3 (M = Ti, V, Cr, Mn, Fe, Co, Ni) using density functional theory. Our results demonstrate that this large spin-driven polarization is a consequence of symmetry breaking due to competition between ferroelectric distortions and anti-ferrodistortive octahedral rotations. Furthermore, we find a strong dependence of these enhanced spin-driven polarizations on the crystal structure; with the rhombohedral phase having the largest spin-induced atomic distortions along [111]. These results give us significant insights into the magneto-electric coupling in these materials which is essential to the magnetic and electric field control of electric polarization and magnetization in multiferroic based devices. Research is supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division and the Office of Science Early Career Research Program (V.R.C) and used computational resources at NERSC.

  9. Thermochemistry of perovskites in the lanthanum-strontium-manganese-iron oxide system

    NASA Astrophysics Data System (ADS)

    Marinescu, Cornelia; Vradman, Leonid; Tanasescu, Speranta; Navrotsky, Alexandra

    2015-10-01

    The enthalpies of formation from binary oxides of perovskites (ABO3) based on lanthanum strontium manganite La(Sr)MnO3 (LSM) and lanthanum strontium ferrite La(Sr)FeO3 (LSF) and mixed lanthanum strontium manganite ferrite La(Sr)Mn(Fe)O3 (LSMF) were measured by high temperature oxide melt solution calorimetry. Using iodometric titration, the oxygen content was derived. The perovskites with A-site cation deficiency have greater oxygen deficiency than the corresponding A-site stoichiometric series. Stability of LSMF decreases with increasing iron content. Increasing oxygen deficiency clearly destabilizes the perovskites. The results suggest an enthalpy of oxygen incorporation that is approximately independent of composition. 0.35La2O3 (xl, 25 °C)+Mn2O3 (xl, 25 °C)+0.3SrO (xl, 25 °C)+Fe2O3 (xl, 25 °C)+O2 (g, 25 °C)→La0.7Sr0.3Mn1-yFeyO3-δ (xl, 25 °C). (b) ∆ Hf,ox* (La0.7Sr0.3Mn1-yFeyO3-δ) .0.35 La2O3 (xl, 25 ººC) + (0.7-y+ 2δ)/2 Mn2O3 (xl, 25 ºC) + 0.3 SrO (xl, 25 ºC) + y/2Fe2O3 (xl, 25 ºC) + (0.3-2δ) MnO2 (xl, 25 ºC)→La0.7Sr0.3Mn1-yFeyO3-δ (xl, 25 ºC).

  10. Thermomechanical properties of 3d transition metals

    SciTech Connect

    Karaoglu, B.; Rahman, S.M.M. . Dept. of Physics)

    1994-05-15

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

  11. Transition-Metal Hydride Radical Cations.

    PubMed

    Hu, Yue; Shaw, Anthony P; Estes, Deven P; Norton, Jack R

    2016-08-10

    Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pertaining to the M-H bond, are described, followed by a detailed treatment of decomposition pathways. Finally, reactions involving TMHRCs as intermediates are described. PMID:26828562

  12. Transition-Metal Hydride Radical Cations.

    PubMed

    Hu, Yue; Shaw, Anthony P; Estes, Deven P; Norton, Jack R

    2016-08-10

    Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pertaining to the M-H bond, are described, followed by a detailed treatment of decomposition pathways. Finally, reactions involving TMHRCs as intermediates are described.

  13. Stable and null current hysteresis perovskite solar cells based nitrogen doped graphene oxide nanoribbons hole transport layer

    PubMed Central

    Kim, Jeongmo; Mat Teridi, Mohd Asri; Mohd Yusoff, Abd. Rashid bin; Jang, Jin

    2016-01-01

    Perovskite solar cells are becoming one of the leading technologies to reduce our dependency on traditional power sources. However, the frequently used component poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has several shortcomings, such as an easily corroded indium-tin-oxide (ITO) interface at elevated temperatures and induced electrical inhomogeneity. Herein, we propose solution-processed nitrogen-doped graphene oxide nanoribbons (NGONRs) as a hole transport layer (HTL) in perovskite solar cells, replacing the conducting polymer PEDOT:PSS. The conversion efficiency of NGONR-based perovskite solar cells has outperformed a control device constructed using PEDOT:PSS. Moreover, our proposed NGONR-based devices also demonstrate a negligible current hysteresis along with improved stability. This work provides an effective route for substituting PEDOT:PSS as the effective HTL. PMID:27277388

  14. Stable and null current hysteresis perovskite solar cells based nitrogen doped graphene oxide nanoribbons hole transport layer

    NASA Astrophysics Data System (ADS)

    Kim, Jeongmo; Mat Teridi, Mohd Asri; Mohd Yusoff, Abd. Rashid Bin; Jang, Jin

    2016-06-01

    Perovskite solar cells are becoming one of the leading technologies to reduce our dependency on traditional power sources. However, the frequently used component poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has several shortcomings, such as an easily corroded indium-tin-oxide (ITO) interface at elevated temperatures and induced electrical inhomogeneity. Herein, we propose solution-processed nitrogen-doped graphene oxide nanoribbons (NGONRs) as a hole transport layer (HTL) in perovskite solar cells, replacing the conducting polymer PEDOT:PSS. The conversion efficiency of NGONR-based perovskite solar cells has outperformed a control device constructed using PEDOT:PSS. Moreover, our proposed NGONR-based devices also demonstrate a negligible current hysteresis along with improved stability. This work provides an effective route for substituting PEDOT:PSS as the effective HTL.

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

    DOEpatents

    Rieke, Peter C.; Coffey, Gregory W.; Pederson, Larry R.; Marina, Olga A.; Hardy, John S.; Singh, Prabhaker; Thomsen, Edwin C.

    2010-07-20

    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.

  16. Transition Metal Nitrides for Electrocatalytic Energy Conversion: Opportunities and Challenges.

    PubMed

    Xie, Junfeng; Xie, Yi

    2016-03-01

    Electrocatalytic energy conversion has been considered as one of the most efficient and promising pathways for realizing energy storage and energy utilization in modern society. To improve electrocatalytic reactions, specific catalysts are needed to lower the overpotential. In the search for efficient alternatives to noble metal catalysts, transition metal nitrides have attracted considerable interest due to their high catalytic activity and unique electronic structure. Over the past few decades, numerous nitride-based catalysts have been explored with respect to their ability to drive various electrocatalytic reactions, such as the hydrogen evolution reaction and the oxygen evolution reaction to achieve water splitting and the oxygen reduction reaction coupled with the methanol oxidation reaction to construct fuel cells or rechargeable Li-O2 batteries. This Minireview provides a brief overview of recent progress on electrocatalysts based on transition metal nitrides, and outlines the current challenges and future opportunities. PMID:26494184

  17. Multiferroic materials based on organic transition-metal molecular nanowires.

    PubMed

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

    2012-09-01

    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 μC/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

  18. Scanning tunneling microscopy/spectroscopy on perovskite oxide thin films deposited in situ.

    PubMed

    Hitosugi, Taro; Shimizu, Ryota; Ohsawa, Takeo; Iwaya, Katsuya

    2014-10-01

    Complex oxide surfaces and interfaces, consisting of two or more cations and oxygen anions, have attracted a great deal of attention because their properties are crucial factors in the performance of catalysts, fuel cells, and Li-ion batteries. However, atomic-scale investigations of these oxide surfaces have been hindered because of the difficulties in surface preparation. Here, we demonstrate atomic-scale surface studies of complex perovskite oxides and the initial growth processes in oxide epitaxial films deposited on (✓13 × ✓13)-R33.7° reconstructed SrTiO3 (001) substrates using a scanning tunneling microscope integrated with a pulsed laser deposition system. The atomically ordered, reconstructed SrTiO3 (001) surface is stable under the typical conditions necessary for the growth of oxide thin films, and hence is considered suitable for the study of the initial growth processes in oxide films. The atomic-scale microscopic/spectroscopic characterizations performed here shed light on the microscopic origin of electronic properties observed in complex oxides and their heterostructures.

  19. Structural and Electronic Properties of Reduced Transition Metal Oxide Clusters, M 3 O 8 and M 3 O 8 - (M = Cr, W), from Photoelectron Spectroscopy and Quantum Chemical Calculations

    SciTech Connect

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

    2009-09-28

    We report a comparative study of reduced transition metal oxide clusters, M₃O₈⁻ (M = Cr, W) anions and their neutrals, via anion photoelectron spectroscopy (PES) and density functional theory (DFT) and molecular orbital theory (CCSD(T)) calculations. Well-resolved PES spectra are obtained for M₃O₈⁻ (M = Cr, W) at 193 and 157 nm photon energies. Different PES spectra are observed for M = Cr versus M = W. ExtensiveDFT and CCSD(T) calculations are performed to locate the ground and low-lying excited states for the neutrals and anions. The ground states of Cr₃O₈ and Cr₃O₈⁻ are predicted to be the ³B₂ and ⁴B₂ states of a C₂v structure, respectively, revealing ferromagnetic spin coupling for Cr 3d electrons. In contrast, the ground states of W₃O₈ and W₃O₈⁻ are predicted to be the ¹A' state (Cs symmetry) and the ²A₁ state (C₂v symmetry), respectively, showing metal-metal d-d bonding in the anion. The current cluster geometries are in qualitative agreement with prior DFT studies at the PBE level for M = Cr and the B3LYP level for M = W. The BP86 and PW91 functionals significantly outperform the B3LYP functional for the Cr species, in terms of relative energies, electron detachment energies, and electronic excitation energies, whereas the B3LYP functional is better for the W species. Accurate heats of formation for the ground states of M₃O₈ are calculated from the clustering energies and the heats of formation of MO₂ and MO₃. The energetics have been used to predict redox reaction thermochemistry.

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

    PubMed

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

    2011-08-01

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

  1. Microwave-assisted synthesis of transition metal phosphide

    DOEpatents

    Viswanathan, Tito

    2014-12-30

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

  2. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

    NASA Astrophysics Data System (ADS)

    Fernández-Posada, Carmen M.; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-09-01

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3-BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3-BiMnO3-PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

  3. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

    PubMed Central

    Fernández-Posada, Carmen M.; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-01-01

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3–BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3–BiMnO3–PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses. PMID:27677353

  4. Covalent bonds against magnetism in transition metal compounds.

    PubMed

    Streltsov, Sergey V; Khomskii, Daniel I

    2016-09-20

    Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an "exclusion" of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system. This effect is especially prominent for noninteger electron number, when it results in suppression of the famous double exchange, the main mechanism of ferromagnetism in transition metal compounds. We study this mechanism analytically and numerically and show that it explains magnetic properties of not only several 4d-5d materials, including Nb2O2F3 and Ba5AlIr2O11, but can also be operative in 3d transition metal oxides, e.g., in CrO2 under pressure. We also discuss the role of spin-orbit coupling on the competition between covalency and magnetism. Our results demonstrate that strong intersite coupling may invalidate the standard single-site starting point for considering magnetism, and can lead to a qualitatively new behavior. PMID:27601669

  5. Covalent bonds against magnetism in transition metal compounds.

    PubMed

    Streltsov, Sergey V; Khomskii, Daniel I

    2016-09-20

    Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an "exclusion" of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system. This effect is especially prominent for noninteger electron number, when it results in suppression of the famous double exchange, the main mechanism of ferromagnetism in transition metal compounds. We study this mechanism analytically and numerically and show that it explains magnetic properties of not only several 4d-5d materials, including Nb2O2F3 and Ba5AlIr2O11, but can also be operative in 3d transition metal oxides, e.g., in CrO2 under pressure. We also discuss the role of spin-orbit coupling on the competition between covalency and magnetism. Our results demonstrate that strong intersite coupling may invalidate the standard single-site starting point for considering magnetism, and can lead to a qualitatively new behavior.

  6. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi

    1983-01-01

    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.

  7. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi.

    1983-08-16

    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.

  8. Transition metal catalysis in confined spaces.

    PubMed

    Leenders, Stefan H A M; Gramage-Doria, Rafael; de Bruin, Bas; Reek, Joost N H

    2015-01-21

    Transition metal catalysis plays an important role in both industry and in academia where selectivity, activity and stability are crucial parameters to control. Next to changing the structure of the ligand, introducing a confined space as a second coordination sphere around a metal catalyst has recently been shown to be a viable method to induce new selectivity and activity in transition metal catalysis. In this review we focus on supramolecular strategies to encapsulate transition metal complexes with the aim of controlling the selectivity via the second coordination sphere. As we will discuss, catalyst confinement can result in selective processes that are impossible or difficult to achieve by traditional methods. We will describe the template-ligand approach as well as the host-guest approach to arrive at such supramolecular systems and discuss how the performance of the catalyst is enhanced by confining it in a molecular container.

  9. Single-Layer Light-Emitting Diodes Using Organometal Halide Perovskite/Poly(ethylene oxide) Composite Thin Films.

    PubMed

    Li, Junqiang; Bade, Sri Ganesh R; Shan, Xin; Yu, Zhibin

    2015-09-16

    Organometal halide perovskite and poly(ethylene oxide) composite thin films are studied. Single-layer light-emitting diodes using the composite thin film sandwiched between indium tin oxide and indium-gallium eutectic alloy exhibit a low turn-on voltage and high brightness because of the ionic conductivity of the composite film and the formation of a p-i-n homojunction. PMID:26247326

  10. Transition-metal-catalyzed Chelation-assisted C-H Functionalization of Aromatic Substrates.

    PubMed

    Zhao, Binlin; Shi, Zhuangzhi; Yuan, Yu

    2016-04-01

    In the past decade, transition-metal-catalyzed C-H activations have been very popular in the research field of organometallic chemistry, and have been considered as efficient and convenient strategies to afford complex natural products, functional advanced materials, fluorescent compounds, and pharmaceutical compounds. In this account, we begin with a brief introduction to the development of transition-metal-catalyzed C-H activation, especially the development of transition-metal-catalyzed chelation-assisted C-H activation. Then, a more detailed discussion is directed towards our recent studies on the transition-metal-catalyzed chelation-assisted oxidative C-H/C-H functionalization of aromatic substrates bearing directing functional groups.

  11. Transition-metal-catalyzed Chelation-assisted C-H Functionalization of Aromatic Substrates.

    PubMed

    Zhao, Binlin; Shi, Zhuangzhi; Yuan, Yu

    2016-04-01

    In the past decade, transition-metal-catalyzed C-H activations have been very popular in the research field of organometallic chemistry, and have been considered as efficient and convenient strategies to afford complex natural products, functional advanced materials, fluorescent compounds, and pharmaceutical compounds. In this account, we begin with a brief introduction to the development of transition-metal-catalyzed C-H activation, especially the development of transition-metal-catalyzed chelation-assisted C-H activation. Then, a more detailed discussion is directed towards our recent studies on the transition-metal-catalyzed chelation-assisted oxidative C-H/C-H functionalization of aromatic substrates bearing directing functional groups. PMID:26968749

  12. Periodic trends in the hydrodenitrogenation activity of carbon-supported transition metal sulfide catalysts

    SciTech Connect

    Eijsbouts, S.; De Beer, V.H.J.; Prins, R.

    1988-01-01

    Periodic trends of transition metals for the catalysis of reactions such as hydrogenation, hydrogenolysis, isomerization and hydrogen oxidation have been well studied. When activity versus position of the transition metal in the periodic table is plotted, quite often these trends are manifested in the form of so-called volcano-type curves. In the present study, the authors have chosen the HDN of quinoline at moderately high pressure as a model reaction, and they have used the same carbon-supported transition metal sulfide catalysts studied by Vissers et al. Results are shown for the following transition metals: V, Cr, Mn, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt. 9 references.

  13. Generic trend of work functions in transition-metal carbides and nitrides

    SciTech Connect

    Yoshitake, Michiko

    2014-11-15

    Transition-metal carbides and nitrides (TMCs and TMNs) are promising electrode materials for various electronic devices such as metal-oxide-semiconductor field-effect transistors and metal-insulator-metal capacitors. In this paper, the work functions of TMCs and TMNs are discussed systematically. Based upon the origin of the work function, the effect upon transition metal species by different periodic table groups is explained, carbides are compared with nitrides for the same transition metal, and the effect of carbon or nitrogen vacancies is discussed. In addition, a method to estimate the generic trend of the work function is proposed for TMC{sub x}, TMN{sub x}, TMC{sub 1−y}N{sub y} (transition metal carbonitrides), and TM{sub 1−z}TM′{sub z}C (alloy carbides)

  14. Activation of methane by transition metal-substituted aluminophosphate molecular sieves

    DOEpatents

    Iton, Lennox E.; Maroni, Victor A.

    1991-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Zeng, Pingying

    In recent decades, ceramic membranes based on mixed ionic and electronic conducting (MIEC) perovskite-structured oxides have received many attentions for their applications for air separation, or as a membrane reactor for methane oxidation. While numerous perovskite oxide materials have been explored over the past two decades; there are hardly any materials with sufficient practical economic value and performance for large scale applications, which justifies continuing the search for new materials. The main purposes of this thesis study are: (1) develop several novel SrCoO3-delta based MIEC oxides, SrCoCo1-xMxO3-delta, based on which membranes exhibit excellent oxygen permeability; (2) investigate the significant effects of the species and concentration of the dopants M (metal ions with fixed valences) on the various properties of these membranes; (3) investigate the significant effects of sintering temperature on the microstructures and performance of oxygen permeation membranes; and (4) study the performance of oxygen permeation membranes as a membrane reactor for methane combustion. To stabilize the cubic phase structure of the SrCoO3-delta oxide, various amounts of scandium was doped into the B-site of SrCoO 3-delta to form a series of new perovskite oxides, SrScxCoCo 1-xO3-delta (SSCx, x = 0-0.7). The significant effects of scandium-doping concentration on the phase structure, electrical conductivity, sintering performance, thermal and structural stability, cathode performance, and oxygen permeation performance of the SSCx membranes, were systematically studied. Also for a more in-depth understanding, the rate determination steps for the oxygen transport process through the membranes were clarified by theoretical and experimental investigation. It was found that only a minor amount of scandium (5 mol%) doping into the B-site of SrCoO3-delta can effectively stabilize the cubic phase structure, and thus significantly improve the electrical conductivity and

  16. Transition metal-catalyzed functionalization of pyrazines.

    PubMed

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

    2013-06-14

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

  17. Theoretical Investigation of H₂ Oxidation on the Sr2Fe1.5Mo0.5O6 (001) Perovskite Surface Under Anodic Solid Oxide Fuel Cell Conditions

    SciTech Connect

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

    2014-06-11

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

  18. Metalloporphyrin-modified perovskite-type oxide for the electroreduction of oxygen

    NASA Astrophysics Data System (ADS)

    Nagai, Tsukasa; Yamazaki, Shin-ichi; Asahi, Masafumi; Siroma, Zyun; Fujiwara, Naoko; Ioroi, Tsutomu

    2015-10-01

    Perovskite-type oxide-carbon (Vulcan XC72) mixture (La0.6Sr0.4Mn0.6Fe0.4O3/C) was modified by a metalloporphyrin (cobalt octaethylporphyrin: Co-OEP) having two-electron O2 reduction activity, and its electrochemical reduction activity for O2 (ORR) was investigated in an alkaline solution by rotating ring disk electrode (RRDE) voltammetry. The Co-OEP/La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst showed improved ORR activity, with a positive shift of the onset potential. In addition, a decreased ring current compared to Co-OEP/C suggested that the quasi-four-electron reduction of O2 was also enhanced. Further experiments showed that ORR activity was also enhanced by Co-OEP-modification of other types of carbon (Ketjenblack EC600JD, Denka Black) or perovskite-type oxide (La0.6Ca0.4Mn0.6Fe0.4O3, La0.8Sr0.2Co0.6Fe0.4O3). In the case of the addition of other porphyrin complexes (cobalt tetraphenylporphyrin (Co-TPP), iron octaethylporphyrin (Fe-OEP)) to a La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst, the onset potential did not shift to the positive side due to the lower activity compared to Co-OEP.

  19. Enhancing Perovskite Electrocatalysis through Strain Tuning of the Oxygen Deficiency.

    PubMed

    Petrie, Jonathan R; Jeen, Hyoungjeen; Barron, Sara C; Meyer, Tricia L; Lee, Ho Nyung

    2016-06-15

    Oxygen vacancies in transition-metal oxides facilitate catalysis critical for energy storage and generation. However, promoting vacancies at the lower temperatures required for operation in devices such as metal-air batteries and portable fuel cells has proven elusive. Here we used thin films of perovskite-based strontium cobaltite (SrCoOx) to show that epitaxial strain is a powerful tool for manipulating the oxygen content under conditions consistent with the oxygen evolution reaction, yielding increasingly oxygen-deficient states in an environment where the cobaltite would normally be fully oxidized. The additional oxygen vacancies created through tensile strain enhance the cobaltite's catalytic activity toward this important reaction by over an order of magnitude, equaling that of precious-metal catalysts, including IrO2. Our findings demonstrate that strain in these oxides can dictate the oxygen stoichiometry independent of ambient conditions, allowing unprecedented control over oxygen vacancies essential in catalysis near room temperature. PMID:27232374

  20. NdBaCo2/3Fe2/3Cu2/3O5+δ double perovskite as a novel cathode material for CeO2- and LaGaO3-based solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Jin, Fangjun; Li, Lei; He, Tianmin

    2015-01-01

    Double perovskites LnBaCo2O5+δ (Ln = rare earth) are explored as cathode materials for intermediate-temperature solid oxide fuel cell. Barriers to the applicability of double perovskite cathodes include high thermal expansion coefficient (TEC) and poor chemical compatibility with common electrolytes. In this paper, we report the characteristics and applicability of a double perovskite NdBaCo2/3Fe2/3Cu2/3O5+δ (NBCFC) cathode on CeO2- and LaGaO3-based electrolytes. NBCFC is found to crystallize in a tetragonal structure. Partial substitution of Fe and Cu for cobalt in NBCFC demonstrates significantly decreased TEC and good chemical compatibility with both Gd0.1Ce0.9O1.95 (GDC) and La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolytes, while maintaining its good electrochemical performance. The oxidation states of transition metal cations are Co3+/Co4+, Fe3+/Fe4+, and Cu+/Cu2+, respectively. The average TEC of NBCFC is 15.7 × 10-6 K-1 between 30 and 850 °C, and the polarization resistance values are 0.056 and 0.023 Ω cm2 at 800 °C with GDC and LSGM electrolytes, respectively. The absence of spin-state transition in copper contributes to the TEC reduction. Addition of appropriate amounts of GDC into NBCFC to form NBCFC-GDC composite cathodes further reduce the TEC and improve cathode performance. These results can be used to improve and develop novel double perovskite cathode materials.

  1. Oxygen vacancy formation characteristics in the bulk and across different surface terminations of La(1₋x)SrxFe(1₋y)CoyO(3₋δ) perovskite oxides for CO2 conversion

    SciTech Connect

    Maiti, Debtanu; Daza, Yolanda A.; Yung, Matthew M.; Kuhn, John N.; Bhethanabotla, Venkat R.

    2016-01-01

    Density functional theory (DFT) based investigation of two parameters of prime interest -- oxygen vacancy and surface terminations along (100) and (110) planes -- has been conducted for La(1-x)SrxFe(1-y)CoyO(3-..delta..) perovskite oxides in view of their application towards thermochemical carbon dioxide conversion reactions. The bulk oxygen vacancy formation energies for these mixed perovskite oxides are found to increase with increasing lanthanum and iron contents in the 'A' site and 'B' site, respectively. Surface terminations along (100) and (110) crystal planes are studied to probe their stability and their capabilities to accommodate surface oxygen vacancies. Amongst the various terminations, the oxygen-rich (110) surface and strontium-rich (100) surface are the most stable, while transition metal-rich terminations along (100) revealed preference towards the production of oxygen vacancies. The carbon dioxide adsorption strength, a key descriptor for CO2 conversion reactions, is found to increase on oxygen vacant surfaces thus establishing the importance of oxygen vacancies in CO2 conversion reactions. Amongst all the surface terminations, the lanthanum-oxygen terminated surface exhibited the strongest CO2 adsorption strength. The theoretical prediction of the oxygen vacancy trends and the stability of the samples were corroborated by the temperature-programmed reduction and oxidation reactions and in situ XRD crystallography.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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-δ (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.

  3. High Pressure Synthesis of Transition Metal Carbonyls.

    ERIC Educational Resources Information Center

    Hagen, A. P.; And Others

    1979-01-01

    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)

  4. Quantitative computational thermochemistry of transition metal species.

    PubMed

    Deyonker, Nathan J; Peterson, Kirk A; Steyl, Gideon; Wilson, Angela K; Cundari, Thomas R

    2007-11-01

    The correlation consistent Composite Approach (ccCA), which has been shown to achieve chemical accuracy (+/-1 kcal mol-1) for a large benchmark set of main group and s-block metal compounds, is used to compute enthalpies of formation for a set of 17 3d transition metal species. The training set includes a variety of metals, ligands, and bonding types. Using the correlation consistent basis sets for the 3d transition metals, we find that gas-phase enthalpies of formation can be efficiently calculated for inorganic and organometallic molecules with ccCA. However, until the reliability of gas-phase transition metal thermochemistry is improved, both experimentally and theoretically, a large experimental training set where uncertainties are near +/-1 kcal mol-1 (akin to commonly used main group benchmarking sets) remains an ambitious goal. For now, an average deviation of +/-3 kcal mol-1 appears to be the initial goal of "chemical accuracy" for ab initio transition metal model chemistries. The ccCA is also compared to a more robust but relatively expensive composite approach primarily utilizing large basis set coupled cluster computations. For a smaller training set of eight molecules, ccCA has a mean absolute deviation (MAD) of 3.4 kcal mol-1 versus the large basis set coupled-cluster-based model chemistry, which has a MAD of 3.1 kcal mol-1. However, the agreement for transition metal complexes is more system dependent than observed in previous benchmark studies of composite methods and main group compounds. PMID:17500547

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

    PubMed

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

    2014-11-10

    A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO2. This new method involves three consecutive steps: oxidation of NO to NO2 over a PBO catalyst, adsorption of NOx onto the PBO and K2O/Al2O3, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K2O/Al2O3 for NO2 (α) and NO (β), and the time-average fraction of NO included in the NOx feed stream (ξ). The results demonstrated that the amounts of NO2 produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La0.5Ag0.5MnO3 has been identified as the best chemical formulation for oxidation of NO to NO2 by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations.

  6. Perovskite Sr-doped LaCrO3 as a new p-type transparent conducting oxide

    SciTech Connect

    Zhang, Hongliang; Du, Yingge; Papadogianni, Alexandra; Bierwagen, Oliver; Sallis, Shawn; Piper, Louis F. J.; Bowden, Mark E.; Shutthanandan, V.; Sushko, Petr; Chambers, Scott A.

    2015-09-16

    Transparent conducting oxides (TCOs) constitute a unique class of materials which combine the seemingly mutually exclusive properties of electrical conductivity and optical transparency in a single material. TCOs are useful for a wide range of applications including solar cells, displays, light emitting diodes and transparent electronics. Simple post-transition metal oxides such as ZnO, In2O3 and SnO2 are wide gap insulators in which the ionic character generates an oxygen 2p-derived valence band (VB) and a metal s-derived conduction band (CB), resulting in large optical band gaps (>3.0 eV) and excellent n-type conductivity when donor doped. In contrast, the development of efficient p-type TCOs remains a global materials challenge. Converting n-type oxides to p-type analogs by acceptor doping is extremely difficult and these materials display poor conductivity.

  7. Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  8. Flexible high power-per-weight perovskite solar cells with chromium oxide-metal contacts for improved stability in air.

    PubMed

    Kaltenbrunner, Martin; Adam, Getachew; Głowacki, Eric Daniel; Drack, Michael; Schwödiauer, Reinhard; Leonat, Lucia; Apaydin, Dogukan Hazar; Groiss, Heiko; Scharber, Markus Clark; White, Matthew Schuette; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2015-10-01

    Photovoltaic technology requires light-absorbing materials that are highly efficient, lightweight, low cost and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. Here, we report ultrathin (3 μm), highly flexible perovskite solar cells with stabilized 12% efficiency and a power-per-weight as high as 23 W g(-1). To facilitate air-stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. The use of a transparent polymer electrode treated with dimethylsulphoxide as the bottom layer allows the deposition-from solution at low temperature-of pinhole-free perovskite films at high yield on arbitrary substrates, including thin plastic foils. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles-from airplanes to quadcopters and weather balloons-for environmental and industrial monitoring, rescue and emergency response, and tactical security applications.

  9. Flexible high power-per-weight perovskite solar cells with chromium oxide-metal contacts for improved stability in air

    NASA Astrophysics Data System (ADS)

    Kaltenbrunner, Martin; Adam, Getachew; Głowacki, Eric Daniel; Drack, Michael; Schwödiauer, Reinhard; Leonat, Lucia; Apaydin, Dogukan Hazar; Groiss, Heiko; Scharber, Markus Clark; White, Matthew Schuette; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2015-10-01

    Photovoltaic technology requires light-absorbing materials that are highly efficient, lightweight, low cost and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. Here, we report ultrathin (3 μm), highly flexible perovskite solar cells with stabilized 12% efficiency and a power-per-weight as high as 23 W g-1. To facilitate air-stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. The use of a transparent polymer electrode treated with dimethylsulphoxide as the bottom layer allows the deposition--from solution at low temperature--of pinhole-free perovskite films at high yield on arbitrary substrates, including thin plastic foils. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles--from airplanes to quadcopters and weather balloons--for environmental and industrial monitoring, rescue and emergency response, and tactical security applications.

  10. Electrochemical properties of mixed conducting (La,M)(CoFe) oxide perovskites (M=3DSr, Ca, and Ba)

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Bates, J.L.

    1996-04-01

    Electrical properties and oxygen permeation properties of solid mixed-conducting electrolytes (La,M)(CoFe) oxide perovskites (M=3DSr, Ca, and Ba) have been characterized. These materials are potentially useful as passive membranes to separate high purity oxygen from air and as the cathode in a fuel cell. Dilatometric linear expansion measurements were performed as a function of temperature and oxygen partial pressure to evaluate the stability.

  11. Structural and magnetic properties of double perovskite oxide Ba2CeSbO6

    NASA Astrophysics Data System (ADS)

    Dutta, Alo; Mukhopadhyay, P. K.; Sinha, T. P.; Das, Dipankar; Shannigrahi, Santiranjan

    2016-08-01

    The structural and magnetic properties of a double perovskite oxide Ba2CeSbO6 (BCSO) synthesized by solid state reaction technique have been investigated. The Rietveld refinement of the X-ray diffraction pattern of BCSO suggests the monoclinic crystal structure at room temperature with P21/n space group. The vibrational properties of BCSO are investigated by the Fourier transform Infrared and Raman spectroscopy. The Raman spectrum confirms the B-site ordering of cations in BCSO. The temperature dependent magnetic susceptibility data in the field cooled mode show the anti-ferromagnetic behaviour of BCSO below 59 K. The core level X-ray photoemission (XPS) spectrum of Ce-3d and Sb-3d states confirms the presence of multiple oxidation states of these cations. The presence of both the Ce3+ and Ce4+ ions in BCSO gives the 4f4-δ intermediate valence state which may reduce the effective magnetic moment with respect to the system having single valence Ce3+ ion.

  12. Growth of transition metals on cerium tungstate model catalyst layers

    NASA Astrophysics Data System (ADS)

    Skála, T.; Tsud, N.; Stetsovych, V.; Mysliveček, J.; Matolín, V.

    2016-10-01

    Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed.

  13. Growth of transition metals on cerium tungstate model catalyst layers.

    PubMed

    Skála, T; Tsud, N; Stetsovych, V; Mysliveček, J; Matolín, V

    2016-10-01

    Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed. PMID:27494195

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

    PubMed

    Sengodan, Sivaprakash; Choi, Sihyuk; Jun, Areum; Shin, Tae Ho; Ju, Young-Wan; Jeong, Hu Young; Shin, Jeeyoung; Irvine, John T S; Kim, Guntae

    2015-02-01

    Different layered perovskite-related oxides are known to exhibit important electronic, magnetic and electrochemical properties. Owing to their excellent mixed-ionic and electronic conductivity and fast oxygen kinetics, cation layered double perovskite oxides such as PrBaCo2O5 in particular have exhibited excellent properties as solid oxide fuel cell oxygen electrodes. Here, we show for the first time that related layered materials can be used as high-performance fuel electrodes. Good redox stability with tolerance to coking and sulphur contamination from hydrocarbon fuels is demonstrated for the layered perovskite anode PrBaMn2O5+δ (PBMO). The PBMO anode is fabricated by in situ annealing of Pr0.5Ba0.5MnO3-δ in fuel conditions and actual fuel cell operation is demonstrated. At 800 °C, layered PBMO shows high electrical conductivity of 8.16 S cm(-1) in 5% H2 and demonstrates peak power densities of 1.7 and 1.3 W cm(-2) at 850 °C using humidified hydrogen and propane fuels, respectively.

  15. (Electronic structure and reactivities of transition metal clusters)

    SciTech Connect

    Not Available

    1992-01-01

    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.

  16. Redox noninnocence of nitrosoarene ligands in transition metal complexes.

    PubMed

    Tomson, Neil C; Labios, Liezel A; Weyhermüller, Thomas; Figueroa, Joshua S; Wieghardt, Karl

    2011-06-20

    Studies on the coordination of nitrosoarene (ArNO) ligands to late-transition metals are used to provide the first definition of the geometric, spectroscopic, and computational parameters associated with a PhNO electron-transfer series. Experimentally, the Pd complexes PdCl(2)(PhNO)(2), PdL(2)(PhNO)(2), and PdL(2)(TolNO) (L = CNAr(Dipp2); Ar(Dipp2) = 2,6-(2,6-(i)Pr(2)C(6)H(3))(2)-C(6)H(3)) are characterized as containing (PhNO)(0), (PhNO)(•1-), and (TolNO)(2-) ligands, respectively, and the structural and spectroscopic changes associated with this electron transfer series provide the basis for an extensive computational study of these and related ArNO-containing late-transition metal complexes. Most notable from the results is the unambiguous characterization of the ground state electronic structure of PdL(2)(PhNO)(2), found to be the first isolable, transition metal ion complex containing an η(1)-N-bound π-nitrosoarene radical anion. In addition to the electron transfer series, the synthesis and characterization of the Fe complex [Fe(TIM)(NCCH(3))(PhNO)][(PF(6))(2)] (TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) allows for comparison of the geometric and spectroscopic features associated with metal-to-ligand π-backbonding as opposed to (PhNO)(•1-) formation. Throughout these series of complexes, the N-O, M-N, and C-N bond distances as well as the N-O stretching frequencies and the planarity of the ArNO ligands provided distinct parameters for each ligand oxidation state. Together, these data provide a delineation of the factors needed for evaluating the oxidation state of nitrosoarene ligands bound to transition metals in varying coordination modes.

  17. Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Fitting Kourkoutis, L.

    2010-03-01

    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).

  18. Structure, bonding, and catalytic activity of monodisperse, transition-metal-substituted CeO2 nanoparticles.

    PubMed

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

    2014-12-10

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

  19. Single-layer transition metal sulfide catalysts

    SciTech Connect

    Thoma, Steven G.

    2011-05-31

    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.

  20. Corrosion behavior of mesoporous transition metal nitrides

    SciTech Connect

    Yang, Minghui; Allen, Amy J.; Nguyen, Minh T.; Ralston, Walter T.; MacLeod, Michelle J.; DiSalvo, Francis J.

    2013-09-15

    Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 °C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1 Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 °C for 2 weeks. Display Omitted - highlights: • Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. • The mesoporous TMNs had surface areas of 25–60 m{sup 2}/g. • CrN is the most corrosion resistant under the conditions studied.

  1. Transition metal-induced degradation of a pharmaceutical compound in reversed-phase liquid chromatographic analysis.

    PubMed

    Wang, Qinggang; He, Brian Lingfeng; Zhang, Jin; Huang, Yande; Kleintop, Brent; Raglione, Thomas

    2015-01-01

    Drug degradation that occurs in HPLC analysis, during either sample preparation or chromatographic separation, can greatly impact method robustness and result accuracy. In this work, we report a case study of drug dimerization in HPLC analysis where proximate causes were attributed to either the LC columns or the HPLC instrument. Solution stress studies indicated that the same pseudo-dimeric degradants could also be formed rapidly when the compound was exposed to certain oxidative transition metal ions, such as Cu(II) and Fe(III). Two pseudo-dimeric degradants were isolated from transition metal stressed samples and their structures were elucidated. A degradation pathway was proposed, whereby the degradation was initiated through transition metal-induced single electron transfer oxidation. Further studies confirmed that the dimerization was induced by trace transition metals in the HPLC flow path, which could arise from either the stainless steel frits in the LC column or stainless steel tubing in the HPLC instrument. Various procedures to prevent transition metal-induced drug degradation were explored, and a general strategy to mitigate such risks is briefly discussed.

  2. Recognition- and reactivity-based fluorescent probes for studying transition metal signaling in living systems.

    PubMed

    Aron, Allegra T; Ramos-Torres, Karla M; Cotruvo, Joseph A; Chang, Christopher J

    2015-08-18

    Metals are essential for life, playing critical roles in all aspects of the central dogma of biology (e.g., the transcription and translation of nucleic acids and synthesis of proteins). Redox-inactive alkali, alkaline earth, and transition metals such as sodium, potassium, calcium, and zinc are widely recognized as dynamic signals, whereas redox-active transition metals such as copper and iron are traditionally thought of as sequestered by protein ligands, including as static enzyme cofactors, in part because of their potential to trigger oxidative stress and damage via Fenton chemistry. Metals in biology can be broadly categorized into two pools: static and labile. In the former, proteins and other macromolecules tightly bind metals; in the latter, metals are bound relatively weakly to cellular ligands, including proteins and low molecular weight ligands. Fluorescent probes can be useful tools for studying the roles of transition metals in their labile forms. Probes for imaging transition metal dynamics in living systems must meet several stringent criteria. In addition to exhibiting desirable photophysical properties and biocompatibility, they must be selective and show a fluorescence turn-on response to the metal of interest. To meet this challenge, we have pursued two general strategies for metal detection, termed "recognition" and "reactivity". Our design of transition metal probes makes use of a recognition-based approach for copper and nickel and a reactivity-based approach for cobalt and iron. This Account summarizes progress in our laboratory on both the development and application of fluorescent probes to identify and study the signaling roles of transition metals in biology. In conjunction with complementary methods for direct metal detection and genetic and/or pharmacological manipulations, fluorescent probes for transition metals have helped reveal a number of principles underlying transition metal dynamics. In this Account, we give three recent

  3. Thermochemistry and Reactivity of Transition Metal Cluster Ions

    NASA Astrophysics Data System (ADS)

    Armentrout, P. B.; Griffin, J. B.; Conceićão, J.

    Reactions of transition metal cluster cations with several small molecules have been examined using guided ion beam mass spectrometry. This technique allows the kinetic energy dependence of the reactions to be measured, thereby allowing thermodynamic information to be extracted. Reactions of iron, chromium, and vanadium clusters with D2, O2, and CO2 are described. Reactions with D2 are endothermic and yield only two types of products. Oxidation of metal clusters by O2 proceeds is very efficient, proceeding at the collision limit, and forms many different products. The CO2 systems exhibit interesting dynamics that appears to be related to interactions of two surfaces of different spin. Bond energies for cluster monodeuterides, monoxides, and dioxides are derived from these studies. The deuteride bond energies appear to be sensitive to the cluster geometry while little variation in oxide bond energies is observed as a function of cluster size. Comparison of these cluster bond energies to bulk phase values finds similar thermochemistry.

  4. Colloidal transition-metal-doped ZnO quantum dots.

    PubMed

    Radovanovic, Pavle V; Norberg, Nick S; McNally, Kathryn E; Gamelin, Daniel R

    2002-12-25

    Methods for introducing new magnetic, optical, electronic, photophysical, or photochemical properties to semiconductor nanocrystals are attracting intense applications-oriented interest. In this communication, we report the preparation and electronic absorption spectroscopy of colloidal ZnO DMS-QDs. Our synthetic procedure involves modification of literature methods known to yield highly crystalline and relatively monodisperse nanocrystals of pure ZnO to allow introduction of transition-metal dopants. We use ligand-field electronic absorption spectroscopy as a dopant-specific optical probe to monitor dopant incorporation during nanocrystal growth and to verify internal substitutional doping in Co2+:ZnO and Ni2+:ZnO DMS-QDs. To the best of our knowledge, these are the first free-standing oxide DMS-QDs reported. The synthesis of colloidal oxide DMS-QDs introduces a new category of magnetic semiconductor materials available for detailed physical study and application in nanotechnology.

  5. Dielectric Relaxation of Rare Earth Ordered Double Perovskite Oxide Ba2ErTaO6

    NASA Astrophysics Data System (ADS)

    Mukherjee, Rajesh; Dutta, Alo; Sinha, T. P.

    2016-01-01

    The electrical properties of rare-earth based ordered double perovskite oxide barium erbium tantalate, Ba2ErTaO6 synthesized by solid-state reaction method are investigated. The x-ray diffraction pattern of the sample shows cubic Fm3m phase at room temperature with ordering of the B cations. Fourier transform infrared spectrum shows two primary phonon modes of the sample at around 350 cm-1 and 600 cm-1. The dielectric relaxation of the sample is investigated in the frequency range from 50 Hz to 1.1 MHz and in the temperature range from 303 K to 673 K. Electric modulus and electrical impedance data are fitted to the Cole-Cole equation. The frequency dependent conductivity spectra follow the power law. Summerfield scaling is used to explain the conduction mechanism. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures. The complex impedance plane plots show that the relaxation (conduction) mechanism in this material is mainly due to grain boundary effect for all temperatures and grain effect for low temperature. The relaxation frequency corresponding to dielectric loss is found to obey Arrhenius law with activation energy of 0.50 eV. The values of activation energy indicate that the dielectric relaxation and the conduction mechanism are due to adiabatic small polaronic hole hopping mechanism.

  6. Perovskite Solar Cells Based on Low-Temperature Processed Indium Oxide Electron Selective Layers.

    PubMed

    Qin, Minchao; Ma, Junjie; Ke, Weijun; Qin, Pingli; Lei, Hongwei; Tao, Hong; Zheng, Xiaolu; Xiong, Liangbin; Liu, Qin; Chen, Zhiliang; Lu, Junzheng; Yang, Guang; Fang, Guojia

    2016-04-01

    Indium oxide (In2O3) as a promising n-type semiconductor material has been widely employed in optoelectronic applications. In this work, we applied low-temperature solution-processed In2O3 nanocrystalline film as an electron selective layer (ESL) in perovskite solar cells (PSCs) for the first time. By taking advantages of good optical and electrical properties of In2O3 such as high mobility, wide band gap, and high transmittance, we obtained In2O3-based PSCs with a good efficiency exceeding 13% after optimizing the concentration of the precursor solution and the annealing temperature. Furthermore, to enhance the performance of the In2O3-based PSCs, a phenyl-C61-butyric acid methyl ester (PCBM) layer was introduced to modify the surface of the In2O3 film. The PCBM film could fill up the pinholes or cracks along In2O3 grain boundaries to passivate the defects and make the ESL extremely compact and uniform, which is conducive to suppressing the charge recombination. As a result, the efficiency of the In2O3-based PSC was improved to 14.83% accompanied with V(OC), J(SC), and FF being 1.08 V, 20.06 mA cm(-2), and 0.685, respectively.

  7. Nanostructured Double Perovskite Cathode With Low Sintering Temperature For Intermediate Temperature Solid Oxide Fuel Cells.

    PubMed

    Kim, Seona; Jun, Areum; Kwon, Ohhun; Kim, Junyoung; Yoo, Seonyoung; Jeong, Hu Young; Shin, Jeeyoung; Kim, Guntae

    2015-09-21

    This study focuses on reducing the cathode polarization resistance through the use of mixed ionic electronic conductors and the optimization of cathode microstructure to increase the number of electrochemically active sites. Among the available mixed ionic electronic conductors (MIECs), the layered perovskite GdBa0.5 Sr0.5 CoFeO5+δ (GBSCF) was chosen as a cathode material for intermediate temperature solid oxide fuel cells owing to its excellent electrochemical performance and structural stability. The optimized microstructure of a GBSCF-yttria-stabilized zirconia (YSZ) composite cathode was prepared through an infiltration method with careful control of the sintering temperature to achieve high surface area, adequate porosity, and well-organized connection between nanosized particles to transfer electrons. A symmetric cell shows outstanding results, with the cathode exhibiting an area-specific resistance of 0.006 Ω cm(2) at 700 °C. The maximum power density of a single cell using Ce-Pd anode with a thickness of ∼80 μm electrolyte was ∼0.6 W cm(-2) at 700 °C.

  8. Dielectric relaxation in a new double perovskite oxide Ho 2MgZrO 6

    NASA Astrophysics Data System (ADS)

    Mahato, Dev K.; Dutta, Alo; Sinha, T. P.

    2012-01-01

    A new double perovskite oxide holmium magnesium zirconate Ho 2MgZrO 6 (HMZ) was prepared by solid state reaction technique. The crystal structure has been determined by powder X-ray diffraction which shows monoclinic phase at room temperature with cell parameters a = 9.3028 ± 0.0030 Å, b = 5.2293 ± 0.0008 Å, c = 4.4009 ± 0.0009 Å, β = 103.3746 ± 0.0166°. An analysis of complex permittivity with frequency was carried out assuming a distribution of relaxation times. The frequency dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. At the high temperature range, conductivity data satisfy the variable range hopping (VRH) model. In this regime, the conductivity of sample obeys Mott's T1/4 law, characteristic of VRH. High temperature data indicates the formation of thermally activated small polarons. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures.

  9. Thickness dependence of exchange coupling in (111)-oriented perovskite oxide superlattices

    NASA Astrophysics Data System (ADS)

    Jia, Yue; Chopdekar, Rajesh V.; Arenholz, Elke; Liu, Zhiqi; Biegalski, Michael D.; Porter, Zachary D.; Mehta, Apurva; Takamura, Yayoi

    2016-03-01

    Epitaxial L a0.7S r0.3Mn O3(LSMO )/L a0.7S r0.3Fe O3 (LSFO) superlattices on (111)-oriented SrTi O3 substrates with sublayer thicknesses ranging from 3 to 60 unit cells (u.c.) were synthesized and characterized. Detailed analysis of their structural, electronic, and magnetic properties were performed to explore the effect of sublayer thickness on the magnetic structure and exchange coupling at (111)-oriented perovskite oxide interfaces. In the ultrathin limit (3-6 u.c.), we find that the antiferromagnetic (AF) properties of the LSFO sublayers are preserved with an out-of-plane canting of the AF spin axis, while the ferromagnetic (FM) properties of the LSMO sublayers are significantly depressed. For thicker LSFO layers (>9 u.c.), the out-of-plane canting of the AF spin axis is only present in superlattices with thick LSMO sublayers. As a result, exchange coupling in the form of spin-flop coupling exists only in superlattices which display both robust ferromagnetism and out-of-plane canting of the AF spin axis.

  10. Magnetism In 3d Transition Metals at High Pressures

    SciTech Connect

    Iota, V

    2006-02-09

    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 of this LDRD project, we developed new measurement techniques and adapted synchrotron-based electronic and magnetic measurements for use in the diamond anvil cell. We have performed state-of-the-art X-ray spectroscopy experiments at the dedicated high-pressure beamline HP-CAT (Sector 16 Advanced Photon Source, Argonne National Laboratory), maintained in collaboration with of University of Nevada, Las Vegas and Geophysical Laboratory of The Carnegie Institution of Washington. Using these advanced measurements, we determined the evolution of the magnetic order in the ferromagnetic 3d transition metals (Fe, Co and Ni) under pressure, and found that at high densities, 3d band broadening results in diminished long range magnetic coupling. Our experiments have allowed us to paint a unified picture of the effects of pressure on the evolution of magnetic spin in 3d electron systems. The technical and scientific advances made during this LDRD project have been reported at a number of scientific meetings and conferences, and have been submitted for publication in technical journals. Both the technical advances and the physical understanding of correlated systems derived from this LDRD are being applied to research on the 4f and 5f electron systems under pressure.

  11. Chemical Trends for Transition Metal Compound Bonding to Graphene

    NASA Astrophysics Data System (ADS)

    Lange, Bjoern; Blum, Volker

    2015-03-01

    Transition metal compounds are of interest as catalysts for the hydrogen evolution reaction (HER). However, a perfect candidate to replace expensive platinum has not yet been identified. To tailor a specific compound, several properties come into play. One is the bonding to the underlying substrate, for which π-bonded carbon nanostructures are promising candidates. Here we analyze the bonding of small transition metal compound nanoclusters to a graphene layer for a range of chemical compositions: MxAy (M = Mo, Ti; A = S, O, B, N, C). The clusters are generated by an unbiased random search algorithm. We perform total energy calculations based on density functional theory to identify lowest energy clusters. We calculate binding energies using the PBE and HSE functionals with explicit van der Waals treatment and benchmark those against RPA cluster calculations. Our results indicate that molybdenum-carbides and -nitrides tend to bond tightly to graphene. Mo-oxides and -sulfides show small binding energies, indicating van der Waals bonding.

  12. Transition metal bimetallic oxycarbides: Synthesis, characterization, and activity studies

    SciTech Connect

    Oyama, S.T.; Yu, C.C.; Ramanathan, S.

    1999-06-10

    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.

  13. Non-collinear magnetism in multiferroic perovskites.

    PubMed

    Bousquet, Eric; Cano, Andrés

    2016-03-31

    We present an overview of the current interest in non-collinear magnetism in multiferroic perovskite crystals. We first describe the different microscopic mechanisms giving rise to the non-collinearity of spins in this class of materials. We discuss, in particular, the interplay between non-collinear magnetism and ferroelectric and antiferrodistortive distortions of the perovskite structure, and how this can promote magnetoelectric responses. We then provide a literature survey on non-collinear multiferroic perovskites. We discuss numerous examples of spin cantings driving weak ferromagnetism in transition metal perovskites, and of spin-induced ferroelectricity as observed in the rare-earth based perovskites. These examples are chosen to best illustrate the fundamental role of non-collinear magnetism in the design of multiferroicity.

  14. Vibrational scaling factors for transition metal carbonyls

    NASA Astrophysics Data System (ADS)

    Assefa, M. K.; Devera, J. L.; Brathwaite, A. D.; Mosley, J. D.; Duncan, M. A.

    2015-11-01

    Vibrational frequencies for a selected set of transition metal carbonyl complexes are computed with various forms of density functional theory (B3LYP, BP86, M06, and M06-L), employing several different basis sets. The computed frequencies for the carbonyl stretches are compared to the experimental values obtained from gas phase infrared spectra of isolated neutrals and ions. Recommended carbonyl-stretch scaling factors which are developed vary significantly for different functionals, but there is little variation with basis set. Scaled frequencies compared to experimental spectra for cobalt and tantalum carbonyl cations reveal additional variations in multiplet patterns and relative band intensities for different functionals.

  15. Strain Engineering of Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Dadgar, Ali; Pasupathy, Abhay; Herman, Irving; Wang, Dennis; Kang, Kyungnam; Yang, Eui-Hyeok

    The application of strain to materials can cause changes to bandwidth, effective masses, degeneracies and even structural phases. In the case of the transition metal dichalcogenide (TMD) semiconductors, small strain (around 1 percent) is expected to change band gaps and mobilities, while larger strains are expected to cause phase changes from the triangular 2H phase to orthorhombic 1T' phases. We will describe experimental techniques to apply small and large (around 10 percent) strains to one or few layer samples of the TMD semiconductors, and describe the effect of the strain using optical (Raman, photoluminescence) and cryogenic transport techniques.

  16. Ferroelectricity in d0 double perovskite fluoroscandates

    NASA Astrophysics Data System (ADS)

    Charles, Nenian; Rondinelli, James M.

    2015-08-01

    Ferroelectricity in strain-free and strained double perovskite fluorides, Na3ScF6 and K2NaScF6 , is investigated using first-principles density functional theory. Although the experimental room temperature crystal structures of these fluoroscandates are centrosymmetric, i.e., Na3ScF6 (P 21/n ) and K2NaScF6 (F m 3 ¯m ), lattice dynamical calculations reveal that soft polar instabilities exist in each prototypical cubic phase and that the modes harden as the tolerance factor approaches unity. Thus the double fluoroperovskites bear some similarities to A B O3 perovskite oxides; however, in contrast, these fluorides exhibit large acentric displacements of alkali metal cations (Na, K) rather than polar displacements of the transition metal cations. Biaxial strain investigations of the centrosymmetric and polar Na3ScF6 and K2NaScF6 phases reveal that the paraelectric structures are favored under compressive strain, whereas polar structures with in-plane electric polarizations (˜5 -18 μ C cm-2 ) are realized at sufficiently large tensile strains. The electric polarization and stability of the polar structures for both chemistries are found to be further enhanced and stabilized by a coexisting single octahedral tilt system. Our results suggest that polar double perovskite fluorides may be realized by suppression of octahedral rotations about more than one Cartesian axis; structures exhibiting in- or out-of-phase octahedral rotations about the c axis are more susceptible to polar symmetries.

  17. Comparative study of the synthesis of layered transition metal molybdates

    SciTech Connect

    Mitchell, S.; Gomez-Aviles, A.; Gardner, C.; Jones, W.

    2010-01-15

    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 +}).

  18. Cobalt based layered perovskites as cathode material for intermediate temperature Solid Oxide Fuel Cells: A brief review

    NASA Astrophysics Data System (ADS)

    Pelosato, Renato; Cordaro, Giulio; Stucchi, Davide; Cristiani, Cinzia; Dotelli, Giovanni

    2015-12-01

    Nowadays, the cathode is the most studied component in Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFCs). Decreasing SOFCs operating temperature implies slow oxygen reduction kinetics and large polarization losses. Double perovskites with general formula REBaCo2O5+δ are promising mixed ionic-electronic conductors, offering a remarkable enhancement of the oxygen diffusivity and surface exchange respect to disordered perovskites. In this review, more than 250 compositions investigated in the literature were analyzed. The evaluation was performed in terms of electrical conductivity, Area Specific Resistance (ASR), chemical compatibility with electrolytes and Thermal Expansion Coefficient (TEC). The most promising materials have been identified as those bearing the mid-sized rare earths (Pr, Nd, Sm, Gd). Doping strategies have been analyzed: Sr doping on A site promotes higher electrical conductivity, but worsen ASR and TECs; B-site doping (Fe, Ni, Mn) helps lowering TECs, but is detrimental for the electrochemical properties. A promising boost of the electrochemical activity is obtained by simply introducing a slight Ba under-stoichiometry. Still, the high sensitivity of the electrochemical properties against slight changes in the stoichiometry hamper a conclusive comparison of all the investigated compounds. Opportunities for an improvement of double perovskite cathodes performance is tentatively foreseen in combining together the diverse effective doping strategies.

  19. Ultrafast Dynamics of Hole Injection and Recombination in Organometal Halide Perovskite Using Nickel Oxide as p-Type Contact Electrode.

    PubMed

    Corani, Alice; Li, Ming-Hsien; Shen, Po-Shen; Chen, Peter; Guo, Tzung-Fang; El Nahhas, Amal; Zheng, Kaibo; Yartsev, Arkady; Sundström, Villy; Ponseca, Carlito S

    2016-04-01

    There is a mounting effort to use nickel oxide (NiO) as p-type selective electrode for organometal halide perovskite-based solar cells. Recently, an overall power conversion efficiency using this hole acceptor has reached 18%. However, ultrafast spectroscopic investigations on the mechanism of charge injection as well as recombination dynamics have yet to be studied and understood. Using time-resolved terahertz spectroscopy, we show that hole transfer is complete on the subpicosecond time scale, driven by the favorable band alignment between the valence bands of perovskite and NiO nanoparticles (NiO(np)). Recombination time between holes injected into NiO(np) and mobile electrons in the perovskite material is shown to be hundreds of picoseconds to a few nanoseconds. Because of the low conductivity of NiO(np), holes are pinned at the interface, and it is electrons that determine the recombination rate. This recombination competes with charge collection and therefore must be minimized. Doping NiO to promote higher mobility of holes is desirable in order to prevent back recombination.

  20. Graphene oxide/PEDOT:PSS composite hole transport layer for efficient and stable planar heterojunction perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Da-Young; Na, Seok-In; Kim, Seok-Soon

    2016-01-01

    We investigated a graphene oxide (GO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) composite as a promising candidate for the practical application of a 2-D carbonaceous hole transport layer (HTL) to planar heterojunction perovskite solar cells (PeSCs) consisting of a transparent electrode/HTL/perovskite/fullerene/metal electrode. Both the insulating properties of GO and the non-uniform coating of the transparent electrode with GO cause the poor morphology of perovskite induced low power conversion efficiency (PCE) of 6.4%. On the other hand, PeSCs with a GO/PEDOT:PSS composite HTL, exhibited a higher PCE of 9.7% than that of a device fabricated with conventional PEDOT:PSS showing a PCE of 8.2%. The higher performance is attributed to the decreased series resistance (RS) and increased shunt resistance (RSh). The well-matched work-function between GO (4.9 eV) and PEDOT:PSS (5.1 eV) probably results in more efficient charge transport and an overall decrease in RS. The existence of GO with a large bandgap of ~3.6 eV might induce the effective blocking of electrons, leading to an increase of RSh. Moreover, improvement in the long-term stability under atmospheric conditions was observed.

  1. Methyl Complexes of the Transition Metals.

    PubMed

    Campos, Jesús; López-Serrano, Joaquín; Peloso, Riccardo; Carmona, Ernesto

    2016-05-01

    Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH3 compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

  2. Transition-Metal-Catalyzed Bioorthogonal Cycloaddition Reactions.

    PubMed

    Yang, Maiyun; Yang, Yi; Chen, Peng R

    2016-02-01

    In recent years, bioorthogonal reactions have emerged as a powerful toolbox for specific labeling and visualization of biomolecules, even within the highly complex and fragile living systems. Among them, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is one of the most widely studied and used biocompatible reactions. The cytotoxicity of Cu(I) ions has been greatly reduced due to the use of Cu(I) ligands, which enabled the CuAAC reaction to proceed on the cell surface, as well as within an intracellular environment. Meanwhile, other transition metals such as ruthenium, rhodium and silver are now under development as alternative sources for catalyzing bioorthogonal cycloadditions. In this review, we summarize the development of CuAAC reaction as a prominent bioorthogonal reaction, discuss various ligands used in reducing Cu(I) toxicity while promoting the reaction rate, and illustrate some of its important biological applications. The development of additional transition metals in catalyzing cycloaddition reactions will also be briefly introduced. PMID:27572985

  3. Transition-Metal-Catalyzed Redox-Neutral and Redox-Green C-H Bond Functionalization.

    PubMed

    Wang, Hongli; Huang, Hanmin

    2016-08-01

    Transition-metal-catalyzed C-H bond functionalization has become one of the most promising strategies to prepare complex molecules from simple precursors. However, the utilization of environmentally unfriendly oxidants in the oxidative C-H bond functionalization reactions reduces their potential applications in organic synthesis. This account describes our recent efforts in the development of a redox-neutral C-H bond functionalization strategy for direct addition of inert C-H bonds to unsaturated double bonds and a redox-green C-H bond functionalization strategy for realization of oxidative C-H functionalization with O2 as the sole oxidant, aiming to circumvent the problems posed by utilizing environmentally unfriendly oxidants. In principle, these redox-neutral and redox-green strategies pave the way for establishing new environmentally benign transition-metal-catalyzed C-H bond functionalization strategies.

  4. Transition-Metal-Catalyzed Redox-Neutral and Redox-Green C-H Bond Functionalization.

    PubMed

    Wang, Hongli; Huang, Hanmin

    2016-08-01

    Transition-metal-catalyzed C-H bond functionalization has become one of the most promising strategies to prepare complex molecules from simple precursors. However, the utilization of environmentally unfriendly oxidants in the oxidative C-H bond functionalization reactions reduces their potential applications in organic synthesis. This account describes our recent efforts in the development of a redox-neutral C-H bond functionalization strategy for direct addition of inert C-H bonds to unsaturated double bonds and a redox-green C-H bond functionalization strategy for realization of oxidative C-H functionalization with O2 as the sole oxidant, aiming to circumvent the problems posed by utilizing environmentally unfriendly oxidants. In principle, these redox-neutral and redox-green strategies pave the way for establishing new environmentally benign transition-metal-catalyzed C-H bond functionalization strategies. PMID:27258190

  5. Defect characterization of electronic conducting pseudo-perovskite systems. Final report

    SciTech Connect

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

    1994-12-31

    The goal of the program has been to study the interrelationships between electrical conductivity, oxidation-reduction kinetics, defect structure, and composition of n- and p-type binary and ternary transition metal oxides. The stimulus for making these studies was the observation that both conducting n and p type oxides displayed a dependence on oxygen activity that was not predicted by the defect chemistry of their majority defects. The project has focused primarily on the understanding of electronic and ionic conduction in the REBO{sub 3} oxides, where RE is a rare earth ion and B is a transition metal ion. This is being done by studying the interrelationships between the electronic and ionic conductivity, the electronic structure of the B site transition metal ion, and the acceptor concentration. The dependence of these characteristics on the oxygen activity, the temperature, and the defect chemistry of the oxide system is being determined. Theoretical mechanisms and models are being developed from the body of experimental results to provide a predictive tool. The effect of dopants and impurities, processing, electrical and thermal stability as a function of oxygen activity and temperature and their relationship to defect chemistry of the perovskite type oxides have been studied extensively by this research team. As a result of the difference in mobility between electronic and ionic defects, the electrical conductivity changes as the concentration of electronic defects changes. Thus, electrodes or resistors consisting of such oxides are susceptible to instabilities in resistance as they are cycled into temperature regimes where thermodynamic equilibrium may be attained. Many of the new energy conversion systems which use such oxides are encountering difficulties as a result of this instability in resistivity.

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

    SciTech Connect

    James P. Lewis , Dorian M. Hatch , and Harold T. Stokes

    2006-12-31

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    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.

  8. Exclusion of metal oxide by an RF sputtered Ti layer in flexible perovskite solar cells: energetic interface between a Ti layer and an organic charge transporting layer.

    PubMed

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

    2015-04-14

    In this work, the effects of a titanium (Ti) layer on the charge transport and recombination rates of flexible perovskite solar cells were studied. Ti as an efficient barrier layer was deposited directly on PET-ITO flexible substrates through RF magnetic sputtering using a Ti-source and a pressure of ∼5 mTorr. A Ti coated PET-ITO was used for the fabrication of a flexible perovskite solar cell without using any metal oxide layer. The fabricated flexible perovskite solar cell was composed of a PET-ITO/Ti/perovskite (CH3NH3PbI3)/organic hole transport layer of 2,2',7,7'-tetrakis [N,N'-di-p-methoxyphenylamine]-9,9'-spirobifluorene (spiro-OMeTAD)-Li-TFSI/Ag. A high conversion efficiency of ∼8.39% along with a high short circuit current (JSC) of ∼15.24 mA cm(-2), an open circuit voltage (VOC) of ∼0.830 V and a high fill factor (FF) of ∼0.66 was accomplished by the fabricated flexible perovskite solar cell under a light illumination of ∼100 mW cm(-2) (1.5 AM). Intensity-modulated photocurrent (IMPS)/photovoltage spectroscopy (IMVS) studies demonstrated that the fabricated flexible perovskite solar cell considerably reduced the recombination rate.

  9. Raman spectroscopy of transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Saito, R.; Tatsumi, Y.; Huang, S.; Ling, X.; Dresselhaus, M. S.

    2016-09-01

    Raman spectroscopy of transition metal dichalcogenides (TMDs) is reviewed based on our recent theoretical and experimental works. First, we discuss the semi-classical and quantum mechanical description for the polarization dependence of Raman spectra of TMDs in which the optical dipole transition matrix elements as a function of laser excitation energy are important for understanding the polarization dependence of the Raman intensity and Raman tensor. Overviewing the symmetry of TMDs, we discuss the dependence of the Raman spectra of TMDs on layer thickness, polarization, laser energy and the structural phase. Furthermore, we discuss the Raman spectra of twisted bilayer and heterostructures of TMDs. Finally, we give our perspectives on the Raman spectroscopy of TMDs.

  10. Radiation damage of transition metal carbides

    SciTech Connect

    Dixon, G.

    1991-01-01

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

  11. Multifunctional Ligands in Transition Metal Catalysis

    SciTech Connect

    Crabtree, Robert H

    2011-01-01

    Sophisticated ligands are now being designed that do far more than just fulfil their traditional spectator roles by binding to the metal and providing a sterically-defined binding pocket for the substrate in homogeneous transition metal catalysis. This Focus review emphasizes selected cases in which ligands carry additional functional groups that change the properties of the ligand as a result of an external stimulus or undergo catalytically-relevant ligand-based reactivity. These include proton responsive ligands capable of gaining or losing one or more protons, ligands having a hydrogen bonding function, electroresponsive ligands capable of gaining or losing one or more electrons, and photoresponsive ligands capable of undergoing a useful change of properties upon irradiation. Molecular recognition ligands and proton coupled electron transfer (PCET) are briefly discussed.

  12. Theoretical studies of transition metal dimers

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Bauschlicher, Charles W., Jr.

    1985-01-01

    The CASSCF approach was used to perform the MCSCF calculations for a number of transition metal dimers, including the Sc2, Ti2, Cr2, Cu2, TiV, Y2, Nb2, and Mo2 molecules; in addition, CASSCF/CI calculations were carried out for Sc2, Ti2, Cu2, and Y2. The CASSCF procedure is shown to provide a consistent set of calculations for these molecules, from which trends and a simple qualitative picture of the electronic structure may be derived. In particular, the calculations confirmed the ground states of the Sc2 and the TiV, and led to predictions for other molecules in this series. In addition to specific predictions, the study provides a simple qualitative picture of the bonding in these dimers.

  13. One-Dimensional Perovskite Manganite Oxide Nanostructures: Recent Developments in Synthesis, Characterization, Transport Properties, and Applications

    NASA Astrophysics Data System (ADS)

    Li, Lei; Liang, Lizhi; Wu, Heng; Zhu, Xinhua

    2016-03-01

    One-dimensional nanostructures, including nanowires, nanorods, nanotubes, nanofibers, and nanobelts, have promising applications in mesoscopic physics and nanoscale devices. In contrast to other nanostructures, one-dimensional nanostructures can provide unique advantages in investigating the size and dimensionality dependence of the materials' physical properties, such as electrical, thermal, and mechanical performances, and in constructing nanoscale electronic and optoelectronic devices. Among the one-dimensional nanostructures, one-dimensional perovskite manganite nanostructures have been received much attention due to their unusual electron transport and magnetic properties, which are indispensable for the applications in microelectronic, magnetic, and spintronic devices. In the past two decades, much effort has been made to synthesize and characterize one-dimensional perovskite manganite nanostructures in the forms of nanorods, nanowires, nanotubes, and nanobelts. Various physical and chemical deposition techniques and growth mechanisms are explored and developed to control the morphology, identical shape, uniform size, crystalline structure, defects, and homogenous stoichiometry of the one-dimensional perovskite manganite nanostructures. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, structural characterization, fundamental properties, and unique applications of one-dimensional perovskite manganite nanostructures in nanotechnology. It begins with the rational synthesis of one-dimensional perovskite manganite nanostructures and then summarizes their structural characterizations. Fundamental physical properties of one-dimensional perovskite manganite nanostructures are also highlighted, and a range of unique applications in information storages, field-effect transistors, and spintronic devices are discussed. Finally, we conclude this review with some perspectives/outlook and future

  14. Niobium doped lanthanum calcium ferrite perovskite as a novel electrode material for symmetrical solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kong, Xiaowei; Zhou, Xiaoliang; Tian, Yu; Wu, Xiaoyan; Zhang, Jun; Zuo, Wei

    2016-09-01

    Development of cost-effective and efficient electrochemical catalysts for the fuel cells electrode is of prime importance to emerging renewable energy technologies. Here, we report for the first time the novel La0.9Ca0.1Fe0.9Nb0.1O3-δ (LCFNb) perovskite with good potentiality for the electrode material of the symmetrical solid oxide fuel cells (SSOFC). The Sc0.2Zr0.8O2-δ (SSZ) electrolyte supported symmetrical cells with impregnated LCFNb and LCFNb/SDC (Ce0.8Sm0.2O2-δ) electrodes achieve relatively high power outputs with maximum power densities (MPDs) reaching up to 392 and 528.6 mW cm-2 at 850 °C in dry H2, respectively, indicating the excellent electro-catalytic activity of LCFNb towards both hydrogen oxidation and oxygen reduction. Besides, the MPDs of the symmetrical cells with LCFNb/SDC composite electrodes in CO and syngas (CO: H2 = 1:1) are almost identical to those in H2, implying that LCFNb material has similar catalytic activities to carbon monoxide compared with hydrogen. High durability in both H2, CO and syngas during the short term stability tests for 50 h are also obtained, showing desirable structure stability, and carbon deposition resistance of LCFNb based electrodes. The present results indicate that the LCFNb perovskite with remarkable cell performance is a promising electrode material for symmetrical SOFCs.

  15. Stability Comparison of Perovskite Solar Cells Based on Zinc Oxide and Titania on Polymer Substrates.

    PubMed

    Dkhissi, Yasmina; Meyer, Steffen; Chen, Dehong; Weerasinghe, Hasitha C; Spiccia, Leone; Cheng, Yi-Bing; Caruso, Rachel A

    2016-04-01

    Device scale-up and long-term stability constitute two major hurdles that the emerging perovskite solar technology will have to overcome before commercialization. Here, a comparative study was performed between ZnO and TiO2 electron-selective layers, two materials that allow the low-temperature processing of perovskite solar cells on polymer substrates. Although the use of TiO2 is well established on glass substrates, ZnO was chosen because it can be readily printed at low temperature and offers the potential for the large-scale roll-to-roll manufacturing of flexible photovoltaics at a low cost. However, a rapid degradation of CH3 NH3 PbI3 was observed if it was deposited on ZnO, therefore, the influence of the perovskite film preparation conditions on its morphology and degradation kinetics was investigated. This study showed that CH3 NH3 PbI3 could withstand a higher temperature on TiO2 than ZnO and that TiO2-based perovskite devices were more stable than their ZnO analogues. PMID:26893225

  16. Trends in Ionization Energy of Transition-Metal Elements

    ERIC Educational Resources Information Center

    Matsumoto, Paul S.

    2005-01-01

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

  17. Aromaticity and Antiaromaticity in Transition-Metal Systems

    SciTech Connect

    Zubarev, Dmitry Y.; Averkiev, Boris B.; Zhai, Hua Jin; Wang, Lai S.; Boldyrev, Alexander I.

    2007-11-05

    Aromaticity is an important concept in chemistry primarily for hydrocarbon compounds, but it has been extended to compounds containing transition-metal atoms. Recent findings of aromaticity and antiaromaticy in all-metal clusters have stimulated further researches in describing the chemical bonding, structures, and stability in transition-metal clusters and compounds on the basis of aromaticity and antiaromaticity, which are reviewed here. The presence of d-orbitals endows much more diverse chemistry, structure, and chemical bonding to transition-metal clusters and compounds. One interesting feature is the existence of a new type of δ-aromaticity, in addition to σ- and π-aromaticity that are only possible for main group compounds. Another striking characteristic in the chemical bonding of transition-metal systems is the multi-fold nature of aromaticity, antiaromaticity, or even conflicting aromaticity. Separate sets of counting rules have been proposed for cyclic transition-metal systems to account for the three types of σ-, π-, and δ-aromaticity/antiaromaticity. The diverse transition-metal clusters and compounds reviewed here indicate that multiple aromaticity and antiaromaticity may be much more common in chemistry than one would anticipate. It is hoped that the current review will stimulate interest in further understanding the structure and bonding, on the basis of aromaticity and antiaromaticity, of other known or unknown transition-metal systems, such as the active sites of enzymes or other biomolecules, which contain transition-metal atoms and clusters.

  18. Dysregulation of transition metal ion homeostasis is the molecular basis for cadmium toxicity in Streptococcus pneumoniae

    PubMed Central

    Begg, Stephanie L.; Eijkelkamp, Bart A.; Luo, Zhenyao; Couñago, Rafael M.; Morey, Jacqueline R.; Maher, Megan J.; Ong, Cheryl-lynn Y.; McEwan, Alastair G.; Kobe, Bostjan; O’Mara, Megan L.; Paton, James C.; McDevitt, Christopher A.

    2015-01-01

    Cadmium is a transition metal ion that is highly toxic in biological systems. Although relatively rare in the Earth’s crust, anthropogenic release of cadmium since industrialization has increased biogeochemical cycling and the abundance of the ion in the biosphere. Despite this, the molecular basis of its toxicity remains unclear. Here we combine metal-accumulation assays, high-resolution structural data and biochemical analyses to show that cadmium toxicity, in Streptococcus pneumoniae, occurs via perturbation of first row transition metal ion homeostasis. We show that cadmium uptake reduces the millimolar cellular accumulation of manganese and zinc, and thereby increases sensitivity to oxidative stress. Despite this, high cellular concentrations of cadmium (~17 mM) are tolerated, with negligible impact on growth or sensitivity to oxidative stress, when manganese and glutathione are abundant. Collectively, this work provides insight into the molecular basis of cadmium toxicity in prokaryotes, and the connection between cadmium accumulation and oxidative stress. PMID:25731976

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

    PubMed

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

    2014-06-16

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

  20. Incorporation effect of nanosized perovskite LaFe₀.₇Co₀.₃O₃ on the electrochemical activity of Pt nanoparticles-multi walled carbon nanotube composite toward methanol oxidation

    SciTech Connect

    Noroozifar, Meissam; Khorasani-Motlagh, Mozhgan; Khaleghian-Moghadam, Roghayeh; Ekrami-Kakhki, Mehri-Saddat; Shahraki, Mohammad

    2013-05-01

    Nanosized perovskite LaFe₀.₇Co₀.₃O₃ (LFCO) is synthesized through conventional co-precipitation method and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The incorporation effect of the mentioned perovskite to catalytic activity of the PtNPs-MWCNTs-nafion (or -chitosan) catalyst toward methanol oxidation has been studied by cyclic voltammetry. Based on the electrochemical studies, all MWCNTs-PtNPs-nafion (or chitosan) and MWCNTs-PtNPs-LFCO-nafion (or chitosan) catalysts show a considerable activity for methanol oxidation. However, a synergistic effect is observed when LFCO is added to the catalyst by decreasing the poisoning rate of the Pt catalyst. - Graphical abstract: Nanosized perovskite LaFe₀.₇Co₀.₃O₃ is synthesized and characterized. The incorporation effect of the mentioned perovskite to catalytic activity of the PtNPS-MWCNTs-nafion (or -chitosan) catalyst toward methanol oxidation is studied. Highlights: • Nanocrystalline LaFe₀.₇Co₀.₃O₃ (LFCO) is prepared by a new simple co-precipitation method. • Effect of LFCO to catalytic activity of PtNPS for methanol oxidation is studied. • A synergistic effect is observed when LFCO is added to the Pt catalyst. • Oxygen of LFCO could be considered as active oxygen to remove CO intermediates.

  1. Rh promoted La0.75Sr0.25(Fe0.8Co0.2)1-xGaxO3-δ perovskite catalysts: Characterization and catalytic performance for methane partial oxidation to synthesis gas

    NASA Astrophysics Data System (ADS)

    Palcheva, R.; Olsbye, U.; Palcut, M.; Rauwel, P.; Tyuliev, G.; Velinov, N.; Fjellvåg, H. H.

    2015-12-01

    Synthesis gas production via selective oxidation of methane at 600 °C in a pulse reaction over La0.75Sr0.25(Fe0.8Co0.2)1-xGaxO3-δ (x = 0.1, 0.25, 0.4) perovskite-supported rhodium catalysts, was investigated. The perovskite oxides were prepared by sol-gel citrate method and characterized by X-ray Diffraction (XRD), Moessbauer Spectroscopy (MS), Temperature Programmed Reduction (TPR-H2), X-ray Photoelectron Spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM). According to XRD analysis, the synthesized samples were a single perovskite phase. The perovskite structure of Ga substituted samples remained stable after TPR-H2, as confirmed by XRD. Data of MS identified Fe3+ ions in two distinctive coordination environments, and Fe4+ ions. The Rh2O3 thin overlayer was detected by the HRTEM for the Rh impregnated perovskite oxides. During the interaction of methane with oxidized perovskite-supported Rh (0.5 wt.%) catalysts, besides CO, H2, and surface carbon, CO2 and H2O were formed. The Rh perovskite catalyst with x = 0.25 gallium exhibits the highest catalytic activity of 83% at 600 °C. The CO selectivity was affected by the reducibility of La0.75Sr0.25(Fe0.8Co0.2)1-xGaxO3-δ perovskite materials.

  2. Trion formation in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Kezerashvili, Roman Ya.; Tsiklauri, Shalva M.

    We present three-body calculations for trions binding energy in monolayer transition metal dichalcogenides using the method of hyperspherical harmonics (HH). In numerical calculations for a proper treatment of Coulomb screening in two dimensions we assume that electrons and holes are interacted via Keldysh potential. The convergences of binding energy calculations for the ground state of the trion as a function of the grand angular momentum are studied. For the trion binding energy in MoS2 we obtain 19.2 mev. This value is remarkably close to the experimental one of 18 meV. A comparison with results of other calculations are presented. We also study solutions of a hyperradial equation in a minimal approximation for the ground angular momentum to examine two regimes: a long range and a short range cases when the inter particle distance is much greater and much less than the screening length. For these cases, we find analytical expressions for the energy and wave function for trion states

  3. Patterning Superatom Dopants on Transition Metal Dichalcogenides.

    PubMed

    Yu, Jaeeun; Lee, Chul-Ho; Bouilly, Delphine; Han, Minyong; Kim, Philip; Steigerwald, Michael L; Roy, Xavier; Nuckolls, Colin

    2016-05-11

    This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS2 samples from moderately to heavily electron-doped states. The same approach applied on WSe2 films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p-n junction by selectively doping only a portion of the channel in a WSe2 device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment. PMID:27082448

  4. Transition-metal substitutions in iron chalcogenides

    NASA Astrophysics Data System (ADS)

    Bezusyy, V. L.; Gawryluk, D. J.; Malinowski, A.; Cieplak, Marta Z.

    2015-03-01

    The a b -plane resistivity and Hall effect are studied in Fe1 -yMyTe0.65Se0.35 single crystals doped with two transition-metal elements, M = Co or Ni, over a wide doping range, 0 ≤y ≤0.2 . The superconducting transition temperature, Tc, reaches zero for Co at y ≃0.14 and for Ni at y ≃0.032 , while the resistivity at the Tc onset increases weakly with Co doping, and strongly with Ni doping. The Hall coefficient RH, positive for y =0 , remains so at high temperatures for all y , while it changes sign to negative at low T for y >0.135 (Co) and y >0.06 (Ni). The analysis based on a two-band model suggests that at high T residual hole pockets survive the doping, but holes get localized upon the lowering of T , so that the effect of the electron doping on the transport becomes evident. The suppression of the Tc by Co impurity is related to electron doping, while in the case of the Ni impurity strong electron localization most likely contributes to fast decrease of the Tc.

  5. Transition metal-free olefin polymerization catalyst

    DOEpatents

    Sen, Ayusman; Wojcinski, II, Louis M.; Liu, Shengsheng

    2001-01-01

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

  6. Tunable magnetocaloric effect in transition metal alloys

    PubMed Central

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  7. Properties of Transition Metal Doped Alumina

    NASA Astrophysics Data System (ADS)

    Nykwest, Erik; Limmer, Krista; Brennan, Ray; Blair, Victoria; Ramprasad, Rampi

    Crystallographic texture can have profound effects on the properties of a material. One method of texturing is through the application of an external magnetic field during processing. While this method works with highly magnetic systems, doping is required to couple non-magnetic systems with the external field. Experiments have shown that low concentrations of rare earth (RE) dopants in alumina powders have enabled this kind of texturing. The magnetic properties of RE elements are directly related to their f orbital, which can have as many as 7 unpaired electrons. Since d-block elements can have as many as 5 unpaired electrons the effects of substitutional doping of 3d transition metals (TM) for Al in alpha (stable) and theta (metastable) alumina on the local structure and magnetic properties, in addition to the energetic cost, have been calculated by performing first-principles calculations based on density functional theory. This study has led to the development of general guidelines for the magnetic moment distribution at and around the dopant atom, and the dependence of this distribution on the dopant atom type and its coordination environment. It is anticipated that these findings can aid in the selection of suitable dopants help to guide parallel experimental efforts. This project was supported in part by an internship at the Army Research Laboratory, administered by the Oak Ridge Institute for Science and Education, along with a grant of computer time from the DoD High Performance Computing Modernization Program.

  8. Defect-Tolerant Monolayer Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Pandey, Mohnish; Rasmussen, Filip A.; Kuhar, Korina; Olsen, Thomas; Jacobsen, Karsten W.; Thygesen, Kristian S.

    2016-04-01

    Localized electronic states formed inside the band gap of a semiconductor due to crystal defects can be detrimental to the material's optoelectronic properties. Semiconductors with lower tendency to form defect induced deep gap states are termed defect tolerant. Here we provide a systematic first principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy while the TMDs based on group IV metals form only shallow defect levels and are thus predicted to be defect tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with very similar orbital composition. This indicates a bonding/anti-bonding nature of the gap which in turn suggests that dangling bonds will fall inside the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to non-polar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within the band gap.

  9. Transition Metal Phosphide Hydroprocessing Catalysts: A review

    SciTech Connect

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

    2009-01-01

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

  10. Polytypism in superhard transition-metal triborides

    PubMed Central

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

    2014-01-01

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

  11. Tunable magnetocaloric effect in transition metal alloys.

    PubMed

    Belyea, Dustin D; Lucas, M S; Michel, E; Horwath, J; Miller, Casey W

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based "high entropy alloys" in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  12. Tunable magnetocaloric effect in transition metal alloys

    NASA Astrophysics Data System (ADS)

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-10-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

  13. New Gallides and Germanides of Transition Metals

    NASA Astrophysics Data System (ADS)

    Popova, S. V.

    1982-01-01

    The analysis of the average atomic volumes (AAV) of the intermediate phases from the concentration was done in many two-component systems. It was shown that in some systems (namely transition metal with non-transition element from the IIIrd or IVth group of the periodic table) the AAV of the intermediate phases are much more less than the sum of the volumes of the pure components. It means that the formation of the intermediate phases in such systems is accompanied by a rather large decreasing of the volume in comparison with the mixture of elements. For this reason the high pressure conditions are favourable for the formation of the intermediate phases in such systems from the thermodynamical point of view. On the ground of these data the systems W-Ga, W-Ge, Re-Ga, Os-Ga, Sc-Ga, Ta-Ga, were investigated at high pressures and temperatures. It was found that many new phases are crystallised in these systems. All of them are metastable at room pressure. The composition and crystal structures of these phases were investigated at ordinary conditions.

  14. Enhanced Bifunctional Oxygen Catalysis in Strained LaNiO3 Perovskites

    DOE PAGES

    Petrie, Jonathan R.; Cooper, Valentino R.; Freeland, John W.; Meyer, Tricia L.; Zhang, Zhiyong; Lutterman, Daniel A.; Lee, Ho Nyung

    2016-02-11

    Strain is known to greatly influence low-temperature oxygen electrocatalysis on noble metal films, leading to significant enhancements in bifunctional activity essential for fuel cells and metal-air batteries. Still, its catalytic impact on transition-metal oxide thin films, such as perovskites, is not widely understood. Here, we epitaxially strain the conducting perovskite LaNiO3 to systematically determine its influence on both the oxygen reduction and oxygen evolution reaction. Uniquely, we found that compressive strain could significantly enhance both reactions, yielding a bifunctional catalyst that surpasses the performance of noble metals such as Pt. We attribute the improved bifunctionality to strain-induced splitting of themore » eg orbitals, which can customize orbital asymmetry at the surface. Lastly, analogous to strain-induced shifts in the d-band center of noble metals relative to the Fermi level, such splitting can dramatically affect catalytic activity in this perovskite and other potentially more active oxides.« less

  15. Achieving High Efficiency and Eliminating Degradation in Solid Oxide Electrochemical Cells Using High Oxygen-Capacity Perovskite.

    PubMed

    Jun, Areum; Kim, Junyoung; Shin, Jeeyoung; Kim, Guntae

    2016-09-26

    Recently, there have been efforts to use clean and renewable energy because of finite fossil fuels and environmental problems. Owing to the site-specific and weather-dependent characteristics of the renewable energy supply, solid oxide electrolysis cells (SOECs) have received considerable attention to store energy as hydrogen. Conventional SOECs use Ni-YSZ (yttria-stabilized zirconia) and LSM (strontium-doped lanthanum manganites)-YSZ as electrodes. These electrodes, however, suffer from redox-instability and coarsening of the Ni electrode along with delamination of the LSM electrode during steam electrolysis. In this study, we successfully design and fabricate highly efficient SOECs using layered perovskites, PrBaMn2 O5+δ (PBM) and PrBa0.5 Sr0.5 Co1.5 Fe0.5 O5+δ (PBSCF50), as both electrodes for the first time. The SOEC with layered perovskites as both-side electrodes shows outstanding performance, reversible cycling, and remarkable stability over 600 hours. PMID:27604172

  16. Achieving High Efficiency and Eliminating Degradation in Solid Oxide Electrochemical Cells Using High Oxygen-Capacity Perovskite.

    PubMed

    Jun, Areum; Kim, Junyoung; Shin, Jeeyoung; Kim, Guntae

    2016-09-26

    Recently, there have been efforts to use clean and renewable energy because of finite fossil fuels and environmental problems. Owing to the site-specific and weather-dependent characteristics of the renewable energy supply, solid oxide electrolysis cells (SOECs) have received considerable attention to store energy as hydrogen. Conventional SOECs use Ni-YSZ (yttria-stabilized zirconia) and LSM (strontium-doped lanthanum manganites)-YSZ as electrodes. These electrodes, however, suffer from redox-instability and coarsening of the Ni electrode along with delamination of the LSM electrode during steam electrolysis. In this study, we successfully design and fabricate highly efficient SOECs using layered perovskites, PrBaMn2 O5+δ (PBM) and PrBa0.5 Sr0.5 Co1.5 Fe0.5 O5+δ (PBSCF50), as both electrodes for the first time. The SOEC with layered perovskites as both-side electrodes shows outstanding performance, reversible cycling, and remarkable stability over 600 hours.

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

    NASA Astrophysics Data System (ADS)

    Zeb, M. Ahsan; Kee, Hae-Young

    2012-08-01

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

  18. Spectroscopic study of mixed oxide SAT 1- x:LA x perovskite crystals

    NASA Astrophysics Data System (ADS)

    Runka, T.; Łapsa, K.; Łapiński, A.; Aleksiyko, R.; Berkowski, M.; Drozdowski, M.

    2004-10-01

    Mixed perovskite crystals have been grown from multicomponent melts using the Czochralski method. The Raman, FT-IR and Brillouin investigations of perovskite (1- x)Sr(Al 0.5Ta 0.5)O 3: xLaAlO 3 crystals are reported. The measurements have been performed for several LA concentrations in the range 0.22≤ x≤0.36 at room temperature. The assignment of vibrational modes of IR and Raman spectra was proposed. The experimental results were correlated with structural data, obtained from X-ray diffraction study. The dependence of hypersonic velocity of transverse and longitudinal modes as a function of LA content was also determined. Spectroscopic investigations confirmed the disordered Al/Ta distribution, which increases with the increase of LA content.

  19. An efficient electron transport material of tin oxide for planar structure perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Murugadoss, Govindhasamy; Kanda, Hiroyuki; Tanaka, Soichiro; Nishino, Hitoshi; Ito, Seigo; Imahoric, Hiroshi; Umeyama, Tomokazu

    2016-03-01

    The photovoltaic performance of a perovskite solar cell based on a new electron conducting SnO2 film prepared at low temperature using different solvents was investigated. SnO2 was selected as an electron conducting medium due to its superior properties over TiO2, such as better antireflective properties, higher electron mobility, more suitable band edges and a wider band gap. A SnO2 layer was developed by spin-coating SnCl2 solution followed by annealing at 200 °C in air. The low-temperature (200 °C) annealed SnO2 layer exhibits enhanced crystallization, high transmittance, and uniform surface morphology using ethanol as a solvent rather than water. Solid state CuSCN hole conductor was used as HTM for reducing the device cost. A planar solar cell fabricated with CH3NH3PbI3 perovskite infiltrated SnO2 showed a power conversion efficiency of 8.38% with short-circuit current density of 18.99 mA cm-2, an open-circuit voltage of 0.96 mV and a fill factor of 45%. The devices were fabricated at >60% humidity level at room temperature. The results suggest that SnO2 is an effective charge collection system for CH3NH3PbI3 based planar perovskite solar cells. In addition, these results provide a new direction for the future improvement of perovskite solar cells using new electron conducting layers.

  20. Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures

    NASA Astrophysics Data System (ADS)

    Sadykov, Vladislav; Mezentseva, Natalia; Usoltsev, Vladimir; Sadovskaya, Ekaterina; Ishchenko, Arkady; Pavlova, Svetlana; Bespalko, Yulia; Kharlamova, Tamara; Zevak, Ekaterina; Salanov, Aleksei; Krieger, Tamara; Belyaev, Vladimir; Bobrenok, Oleg; Uvarov, Nikolai; Okhlupin, Yury; Smorygo, Oleg; Smirnova, Alevtina; Singh, Prabhakar; Vlasov, Aleksandr; Korobeynikov, Mikhail; Bryazgin, Aleksandr; Kalinin, Peter; Arzhannikov, Andrei

    This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm -2 at 700 °C in wet H 2/air feeds was demonstrated.

  1. Evolution of electronic correlations across the rutile, perovskite, and Ruddelsden-Popper iridates with octahedral connectivity

    NASA Astrophysics Data System (ADS)

    Kawasaki, Jason K.; Uchida, Masaki; Paik, Hanjong; Schlom, Darrell G.; Shen, Kyle M.

    2016-09-01

    The confluence of electron correlations and spin-orbit interactions is critical to realizing quantum phases in 5 d transition metal oxides. Here, we investigate how the strength of the effective electron correlations evolve across a series of d5 iridates comprised of IrO6 octahedra, ranging from the layered correlated insulator Sr2IrO4 , to the three-dimensional perovskite semimetal SrIrO3, to metallic rutile IrO2 in which the octahedra are arranged in a mixed edge and corner sharing network. Through a combination of reactive oxide molecular-beam epitaxy, in situ angle-resolved photoemission spectroscopy, core level photoemission, and density functional theory, we show how the effective electron correlations weaken as a function of increasing connectivity of the IrO6 network and p -d hybridization. Our results demonstrate how structure and connectivity can be used to control the strength of correlations in the iridates.

  2. Phase stabilisation of hexagonal barium titanate doped with transition metals: A computational study

    SciTech Connect

    Dawson, J.A.; Freeman, C.L.; Harding, J.H.; Sinclair, D.C.

    2013-04-15

    Interatomic potentials recently developed for the modelling of BaTiO{sub 3} have been used to explore the stabilisation of the hexagonal polymorph of BaTiO{sub 3} by doping with transition metals (namely Mn, Co, Fe and Ni) at the Ti-site. Classical simulations have been completed on both the cubic and hexagonal polymorphs to investigate the energetic consequences of transition metal doping on each polymorph. Ti-site charge compensation mechanisms have been used for the multi-valent transition metal ions and cluster binding energies have been considered. Simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti{sub 2} sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. This energetic difference between the two polymorphs is true for all transition metals tested and all charge states and in the case of tri- and tetra-valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions as observed experimentally. Oxidation during incorporation of Ni{sup 2+} and Fe{sup 3+} ions has also been considered. - Graphical abstract: The representation of the strongest binding energy clusters for tri-valent dopants—(a) Ti{sub 2}/O{sub 1} cluster and (b) Ti{sub 2}/O{sub 2} cluster. Highlights: ► Classical simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti2 sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. ► This energetic difference between the two polymorphs is true for all transition metals tested and all charge states. ► In the case of tri- and tetra- valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions.

  3. Nutritional immunity: transition metals at the pathogen-host interface

    PubMed Central

    Hood, M. Indriati; Skaar, Eric P.

    2013-01-01

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

  4. Nutritional immunity: transition metals at the pathogen-host interface.

    PubMed

    Hood, M Indriati; Skaar, Eric P

    2012-07-16

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

  5. Uniform electron gas for transition metals: Input parameters

    SciTech Connect

    Rose, J.H. ); Shore, H.B. )

    1993-12-15

    Input parameters are reported for the theory of ideal metals, a uniform electron-gas model of the elemental transition metals. These input parameters, the electron density, and the bonding valence,'' have been given previously for the 3[ital d] and 4[ital d] series of transition metals. Here, we extend our work based on recent calculations of Sigalas [ital et] [ital al]. [Phys. Rev. B 45, 5777 (1992)] to include the 5[ital d] series. We have also calculated the cohesive energies of the 5[ital d] transition metals using the theory of ideal metals with these parameters. The calculations agree with experiment to within [plus minus]25%.

  6. High-pressure synthesis, crystal structure and magnetic properties of double perovskite oxide Ba{sub 2}CuOsO{sub 6}

    SciTech Connect

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

    2014-09-15

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

  7. Perovskite ferroelectric nanomaterials

    NASA Astrophysics Data System (ADS)

    Nuraje, Nurxat; Su, Kai

    2013-09-01

    In this review, the main concept of ferroelectricity of perovskite oxides and related materials at nanometer scale and existing difficulties in the synthesis of those nanocrystals are discussed. Important effects, such as depolarization field and size effect, on the existence of ferroelectricity in perovskite nanocrystals are deliberated. In the discussion of modeling works, different theoretical calculations are pinpointed focusing on their studies of lattice dynamics, phase transitions, new origin of ferroelectricity in nanostructures, etc. As the major part of this review, recent research progress in the facile synthesis, characterization and various applications of perovskite ferroelectric nanomaterials, such as BaTiO3, PbTiO3, PbZrO3, and BiFeO3, are also scrutinized. Perspectives concerning the future direction of ferroelectric nanomaterials research and its potential applications in renewable energy, etc., are presented. This review provides an overview in this area and guidance for further studies in perovskite ferroelectric nanomaterials and their applications.In this review, the main concept of ferroelectricity of perovskite oxides and related materials at nanometer scale and existing difficulties in the synthesis of those nanocrystals are discussed. Important effects, such as depolarization field and size effect, on the existence of ferroelectricity in perovskite nanocrystals are deliberated. In the discussion of modeling works, different theoretical calculations are pinpointed focusing on their studies of lattice dynamics, phase transitions, new origin of ferroelectricity in nanostructures, etc. As the major part of this review, recent research progress in the facile synthesis, characterization and various applications of perovskite ferroelectric nanomaterials, such as BaTiO3, PbTiO3, PbZrO3, and BiFeO3, are also scrutinized. Perspectives concerning the future direction of ferroelectric nanomaterials research and its potential applications in renewable

  8. Polaronic Transport in Phosphate Glasses Containing Transition Metal Ions

    NASA Astrophysics Data System (ADS)

    Henderson, Mark

    The goal of this dissertation is to characterize the basic transport properties of phosphate glasses containing various amounts of TIs and to identify and explain any electronic phase transitions which may occur. The P2 O5-V2O5-WO3 (PVW) glass system will be analyzed to find the effect of TI concentration on conduction. In addition, the effect of the relative concentrations of network forming ions (SiO2 and P2O5) on transport will be studied in the P2O5-SiO2-Fe2O 3 (PSF) system. Also presented is a numerical study on a tight-binding model adapted for the purposes of modelling Gaussian traps, mimicking TI's, which are arranged in an extended network. The results of this project will contribute to the development of fundamental theories on the electronic transport in glasses containing mixtures of transition oxides as well as those containing multiple network formers without discernible phase separation. The present study on the PVW follows up on previous investigation into the effect on mixed transition ions in oxide glasses. Past research has focused on glasses containing transition metal ions from the 3d row. The inclusion of tungsten, a 5d transition metal, adds a layer of complexity through the mismatch of the energies of the orbitals contributing to localized states. The data have indicated that a transition reminiscent of a metal-insulator transition (MIT) occurs in this system as the concentration of tungsten increases. As opposed to some other MIT-like transitions found in phosphate glass systems, there seems to be no polaron to bipolaron conversion. Instead, the individual localization parameter for tungsten noticeably decreases dramatically at the transition point as well as the adiabaticity. Another distinctive feature of this project is the study of the PSF system, which contains two true network formers, phosphorous pentoxide (P2O 5) and silicon dioxide (SiO2). It is not usually possible to do a reliable investigation of the conduction properties of

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

    SciTech Connect

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

    2014-01-01

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

  10. Dominance of interface chemistry over the bulk properties in determining the electronic structure of epitaxial metal/perovskite oxide heterojunctions

    SciTech Connect

    Chambers, Scott A.; Du, Yingge; Gu, Meng; Droubay, Timothy C.; Hepplestone, Steven; Sushko, Petr

    2015-06-09

    We show that despite very similar crystallographic properties and work function values in the bulk, epitaxial Fe and Cr metallizations on Nb:SrTiO3(001) generate completely different heterojunction electronic properties. Cr is Ohmic whereas Fe forms a Schottky barrier with a barrier height of 0.50 eV. This contrast arises because of differences in interface chemistry. In contrast to Cr [Chambers, S. A. et al., Adv. Mater. 2013, 25, 4001.], Fe exhibits a +2 oxidation state and occupies Ti sites in the perovskite lattice, resulting in negligible charge transfer to Ti, upward band bending, and Schottky barrier formation. The differences between Cr and Fe are understood by performing first-principles calculations of the energetics of defect formation which corroborate the observed interface chemistry and structure.

  11. Promotion of Oxygen Reduction by Exsolved Silver Nanoparticles on a Perovskite Scaffold for Low-Temperature Solid Oxide Fuel Cells.

    PubMed

    Zhu, Yinlong; Zhou, Wei; Ran, Ran; Chen, Yubo; Shao, Zongping; Liu, Meilin

    2016-01-13

    Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient electrochemical energy conversion devices with excellent fuel flexibility. To make SOFC systems more durable and economically competitive, however, the operation temperature must be significantly reduced, which depends sensitively on the development of highly active electrocatalysts for oxygen reduction reaction (ORR) at low temperatures. Here we report a novel silver nanoparticle-decorated perovskite oxide, prepared via a facile exsolution process from a Sr0.95Ag0.05Nb0.1Co0.9O3-δ (SANC) perovskite precursor, as a highly active and robust ORR electrocatalyst for low-temperature SOFCs. The exsolved Sr0.95Ag0.05Nb0.1Co0.9O3-δ (denoted as e-SANC) electrode is very active for ORR, achieving a very low area specific resistance (∼0.214 Ω cm(2) at 500 °C). An anode-supported cell with the new heterostructured cathode demonstrates very high peak power density (1116 mW cm(-2) at 500 °C) and stable operation for 140 h at a current density of 625 mA cm(-2). The superior ORR activity and stability are attributed to the fast oxygen surface exchange kinetics and the firm adhesion of the Ag nanoparticles to the Sr0.95Nb0.1Co0.9O3-δ (SNC0.95) support. Moreover, the e-SANC cathode displays improved tolerance to CO2. These unique features make the new heterostructured material a highly promising cathode for low-temperature SOFCs.

  12. Process for making transition metal nitride whiskers

    DOEpatents

    Bamberger, C.E.

    1988-04-12

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

  13. Process for making transition metal nitride whiskers

    DOEpatents

    Bamberger, Carlos E.

    1989-01-01

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

  14. More Cu, more problems: Decreased CO2 conversion ability by Cu-doped La0.75Sr0.25FeO3 perovskite oxides

    NASA Astrophysics Data System (ADS)

    Daza, Yolanda A.; Maiti, Debtanu; Hare, Bryan J.; Bhethanabotla, Venkat R.; Kuhn, John N.

    2016-06-01

    The effect of Cu doping on the conversion of CO2 to CO was investigated on H2-reduced La0.75Sr0.25FeO3 perovskite oxides. Six La0.75Sr0.25Fe1 -YCuYO3 perovskites, labeled Cu100*Y (with Y = 0, 0.10, 0.25, 0.50, 0.75, and 1) were synthesized and characterized through X-ray diffraction (XRD), temperature-programmed oxygen vacancy formation, and temperature-programmed reduction (TPR). The incorporation of Cu facilitates the formation of oxygen vacancies at lower temperatures but also increased the instability of the perovskite. DFT simulations suggested that the Cu10 sample is favored to produce oxygen vacancies compared to Cu0 and Cu25 samples, which was consistent with experimental oxygen vacancy formation results. For the Cu0, Cu10, and Cu25 samples, temperature-programmed CO2 conversion (TPO-CO2) after isothermal H2-reduction at 450 °C and post-reduction XRD were performed to evaluate the ability of the materials to convert CO2 at low temperatures and to identify the crystalline phases active in the reaction. The peak conversion of CO2 to CO was achieved 30 °C lower on the Cu10 sample versus the Cu0, but less CO was produced, due to a decreased re-oxidation activity of the Cu-doped samples. CO production was inhibited in the Cu25 sample, likely due to a combined effect of poor CO2 dissociative chemisorption energies on metallic Cu and increased thermodynamic stability of the oxygen vacant perovskites. Control experiments (Cu deposited onto La0.75Sr0.25FeO3) indicated the stability of the copper-containing perovskite oxides phases was the primary limiting factor preventing CO formation from CO2.

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

    NASA Astrophysics Data System (ADS)

    Baek, Doohyun; Takamura, Hitoshi

    2013-07-01

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

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

    PubMed

    Maeda, Kazuhiko; Eguchi, Miharu; Oshima, Takayoshi

    2014-11-24

    Perovskite nanosheets of HCa(2-x)Sr(x)Nb3O10 and HCa2Nb(3-y)Ta(y)O10 with controlled band-edge potentials were prepared. They worked as highly efficient heterogeneous photocatalysts for H2 evolution from a water/methanol mixture under band-gap irradiation. The activity was found to depend on the composition. The highest activity was obtained with HCa2Nb2TaO10 nanosheets, recording an apparent quantum yield of approximately 80% at 300 nm, which is the highest value for a nanosheet-based photocatalyst reported to date.

  17. Transition-Metal-Free Biomolecule-Based Flexible Asymmetric Supercapacitors.

    PubMed

    Yang, Yun; Wang, Hua; Hao, Rui; Guo, Lin

    2016-09-01

    A transition-metal-free asymmetric supercapacitor (ASC) is successfully fabricated based on an earth-abundant biomass derived redox-active biomolecule, named lawsone. Such an ASC exhibits comparable or even higher energy densities than most of the recently reported transition-metal-based ASCs, and this green ASC generation from renewable resources is promising for addressing current issues of electronic hazard processing, high cost, and unsustainability. PMID:26890876

  18. Theory of semiconductor and transition metal alloys

    NASA Astrophysics Data System (ADS)

    Zunger, Alex

    1997-03-01

    There is a lot of talk about computer-aided discoveries/design of new materials, but the simple fact is that even limiting oneself to materials made of just two elements, (e.g., Cu-Au or Si-Ge), and to a substitutional system, there can exist as many as 2^N configurations that include compounds, alloys, superlattices, and impurities. Indeed, even for modest number of sites N, this is an astronomical number. Thus, the conventional energy minimization approach (e.g., first-principles pseudopotentials) for selecting the most stable crystal structure for A_qBq is hopeless if one considers the full 2^N space configurations of A, B on a lattice of N points. Molecular-dynamics is of no help, since it does not explore effectively the space of lattice configurations. Thus, contemporary energy minimization approaches use instead the method of ``rounding-up the usual suspects'': selecting the lowest energy from only a small number of well-known candidate configurations. The potential for missing new and important structures is obviously large. This talk gives an outline of the solution. It addresses the questions of (i) finding the lowest energy configuration of substitutional systems, (ii) calculating their composition-temperature phase diagram, and (iii) their finite-temperature thermodynamic properties, using the first-principles local density approximation (LDA). Mapping of the LDA energies of only 10-20 A_qBq compounds onto an Ising-like ``cluster-expansion'' enables use of lattice statistical mechanics techniques that elegantly solve the above problems. This extends the utility of the LDA from simple, perfectly-ordered compounds to truly complex structures, beyond the reach of direct LDA calculations. I will illustrate the method for semiconductor systems and transition-metal intermetallic systems, showing how previously unsuspected structures and materials are predicted, and how one can calculate free energies, short range-order and phase-diagrams of alloys. See

  19. Interactions between lasers and two-dimensional transition metal dichalcogenides.

    PubMed

    Lu, Junpeng; Liu, Hongwei; Tok, Eng Soon; Sow, Chorng-Haur

    2016-05-01

    The recent increasing research interest in two-dimensional (2D) layered materials has led to an explosion of in the discovery of novel physical and chemical phenomena in these materials. Among the 2D family, group-VI transition metal dichalcogenides (TMDs), such as represented by MoS2 and WSe2, are remarkable semiconductors with sizable energy band gaps, which make the TMDs promising building blocks for new generation optoelectronics. On the other hand, the specificity and tunability of the band gaps can generate particularly strong light-matter interactions between TMD crystals and specific photons, which can trigger complex and interesting phenomena such as photo-scattering, photo-excitation, photo-destruction, photo-physical modification, photochemical reaction and photo-oxidation. Herein, we provide an overview of the phenomena explained by various interactions between lasers and the 2D TMDs. Characterizations of the optical fundamentals of the TMDs via laser spectroscopies are reviewed. Subsequently, photoelectric conversion devices enabled by laser excitation and the functionality extension and performance improvement of the TMDs materials via laser modification are comprehensively summarized. Finally, we conclude the review by discussing the prospects for further development in this research area.

  20. New catalysts for hydroprocessing: Transition metal carbides and nitrides

    SciTech Connect

    Ramanathan, S.; Oyama, S.T. |

    1995-11-02

    A series of moderate surface area transition metal carbides and nitrides of molybdenum, tungsten, vanadium, niobium, and titanium were prepared by temperature-programmed reaction of the oxide precursor with a reactant gas (20% CH{sub 4}/H{sub 2} for the carbides and 100% NH{sub 3} for the nitrides). The phase purity and composition of the samples were established by X-ray diffraction photoelectron spectroscopy (XPS), while surface properties were determined by N{sub 2} BET and CO chemisorption measurements. The catalysts were tested in three-phase trickle-bed reactor for their activity in hydrodenitrogenation (HDN), hydrodesulfurization, and hydrodeoxygenation, with particular emphasis on HDN. The catalytic tests were carried out using a model liquid feed mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The carbides and nitrides were found to be active for HDN of quinoline with activity following the order group 6 > group 5 > group 4. Notably, Mo{sub 2}C showed superior areal HDN activity than a commercial sulfided Ni-Mo/Al{sub 2} O{sub 3} catalyst (shell 324). The XRD analysis of the spent catalysts indicated no change in the bulk structure, while XPS results showed little incorporation of sulfur in the surface region of the catalysts, suggesting that these materials are tolerant of sulfur. 42 refs., 11 figs., 7 tabs.