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Sample records for actinoid metal-transition metal-boron

  1. Future in actinoids coordination chemistry

    International Nuclear Information System (INIS)

    Kitazawa, Takafumi

    2006-01-01

    Actinoids coordination chemistry is concerned with spent nuclear fuel reprocessing, specifically with solid-state chemistry of nuclear fuels, separation process with radioactive substances, and geological disposal of high-level radioactive substances. In the 21st century, accumulation of minor actinides, Np, Am, Cm, and others will be realized according with the present program of nuclear energy development. The present article briefly introduces general properties of actinide elements, followed by their coordination chemistry compared with rare earths coordination chemistry. Special facility needed to treat actinoids as well as their chemistry is briefly explained, together with the specific experimental apparatus such as X-ray Absorption Fine Structure (XAFS) and time-resolved laser-induced fluorescence spectrometry (TRLFS) with synchrotron radiation facilities. The effect of coordination with actinoids in the environment chemistry is important in underground disposal of high-level radioactive wastes. For theoretical analysis of the results with actinoids chemistry, relativistic calculation is needed. (S. Ohno)

  2. Development of transmutation technologies of radioactive waste by actinoid hydride

    International Nuclear Information System (INIS)

    Konashi, Kenji; Matsui, Hideki; Yamawaki, Michio

    2001-01-01

    Two waste treatment methods, geological disposal and transmutation, have been studied. The transmutation method changes long-lived radioactive nuclides to short-lived one or stabilizes them by nuclear transformation. The transmutation by actinoid hydride is exactly alike that transformation method from actinoid disposal waste to Pu fuel. For this object, OMEGA project is processing now. The transmutation is difficult by two causes such as large amount of long-lived radioactive nuclides and not enough development of control technologies of nuclear reaction except atomic reactor. The transmutation using actinoid hydride has merits that the amount of actinoid charged in the target increases and the effect of thermal neutrons on fuel decreases depending on homogeneous transmutation velocity in the target. Development of stable actinoid hydride under the conditions of reactor temperature and irradiation environment is important. The experimental results of U-ZrH 1.6 are shown in this paper. The irradiation experiment using Th hydride has been proceeding. (S.Y.)

  3. Inorganic chemistry. Vol. 2. Subgroup elements, lanthanoids, actinoids, transactinoids. 103. ed.; Anorganische Chemie. Bd. 2. Nebengruppenelemente, Lanthanoide, Actinoide, Transactinoide

    Energy Technology Data Exchange (ETDEWEB)

    Holleman, Arnold Frederik; Wiberg, Egon; Wiberg, Nils

    2017-06-01

    For decades, the ''Holleman/Wiberg '' has offered a comprehensive knowledge of inorganic and organometallic chemistry. With the 103rd edition, a new work has been created, which has been designed for the comprehensive preparation of the examination and as a reference book. This second volume comprises the parts C (''subgroups of the periodic system'', the ''d-block elements'') that of the outer transition elements (expansion of the second outermost electron shells) and in the part D (''lanthanides and actinoids''; f-block elements) of the inner transition elements (expansion of the third outermost electron shells). [German] Das ''Holleman/Wiberg'' bietet seit Jahrzehnten ein umfassendes Stoffwissen der anorganischen und metallorganischen Chemie. Mit der 103. Auflage ist nach umfangreicher Umgestaltung der Vorauflage ein neues Werk entstanden, das zur umfassenden Pruefungsvorbereitung und als Nachschlagewerk bestimmt ist. Dieser 2. Band fasst die Teile C (''Nebengruppen des Periodensystems''; ''d-Block-Elemente'') die der aeusseren Uebergangselemente (Ausbau der zweitaeussersten Elektronenschalen) und im Teil D (''Lanthanoide und Actinoide''; ''f-Block-Elemente) die der inneren Uebergangselemente (Ausbau der drittaeussersten Elektronenschalen) zusammen.

  4. Characteristic of metallic state preperties of mendelevium and other actinoids by thermochcomatography

    International Nuclear Information System (INIS)

    Hubener, S.; Zvara, I.

    1982-01-01

    The adsorption of the heavy actinoids Cf, Es, Fm, and Md on polycrystalline titanium and molybdenum has been studied by thermochromatography in comparison with several well-known metallic elements, in trace amounts. The data lead us to suggest that Es, Fm, and Md are divalent in the metallic state and, moreover, that the position of their f energy levels relativg to the Fermi-energy is lower than in the cases of Cf and Yb. A correlation was found between the experimental enthalpies of adsorption of the heavy actinoids and their predicted enthalpies of sublimation

  5. Polyacrylonitrile based composite materials with extracting agents containing chemically bonded CMPO groups for separation of actinoids

    Czech Academy of Sciences Publication Activity Database

    Kameník, Jan; Šebesta, F.; John, J.; Böhmer, V.; Rudzevich, V.; Grüner, Bohumír

    2015-01-01

    Roč. 304, č. 1 (2015), s. 313-319 ISSN 0236-5731 Institutional support: RVO:61388980 ; RVO:61389005 Keywords : actinoids * CMPO * Calix[4]arene * cobalt bis(dicarbollide) * polyacrylonitrile * composite material Subject RIV: CB - Analytical Chemistry, Separation Impact factor: 0.983, year: 2015

  6. Effects of natural organic compounds on adsorption of actinoid on solid phase and interaction between colloid

    Energy Technology Data Exchange (ETDEWEB)

    Tominaga, Takeshi; Minai, Yoshitaka; Takahashi, Yoshio; Kohashi, Asaya [Tokyo Univ. (Japan); Yoshida, Zenko; Meguro, Yoshihiro; Kimura, Takaumi

    1996-01-01

    Two problems were studied such as, at first, the effects of calcium and magnesium on formation of complex of actinoid (III) and humic acid and, second, estimation of number of hydrate of europium (III) in polycarbonic acid complex by fluorescence lifetime measurements. With adding calcium and magnesium, the solubility of humic acid and apparent complex formation constant of actinoid (III)-humic acid complex decreased and amount of adsorption of humic acid on kaolinite increased. Apparent complex formation constant increased with increasing the dissociation degree but decreased with increasing the concentration of supporting electrolyte as same as that of humic acid. This result can be explained by the model of polymer electrolyte on the static electrical interaction with metal ions, because polycarbonic acid is polymer electrolyte with many dissociation groups in a molecule. (S.Y.)

  7. Study on actinoids in boundary ion transfer from an aspect of solution chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Kihara, Sorin; Shirai, Makoto; Matsui, Masakazu [Kyoto Univ., Uji (Japan). Inst. for Chemical Research; Yoshida, Zenko; Aoyagi, Hisao; Kitatsuji, Yoshihiro

    1996-01-01

    This study aimed to elucidate the fundamental properties of boundary ion transfer between water (W) and organic solvent (O) and to apply the results to the study on actinoid ions. First, dissolved states of ion in W and O in relation to boundary transfer were investigated and the transfer stimulation effects by an addition of some agents which can induce their complex formation were examined. Then, a theoretical equation which expresses a relationship between ion-pair extraction reaction and {Delta}Gtr was proposed and proved with {Delta}Gtr of single ion obtained by the use of VITIES, which is an apparatus for voltammetric determination of boundary ion transfer developed by the authors. Single ion transfer in W/O was estimated from the voltammogram based on I-{Delta}V curve (I; electric current which corresponds to the amount of ion transfer and {Delta}V; phase boundary voltage). In addition, determination of actinoid ion transfer in W/O boundary was made by VITIES to clarify the ion transfer energy, velocity and transferred molecular species. Thus, developments of a new isolation method and a trial sensor for actinoid ions were undertaken based on these results. (M.N.)

  8. Nonmetal-metal transition in metal–molten-salt solutions

    NARCIS (Netherlands)

    Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.

    1996-01-01

    The method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to study the nonmetal-metal transition in two different metal–molten-salt solutions, Kx(KCl)1-x and Nax(NaBr)1-x. As the excess metal concentration is increased the electronic density becomes

  9. Semiconductor-Metal transition in a quantum well

    International Nuclear Information System (INIS)

    Nithiananthi, P.; Jayakumar, K.

    2007-01-01

    We demonstrate semiconductor-metal transition through diamagnetic susceptibility of a donor in a GaAs/Al x Ga 1- x As quantum well for both infinite and finite barrier models. We have also considered the non-parabolicity of the conduction band in our calculation. Our results agree with the earlier theoretical result and also with the recent experimental result

  10. Study on radiation-induced oxide-reduction of actinoid ions in acid solution

    Energy Technology Data Exchange (ETDEWEB)

    Ishigure, Kenkichi; Katsumura, Yosuke; Hiroishi, Daisuke [Tokyo Univ. (Japan). Faculty of Engineering; and others

    1996-01-01

    Many studies have been made on the application of actinoid ion, especially UO{sub 2}{sup 2+} to change atomic valance but the mechanism of photoreduction has not yet been solved. In this study, the mechanism of photoreduction of UO{sub 2}{sup 2+} in acid solution was investigated. As functions of alcohol and acid concentrations, {phi}(U{sup IV}) was determined and photoreduction of UO{sub 2}{sup 2+} was investigated as well as NpO{sub 2}{sup 2+}. As an increase of alcohol content (EtOH, MtOH, iso-PrOH), {phi}(U{sup IV}) increased to reach a plateau ({approx}0.6). In addition, {phi}(U{sup IV}) increased linearly with an increase of acid content and the value became smaller in the order, H{sub 3}PO{sub 4}, H{sub 2}SO{sub 4}, HClO{sub 4} solution. Comparing with these results of UO{sub 2}{sup 2+}, photoreduction of NpO{sub 2}{sup 2+} was investigated. Only NpO{sub 2}{sup +} was produced as the final products, but not Np{sup IV} and NP{sup III}. Alcohol dependency of NpO{sub 2}{sup 2+} photoreduction was similar to that of UO{sub 2}{sup 2+} system but the plateau level of {phi} (NpO{sub 2}{sup 2+}) was lower ({approx}0.15) than the latter. (M.N.)

  11. Opticofiber photoacoustic spectrometry in single-ray two-cell grouping for analytical determination of actinoids in solutions of reprocessing

    International Nuclear Information System (INIS)

    Yin'kov, S.I.; Myasoedov, B.F.; Kikhara, T.; Fuine, S.; Maeda, M.

    1996-01-01

    Single-ray two-cell version of photoacoustic spectrometry with laser excitation (Laser Induced Photoacoustic Spectroscopy, LIPAS) for remote determination of actinoids ions in solutions is developed. The spectrometer characteristics were specified by means of uranium-containing solutions, including a great number of non-radioactive ions, the absorption bonds where of imitated the absorption of Pu(3) and Pu(4). The possibilities of the LIPAS technique were studied by analysis of ions, imitating plutonium within the range of 650-724 nm on synthetic solutions with high uranium(6) content and a great number of nonradioactive isotopes of fragmentation-type elements. 8 refs., 9 figs., 1 tab

  12. Investigations in anhydrous liquid ammonia. Reaction of group 2, 4, 5, 11 metal and actinoids compounds

    International Nuclear Information System (INIS)

    Woidy, Patrick

    2014-01-01

    The solubility and reactivity of metal halides, transition metal halides, and actinoid halides in liquid ammonia can lead to new starting materials for the synthesis of fluorides in low oxidation states or for nitrides via a ''low-temperature route''. In this context the ability of metal and actinoid halides to act as an acceptor for or donor of fluoride ions is also of interest. Four different systems were investigated in this study. In the first section, the synthesis and characterization of new compounds were carried out in the system CuX/NH 3 (X = F, Cl, Br, I, and CN) and lead to a ligand stabilized monovalent copper fluoride as a main result. In the second section, the solubility of uranyl compounds and uranium halides in liquid ammonia was investigated and the products were characterized. In the third section, alkali metal thorates were synthesized. Their solubility in liquid ammonia and their behavior as an acceptor for fluoride ions was investigated. In the last section, the results on the solubility behavior of transition metal halides in liquid ammonia and their coordination behavior are presented. In the first system CuX/NH 3 several new compounds, such as [Cu(NH 3 ) 3 ]X (X = Br, I or CN) were synthesized and characterized. The reactions of this compounds with fluoride ion donors (NH 4 F or Me 4 NF) led unfortunately not to the monovalent copper fluoride CuF. The comproportionation reaction of Cu and CuF 2 in liquid ammonia lead to the compounds [Cu(NH 3 ) 3 ] 2 [Cu 2 (NH 3 ) 2 ] . 4 NH 3 and [Cu(NH 3 ) 2 ]F . NH 3 . For the preparation of binary CuF, various decomposition experiments were executed on the compound [Cu(NH 3 ) 2 ]F . NH 3 which resulted in different decomposition products. In additional studies various complexes of divalent copper was investigated and with the compound [Cu(NH 3 ) 5 ]F 2 . NH 3 the solubility of fluoride containing substances in liquid ammonia could be shown. Studies of six- and tetravalent uranium

  13. Ferromagnetic semiconductor-metal transition in europium monoxide

    International Nuclear Information System (INIS)

    Arnold, M.

    2007-10-01

    We present a microscopical model to describe the simultaneous para-to-ferromagnetic and semiconductor-to-metal transition in electron-doped EuO. The physical properties of the model are systematically studied, whereas the main remark is on the interplay between magnetic order and the transport properties. The theory correctly describes detailed experimental features of the conductivity and of the magnetization, obtained for EuO 1-x or Gd-doped Gd x Eu 1-x 0. In particular the doping dependence of the Curie temperature is reproduced The existence of correlation-induced local moments on the impurity sites is essential for this description. (orig.)

  14. Ferromagnetic semiconductor-metal transition in heterostructures of europium monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Stollenwerk, Tobias; Kroha, Johann [Physikalisches Institut der Universitaet Bonn (Germany)

    2012-07-01

    Experiments on thin films of electron doped europium monoxide show a simultaneous ferromagnetic semiconductor-metal transition which goes along with a huge drop in resistivity over several orders of magnitude. Therefore, this material is a very promising candidate for spintronics applications. We have developed a theory which correctly predicts the simultaneous phase transition in thin films of electron doped EuO and the increase of the Curie temperature T{sub C} with doping concentration. The origin of the increased T{sub C} lies in the enhanced RKKY interaction between the localized 4f moments of the Eu atoms. Therefore, the phase transition is controlled by the population of the conduction band. We investigate the influence of film thickness and interface effects on the population of the conduction band and on the magnetic and electronic properties of the EuO film.

  15. Ferromagnetic semiconductor-metal transition in europium monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, M.

    2007-10-15

    We present a microscopical model to describe the simultaneous para-to-ferromagnetic and semiconductor-to-metal transition in electron-doped EuO. The physical properties of the model are systematically studied, whereas the main remark is on the interplay between magnetic order and the transport properties. The theory correctly describes detailed experimental features of the conductivity and of the magnetization, obtained for EuO{sub 1-x} or Gd-doped Gd{sub x}Eu{sub 1-x}0. In particular the doping dependence of the Curie temperature is reproduced The existence of correlation-induced local moments on the impurity sites is essential for this description. (orig.)

  16. Drawing the geometry of 3d transition metal-boron pairs in silicon from electron emission channeling experiments

    CERN Document Server

    Silva, Daniel; Wahl, Ulrich; Martins Correia, Joao; Augustyns, Valerie; De Lemos Lima, Tiago Abel; Granadeiro Costa, Angelo Rafael; David Bosne, Eric; Castro Ribeiro Da Silva, Manuel; Esteves De Araujo, Araujo Joao Pedro; Da Costa Pereira, Lino Miguel

    2016-01-01

    Although the formation of transition metal-boron pairs is currently well established in silicon processing, the geometry of these complexes is still not completely understood. We investigated the lattice location of the transition metals manganese, iron, cobalt and nickel in n- and p+-type silicon by means of electron emission channeling. For manganese, iron and cobalt, we observed an increase of sites near the ideal tetrahedral interstitial position by changing the doping from n- to p+-type Si. Such increase was not observed for Ni. We ascribe this increase to the formation of pairs with boron, driven by Coulomb interactions, since the majority of iron, manganese and cobalt is positively charged in p+-type silicon while Ni is neutral. We propose that breathing mode relaxation around the boron ion within the pair causes the observed displacement from the ideal tetrahedral interstitial site. We discuss the application of the emission channeling technique in this system and, in particular, how it provides insi...

  17. JAEA thermodynamic database for performance assessment of geological disposal of high-level and TRU wastes. Refinement of thermodynamic data for trivalent actinoids and samarium

    International Nuclear Information System (INIS)

    Kitamura, Akira; Fujiwara, Kenso; Yui, Mikazu

    2010-01-01

    Within the scope of the JAEA thermodynamic database project for performance assessment of geological disposal of high-level radioactive and TRU wastes, the refinement of the thermodynamic data for the inorganic compounds and complexes of trivalent actinoids (actinium(III), plutonium(III), americium(III) and curium(III)) and samarium(III) was carried out. Refinement of thermodynamic data for these elements was based on the thermodynamic database for americium published by the Nuclear Energy Agency in the Organisation for Economic Co-operation and Development (OECD/NEA). Based on the similarity of chemical properties among trivalent actinoids and samarium, complementary thermodynamic data for their species expected under the geological disposal conditions were selected to complete the thermodynamic data set for the performance assessment of geological disposal of radioactive wastes. (author)

  18. Positron annihilation study of the semiconductor to metal transition in Ti2O3

    International Nuclear Information System (INIS)

    Tao, S.J.; Rao, C.N.R.

    1977-01-01

    An increase of positron mean life is found to accompany the semiconductor-metal transition in Ti 2 O 3 . This agrees well with the recent finding that the unit cell volume increases during the transition. (orig.) [de

  19. Semiconductor-metal transition induced by giant Stark effect in blue phosphorene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, Peng-Yu; Chen, Shi-Zhang; Zhou, Wu-Xing; Chen, Ke-Qiu, E-mail: keqiuchen@hnu.edu.cn

    2017-06-28

    The electronic structures and transport properties in monolayer blue phosphorene nanoribbons (BPNRs) with transverse electric field have been studied by using density functional theory and nonequilibrium Green's functions method. The results show that the band gaps of BPNRs with both armchair and zigzag edges are linearly decreased with the increasing of the strength of transverse electric field. A semiconductor-metal transition occurs when the electric field strength reaches to 5 V/nm. The Stark coefficient presents a linear dependency on BPNRs widths, and the slopes of both zBPNRs and aBPNRs are 0.41 and 0.54, respectively, which shows a giant Stark effect occurs. Our studies show that the semiconductor-metal transition originates from the giant Stark effect. - Highlights: • The electronic transport in blue phosphorene nanoribbons. • Semiconductor-metal transition can be observed. • The semiconductor-metal transition originates from the giant Stark effect.

  20. Photoinduced Coherent Spin Fluctuation in Primary Dynamics of Insulator to Metal Transition in Perovskite Cobalt Oxide

    Directory of Open Access Journals (Sweden)

    Arima T.

    2013-03-01

    Full Text Available Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.

  1. First principles description of the insulator-metal transition in europium monoxide

    KAUST Repository

    Wang, Hao

    2012-02-01

    Europium monoxide, EuO, is a ferromagnetic insulator. Its electronic structure under pressure and doping is investigated by means of density functional theory. We employ spin polarized electronic structure calculations including onsite electron-electron interaction for the localized Eu 4f and 5d electrons. Our results show that under pressure the ferromagnetism is stable, both for hydrostatic and uniaxial pressure, while the compound undergoes an insulator-metal transition. The insulator-metal transition in O deficient and Gd doped EuO is reproduced for an impurity concentration of 6.25%. A 10 monolayer thick EuO(1 0 0) thin film is predicted to be an insulator with a narrow band gap of 0.08 eV. © 2011 Elsevier B.V. All rights reserved.

  2. Using a Semiconductor-to-Metal Transition to Control Optical Transmission through Subwavelength Hole Arrays

    Directory of Open Access Journals (Sweden)

    E. U. Donev

    2008-01-01

    Full Text Available We describe a simple configuration in which the extraordinary optical transmission effect through subwavelength hole arrays in noble-metal films can be switched by the semiconductor-to-metal transition in an underlying thin film of vanadium dioxide. In these experiments, the transition is brought about by thermal heating of the bilayer film. The surprising reverse hysteretic behavior of the transmission through the subwavelength holes in the vanadium oxide suggest that this modulation is accomplished by a dielectric-matching condition rather than plasmon coupling through the bilayer film. The results of this switching, including the wavelength dependence, are qualitatively reproduced by a transfer matrix model. The prospects for effecting a similar modulation on a much faster time scale by using ultrafast laser pulses to trigger the semiconductor-to-metal transition are also discussed.

  3. Broadband terahertz generation using the semiconductor-metal transition in VO2

    Directory of Open Access Journals (Sweden)

    Nicholas A. Charipar

    2016-01-01

    Full Text Available We report the design, fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2 (vanadium dioxide. With the appropriate geometry, picosecond electrical pulses are generated by illuminating 120 nm thick VO2 with 280 fs pulses from a femtosecond laser. These ultrafast electrical pulses are used to drive a simple dipole antenna, generating broadband terahertz radiation.

  4. Direct Observation of the Pressure-Induced Semiconductor-To-Metal Transition in Yb Monochalcogenides

    International Nuclear Information System (INIS)

    Matsunami, M.; Chen, L.; Nanba, T.; Ochiai, A.

    2003-01-01

    We have measured infrared absorption spectra under pressure and reflectivity spectra of YbS in the wide photon energy range from 7 meV to 30 eV. The absorption edge shifts linearly toward lower energy with pressure, and above 11 GPa it disappeared in the infrared energy region. The results are considered to correspond to the development of a f-d mixing above this pressure, which lead to an occurrence of the semiconductor-to- metal transition. (author)

  5. Pressure study on the semiconductor-metal transition in a quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Nithiananthi, P.; Jayakumar, K. [Department of Physics, Gandhigram Rural University, Tamilnadu (India)

    2009-06-15

    The effect of {gamma}-X band crossing due to the applied hydrostatic pressure on the semiconductor-metal transition in a quasi-two-dimensional system like GaAs/Al{sub x}Ga{sub 1-x}As quantum well has been shown through the drastic change in diamagnetic susceptibility of donors at critical concentration in the effective mass approximation using the variational principle. The nonparabolicity of the conduction band has been taken into account in the calculation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. VO2 microcrystals as an advanced smart window material at semiconductor to metal transition

    Science.gov (United States)

    Basu, Raktima; Magudapathy, P.; Sardar, Manas; Pandian, Ramanathaswamy; Dhara, Sandip

    2017-11-01

    Textured VO2(0 1 1) microcrystals are grown in the monoclinic, M1 phase which undergoes a reversible first order semiconductor to metal transition (SMT) accompanied by a structural phase transition to rutile tetragonal, R phase. Around the phase transition, VO2 also experiences noticeable change in its optical and electrical properties. A change in color of the VO2 micro crystals from white to cyan around the transition temperature is observed, which is further understood by absorption of red light using temperature dependent ultraviolet-visible spectroscopic analysis and photoluminescence studies. The absorption of light in the red region is explained by the optical transition between Hubbard states, confirming the electronic correlation as the driving force for SMT in VO2. The thermochromism in VO2 has been studied for smart window applications so far in the IR region, which supports the opening of the band gap in semiconducting phase; whereas there is hardly any report in the management of visible light. The filtering of blue light along with reflection of infrared above the semiconductor to metal transition temperature make VO2 applicable as advanced smart windows for overall heat management of a closure.

  7. VO2 microcrystals as an advanced smart window material at semiconductor to metal transition

    International Nuclear Information System (INIS)

    Basu, Raktima; Pandian, Ramanathaswamy; Dhara, Sandip; Magudapathy, P; Sardar, Manas

    2017-01-01

    Textured VO 2 (0 1 1) microcrystals are grown in the monoclinic, M1 phase which undergoes a reversible first order semiconductor to metal transition (SMT) accompanied by a structural phase transition to rutile tetragonal, R phase. Around the phase transition, VO 2 also experiences noticeable change in its optical and electrical properties. A change in color of the VO 2 micro crystals from white to cyan around the transition temperature is observed, which is further understood by absorption of red light using temperature dependent ultraviolet–visible spectroscopic analysis and photoluminescence studies. The absorption of light in the red region is explained by the optical transition between Hubbard states, confirming the electronic correlation as the driving force for SMT in VO 2 . The thermochromism in VO 2 has been studied for smart window applications so far in the IR region, which supports the opening of the band gap in semiconducting phase; whereas there is hardly any report in the management of visible light. The filtering of blue light along with reflection of infrared above the semiconductor to metal transition temperature make VO 2 applicable as advanced smart windows for overall heat management of a closure. (paper)

  8. Ferromagnetic semiconductor-metal transition in heterostructures of electron doped europium monoxide

    International Nuclear Information System (INIS)

    Stollenwerk, Tobias

    2013-09-01

    In the present work, we develop and solve a self-consistent theory for the description of the simultaneous ferromagnetic semiconductor-metal transition in electron doped Europium monoxide. We investigate two different types of electron doping, Gadolinium impurities and Oxygen vacancies. Besides the conduction band occupation, we can identify low lying spin fluctuations on magnetic impurities as the driving force behind the doping induced enhancement of the Curie temperature. Moreover, we predict the signatures of these magnetic impurities in the spectra of scanning tunneling microscope experiments. By extending the theory to allow for inhomogeneities in one spatial direction, we are able to investigate thin films and heterostructures of Gadolinium doped Europium monoxide. Here, we are able to reproduce the experimentally observed decrease of the Curie temperature with the film thickness. This behavior is attributed to missing coupling partners of the localized 4f moments as well as to an electron depletion at the surface which leads to a reduction of the number of itinerant electrons. By investigating the influence of a metallic substrate onto the phase transition in Gadolinium doped Europium monoxide, we find that the Curie temperature can be increased up to 20%. However, as we show, the underlying mechanism of metal-interface induced charge carrier accumulation is inextricably connected to a suppression of the semiconductor-metal transition.

  9. Ferromagnetic semiconductor-metal transition in heterostructures of electron doped europium monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Stollenwerk, Tobias

    2013-09-15

    In the present work, we develop and solve a self-consistent theory for the description of the simultaneous ferromagnetic semiconductor-metal transition in electron doped Europium monoxide. We investigate two different types of electron doping, Gadolinium impurities and Oxygen vacancies. Besides the conduction band occupation, we can identify low lying spin fluctuations on magnetic impurities as the driving force behind the doping induced enhancement of the Curie temperature. Moreover, we predict the signatures of these magnetic impurities in the spectra of scanning tunneling microscope experiments. By extending the theory to allow for inhomogeneities in one spatial direction, we are able to investigate thin films and heterostructures of Gadolinium doped Europium monoxide. Here, we are able to reproduce the experimentally observed decrease of the Curie temperature with the film thickness. This behavior is attributed to missing coupling partners of the localized 4f moments as well as to an electron depletion at the surface which leads to a reduction of the number of itinerant electrons. By investigating the influence of a metallic substrate onto the phase transition in Gadolinium doped Europium monoxide, we find that the Curie temperature can be increased up to 20%. However, as we show, the underlying mechanism of metal-interface induced charge carrier accumulation is inextricably connected to a suppression of the semiconductor-metal transition.

  10. The role of the excited impurity levels on the metal-non metal transition

    International Nuclear Information System (INIS)

    Silva, M.S.F. da; Makler, S.S.; Anda, E.V.

    1983-01-01

    The electronic density of states for the impurity bands in doped semiconductors is calculated using the Green function method. The system is described by a Hamiltonian with local Coulomb interactions represented in a tight binding basis composed by two orbitals per site. The electronic correlation is treated in the CPA approximation. To calculate the configurational average for this structural disordered system a diagrammatic scheme is developed. It represents an extension of the Matsubara and Toyozawa method for the case of two hybridized bands in the presence of electronic correlation. The excited levels show to play a crutial role in the undestanding of the metal-non metal transition. This work represents an improvement of a previous result. The particular case of Si : P is analyzed. (author) [pt

  11. The role of the excited impurity levels on the metal-non metal transition

    International Nuclear Information System (INIS)

    Silva, M.S.F. da; Makler, S.S.; Anda, E.V.

    1983-01-01

    The electronic density of states for the impurity bands in doped semiconductors is calculated using the Green function method. The system is described by a Hamiltonian with local Coulomb interactions represented in a tight binding basis composed by two orbitals per site. The electronic correlation is treated in the CPA approximation. To calculate the configurational average for this structural disordered system a diagrammatic scheme is developed. It represents an extension of the Matsubara and Toyozawa method for the case of two hybridized bands in the presence of electronic correlation. The excited levels shown to play a crutial role in the understanding of the metal-non metal transition. This work represents an improvement of a previous result. The particular case of Si:P is analyzed. (Author) [pt

  12. Semiconductor-metal transition of Se in Ru-Se Catalyst Nanoparticles

    Science.gov (United States)

    Babu, P. K.; Lewera, Adam; Oldfield, Eric; Wieckowski, Andrzej

    2009-03-01

    Ru-Se composite nanoparticles are promising catalysts for the oxygen reduction reaction (ORR) in fuel cells. Though the role of Se in enhancing the chemical stability of Ru nanoparticles is well established, the microscopic nature of Ru-Se interaction was not clearly understood. We carried out a combined investigation of ^77Se NMR and XPS on Ru-Se nanoparticles and our results indicate that Se, a semiconductor in elemental form, becomes metallic when interacting with Ru. ^77Se spin-lattice relaxation rates are found to be proportional to T, the well-known Korringa behavior characteristic of metals. The NMR results are supported by the XPS binding energy shifts which suggest that a possible Ru->Se charge transfer could be responsible for the semiconductor->metal transition of Se which also makes Ru less susceptible to oxidation during ORR.

  13. Pressure-driven insulator-metal transition in cubic phase UO2

    Science.gov (United States)

    Huang, Li; Wang, Yilin; Werner, Philipp

    2017-09-01

    Understanding the electronic properties of actinide oxides under pressure poses a great challenge for experimental and theoretical studies. Here, we investigate the electronic structure of cubic phase uranium dioxide at different volumes using a combination of density functional theory and dynamical mean-field theory. The ab initio calculations predict an orbital-selective insulator-metal transition at a moderate pressure of ∼45 GPa. At this pressure the uranium's 5f 5/2 state becomes metallic, while the 5f 7/2 state remains insulating up to about 60 GPa. In the metallic state, we observe a rapid decrease of the 5f occupation and total angular momentum with pressure. Simultaneously, the so-called “Zhang-Rice state”, which is of predominantly 5f 5/2 character, quickly disappears after the transition into the metallic phase.

  14. Development of dissimilar metal transition joint by hot roll bonding technique

    International Nuclear Information System (INIS)

    Nagai, Takayuki; Takeda, Seiichiro; Tanaka, Yasumasa; Ogawa, Kazuhiro; Nakasuji, Kazuyuki; Ikenaga, Yoshiaki.

    1994-01-01

    Metallurgically bonded transition joints which enable to connect reprocessing equipments made of superior corrosion resistant valve metals (Ti-5Ta, Zr or Ti) with stainless steel piping is needed for nuclear fuel reprocessing plants. The authors have developed dissimilar metal transition joints between stainless steel and Ti-5Ta, Zr or Ti with an insert metal of Ta by the hot roll bonding process, using the newly developed mill called 'rotary reduction mill'. In the R and D program, appropriate bonding conditions in the manufacturing process of the joints were established. This report presents the structure of transition joints and the manufacturing process by the hot roll bonding technique. Then, the evaluation of mechanical and corrosion properties and the results of demonstration test of joints for practical use are described. (author)

  15. Development of dissimilar metal transition joint by hot roll bonding technique

    International Nuclear Information System (INIS)

    Nagai, Takayuki; Takeuchi, Masayuki; Takeda, Seiichiro; Shikakura, Sakae; Ogawa, Kazuhiro; Nakasuji, Kazuyuki; Kajimura, Haruhiko.

    1995-01-01

    Metallurgically bonded transition joints which enable to connect reprocessing equipments made of superior corrosion resistant valve metals (Ti-5Ta, Zr or Ti) with stainless steel piping is needed for nuclear fuel reprocessing plants. The authors have developed dissimilar metal transition joints between stainless steel and Ti-5Ta, Zr or Ti with an insert metal of Ta by the hot roll bonding process, using the newly developed mill called 'rotary reduction mill'. In the R and D program, appropriate bonding conditions in the manufacturing process of the joints were established. This report presents the structure of transition joints and the manufacturing process by hot roll bonding technique. Then, the evaluation of mechanical and corrosion properties and the results of demonstration test of joints for practical use are described. (author)

  16. High-pressure phase transition of alkali metal-transition metal deuteride Li2PdD2

    Science.gov (United States)

    Yao, Yansun; Stavrou, Elissaios; Goncharov, Alexander F.; Majumdar, Arnab; Wang, Hui; Prakapenka, Vitali B.; Epshteyn, Albert; Purdy, Andrew P.

    2017-06-01

    A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal-transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal-transition metal hydrides in general.

  17. Electric-field driven insulator-metal transition and tunable magnetoresistance in ZnO thin film

    Science.gov (United States)

    Zhang, Le; Chen, Shanshan; Chen, Xiangyang; Ye, Zhizhen; Zhu, Liping

    2018-04-01

    Electrical control of the multistate phase in semiconductors offers the promise of nonvolatile functionality in the future semiconductor spintronics. Here, by applying an external electric field, we have observed a gate-induced insulator-metal transition (MIT) with the temperature dependence of resistivity in ZnO thin films. Due to a high-density carrier accumulation, we have shown the ability to inverse change magnetoresistance in ZnO by ionic liquid gating from 10% to -2.5%. The evolution of photoluminescence under gate voltage was also consistent with the MIT, which is due to the reduction of dislocation. Our in-situ gate-controlled photoluminescence, insulator-metal transition, and the conversion of magnetoresistance open up opportunities in searching for quantum materials and ZnO based photoelectric devices.

  18. Phase-field model of insulator-to-metal transition in VO2 under an electric field

    Science.gov (United States)

    Shi, Yin; Chen, Long-Qing

    2018-05-01

    The roles of an electric field and electronic doping in insulator-to-metal transitions are still not well understood. Here we formulated a phase-field model of insulator-to-metal transitions by taking into account both structural and electronic instabilities as well as free electrons and holes in VO2, a strongly correlated transition-metal oxide. Our phase-field simulations demonstrate that in a VO2 slab under a uniform electric field, an abrupt universal resistive transition occurs inside the supercooling region, in sharp contrast to the conventional Landau-Zener smooth electric breakdown. We also show that hole doping may decouple the structural and electronic phase transitions in VO2, leading to a metastable metallic monoclinic phase which could be stabilized through a geometrical confinement and the size effect. This work provides a general mesoscale thermodynamic framework for understanding the influences of electric field, electronic doping, and stress and strain on insulator-to-metal transitions and the corresponding mesoscale domain structure evolution in VO2 and related strongly correlated systems.

  19. Stochastic IMT (Insulator-Metal-Transition Neurons: An Interplay of Thermal and Threshold Noise at Bifurcation

    Directory of Open Access Journals (Sweden)

    Abhinav Parihar

    2018-04-01

    Full Text Available Artificial neural networks can harness stochasticity in multiple ways to enable a vast class of computationally powerful models. Boltzmann machines and other stochastic neural networks have been shown to outperform their deterministic counterparts by allowing dynamical systems to escape local energy minima. Electronic implementation of such stochastic networks is currently limited to addition of algorithmic noise to digital machines which is inherently inefficient; albeit recent efforts to harness physical noise in devices for stochasticity have shown promise. To succeed in fabricating electronic neuromorphic networks we need experimental evidence of devices with measurable and controllable stochasticity which is complemented with the development of reliable statistical models of such observed stochasticity. Current research literature has sparse evidence of the former and a complete lack of the latter. This motivates the current article where we demonstrate a stochastic neuron using an insulator-metal-transition (IMT device, based on electrically induced phase-transition, in series with a tunable resistance. We show that an IMT neuron has dynamics similar to a piecewise linear FitzHugh-Nagumo (FHN neuron and incorporates all characteristics of a spiking neuron in the device phenomena. We experimentally demonstrate spontaneous stochastic spiking along with electrically controllable firing probabilities using Vanadium Dioxide (VO2 based IMT neurons which show a sigmoid-like transfer function. The stochastic spiking is explained by two noise sources - thermal noise and threshold fluctuations, which act as precursors of bifurcation. As such, the IMT neuron is modeled as an Ornstein-Uhlenbeck (OU process with a fluctuating boundary resulting in transfer curves that closely match experiments. The moments of interspike intervals are calculated analytically by extending the first-passage-time (FPT models for Ornstein-Uhlenbeck (OU process to include a

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

    International Nuclear Information System (INIS)

    Richard T. Scalettar; Warren E. Pickett

    2005-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Scalettar, Richard T.; Pickett, Warren E.

    2004-07-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Richard T. Scalettar; Warren E. Pickett

    2005-08-02

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

  3. Effects of thickness on the nanocrystalline structure and semiconductor-metal transition characteristics of vanadium dioxide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Zhenfei, E-mail: zhfluo8@yahoo.com [Terahertz Research Center, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Zhou, Xun, E-mail: zx_zky@yahoo.com [Terahertz Research Center, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Yan, Dawei [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Wang, Du; Li, Zeyu [Terahertz Research Center, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Yang, Cunbang [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang Sichuan 621900 (China); Jiang, Yadong [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054 (China)

    2014-01-01

    Nanocrystalline vanadium dioxide (VO{sub 2}) thin films were grown on glass substrates by using reactive direct current magnetron sputtering and in situ thermal treatments at low preparation temperatures (≤ 350 °C). The VO{sub 2} thin films were characterized by grazing-incidence X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy and spectroscopic ellipsometry (SE). The semiconductor-metal transition (SMT) characteristics of the films were investigated by four-point probe resistivity measurements and infrared spectrometer equipped with heating pads. The testing results showed that the crystal structure, morphology, grain size and semiconductor-metal transition temperature (T{sub SMT}) significantly changed as the film thickness decreased. Multilayer structures were observed in the particles of thinner films whose average particle size is much larger than the film thickness and average VO{sub 2} grain size. A competition mechanism between the suppression effect of decreased thickness and coalescence of nanograins was proposed to understand the film growth and the formation of multilayer structure. The value of T{sub SMT} was found to decrease as average VO{sub 2} grain size became smaller, and SE results showed that small nanograin size significantly affected the electronic structure of VO{sub 2} film. - Highlights: • Nanocrystalline vanadium dioxide thin films were prepared. • Multilayer structures were observed in the films with large particles. • The transition temperature of the film is correlated with its electronic structure.

  4. Effects of thickness on the nanocrystalline structure and semiconductor-metal transition characteristics of vanadium dioxide thin films

    International Nuclear Information System (INIS)

    Luo, Zhenfei; Zhou, Xun; Yan, Dawei; Wang, Du; Li, Zeyu; Yang, Cunbang; Jiang, Yadong

    2014-01-01

    Nanocrystalline vanadium dioxide (VO 2 ) thin films were grown on glass substrates by using reactive direct current magnetron sputtering and in situ thermal treatments at low preparation temperatures (≤ 350 °C). The VO 2 thin films were characterized by grazing-incidence X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy and spectroscopic ellipsometry (SE). The semiconductor-metal transition (SMT) characteristics of the films were investigated by four-point probe resistivity measurements and infrared spectrometer equipped with heating pads. The testing results showed that the crystal structure, morphology, grain size and semiconductor-metal transition temperature (T SMT ) significantly changed as the film thickness decreased. Multilayer structures were observed in the particles of thinner films whose average particle size is much larger than the film thickness and average VO 2 grain size. A competition mechanism between the suppression effect of decreased thickness and coalescence of nanograins was proposed to understand the film growth and the formation of multilayer structure. The value of T SMT was found to decrease as average VO 2 grain size became smaller, and SE results showed that small nanograin size significantly affected the electronic structure of VO 2 film. - Highlights: • Nanocrystalline vanadium dioxide thin films were prepared. • Multilayer structures were observed in the films with large particles. • The transition temperature of the film is correlated with its electronic structure

  5. Reduction of the Jahn-Teller distortion at the insulator-to-metal transition in mixed valence manganites

    International Nuclear Information System (INIS)

    Garcia-Munoz, J.L.; Suaaidi, M.; Fontcuberta, J.; Rodriguez-Carvajal, J.

    1997-01-01

    The insulator-to-metal transition in the manganite La 0.52 Y 0.15 Ca 0.33 MnO 3 (T IM ∼115 K) has been studied by high-resolution neutron powder diffraction. The cell volume contraction at the Curie point is accompanied by a remarkable decrease of the Jahn-Teller distortion in MnO 6 octahedra. The change of the Mn-O bond lengths at T IM is anisotropic and brings about a drop out of the basal-plane collective distortion mode Q 2 , proposed to be the deformation responsible for the band split of e g↑ orbitals. This is consistent with the double-exchange picture, and precludes simple ferromagnetic exchange. copyright 1997 The American Physical Society

  6. c -Axis Dimer and Its Electronic Breakup: The Insulator-to-Metal Transition in Ti2 O3

    Science.gov (United States)

    Chang, C. F.; Koethe, T. C.; Hu, Z.; Weinen, J.; Agrestini, S.; Zhao, L.; Gegner, J.; Ott, H.; Panaccione, G.; Wu, Hua; Haverkort, M. W.; Roth, H.; Komarek, A. C.; Offi, F.; Monaco, G.; Liao, Y.-F.; Tsuei, K.-D.; Lin, H.-J.; Chen, C. T.; Tanaka, A.; Tjeng, L. H.

    2018-04-01

    We report on our investigation of the electronic structure of Ti2 O3 using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. From the distinct satellite structures in the spectra, we have been able to establish unambiguously that the Ti-Ti c -axis dimer in the corundum crystal structure is electronically present and forms an a1 ga1 g molecular singlet in the low-temperature insulating phase. Upon heating, we observe a considerable spectral weight transfer to lower energies with orbital reconstruction. The insulator-metal transition may be viewed as a transition from a solid of isolated Ti-Ti molecules into a solid of electronically partially broken dimers, where the Ti ions acquire additional hopping in the a -b plane via the egπ channel, the opening of which requires consideration of the multiplet structure of the on-site Coulomb interaction.

  7. GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

    Science.gov (United States)

    Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

    2018-05-01

    Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

  8. Insulator-metal transition in substrate-independent VO2 thin film for phase-change devices.

    Science.gov (United States)

    Taha, Mohammad; Walia, Sumeet; Ahmed, Taimur; Headland, Daniel; Withayachumnankul, Withawat; Sriram, Sharath; Bhaskaran, Madhu

    2017-12-20

    Vanadium has 11 oxide phases, with the binary VO 2 presenting stimuli-dependent phase transitions that manifest as switchable electronic and optical features. An elevated temperature induces an insulator-to-metal transition (IMT) as the crystal reorients from a monoclinic state (insulator) to a tetragonal arrangement (metallic). This transition is accompanied by a simultaneous change in optical properties making VO 2 a versatile optoelectronic material. However, its deployment in scalable devices suffers because of the requirement of specialised substrates to retain the functionality of the material. Sensitivity to oxygen concentration and larger-scale VO 2 synthesis have also been standing issues in VO 2 fabrication. Here, we address these major challenges in harnessing the functionality in VO 2 by demonstrating an approach that enables crystalline, switchable VO 2 on any substrate. Glass, silicon, and quartz are used as model platforms to show the effectiveness of the process. Temperature-dependent electrical and optical characterisation is used demonstrating three to four orders of magnitude in resistive switching, >60% chromic discrimination at infrared wavelengths, and terahertz property extraction. This capability will significantly broaden the horizon of applications that have been envisioned but remained unrealised due to the lack of ability to realise VO 2 on any substrate, thereby exploiting its untapped potential.

  9. Electric-Field-Driven Dual Vacancies Evolution in Ultrathin Nanosheets Realizing Reversible Semiconductor to Half-Metal Transition.

    Science.gov (United States)

    Lyu, Mengjie; Liu, Youwen; Zhi, Yuduo; Xiao, Chong; Gu, Bingchuan; Hua, Xuemin; Fan, Shaojuan; Lin, Yue; Bai, Wei; Tong, Wei; Zou, Youming; Pan, Bicai; Ye, Bangjiao; Xie, Yi

    2015-12-02

    Fabricating a flexible room-temperature ferromagnetic resistive-switching random access memory (RRAM) device is of fundamental importance to integrate nonvolatile memory and spintronics both in theory and practice for modern information technology and has the potential to bring about revolutionary new foldable information-storage devices. Here, we show that a relatively low operating voltage (+1.4 V/-1.5 V, the corresponding electric field is around 20,000 V/cm) drives the dual vacancies evolution in ultrathin SnO2 nanosheets at room temperature, which causes the reversible transition between semiconductor and half-metal, accompanyied by an abrupt conductivity change up to 10(3) times, exhibiting room-temperature ferromagnetism in two resistance states. Positron annihilation spectroscopy and electron spin resonance results show that the Sn/O dual vacancies in the ultrathin SnO2 nanosheets evolve to isolated Sn vacancy under electric field, accounting for the switching behavior of SnO2 ultrathin nanosheets; on the other hand, the different defect types correspond to different conduction natures, realizing the transition between semiconductor and half-metal. Our result represents a crucial step to create new a information-storage device realizing the reversible transition between semiconductor and half-metal with flexibility and room-temperature ferromagnetism at low energy consumption. The as-obtained half-metal in the low-resistance state broadens the application of the device in spintronics and the semiconductor to half-metal transition on the basis of defects evolution and also opens up a new avenue for exploring random access memory mechanisms and finding new half-metals for spintronics.

  10. La interstitial defect-induced insulator-metal transition in the oxide heterostructures LaAl O3 /SrTi O3

    Science.gov (United States)

    Zhou, Jun; Yang, Ming; Feng, Yuan Ping; Rusydi, Andrivo

    2017-11-01

    Perovskite oxide interfaces have attracted tremendous research interest for their fundamental physics and promising all-oxide electronic applications. Here, based on first-principles calculations, we propose a surface La interstitial promoted interface insulator-metal transition in LaAl O3 /SrTi O3 (110). Compared with surface oxygen vacancies, which play a determining role on the insulator-metal transition of LaAl O3 /SrTi O3 (001) interfaces, we find that surface La interstitials can be more experimentally realistic and accessible for manipulation and more stable in an ambient atmospheric environment. Interestingly, these surface La interstitials also induce significant spin-splitting states with a Ti dy z/dx z character at a conducting LaAl O3 /SrTi O3 (110) interface. On the other hand, for insulating LaAl O3 /SrTi O3 (110) (<4 unit cells LaAl O3 thickness), a distortion between La (Al) and O atoms is found at the LaAl O3 side, partially compensating the polarization divergence. Our results reveal the origin of the metal-insulator transition in LaAl O3 /SrTi O3 (110) heterostructures, and also shed light on the manipulation of the superior properties of LaAl O3 /SrTi O3 (110) for different possibilities in electronic and magnetic applications.

  11. Observation of semiconductor to metallic transition and polaron hopping in double perovskite Pr{sub 2}CoTiO{sub 6} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Mahato, Dev K., E-mail: drdevkumar@yahoo.com [Department of Physics, National Institute of Technology Patna, Patna 800005 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1, APC Road, Kolkata 700009 (India)

    2017-05-01

    This paper describes semiconductor to metal transition and polaron conduction in double perovskite Pr{sub 2}CoTiO{sub 6} (PCTO) ceramics. The XRD pattern recorded at room temperature confirmed the pure phase, single crystalline structure. The semicircle arc in the impedance plot at each temperature can be attributed to the grain boundary contribution, indicating one dominating response in the measurement frequency range. The semiconductor to metallic transition was also confirmed by the variation of grain boundary resistance (R{sub gb}) with temperature. The activation energy estimated from the imaginary part of electrical modulus and impedance are found to be the characteristic of polaron conduction in PCTO. Ac conductivity followed power law dependence σ{sub ac} = Bω{sup n}. The observed variation of the exponent ‘n’ with temperature suggests the typical of charge transport assisted by a hopping process. The observed minimum in the temperature dependence of frequency exponent ‘n’ strongly suggests that the large polaron tunneling is the dominant transport process.

  12. Sc, Y, the lanthanoids and the actinoids

    International Nuclear Information System (INIS)

    Miller, J.D.

    1985-01-01

    Highlights of work published in 1984 are given. Solid state, studies in solution, coordination chemistry and organometallic chemistry aspects of scandium, yttrium, the rare earths and actinide compounds are covered. (U.K.)

  13. Study on thermodynamic properties of actinoid oxides

    Energy Technology Data Exchange (ETDEWEB)

    Tsuji, Toshihide; Miyajima, Nobuyoshi; Kato, Tetsuya; Ochida, Manabu [Nagoya Univ. (Japan). School of Engineering; Mumomura, Tadasumi; Yamashita, Toshiyuki; Nitani, Noriko; Ouchi, Kinji

    1996-01-01

    Since long-life transuranium elements (TRU) accumulate associated with a progress of high-burnup of fuel, TRU quenching in a reactor or an accelerator has been examined in Japan. To design a fuel for TRU quenching, thermal expansion is an important thermal parameter along with thermal capacity and heat transfer coefficient. Here, lattice constants of PuO{sub 2} ThO{sub 2}, UO{sub 2} and NpO{sub 2} were investigated by high temperature X-ray diffraction, showing that the lattice constants of these dioxides but UO{sub 2} obtained in this study were well coincident with Tailor`s values. The linear expansion coefficients for ThO{sub 2}, UO{sub 2} and PuO{sub 2} agreed with TPRC data and that of NpO{sub 2} with Fahey`s measurement. The linear expansion coefficient of NpO{sub 2} was found to be temperature dependent as well as other three dioxides. Those values were in inverse proportion to their melting points in a higher temperature range, whereas in a lower temperature one, the coefficient of UO{sub 2} was larger than those of NpO{sub 2} and PuO{sub 2}. Therefore, such abnormal behavior of the coefficient in a low temperature range was considered to be related to the lower Debye temperature of UO{sub 2} compared with the other dioxides. (M.N.)

  14. Evidence of the semiconductor-metal transition in V{sub 2}O{sub 5} thin films by the pulsed laser photoacoustic method

    Energy Technology Data Exchange (ETDEWEB)

    Perez-Pacheco, A.; Acosta-Najarro, D. R.; Cruz-Manjarrez, H.; Rodriguez-Fernandez, L.; Pineda-Santamaria, J. C; Aguilar-Franco, M. [Instituto de Fisica-Universidad Nacional Autonoma de Mexico, Mexico DF (Mexico); Castaneda-Guzman, R. [Laboratorio de Fotofisica y Peliculas Delgadas, CCADET-UNAM, Mexico DF (Mexico)

    2013-05-14

    In this work, the pulsed photoacoustic technique was used to investigate the semiconductor-metal transition of thin vanadium pentoxide films (V{sub 2}O{sub 5}) under increasing temperature. The V{sub 2}O{sub 5} thin films were simultaneously deposited by RF magnetron sputtering at room temperature, on corning glass and SnO{sub 2}:F/glass substrates, in order to compare the photoacoustic response. The elemental and structural analysis of the V{sub 2}O{sub 5} films was performed by Rutherford backscattering spectroscopy and X-ray diffraction. The optical transmission and band gap were determined using UV-Vis spectroscopy. The electrical properties were measured using four-point probe measurements with the Van der Pauw geometry.

  15. UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Saha, D., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in; Misra, P., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in; Joshi, M. P.; Kukreja, L. M. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013 (India)

    2016-08-28

    In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1–7) of ZnO/TiO{sub x} layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O{sub 2} and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ∼ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality

  16. Making the semiconductor-metal transition in a growth-dominant phase-change alloy InSb for double density blu-ray super-RENS-ROM disc

    Energy Technology Data Exchange (ETDEWEB)

    Hyot, Berangere [CEA, LETI, MINATEC, F- 38054 Grenoble (France)

    2012-10-15

    Phenomenologically, a semiconductor-metal transition is characterized by a sudden change in electrical properties but also in optical behaviours, as a consequence of a change in electron behaviour. The ability to induce a reversible semiconductor-metal transition in a material by varying conditions such as applied temperature or electrical field, results in attractive changes in properties that have fuelled the curiosity of scientists. In this paper, we discuss the interest of such materials exhibiting the reversible semiconductor-metal transition in the development of the next generation of optical Bly-ray discs (BD), the so-called super-resolution near field structure (super-RENS) discs and we show that InSb semiconductor material exhibits huge variations of its optical properties during the optically (thermally)-induced solid-to-liquid change corresponding to a semiconductor-metal transition. First success in the video playback on HDTV (High Definition TeleVision) display from 50 GB (BD capacity x 2) InSb-based super-RENS-ROM discs including a high definition video content with 1920 x 1080 pixels was realized in September 2009 by the super-RENS consortium joining three partners: AIST (National Institute of Advanced Industrial Science and Technology), Mitsubishi Electric Co. and LETI. Snapshot of high definition video content from InSb-based super-RENS-ROM disc corresponding to 50 GB per layer (BD capacity x 2) displayed on HDTV. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Pressure-induced structural changes and insulator-metal transition in layered bismuth triiodide, BiI3: a combined experimental and theoretical study

    International Nuclear Information System (INIS)

    Devidas, T R; Chandra Shekar, N V; Sundar, C S; Chithaiah, P; Rao, C N R; Sorb, Y A; Bhadram, V S; Chandrabhas, N; Pal, K; Waghmare, U V

    2014-01-01

    Noting that BiI 3 and the well-known topological insulator (TI) Bi 2 Se 3 have the same high symmetry parent structures, and that it is desirable to find a wide-band gap TI, we determine here the effects of pressure on the structure, phonons and electronic properties of rhombohedral BiI 3 . We report a pressure-induced insulator-metal transition near 1.5 GPa, using high pressure electrical resistivity and Raman measurements. X-ray diffraction studies, as a function of pressure, reveal a structural peculiarity of the BiI 3 crystal, with a drastic drop in c/a ratio at 1.5 GPa, and a structural phase transition from rhombohedral to monoclinic structure at 8.8 GPa. Interestingly, the metallic phase, at relatively low pressures, exhibits minimal resistivity at low temperatures, similar to that in Bi 2 Se 3 . We corroborate these findings with first-principles calculations and suggest that the drop in the resistivity of BiI 3 in the 1–3 GPa range of pressure arises possibly from the appearance of an intermediate crystal phase with a lower band-gap and hexagonal crystal structure. Calculated Born effective charges reveal the presence of metallic states in the structural vicinity of rhombohedral BiI 3 . Changes in the topology of the electronic bands of BiI 3 with pressure, and a sharp decrease in the c/a ratio below 2 GPa, are shown to give rise to changes in the slope of phonon frequencies near that pressure. (paper)

  18. Pressure induced insulator–metal transition and giant negative piezoresistance in Pr{sub 0.6}Ca{sub 0.4}Mn{sub 0.96}Al{sub 0.04}O{sub 3} polycrystal

    Energy Technology Data Exchange (ETDEWEB)

    Arumugam, S., E-mail: sarumugam1963@yahoo.com [Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirapalli 620024, Tamil Nadu (India); Thiyagarajan, R. [Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203 (China); Kalaiselvan, G.; Sivaprakash, P. [Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirapalli 620024, Tamil Nadu (India)

    2016-11-01

    The effect of external hydrostatic pressure (P) on the magnetization (M) and resistivity (ρ) properties of charge-orbital (CO) ordered-insulating phase-separated manganite Pr{sub 0.6}Ca{sub 0.4}Mn{sub 0.96}Al{sub 0.04}O{sub 3} system is reported here. At ambient P, CO ordering transition and spin-canting in the AFM are observed at 223 K and 55 K respectively in M(T) and ρ(T) measurements. Application of P increases simultaneously the magnitude of magnetization (M) and transition temperature, and weakens the CO ordering in M(T) measurements up to 0.98 GPa. During ρ(T) measurements, P induces an insulator–metallic transition (T{sub IM}) at 1.02 GPa, and further increase of P up to 2.84 GPa leads to increase of T{sub IM} (dT{sub IM}/dP =21.6 K/GPa). ρ at T{sub IM} is reduced about three orders of magnitude at 2.84 GPa, and leads to the giant negative piezoresistance (~98%). These results are analyzed separately in two temperature regions i.e., below and above T{sub IM} by power function equation and small polaronic hopping model respectively. It is understood from these analyses that the application of P suppresses the Jahn–Teller distortions, electron–electron and electron–magnon scattering factors, and induces the insulator–metal transition in Pr{sub 0.6}Ca{sub 0.4}Mn{sub 0.96}Al{sub 0.04}O{sub 3} system. - Highlights: • Application of P on Pr{sub 0.6}Ca{sub 0.4}Mn{sub 0.96}Al{sub 0.04}O{sub 3} reduces resistivity (ρ) remarkably at low-temperatures, and exhibits an insulator to metallic transition at 1.02 GPa. • The reduction in ρ by P is about three orders of magnitude at 2.84 GPa, leads to the giant negative piezoresistance about 98%. • The effect of the suppression of Jahn–Teller distortions, electron–electron and electron–magnon scattering under an applied P exhibits to the metal-Insulator transition. • The phase-separation in this system has been tuned by both internal and external perturbations.

  19. Mechanism of fission of neutron-deficient actinoids nuclides

    International Nuclear Information System (INIS)

    Sueki, Keisuke; Nakahara, Hiromichi; Tanase, Masakazu; Nagame, Yuichiro; Shinohara, Nobuo; Tsukada, Kazuaki.

    1996-01-01

    A heavy ion reaction ( 19 F+ 209 Bi) is selected. The reaction produces neutron-deficient 228 U which is compound nucleus with a pair of Rb(z=37) and Cs(Z=55). Energy dissipation problem of nucleus was studied by measuring the isotope distribution of two fissile nuclides. Bismuth metal evaporated on aluminium foil was irradiated by 19 F with the incident energy of 105-128 MeV. We concluded from the results that the excess energy of reaction system obtained with increasing the incident energy is consumed by (1) light Rb much more than Cs and (2) about 60% of energy is given to two fission fragments and the rest 40% to the translational kinetic energy or unknown anomalous γ-ray irradiation. (S.Y.)

  20. Study of composition and properties of pentavalenct actinoid carbonates

    Energy Technology Data Exchange (ETDEWEB)

    Volkov, Yu F; Visyashcheva, G I; Kapshukov, I I; Simakin, G A; Yakovlev, G N

    1976-01-01

    Monocarbonates and dicarbonates of Npsup((4)), Pusup((5)), and Amsup((5)) with cations Na/sup +/, K/sup +/, and NH/sub 4//sup +/ have been synthesized. The compounds have the following composition: KXO/sub 2/CO/sub 3/xnH/sub 2/O and NH/sub 4/NpO/sub 2/CO/sub 3/xnH/sub 3/O, where x=Np, Pu, or Am; n (<=) 2. They have been studied chemically, thermogravimetrically and by X-ray diffraction method. It has been established that monocarbonates have a hexagonal structure and complex composition corresponding to the formula MXO/sub 2/CO/sub 3/xnH/sub 2/O with a zeolite nature of water molecules. Thermal stability of dicarbonates within the temperature range 20-500/sup 0/C has been studied. An effect of hydration and dehydration on a change in the lattice parameters has been investigated. The data are given on separation, identification, and properties of some sodium carbonatoneptunailates which differ in their physico-chemical properties from other monocarbonates. The main distinctive feature is th eir ability to lose and accept water molecules readily, forming different hydrate forms.

  1. Substituted polyethylene glycols in extraction of fission products and actinoids

    International Nuclear Information System (INIS)

    Smirnov, I.V.; Efremova, T.I.; Shadrin, A.Yu.; Baulin, V.E.; Tsvetkov, E.N.

    1993-01-01

    Europium and americium extraction from nitric acid media by solutions of phosphoryl-containing podands in o-nitroethylbenzene was studied. Extractive capacity of podands is determined by the length of polyether chain and the structure of terminal groups. Podand Ph 2 P(O)CH 2 CH 2 OCH 2 xCH 2 P(O)PH 2 as regards its extractive, capacity is similar to carbamoylphosphineoxides. Introduction of rigid o-phenylene fragments to polyether chain brigs, about a sharp decrease in extractive capacity of the podands

  2. Study on actinoid isolation by antimonide ion exchanger

    Energy Technology Data Exchange (ETDEWEB)

    Tsuji, Masamichi [Tokyo Inst. of Tech. (Japan). Faculty of Science; Kubota, Masumitsu; Yamagishi, Isao

    1996-01-01

    To establish a containment of long-life nuclides and an effective reduction of waste volume is important to reduce the loadings on the natural environment. Chemical isolation of radioactive nuclides from wastes was attempted by using inorganic ion exchanger with high specificity and thermal stability. In this study, titanium antimonide was used as an ion exchanger to investigate the adsorption of trivalent metallic ions according to Kielland plot curves. When the ionic equivalent fraction (X-bar{sub M}) was around 0.005, Kielland plot curve of either of 3-valent metallic ions was bent, suggesting the exchanger had two different adsorption sites. The slope of the curve became smaller as an elevation of temperature. These results show that the ion radius was decreased resulting from partial elimination of the hydrated water of ion and thus, the steric conditions around the exchange site might be improved. (M.N.)

  3. Effects of organic compounds on actinoid transfer in natural environment

    Energy Technology Data Exchange (ETDEWEB)

    Hiraki, Keizo; Nakaguchi, Yuzuru; Suzuki, Yasuhiro [Kinki Univ., Higashi-Osaka, Osaka (Japan). Faculty of Science and Technology; Senoo, Muneaki; Nagao, Seiya; Sakamoto, Yoshiaki

    1996-01-01

    For safety evaluation of geological disposal of radioactive wastes, it seems necessary to elucidate the geological transfer of radioactive nuclides in the soil and the undersea sediments. It has been known that there exist various organic compounds highly potential to form a complex with TRU elements, uranium, copper etc. in the soil and the sediments and those compounds may play an important role for geological transfer of nuclides. In this study, fluorescent substances contained in underground and river water were focused as the measures to identify the molecular species of organic compounds in natural water and their interactions with radionuclides and minor metals, and their geological transfers were investigated. Spectrophotometric properties of humic acid obtained in the market were examined. Its fluorescent intensity was strongest at pH 10 and stable for 2 weeks or more. Then, highly polluted river water was taken from Yamato river to determine the contents of humic acid and other fluorescent substances. Further, the effects of the additions of Cu and Fe on the fluorescent intensity were examined. (M.N.)

  4. Mechanism of fission of neutron-deficient actinoids nuclides

    Energy Technology Data Exchange (ETDEWEB)

    Sueki, Keisuke; Nakahara, Hiromichi [Tokyo Metropolitan Univ., Hachioji (Japan). Faculty of Science; Tanase, Masakazu; Nagame, Yuichiro; Shinohara, Nobuo; Tsukada, Kazuaki

    1996-01-01

    A heavy ion reaction ({sup 19}F+{sup 209}Bi) is selected. The reaction produces neutron-deficient {sup 228}U which is compound nucleus with a pair of Rb(z=37) and Cs(Z=55). Energy dissipation problem of nucleus was studied by measuring the isotope distribution of two fissile nuclides. Bismuth metal evaporated on aluminium foil was irradiated by {sup 19}F with the incident energy of 105-128 MeV. We concluded from the results that the excess energy of reaction system obtained with increasing the incident energy is consumed by (1) light Rb much more than Cs and (2) about 60% of energy is given to two fission fragments and the rest 40% to the translational kinetic energy or unknown anomalous {gamma}-ray irradiation. (S.Y.)

  5. Insights on semiconductor-metal transition in indium-doped zinc oxide from x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and x-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Saw, K. G., E-mail: kgsaw@usm.my; Aznan, N. M., E-mail: nanieaz1004@gmail.com [Physics Programme, School of Distance Education, Universiti Sains Malaysia, 11800 Penang (Malaysia); Yam, F. K., E-mail: yamfk@yahoo.com; Ng, S. S., E-mail: shashiong@usm.my [Nano-optoelectronics Research Laboratory, Universiti Sains Malaysia, 11800 Penang (Malaysia); Pung, S. Y., E-mail: sypung@usm.my [School of Materials and Mineral Resources Eng., Universiti Sains Malaysia, 14300 Nibong Tebal (Malaysia)

    2016-07-06

    ZnO thin films doped with various amounts of In impurities were prepared by magnetron sputtering at a substrate temperature of 150°C. The shift in optical bandgap of the In-doped ZnO films is studied as a function of carrier concentration. Nominally doped ZnO films exhibit an increase in the measured optical band gap known as the Burstein-Moss effect. Dominant band gap narrowing is observed with increased doping. XPS and TOFSIMS analyses confirm that In is incorporated in the ZnO material. The In 3d peaks show that no metallic In is present as a result of heavy doping. The XRD phase analysis shows a preferential c-axis growth but a shift of the ZnO (002) peak to lower 2-theta values with increasing FWHM as the carrier concentration increases indicates the decline in the quality of crystallinity. An elongation of the c lattice constant is also observed and is likely to be caused by intersitital In as the amount of In dopants increases. The incorporation of In induces a semiconductor-metal transition between the carrier concentrations of 3.58 – 5.61×10{sup 19} cm{sup −3} and structural changes in the ZnO host material.

  6. Photo-induced insulator-metal transition in Pr0.6Ca0.4MnO3 thin films grown by pulsed laser deposition: Effect of thickness dependent structural and transport properties

    Science.gov (United States)

    Elovaara, Tomi; Huhtinen, Hannu; Majumdar, Sayani; Paturi, Petriina

    2016-09-01

    We report photo-induced colossal magnetoresistive insulator-metal transition (IMT) in Pr0.6Ca0.4MnO3 thin films under much reduced applied magnetic field. The colossal effect was studied as a function of film thickness and thus with variable structural properties. Thorough structural, magnetic and magnetotransport characterization under light shows that the highest effect on the transition field can be obtained in the thinnest film (38 nm). However, due to the substrate induced strain of this film the required magnetic field for IMT is quite high. The best crystalline properties of the 110 nm film lead to the lowest IMT field under light and 109% change in resistance at 10 K. With increasing thickness, the film properties start to move more toward the bulk material and, hence, IMT is no more observed under the applied field of 9 T. Our results indicate that for obtaining large photo-induced CMR, the best epitaxial quality of thin films is essential.

  7. Pressure effect on magnetic and insulator-metal transition of La.sub.0.67./sub.Pb.sub.0.33./sub.Mn.sub.0.9./sub.Co.sub.0.1./sub.O.sub.2.97./sub. ceramic

    Czech Academy of Sciences Publication Activity Database

    Mihalik, M.; Zentková, M.; Antoňák, M.; Arnold, Zdeněk; Kamarád, Jiří; Skorokhod, Yuriy; Gritzner, G.; Kiss, L. F.

    2012-01-01

    Roč. 32, č. 1 (2012), s. 145-149 ISSN 0895-7959. [Conference of the European High Pressure Research Group (EHPRG) /49./. Budapest, 28.08.2011-02.09.2011] Grant - others:VEGA(SK) 2/0057/27 Institutional research plan: CEZ:AV0Z10100521 Keywords : magnetic transition: insulator-metal transition * hydrostatic pressure * manganite Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.901, year: 2012 www.tandfonline.com

  8. Enhancement of superconductivity near the pressure-induced semiconductor-metal transition in the BiS₂-based superconductors LnO₀.₅F₀.₅BiS₂ (Ln = La, Ce, Pr, Nd).

    Science.gov (United States)

    Wolowiec, C T; White, B D; Jeon, I; Yazici, D; Huang, K; Maple, M B

    2013-10-23

    Measurements of electrical resistivity were performed between 3 and 300 K at various pressures up to 2.8 GPa on the BiS2-based superconductors LnO0.5F0.5BiS2 (Ln=Pr, Nd). At lower pressures, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 exhibit superconductivity with critical temperatures Tc of 3.5 and 3.9 K, respectively. As pressure is increased, both compounds undergo a transition at a pressure Pt from a low Tc superconducting phase to a high Tc superconducting phase in which Tc reaches maximum values of 7.6 and 6.4 K for PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced transition is characterized by a rapid increase in Tc within a small range in pressure of ∼0.3 GPa for both compounds. In the normal state of PrO0.5F0.5BiS2, the transition pressure Pt correlates with the pressure where the suppression of semiconducting behaviour saturates. In the normal state of NdO0.5F0.5BiS2, Pt is coincident with a semiconductor-metal transition. This behaviour is similar to the results recently reported for the LnO0.5F0.5BiS2 (Ln=La, Ce) compounds. We observe that Pt and the size of the jump in Tc between the two superconducting phases both scale with the lanthanide element in LnO0.5F0.5BiS2 (Ln=La, Ce, Pr, Nd).

  9. Large modification in insulator-metal transition of VO{sub 2} films grown on Al{sub 2}O{sub 3} (001) by high energy ion irradiation in biased reactive sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Azhan, Nurul Hanis; Okimura, Kunio, E-mail: okifn@keyaki.cc.u-tokai.ac.jp [Graduate School of Science and Technology, Tokai University, Hiratsuka 259-1292 (Japan); Ohtsubo, Yoshiyuki; Kimura, Shin-ichi [Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871 (Japan); Zaghrioui, Mustapha; Sakai, Joe [GREMAN, UMR 7347 CNRS, Université François Rabelais de Tours, Parc de Grandmont, 37200 Tours (France)

    2016-02-07

    High energy ion irradiation in biased reactive sputtering enabled significant modification of insulator-metal transition (IMT) properties of VO{sub 2} films grown on Al{sub 2}O{sub 3} (001). Even at a high biasing voltage with mean ion energy of around 325 eV induced by the rf substrate biasing power of 40 W, VO{sub 2} film revealed low IMT temperature (T{sub IMT}) at 309 K (36 °C) together with nearly two orders magnitude of resistance change. Raman measurements from −193 °C evidenced that the monoclinic VO{sub 2} lattice begins to transform to rutile-tetragonal lattice near room temperature. Raman spectra showed the in-plane compressive stress in biased VO{sub 2} films, which results in shortening of V–V distance along a-axis of monoclinic structure, a{sub M}-axis (c{sub R}-axis) and thus lowering the T{sub IMT}. In respect to that matter, significant effects in shortening the in-plane axis were observed through transmission electron microscopy observations. V2p{sub 3/2} spectra from XPS measurements suggested that high energy ion irradiation also induced oxygen vacancies and resulted for an early transition onset and rather broader transition properties. Earlier band gap closing against the temperature in VO{sub 2} film with higher biasing power was also probed by ultraviolet photoelectron spectroscopy. Present results with significant modification of IMT behavior of films deposited at high-energy ion irradiation with T{sub IMT} near the room temperature could be a newly and effective approach to both exploring mechanisms of IMT and further applications of this material, due to the fixed deposition conditions and rather thicker VO{sub 2} films.

  10. Anharmonic Vibrational Spectroscopy on Metal Transition Complexes

    Science.gov (United States)

    Latouche, Camille; Bloino, Julien; Barone, Vincenzo

    2014-06-01

    Advances in hardware performance and the availability of efficient and reliable computational models have made possible the application of computational spectroscopy to ever larger molecular systems. The systematic interpretation of experimental data and the full characterization of complex molecules can then be facilitated. Focusing on vibrational spectroscopy, several approaches have been proposed to simulate spectra beyond the double harmonic approximation, so that more details become available. However, a routine use of such tools requires the preliminary definition of a valid protocol with the most appropriate combination of electronic structure and nuclear calculation models. Several benchmark of anharmonic calculations frequency have been realized on organic molecules. Nevertheless, benchmarks of organometallics or inorganic metal complexes at this level are strongly lacking despite the interest of these systems due to their strong emission and vibrational properties. Herein we report the benchmark study realized with anharmonic calculations on simple metal complexes, along with some pilot applications on systems of direct technological or biological interest.

  11. Transformation of metallic boron into substitutional dopants in graphene on 6H-SIC(0001)

    Czech Academy of Sciences Publication Activity Database

    Sforzini, J.; Telychko, Mykola; Krejčí, Ondřej; Vondráček, Martin; Švec, Martin; Bocquet, F.C.; Tautz, F.S.

    2016-01-01

    Roč. 93, č. 4 (2016), 1-4, č. článku 041302. ISSN 1098-0121 R&D Projects: GA ČR GA15-07172S Institutional support: RVO:68378271 Keywords : heavily nitrogenated graphene * chemisorbed molecules * recent progress * performance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  12. Plasmonic percolation: Plasmon-manifested dielectric-to-metal transition

    KAUST Repository

    Chen, Huanjun

    2012-08-28

    Percolation generally refers to the phenomenon of abrupt variations in electrical, magnetic, or optical properties caused by gradual volume fraction changes of one component across a threshold in bicomponent systems. Percolation behaviors have usually been observed in macroscopic systems, with most studies devoted to electrical percolation. We report on our observation of plasmonic percolation in Au nanorod core-Pd shell nanostructures. When the Pd volume fraction in the shell consisting of palladium and water approaches the plasmonic percolation threshold, ∼70%, the plasmon of the nanostructure transits from red to blue shifts with respect to that of the unshelled Au nanorod. This plasmonic percolation behavior is also confirmed by the scattering measurements on the individual core-shell nanostructures. Quasistatic theory and numerical simulations show that the plasmonic percolation originates from a positive-to-negative transition in the real part of the dielectric function of the shell as the Pd volume fraction is increased. The observed plasmonic percolation is found to be independent of the metal type in the shell. Moreover, compared to the unshelled Au nanorods with similar plasmon wavelengths, the Au nanorod core-Pd shell nanostructures exhibit larger refractive index sensitivities, which is ascribed to the expulsion of the electric field intensity from the Au nanorod core by the adsorbed Pd nanoparticles. © 2012 American Chemical Society.

  13. Theory of the pairbreaking superconductor-metal transition in nanowires

    International Nuclear Information System (INIS)

    Del Maestro, Adrian; Rosenow, Bernd; Sachdev, Subir

    2009-01-01

    We present a detailed description of a zero temperature phase transition between superconducting and diffusive metallic states in very thin wires due to a Cooper pair breaking mechanism. The dissipative critical theory contains current reducing fluctuations in the guise of both quantum and thermally activated phase slips. A full cross-over phase diagram is computed via an expansion in the inverse number of complex components of the superconducting order parameter (one in the physical case). The fluctuation corrections to the electrical (σ) and thermal (κ) conductivities are determined, and we find that σ has a non-monotonic temperature dependence in the metallic phase which may be consistent with recent experimental results on ultra-narrow wires. In the quantum critical regime, the ratio of the thermal to electrical conductivity displays a linear temperature dependence and thus the Wiedemann-Franz law is obeyed, with a new universal experimentally verifiable Lorenz number

  14. Insulator-metal transition of fluid molecular hydrogen

    International Nuclear Information System (INIS)

    Ross, M.

    1996-01-01

    Dynamically compressed fluid hydrogen shows evidence for metallization at the relatively low pressure of 140 GPa (1.4 Mbar) while experiments on solid hydrogen made in a diamond-anvil cell have failed to detect any evidence for gap closure up to a pressure of 230 GPa (2.3 Mbar). Two possible mechanisms for metal- liclike resistivity are put forward. The first is that as a consequence of the large thermal disorder in the fluid (kT∼0.2 endash 0.3 eV) short-range molecular interactions lead to band tailing that extends the band edge into the gap, resulting in closure at a lower pressure than in the solid. The second mechanism argues that molecular dissociation creates H atoms that behave similar to n-type donors in a heavily doped semiconductor and undergo a nonmetal-metal Mott-type transition. copyright 1996 The American Physical Society

  15. Plasmonic percolation: Plasmon-manifested dielectric-to-metal transition

    KAUST Repository

    Chen, Huanjun; Wang, Feng; Li, Kun; Woo, Katchoi; Wang, Jianfang; Li, Quan; Sun, Ling Dong; Zhang, Xixiang; Lin, Haiqing; YAN, Chunhua

    2012-01-01

    Percolation generally refers to the phenomenon of abrupt variations in electrical, magnetic, or optical properties caused by gradual volume fraction changes of one component across a threshold in bicomponent systems. Percolation behaviors have usually been observed in macroscopic systems, with most studies devoted to electrical percolation. We report on our observation of plasmonic percolation in Au nanorod core-Pd shell nanostructures. When the Pd volume fraction in the shell consisting of palladium and water approaches the plasmonic percolation threshold, ∼70%, the plasmon of the nanostructure transits from red to blue shifts with respect to that of the unshelled Au nanorod. This plasmonic percolation behavior is also confirmed by the scattering measurements on the individual core-shell nanostructures. Quasistatic theory and numerical simulations show that the plasmonic percolation originates from a positive-to-negative transition in the real part of the dielectric function of the shell as the Pd volume fraction is increased. The observed plasmonic percolation is found to be independent of the metal type in the shell. Moreover, compared to the unshelled Au nanorods with similar plasmon wavelengths, the Au nanorod core-Pd shell nanostructures exhibit larger refractive index sensitivities, which is ascribed to the expulsion of the electric field intensity from the Au nanorod core by the adsorbed Pd nanoparticles. © 2012 American Chemical Society.

  16. Metal non-metal transitions in doped semiconductors

    International Nuclear Information System (INIS)

    Brezini, A.

    1989-12-01

    A disordered Hubbard model with diagonal disorder is used to examine the electron localization effects associated with both disorder and electron-electron interaction. Extensive results are reported on the ground state properties and compared with other theories. In particular two regimes are observed; when the electron-electron interaction U is greater than the disorder parameter and when is smaller. Furthermore the effect of including conduction-band minima into the calculation of metal-insulator transitions in doped Si and Ge is investigated with use of Berggren approach. Good agreement with experiments are found when both disorder and interactions are included. (author). 37 refs, 7 figs, 3 tabs

  17. Rare-earth metal transition metal borocarbide and nitridoborate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Niewa, Rainer; Shlyk, Larysa; Blaschkowski, Bjoern [Stuttgart Univ. (Germany). Inst. fuer Anorganische Chemie

    2011-07-01

    Few years after the discovery of superconductivity in high-T{sub c} cuprates, borocarbides and shortly after nitridoborates with reasonably high T{sub c}s up to about 23 K attracted considerable attention. Particularly for the rare-earth metal series with composition RNi{sub 2}[B{sub 2}C] it turned out, that several members exhibit superconductivity next to magnetic order with both T{sub c} above or below the magnetic ordering temperature. Therefore, these compounds have been regarded as ideal materials to study the interplay and coexistence of superconductivity and long range magnetic order, due to their comparably high ordering temperatures and similar magnetic and superconducting condensation energies. This review gathers information on the series RNi{sub 2}[B{sub 2}C] and isostructural compounds with different transition metals substituting Ni as well as related series like RM[BC], RM[BN], AM[BN] and R{sub 3}M{sub 2}[BN]{sub 2}N (all with R = rare-earth metal, A = alkaline-earth metal, M = transition metal) with special focus on synthesis, crystal structures and structural trends in correspondence to physical properties. (orig.)

  18. Development of dissimilar metal transition joint by hot bond rolling

    International Nuclear Information System (INIS)

    Kurokawa, Hiroyuki; Nakasuji, Kazuyuki; Kajimura, Haruhiko; Nagai, Takayuki; Takeda, Seiichiro.

    1997-01-01

    Metallurgically bonded transition joints which enable to connect reprocessing equipments made of superior corrosion resistant valve metals (Ti-5Ta, Zr or Ti) to stainless steel piping are required for nuclear fuel reprocessing plants. The authors have developed dissimilar transition joints made of stainless steel and Ti-5Ta, Zr or Ti with an insert metal of Ta by the hot bond rolling process of clad bars and clad pipes, using a newly developed mill called 'rotary reduction mill'. This report presents the manufacturing process of dissimilar transition joints produced from the clad pipe with three layers by the hot bond rolling. First, the method of hot bond rolling of clad pipe is proposed. Then, the mechanical and corrosion properties of the dissimilar transition joints are evaluated in detail by carrying out various tests. Finally, the rolling properties in the clad pipe method are discussed. (author)

  19. Insertion of isocyanides into actinoid-nitrogen bonds of biscyclopentadienyluranium mono- and bis-(dialkylamides)

    International Nuclear Information System (INIS)

    Dormond, A.; Aaliti, A.; Moise, C.

    1985-01-01

    Isocyanides react readily with Ucp 2 (NEt 2 ) 2 (cp = cyclopentadienyl) and U(C 5 Me 5 ) 2 (NEt 2 )Cl giving iminoalkylamido insertion compounds: starting from Ucp 2 (NEt 2 ) 2 and an excess of isocyanide or from the monoinserted compound, a second insertion occurs, affording the highly symmetrical bis(iminoalkylamido) compounds; 1 H n.m.r. data indicate the importance of a 'carbenoid' resonance hybrid and nitrogen lone-pair donation to the 'carbenoid' carbon atom. (author)

  20. Superconductivity and spin fluctuations in the actinoid-platinum metal borides {Th, U}Pt3 B

    Czech Academy of Sciences Publication Activity Database

    Bauer, E.; Royanian, E.; Michor, H.; Sologub, O.; Scheidt, E.-W.; Goncalves, A.P.; Buršík, Jiří; Wolf, W.; Reith, D.; Blass-Schenner, C.; Moser, R.; Podloucky, R.; Rogl, P.

    2015-01-01

    Roč. 92, č. 2 (2015), Art. num. 024511 ISSN 1098-0121 Institutional support: RVO:68081723 Keywords : {Th, U}Pt3 B * x-ray diffraction * TEM Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  1. Modelling of the migration of lanthanoids and actinoids in ground water; the medium dependence of equilibrium constants

    International Nuclear Information System (INIS)

    Biedermann, G.; Bruno, J.; Ferri, D.; Grenthe, I.; Salvatore, F.; Spahiu, K.

    1982-01-01

    The examples given in this communication indicate that it is possible to obtain a good estimate of the medium dependence of equilibrium constants by using the specific interaction theory. The theory is applicable both when extrapolating equilibrium constants to zero ionic strength and for the estimation of activity coefficients in mixtures of electrolytes. Many interaction coefficients are available in the literature, or can be calculated from published mean activity coefficient or isopiestic data. The magnitude of interaction coefficients can often be correlated with the charge and size of ions. This offers a possibility to estimate the coefficients for complexes, for which direct experimental information is difficult to get. The specific interaction theory is superior to the empirical equations of the Davies type. There is superior to the empirical equations of the Davies type. There is sufficient experimental information on interaction coefficients to warrant the implementation of the specific interaction approach in existing specifiation codes

  2. Preparation and characterization of zirconium phosphate ion exchanger samples with respect to the separation of highly active actinoid elements

    International Nuclear Information System (INIS)

    Treplan, J.

    1972-01-01

    Inorganic ion exchangers are of growing interest in connection with separation processes of α-radiators of high specific activity, or with high gamma doses, because they have a considerably higher radiation resistance at their disposal compared to the commonly used organic ion exchangers. In opposition to their use, however, are the worse properties regarding capacity, chemical resistivity, exchange rate and reproducibility of the ion exchange bed. In the present work, an attempt has been made to influence the properties of a typical representative of this group, zirconium phosphate (ZP), by systematic changing of the preparation parameters in such a manner that a sufficient capacity is obtained regarding tri-valent ions. In addition, information is to be gathered in order to clarify the connection between exchanger property and structure of the ZP. (orig./LH) [de

  3. A new concept of fast reactors, the potentialities of burning in them of actinoid and weapon-grade plutonium

    International Nuclear Information System (INIS)

    Murogov, V.M.; Troyanov, M.F.; Ilyunin, V.G.; Rudneva, V.Ya.

    1992-01-01

    The approach to a possible solution of the problem of peaceful utilization of weapon-grade plutonium released in the result of nuclear disarmament in Russia is given in the repot. As the most safe, ecologically acceptable and economically effective way of the plutonium utilization is the usage of such plutonium as a fuel for atomic power station. It is proposed to decide the problem on the basis of BN-600 and BN-800 reactors. In the approach, thorium could be used as a fertile material. The secondary nuclear fuel U-233 is expedient to use in light-water reactors of new generation. (author)

  4. Insulator–metal transition in a conservative system: An evidence for ...

    Indian Academy of Sciences (India)

    substrate, suggest that the mobility coalescence is responsible for the aging in island metal films. ... esting transition observed in a conservative system – after the stoppage of ... Oxidation of islands model and mobility coalescence model.

  5. The nonmetal-metal transition in solutions of metals in molten salts

    International Nuclear Information System (INIS)

    Tosi, M.P.

    1997-04-01

    Solutions of metals in molten salts present a rich phenomenology: localization of electrons in disordered ionic media, activated electron transport increasing with metal concentration towards a nonmetal-metal (NM-M) transition, and liquid-liquid phase separation. A brief review of progress in the study of these systems is given in this article, with main focus on the NM-M transition. After recalling the known NM-M behaviour of the component elements in the case of expanded fluid alkali metals and mercury and of solid halogens under pressure, the article focuses on liquid metal - molten salt solutions and traces the different NM-M behaviours of the alkalis in their halides and of metals added to polyvalent metal halides. (author). 51 refs, 2 figs

  6. Density measurements as a means for detection of semiconductor - metal transitions in melts of chalcogenide systems

    International Nuclear Information System (INIS)

    Thurn, H.; Ruska, J.

    1976-01-01

    It is reported on density measurements from liquidus temperature up to 900 or 1,000 0 C of a number of Se- or Te-containing liquid alloys. Anomalous density variations with temperature were found in many cases. The density measurements have been performed by a γ-ray absorption method. (orig./HK) [de

  7. Anomalous Insulator-Metal Transition in Boron Nitride-Graphene Hybrid Atomic Layers

    Science.gov (United States)

    2012-08-13

    Juan de la Cierva” pro- gram (JCI-2010-08156), Spanish MICINN (FIS2010-21282- C02-01 and PIB2010US-00652), ACI-Promociona (ACI2009- 1036), “ Grupos ...percolation through metallic graphene networks and hopping conduction between edge states on randomly distributed insulating h-BN domains. REPORT...Tallahassee, Florida 32310, USA 3Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Departamento de Fı́sica de Materiales, Centro de Fı́sica

  8. Hydrogenated Graphene Nanoflakes: Semiconductor to Half-Metal Transition and Remarkable Large Magnetism

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yungang; Wang, Zhiguo; Yang, Ping; Sun, Xin; Zu, Xiaotao; Gao, Fei

    2012-03-08

    The electronic and magnetic properties of graphene nanoflakes (GNFs) can be tuned by patterned adsorption of hydrogen. Controlling the H coverage from bare GNFs to half hydrogenated and then to fully hydrogenated GNFs, the transformation of small-gap semiconductor {yields} half-metal {yields} wide-gap semiconductor occurs, accompanied by a magnetic {yields} magnetic {yields} nonmagnetic transfer and a nonmagnetic {yields} magnetic {yields} nonmagnetic transfer for triangular and hexagonal nanoflakes, respectively. The half hydrogenated GNFs, associated with strong spin polarization around the Fermi level, exhibit the unexpected large spin moment that is scaled squarely with the size of flakes. The induced spin magnetizations of these nanoflakes align parallel and lead to a substantial collective character, enabling the half hydrogenated GNFs to be spin-filtering flakes. These hydrogenation-dependent behaviors are then used to realize an attractive approach to engineer the transport properties, which provides a new route to facilitate the design of tunable spin devices.

  9. Atomic structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)

    International Nuclear Information System (INIS)

    Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou

    2005-01-01

    The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed

  10. Crown ether complexes of lanthanoid and actinoid elements. Crystal and molecular structure of Nd(NO/sub 3/)/sub 3/(18-crown-6)

    Energy Technology Data Exchange (ETDEWEB)

    Bombieri, G; De Paoli, G; Benetollo, F [Consiglio Nazionale delle Ricerche, Padua (Italy). Lab. di Chimica e Tecnologia dei Radioelementi; Cassol, A [Padua Univ. (Italy)

    1980-01-01

    Nd(NO/sub 3/)/sub 3/.18-Crown-6 crystallizes in the orthorhombic system, space group Pbca with eight molecules in a cell of dimensions a = 15.512(9), b = 21.662(1), c = 12.141(6) A. The structure has been determined by Patterson heavy-atom methods and refined by full-matrix least squares to R = 0.038. The neodymium atom is coordinated by 6 oxygen atoms of the 18-crown-6 unit and by three bidentate nitrate groups; one on the more hindered side of the ring and two on the opposite side.

  11. Pressure induced Ag{sub 2}Te polymorphs in conjunction with topological non trivial to metal transition

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, J.; Zhang, S. J., E-mail: sjzhang@iphy.ac.cn, E-mail: jin@iphy.ac.cn; Yu, X. H.; Yu, R. C.; Jin, C. Q., E-mail: sjzhang@iphy.ac.cn, E-mail: jin@iphy.ac.cn; Dai, X.; Fang, Z. [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Oganov, A. R. [Department of Geosciences, University of New York at Stony Brook (United States); Feng, W. X.; Yao, Y. G. [Department of Physics, Beijing Institute of Technology, Beijing (China); Zhu, J. L. [High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154 (United States); Zhao, Y. S. [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); South University of Science and Technology of China, Shenzhen, Guangdong (China)

    2016-08-15

    Silver telluride (Ag{sub 2}Te) is well known as superionic conductor and topological insulator with polymorphs. Pressure induced three phase transitions in Ag{sub 2}Te have been reported in previous. Here, we experimentally identified high pressure phase above 13 GPa of Ag{sub 2}Te by using high pressure synchrotron x ray diffraction method in combination with evolutionary crystal structure prediction, showing it crystallizes into a monoclinic structure of space group C2/m with lattice parameters a = 6.081Å, b = 5.744Å, c = 6.797 Å, β = 105.53°. The electronic properties measurements of Ag{sub 2}Te reveal that the topologically non-trivial semiconducting phase I and semimetallic phase II previously predicated by theory transformed into bulk metals for high pressure phases in consistent with the first principles calculations.

  12. Femtosecond terahertz studies of many-body correlations. From ultrafast phonon-plasmon dynamics to an insulator-metal transition

    International Nuclear Information System (INIS)

    Kuebler, C.

    2007-01-01

    Phase-matched optical rectification together with standard EOS methods gives direct access to the real-time evolution of the electric field of ultrashort THz pulses. This opens up a new field of experiments, in which the complex dielectric function or equivalently the frequency-dependent conductivity of solid state systems is monitored resonantly throughout the MIR and FIR with a femtosecond temporal resolution. Optical rectification of amplified laser pulses allows for the generation of electric fields of several 10 kV cm-1 up to 1 MV cm-1, depending on the laser pulse energy. Such highly energetic field transients may be employed to coherently drive low-energy transitions into the nonlinear regime. The problems which are inherent to standard EOS, i.e. a fixed detector response and a limited bandwidth, are absent in phase-matched EOS. If this novel detection technique is combined with phase-matched optical rectification, an extremely versatile multi-THz spectrometer is obtained. The accessible frequency range is extended toward the near infrared. In addition, both the emission spectrum and the detector response may be custom tailored to fit specific spectroscopic requirements. Proper choice of the phasematching geometry eliminates multiple time delayed reflections of the main THz pulse, resulting in an essentially unlimited frequency resolution. In the context of optical pump - multi-THz probe experiments the implementation of a photoelastic modulator results in significant improvement of the signal-to-noise ratio: Balancing of the differential detector is rendered less critical and the measurement time in a 2D time-resolved experiment is reduced by up to two orders of magnitude. Finally, the combination of phase-matched optical rectification and phasematched electro-optic sampling shows great scaling potential with respect to both achieving higher field energies and shorter wavelengths. (orig.)

  13. Semiconductor-metal transitions in liquid In100-xSex alloys: A concentration-induced transition

    International Nuclear Information System (INIS)

    Ferlat, G.; San Miguel, A.; Xu, H.; Aouizerat, A.; Blase, X.; Zuniga, J.; Munoz-Sanjose, V.

    2004-01-01

    The electronic and structural properties of In 100-x Se x liquid alloys close to their melting points have been investigated by combining x-ray-absorption experiments with ab initio molecular-dynamics simulations. Extended x-ray-absorption fine-structure data have been acquired at both the In and Se K edges in a large concentration range (x=20% to x=50% of Se content). Ab initio molecular-dynamics simulations have been carried out at the two most extreme concentrations explored experimentally. Liquid InSe is found to retain a semiconducting behavior which results from a low-dimensional structure, reminiscent of that of the ambient solid phase, characterized by strong In-Se interactions within tetrahedral units. On the other side, the In 80 Se 20 liquid alloy shows a metalliclike behavior which is correlated to a more dense-packed structure

  14. Solid-gate control of insulator to 2D metal transition at SrTiO3 surface

    Science.gov (United States)

    Schulman, Alejandro; Stoliar, Pablo; Kitoh, Ai; Rozenberg, Marcelo; Inoue, Isao H.

    As miniaturization of the semiconductor transistor approaches its limit, semiconductor industries are facing a major challenge to extend information processing beyond what can be attainable by conventional Si-based transistors. Innovative combinations of new materials and new processing platforms are desired. Recent discovery of the 2D electron gas (2DEG) at the surface of SrTiO3 (STO) and its electrostatic control, have carried it to the top of promising materials to be utilized in innovative devices. We report an electrostatic control of the carrier density of the 2DEG formed at the channel of bilayer-gated STO field-effect devices. By applying a gate electric field at room temperature, its highly insulating channel exhibits a transition to metallic one. This transition is accompanied by non-monotonic voltage-gain transfer characteristic with both negative and positive slope regions and unexpected enhancement of the sheet carrier density. We will introduce a numerical model to rationalize the observed features in terms of the established physics of field-effect transistors and the physics of percolation. Furthermore, we have found a clear signature of a Kondo effect that arises due to the interaction between the dilute 2DEG and localized Ti 3d orbitals originated by oxygen vacancies near the channel. On leave from CIC nanoGUNE, Spain.

  15. Semiconductor-metal transition in CaMO3-CaTiO2 (M-Ru,Ir) systems

    International Nuclear Information System (INIS)

    Lazarev, V.B.; Shaplygin, I.S.

    1982-01-01

    Properties of CaRusub(x)Tisub(1-x)Osub(3) and CaIsub(2x)Tisub(1-x)Osub(3) solid solutions were studied in the whole range of concentrations by the methods of X-ray diffraction, electric conductivity and magnetic susceptibility. It was ascertained that the transition of semiconductor-metal type proceeded in the both families of solid solutions at x approximately 0.77 and 0.85 respectively and was accompanied by the change of structural type of solid solutions

  16. Reactivity of Heteropolytungstate and Heteropolymolybdate Metal Transition Salts in the Synthesis of Dimethyl Carbonate from Methanol and CO2

    Directory of Open Access Journals (Sweden)

    Amro Al-Amro

    2010-07-01

    Full Text Available A series of Keggin-type heteropoly compounds (HPC having different countercations (Co, Fe and different addenda atoms (W, Mo were synthesized and characterized by means of Fourier-Transform Infrared Spectrometer (FT-IR and X-ray powder diffraction (XRD. The catalytic properties of the prepared catalysts for the dimethyl carbonate (DMC synthesis from CO2 and CH3OH were investigated. The experimental results showed that the catalytic activity is significantly influenced by the type of the countercation and addenda atoms transition metal. Among the catalysts examined, Co1.5PW12O40 is the most active for the DMC synthesis, owing to the synergetic effect between Co and W. Investigating the effect of the support showed that the least acidic one (Al2O3 enhanced the conversion but decreased the DMC selectivity in favor of that of methyl formate (MF, while that of dimethoxy methane remained stable.

  17. Ultrafast Dynamics of the VO2 Insulator-to-Metal Transition Observed by Nondegenerate Pump-Probe Spectroscopy

    Directory of Open Access Journals (Sweden)

    Haglund R. F.

    2013-03-01

    Full Text Available Non-degenerate pump (1.5 eV-probe (0.4 eV transmission spectroscopy on vanadium dioxide films grown on glass and three different sapphire substrates shows systematic variations with substrate that correlate with VO2 grain size and laser fluence. Temperature dependent measurements showed changes in the electronic response that is proportional to the metallic fraction.

  18. Semiconductor to metallic transition in bulk accumulated amorphous indium-gallium-zinc-oxide dual gate thin-film transistor

    Directory of Open Access Journals (Sweden)

    Minkyu Chun

    2015-05-01

    Full Text Available We investigated the effects of top gate voltage (VTG and temperature (in the range of 25 to 70 oC on dual-gate (DG back-channel-etched (BCE amorphous-indium-gallium-zinc-oxide (a-IGZO thin film transistors (TFTs characteristics. The increment of VTG from -20V to +20V, decreases the threshold voltage (VTH from 19.6V to 3.8V and increases the electron density to 8.8 x 1018cm−3. Temperature dependent field-effect mobility in saturation regime, extracted from bottom gate sweep, show a critical dependency on VTG. At VTG of 20V, the mobility decreases from 19.1 to 15.4 cm2/V ⋅ s with increasing temperature, showing a metallic conduction. On the other hand, at VTG of - 20V, the mobility increases from 6.4 to 7.5cm2/V ⋅ s with increasing temperature. Since the top gate bias controls the position of Fermi level, the temperature dependent mobility shows metallic conduction when the Fermi level is above the conduction band edge, by applying high positive bias to the top gate.

  19. Semiconductor to metallic transition in bulk accumulated amorphous indium-gallium-zinc-oxide dual gate thin-film transistor

    Energy Technology Data Exchange (ETDEWEB)

    Chun, Minkyu; Chowdhury, Md Delwar Hossain; Jang, Jin, E-mail: jjang@khu.ac.kr [Advanced Display Research Center and Department of Information Display, Kyung Hee University, Seoul 130-701 (Korea, Republic of)

    2015-05-15

    We investigated the effects of top gate voltage (V{sub TG}) and temperature (in the range of 25 to 70 {sup o}C) on dual-gate (DG) back-channel-etched (BCE) amorphous-indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) characteristics. The increment of V{sub TG} from -20V to +20V, decreases the threshold voltage (V{sub TH}) from 19.6V to 3.8V and increases the electron density to 8.8 x 10{sup 18}cm{sup −3}. Temperature dependent field-effect mobility in saturation regime, extracted from bottom gate sweep, show a critical dependency on V{sub TG}. At V{sub TG} of 20V, the mobility decreases from 19.1 to 15.4 cm{sup 2}/V ⋅ s with increasing temperature, showing a metallic conduction. On the other hand, at V{sub TG} of - 20V, the mobility increases from 6.4 to 7.5cm{sup 2}/V ⋅ s with increasing temperature. Since the top gate bias controls the position of Fermi level, the temperature dependent mobility shows metallic conduction when the Fermi level is above the conduction band edge, by applying high positive bias to the top gate.

  20. Femtosecond terahertz studies of many-body correlations. From ultrafast phonon-plasmon dynamics to an insulator-metal transition

    Energy Technology Data Exchange (ETDEWEB)

    Kuebler, C.

    2007-07-30

    Phase-matched optical rectification together with standard EOS methods gives direct access to the real-time evolution of the electric field of ultrashort THz pulses. This opens up a new field of experiments, in which the complex dielectric function or equivalently the frequency-dependent conductivity of solid state systems is monitored resonantly throughout the MIR and FIR with a femtosecond temporal resolution. Optical rectification of amplified laser pulses allows for the generation of electric fields of several 10 kV cm-1 up to 1 MV cm-1, depending on the laser pulse energy. Such highly energetic field transients may be employed to coherently drive low-energy transitions into the nonlinear regime. The problems which are inherent to standard EOS, i.e. a fixed detector response and a limited bandwidth, are absent in phase-matched EOS. If this novel detection technique is combined with phase-matched optical rectification, an extremely versatile multi-THz spectrometer is obtained. The accessible frequency range is extended toward the near infrared. In addition, both the emission spectrum and the detector response may be custom tailored to fit specific spectroscopic requirements. Proper choice of the phasematching geometry eliminates multiple time delayed reflections of the main THz pulse, resulting in an essentially unlimited frequency resolution. In the context of optical pump - multi-THz probe experiments the implementation of a photoelastic modulator results in significant improvement of the signal-to-noise ratio: Balancing of the differential detector is rendered less critical and the measurement time in a 2D time-resolved experiment is reduced by up to two orders of magnitude. Finally, the combination of phase-matched optical rectification and phasematched electro-optic sampling shows great scaling potential with respect to both achieving higher field energies and shorter wavelengths. (orig.)

  1. Methods for separation of actinides

    International Nuclear Information System (INIS)

    Keller, C.

    1976-01-01

    Methods of actinoids separation are reviewed, including precipitation, sublimation, paper chromatography and electrophoresis. Compounds typically used for co-precipitation of actinoid ions are listed. Ion-exchange methods considered include cation and ion exchange. Factors are described, which affect the efficiency of separation of transuranium elements in the same degrees of oxidation: complex-forming agents, temperature, ion-exchange resin, rate of elution, the size of the column, the influence of salts. Extraction of actinoid ions upon formation of solvate complexes, inner complex compounds and metal salts is discussed. Combining the advantages of ion exchange and extraction, the method of extraction chromatography can be widely used for separation of actinoids

  2. Synchronous γ (Co60) photons and thermal processing induced insulator metal transition in amorphous chalcogenide As4Se3Te3 composition

    Science.gov (United States)

    El-Sayed, S. A.; Morsy, M. A.

    2018-05-01

    Amorphous chalcogenide composition AS4Se3Te3 is prepared by conventional quenching technique. The separate annealing or γ quanta irradiation not effect on the dc conductivity properties of the prepared composition. When the prepared samples are subjected to simultaneous annealing at temperature 413 K and γ quanta irradiation the dc conductivity increases. The dark dc conductivity increases by increasing the time of exposure to γ irradiation. At irradiation dose 1.47 × 104 Gy the dc conductivity starts to have metallic like conductivity character. These samples could be used as high temperature γ quanta dosimeter. By applying scaling theory on the samples irradiated with different dose of γ irradiation the critical exponents are determined and found to be temperature tends to zero. The steric value is low in the insulator side of conductivity, but high and almost saturated in the metallic side of conductivity.

  3. Theoretical formulation of optical conductivity of La0.7Ca0.3MnO3 exhibiting paramagnetic insulator - ferromagnetic metal transition

    Science.gov (United States)

    Satiawati, L.; Majidi, M. A.

    2017-07-01

    A theory of high-energy optical conductivity of La0.7Ca0.3MnO3 has been proposed previously. The proposed theory works to explain the temperature-dependence of the optical conductivity for the photon energy region above ˜0.5 eV for up to ˜22 eV, but fails to capture the correct physics close to the dc limit in which metal-insulator transition occurs. The missing physics at the low energy has been acknowledged as mainly due to not incorporating phonon degree of freedom and electron-phonon interactions. In this study, we aim to complete the above theory by proposing a more complete Hamiltonian incorporating additional terms such as crystal field, two modes of Jahn-Teller vibrations, and coupling between electrons and the two Jahn-Teller vibrational modes. We solve the model by means of dynamical mean-field theory. At this stage, we aim to derive the analytical formulae involved in the calculation, and formulate the algorithmic implementation for the self-consistent calculation process. Our final goal is to compute the density of states and the optical conductivity for the complete photon energy range from 0 to 22 eV at various temperatures, and compare them with the experimental data. We expect that the improved model preserves the correct temperature-dependent physics at high photon energies, as already captured by the previous model, while it would also reveal ferromagnetic metal - paramagnetic insulator transition at the dc limit.

  4. Tunable Q-switched erbium doped fiber laser based on metal transition oxide saturable absorber and refractive index characteristic of multimode interference effects

    Science.gov (United States)

    Mohammed, D. Z.; Khaleel, Wurood Abdulkhaleq; Al-Janabi, A. H.

    2017-12-01

    Ferro-oxide (Fe3O4) nanoparticles were used as a saturable absorber (SA) for a passively Q-switched erbium doped fiber laser (EDFL) with ring cavity. The Q-switching operation was achieved at a pump threshold of 80 mW. The proposed fiber laser produces stable pulses train of repetition rate ranging from 25 kHz to 80 kHz as the pump power increases from threshold to 342 mW. The minimum recorded pulse width was 2.7 μs at 342 mW. The C-band tunability operation was performed using single mode-multimode-single mode fiber (SM-MM-SM) structure. The laser exhibited a total tuning range of 7 nm, maximum sensitivity of 106.9 nm, optical signal to noise ratio (OSNR) of 38 dB and 3-dB linewidth of 0.06 nm.

  5. Size dependence of structural, magnetic, and electrical properties in corundum-type Ti2O3 nanoparticles showing insulator–metal transition

    Directory of Open Access Journals (Sweden)

    Yoshihiro Tsujimoto

    2015-09-01

    Full Text Available Corundum-type Ti2O3 has been investigated over the last half century because it shows unusual insulator–metal (I-M transition over a broad temperature range (420–550 K. In this work, we successfully synthesized Ti2O3 nanoparticles (20, 70, 300 nm in size by the low-temperature reduction between precursors of rutile-type TiO2 and the reductant CaH2, in a non-topotactic manner. The reaction time required for obtaining the reduced phase increases with increasing the particle size. Synchrotron X-ray powder diffraction and electron microscopy studies reveal that the symmetry of all the present samples remains the same as that of bulk samples. However, the particle-size reduction results in three important features compared with bulk samples as follows, (i color shift from dark brown to bluish black, (ii anisotropic volume contraction involving the shrinkage of Ti–Ti bonds in the ab plane and along the c axis, (iii reduction of the I-M transition temperature from 420 K to 350 K. These suggest that the a1g band broadening caused by the surface strain effects, which favors narrowing of the band gap, may play a critical role in the suppression of IM transition.

  6. Size dependence of structural, magnetic, and electrical properties in corundum-type Ti2O3 nanoparticles showing insulator–metal transition

    OpenAIRE

    Yoshihiro Tsujimoto; Yoshitaka Matsushita; Shan Yu; Kazunari Yamaura; Tetsuo Uchikoshi

    2015-01-01

    Corundum-type Ti2O3 has been investigated over the last half century because it shows unusual insulator–metal (I-M) transition over a broad temperature range (420–550 K). In this work, we successfully synthesized Ti2O3 nanoparticles (20, 70, 300 nm in size) by the low-temperature reduction between precursors of rutile-type TiO2 and the reductant CaH2, in a non-topotactic manner. The reaction time required for obtaining the reduced phase increases with increasing the particle size. Synchrotron...

  7. JENDL-4.0: A new library for nuclear science and engineering

    International Nuclear Information System (INIS)

    Shibata, Keiichi; Iwamoto, Osamu; Nakagawa, Tsuneo; Iwamoto, Nobuyuki; Ichihara, Akira; Kunieda, Satoshi; Chiba, Satoshi; Furutaka, Kazuyoshi; Katakura, Jun-ichi; Otuka, Naohiko; Ohsawa, Takaaki; Murata, Toru; Matsunobu, Hiroyuki; Zukeran, Atsushi; Kamada, So

    2011-01-01

    The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the improvements of fission product and minor actinoid data. Two nuclear model codes were developed in order to evaluate the cross sections of fission products and minor actinoids. Coupled-channel optical model parameters, which can be applied to wide mass and energy regions, were obtained for nuclear model calculations. Thermal cross sections of actinoids were carefully examined by considering experimental data or by the systematics of neighboring nuclei. Most of the fission cross sections were derived from experimental data. A simultaneous evaluation was performed for the fission cross sections of important uranium and plutonium isotopes above 10 keV. New evaluations were performed for the thirty fission-product nuclides that had not been contained in the previous library JENDL-3.3. The data for light elements and structural materials were partly reevaluated. Moreover, covariances were estimated mainly for actinoids. The new library was released as JENDL-4.0, and the data can be retrieved from the Web site of the JAEA Nuclear Data Center. (author)

  8. Biologically active compounds of semi-metals

    Czech Academy of Sciences Publication Activity Database

    Řezanka, Tomáš; Sigler, Karel

    2008-01-01

    Roč. 69, č. 3 (2008), s. 585-606 ISSN 0031-9422 Institutional research plan: CEZ:AV0Z50200510 Keywords : semi-metals * boron * silicon Subject RIV: CE - Biochemistry Impact factor: 2.946, year: 2008

  9. Bimodal nature in low-energy fission of light actinides

    International Nuclear Information System (INIS)

    Nagame, Yuichiro; Nishinaka, Ichiro; Tsukada, Kazuaki; Ikezoe, Hiroshi; Otsuki, Tsutomu; Sueki, Keisuke; Nakahara, Hiromichi; Kudo, Hisaaki.

    1995-01-01

    To solve various problems in the mass division process of light actinoids, some experiments on the basis of bimodal fission were carried. Mass and kinetic energy distribution of Th-232 and U-238 were determined. Pa-225 (N= 134) and Pa-227 (N=136), fission nuclei, were produced by Bi-209 + 0-16 and Bi-209 + 0-18 heavy ion nucleus reactions, and the mass yield distribution were determined by the time-of-flight method and the radiochemical procedure. From the results, two independent deforming processes were proved in the fission process of light actinoid nuclei. On the deforming process through the low fission barrier, nucleus fissioned after small deformation under the influence of stabilization of the shell structure of fission product. In the case of process through the high barrier, however, the nucleus fissioned after large deformation. The unsymmetrical mass division was derived from the former and the symmetrical one from the latter. (S.Y.)

  10. Anion exchange separation of the light lanthanoids with nitric acid-methyl alcohol mixed media at elevated temperature

    International Nuclear Information System (INIS)

    Usuda, S.; Magara, M.

    1987-01-01

    Anion exchange chromatography with nitric acid-methyl alcohol mixed media at elevated temperature was applied to mutual separation of the light lanthanoids, La, Ce, Pr, Nd and Pm. The individual elements could be effectively separated from each other, main fission products and actinoids with 0.01M HNO 3 -90% CH 3 OH or 0.5M HNO 3 -80% CH 3 OH eluent at 90 deg C. (author) 14 refs.; 3 tables

  11. The influence of ultrasound on the reduction of plutonium (4) by hydrazine and hydroxylamine in nitric acid and hydrochloric acid media

    International Nuclear Information System (INIS)

    Nikonov, M.V.; Shilov, V.P.

    1989-01-01

    Spectrophotometric method was used to study reduction of Pu(4) by hydrazine and hydroxylamine in HNO 3 and HCl solutions under the effect of ultrasonic waves at 18-20 deg C. It is shown that reaction of Pu(4) with hydrazine is accelerated in ultrasonic field approximately 10 times; ultrasound doesn't produce noticeable effect on behaviour of the actinoid in the case of hydroxylamine

  12. The possible effects of alfa and beta radiolysis on the matrix dissolution of spent nuclear fuel

    International Nuclear Information System (INIS)

    Grenthe, I.; Puigdomenech, I.; Bruno, J.

    1983-01-01

    The effects of oxidants on the retainment of actinides in a nuclear repository have been modelled by using an equilirium procedure. The oxidants are formed as a result of α- and #betta#-radiolysis when spent nuclear fuel is exposed to ground water. From an equilibrium point of view, the strongest reductants in the system (Zr, Pb and Cu) are expected to be oxidized first, leaving the actinoids in the oxidation states they have in the fuel matrix. This is expected to result in a negligible mobilization of the actinoids due to the very low solubility of the MO 2 oxides. However, the formation of protective layers of oxides will most likely decrease the effectiveness of the metallic reducing agents. This will lead to an increased oxidation of the spent fuel which results in an increased actinoid mobilization. The results of the equilibrium calculations show that the oxidation of the fuel matrix results in the formation of UO 2 (OH) 2 (s) and to the formation of the soluble complex UO 2 (CO 3 ) 3 4 . The transport of uranium is limited by the total concentration of carbonate in the aqueous phase. Neptunium may be quantitatvely solubilized as various Np(V) species and transported by ground water from the repository. Plutonium is retained at the repository site as insoluble PuO 2 . Only very small amounts are transported by ground water. The mobile actinoids may be reprecipitated when they encounter reducing conditions along the flow path. The conditions for repricipitation for typical ground water compositions have been modelled by using solubility - pe diagrams. (Authors)

  13. Experimental and computation method for determination of burnup and isotopic composition of the WWER-440 fuel using the 134Cs and 137Cs concentrations

    International Nuclear Information System (INIS)

    Babichev, B.A.; Kozharin, V.V.

    1990-01-01

    An experimental and computational method for determination of burnup and actinoid concentrations in WWER fuel elements using 134 Cs and 137 Cs concentrations in fuel is considered. It is shown that the error in calculation of fuel burnup and U and Pu isotope concentrations in WWER-440 fuel elements is 1.3-4.9% provided that the error in 134 Cs and 137 Cs concentration measurements does not exceed 1.7 and 1.2%. 9 refs.; 10 figs.; 4 tabs

  14. Radiation exposure from anthropogenic actinides in the northern Ukraine

    International Nuclear Information System (INIS)

    Hippler, Sven

    2006-01-01

    As a consequence of the Chernobyl accident, a large area of the northern Ukraine has been contaminated with many different radioactive substances to such an extent that the population hat to be evacuated. Officially, this exclusion still persists today. Meanwhile, people started returning to their dwellings without permission, and they continue living today within the contaminated area. This raises the question of how severe the radiation exposure to the illegal resettlers really is and of whether the restrictions are still justified. Currently, the radiation exposure is mainly being caused by 137 Cs and 90 Sr. But in the long-term, the influence of the long-living man-made actinoids will become important. In this study, their portion of the contamination of the evacuated area and the resulting contribution to the radiation exposure were examined in detail by considering the situation of the village Khristinovka as an example. For these purposes, many different environmental samples from Khristinovka (e.g. soil, food) have been analysed. The determination of the activity concentration of the actinoids was carried out by α-spectrometric measurements after radiochemical separations. Among the different man-made actinoids, only the nuclides 238 Pu, 239 Pu, 240 Pu and 241 Am are of immediate relevance. The most important actinoid is plutonium because of its slow migration in soil. Therefore, the long-living plutonium nuclides will contribute to the radiation exposure even when 90 Sr and 137 Cs will have decayed nearly completely. The observed deposition densities of (126 ± 7) Bq m -2 239, 240 Pu and (38.7 ± 3.4) Bq m -2 238 Pu are comparable to the official statements for this area. Thereby it is possible to distinguish between the contributions which originate from Chernobyl and the nuclear weapons fallout by means of the activity ratios between various radionuclides present. The additional annual dose to the general public of Khristinovka caused by man

  15. Pollution and the biological resources of the oceans

    National Research Council Canada - National Science Library

    Patin, Stanislav Aleksandrovich

    1982-01-01

    This book surveys and presents in a systematic manner, experimental work on the effects of the major classes of toxicants - heavy metals, transition metals, petroleum compounds, chlorine containing...

  16. Metal interactions with boron clusters

    International Nuclear Information System (INIS)

    Grimes, R.N.

    1982-01-01

    This book presents information on the following topics: the structural and bonding features of metallaboranes and metallacarboranes; transition-metal derivatives of nido-boranes and some related species; interactions of metal groups with the octahydrotriborate (1-) anion, B 3 H 8 ; metallaboron cage compounds of the main group metals; closo-carborane-metal complexes containing metal-carbon and metal-boron omega-bonds; electrochemistry of metallaboron cage compounds; and boron clusters with transition metal-hydrogen bonds

  17. Lattice Thermal Conductivity of Ultra High Temperature Ceramics ZrB2 and HfB2 from Atomistic Simulations

    Science.gov (United States)

    Lawson, John W.; Murray, Daw S.; Bauschlicher, Charles W., Jr.

    2011-01-01

    Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB2 and HfB2 for a range of temperatures. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations which can be identified with mixed metal-Boron optical phonon modes. Agreement with available experimental data is good.

  18. The future of urban waste water reuse. El futuro de la reutilizacion de las aguas residuales

    Energy Technology Data Exchange (ETDEWEB)

    Farias Iglesias, M. (PRIDESA. Madrid (Spain))

    1992-11-01

    An explanation is given for the interest in the re-use of urban waste water, together with the possible uses for it. Water quality parameters such as the quantity of material in suspension, fertilizers, heavy metals, boron, bacteria and viruses, salinity, toxicity and pathogenous agents are given for water to be re-used, whether it be for drinking purposes or industrial use. Consideration is also given to the possibility of injecting this water into aquifers. (Author)

  19. Magnetic Properties of Nanometer-sized Crystalline and Amorphous Particles

    DEFF Research Database (Denmark)

    Mørup, Steen; Bødker, Franz; Hansen, Mikkel Fougt

    1997-01-01

    Amorphous transition metal-metalloid alloy particles can be prepared by chemical preparation techniques. We discuss the preparation of transition metal-boron and iron-carbon particles and their magnetic properties. Nanometer-sized particles of both crystalline and amorphous magnetic materials...... are superparamagnetic at finite temperatures. The temperature dependence of the superparamagnetic relaxation time and the influence of inter-particle interactions is discussed. Finally, some examples of studies of surface magnetization of alpha-Fe particles are presented....

  20. Systematics of fission cross sections at the intermediate energy region

    Energy Technology Data Exchange (ETDEWEB)

    Fukahori, Tokio; Chiba, Satoshi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1997-03-01

    The systematics was obtained with fitting experimental data for proton induced fission cross sections of Ag, {sup 181}Ta, {sup 197}Au, {sup 206,207,208}Pb, {sup 209}Bi, {sup 232}Th, {sup 233,235,238}U, {sup 237}Np and {sup 239}Pu above 20 MeV. The low energy cross section of actinoid nuclei is omitted from systematics study, since the cross section has a complicated shape and strongly depends on characteristic of nucleus. The fission cross sections calculated by the systematics are in good agreement with experimental data. (author)

  1. Validation of methods for the determination of radium in waters and soil

    International Nuclear Information System (INIS)

    Decaillon, J.-G.; Bickel, M.; Hill, C.; Altzitzoglou, T.

    2004-01-01

    This article describes the advantages and disadvantages of several analytical methods used to prepare the alpha-particle source. As a result of this study, a new method combining commercial extraction and ion chromatography prior to a final co-precipitation step is proposed. This method has been applied and validated on several matrices (soil, waters) in the framework of international intercomparisons. The integration of this method in a global procedure to analyze actinoids and radium from a single solution (or digested soil) is also described

  2. Radioactive nuclides in nuclear reactors

    International Nuclear Information System (INIS)

    Akatsu, Eiko

    1982-12-01

    In the Nuclear Engineering School of JAERI, many courses are presented for the people working in and around nuclear reactors. The curricula of the courses contain also chemical subject materials. With reference to the foreign curricula, a plan of educational subject material of chemistry was considered for students of the school in the previous report (JAERI-M 9827), where the first part of the plan, ''Fundamentals of Reactor Chemistry'', was reviewed. This report is a review of the second part of the plan containing fission products chemistry, actinoids elements chemistry and activated reactor materials chemistry. (author)

  3. General chemistry

    International Nuclear Information System (INIS)

    Kwon, Yeong Sik; Lee, Dong Seop; Ryu, Haung Ryong; Jang, Cheol Hyeon; Choi, Bong Jong; Choi, Sang Won

    1993-07-01

    The book concentrates on the latest general chemistry, which is divided int twenty-three chapters. It deals with basic conception and stoichiometry, nature of gas, structure of atoms, quantum mechanics, symbol and structure of an electron of ion and molecule, chemical thermodynamics, nature of solid, change of state and liquid, properties of solution, chemical equilibrium, solution and acid-base, equilibrium of aqueous solution, electrochemistry, chemical reaction speed, molecule spectroscopy, hydrogen, oxygen and water, metallic atom; 1A, IIA, IIIA, carbon and atom IVA, nonmetal atom and an inert gas, transition metals, lanthanons, and actinoids, nuclear properties and radioactivity, biochemistry and environment chemistry.

  4. Present status of JENDL-4

    International Nuclear Information System (INIS)

    Shibata, Keiichi

    2009-01-01

    The fourth version of Japanese Evaluated Nuclear Data Library is being developed at the JAEA Nuclear Data Center in cooperation with the Japanese Nuclear Data Committee. As for actinides, we already released JENDL Actinoid File 2008, which contains the evaluated data for 79 nuclei. The high-energy cross sections of FP nuclei have been evaluated by using the CCONE and POD statistical model codes. The nuclear data for structural materials and light nuclei are being revised. The fission product yields were updated on the basis of ENDF/B-VII.0. Ternary fission was included in the yield data. (author)

  5. The use of Rich and Suter diagrams to explain the electron configurations of transition elements

    Energy Technology Data Exchange (ETDEWEB)

    Orofino, Hugo; Machado, Sergio P.; Faria, Roberto B., E-mail: faria@iq.ufrj.br [Instituto de Quimica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ (Brazil)

    2013-09-01

    Rich and Suter diagrams are a very useful tool to explain the electron configurations of all transition elements, and in particular, the s{sup 1} and s{sup 0} configurations of the elements Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, and Pt. The application of these diagrams to the inner transition elements also explains the electron configurations of lanthanoids and actinoids, except for Ce, Pa, U, Np, and Cm, whose electron configurations are indeed very special because they are a mixture of several configurations. (author)

  6. Evaluation of nuclear data of 244Pu and 237Pu

    International Nuclear Information System (INIS)

    Nakagawa, Tsuneo; Konshin, V.A.

    1995-10-01

    The evaluation of nuclear data for 244 Pu and 237 Pu was made in the neutron energy region from 10 -5 eV to 20 MeV. For the both nuclides, the total, elastic and inelastic scattering, fission, capture, (n,2n) and (n,3n) reaction cross sections were evaluated on the basis of theoretical calculation. The resonance parameters were given for 244 Pu. The angular and energy distributions of secondary neutrons were also estimated for the both nuclides. The results were compiled in the ENDF-5 format and will be adopted in JENDL Actinoid File. (author)

  7. Evaluation of nuclear data of {sup 244}Pu and {sup 237}Pu

    Energy Technology Data Exchange (ETDEWEB)

    Nakagawa, Tsuneo; Konshin, V.A. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1995-10-01

    The evaluation of nuclear data for {sup 244}Pu and {sup 237}Pu was made in the neutron energy region from 10{sup -5} eV to 20 MeV. For the both nuclides, the total, elastic and inelastic scattering, fission, capture, (n,2n) and (n,3n) reaction cross sections were evaluated on the basis of theoretical calculation. The resonance parameters were given for {sup 244}Pu. The angular and energy distributions of secondary neutrons were also estimated for the both nuclides. The results were compiled in the ENDF-5 format and will be adopted in JENDL Actinoid File. (author).

  8. The use of Rich and Suter diagrams to explain the electron configurations of transition elements

    Directory of Open Access Journals (Sweden)

    Hugo Orofino

    2013-01-01

    Full Text Available Rich and Suter diagrams are a very useful tool to explain the electron configurations of all transition elements, and in particular, the s¹ and s0 configurations of the elements Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, and Pt. The application of these diagrams to the inner transition elements also explains the electron configurations of lanthanoids and actinoids, except for Ce, Pa, U, Np, and Cm, whose electron configurations are indeed very special because they are a mixture of several configurations.

  9. Study on decay of rare earth nuclei produced by fission

    Energy Technology Data Exchange (ETDEWEB)

    Kawade, Kiyoshi; Yamamoto, Hiroshi; Shibata, Michihiro; Asai, Masato [Nagoya Univ. (Japan); Tsukada, Kazuaki; Osa, Akihiko; Shinohara, Nobuo; Iimura, Hideki

    1996-01-01

    JAERI-ISOL utilizes charge particle induced fission by proton and heavy proton produced by the tandem type accelerator (JAERI). To study the decay mechanism and nuclei structure of neutron and excess nuclei produced by actinoid fission, JAERI-ISOL was improved by developing the multilayer target tank. So that, the intensity of mass separated ion beam increased enough to use. New 76.6 KeV {gamma}-ray with about 10s of half life was found in the preliminary experiment. (S.Y.)

  10. Chemical Reduction of SIM MOX in Molten Lithium Chloride Using Lithium Metal Reductant

    Science.gov (United States)

    Kato, Tetsuya; Usami, Tsuyoshi; Kurata, Masaki; Inoue, Tadashi; Sims, Howard E.; Jenkins, Jan A.

    2007-09-01

    A simulated spent oxide fuel in a sintered pellet form, which contained the twelve elements U, Pu, Am, Np, Cm, Ce, Nd, Sm, Ba, Zr,Mo, and Pd, was reduced with Li metal in a molten LiCl bath at 923 K. More than 90% of U and Pu were reduced to metal to form a porous alloy without significant change in the Pu/U ratio. Small fractions of Pu were also combined with Pd to form stable alloys. In the gap of the porous U-Pu alloy, the aggregation of the rare-earth (RE) oxide was observed. Some amount of the RE elements and the actinoides leached from the pellet. The leaching ratio of Am to the initially loaded amount was only several percent, which was far from about 80% obtained in the previous ones on simple MOX including U, Pu, and Am. The difference suggests that a large part of Am existed in the RE oxide rather than in the U-Pu alloy. The detection of the RE elements and actinoides in the molten LiCl bath seemed to indicate that they dissolved into the molten LiCl bath containing the oxide ion, which is the by-product of the reduction, as solubility of RE elements was measured in the molten LiCl-Li2O previously.

  11. Complexometric determination of trivalent rare earths and actinides with diethylene-triaminepentaacetic acid

    International Nuclear Information System (INIS)

    Timofeev, G.A.; Simakin, G.A.; Baklanova, P.F.; Kuznetsov, G.F.; Ivanov, V.I.

    1976-01-01

    Optimal conditions have been found for the separate quantitative determination of 200 to 500 mcg of trivalent Eu, La, Nd, Pr, Am and Cm by complexometric titration with diethylenetriaminepentaacetic acid. The final titration point (FTP) has been determined by using one of the following three methods, namely by visual inspection with the aid of xylene orange as an indicator, spectrophotometrically at pH 4.5-4.7 with xylene orange and potentiometrically at pH 4.0-5.5 through the backward titration of the excess complexone with the solution of Fe(3) in HNO 3 . The relative standard errors Ssub(r)=0.004 (Eu), 0.011 Cm with the visual indication of FTP; Ssub(r)=0.005 (Am) with the spectrophotometric indication of FTP; Ssub(r)=0.0O9 (Eu), 0.011 (Pr) and 0.02 (Am) with the potentiometric indication of FTP. Determination of trivalent lanthanides and actinoids is adversely affected by tetravalent actinoids, Zr, U(6), Hg(2) and Fe(3). Titration conditions chosen have been checked in the analysis of the mixture containing the sum of trivalent rare earths, Am and Cm [ru

  12. Author Index 1227..1239

    Indian Academy of Sciences (India)

    Damping properties of epoxy-based composite embedded with ... triaxial porcelain composition. 897 ... Analysis on insulator–metal transition in yttrium doped .... TiO2/polyaniline core-shell nanocomposite .... filtration hollow fibre membranes.

  13. Subject Index 1207..1226

    Indian Academy of Sciences (India)

    Application of polyaniline/manganese dioxide composites for .... triaxial porcelain composition. 897 ... Analysis on insulator–metal transition in yttrium doped ... TiO2/polyaniline core-shell nanocomposite ..... filtration hollow fibre membranes.

  14. Bulletin of Materials Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Recent analytical applications of nanoparticle sensitized lucigenin and luminol ..... Analysis on insulator–metal transition in yttrium doped LSMO from electron ... Synthesis and luminescence properties of Eu-activated Ca4Mg5(PO4)6 for ...

  15. Bismuth-boron multiple bonding in BiB{sub 2}O{sup -} and Bi{sub 2}B{sup -}

    Energy Technology Data Exchange (ETDEWEB)

    Jian, Tian; Cheung, Ling Fung; Chen, Teng-Teng; Wang, Lai-Sheng [Department of Chemistry, Brown University, Providence, RI (United States)

    2017-08-01

    Despite its electron deficiency, boron is versatile in forming multiple bonds. Transition-metal-boron double bonding is known, but boron-metal triple bonds have been elusive. Two bismuth boron cluster anions, BiB{sub 2}O{sup -} and Bi{sub 2}B{sup -}, containing triple and double B-Bi bonds are presented. The BiB{sub 2}O{sup -} and Bi{sub 2}B{sup -} clusters are produced by laser vaporization of a mixed B/Bi target and characterized by photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra are obtained and interpreted with the help of ab initio calculations, which show that both species are linear. Chemical bonding analyses reveal that Bi forms triple and double bonds with boron in BiB{sub 2}O{sup -} ([Bi≡B-B≡O]{sup -}) and Bi{sub 2}B{sup -} ([Bi=B=Bi]{sup -}), respectively. The Bi-B double and triple bond strengths are calculated to be 3.21 and 4.70 eV, respectively. This is the first experimental observation of Bi-B double and triple bonds, opening the door to design main-group metal-boron complexes with multiple bonding. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Bismuth-boron multiple bonding in BiB_2O"- and Bi_2B"-

    International Nuclear Information System (INIS)

    Jian, Tian; Cheung, Ling Fung; Chen, Teng-Teng; Wang, Lai-Sheng

    2017-01-01

    Despite its electron deficiency, boron is versatile in forming multiple bonds. Transition-metal-boron double bonding is known, but boron-metal triple bonds have been elusive. Two bismuth boron cluster anions, BiB_2O"- and Bi_2B"-, containing triple and double B-Bi bonds are presented. The BiB_2O"- and Bi_2B"- clusters are produced by laser vaporization of a mixed B/Bi target and characterized by photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra are obtained and interpreted with the help of ab initio calculations, which show that both species are linear. Chemical bonding analyses reveal that Bi forms triple and double bonds with boron in BiB_2O"- ([Bi≡B-B≡O]"-) and Bi_2B"- ([Bi=B=Bi]"-), respectively. The Bi-B double and triple bond strengths are calculated to be 3.21 and 4.70 eV, respectively. This is the first experimental observation of Bi-B double and triple bonds, opening the door to design main-group metal-boron complexes with multiple bonding. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Microstructural characterization of as-cast hf-b alloys

    Directory of Open Access Journals (Sweden)

    João Carlos Jânio Gigolotti

    2012-04-01

    Full Text Available An accurate knowledge of several metal-boron phase diagrams is important to evaluation of higher order systems such as metal-silicon-boron ternaries. The refinement and reassessment of phase diagram data is a continuous work, thus the reevaluation of metal-boron systems provides the possibility to confirm previous data from an investigation using higher purity materials and better analytical techniques. This work presents results of rigorous microstructural characterization of as-cast hafnium-boron alloys which are significant to assess the liquid composition associated to most of the invariant reactions of this system. Alloys were prepared by arc melting high purity hafnium (minimum 99.8% and boron (minimum 99.5% slices under argon atmosphere in water-cooled copper crucible with non consumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy, using back-scattered electron image mode and X-ray diffraction. In general, a good agreement was found between our data and those from the currently accepted Hafnium-Boron phase diagram. The phases identified are αHfSS and B-RhomSS, the intermediate compounds HfB and HfB2 and the liquide L. The reactions are the eutectic L ⇔ αHfSS + HfB and L ⇔ HfB2 + B-Rhom, the peritectic L + HfB2 ⇔ HfB and the congruent formation of HfB2.

  18. Fiscal 1982 progress report of 'comprehensive research on the management of long-lived radioactive wastes' in the Research Center for Nuclear Science and Technology, University of Tokyo

    International Nuclear Information System (INIS)

    Sekiguchi, Akira; Kosako, Toshiso

    1983-01-01

    In the Research Center for Nuclear Science and Technology, University of Tokyo, the special research project ''Comprehensive Research on the Management of Long-lived Radioactive Wastes'' is carried out in the three-year period from fiscal 1982 to 1984. The works performed in the fiscal year 1982 are described individually, each short description on research purposes and contents, results, future plans, etc. the research works in the three fields of material science, biology and process technology are buffer materials in land disposal, canisters, corrosion of waste-container materials, thermal analysis of high-level wastes, effects of tritium on cells and marine life, biological effect of long-lived nuclides, separation of tritium wastes, actinoids and krypton-iodine, environmental migration of radionuclides, and accident analysis. (Mori, K.)

  19. Extraction chromatography of fission products

    International Nuclear Information System (INIS)

    Bonnevie-Svendsen, M.; Goon, K.

    1978-01-01

    Various cases of using extraction chromatography during analysis of fission products are reviewed. The use of the extraction chromatography method is considered while analysing reprocessed products of nuclear fuel for quantitative radiochemical analysis and control of fission product and actinoide separation during extraction and their chemical state in production solutions. The method is used to obtain pure fractions of typical burnup monitors (neodymium, molybdenum, cerium, cesium, europium, lanthanides) during determination of nuclear fuel burnup degree. While studying the nature of nuclear reactions the method is used to separate quickly short-life isotopes, to purify β-radiator fractions before measuring their half-life periods, to enrich isotopes forming with low output during fission. Examples of using extraction chromatography are given to separate long half-life or stable fission products from spent solutions, to control environment object contamination

  20. Complex chemistry of Np(V) in aqueous solutions

    International Nuclear Information System (INIS)

    Inoue, Yasushi

    1989-01-01

    Despite the importance of Np(V) in both the nuclear chemical engineering and the actinoid chemistry, little work has been performed on the complex chemistry of Np(V) in aqueous solutions, since Np(V) reacts less readily with various ligands. The author has directed his effort to understand the chemical behavior of Np(V) in aqueous solutions, especially the determination of the stability constants of Np(V) complexes with various ligands. A part of the results obtained so far is presented in the following order. (1) The synergistic extraction of Np(V) as a method for studying the complex chemistry of Np(V): TTA-MTOA(methyltrioctylammonium chloride), TTA-phen and TTA-TOPO. (2) The determination of the stability constants of Np(V) complexes with 22 organic- and 5 inorganic ligands by means of the solvent extraction. (3) The distribution of the chemical species of Np(V) in solutions under various conditions

  1. A report of the symposium on 'comprehensive research on the management of long-lived radioactive wastes' in the Research Center for Nuclear Science and Technology, University of Tokyo

    International Nuclear Information System (INIS)

    Sekiguchi, Akira; Naito, Keiji; Suzuki, Susumu; Furuya, Hirotaka; Sato, Masatomo.

    1983-01-01

    In the Research Center for Nuclear Science and Technology, University of Tokyo, the special research project ''Comprehensive Research on the Management of Long-lived Radioactive WasΩtes'' is carried out in the three-year period from fiscal 1982 to 1984. In this connection, a symposium has been held on January 25, 1983. Seven lectures given by the respective speakers are summarized individually: (1) the research of transuranic elements in educational institutions, (2) an outline of the actinoid research facilities planned in Tohoku University, (3) the radiation damage and leachability of glass solids, (4) the situation and trend in Japan and abroad of the disposal of long-lived nuclide wastes, (5) practical site tests concerning the geologic-formation disposal of low-level wastes, (6) the trend in the research of geologic formations for the disposal of high-level wastes, (7) the safety in the management of long-lived radioactive wastes. (Mori, K.)

  2. Interaction of neptunium(V) with polyacrylic acid

    International Nuclear Information System (INIS)

    Kubota, Takumi; Tochiyama, Osamu; Yamazaki, Hiromichi; Sato, Nobuharu

    1996-01-01

    For the quantitative description of the interaction of actinoids with humic substances, it is necessary to clarify the effects of both polyelectrolyte and heterogeneous nature of humic substances. To estimate these effects separately, polyacrylic acid has been selected as representative of well-defined, homogenous polymeric weak acids, and its interaction with Np(V) has been investigated by a solvent extraction method. By expressing the effective concentration of the complexing ligand by the concentration of ionized carboxylate groups, the apparent complex formation constant has been obtained at several pH, ionic strength and average molecular weights. The results indicated that the apparent complex formation constant varied with the degree of ionization(α) of polyacrylic acid and that the manner of variation resembled that of its apparent proton association constant. (author)

  3. Investigation and analytical application of thorium and uranium complexes with amino acids

    International Nuclear Information System (INIS)

    Korenman, I.M.; Sergeev, G.M.

    1979-01-01

    The coordination is investigated of thorium (4) and uranium (6) with aminoacids, particularly, with aspartic acid. With the latter the metals form chelates, which have a particular structure and a stationary inner sphere. A description is made of the composition, conditions of formation (gr H), and a stability of some asparaginate complexes of actinoids, the coordination methods of aspartic acid. An asparaginatometric method is proposed for a direct complexometric titration of microgram amounts of thorium in the presence of uranium, zirconium and rare earth elements with photometric indication. As metal-chromic indicators the sulfophthaleins are applied. The given procedure allows measurement of impurities of accompanying elements, viz., beryllium (up to 1%) in thorium preparations. Application of aspartic acid and arsenazo 1 indicator permits us to define Be(2) with a relative error not higher than 5% in thorium compounds, which exclude the analysis by other methods

  4. Electronic structure of nitrides PuN and UN

    Science.gov (United States)

    Lukoyanov, A. V.; Anisimov, V. I.

    2016-11-01

    The electronic structure of uranium and plutonium nitrides in ambient conditions and under pressure is investigated using the LDA + U + SO band method taking into account the spin-orbit coupling and the strong correlations of 5 f electrons of actinoid ions. The parameters of these interactions for the equilibrium cubic structure are calculated additionally. The application of pressure reduces the magnetic moment in PuN due to predominance of the f 6 configuration and the jj-type coupling. An increase in the occupancy of the 5 f state in UN leads to a decrease in the magnetic moment, which is also detected in the trigonal structure of the UN x β phase (La2O3-type structure). The theoretical results are in good agreement with the available experimental data.

  5. Method of processing radiation-contaminated organic polymer materials

    International Nuclear Information System (INIS)

    Kobayashi, Yoshii.

    1980-01-01

    Purpose: To process radiation contaminated organic high polymer materials with no evolution of toxic gases, at low temperature and with safety by hot-acid immersion process using sulfuric acid-hydrogen peroxide. Method: Less flammable or easily flammable organic polymers contaminated with radioactive substances, particularly with long life actinoid are heated and carbonized in concentrated sulfuric acid. Then, aqueous 30% H 2 O 2 solution is continuously added dropwise as an oxidizing agent till the solution turns colourless. If the carbonization was insufficient, addition of H 2 O 2 solution is stopped temporarily and the carbonization is conducted again. Thus, the organic polymers are completely decomposed by the wet oxidization. Then, the volume of the organic materials to be discharged is decreased and the radioactive substances contained are simultaneously concentrated and collected. (Seki, T.)

  6. Plasma Mass Filters For Nuclear Waste Reprocessing

    International Nuclear Information System (INIS)

    Fetterman, Abraham J.; Fisch, Nathaniel J.

    2011-01-01

    Practical disposal of nuclear waste requires high-throughput separation techniques. The most dangerous part of nuclear waste is the fission product, which contains the most active and mobile radioisotopes and produces most of the heat. We suggest that the fission products could be separated as a group from nuclear waste using plasma mass filters. Plasmabased processes are well suited to separating nuclear waste, because mass rather than chemical properties are used for separation. A single plasma stage can replace several stages of chemical separation, producing separate streams of bulk elements, fission products, and actinoids. The plasma mass filters may have lower cost and produce less auxiliary waste than chemical processing plants. Three rotating plasma configurations are considered that act as mass filters: the plasma centrifuge, the Ohkawa filter, and the asymmetric centrifugal trap.

  7. Immobilization of actinides in stable mineral type and ceramic materials (high temperature synthesis)

    Energy Technology Data Exchange (ETDEWEB)

    Starkov, O.; Konovalov, E.

    1996-05-01

    Alternative vitrification technologies are being developed in the world for the immobilization of high radioactive waste in materials with improved thermodynamic stability, as well as improved chemical and thermal stability and stability to radiation. Oxides, synthesized in the form of analogs to rock-forming minerals and ceramics, are among those materials that have highly stable properties and are compatible with the environment. In choosing the appropriate material, we need to be guided by its geometric stability, the minimal number of cations in the structure of the material and the presence of structural elements in the mineral that are isomorphs of uranium and thorium, actinoids found in nature. Rare earth elements, yttrium, zirconium and calcium are therefore suitable. The minerals listed in the table (with the exception of the zircon) are pegatites by origin, i.e. they are formed towards the end of the magma crystallization of silicates form the residual melt, enriched with Ta, Nb, Ti, Zr, Ce, Y, U and Th. Uranium and thorium in the form of isomorphic admixtures form part of the lattice of the mineral. These minerals, which are rather simple in composition and structure and are formed under high temperatures, may be viewed as natural physio-chemical systems that are stable and long-lived in natural environments. The similarity of the properties of actinoids and lanthanoids plays an important role in the geochemistry of uranium and thorium; however, uranium (IV) is closer to the {open_quotes}heavy{close_quotes} group of lanthanoids (the yttrium group) while thorium (IV) is closer to the {open_quotes}light{close_quotes} group (the cerium group). That is why rare earth minerals contain uranium and thorium in the form of isomorphic admixtures.

  8. The influence of nonlocal hybridization on ground-state properties of the Falicov-Kimball model

    International Nuclear Information System (INIS)

    Farkasovsky, Pavol

    2005-01-01

    The density matrix renormalization group is used to examine effects of nonlocal hybridization on ground-state properties of the Falicov-Kimball model (FKM) in one dimension. Special attention is devoted to the problem of hybridization-induced insulator-metal transition. It is shown that the picture of insulator-metal transitions found for the FKM with nonlocal hybridization strongly differs from one found for the FKM without hybridization (as well as with local hybridization). The effect of nonlocal hybridization is so strong that it can induce the insulator-metal transition, even in the half-filled band case where the ground states of the FKM without hybridization are insulating for all finite Coulomb interactions. Outside the half-filled band case the metal-insulator transition driven by pressure is found for finite values of nonlocal hybridization

  9. X-ray diffraction study on pressure-induced phase transformation in nanocrystalline GaAs

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Olsen, J. S.; Gerward, Leif

    2002-01-01

    We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two-component ......We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two...

  10. Silver(I) and copper(I) complexes with the closo-decaborate anion B10H102- as a ligand

    International Nuclear Information System (INIS)

    Malinina, E.A.; Zhizhin, K.Yu.; Polyakova, I.N.; Lisovskij, M.V.; Kuznetsov, N.T.

    2002-01-01

    Studying the process of silver(I) and copper(I) complexing with closo-borate anion B 10 H 10 2- it is determined that the last can to play a role of intraspherical ligand forming stable coordination compounds of two types: Cat[MB 10 H 10 ] and [M 2 B 10 H 10 ] (M=Ag(I), Cu(I)). In these compounds the bond metal-boron skeleton is realized by means of formation of three-center bonds M-H-B. Structure of the complexes Cs[AgB 10 H 10 ] and [(C 2 H 5 ) 3 NH][AgB 10 H 10 ] and possible mechanism of their formation are discussed [ru

  11. Onset of itinerant ferromagnetism associated with semiconductor ...

    Indian Academy of Sciences (India)

    In this paper, the magnetic and transport properties of the TiNb1−CoSn solid solution compounds with half Heusler cubic MgAgAs-type structure have been studied. This work shows the onset of ferromagnetism associated with a semiconductor to metal transition. The transition occurs directly from ferromagnetic metal to ...

  12. Femtosecond Near Edge X-ray Absorption Measurement of the VO2 Phase Transition

    International Nuclear Information System (INIS)

    Cavalleri, A.; Chong, H.H.W.; Fourmaux, S.; Glover, T.E.; Heimann, P.A; Kieffer, J.C.; Padmore, H.A.; Schoenlein, R.W.

    2004-01-01

    The authors measure the insulator-to-metal transition in VO 2 using femtosecond Near-Edge X-ray Absorption. Sliced pulses of synchrotron radiation are used to detect the photo-induced dynamics at the 516-eV Vanadium L 3 edge

  13. Strain, size and field effects in (La,Ca)MnO3 thin films

    NARCIS (Netherlands)

    Beekman, Christianne

    2010-01-01

    Doped manganese oxides such as La0.67Ca0.33MnO3 (LCMO) are strongly correlated electron systems which display an insulator to metal transition upon cooling at a temperature T_MI. At low temperature the material is ferromagnetic. Above the transition the material is a paramagnetic insulator in which

  14. Adlayer Core-Level Shifts of Random Metal Overlayers on Transition-Metal Substrates

    DEFF Research Database (Denmark)

    Ganduglia-Pirovano, M. V.; Kudrnovský, J.; Scheffler, M.

    1997-01-01

    and the screening effects induced by the core hole, and study the influence of the alloy composition for a number of noble metal-transition metal systems. Our analysis clearly indicates the importance of final-state screening effects for the interpretation of measured core-level shifts. Calculated deviations from...

  15. Bulletin of Materials Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Gold–gold sulfide core-shell nanorods exhibited a number of optical absorption peaks which arose because of their structural characteristics. ... Optical properties of iron core–iron oxide shell nanocomposites when analysed by effective medium theory led to the result of a metal non-metal transition for particle diameters ...

  16. Report of short term research group on environment safety in nuclear fuel cycle, 1983

    International Nuclear Information System (INIS)

    1984-01-01

    The research group on environment safety in nuclear fuel cycle was organized in fiscal 1979 as the research group in the range of the common utilization of Yayoi, and this is the third year since it developed into the short term research group in the Nuclear Engineering Research Laboratory. The results obtained so far were summarized in three reports, UTNL-R110, 134 and 147. In this fiscal year, ''The chemistry of reprocessing'' is the subtheme, and this short term research is to be carried out. The meeting is held on March 23 and 24, 1984, in this Laboratory, and the following reports are presented. The conference on institutional stability and the disposal of nuclear and chemically toxic wastes held at MIT, the social scientific analysis of nuclear power development, the present status of reprocessing research in foreign countries, the problems based on the operation experience of actual plants, the chemistry of fuel dissolution, the chemistry of solvent extraction, reprocessing offgas treatment and problems, the chemistry of fixing Kr and I in zeolite, waste treatment in the Tokai Reprocessing Plant of Power Reactor and Nuclear Fuel Development Corp., the chemistry of actinoids, denitration process and the chemistry of MOX production, and future reprocessing research. (Kako, I.)

  17. Annual report of JMTR, No.14. FY1999 (April 1, 1999 - March 31, 2000)

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-03-01

    During the FY1999 (April 1999 to March 2000), the JMTR (Japan Materials Testing Reactor) was operated 5 operation cycles (130 days) for irradiation studies on the IASCC of the LWR materials, power ramp tests of high burn-up BWR fuels, development of actinoid contained uranium-hydride fuels, development of fusion blanket materials, and so on. Total number of capsules and hydraulic rabbits irradiated were 138 and 80, respectively. Technology development programs were conducted in the following fields. As concerning to the utilization of JMTR, improvements were made in local gamma spectrum evaluation technique and advanced oxygen potential sensor for the fuel irradiation. Remote controlled high temperature fatigue test machine was developed at the hot laboratories. Efficient production process was developed for new pebble type tritium breeder material for fusion reactor blanket, and tritium generation/recovery behavior was investigated under irradiation using pebble packed test piece. This report summarizes these activities performed in the department of JMTR during the FY1999. (author)

  18. Sorption of uranium on rocks in anaerobic groundwater

    International Nuclear Information System (INIS)

    Hakanen, M.

    1992-12-01

    Spent nuclear fuel contains substantial amounts of long lived isotopes of actinoide elements, the most abundant of which is the oxide from uranium in the fuel matrix. The behaviour of uranium, also present in small concentrations in natural rocks and waters, is redox sensitive. The concentration controlling mechanisms in groundwaters of uranium are not well-known. In this work a series of laboratory experiments was made to study the redox and sorption behaviour of uranium under anaerobic conditions. The experiments indicated that a part of uranium(VI) was reduced to uranium(IV). The sorbed uranium was of mixed oxidation states. The redox potential of water was not an appropriate indicator of the U(IV)/U(VI) ratio. Spiking of the water with the U(IV) was followed by very strong sorption. The derived lower limit (conservative) and the realistic mass distribution ratios (R d ) for U(IV) are 0.7 m 3 /kg and 3.5 m 3 /kg. (orig.)

  19. JENDL special purpose file

    International Nuclear Information System (INIS)

    Nakagawa, Tsuneo

    1995-01-01

    In JENDL-3,2, the data on all the reactions having significant cross section over the neutron energy from 0.01 meV to 20 MeV are given for 340 nuclides. The object range of application extends widely, such as the neutron engineering, shield and others of fast reactors, thermal neutron reactors and nuclear fusion reactors. This is a general purpose data file. On the contrary to this, the file in which only the data required for a specific application field are collected is called special purpose file. The file for dosimetry is a typical special purpose file. The Nuclear Data Center, Japan Atomic Energy Research Institute, is making ten kinds of JENDL special purpose files. The files, of which the working groups of Sigma Committee are in charge, are listed. As to the format of the files, ENDF format is used similarly to JENDL-3,2. Dosimetry file, activation cross section file, (α, n) reaction data file, fusion file, actinoid file, high energy data file, photonuclear data file, PKA/KERMA file, gas production cross section file and decay data file are described on their contents, the course of development and their verification. Dosimetry file and gas production cross section file have been completed already. As for the others, the expected time of completion is shown. When these files are completed, they are opened to the public. (K.I.)

  20. Extraction of transplutonium elements from carbonate solutions by alkylpyrocatechol

    International Nuclear Information System (INIS)

    Karalova, Z.K.; Myasoedov, B.F.; Rodionova, L.M.; Kuznetsova, V.S.

    1983-01-01

    Extraction of americium, berkelium as well as Ce, Eu, Th, U, Zr, Cs, Fe with solution of 4(α, α-dioctylethyl)pyrocatechol (DOP) in toluene from carbonate solutions to determine conditions of their separation has been studied. It is established that americium extraction is quite sensitive to the changes of potassium carbonate concentration. The maximum extraction of americium (R >90%) is observed in the case of 0.1-0.5 mol/l of K 2 CO 3 solutions and the minimum one (R=2.5%) - in the case of 8 mol/l K 2 CO 3 . Americium extraction increases sharply when sodium hydroxide is introduced in carbonate solutions. It is shown that varying sodium hydroxide concentration it is possible to achieve qualitative extraction of americium even from saturated solution of potassium carbonate. Reextraction of TPE is easily realized with 3 mol/l HCl solution. The system K 2 CO 3 (KOH)-DOP proved to be perspective for Am separation from Bk, Ce, Cs, actinoid elements as well as from Fe

  1. A research paper of 'the basic sciences of the radioactive waste treatment' (Jul. 28,29, 1994) and 'Interface and surface science of solid waste processing and disposal -differences between cement and bentonite' (Dec. 14, 1995)

    International Nuclear Information System (INIS)

    1995-12-01

    This report contains copies of OHP at the meetings of which discussions were centered upon the points of sameness and difference between cement and bentonite. There are sixteen papers, eleven in the first meeting and five in the second one. The following studies were read as under, on the first meeting, the role of retardation effect on the safety of high level atomic waste stratum processing, determination of colloid particle diameters by use of fieldflow fractionation, adsorption behavior of uranium, into black mica in granite, masstransfer mechanism of Cs and Se in the compression-bentonite, delay mechanism under conditions of mineral alteration, effects of humus on the behavior of radionuclides in stratum, formation of actinoids - humic acid complex and its effect on adsorption behavior, characteristic properties of water in bentonite, measurement of solubility of uranium and niobium, behavior of colloidal Am in the bentonite, illite - water system, effects of aging deterioration of bentonite on diffusion of nuclides, and on the second meeting, a view of cement materials, chemical behavior and long period stability of cement - relating to Atkinson model -, the present conditions of studies about sorption in cement, chemical properties of pore water in bentonite and interaction of bentonite and nuclides in solid - liquid interface. (S.Y.)

  2. Lipoquinones of some spore-forming rods, lactic-acid bacteria and actinomycetes.

    Science.gov (United States)

    Hess, A; Holländer, R; Mannheim, W

    1979-11-01

    The respiratory quinones of 73 strains of Gram-positive bacteria including spore-forming rods, lactic-acid bacteria and actinomyctes were examined. Menaquinones with seven isoprenoid units (MK-7) were the main quinone type found in representatives of the genus Bacillus and in Sporolactobacillus inulinus. However, a strain of B. thuringiensis produced MK-8 in addition to MK-7, and strains of B. lentus and B. pantothenticus appeared to produce MK-9 and MK-8, respectively, with no MK-7. In the clostridia and lactic-acid bacteria, no quinones were found, except in Pediococcus cerevisiae NCTC 8066 and Lactobacillus casei subsp. rhamnosus ATCC 7469, which contained menaquinones, and Streptococcus faecalis NCTC 775 and HIM 478-1, which contained demethylmenaquinones, in relatively low concentrations. Menaquinones were also found in the actinomycetes (except Actinomyces odontolyticus and Bifidobacterium bifidum which did not produce any quinones) and in Protaminobacter alboflavus ATCC 8458, the so-called Actinobacillus actinoides ATCC 15900 and Noguchia granulosis NCTC 10559.

  3. Phthalocyaninato complexes of thorium, protactinium and uranium

    International Nuclear Information System (INIS)

    Beck, O.F.

    1985-01-01

    For the preparation of Bis(phthalocyaninato)-actinoid(IV) complexes, AnPc 2 , a new optimizing synthesis procedure was developed, with which it was possible to prepare spectrally pure, that is, H 2 Pc-free, ThPc 2 , UPc 2 and the isostructurally similar 231 PaPc 2 .PaPc 2 . This was verified with the help of electron spectra, which were compared to preparations which were synthesized in another manner. The corresponding perfluorinated compounds were also produced for thorium and uranium by use of tetrafluorophthalic acid nitrile instead of phthalic acid nitrile as initial product. Electron and infrared spectra show the typical bands of the non-substituted complexes. By the attempt to produce a mono(phthalocyaninato)-thorium complex with the use of ThI 4 as initial material a pyridine-extracted pure ThPcI 2 (py) 2 was obtained with a typical mono(phthalocyaninato) complex electron spectrum, an extremely moisture sensitive compound which in water or acids decomposes and produces H 2 Pc. (orig./RB) [de

  4. A research paper of `the basic sciences of the radioactive waste treatment` (Jul. 28,29, 1994) and `Interface and surface science of solid waste processing and disposal -differences between cement and bentonite` (Dec. 14, 1995)

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-12-01

    This report contains copies of OHP at the meetings of which discussions were centered upon the points of sameness and difference between cement and bentonite. There are sixteen papers, eleven in the first meeting and five in the second one. The following studies were read as under, on the first meeting, the role of retardation effect on the safety of high level atomic waste stratum processing, determination of colloid particle diameters by use of fieldflow fractionation, adsorption behavior of uranium, into black mica in granite, masstransfer mechanism of Cs and Se in the compression-bentonite, delay mechanism under conditions of mineral alteration, effects of humus on the behavior of radionuclides in stratum, formation of actinoids - humic acid complex and its effect on adsorption behavior, characteristic properties of water in bentonite, measurement of solubility of uranium and niobium, behavior of colloidal Am in the bentonite, illite - water system, effects of aging deterioration of bentonite on diffusion of nuclides, and on the second meeting, a view of cement materials, chemical behavior and long period stability of cement - relating to Atkinson model -, the present conditions of studies about sorption in cement, chemical properties of pore water in bentonite and interaction of bentonite and nuclides in solid - liquid interface. (S.Y.)

  5. XAS study of the local environment of impurities in doped TiO{sub 2} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez Torres, C.E. [Departamento de Fisica e IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (Argentina)]. E-mail: torres@fisica.unlp.edu.ar; Cabrera, A.F. [Departamento de Fisica e IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (Argentina); Errico, L.A. [Departamento de Fisica e IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (Argentina); Duhalde, S. [Lab. de Ablacion Laser, FI-UBA (Argentina); Renteria, M. [Departamento de Fisica e IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (Argentina); Golmar, F. [Lab. de Ablacion Laser, FI-UBA (Argentina); Sanchez, F.H. [Departamento de Fisica e IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (Argentina)

    2007-09-01

    In this work, we present an X-ray absorption spectroscopy (XAS) characterization of the local environment of the impurity in room temperature ferromagnetic (RTF) anatase TiO{sub 2} thin films doped with Co, Ni, Cu, or Zn, deposited on LaAlO{sub 3} substrate by pulsed laser deposition (PLD). It was found that there is a considerable amount of impurity atoms substituting Ti in TiO{sub 2} anatase, although the presence of metal transition monoxide clusters can not be discarded. From our results, we infer that the observed RT ferromagnetism of the samples could be assigned to the metal transition atoms replacing Ti in TiO{sub 2} anatase.

  6. Austenitic stainless steel-to-ferritic steel transition joint welding for elevated temperature service

    International Nuclear Information System (INIS)

    King, J.F.; Goodwin, G.M.; Slaughter, G.M.

    1978-01-01

    Transition weld joints between ferritic steels and austenitic stainless steels are required for fossil-fired power plants and proposed nuclear plants. The experience with these dissimilar-metal transition joints has been generally satisfactory, but an increasing number of failures of these joints is occurring prematurely in service. These concerns with transition joint service history prompted a program to develop more reliable joints for application in proposed nuclear power plants

  7. Attosecond Electron Processes in Materials: Excitons, Plasmons, and Charge Dynamics

    Science.gov (United States)

    2015-05-19

    focused using a f=1.5 m lens into a 250 micron hollow core fiber (HCF) filled with neon gas at atmospheric pressure to stretch the pulse spectrum from... insulator to metal transition. Introduction: The goal of this work was to understand the generation, transport, and manipulation of electronic charge...chemically sensitive probe pulse utilizing specific core level transitions in atoms that are part of a material under study. The measurements follow

  8. The electron spin resonance study of heavily nitrogen doped 6H SiC crystals

    Czech Academy of Sciences Publication Activity Database

    Savchenko, Dariia

    2015-01-01

    Roč. 117, č. 4 (2015), "045708-1"-"045708-6" ISSN 0021-8979 R&D Projects: GA ČR GP13-06697P; GA MŠk(CZ) LM2011029 Grant - others:SAFMAT(XE) CZ.2.16/3.1.00/22132 Institutional support: RVO:68378271 Keywords : electron spin resonance * conduction electrons * 6H SiC * insulator-metal transition Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.101, year: 2015

  9. Herstellung und Untersuchung metallischer Einzel-Elektronen-Transistoren

    OpenAIRE

    Hofmann, Karl

    2001-01-01

    Single-electron transistors (SETs) are quantum devices and are based on the controlling of the Coulomb blockade. They are the ultimate development of low-power devices with an extreme high potential of integration. Their dominant purpose is seen in future memory devices. Usually the key element of all metallic SETs is a tunnel junction consisting of a metal-insulator-metal transition. In this current thesis the microscopic and electrical investigations of e-gun evaporated titanium thin films ...

  10. Self-limiting filters for band-selective interferer rejection or cognitive receiver protection

    Science.gov (United States)

    Nordquist, Christopher; Scott, Sean Michael; Custer, Joyce Olsen; Leonhardt, Darin; Jordan, Tyler Scott; Rodenbeck, Christopher T.; Clem, Paul G.; Hunker, Jeff; Wolfley, Steven L.

    2017-03-07

    The present invention related to self-limiting filters, arrays of such filters, and methods thereof. In particular embodiments, the filters include a metal transition film (e.g., a VO.sub.2 film) capable of undergoing a phase transition that modifies the film's resistivity. Arrays of such filters could allow for band-selective interferer rejection, while permitting transmission of non-interferer signals.

  11. Self-limiting filters for band-selective interferer rejection or cognitive receiver protection

    Energy Technology Data Exchange (ETDEWEB)

    Nordquist, Christopher; Scott, Sean Michael; Custer, Joyce Olsen; Leonhardt, Darin; Jordan, Tyler Scott; Rodenbeck, Christopher T.; Clem, Paul G.; Hunker, Jeff; Wolfley, Steven L.

    2017-03-07

    The present invention related to self-limiting filters, arrays of such filters, and methods thereof. In particular embodiments, the filters include a metal transition film (e.g., a VO.sub.2 film) capable of undergoing a phase transition that modifies the film's resistivity. Arrays of such filters could allow for band-selective interferer rejection, while permitting transmission of non-interferer signals.

  12. Quantum molecular dynamics simulations of thermophysical properties of fluid ethane

    OpenAIRE

    Zhang, Yujuan; Wang, Cong; Zheng, Fawei; Zhang, Ping

    2012-01-01

    We have performed first-principles molecular-dynamics simulations based on density-functional theory to study the thermophysical properties of ethane under extreme conditions. We present new results for the equation of state of fluid ethane in the warm dense region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity and optical reflectivity are derived. The close correlation between the nonmetal-metal transition of ethane and its decomposition...

  13. High pressure metallization of Mott Insulators: Magnetic, structural and electronic properties

    International Nuclear Information System (INIS)

    Pasternak, M.P.; Hearne, G.; Sterer, E.; Taylor, R.D.; Jeanloz, R.

    1993-01-01

    High pressure studies of the insulator-metal transition in the (TM)I 2 (TM = V, Fe, Co and Ni) compounds are described. Those divalent transition-metal iodides are structurally isomorphous and classified as Mott Insulators. Resistivity, X-ray diffraction and Moessbauer Spectroscopy were employed to investigate the electronic, structural, and magnetic properties as a function of pressure both on the highly correlated and on the metallic regimes

  14. High Pressure Optical Studies of the Thallous Halides and of Charge-Transfer Complexes

    Science.gov (United States)

    Jurgensen, Charles Willard

    High pressure was used to study the insulator -to-metal transition in sulfur and the thallous halides and to study the intermolecular interactions in charge -transfer complexes. The approach to the band overlap insulator -to-metal transition was studied in three thallous halides and sulfur by optical absorption measurements of the band gap as a function of pressure. The band gap of sulfur continuously decreases with pressure up to the insulator -to-metal transition which occurs between 450 and 485 kbars. The results on the thallous halides indicate that the indirect gap decreases more rapidly than the direct gap; the closing of the indirect gap is responsible for the observed insulator -to-metal transitions. High pressure electronic and vibrational spectroscopic measurements on the solid-state complexes of HMB-TCNE were used to study the intermolecular interactions of charge -transfer complexes. The vibrational frequency shifts indicate that the degree of charge transfer increases with pressure which is independently confirmed by an increase in the molar absorptivity of the electronic charge-transfer peak. Induction and dispersion forces contribute towards a red shift of the charge-transfer peak; however, charge-transfer resonance contributes toward a blue shift and this effect is dominant for the HMB-TCNE complexes. High pressure electronic spectra were used to study the effect of intermolecular interactions on the electronic states of TCNQ and its complexes. The red shifts with pressure of the electronic spectra of TCNQ and (TCNQ)(' -) in polymer media and of crystalline TCNQ can be understood in terms of Van der Waals interactions. None of the calculations which considered intradimer distance obtained the proper behavior for either the charge-transfer of the locally excited states of the complexes. The qualitative behavior of both states can be interpreted as the effect of increased mixing of the locally excited and charge transfer states.

  15. The complex metal-rich boride Ti{sub 1+x}Rh{sub 2-x+y}Ir{sub 3-y}B{sub 3} (x=0.68, y=1.06) with a new structure type containing B{sub 4} zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

    Energy Technology Data Exchange (ETDEWEB)

    Goerens, Christian [Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52064 Aachen (Germany); Fokwa, Boniface P.T., E-mail: boniface.fokwa@ac.rwth-aachen.de [Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52064 Aachen (Germany)

    2012-08-15

    Polycrystalline samples and single crystals of the new complex boride Ti{sub 1+x}Rh{sub 2-x+y}Ir{sub 3-y}B{sub 3} (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B{sub 4} fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1) A, b=14.995(2) A and c=3.234(1) A. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron-boron interactions are observed in the trans zigzag B{sub 4} fragment, which induce a clear differentiation of two types of metal-boron contacts with different strength. The observed three-dimensional metal-metal interaction is in good agreement with the predicted metallic behavior. - graphical abstract: The structure of Ti{sub 1.68(2)}Rh{sub 2.38(6)}Ir{sub 1.94(4)} B{sub 3}, a new structure type containing planar trans zigzag B{sub 4} units, is another example which illustrates the tendency of metal-rich borides to form B-B bonds with increasing boron content. Beside the B{sub 4} fragment it exhibits one-dimensional chains of titanium atoms and hold one-dimensional strings of face-sharing empty tetrahedral and square pyramidal clusters (see figure). Highlights

  16. Temperature dependent dual hydrogen sensor response of Pd nanoparticle decorated Al doped ZnO surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, D.; Barman, P. B.; Hazra, S. K., E-mail: surajithazra@yahoo.co.in [Department of Physics and Materials Science, Jaypee University of Information Technology, Waknaghat, Solan, Himachal Pradesh-173234 (India); Dutta, D. [IC Design and Fabrication Centre, Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata-700032 (India); Kumar, M.; Som, T. [SUNAG Laboratory, Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India)

    2015-10-28

    Sputter deposited Al doped ZnO (AZO) thin films exhibit a dual hydrogen sensing response in the temperature range 40 °C–150 °C after surface modifications with palladium nanoparticles. The unmodified AZO films showed no response in hydrogen in the temperature range 40 °C–150 °C. The operational temperature windows on the low and high temperature sides have been estimated by isolating the semiconductor-to-metal transition temperature zone of the sensor device. The gas response pattern was modeled by considering various adsorption isotherms, which revealed the dominance of heterogeneous adsorption characteristics. The Arrhenius adsorption barrier showed dual variation with change in hydrogen gas concentration on either side of the semiconductor-to-metal transition. A detailed analysis of the hydrogen gas response pattern by considering the changes in nano palladium due to hydrogen adsorption, and semiconductor-to-metal transition of nanocrystalline Al doped ZnO layer due to temperature, along with material characterization studies by glancing incidence X-ray diffraction, atomic force microscopy, and transmission electron microscopy, are presented.

  17. The Raman spectrum and lattice parameters of MgB2 as a function of temperature

    International Nuclear Information System (INIS)

    Shi Lei; Zhang Huarong; Chen Lin; Feng Yong

    2004-01-01

    The temperature dependences of the Raman spectrum and lattice parameters of polycrystalline MgB 2 have been investigated by means of Raman spectroscopy and x-ray diffraction. It is found that the lattice parameters show an approximately linear change with the temperature decrease, giving different thermal expansions along the a- and c-axes, which is caused by the comparatively weak metal-boron bonding in MgB 2 . The grain size of MgB 2 determined by means of x-ray diffraction is around 45 nm for both [100] and [001] directions. There is no evidence for any structural transition while the temperature changes from 300 K down to 12 K. An anomalous Raman band at 603 cm -1 is observed, which is consistent with the theoretical prediction for the E 2g in-plane boron stretching mode. The Raman frequency increases and the linewidth decreases as the temperature decreases. A possible origin of the temperature dependences of the Raman frequency and the linewidth is discussed. It is suggested that the grain size effect of MgB 2 on the nanometric scale will have a clear influence on the frequency and the linewidth of the Raman spectrum

  18. Burnable neutron absorbers

    International Nuclear Information System (INIS)

    Radford, K.C.; Carlson, W.G.

    1985-01-01

    This patent deals with the fabrication of pellets for neutron absorber rods. Such a pellet includes a matrix of a refractory material which may be aluminum or zirconium oxide, and a burnable poison distributed throughout the matrix. The neutron absorber material may consist of one or more elements or compounds of the metals boron, gadolinium, samarium, cadmium, europium, hafnium, dysprosium and indium. The method of fabricating pellets of these materials outlined in this patent is designed to produce pores or voids in the pellets that can be used to take up the expansion of the burnable poison and to absorb the helium gas generated. In the practice of this invention a slurry of Al 2 O 3 is produced. A hard binder is added and the slurry and binder are spray dried. This powder is mixed with dry B 4 C powder, forming a homogeneous mixture. This mixture is pressed into green tubes which are then sintered. During sintering the binder volatilizes leaving a ceramic with nearly spherical high-density regions of

  19. Resonant soft x-ray reflectivity of Me/B4C multilayers near the boron K edge

    Energy Technology Data Exchange (ETDEWEB)

    Ksenzov, Dmitriy; Schlemper, Christoph; Pietsch, Ullrich

    2010-09-01

    Energy dependence of the optical constants of boron carbide in the short period Ru/B4C and Mo/B4C multilayers (MLs) are evaluated from complete reflectivity scans across the boron K edge using the energy-resolved photon-in-photon-out method. Differences between the refractive indices of the B4Cmaterial inside and close to the surface are obtained from the peak profile of the first order ML Bragg peak and the reflection profile near the critical angle of total external reflection close to the surface. Where a Mo/B4C ML with narrow barrier layers appears as a homogeneous ML at all energies, a Ru/B4C ML exhibits another chemical nature of boron at the surface compared to the bulk. From evaluation of the critical angle of total external reflection in the energy range between 184 and 186 eV, we found an enriched concentration of metallic boron inside the Ru-rich layer at the surface, which is not visible in other energy ranges.

  20. A search for superconductivity below 1 K in transition metal borides

    International Nuclear Information System (INIS)

    Leyarovska, L.; Leyarovski, E.

    1979-01-01

    Some AlB 2 -type (C32 structure) boron compounds were examined for superconductivity down to 0.42 K; the compounds have the formula MeB 2 (Me equivalent to Ti, Zr, Hf, V, Nb, Ta, Cr, Mo) (the atomic ratio of metal to boron was 0.5). Only NbB 2 was found to be superconducting with Tsub(c) = 0.62 K and a surprisingly high value of Hsub(c)(0), about 1600 Oe. Other transition metal as well as non-transition metal boron phases were also tested for superconductivity down to 0.42 K; these compounds were MeB 2 (Me equivalent to Ca, Sr, Ba), W 2 B 5 , CrB, Cr 5 B 3 , UB 2 , UB 4 and UB 12 . None of these compounds proved to be superconducting above 0.42 K; nor was any trace of superconductivity down to 0.42 K observed in MoB and NbB. (Auth.)

  1. Synthesis, structure and magnetic properties of Fe-Gd nanocapsules coated with B2O3/H3BO3 and Fe3BO5+GdBO3

    International Nuclear Information System (INIS)

    Si, P.Z.; Brueck, E.; Zhang, Z.D.; Tegus, O.; Buschow, K.H.J.; Zhang, W.S.; Klaasse, J.C.P.; Boer, F.R. de

    2004-01-01

    Nanocapsules consisting of B 2 O 3 /H 3 BO 3 encapsulating Fe-Gd cores have been synthesized by an arc-discharge process using metal-boron alloys as cathode. Most of the nanocapsules have a well-constructed shell/core structure with a uniform B 2 O 3 /H 3 BO 3 shell. Heat-treatment induces reactions between the shell and the core, resulting in the formation of a Fe 3 BO 5 +GdBO 3 matrix embedded with Fe nanoparticles, reduction of the metallic-core size and decrease of the blocking temperature T B . Above T B , the magnetization curves plotted vs. H/T overlap and show zero coercivity. Below T B , the coercivity shows a linear dependence when plotted vs. T 1/2 . However, the coercivity-T 1/2 curve below 60 K has a different slope from that above 60 K, indicating the existence of two different magnetic phases in the nanocapsules. Different from bulk Fe 3 BO 5 , nanoscale Fe 3 BO 5 particles have a lower transition temperature to the weak-ferromagnetic state, and magnetic hysteresis is absent due to size effects

  2. Standard specification for boron-Based neutron absorbing material systems for use in nuclear spent fuel storage racks

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2011-01-01

    1.1 This specification defines criteria for boron-based neutron absorbing material systems used in racks in a pool environment for storage of nuclear light water reactor (LWR) spent-fuel assemblies or disassembled components to maintain sub-criticality in the storage rack system. 1.2 Boron-based neutron absorbing material systems normally consist of metallic boron or a chemical compound containing boron (for example, boron carbide, B4C) supported by a matrix of aluminum, steel, or other materials. 1.3 In a boron-based absorber, neutron absorption occurs primarily by the boron-10 isotope that is present in natural boron to the extent of 18.3 ± 0.2 % by weight (depending upon the geological origin of the boron). Boron, enriched in boron-10 could also be used. 1.4 The materials systems described herein shall be functional – that is always be capable to maintain a B10 areal density such that subcriticality Keff <0.95 or Keff <0.98 or Keff < 1.0 depending on the design specification for the service...

  3. Carrier-mediated transport of actinides and rare earth elements through liquid and plasticized membranes

    International Nuclear Information System (INIS)

    Kopunec, R.; Ngo Manh, Th.

    1994-01-01

    The first works in this field were realized approximately 25 years ago, when BLOCK et al. reported their studies about carrier-mediated transport (also called pertraction or membrane extraction) of uranium through plasticized membranes with neutral esters derived from phosphoric acid. At this time, the methodical principles of selective pertraction of ionic compounds through so-called bulk liquid membranes containing carriers were known. However, these membranes, similarly as plasticized membranes, have not achieved a broader use. This is probably because bulk liquid membranes are from a technical point of view fairly distant from the idea of a typical membrane system, and plasticized membranes (sometimes also called gel membranes) present great resistance. By the end of the 1960's and at the beginning of the 1970's, LI and CUSSLER worked out the principles for two widely used pertraction techniques, called pertraction through emulsion liquid and supported liquid membranes (ELM and SLM). These two techniques not only have greatest significance in laboratory practice, but they also are interesting for technological aims because of the attainable large phase boundaries, e.g. 10 3 -10 4 m 2 /m 3 . Many ways to arrange membrane systems are described in papers. Recently, the significance of carrier-mediated transport through liquid membranes has grown to have (since 1980) separate section at the International Solvent Extraction Conference. This paper does not deal with mathematical models and the mechanism of pertraction in general, but it gives an overview of results obtained in publications referring to pertraction of two related element groups - actinoids and rare earth elements - using various membrane types. (author) 154 refs

  4. Radioactive waste management and plutonium recovery within the context of the development of nuclear energy in Russia

    Energy Technology Data Exchange (ETDEWEB)

    Kushnikov, V. [V.G. Khlopin Radium Institute, St. Petersburg (Russian Federation)

    1996-05-01

    The Russian strategy for radioactive waste and plutonium management is based on the concept of the closed fuel cycle that has been adopted in Russia, and, to a great degree, falls under the jurisdiction of the existing Russian nuclear energy structures. From its very beginning, Russian atomic energy policy was based on finding the most effective method of developing the new fuel direction with the maximum possible utilization of the energy potential from the fission of heavy atoms and the achievement of fuel self-sufficiency through the recycling of secondary fuel. Although there can be no doubt about the importance of economic considerations (for the future), concerns for the safety of the environment are currently of the utmost importance. In this context, spent NPP fuel can be viewed as a waste to be buried only if there is persuasive evidence that such an approach is both economically and environmentally sound. The production of I GW of energy per year is accompanied by the accumulation of up to 800-1000 kg of highly radioactive fission products and approximately 250 kg of plutonium. Currently, spent fuel from the VVER 100 and the RBNK reactors contains approximately 25 tons of plutonium. There is an additional 30 tons of fuel-grade plutonium in the form of purified oxide, separated from spent fuels used in VVER440 reactors and other power production facilities, as well as approximately 100 tons of weapons-grade plutonium from dismantled warheads. The spent fuel accumulates significant amounts of small actinoids - neptunium americium, and curium. Science and technology have not yet found technical solutions for safe and secure burial of non-reprocessed spent fuel with such a broad range of products, which are typically highly radioactive and will continue to pose a threat for hundreds of thousands of years.

  5. Varying the charge of small cations in liquid water: Structural, transport, and thermodynamical properties

    Science.gov (United States)

    Martelli, Fausto; Vuilleumier, Rodolphe; Simonin, Jean-Pierre; Spezia, Riccardo

    2012-10-01

    In this work, we show how increasing the charge of small cations affects the structural, thermodynamical, and dynamical properties of these ions in liquid water. We have studied the case of lanthanoid and actinoid ions, for which we have recently developed accurate polarizable force fields, and the ionic radius is in the 0.995-1.250 Å range, and explored the valency range from 0 to 4+. We found that the ion charge strongly structures the neighboring water molecules and that, in this range of charges, the hydration enthalpies exhibit a quadratic dependence with respect to the charge, in line with the Born model. The diffusion process follows two main regimes: a hydrodynamical regime for neutral or low charges, and a dielectric friction regime for high charges in which the contraction of the ionic radius along the series of elements causes a decrease of the diffusion coefficient. This latter behavior can be qualitatively described by theoretical models, such as the Zwanzig and the solvated ion models. However, these models need be modified in order to obtain agreement with the observed behavior in the full charge range. We have thus modified the solvated ion model by introducing a dependence of the bare ion radius as a function of the ionic charge. Besides agreement between theory and simulation this modification allows one to obtain an empirical unified model. Thus, by analyzing the contributions to the drag coefficient from the viscous and the dielectric terms, we are able to explain the transition from a regime in which the effect of viscosity dominates to one in which dielectric friction governs the motion of ions with radii of ca. 1 Å.

  6. Comparison of the reactivity of 2-Li-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2} with MCl{sub 4} (M=Th, U). Isolation of a thorium aryl complex or a uranium benzyne complex

    Energy Technology Data Exchange (ETDEWEB)

    Seaman, Lani A.; Pedrick, Elizabeth A.; Wu, Guang; Hayton, Trevor W. [California Univ., Santa Barbara, CA (United States). Dept. of Chemistry and Biochemistry; Tsuchiya, Takashi; Jakubikova, Elena [North Carolina State Univ., Raleigh, NC (United States). Dept. of Chemistry

    2013-09-27

    Individualism under actinoids: The reaction of 2-Li-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2} with [MCl{sub 4} (dme) {sub n}] (M=Th, n=2; M=U, n=0) gives the thorium aryl complex [Th(2-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2}){sub 4}] or the uranium benzene complex Li[U(2,3-C{sub 6}H{sub 3}CH{sub 2}NMe{sub 2})(2-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2}){sub 3}]. A DFT analysis suggests that the formation of a benzyne complex with uranium but not with thorium is a kinetic and not thermodynamic effect. [German] Individualismus unter Actinoiden: Die Reaktion von 2-Li-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2} mit [MCl{sub 4} (dme) {sub n}] (M=Th, n=2; M=U, n=0) ergibt den Thoriumarylkomplex [Th(2-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2}){sub 4}] bzw. den Uranbenz-inkomplex Li[U(2,3-C{sub 6}H{sub 3}CH{sub 2}NMe{sub 2})(2-C{sub 6}H{sub 4}CH{sub 2}NMe{sub 2}){sub 3}]. Einer dichtefunktionaltheoretischen Analyse zufolge ist es kinetisch und nicht thermodynamisch bedingt, dass der Benz-inkomplex im Fall von Uran entsteht, nicht aber im Fall von Thorium.

  7. The construction of TRIGA-TRAP and direct high-precision Penning trap mass measurements on rare-earth elements and americium

    Energy Technology Data Exchange (ETDEWEB)

    Ketelaer, Jens

    2010-06-14

    The construction of TRIGA-TRAP and direct high-precision Penning trap mass measurements on rare-earth elements and americium: Nuclear masses are an important quantity to study nuclear structure since they reflect the sum of all nucleonic interactions. Many experimental possibilities exist to precisely measure masses, out of which the Penning trap is the tool to reach the highest precision. Moreover, absolute mass measurements can be performed using carbon, the atomic-mass standard, as a reference. The new double-Penning trap mass spectrometer TRIGA-TRAP has been installed and commissioned within this thesis work, which is the very first experimental setup of this kind located at a nuclear reactor. New technical developments have been carried out such as a reliable non-resonant laser ablation ion source for the production of carbon cluster ions and are still continued, like a non-destructive ion detection technique for single-ion measurements. Neutron-rich fission products will be available by the reactor that are important for nuclear astrophysics, especially the r-process. Prior to the on-line coupling to the reactor, TRIGA-TRAP already performed off-line mass measurements on stable and long-lived isotopes and will continue this program. The main focus within this thesis was on certain rare-earth nuclides in the well-established region of deformation around N {proportional_to} 90. Another field of interest are mass measurements on actinoids to test mass models and to provide direct links to the mass standard. Within this thesis, the mass of {sup 241}Am could be measured directly for the first time. (orig.)

  8. The construction of TRIGA-TRAP and direct high-precision Penning trap mass measurements on rare-earth elements and americium

    International Nuclear Information System (INIS)

    Ketelaer, Jens

    2010-01-01

    The construction of TRIGA-TRAP and direct high-precision Penning trap mass measurements on rare-earth elements and americium: Nuclear masses are an important quantity to study nuclear structure since they reflect the sum of all nucleonic interactions. Many experimental possibilities exist to precisely measure masses, out of which the Penning trap is the tool to reach the highest precision. Moreover, absolute mass measurements can be performed using carbon, the atomic-mass standard, as a reference. The new double-Penning trap mass spectrometer TRIGA-TRAP has been installed and commissioned within this thesis work, which is the very first experimental setup of this kind located at a nuclear reactor. New technical developments have been carried out such as a reliable non-resonant laser ablation ion source for the production of carbon cluster ions and are still continued, like a non-destructive ion detection technique for single-ion measurements. Neutron-rich fission products will be available by the reactor that are important for nuclear astrophysics, especially the r-process. Prior to the on-line coupling to the reactor, TRIGA-TRAP already performed off-line mass measurements on stable and long-lived isotopes and will continue this program. The main focus within this thesis was on certain rare-earth nuclides in the well-established region of deformation around N ∝ 90. Another field of interest are mass measurements on actinoids to test mass models and to provide direct links to the mass standard. Within this thesis, the mass of 241 Am could be measured directly for the first time. (orig.)

  9. Ultrafast Dynamics in Vanadium Dioxide: Separating Spatially Segregated Mixed Phase Dynamics in the Time-domain

    Science.gov (United States)

    Hilton, David

    2011-10-01

    In correlated electronic systems, observed electronic and structural behavior results from the complex interplay between multiple, sometimes competing degrees-of- freedom. One such material used to study insulator-to-metal transitions is vanadium dioxide, which undergoes a phase transition from a monoclinic-insulating phase to a rutile-metallic phase when the sample is heated to 340 K. The major open question with this material is the relative influence of this structural phase transition (Peirels transition) and the effects of electronic correlations (Mott transition) on the observed insulator-to-metal transition. Answers to these major questions are complicated by vanadium dioxide's sensitivity to perturbations in the chemical structure in VO2. For example, related VxOy oxides with nearly a 2:1 ratio do not demonstrate the insulator-to- metal transition, while recent work has demonstrated that W:VO2 has demonstrated a tunable transition temperature controllable with tungsten doping. All of these preexisting results suggest that the observed electronic properties are exquisitely sensitive to the sample disorder. Using ultrafast spectroscopic techniques, it is now possible to impulsively excite this transition and investigate the photoinduced counterpart to this thermal phase transition in a strongly nonequilibrium regime. I will discuss our recent results studying the terahertz-frequency conductivity dynamics of this photoinduced phase transition in the poorly understood near threshold temperature range. We find a dramatic softening of the transition near the critical temperature, which results primarily from the mixed phase coexistence near the transition temperature. To directly study this mixed phase behavior, we directly study the nucleation and growth rates of the metallic phase in the parent insulator using non-degenerate optical pump-probe spectroscopy. These experiments measure, in the time- domain, the coexistent phase separation in VO2 (spatially

  10. ‘… a metal conducts and a non-metal doesn't’

    Science.gov (United States)

    Edwards, P. P.; Lodge, M. T. J.; Hensel, F.; Redmer, R.

    2010-01-01

    In a letter to one of the authors, Sir Nevill Mott, then in his tenth decade, highlighted the fact that the statement ‘… a metal conducts, and a non-metal doesn’t’ can be true only at the absolute zero of temperature, T=0 K. But, of course, experimental studies of metals, non-metals and, indeed, the electronic and thermodynamic transition between these canonical states of matter must always occur above T=0 K, and, in many important cases, for temperatures far above the absolute zero. Here, we review the issues—theoretical and experimental—attendant on studies of the metal to non-metal transition in doped semiconductors at temperatures close to absolute zero (T=0.03 K) and fluid chemical elements at temperatures far above absolute zero (T>1000 K). We attempt to illustrate Mott’s insights for delving into such complex phenomena and experimental systems, finding intuitively the dominant features of the science, and developing a coherent picture of the different competing electronic processes. A particular emphasis is placed on the idea of a ‘Mott metal to non-metal transition’ in the nominally metallic chemical elements rubidium, caesium and mercury, and the converse metallization transition in the nominally non-metal elements hydrogen and oxygen. We also review major innovations by D. A. Goldhammer (Goldhammer 1913 Dispersion und absorption des lichtes) and K. F. Herzfeld (Herzfeld 1927 Phys. Rev. 29, 701–705. (doi:10.1103/PhysRev.29.701)) in a pre-quantum theory description of the metal–non-metal transition, which emphasize the pivotal role of atomic properties in dictating the metallic or non-metallic status of the chemical elements of the periodic table under ambient and extreme conditions; a link with Pauling’s ‘metallic orbital’ is also established here. PMID:20123742

  11. Electronic, mechanical and dielectric properties of silicane under tensile strain

    International Nuclear Information System (INIS)

    Jamdagni, Pooja; Sharma, Munish; Ahluwalia, P. K.; Kumar, Ashok; Thakur, Anil

    2015-01-01

    The electronic, mechanical and dielectric properties of fully hydrogenated silicene i.e. silicane in stable configuration are studied by means of density functional theory based calculations. The band gap of silicane monolayer can be flexibly reduced to zero when subjected to bi-axial tensile strain, leading to semi-conducting to metallic transition, whereas the static dielectric constant for in-plane polarization increases monotonically with increasing strain. Also the EEL function show the red shift in resonance peak with tensile strain. Our results offer useful insight for the application of silicane monolayer in nano-optical and electronics devices

  12. Electronic transport coefficients from ab initio simulations and application to dense liquid hydrogen

    International Nuclear Information System (INIS)

    Holst, Bastian; French, Martin; Redmer, Ronald

    2011-01-01

    Using Kubo's linear response theory, we derive expressions for the frequency-dependent electrical conductivity (Kubo-Greenwood formula), thermopower, and thermal conductivity in a strongly correlated electron system. These are evaluated within ab initio molecular dynamics simulations in order to study the thermoelectric transport coefficients in dense liquid hydrogen, especially near the nonmetal-to-metal transition region. We also observe significant deviations from the widely used Wiedemann-Franz law, which is strictly valid only for degenerate systems, and give an estimate for its valid scope of application toward lower densities.

  13. On the conductivity of a one-dimensional system of interacting fermions in a random potential

    International Nuclear Information System (INIS)

    Apel, W.

    1981-01-01

    A one-dimensional system of interacting fermions in an external potential is studied. The problem was for this purpose transformed to two classical models of statistical mechanics in two dimensions in which occasionally results were found in complementary ranges of the interaction constants of the fermion system. The conductivity appeared as a simple correlation function in both classical models. It was shown that the interaction in a one-dimensional polluted fermion system can cause an isolator-metal transition. (orig./HSI) [de

  14. The electronic and optical properties of warm dense nitrous oxide using quantum molecular dynamics simulations

    International Nuclear Information System (INIS)

    Zhang Yujuan; Wang Cong; Zhang Ping

    2012-01-01

    First-principles molecular-dynamics simulations based on density-functional theory have been used to study the electronic and optical properties of fluid nitrous oxide under extreme conditions. Systematic descriptions of pair-correlation function, atomic structure, and the charge density distribution are used to investigate the dissociation of fluid nitrous oxide. The electrical and optical properties are derived from the Kubo-Greenwood formula. It is found that the nonmetal-metal transition for fluid nitrous oxide can be directly associated to the dissociation and has significant influence on the optical properties of the fluid.

  15. Magnetoelectronic properties of chiral carbon nanotubes and tori

    International Nuclear Information System (INIS)

    Shyu, F L; Tsai, C C; Lee, C H; Lin, M F

    2006-01-01

    Magnetoelectronic properties of chiral carbon nanotubes and toroids are studied for any magnetic field. They are sensitive to the changes in the magnitude and the direction of the magnetic field, as well as the chirality. The important differences between chiral and achiral carbon nanotubes include band symmetry, band curvature, band crossing, band-edge state, state degeneracy, band spacing, energy gap, and semiconductor-metal transition. Carbon tori also exhibit the strong chirality dependence on the field modulation of discrete states. Chiral carbon tori might differ from chiral carbon nanotubes in energy-gap modulation, density of states, and state degeneracy

  16. All ceramic structure for molten carbonate fuel cell

    Science.gov (United States)

    Smith, James L.; Kucera, Eugenia H.

    1992-01-01

    An all-ceramic molten carbonate fuel cell having a composition formed of a multivalent metal oxide or oxygenate such as an alkali metal, transition metal oxygenate. The structure includes an anode and cathode separated by an electronically conductive interconnect. The electrodes and interconnect are compositions ceramic materials. Various combinations of ceramic compositions for the anode, cathode and interconnect are disclosed. The fuel cell exhibits stability in the fuel gas and oxidizing environments. It presents reduced sealing and expansion problems in fabrication and has improved long-term corrosion resistance.

  17. Strain- and electric field-induced band gap modulation in nitride nanomembranes

    International Nuclear Information System (INIS)

    Amorim, Rodrigo G; Zhong Xiaoliang; Mukhopadhyay, Saikat; Pandey, Ravindra; Rocha, Alexandre R; Karna, Shashi P

    2013-01-01

    The hexagonal nanomembranes of the group III-nitrides are a subject of interest due to their novel technological applications. In this paper, we investigate the strain- and electric field-induced modulation of their band gaps in the framework of density functional theory. For AlN, the field-dependent modulation of the bandgap is found to be significant whereas the strain-induced semiconductor-metal transition is predicted for GaN. A relatively flat conduction band in AlN and GaN nanomembranes leads to an enhancement of their electronic mobility compared to that of their bulk counterparts. (paper)

  18. Tracking the density evolution in counter-propagating shock waves using imaging X-ray scattering

    Czech Academy of Sciences Publication Activity Database

    Zastrau, U.; Gamboa, E. J.; Kraus, D.; Benage, J. F.; Drake, R. P.; Efthimion, P.; Falk, Kateřina; Falcone, R.W.; Fletcher, L. B.; Galtier, E.; Gauthier, M.; Granados, E.; Hastings, J.B.; Heimann, P.; Hill, K.; Keiter, P. A.; Lu, J.; MacDonald, M. J.; Montgomery, D. S.; Nagler, B.; Pablant, N.; Schropp, A.; Tobias, B.; Gericke, D.O.; Glenzer, S. H.; Lee, H. J.

    2016-01-01

    Roč. 109, č. 3 (2016), 1-4, č. článku 031108. ISSN 0003-6951 R&D Projects: GA MŠk LQ1606; GA MŠk EF15_008/0000162 Grant - others:ELI Beamlines(XE) CZ.02.1.01/0.0/0.0/15_008/0000162 Institutional support: RVO:68378271 Keywords : Thomson scattering * metal transition * compression * deuterium * diamond * carbon * matter Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.411, year: 2016

  19. Electric and magnetic fields effects on the transport properties of La{sub 0.5}Ca{sub 0.5}MnO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Villafuerte, M. E-mail: mvillafeurte@herrera.unt.edu.ar; Duhalde, S. E-mail: sduhald@fi.uba.ar; Rubi, D.; Bridoux, G.; Heluani, S.; Sirena, M.; Steren, L

    2004-05-01

    The insulator to metal transition in manganites can be drastically influenced by internal factors, such as chemical composition, or under a variety of external perturbations, like magnetic or electric fields. In this work, the electrical resistance of La{sub 0.5}Ca{sub 0.5}MnO{sub 3} thin films was investigated using different constant voltages. At low temperature the conductivity of the films is non-Ohmic and moderate electric fields results in resistivity switching to metastable states. Comparisons between the influence of magnetic and electric fields on transport measurements are reported.

  20. Electric and magnetic fields effects on the transport properties of La0.5Ca0.5MnO3 thin films

    International Nuclear Information System (INIS)

    Villafuerte, M.; Duhalde, S.; Rubi, D.; Bridoux, G.; Heluani, S.; Sirena, M.; Steren, L.

    2004-01-01

    The insulator to metal transition in manganites can be drastically influenced by internal factors, such as chemical composition, or under a variety of external perturbations, like magnetic or electric fields. In this work, the electrical resistance of La 0.5 Ca 0.5 MnO 3 thin films was investigated using different constant voltages. At low temperature the conductivity of the films is non-Ohmic and moderate electric fields results in resistivity switching to metastable states. Comparisons between the influence of magnetic and electric fields on transport measurements are reported

  1. Thermophysical properties of liquid carbon dioxide under shock compressions: quantum molecular dynamic simulations.

    Science.gov (United States)

    Wang, Cong; Zhang, Ping

    2010-10-07

    Quantum molecular dynamics were used to calculate the equation of state, electrical, and optical properties of liquid carbon dioxide along the Hugoniot at shock pressures up to 74 GPa. The principal Hugoniot derived from the calculated equation of state is in good agreement with experimental results. Molecular dissociation and recombination are investigated through pair correlation functions and decomposition of carbon dioxide is found to be between 40 and 50 GPa along the Hugoniot, where nonmetal-metal transition is observed. In addition, the optical properties of shock compressed carbon dioxide are also theoretically predicted along the Hugoniot.

  2. Conductive ceramic composition and method of preparation

    Science.gov (United States)

    Smith, J.L.; Kucera, E.H.

    1991-04-16

    A ceramic anode composition is formed of a multivalent metal oxide or oxygenate such as an alkali metal, transition metal oxygenate. The anode is prepared as a non-stoichiometric crystalline structure by reaction and conditioning in a hydrogen gas cover containing minor proportions of carbon dioxide and water vapor. The structure exhibits a single phase and substantially enhanced electrical conductivity over that of the corresponding stoichiometric structure. Unexpectedly, such oxides and oxygenates are found to be stable in the reducing anode fuel gas of a molten carbonate fuel cell. 4 figures.

  3. Thin-film VO2 submillimeter-wave modulators and polarizers

    International Nuclear Information System (INIS)

    Fan, J.C.C.; Fetterman, H.R.; Bachner, F.J.; Zavracky, P.M.; Parker, C.D.

    1977-01-01

    Submillimeter-wave modulators and switchable polarizers have been fabricated from VO 2 thin films deposited on sapphire substrates. By passing electric current pulses through elements made from these films, the films can be thermally cycled through the insulator-to-metal transition that occurs in VO 2 at about 65 degreeC. In the insulating state, the films are found to have negligible effect on the transmission at submillimeter wavelengths, while above the phase transition the transmission is strongly reduced by the free-electron effects characteristic of a metal. Other possible applications of such switchable VO 2 elements include variable bandpass filters and diffraction grating beam-steering devices

  4. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    Energy Technology Data Exchange (ETDEWEB)

    Achatz, Philipp

    2009-05-15

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n{sub c} for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers ({approx} 500 cm{sup -1}) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g{sub c}. The granularity also influences significantly the superconducting properties by introducing the superconducting gap {delta} in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the

  5. The complex metal-rich boride Ti1+xRh2-x+yIr3-yB3 (x=0.68, y=1.06) with a new structure type containing B4 zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

    Science.gov (United States)

    Goerens, Christian; Fokwa, Boniface P. T.

    2012-08-01

    Polycrystalline samples and single crystals of the new complex boride Ti1+xRh2-x+yIr3-yB3 (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B4 fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1) Å, b=14.995(2) Å and c=3.234(1) Å. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron-boron interactions are observed in the trans zigzag B4 fragment, which induce a clear differentiation of two types of metal-boron contacts with different strength. The observed three-dimensional metal-metal interaction is in good agreement with the predicted metallic behavior.

  6. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    International Nuclear Information System (INIS)

    Achatz, Philipp

    2009-01-01

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n c for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers (∼ 500 cm -1 ) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g c . The granularity also influences significantly the superconducting properties by introducing the superconducting gap Δ in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the first time in aluminum

  7. Thermodynamic and electrical properties of laser-shocked liquid deuterium

    Science.gov (United States)

    He, Zhiyu; Jia, Guo; Zhang, Fan; Luo, Kui; Huang, Xiuguang; Shu, Hua; Fang, Zhiheng; Ye, Junjian; Xie, Zhiyong; Xia, Miao; Fu, Sizu

    2018-01-01

    Liquid deuterium at high pressure and temperature has been observed to undergo significant electronic structural changes. Reflectivity and temperature measurements of liquid deuterium up to around 70 GPa were obtained using a quartz standard. The observed specific heat of liquid deuterium approaches the Dulong-Petit limit above 1 eV. Discussions on specific heat indicate a molecular dissociation below 1 eV and fully dissociated above 1.5 eV. Also, the electrical conductivity of deuterium estimated from reflectivity reaches 1.3 × 105 (Ωṡm)-1, proving that deuterium in this condition is a conducting degenerate liquid metal and undergo an insulator-metal transition. The results from specific heat, carrier density and conductivity agreed well with each other, which might be a reinforcement of the insulator-metal transition and the molecular dissociation. In addition, a new correction method of reflectivity in temperature calculation was proposed to improve the accuracy of temperature results. A new "dynamic calibration" was introduced in this work to make the experiments simpler and more accurate.

  8. Nanoscale Phase Separation and Lattice Complexity in VO2: The Metal–Insulator Transition Investigated by XANES via Auger Electron Yield at the Vanadium L23-Edge and Resonant Photoemission

    Directory of Open Access Journals (Sweden)

    Augusto Marcelli

    2017-12-01

    Full Text Available Among transition metal oxides, VO2 is a particularly interesting and challenging correlated electron material where an insulator to metal transition (MIT occurs near room temperature. Here we investigate a 16 nm thick strained vanadium dioxide film, trying to clarify the dynamic behavior of the insulator/metal transition. We measured (resonant photoemission below and above the MIT transition temperature, focusing on heating and cooling effects at the vanadium L23-edge using X-ray Absorption Near-Edge Structure (XANES. The vanadium L23-edges probe the transitions from the 2p core level to final unoccupied states with 3d orbital symmetry above the Fermi level. The dynamics of the 3d unoccupied states both at the L3- and at the L2-edge are in agreement with the hysteretic behavior of this thin film. In the first stage of the cooling, the 3d unoccupied states do not change while the transition in the insulating phase appears below 60 °C. Finally, Resonant Photoemission Spectra (ResPES point out a shift of the Fermi level of ~0.75 eV, which can be correlated to the dynamics of the 3d// orbitals, the electron–electron correlation, and the stability of the metallic state.

  9. Electronic reconstruction at the interface between the Mott insulator LaVO{sub 3} and the band insulator SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Stuebinger, Martin; Gabel, Judith; Gagel, Philipp; Sing, Michael; Claessen, Ralph [Universitaet Wuerzburg, Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), 97074 Wuerzburg (Germany)

    2016-07-01

    Akin to the well known oxide heterostructure LaAlO{sub 3}/SrTiO{sub 3} (LAO/STO) the formation of a conducting interface is found between the strongly correlated, polar Mott insulator LaV{sup 3+}O{sub 3} (LVO) and the non-polar band insulator STO. Since LaV{sup 3+}O{sub 3} tends to overoxidize to the thermodynamically more favourable LaV{sup 5+}O{sub 4} phase when exposed to air, a suitable passivation is required. Therefore, we have employed pulsed laser deposition thin film growth of LVO films with a crystalline LAO capping layer. In situ photoemission measurements of samples before and after being exposed to air show that the V oxidation state can indeed be stabilized by the LAO capping layer. By transport measurements, we identify an insulator-to-metal transition at a combined LAO/LVO overlayer thickness of 4 to 5 unit cells. With LVO being a Mott insulator, passivation by the LAO capping opens the opportunity to study a band-filling controlled Mott insulator to metal transition induced by a purely electrostatic mechanism without interfering overoxidation of the LVO film.

  10. Thickness dependent properties of CMR Manganite thin films on lattice mismatched substrates: Distinguishing Strain and Interface Effects

    Science.gov (United States)

    Davidson, Anthony, III; Kolagani, Rajeswari; Bacharova, Ellisaveta; Yong, Grace; Smolyaninova, Vera; Schaefer, David; Mundle, Rajeh

    2007-03-01

    Epitaxial thin films of CMR manganite materials have been known to show thickness dependent electrical and magnetic properties on lattice mismatched substrates. Below a critical thickness, insulator-metal transition is suppressed. These effects have been largely attributed to the role of bi-axial lattice mismatch strain. Our recent results of epitaxial thin films of La0.67Ca0.33MnO3 (LCMO) on two substrates with varying degrees of compressive lattice mismatch indicate that, in addition to the effect of lattice mismatch strain, the thickness dependence of the properties are influenced by other factors possibly related to the nature of the film substrate interface and defects such as twin boundaries. We have compared the properties of LCMO films on (100) oriented LaAlO3 and (001) oriented NdCaAlO4 both of which induce compressive bi-axial strain. Interestingly, the suppression of the insulator-metal transition is less in films on NCAO which has a larger lattice mismatch. We will present results correlating the electrical and magneto transport properties with the structure and morphology of the films.

  11. Colossal magnetotransport phenomena due to phase competition in Pr1-x(CaySr1-y)xMnO3 single crystals

    International Nuclear Information System (INIS)

    Wu, J.; Zheng, H.; Mitchell, J.F.; Leighton, C.

    2005-01-01

    We present a magnetotransport investigation of single crystal Pr 0.65 (Ca 0.75 Sr 0.25 ) 0.35 MnO 3 , a manganite system specifically tailored to result in a close competition between ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Below 165 K these phases coexist spatially, with application of a magnetic field favoring the ferromagnetic metallic phase, leading to a magnetoresistance ratio of>10 10 in a 2 T magnetic field. Isothermal resistivity vs. field measurements reveal some previously unobserved features accompanying the insulator to metal transition. In addition to unexpected fine structure that occurs as the ferromagnetic metallic phase grows to engulf the entire sample, we observe an intriguing 'overshoot' phenomenon in both temperature and field-driven insulator-metal transitions. The resistivity is found to reach a sharp minimum (lower even than the pure ferromagnetic metallic phase) close to the point where the metallic phase percolates. These features are explored in detail and we discuss possible explanations of the effects in terms of pinning of the spatial boundary between the magnetic phases, and the unusual transport effects that could occur when the current flows through a barely percolated path

  12. First-Principles Investigations on Europium Monoxide

    KAUST Repository

    Wang, Hao

    2011-05-01

    Europium monoxide is both an insulator and a Heisenberg ferromagnet (Tc=69 K). In the present thesis, the author has investigated the electronic structure of different types of EuO by density functional theory. The on-site Coulomb interaction of the localized Eu 4f and 5d electrons, which is wrongly treated in the standard generalized gradient approximation method, is found to be crucial to obtain the correct insulating ground state as observed in experiments. Our results show that the ferromagnetism is stable under pressure, both hydrostatic and uniaxial. For both types of pressure an insulator-metal transition is demonstrated. Moreover, the experimentally observed insulator-metal transition in oxygen deficient and gadolinium-doped EuO is reproduced in our calculations for impurity concentrations of 6.25% and 25%. Furthermore, a 10- layer EuO thin film is theoretically predicted to be an insulator with a narrow band gap of around 0.08 eV, while the Si/EuO interface shows metallic properties with the Si and O 2p as well as Eu 5d bands crossing the Fermi level.

  13. Disorder and pseudogap in strongly correlated systems: Phase diagram in the DMFT + Σ approach

    International Nuclear Information System (INIS)

    Kuleeva, N. A.; Kuchinskii, E. Z.

    2013-01-01

    The influence of disorder and pseudogap fluctuations on the Mott insulator-metal transition in strongly correlated systems has been studied in the framework of the generalized dynamic mean field theory (DMFT + Σ approach). Using the results of investigations of the density of states (DOS) and optical conductivity, a phase diagram (disorder-Hubbard interaction-temperature) is constructed for the paramagnetic Anderson-Hubbard model, which allows both the effects of strong electron correlations and the influence of strong disorder to be considered. Strong correlations are described using the DMFT, while a strong disorder is described using a generalized self-consistent theory of localization. The DOS and optical conductivity of the paramagnetic Hubbard model have been studied in a pseudogap state caused by antiferromagnetic spin (or charge) short-range order fluctuations with a finite correlation length, which have been modeled by a static Gaussian random field. The effect of a pseudogap on the Mott insulator-metal transition has been studied. It is established that, in both cases, the static Gaussian random field (related to the disorder or pseudogap fluctuations) leads to suppression of the Mott transition, broadening of the coexistence region of the insulator and metal phases, and an increase in the critical temperature at which the coexistence region disappears

  14. Solid state amorphisation in binary systems prepared by mechanical alloying

    International Nuclear Information System (INIS)

    Gonzalez, G.; Sagarzazu, A.; Bonyuet, D.; D'Angelo, L.; Villalba, R.

    2009-01-01

    In the present work a detailed study of amorphisation in different systems prepared by mechanical alloying under the same experimental conditions was carried out, milling up to 50 and 100 h in some cases. The systems studied were: AlTi, AlNi, AlFe, FeNi, FeCo, NiMo, NiW, NiCo, MoW, CoMo. These systems were chosen to study the effect of Al-transition metal, transition metal-transition metal and also systems with large and small negative heat of mixing, different and similar crystal structures, atomic sizes and diffusion coefficients. Calculations based on the Miedema model for alloy formation and amorphisation on all the alloys studied were performed. The experimental results from X-ray diffraction and transmission electron microscopy showed that the systems based on Fe (FeNi, FeCo and FeAl) did not amorphised, even after milling for 100 h, and formed a stable solid solution with a nanometric grain size of 7 nm. The systems NiMo, NiW, MoW and CoMo (systems with small negative heat of mixing), showed amorphisation after 50 h of milling. NiAl and TiAl form an intermediate amorphous phase after around 20 h of milling and with further milling they recrystallize into a fcc solid solution. Agreement between the theoretical calculations based on the Miedema model and the experimental results was found in most of the systems.

  15. Potential spin-polarized transport in gold-doped armchair graphene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Pankaj, E-mail: pankajs@iiitm.ac.in [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior 474015, MP (India); Dhar, Subhra [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior 474015, MP (India); Jaiswal, Neeraj K. [Discipline of Physics, PDPM-Indian Institute of Information Technology, Design and Manufacturing (IIITDM), Jabalpur 482005 (India)

    2015-04-17

    Based on NEGF-DFT computations, systematic investigation of electronic, magnetic and transport properties of AGNRs are done by employing Au through different doping mechanisms. Remarkable Au–AGNR bonding is observed in case of substitution due to the presence of impurity at the edges. Both substitution and adsorption of Au on AGNR surface induce significant changes in the electronic spin transport of the sp{sup 2} hybridized carbon sheets. AGNRs are semiconducting with lower total energy for the FM configuration, and the I–V characteristics reveal semiconductor to metal transition of Au-doped AGNR. The spin injection is voltage controlled in all the investigated Au-doped AGNRs. - Highlights: • Edge Au-substitution promotes semiconductor–metal transition in AGNR. • NDR due to bias-dependent transmission in Au-substituted AGNRs. • Voltage controlled spin injection in all investigated Au-doped AGNRs. • Strong spin polarization occurs at 0.5 V in Au-hole adsorbed AGNRs.

  16. Pressure-Induced Confined Metal from the Mott Insulator Sr3Ir2O7

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Yang; Yang, Liuxiang; Chen, Cheng-Chien; Kim, Heung-Sik; Han, Myung Joon; Luo, Wei; Feng, Zhenxing; Upton, Mary; Casa, Diego; Kim, Jungho; Gog, Thomas; Zeng, Zhidan; Cao, Gang; Mao, Ho-kwang; van Veenendaal, Michel

    2016-05-24

    The spin-orbit Mott insulator Sr3Ir2O7 provides a fascinating playground to explore insulator-metal transition driven by intertwined charge, spin, and lattice degrees of freedom. Here, we report high-pressure electric resistance and resonant inelastic x-ray scattering measurements on single-crystal Sr3Ir2O7 up to 63-65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa, showing metallicity in the ab plane but an insulating behavior along the c axis. Such an unusual phenomenon resembles the strange metal phase in cuprate superconductors. Since there is no sign of the collapse of spin-orbit or Coulomb interactions in x-ray measurements, this novel insulator-metal transition is potentially driven by a first-order structural change at nearby pressures. Our discovery points to a new approach for synthesizing functional materials.

  17. Metal-to-nonmetal transitions

    CERN Document Server

    Hensel, Friedrich; Holst, Bastian

    2010-01-01

    This book is devoted to nonmetal-to-metal transitions. The original ideas of Mott for such a transition in solids have been adapted to describe a broad variety of phenomena in condensed matter physics (solids, liquids, and fluids), in plasma and cluster physics, as well as in nuclear physics (nuclear matter and quark-gluon systems). The book gives a comprehensive overview of theoretical methods and experimental results of the current research on the Mott effect for this wide spectrum of topics. The fundamental problem is the transition from localized to delocalized states which describes the nonmetal-to-metal transition in these diverse systems. Based on the ideas of Mott, Hubbard, Anderson as well as Landau and Zeldovich, internationally respected scientists present the scientific challenges and highlight the enormous progress which has been achieved over the last years. The level of description is aimed to specialists in these fields as well as to young scientists who will get an overview for their own work...

  18. Magnetic engineering in 3d transition metals on phosphorene by strain

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Xiaolin [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, 454000 (China); Niu, Chunyao, E-mail: niuchunyao@zzu.edu.cn [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); Wang, Jianjun [College of Science, Zhongyuan University of Technology, Zhengzhou 450007 (China); Yu, Weiyang [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, 454000 (China); Ren, XiaoYan; Zhu, Zhili [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China)

    2017-04-11

    Using first-principles density functional theory (DFT) calculations, we systematically investigate the strain effects on the adsorption energies, magnetic ordering and electronic properties of 3d transition metal (TM) atoms (from Sc to Co) adsorbed on phosphorene (P). We find that the adsorption energy of TM can be enhanced by compressive strain whereas weakened by tensile strain. Our results show that strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. Importantly, the transitions from antiferromagnetic (AFM) state to ferromagnetic (FM) state or to another different AFM ordering can be induced by strain effect. In addition, we observe the semiconductor to metal or half-metal transitions in some TM@P systems by applying strain. Our findings shed a new light on precisely engineering the magnetic properties and electronic properties of the TM@P systems, which will have great potential applications in spin electronics and other related fields. - Highlights: • The adsorption of TM atoms on phosphorene can be enhanced by compressive strain whereas weakened by tensile strain. • Strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. • Applying strain can induce the semiconductor to metal or half-metal transitions in some TM@P systems.

  19. Morphology, optical and electrical properties of Cu-Ni nanoparticles in a-C:H prepared by co-deposition of RF-sputtering and RF-PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Ghodselahi, T., E-mail: ghodselahi@ipm.ir [School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Vesaghi, M.A. [School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Gelali, A.; Zahrabi, H.; Solaymani, S. [Young Researchers Club, Islamic Azad University, Kermanshah Branch, Kermanshah (Iran, Islamic Republic of)

    2011-11-01

    We report optical and electrical properties of Cu-Ni nanoparticles in hydrogenated amorphous carbon (Cu-Ni NPs - a-C:H) with different surface morphology. Ni NPs with layer thicknesses of 5, 10 and 15 nm over Cu NPs - a-C:H were prepared by co-deposition of RF-sputtering and RF-Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. A nonmetal-metal transition was observed as the thickness of Ni over layer increases. The surface morphology of the sample was described by a two dimensional (2D) Gaussian self-affine fractal, except the sample with 10 nm thickness of Ni over layer, which is in the nonmetal-metal transition region. X-ray diffraction profile indicates that Cu NPs and Ni NPs with fcc crystalline structure are formed in these films. Localized Surface Plasmon Resonance (LSPR) peak of Cu NPs is observed around 600 nm in visible spectra, which is widen and shifted to lower wavelengths as the thickness of Ni over layer increases. The variation of LSPR peak width correlates with conductivity variation of these bilayers. We assign both effects to surface electron delocalization of Cu NPs.

  20. Magnetic engineering in 3d transition metals on phosphorene by strain

    International Nuclear Information System (INIS)

    Cai, Xiaolin; Niu, Chunyao; Wang, Jianjun; Yu, Weiyang; Ren, XiaoYan; Zhu, Zhili

    2017-01-01

    Using first-principles density functional theory (DFT) calculations, we systematically investigate the strain effects on the adsorption energies, magnetic ordering and electronic properties of 3d transition metal (TM) atoms (from Sc to Co) adsorbed on phosphorene (P). We find that the adsorption energy of TM can be enhanced by compressive strain whereas weakened by tensile strain. Our results show that strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. Importantly, the transitions from antiferromagnetic (AFM) state to ferromagnetic (FM) state or to another different AFM ordering can be induced by strain effect. In addition, we observe the semiconductor to metal or half-metal transitions in some TM@P systems by applying strain. Our findings shed a new light on precisely engineering the magnetic properties and electronic properties of the TM@P systems, which will have great potential applications in spin electronics and other related fields. - Highlights: • The adsorption of TM atoms on phosphorene can be enhanced by compressive strain whereas weakened by tensile strain. • Strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. • Applying strain can induce the semiconductor to metal or half-metal transitions in some TM@P systems.

  1. Low temperature intermediate band metallic behavior in Ti implanted Si

    Energy Technology Data Exchange (ETDEWEB)

    Olea, Javier, E-mail: oleaariza@fis.ucm.es; Pastor, David; Garcia-Hemme, Eric; Garcia-Hernansanz, Rodrigo; Prado, Alvaro del; Martil, Ignacio; Gonzalez-Diaz, German

    2012-08-31

    Si samples implanted with very high Ti doses and subjected to Pulsed-Laser Melting (PLM) have been electrically analyzed in the scope of a two-layer model previously reported based on the Intermediate Band (IB) theory. Conductivity and Hall effect measurements using the van der Pauw technique suggest that the insulator-metal transition takes place for implantation doses in the 10{sup 14}-10{sup 16} cm{sup -2} range. Results of the sample implanted with the 10{sup 16} cm{sup -2} dose show a metallic behavior at low temperature that is explained by the formation of a p-type IB out of the Ti deep levels. This suggests that the IB would be semi-filled, which is essential for IB photovoltaic devices. - Highlights: Black-Right-Pointing-Pointer We fabricated high dose Ti implanted Si samples for intermediate band research. Black-Right-Pointing-Pointer We measured the electronic transport properties in the 7-300 K range. Black-Right-Pointing-Pointer We show an insulator to metallic transition when the intermediate band is formed. Black-Right-Pointing-Pointer The intermediate band is semi-filled and populated by holes. Black-Right-Pointing-Pointer We satisfactorily explain the electrical behavior by an intermediate band model.

  2. Theory of quantum metal to superconductor transitions in highly conducting systems

    Energy Technology Data Exchange (ETDEWEB)

    Spivak, B.

    2010-04-06

    We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure which is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.

  3. Electrical conductivity of hydrogen shocked to megabar pressures

    International Nuclear Information System (INIS)

    Weir, S.T.; Nellis, W.J.; Mitchell, A.C.

    1993-08-01

    The properties of ultra-high pressure hydrogen have been the subject of much experimental and theoretical study. Of particular interest is the pressure-induced insulator-to-metal transition of hydrogen which, according to recent theoretical calculations, is predicted to occur by band-overlap in the pressure range of 1.5-3.0 Mbars on the zero temperature isotherm. Extremely high pressures are required for metallization since the low-pressure band gap is about 15 eV. Recent static-pressure diamond anvil cell experiments have searched for evidence of an insulator-to-metal transition, but no conclusive evidence for such a transition has yet been supplied. Providing conclusive evidence for hydrogen metallization is difficult because no technique has yet been developed for performing static high-pressure electrical conductivity experiments at megabar pressures. The authors report here on electrical conductivity experiments performed on H 2 and D 2 multi-shocked to megabar pressures. Electrical conductivities of dense fluid hydrogen at these pressures and temperatures reached are needed for calculations of the magnetic fields of Jupiter and Saturn, the magnetic fields being generated by convective dynamos of hot, dense, semiconducting fluid hydrogen. Also, since electrical conduction at the pressure-temperature conditions being studied is due to the thermal excitation of charge carriers across the electronic band gap, these experiments yield valuable information on the width of the band gap at high densities

  4. Systematic evaluation of prompt neutron spectra in fission

    International Nuclear Information System (INIS)

    Osawa, Takaaki

    1995-01-01

    To create the nuclear data fail JEND-32, the prompt fission neutron spectra X(E) of 233 U, 235 U, 238 U and 239 Pu were reevaluated and some improvement were added to the calculation models. We tried to extend the calculation method of fission spectra of nuclides with poor measurement data in consideration of increasing the importance of nuclear data of minor actinoids. We improved and extended the following five points. (1) On JENDL-3.1, the fission spectra of principal fissible materials had been calculated by the Modland-Nix model which the neutron emissions of fragments were calculated under the approximation of the constant inverse process cross section. In the paper, the spectra were calculated by the use of the inverse process cross section depend on the energy obtained by the calculation of the optical model. The result showed the increase of low energy components and the softening effect of spectra (2) On JENDL-3.1, the all fission processes were assumed to undergo (n,f) reaction. In the paper, they were calculated by the multi-chance fission such as (n, n'f), (n, 2nf) and (n, 3nf) etc. Softening of the spectra (En > 6 MeV) was obtained by this method. (3) The level density parameter (LDP) has been assumed as a = A/C in either case of light fragment (LF) and heavy fragment (HF) in the original Madland-Nix model. But we used LDP based on the Ignatyuk model under consideration of the shell effects of nuclear fragments, hence the neutron spectra of heavy fragments were hardening. (4) Nuclear temperature of both fragments had been assumed to be the same at original model, but now R T = Tm/TmH was derived to calculate them. The ratio of middle/both side components of spectra was changed. (5) Unknown neutron fission spectra of minor actinide were able to the assumed on the basis of Moriyama-Ohnishi model. (S.Y.)

  5. Development of modern CANDU PHWR cross-section libraries for SCALE

    International Nuclear Information System (INIS)

    Shoman, Nathan T.; Skutnik, Steven E.

    2016-01-01

    Highlights: • New ORIGEN libraries for CANDU 28 and 37-element fuel assemblies have been created. • These new reactor data libraries are based on modern ENDF/B-VII.0 cross-section data. • The updated CANDU data libraries show good agreement with radiochemical assay data. • Eu-154 overestimated when using ENDF-VII.0 due to a lower thermal capture cross-section. - Abstract: A new set of SCALE fuel lattice models have been developed for the 28-element and 37-element CANDU fuel assembly designs using modern cross-section data from ENDF-B/VII.0 in order to produce new reactor data libraries for SCALE/ORIGEN depletion analyses. These new libraries are intended to provide users with a convenient means of evaluating depletion of CANDU fuel assemblies using ORIGEN through pre-generated cross sections based on SCALE lattice physics calculations. The performance of the new CANDU ORIGEN libraries in depletion analysis benchmarks to radiochemical assay data were compared to the previous version of the CANDU libraries provided with SCALE (based on WIMS-AECL models). Benchmark comparisons with available radiochemical assay data indicate that the new cross-section libraries perform well at matching major actinide species (U/Pu), which are generally within 1–4% of experimental values. The library also showed similar or better results over the WIMS-AECL library regarding fission product species and minor actinoids (Np, Am, and Cm). However, a notable exception was in calculated inventories of "1"5"4Eu and "1"5"5Eu, where the new library employing modern nuclear data (ENDF/B-VII.0) performed substantially poorer than the previous WIMS-AECL library (which used ENDF-B/VI.8 cross-sections for these species). The cause for this discrepancy appears to be due to differences in the "1"5"4Eu thermal capture cross-section between ENDF/B-VI.8 and ENDF/B-VII.0, an effect which is exacerbated by the highly thermalized flux of a CANDU heavy water reactor compared to that of a typical

  6. Band gap engineering of MoS{sub 2} upon compression

    Energy Technology Data Exchange (ETDEWEB)

    López-Suárez, Miquel, E-mail: miquel.lopez@nipslab.org [NiPS Laboratory, Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, 06123 Perugia (Italy); Neri, Igor [NiPS Laboratory, Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, 06123 Perugia (Italy); INFN Sezione di Perugia, via Pascoli, 06123 Perugia (Italy); Rurali, Riccardo [Institut de Ciència de Materials de Barcelona (ICMAB–CSIC) Campus de Bellaterra, 08193 Bellaterra, Barcelona (Spain)

    2016-04-28

    Molybdenum disulfide (MoS{sub 2}) is a promising candidate for 2D nanoelectronic devices, which shows a direct band-gap for monolayer structure. In this work we study the electronic structure of MoS{sub 2} upon both compressive and tensile strains with first-principles density-functional calculations for different number of layers. The results show that the band-gap can be engineered for experimentally attainable strains (i.e., ±0.15). However, compressive strain can result in bucking that can prevent the use of large compressive strain. We then studied the stability of the compression, calculating the critical strain that results in the on-set of buckling for free-standing nanoribbons of different lengths. The results demonstrate that short structures, or few-layer MoS{sub 2}, show semi-conductor to metal transition upon compressive strain without bucking.

  7. Role of Interchain Coupling in the Metallic State of Conducting Polymers

    Science.gov (United States)

    Kim, Nara; Lee, Byoung Hoon; Choi, Doowhan; Kim, Geunjin; Kim, Heejoo; Kim, Jae-Ryoung; Lee, Jongjin; Kahng, Yung Ho; Lee, Kwanghee

    2012-09-01

    We investigated the charge dynamics of the conductivity enhancement from 2 to 1000S/cm in poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) as induced by structural changes through the addition of a polar solvent and the following solvent bath treatment. Our results indicate that the addition of a polar solvent selectively enhanced the π-π coupling of the polymer chains, resulting in the reduction of disorder and tremendously increasing the charge carrier mobility, which yielded an insulator-to-metal transition. In contrast, the following solvent bath treatment selectively enhanced the intergrain coupling, which did not affect the disorder or the mobility but increased the charge carrier density. Therefore, we demonstrate that the conduction-character defining disorder in this conducting polymer system is determined by the extent of interchain coupling.

  8. ZnO Nanorods on a LaAlO 3 -SrTiO 3 Interface: Hybrid 1D-2D Diodes with Engineered Electronic Properties

    KAUST Repository

    Bera, Ashok

    2015-12-28

    Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode-type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO3-SrTiO3 interface. Tunable insulator-to-metal transitions, absent in the individual components, are observed as a result of the competing temperature-dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler-Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles

    Directory of Open Access Journals (Sweden)

    Ting Jia

    2017-05-01

    Full Text Available The serial system Srn+1FenO2n+1(n=1,2,3… with the FeO4 square planar motif exhibits abundant phase transitions under pressure. In this work, we investigate the pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles. Our results show that the system undergoes a structural transition from Immm to Ammm when the volume decreases by 30%, together with a spin-state transition (SST from high-spin (S = 2 to intermediate-spin (S = 1, an antiferromagnetic-to-ferromagnetic transition and an insulator-to-metal transition (IMT. Besides, the IMT here is a bandwidth controlled transition, but little influenced by the SST.

  10. Syntheses and properties of several metastable and stable hydrides derived from intermetallic compounds under high hydrogen pressure

    Energy Technology Data Exchange (ETDEWEB)

    Filipek, S.M., E-mail: sfilipek@unipress.waw.pl [Institute of High Pressure Physics PAS, ul. Sokolowska 29, 01-142 Warsaw (Poland); Paul-Boncour, V. [ICMPE-CMTR, CNRS-UPEC, 2-8 rue Henri Dunant, 94320 Thiais (France); Liu, R.S. [Department of Chemistry, National Taiwan University, Taipei 106, Taiwan (China); Jacob, I. [Unit Nuclear Eng., Ben Gurion University of the Negev, Beer-Sheva (Israel); Tsutaoka, T. [Dept. of Sci. Educ., Grad. School of Educ., Hiroshima University, Hiroshima (Japan); Budziak, A. [Institute of Nuclear Physics PAS, 31-342 Kraków (Poland); Morawski, A. [Institute of High Pressure Physics PAS, ul. Sokolowska 29, 01-142 Warsaw (Poland); Sugiura, H. [Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027 (Japan); Zachariasz, P. [Institute of Electron Technology Cracow Division, ul. Zablocie 39, 30-701 Krakow (Poland); Dybko, K. [Institute of Physics, PAS, 02-668 Warsaw (Poland); Diduszko, R. [Tele and Radio Research Institute, ul. Ratuszowa 11, Warsaw (Poland)

    2016-12-01

    Brief summary of our former work on high hydrogen pressure syntheses of novel hydrides and studies of their properties is supplemented with new results. Syntheses and properties of a number of hydrides (unstable, metastable or stable in ambient conditions) derived under high hydrogen pressure from intermetallic compounds, like MeT{sub 2}, MeNi{sub 5}, Me{sub 7}T{sub 3}, Y{sub 6}Mn{sub 23} and YMn{sub 12} (where Me = zirconium, yttrium or rare earth; T = transition metal) are presented. Stabilization of ZrFe{sub 2}H{sub 4} due to surface phenomena was revealed. Unusual role of manganese in hydride forming processes is pointed out. Hydrogen induced phase transitions, suppression of magnetism, antiferromagnetic-ferromagnetic and metal-insulator or semimetal-metal transitions are described. Equations of state (EOS) of hydrides submitted to hydrostatic pressures up to 30 GPa are presented and discussed.

  11. Coulomb Correlations Intertwined with Spin and Orbital Excitations in LaCoO_{3}.

    Science.gov (United States)

    Tomiyasu, K; Okamoto, J; Huang, H Y; Chen, Z Y; Sinaga, E P; Wu, W B; Chu, Y Y; Singh, A; Wang, R-P; de Groot, F M F; Chainani, A; Ishihara, S; Chen, C T; Huang, D J

    2017-11-10

    We carried out temperature-dependent (20-550 K) measurements of resonant inelastic x-ray scattering on LaCoO_{3} to investigate the evolution of its electronic structure across the spin-state crossover. In combination with charge-transfer multiplet calculations, we accurately quantified the renomalized crystal-field excitation energies and spin-state populations. We show that the screening of the effective on-site Coulomb interaction of 3d electrons is orbital selective and coupled to the spin-state crossover in LaCoO_{3}. The results establish that the gradual spin-state crossover is associated with a relative change of Coulomb energy versus bandwidth, leading to a Mott-type insulator-to-metal transition.

  12. Comparative study of heterogeneous magnetic state above TC in La0.82Sr0.18CoO3 cobaltite and La0.83Sr0.17MnO3 manganite

    Science.gov (United States)

    Ryzhov, V. A.; Lazuta, A. V.; Molkanov, P. L.; Khavronin, V. P.; Kurbakov, A. I.; Runov, V. V.; Mukovskii, Ya. M.; Pestun, A. E.; Privezentsev, R. V.

    2012-10-01

    The magnetic, transport and structural properties are studied for La0.83Sr0.17MnO3 and La0.82Sr0.18CoO3 single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т*>TC in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator-metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn3+ and Co3+ ions.

  13. Atomic and electronic structure of clusters from car-Parrinello method

    International Nuclear Information System (INIS)

    Kumar, V.

    1994-06-01

    With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs

  14. Dynamic conductivity and partial ionization in dense fluid hydrogen

    Science.gov (United States)

    Zaghoo, Mohamed

    2018-04-01

    A theoretical description for optical conduction experiments in dense fluid hydrogen is presented. Different quantum statistical approaches are used to describe the mechanism of electronic transport in hydrogen's high-temperature dense phase. We show that at the onset of the metallic transition, optical conduction could be described by a strong rise in atomic polarizability, due to increased ionization, whereas in the highly degenerate limit, the Ziman weak scattering model better accounts for the observed saturation of reflectance. The inclusion of effects of partial ionization in the highly degenerate region provides great agreement with experimental results. Hydrogen's fluid metallic state is revealed to be a partially ionized free-electron plasma. Our results provide some of the first theoretical transport models that are experimentally benchmarked, as well as an important guide for future studies.

  15. Structural and electrochemical properties of La 0.8Sr 0.2Ga 1-xFe xO 3

    Science.gov (United States)

    Mori, Kazuhiro; Onodera, Yohei; Kiyanagi, Ryoji; Richardson, James W.; Itoh, Keiji; Sugiyama, Masaaki; Kamiyama, Takashi; Fukunaga, Toshiharu

    2009-02-01

    Mixed ionic-electronic conductor of Fe doped lanthanum gallate, La 0.8Sr 0.2Ga 1-xFe xO 3, has been studied by the dc four-probe method and the neutron powder diffraction. In the electrical conductivity measurement at RT, insulator-metal transition-like phenomenon was observed at around x˜0.35; this suggests an existence of the percolation limit for the electronic conductivity. Simultaneously, a bond length between O atoms, lO-O, in a MO 6 octahedron (M dbnd Ga 1-xFe x) drastically expands over x˜0.4, according to the result of crystal structure refinement based on the hexagonal phase. Such a drastic expansion in the lO-O would induce the decrease in the oxygen ionic conductivity.

  16. Structural and electrochemical properties of La{sub 0.8}Sr{sub 0.2}Ga{sub 1-x}Fe{sub x}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Mori, Kazuhiro [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan)], E-mail: kmori@rri.kyoto-u.ac.jp; Onodera, Yohei [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Kiyanagi, Ryoji; Richardson, James W. [Intense Pulsed Neutron Source Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Itoh, Keiji; Sugiyama, Masaaki [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Kamiyama, Takashi [Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801 (Japan); Fukunaga, Toshiharu [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan)

    2009-02-21

    Mixed ionic-electronic conductor of Fe doped lanthanum gallate, La{sub 0.8}Sr{sub 0.2}Ga{sub 1-x}Fe{sub x}O{sub 3}, has been studied by the dc four-probe method and the neutron powder diffraction. In the electrical conductivity measurement at RT, insulator-metal transition-like phenomenon was observed at around x{approx}0.35; this suggests an existence of the percolation limit for the electronic conductivity. Simultaneously, a bond length between O atoms, l{sub O-O}, in a MO{sub 6} octahedron (M=Ga{sub 1-x}Fe{sub x}) drastically expands over x{approx}0.4, according to the result of crystal structure refinement based on the hexagonal phase. Such a drastic expansion in the l{sub O-O} would induce the decrease in the oxygen ionic conductivity.

  17. Effect of pressure on f-electron delocalization and oxidation in actinide dioxides

    Energy Technology Data Exchange (ETDEWEB)

    Petit, L., E-mail: leon.petit@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Szotek, Z.; Temmerman, W.M. [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Stocks, G.M. [Materials Science and Technology Division and Center for Defect Physics, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Svane, A. [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

    2014-08-01

    Using first principles calculations, we have investigated f-electron delocalization and oxidation in the actinide dioxides under pressure. Whilst UO{sub 2} is found on the verge of an insulator to metal transition at the equilibrium volume, increasingly larger pressures are required to delocalize f-electrons in NpO{sub 2}, PuO{sub 2}, and AmO{sub 2}, respectively 49, 112, and 191 GPa. Compared to this broad range of pressures, the experimentally observed structural transitions, in all four dioxides, occur between 30 and 40 GPa, which leads us to conclude that the associated volume collapse is not due to f-electron delocalization. In contrast, oxidation of the dioxides is found to be linked to the degree of f-electron localization, but it emerges that for naturally occurring pressures (<10 GPa), higher oxides only exist for UO{sub 2}.

  18. Molecular dynamic simulation study of molten cesium

    Directory of Open Access Journals (Sweden)

    Yeganegi Saeid

    2017-01-01

    Full Text Available Molecular dynamics simulations were performed to study thermodynamics and structural properties of expanded caesium fluid. Internal pressure, radial distribution functions (RDFs, coordination numbers and diffusion coefficients have been calculated at temperature range 700–1600 K and pressure range 100–800 bar. We used the internal pressure to predict the metal–non-metal transition occurrence region. RDFs were calculated at wide ranges of temperature and pressure. The coordination numbers decrease and positions of the first peak of RDFs slightly increase as the temperature increases and pressure decreases. The calculated self-diffusion coefficients at various temperatures and pressures show no distinct boundary between Cs metallic fluid and its expanded fluid where it continuously increases with temperature.

  19. AB INITIO INVESTIGATION OF 12-CROWN-4 AND BENZO-12-CROWN-4 COMPLEXES WITH Li+, Na+, K+, Zn2+, Cd2+, AND Hg2+

    Directory of Open Access Journals (Sweden)

    Yahmin Yahmin

    2010-06-01

    Full Text Available The structure and binding energies of 12-crown-4 and benzo-12-crown-4 complexes with Li+, Na+, K+, Zn2+, Cd2+, and Hg2+were investigated with ab initio calculations using Hartree-Fock approximation and second-order perturbation theory. The basis set used in this study is lanl2mb. The structure optimization of cation-crown ether complexes was evaluated at HF/lanl2mb level of theory and interaction energy of the corresponding complexes was calculated at MP2/lanl2mb level of theory (MP2/lanl2mb//HF/lanl2mb. Interactions of the crown ethers and the cations were discussed in term of the structure parameter of crown ether. The binding energies of the complexes show that all complex formed from transition metal cations is more stable than the complexes formed from alkali metal cations.   Keywords: 12-crown-4, benzo-12-crown-4, alkali metals, transition metals

  20. Origin of Superconductivity and Latent Charge Density Wave in NbS2

    Science.gov (United States)

    Heil, Christoph; Poncé, Samuel; Lambert, Henry; Schlipf, Martin; Margine, Elena R.; Giustino, Feliciano

    2017-08-01

    We elucidate the origin of the phonon-mediated superconductivity in 2 H -NbS2 using the ab initio anisotropic Migdal-Eliashberg theory including Coulomb interactions. We demonstrate that superconductivity is associated with Fermi surface hot spots exhibiting an unusually strong electron-phonon interaction. The electron-lattice coupling is dominated by low-energy anharmonic phonons, which place the system on the verge of a charge density wave instability. We also provide definitive evidence for two-gap superconductivity in 2 H -NbS2 , and show that the low- and high-energy peaks observed in tunneling spectra correspond to the Γ - and K -centered Fermi surface pockets, respectively. The present findings call for further efforts to determine whether our proposed mechanism underpins superconductivity in the whole family of metallic transition metal dichalcogenides.

  1. Nonlinear phenomena in the highly excited state of C60

    International Nuclear Information System (INIS)

    Byrne, H.J.; Maser, W.K.; Kaiser, M.; Akselrod, L.; Anders, J.; Ruehle, W.W.; Zhou, X.Q.; Mittelbach, A.; Roth, S.

    1993-01-01

    Under high intensity illumination, the optical and electronic properties of fullerenes are seen to undergo dramatic, nonlinear changes. The photoluminescence emission is seen to increase with approximately the third power of the input intensity above an apparent threshold intensity. Associated with this nonlinear increase is the emergence of a long lifetime emission component and a redshifting of the emission spectrum. Above the threshold intensity the photoconductive response increases with approximately the cube of the input power. In the highly excited state, the photoconductive response becomes relatively temperature independent compared to the thermally activated behaviour observed at low intensities. The characteristics of the temperature dependence are associated with a metallic-like phase in the highly excited state and therefore an optically driven insulator to metal transition is proposed as a description of the observed phenomena. (orig.)

  2. Tunable electronic properties of silicene/GaP heterobilayer: Effects of electric field or biaxial tensile strain

    Science.gov (United States)

    Zhang, Peng; Yang, Xibin; Wu, Wei; Tian, Lifen; Cui, Heping; Zheng, Kai; Jiang, Junke; Chen, Xianping; Ye, Huaiyu

    2018-05-01

    We systematically investigate the electronic properties the two-dimensional (2D) silicene/GaP heterobilayer by using density functional theory calculations. We find the silicene and GaP monolayer are bounded to each other via orbital hybridization, and the charge redistribution occurring at the silicene/GaP interface leads to the opening of a direct energy band gap of about 0.997 eV in silicene. Importantly, by applying external electric field, the band structure of silicene/GaP heterostructure can be effectively modulated, and a semiconductor-metal transition even emerges. These intriguing properties make the silicene/GaP heterobilayer a promising 2D material for future electronics and strain sensors.

  3. Resistance switching in epitaxial SrCoO{sub x} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Tambunan, Octolia T.; Parwanta, Kadek J.; Acharya, Susant K.; Lee, Bo Wha; Jung, Chang Uk, E-mail: cu-jung@hufs.ac.kr [Department of Physics, Hankuk University of Foreign Studies, Yongin 449-791 (Korea, Republic of); Kim, Yeon Soo; Park, Bae Ho [Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-791 (Korea, Republic of); Jeong, Huiseong; Park, Ji-Yong [Department of Physics and Division of Energy System Research, Ajou University, Suwon 443-749 (Korea, Republic of); Cho, Myung Rae; Park, Yun Daniel [Department of Physics and Astronomy and Center for Subwavelength Optics, Seoul National University, Seoul 151-747 (Korea, Republic of); Choi, Woo Seok [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Kim, Dong-Wook [Department of Physics, Ewha Womans University, Seoul 120-750 (Korea, Republic of); Jin, Hyunwoo; Lee, Suyoun [Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Song, Seul Ji; Kang, Sung-Jin; Kim, Miyoung; Hwang, Cheol Seong [Department of Material Science and Engineering, Seoul National University, Seoul 151-747 (Korea, Republic of)

    2014-08-11

    We observed bipolar switching behavior from an epitaxial strontium cobaltite film grown on a SrTiO{sub 3} (001) substrate. The crystal structure of strontium cobaltite has been known to undergo topotactic phase transformation between two distinct phases: insulating brownmillerite (SrCoO{sub 2.5}) and conducting perovskite (SrCoO{sub 3−δ}) depending on the oxygen content. The current–voltage characteristics of the strontium cobaltite film showed that it could have a reversible insulator-to-metal transition triggered by electrical bias voltage. We propose that the resistance switching in the SrCoO{sub x} thin film could be related to the topotactic phase transformation and the peculiar structure of SrCoO{sub 2.5}.

  4. Resistance switching in epitaxial SrCoOx thin films

    Science.gov (United States)

    Tambunan, Octolia T.; Parwanta, Kadek J.; Acharya, Susant K.; Lee, Bo Wha; Jung, Chang Uk; Kim, Yeon Soo; Park, Bae Ho; Jeong, Huiseong; Park, Ji-Yong; Cho, Myung Rae; Park, Yun Daniel; Choi, Woo Seok; Kim, Dong-Wook; Jin, Hyunwoo; Lee, Suyoun; Song, Seul Ji; Kang, Sung-Jin; Kim, Miyoung; Hwang, Cheol Seong

    2014-08-01

    We observed bipolar switching behavior from an epitaxial strontium cobaltite film grown on a SrTiO3 (001) substrate. The crystal structure of strontium cobaltite has been known to undergo topotactic phase transformation between two distinct phases: insulating brownmillerite (SrCoO2.5) and conducting perovskite (SrCoO3-δ) depending on the oxygen content. The current-voltage characteristics of the strontium cobaltite film showed that it could have a reversible insulator-to-metal transition triggered by electrical bias voltage. We propose that the resistance switching in the SrCoOx thin film could be related to the topotactic phase transformation and the peculiar structure of SrCoO2.5.

  5. Resistance switching in epitaxial SrCoOx thin films

    International Nuclear Information System (INIS)

    Tambunan, Octolia T.; Parwanta, Kadek J.; Acharya, Susant K.; Lee, Bo Wha; Jung, Chang Uk; Kim, Yeon Soo; Park, Bae Ho; Jeong, Huiseong; Park, Ji-Yong; Cho, Myung Rae; Park, Yun Daniel; Choi, Woo Seok; Kim, Dong-Wook; Jin, Hyunwoo; Lee, Suyoun; Song, Seul Ji; Kang, Sung-Jin; Kim, Miyoung; Hwang, Cheol Seong

    2014-01-01

    We observed bipolar switching behavior from an epitaxial strontium cobaltite film grown on a SrTiO 3 (001) substrate. The crystal structure of strontium cobaltite has been known to undergo topotactic phase transformation between two distinct phases: insulating brownmillerite (SrCoO 2.5 ) and conducting perovskite (SrCoO 3−δ ) depending on the oxygen content. The current–voltage characteristics of the strontium cobaltite film showed that it could have a reversible insulator-to-metal transition triggered by electrical bias voltage. We propose that the resistance switching in the SrCoO x thin film could be related to the topotactic phase transformation and the peculiar structure of SrCoO 2.5

  6. ZnO Nanorods on a LaAlO 3 -SrTiO 3 Interface: Hybrid 1D-2D Diodes with Engineered Electronic Properties

    KAUST Repository

    Bera, Ashok; Lin, Weinan; Yao, Yingbang; Ding, Junfeng; Lourembam, James; Wu, Tao

    2015-01-01

    Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode-type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO3-SrTiO3 interface. Tunable insulator-to-metal transitions, absent in the individual components, are observed as a result of the competing temperature-dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler-Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Bosonic Confinement and Coherence in Disordered Nanodiamond Arrays.

    Science.gov (United States)

    Zhang, Gufei; Samuely, Tomas; Du, Hongchu; Xu, Zheng; Liu, Liwang; Onufriienko, Oleksandr; May, Paul W; Vanacken, Johan; Szabó, Pavol; Kačmarčík, Jozef; Yuan, Haifeng; Samuely, Peter; Dunin-Borkowski, Rafal E; Hofkens, Johan; Moshchalkov, Victor V

    2017-11-28

    In the presence of disorder, superconductivity exhibits short-range characteristics linked to localized Cooper pairs which are responsible for anomalous phase transitions and the emergence of quantum states such as the bosonic insulating state. Complementary to well-studied homogeneously disordered superconductors, superconductor-normal hybrid arrays provide tunable realizations of the degree of granular disorder for studying anomalous quantum phase transitions. Here, we investigate the superconductor-bosonic dirty metal transition in disordered nanodiamond arrays as a function of the dispersion of intergrain spacing, which ranges from angstroms to micrometers. By monitoring the evolved superconducting gaps and diminished coherence peaks in the single-quasiparticle density of states, we link the destruction of the superconducting state and the emergence of bosonic dirty metallic state to breaking of the global phase coherence and persistence of the localized Cooper pairs. The observed resistive bosonic phase transitions are well modeled using a series-parallel circuit in the framework of bosonic confinement and coherence.

  8. Manipulating Light with Transition Metal Clusters, Organic Dyes, and Metal Organic Frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Ogut, Serdar [Univ. of Illinois, Chicago, IL (United States)

    2017-09-11

    The primary goals of our research program is to develop and apply state-of-the-art first-principles methods to predict electronic and optical properties of three systems of significant scientific and technological interest: transition metal clusters, organic dyes, and metal-organic frameworks. These systems offer great opportunities to manipulate light for a wide ranging list of energy-related scientific problems and applications. During this grant period, we focused our investigations on the development, implementation, and benchmarking of many-body Green’s function methods (GW approximation and the Bethe-Salpeter equation) to examine excited-state properties of transition metal/transition-metal-oxide clusters and organic molecules that comprise the building blocks of dyes and metal-organic frameworks.

  9. Controlling phase separation in vanadium dioxide thin films via substrate engineering

    Science.gov (United States)

    Gilbert Corder, Stephanie N.; Jiang, Jianjuan; Chen, Xinzhong; Kittiwatanakul, Salinporn; Tung, I.-Cheng; Zhu, Yi; Zhang, Jiawei; Bechtel, Hans A.; Martin, Michael C.; Carr, G. Lawrence; Lu, Jiwei; Wolf, Stuart A.; Wen, Haidan; Tao, Tiger H.; Liu, Mengkun

    2017-10-01

    The strong electron-lattice interactions in correlated electron systems provide unique opportunities for altering the material properties with relative ease and flexibility. In this Rapid Communication, we use localized strain control via a focused-ion-beam patterning of Ti O2 substrates to demonstrate that one can selectively engineer the insulator-to-metal transition temperature, the fractional component of the insulating and metallic phases, and the degree of optical anisotropy down to the length scales of the intrinsic phase separation in V O2 thin films without altering the quality of the films. The effects of localized strain control on the strongly correlated electron system are directly visualized by state-of-the-art IR near-field imaging and spectroscopy techniques and x-ray microdiffraction measurements.

  10. Thermally tunable VO2-SiO2 nanocomposite thin-film capacitors

    Science.gov (United States)

    Sun, Yifei; Narayanachari, K. V. L. V.; Wan, Chenghao; Sun, Xing; Wang, Haiyan; Cooley, Kayla A.; Mohney, Suzanne E.; White, Doug; Duwel, Amy; Kats, Mikhail A.; Ramanathan, Shriram

    2018-03-01

    We present a study of co-sputtered VO2-SiO2 nanocomposite dielectric thin-film media possessing continuous temperature tunability of the dielectric constant. The smooth thermal tunability is a result of the insulator-metal transition in the VO2 inclusions dispersed within an insulating matrix. We present a detailed comparison of the dielectric characteristics of this nanocomposite with those of a VO2 control layer and of VO2/SiO2 laminate multilayers of comparable overall thickness. We demonstrated a nanocomposite capacitor that has a thermal capacitance tunability of ˜60% between 25 °C and 100 °C at 1 MHz, with low leakage current. Such thermally tunable capacitors could find potential use in applications such as sensing, thermal cloaks, and phase-change energy storage devices.

  11. Simulation of resonance hyper-Rayleigh scattering of molecules and metal clusters using a time-dependent density functional theory approach.

    Science.gov (United States)

    Hu, Zhongwei; Autschbach, Jochen; Jensen, Lasse

    2014-09-28

    Resonance hyper-Rayleigh scattering (HRS) of molecules and metal clusters have been simulated based on a time-dependent density functional theory approach. The resonance first-order hyperpolarizability (β) is obtained by implementing damped quadratic response theory using the (2n + 1) rule. To test this implementation, the prototypical dipolar molecule para-nitroaniline (p-NA) and the octupolar molecule crystal violet are used as benchmark systems. Moreover, small silver clusters Ag 8 and Ag 20 are tested with a focus on determining the two-photon resonant enhancement arising from the strong metal transition. Our results show that, on a per atom basis, the small silver clusters possess two-photon enhanced HRS comparable to that of larger nanoparticles. This finding indicates the potential interest of using small metal clusters for designing new nonlinear optical materials.

  12. Effect of biaxial strain and external electric field on electronic properties of MoS{sub 2} monolayer: A first-principle study

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Chuong V., E-mail: chuongnguyen11@gmail.com [Institute of Research and Development, Duy Tan University, Da Nang (Viet Nam); School of Mechanical Engineering, Le Quy Don Technical University, Ha Noi (Viet Nam); Hieu, Nguyen N. [Institute of Research and Development, Duy Tan University, Da Nang (Viet Nam)

    2016-04-01

    In this work, making use of density functional theory (DFT) computations, we systematically investigate the effect of biaxial strain engineering and external electric field applied perpendicular to the layers on the band gaps and electronic properties of monolayer MoS{sub 2}. The direct-to-indirect band gaps and semiconductor-to-metal transition are observed in monolayer MoS{sub 2} when strain and electric field are applied in our calculation. We show that when the biaxial strain and external electric field are introduced, the electronic properties including band gaps of monolayer MoS{sub 2} can be reduced to zero. Our results provide many useful insights for the wide applications of monolayer MoS{sub 2} in electronics and optoelectronics.

  13. Instantaneous band gap collapse in VO{sub 2} caused by photocarrier doping

    Energy Technology Data Exchange (ETDEWEB)

    Herzog, Marc; Wegkamp, Daniel; Wolf, Martin; Staehler, Julia [Fritz-Haber-Institut der MPG, Berlin (Germany); Xian, Lede; Cudazzo, Pierluigi [Univ. del Pais Vasco, San Sebastian (Spain); European Theoretical Spectroscopy Facility (ETSF) (France); Gatti, Matteo [European Theoretical Spectroscopy Facility (ETSF) (France); Ecole Polytechnique, Palaiseau (France); McGahan, Christina L.; Marvel, Robert E.; Haglund, Richard F. [Vanderbilt Univ., Nashville, Tennessee (United States); Rubio, Angel [Fritz-Haber-Institut der MPG, Berlin (Germany); Univ. del Pais Vasco, San Sebastian (Spain); European Theoretical Spectroscopy Facility (ETSF) (France); MPI for the Structure and Dynamics of Matter, Hamburg (Germany)

    2015-07-01

    We have investigated the controversially discussed mechanism of the insulator-to-metal transition (IMT) in VO{sub 2} by means of femtosecond time-resolved photoelectron spectroscopy (trPES). Our data show that photoexcitation transforms insulating monoclinic VO{sub 2} quasi-instantaneously into a metal without an 80 fs structural bottleneck for the photoinduced electronic phase transition. First-principles many-body perturbation theory calculations reveal an ultrahigh sensitivity of the VO{sub 2} band gap to variations of the dynamically screened Coulomb interaction thus supporting the fully electronically driven isostructural IMT indicated by our trPES results. We conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred.

  14. Thermophysical properties of shock compressed argon and xenon

    International Nuclear Information System (INIS)

    Fortov, V.E.; Gryaznov, V.K.; Mintsev, V.B.; Ternovoi, V.Ya.

    2001-01-01

    The problem of the nature of thermodynamic properties and the high level electrical conductivity of substances at high pressures and temperatures is one of the most key issues of physics of high energy densities. So called pressure ionization is one of the most impressive demonstrations of the strong coupling effects in plasma under compression. Noble gases are the simplest object of studying of these phenomena because of absence of molecules and spherical symmetry of their atoms. In the present paper we are trying to have a common look from the chemical plasma picture on the whole available massive of the experimental data on Ar and Xe in a wide range of the parameters: from gaseous densities of 0,01 g/cc and pressures of several kilobars up to extremely high densities corresponding to the insulator-metal transition and megabar pressure range. (orig.)

  15. Tuning electronic and magnetic properties of GaN nanosheets by surface modifications and nanosheet thickness.

    Science.gov (United States)

    Xiao, Meixia; Yao, Tingzhen; Ao, Zhimin; Wei, Peng; Wang, Danghui; Song, Haiyang

    2015-04-14

    Density-functional theory calculations are performed to investigate the effects of surface modifications and nanosheet thickness on the electronic and magnetic properties of gallium nitride (GaN) nanosheets (NSs). Unlike the bare GaN NSs terminating with polar surfaces, the systems with hydrogenated Ga (H-GaN), fluorinated Ga (F-GaN), and chlorinated Ga (Cl-GaN) preserve their initial wurtzite structures and exhibit ferromagnetic states. The abovementioned three different decorations on Ga atoms are energetically more favorable for thicker GaN NSs. Moreover, as the thickness increases, H-GaN and F-GaN NSs undergo semiconductor to metal and half-metal to metal transition, respectively, while Cl-GaN NSs remain completely metallic. The predicted diverse and tunable electronic and magnetic properties highlight the potential of GaN NSs for novel electronic and spintronic nanodevices.

  16. Phosphorene under strain:electronic, mechanical and piezoelectric responses

    Science.gov (United States)

    Drissi, L. B.; Sadki, S.; Sadki, K.

    2018-01-01

    Structural, electronic, elastic and piezoelectric properties of pure phosphorene under in-plane strain are investigated using first-principles calculations based on density functional theory. The two critical yielding points are determined along armchair and zigzag directions. It is shown that the buckling, the band gap and the charge transfer can be controlled under strains. A semiconductor to metallic transition is observed in metastable region. Polar plots of Young's modulus, Poisson ratio, sound velocities and Debye temperature exhibit evident anisotropic feature of phosphorene and indicate auxetic behavior for some angles θ. Our calculations show also that phosphorene has both in-plane and out-of-plane piezoelectric responses comparable to known 2D materials. The findings of this work reveal the great potential of pure phosphorene in nanomechanical applications.

  17. Tuning of Transport and Magnetic Properties in Epitaxial LaMnO3+δ Thin Films

    Directory of Open Access Journals (Sweden)

    J. Chen

    2014-01-01

    Full Text Available The effect of compressive strain on the transport and magnetic properties of epitaxial LaMnO3+δ thin films has been investigated. It is found that the transport and magnetic properties of the LaMnO3+δ thin films grown on the LaAlO3 substrates can be tuned by the compressive strain through varying film thickness. And the insulator-metal transition, charge/orbital ordering transition, and paramagnetic-ferromagnetic transition are suppressed by the compressive strain. Consequently, the related electronic and magnetic transition temperatures decrease with an increase in the compressive strain. The present results can be explained by the strain-controlled lattice deformation and the consequent orbital occupation. It indicates that the lattice degree of freedom is crucial for understanding the transport and magnetic properties of the strongly correlated LaMnO3+δ.

  18. Electrical properties of BiSrCaCuO films (2223)

    International Nuclear Information System (INIS)

    Okunev, V.D.; Pafomov, N.N.; Perekrestov, B.I.; Svistunov, V.M.

    1996-01-01

    The mechanisms of electrical conductivity of BiSrCaCuO films (2223) of different structural states are investigated. The films of an amorphous state (ρ = 10 3 - 10 10 Ohm centre dot cm) display a hopping conductivity with a variable hop length. Since the formation of a crystal structure (ρ = 10 - 10 3 Ohm centre dot cm) and up to the transition to a metal conductivity state (ρ ≅ 10 -2 Ohm centre dot cm) their electrical properties are similar to those of granular films featuring the exponential relation between specific resistance and separation between granules of metallic conductivity. In the vicinity of insulators-metal transition they feature the electrical conductivity-temperature relation with exponents 1/2 and 1/3. The transition to the metallic state is of a percolation nature and realized for a metal phase concentration of c m ≅ 0.2

  19. Spin dynamics in the metallic state of the high Tc superconducting system YBa2Cu3O6+x

    International Nuclear Information System (INIS)

    Bourges, P.; Sidis, Y.; Regnault, L.P.; Henry, J.Y.; Burlet, P.

    1994-01-01

    The spin dynamics in single-crystals of YBa 2 Cu 3 O 6+x has been successfully investigated, by inelastic neutron scattering (INS) experiments, as a function of temperature in the metallic state over the whole doping range from the weakly-doped to the heavily-doped and the over-doped regimes. Dynamical AF-correlations persist in all the metallic states. The imaginary part of the magnetic susceptibility, χ '' , consists of two contributions which have different doping and temperature dependences. At low temperature, χ '' exhibits an energy gap in any superconducting samples which becomes much weaker close to the insulating-metallic transition. To emphasize the characteristic features of the spin dynamics in YBCO, INS results obtained elsewhere are compared with the experiments. Several theoretical approaches, which intend to describe the energy lineshape of the dynamical magnetic susceptibility, are also discussed. (authors). 6 figs., 51 refs

  20. Mott-Hubbard transition and Anderson localization: A generalized dynamical mean-field theory approach

    International Nuclear Information System (INIS)

    Kuchinskii, E. Z.; Nekrasov, I. A.; Sadovskii, M. V.

    2008-01-01

    The DOS, the dynamic (optical) conductivity, and the phase diagram of a strongly correlated and strongly disordered paramagnetic Anderson-Hubbard model are analyzed within the generalized dynamical mean field theory (DMFT + Σ approximation). Strong correlations are taken into account by the DMFT, and disorder is taken into account via an appropriate generalization of the self-consistent theory of localization. The DMFT effective single-impurity problem is solved by a numerical renormalization group (NRG); we consider the three-dimensional system with a semielliptic DOS. The correlated metal, Mott insulator, and correlated Anderson insulator phases are identified via the evolution of the DOS and dynamic conductivity, demonstrating both the Mott-Hubbard and Anderson metal-insulator transition and allowing the construction of the complete zero-temperature phase diagram of the Anderson-Hubbard model. Rather unusual is the possibility of a disorder-induced Mott insulator-to-metal transition

  1. Quantum molecular dynamics simulations of thermophysical properties of fluid ethane.

    Science.gov (United States)

    Zhang, Yujuan; Wang, Cong; Zheng, Fawei; Zhang, Ping

    2012-12-01

    We have performed first-principles molecular-dynamics simulations based on density-functional theory to study the thermophysical properties of ethane under extreme conditions. We present results for the equation of state of fluid ethane in the warm dense region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity and optical reflectivity are derived. The close correlation between the nonmetal-metal transition of ethane and its decomposition, that ethane dissociates significantly into molecular and/or atomic hydrogen and some long alkane chains, has been systematically studied by analyzing the optical conductivity spectra, pair correlation functions, electronic density of states, and charge density distribution of fluid ethane.

  2. Spin Dependent Electronic Structure of Doped Manganese Perovskites

    International Nuclear Information System (INIS)

    Park, J.-H.

    1999-01-01

    The spin-resolved photoemission spectra were successfully obtained from La0.7Sr0.3MnO3 190 nm thick epitaxial film on SrTiO3(001). Well below Tc the results clearly manifest the half-metallic nature, i.e., for the majority spin, the photoemission spectrum clearly shows a metallic Fermi cut-off, whereas for the minority spin, it shows an insulating gap with disappearance of the spectral weight at ∼0.6 eV binding energy. On heating through Tc the spectra show no difference for different spins and the spectra weight at the Fermi level (EF disappears, indicating that the Mn 3d spins become disordered) and the system undergoes the ferromagnetic metal to paramagnetic non-metal transition. (c) 2000 American Vacuum Society

  3. Effects of an electric field on the electronic and optical properties of zigzag boron nitride nanotubes

    Science.gov (United States)

    Chegel, Raad; Behzad, Somayeh

    2011-02-01

    We have investigated the electro-optical properties of zigzag BNNTs, under an external electric field, using the tight binding approximation. It is found that an electric field modifies the band structure and splits the band degeneracy. Also the large electric strength leads to coupling the neighbor subbands which these effects reflect in the DOS and JDOS spectrum. It has been shown that, unlike CNTs, the band gap of BNNTs can be reduced linearly by applying a transverse external electric field. Also we show that the larger diameter tubes are more sensitive than small ones. The semiconducting metallic transition can be achieved through increasing the applied fields. The number and position of peaks in the JDOS spectrum are dependent on electric field strength. It is found that at a high electric field, the two lowest subbands are oscillatory with multiple nodes at the Fermi level.

  4. Electronic phase separation in insulating (Ga, Mn) As with low compensation: super-paramagnetism and hopping conduction

    Science.gov (United States)

    Yuan, Ye; Wang, Mao; Xu, Chi; Hübner, René; Böttger, Roman; Jakiela, Rafal; Helm, Manfred; Sawicki, Maciej; Zhou, Shengqiang

    2018-03-01

    In the present work, low compensated insulating (Ga,Mn)As with 0.7% Mn is obtained by ion implantation combined with pulsed laser melting. The sample shows variable-range hopping transport behavior with a Coulomb gap in the vicinity of the Fermi energy, and the activation energy is reduced by an external magnetic field. A blocking super-paramagnetism is observed rather than ferromagnetism. Below the blocking temperature, the sample exhibits a colossal negative magnetoresistance. Our studies confirm that the disorder-induced electronic phase separation occurs in (Ga,Mn)As samples with a Mn concentration in the insulator-metal transition regime, and it can account for the observed superparamagnetism and the colossal magnetoresistance.

  5. Anomalous optical switching and thermal hysteresis during semiconductor-metal phase transition of VO2 films on Si substrate

    International Nuclear Information System (INIS)

    Leahu, G.; Li Voti, R.; Sibilia, C.; Bertolotti, M.

    2013-01-01

    We present a detailed infrared study of the semiconductor-to-metal transition (SMT) in a vanadium dioxide (VO 2 ) film deposited on silicon wafer. The VO 2 phase transition is studied in the mid-infrared region by analyzing the transmittance and the reflectance measurements, and the calculated emissivity. The reflectance has been measured in two configurations: from the side of the VO 2 film and from that of Si wafer. The results show a strong asymmetry between the emissivity in the two configurations, and the fact that the emissivity dynamic range from the silicon side is twice as large than that from the VO 2 side. The temperature behaviour of the emissivity during the SMT put into evidence the phenomenon of the anomalous absorption in VO 2 , which has been explained by applying the Maxwell Garnett effective medium approximation theory

  6. Semiconductor-metal phase transition of vanadium dioxide nanostructures on silicon substrate: Applications for thermal control of spacecraft

    International Nuclear Information System (INIS)

    Leahu, G. L.; Li Voti, R.; Larciprete, M. C.; Belardini, A.; Mura, F.; Sibilia, C.; Bertolotti, M.; Fratoddi, I.

    2013-01-01

    We present a detailed infrared study of the semiconductor-to-metal transition (SMT) in a vanadium dioxide (VO2) film deposited on silicon wafer. The VO2 phase transition is studied in the mid-infrared (MIR) region by analyzing the transmittance and the reflectance measurements, and the calculated emissivity. The temperature behaviour of the emissivity during the SMT put into evidence the phenomenon of the anomalous absorption in VO2 which has been explained by applying the Maxwell Garnett effective medium approximation theory, together with a strong hysteresis phenomenon, both useful to design tunable thermal devices to be applied for the thermal control of spacecraft. We have also applied the photothermal radiometry in order to study the changes in the modulated emissivity induced by laser. Experimental results show how the use of these techniques represent a good tool for a quantitative measurement of the optothermal properties of vanadium dioxide based structures

  7. Reactive molecular beam epitaxial growth and in situ photoemission spectroscopy study of iridate superlattices

    Directory of Open Access Journals (Sweden)

    C. C. Fan

    2017-08-01

    Full Text Available High-quality (001-oriented perovskite [(SrIrO3m/(SrTiO3] superlattices (m=1/2, 1, 2, 3 and ∞ films have been grown on SrTiO3(001 epitaxially using reactive molecular beam epitaxy. Compared to previously reported superlattices synthesized by pulsed laser deposition, our superlattices exhibit superior crystalline, interface and surface structure, which have been confirmed by high-resolution X-ray diffraction, scanning transmission electron microscopy and atomic force microscopy, respectively. The transport measurements confirm a novel insulator-metal transition with the change of dimensionality in these superlattices, and our first systematic in situ photoemission spectroscopy study indicates that the increasing strength of effective correlations induced by reducing dimensionality would be the dominating origin of this transition.

  8. Phase transitions and equation of state of CsI under high pressure and the development of a focusing system for x-rays

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Yan.

    1990-11-01

    The phase transitions and equation of state of ionic solid cesium iodide were studied under high pressure and room temperature in a diamond anvil cell. The studies were carried out using both energy dispersive and angular dispersive diffraction methods on synchrotron radiation sources over the pressure range from atmospheric pressure to over 300 gigapascals (3 million atmospheres). CsI undergoes a distinct phase transition at about 40 GPa, a pressure that is much lower than the reported insulator-metal transition at 110 GPa, from the atmospheric pressure B2(CsCl) structure to an orthorhombic structure. At higher pressures, a continuous distortion in the structure was observed with a final structure similar to a hcp lattice under ultra high pressure. No volume discontinuity was observed at the insulator-metal transition. The newly found transition sequence is different from the result of previous static compression studies. The current structure has a smaller unit cell volume than the previous assignment. This has resolved a long existing controversy among the previous static compression studies, the dynamic compression studies, and the theoretical studies. The current results also explain the apparent discrepancy between the present study and the previous static studies. We also present the development of a focusing system for high energy x-rays (> 12 keV) that is particularly suited for high pressure diffraction studies. This system uses a pair of multilayer coated spherical mirrors in a Kirkpatrick-Baez geometry. A focused beam size less than 10 micron in diameter can be readily achieved with sufficient intensity to perform diffraction studies. 93 refs., 46 figs., 15 tabs.

  9. Phase diagram and transport properties for hydrogen-helium fluid planets

    International Nuclear Information System (INIS)

    Stevenson, D.J.; Salpeter, E.E.

    1977-01-01

    Hydrogen and helium are the major constituents of Jupiter and Saturn, and phase transitions can have important effects on the planetary structure. In this paper, the relevant phase diagrams and microscopic transport properties are analyzed in detail. The following paper (Paper II) applies these results to the evolution and present dynamic structure of the Jovian planets.Pure hydrogen is first discussed, especially the nature of the molecular-metallic transition and the melting curves for the two phases. It is concluded that at the temperatures and pressures of interest (Tapprox. =10 4 K, Papprox. =1--10 Mbar), both phases are fluid, but the transition between them might nevertheless be first-order. The insulator-metal transition in helium occurs at a much higher pressure (approx.70 Mbars) and is not of interest.The phase diagrams for both molecular and metallic hydrogen-helium mixtures are discussed. In the metallic mixture, calculations indicate a miscibility gap for T9 or approx. =10 4 K. Immiscibility in the molecular mixture is more difficult to predict but almost certainly occurs at much lower temperatures. A fluid-state model is constructed which predicts the likely topology of the three-dimensional phase diagram. The greater solubility of helium in the molecular phase leads to the prediction that the He/H mass ratio is typically twice as large in the molecular phase as in the coexisting metallic phase. Under these circumstances a ''density inversion'' is possible in which the molecular phase becomes more dense than the metallic phase.The partitioning of minor constituents is also considered: The deuterium/hydrogen mass ratio is essentially the same for all coexisting hydrogen-helium phases, at least for T> or approx. =5000 K. The partitioning of H 2 O, CH 4 , and NH 3 probably favors the molecular (or helium-rich) phase. Substances with high conduction electron density (e.g., Al) may partition into the metallic phase

  10. Composition-induced structural, electrical, and magnetic phase transitions in AX-type mixed-valence cobalt oxynitride epitaxial thin films

    International Nuclear Information System (INIS)

    Takahashi, Jumpei; Oka, Daichi; Hirose, Yasushi; Yang, Chang; Fukumura, Tomoteru; Hasegawa, Tetsuya; Nakao, Shoichiro; Harayama, Isao; Sekiba, Daiichiro

    2015-01-01

    Synthesis of mid- to late-transition metal oxynitrides is generally difficult by conventional thermal ammonolysis because of thermal instability. In this letter, we synthesized epitaxial thin films of AX-type phase-pure cobalt oxynitrides (CoO x N y ) by using nitrogen-plasma-assisted pulsed laser deposition and investigated their structural, electrical, and magnetic properties. The CoO x N y thin films with 0 ≤ y/(x + y) ≤ 0.63 grown on MgO (100) substrates showed a structural phase transition from rock salt (RS) to zinc blend at the nitrogen content y/(x + y) ∼ 0.5. As the nitrogen content increased, the room-temperature electrical resistivity of the CoO x N y thin films monotonically decreased from the order of 10 5  Ω cm to 10 −4  Ω cm. Furthermore, we observed an insulator-to-metal transition at y/(x + y) ∼ 0.34 in the RS-CoO x N y phase, which has not yet been reported in Co 2+ /Co 3+ mixed-valence cobalt oxides with octahedral coordination. The low resistivity in the RS-CoO x N y phase, on the 10 −3  Ω cm order, may have originated from the intermediate spin state of Co 3+ stabilized by the lowered crystal field symmetry of the CoO 6−n N n octahedra (n = 1, 2,…5). Magnetization measurements suggested that a magnetic phase transition occurred in the RS-CoO x N y films during the insulator-to-metal transition. These results demonstrate that low-temperature epitaxial growth is a promising approach for exploring novel electronic functionalities in oxynitrides

  11. Metallization and stiffness of the Li-intercalated MoS{sub 2} bilayer

    Energy Technology Data Exchange (ETDEWEB)

    Petrova, N.V. [Institute of Physics of National Academy of Sciences of Ukraine, Prospect Nauki 46, Kiev 03028 (Ukraine); Yakovkin, I.N., E-mail: yakov@iop.kiev.ua [Institute of Physics of National Academy of Sciences of Ukraine, Prospect Nauki 46, Kiev 03028 (Ukraine); Zeze, D.A. [School of Engineering & Computing Sciences, Durham University, Durham DH1 3LE (United Kingdom)

    2015-10-30

    Graphical abstract: The band structures, DOS, and Fermi surfaces for the MoS{sub 2} bilayer with adsorbed (a, c, e) and intercalated (b, d, f) Li (1 × 1) layer. - Highlights: • Adsorbed or intercalated Li monolayer makes the MoS{sub 2} surface metallic. • Increasing density of adsorbed Li leads to the nonmetal-to-metal transition in the layer. • Lithium inserted into MoS{sub 2} bilayers increases the interlayer interaction. - Abstract: Performed density-functional theory (DFT) calculations have shown that the Li adsorption on the MoS{sub 2} (0 0 0 1) surface, as well as Li intercalation into the space between MoS{sub 2} layers, transforms the semiconductor band structure of MoS{sub 2} into metallic. For the (√3 × √3) – R30° Li layer, the band structures of the MoS{sub 2} bilayer with adsorbed and intercalated Li are very similar, while for higher Li concentrations, the character of metallization for the adsorbed layer substantially differs from that of the MoS{sub 2}–Li–MoS{sub 2} layered system. In particular, for the adsorbed (1 × 1) Li monolayer, the increased density of the layer leads to the nonmetal-to-metal transition, which is evident from the appearance of the band crossing E{sub F} with an upward dispersion, pertinent to simple metals. It has been demonstrated that intercalated Li substantially increases the interlayer interaction in MoS{sub 2}. Specifically, the estimated 0.12 eV energy of the interlayer interaction in the MoS{sub 2} bilayer increases to 0.60 eV. This result is also consistent with results of earlier DFT calculations and available experimental results for alkali-intercalated graphene layers, which have demonstrated a substantial increase in the stiffness due to intercalation of alkalis.

  12. Phase transitions and equation of state of CsI under high pressure and the development of a focusing system for x-rays

    International Nuclear Information System (INIS)

    Wu, Yan.

    1990-11-01

    The phase transitions and equation of state of ionic solid cesium iodide were studied under high pressure and room temperature in a diamond anvil cell. The studies were carried out using both energy dispersive and angular dispersive diffraction methods on synchrotron radiation sources over the pressure range from atmospheric pressure to over 300 gigapascals (3 million atmospheres). CsI undergoes a distinct phase transition at about 40 GPa, a pressure that is much lower than the reported insulator-metal transition at 110 GPa, from the atmospheric pressure B2(CsCl) structure to an orthorhombic structure. At higher pressures, a continuous distortion in the structure was observed with a final structure similar to a hcp lattice under ultra high pressure. No volume discontinuity was observed at the insulator-metal transition. The newly found transition sequence is different from the result of previous static compression studies. The current structure has a smaller unit cell volume than the previous assignment. This has resolved a long existing controversy among the previous static compression studies, the dynamic compression studies, and the theoretical studies. The current results also explain the apparent discrepancy between the present study and the previous static studies. We also present the development of a focusing system for high energy x-rays (> 12 keV) that is particularly suited for high pressure diffraction studies. This system uses a pair of multilayer coated spherical mirrors in a Kirkpatrick-Baez geometry. A focused beam size less than 10 micron in diameter can be readily achieved with sufficient intensity to perform diffraction studies. 93 refs., 46 figs., 15 tabs

  13. Influence of O{sub 2} exposure on the interaction between CH{sub 4} and amorphous AlYB{sub 14}

    Energy Technology Data Exchange (ETDEWEB)

    Hunold, Oliver, E-mail: hunold@mch.rwth-aachen.de [Materials Chemistry, RWTH Aachen University, Kopernikusstr, 10, D-52074 Aachen (Germany); Wiesing, Martin; Arcos, Teresa de los [Technical and Macromolecular Chemistry, University of Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany); Music, Denis [Materials Chemistry, RWTH Aachen University, Kopernikusstr, 10, D-52074 Aachen (Germany); Grundmeier, Guido [Technical and Macromolecular Chemistry, University of Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany); Schneider, Jochen M. [Materials Chemistry, RWTH Aachen University, Kopernikusstr, 10, D-52074 Aachen (Germany)

    2017-01-15

    Highlights: • Influence of O{sub 2} exposure on the surface chemistry of a-AlYB{sub 14} on the interaction with CH{sub 4} and PE studied by ab initio and UHV-AFM. • Predicted stronger interaction is consistent with experimentally observed trends. • Upon O{sub 2} exposure surface bonding becomes more semiconducting causing a charge redistribution within the adsorbed CH{sub 4} molecule. • The data serve as proof of concept for exploring polymer − hard coating interactions in varying atmospheres. - Abstract: The influence of surface oxidation on the interaction between CH{sub 4} and amorphous AlYB{sub 14} (a-AlYB{sub 14}) has been studied theoretically by using density functional theory and experimentally by ultra-high vacuum atomic force microscopy (UHV-AFM). CH{sub 4} mimics the –CH{sub 3} termination and aliphatic subunits of a polymer chain. Low-energy ion scattering measurements of magnetron sputtered thin films suggest that the bonding at the surfaces of pristine a-AlYB{sub 14} and O{sub 2} exposed a-AlYB{sub 14} (O{sub 2}//a-AlYB{sub 14}) is metal-boron and metal-oxygen dominated, respectively. Based on the ab initio calculations the adsorption energies of CH{sub 4} on a-AlYB{sub 14} and O{sub 2}//a-AlYB{sub 14} decreases from −0.07 to −0.30 eV, respectively. This trend is consistent with experimental data obtained by colloidal probe UHV-AFM studies with a polyethylene sphere, where larger adhesion forces for the O{sub 2} exposed surface as compared to the pristine a-AlYB{sub 14} surface were measured. No charge transfer takes place between CH{sub 4} and the pristine as well as the O{sub 2} exposed a-AlYB{sub 14}. Oxygen chemisorption induces changes in surface bonding. States at the Fermi level are depleted upon oxidation, hence the surface bonding becomes more semiconducting causing a charge redistribution within the adsorbed CH{sub 4} molecule. Hence, these data serve as proof of concept for exploring the effect of O{sub 2} exposure on the

  14. Influence of O_2 exposure on the interaction between CH_4 and amorphous AlYB_1_4

    International Nuclear Information System (INIS)

    Hunold, Oliver; Wiesing, Martin; Arcos, Teresa de los; Music, Denis; Grundmeier, Guido; Schneider, Jochen M.

    2017-01-01

    Highlights: • Influence of O_2 exposure on the surface chemistry of a-AlYB_1_4 on the interaction with CH_4 and PE studied by ab initio and UHV-AFM. • Predicted stronger interaction is consistent with experimentally observed trends. • Upon O_2 exposure surface bonding becomes more semiconducting causing a charge redistribution within the adsorbed CH_4 molecule. • The data serve as proof of concept for exploring polymer − hard coating interactions in varying atmospheres. - Abstract: The influence of surface oxidation on the interaction between CH_4 and amorphous AlYB_1_4 (a-AlYB_1_4) has been studied theoretically by using density functional theory and experimentally by ultra-high vacuum atomic force microscopy (UHV-AFM). CH_4 mimics the –CH_3 termination and aliphatic subunits of a polymer chain. Low-energy ion scattering measurements of magnetron sputtered thin films suggest that the bonding at the surfaces of pristine a-AlYB_1_4 and O_2 exposed a-AlYB_1_4 (O_2//a-AlYB_1_4) is metal-boron and metal-oxygen dominated, respectively. Based on the ab initio calculations the adsorption energies of CH_4 on a-AlYB_1_4 and O_2//a-AlYB_1_4 decreases from −0.07 to −0.30 eV, respectively. This trend is consistent with experimental data obtained by colloidal probe UHV-AFM studies with a polyethylene sphere, where larger adhesion forces for the O_2 exposed surface as compared to the pristine a-AlYB_1_4 surface were measured. No charge transfer takes place between CH_4 and the pristine as well as the O_2 exposed a-AlYB_1_4. Oxygen chemisorption induces changes in surface bonding. States at the Fermi level are depleted upon oxidation, hence the surface bonding becomes more semiconducting causing a charge redistribution within the adsorbed CH_4 molecule. Hence, these data serve as proof of concept for exploring the effect of O_2 exposure on the interaction between aliphatic polymers and a-AlYB_1_4 using a correlative experimental and theoretical research approach.

  15. Multiple magnetic transitions, dynamical magnetic liquid and magnetic glass in La{sub 1−x−y}Pr{sub y}Ca{sub x}MnO{sub 3} (x≈0.42, y≈0.40) thin films: A thickness dependent study

    Energy Technology Data Exchange (ETDEWEB)

    Agarwal, Vasudha; Kandpal, Lalit M.; Siwach, P.K.; Awana, V.P.S. [CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); AcSIR at CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Singh, H.K., E-mail: hks65@nplindia.org [CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); AcSIR at CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012 (India)

    2015-11-15

    The influence of substrate induced strain and its relaxation on the evolution of the multiple magnetic transitions and ensuing modifications in the degree of phase separation, the nature of the dynamical magnetic liquid, the randomly frozen glass and insulator–metal transitions have been investigated in single crystalline La{sub 1−x−y}Pr{sub y}Ca{sub x}MnO{sub 3} (x≈0.42, y≈0.40) in t~20–140 nm thick films deposited on LaAlO{sub 3} (001) substrates. The ferromagnetic (FM) transition temperature (T{sub C}) first decreases as the film thickness is increased from t~20 nm to t~60 nm and then increases with increasing film thickness. In contrast the charge ordering (CO), antiferromagnetic (AFM) and glass transition temperatures shift towards higher values with increasing film thickness. The field cooled cooling (FCC) and field cooled warming (FCW) magnetization (M–T) of films having t≥60 nm shows pronounced hysteresis and ΔT{sub C}=T{sub C}{sup FCW}−T{sub C}{sup FCC} decreases concomitantly from 46 K to 35 K as the thickness increases from ~60 to ~140 nm. The thinnest film shows insulator to metal transitions (IMT) only at magnetic field H>40 kOe. Films with t≥T{sub C} show sharp hysteretic IMT, with ΔT{sub IM}=T{sub IM}{sup W}−T{sub IM}{sup C} decreasing from ~70 K to ~50 K as the thickness increases from ~60 nm to ~140 nm. Such strong hysteresis is a characteristic of first order phase transition and also a signature of magnetic liquid like phase created by the magnetic frustration created by the delicate balance between FM and AFM/CO phases. The H induced AFM/CO to FM transition reduces ΔT{sub IM} and at higher fields the phase transition appears akin to the second order. The observed difference in the magnetic and transport properties have been explained in terms of the substrate induced strain at lower film thickness and its relaxation at higher thickness. - Highlights: • Different thickness La{sub 1−x−y}Pr{sub y}Ca{sub x}MnO{sub 3

  16. Processing and characterization of Sr{sub 2−x}VMoO{sub 6−δ} double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Weisentein, A.J., E-mail: a.weisenstein@gmail.com [Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59717-3800 (United States); Childs, N., E-mail: nick.childs@msu.montana.edu [Department of Physics, Montana State University, Bozeman, MT 59717-3804 (United States); Amendola, R., E-mail: roberta.amendola@coe.montana.edu [Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717-3920 (United States); Driscoll, D., E-mail: davidrobertdriscoll@gmail.com [Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59717-3800 (United States); Sofie, S.W., E-mail: ssofie@me.montana.edu [Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59717-3800 (United States); Gannon, P., E-mail: pgannon@coe.montana.edu [Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717-3920 (United States); Smith, R., E-mail: smith@physics.montana.edu [Department of Physics, Montana State University, Bozeman, MT 59717-3804 (United States)

    2013-05-15

    In this study, the analysis and characterization of the processing and sintering of Sr{sub 2−x}VMoO{sub 6−δ} perovskites, where x = 0.0, 0.1 and 0.2, was investigated with application potential in high temperature fuel cell electrodes and electro-catalysts. Sr{sub 2−x}VMoO{sub 6−δ} substrates were sintered in a reducing (5%H{sub 2} 95%N{sub 2}) atmosphere at 1100 °C, 1200 °C, and 1300 °C. The X-ray diffraction patterns indicate that the double perovskite is the primary phase for Sr{sub 2−x}VMoO{sub 6−δ} pellets sintered at 1200 °C and 1300 °C for 20 h; however, these pellets show a secondary phase of SrMoO{sub 4−δ}. X-ray photoelectron spectroscopy revealed a deficiency of vanadium on the pellet surfaces, in which samples yielded surface vanadium concentrations of less than 5%. The vanadium inhomogeneity can be explained by the formation of the SrMoO{sub 4−δ} scheelite phase (ABO{sub 4}) due to oxygen exposure on the surface of the pellets, which indicates inward vanadium migration to the bulk, and was exhibited in redox cycling. Sr{sub 2−x}VMoO{sub 6−δ} pellets sintered at 1300 °C showed the lowest resistivity at both SOFC operating temperature (800 °C) and room temperature. The resistivity tests also show a semiconductor to metallic transition for all double perovskites, from heating up to 800 °C to cooling down to room temperature in a reducing atmosphere, related to the reduction of Mo{sup 6+} to Mo{sup 4+}. - Highlights: ► Primary Sr{sub 2−x}VMoO{sub 6−δ} phase only shown to form in excess of 1300 °C in reducing. ► Surface formation of secondary phase SrMoO{sub 4−δ} (Mo{sup 6+}) observed at RT in air. ► Surface vanadium deficiency induced by inward atomic diffusion. ► Semiconductor to metallic transition is related to the reduction of Mo{sup 6+} to Mo{sup 4+}.

  17. Processing and characterization of Sr2−xVMoO6−δ double perovskites

    International Nuclear Information System (INIS)

    Weisentein, A.J.; Childs, N.; Amendola, R.; Driscoll, D.; Sofie, S.W.; Gannon, P.; Smith, R.

    2013-01-01

    In this study, the analysis and characterization of the processing and sintering of Sr 2−x VMoO 6−δ perovskites, where x = 0.0, 0.1 and 0.2, was investigated with application potential in high temperature fuel cell electrodes and electro-catalysts. Sr 2−x VMoO 6−δ substrates were sintered in a reducing (5%H 2 95%N 2 ) atmosphere at 1100 °C, 1200 °C, and 1300 °C. The X-ray diffraction patterns indicate that the double perovskite is the primary phase for Sr 2−x VMoO 6−δ pellets sintered at 1200 °C and 1300 °C for 20 h; however, these pellets show a secondary phase of SrMoO 4−δ . X-ray photoelectron spectroscopy revealed a deficiency of vanadium on the pellet surfaces, in which samples yielded surface vanadium concentrations of less than 5%. The vanadium inhomogeneity can be explained by the formation of the SrMoO 4−δ scheelite phase (ABO 4 ) due to oxygen exposure on the surface of the pellets, which indicates inward vanadium migration to the bulk, and was exhibited in redox cycling. Sr 2−x VMoO 6−δ pellets sintered at 1300 °C showed the lowest resistivity at both SOFC operating temperature (800 °C) and room temperature. The resistivity tests also show a semiconductor to metallic transition for all double perovskites, from heating up to 800 °C to cooling down to room temperature in a reducing atmosphere, related to the reduction of Mo 6+ to Mo 4+ . - Highlights: ► Primary Sr 2−x VMoO 6−δ phase only shown to form in excess of 1300 °C in reducing. ► Surface formation of secondary phase SrMoO 4−δ (Mo 6+ ) observed at RT in air. ► Surface vanadium deficiency induced by inward atomic diffusion. ► Semiconductor to metallic transition is related to the reduction of Mo 6+ to Mo 4+

  18. Composition-induced structural, electrical, and magnetic phase transitions in AX-type mixed-valence cobalt oxynitride epitaxial thin films

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Jumpei; Oka, Daichi [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan); Kanagawa Academy of Science and Technology (KAST), 3-2-1 Sakado, Takatsu, Kawasaki 213-0012 (Japan); Hirose, Yasushi, E-mail: hirose@chem.s.u-tokyo.ac.jp; Yang, Chang; Fukumura, Tomoteru; Hasegawa, Tetsuya [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan); Kanagawa Academy of Science and Technology (KAST), 3-2-1 Sakado, Takatsu, Kawasaki 213-0012 (Japan); CREST, Japan Science and Technology Agency, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan); Nakao, Shoichiro [Kanagawa Academy of Science and Technology (KAST), 3-2-1 Sakado, Takatsu, Kawasaki 213-0012 (Japan); CREST, Japan Science and Technology Agency, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan); Harayama, Isao; Sekiba, Daiichiro [University of Tsukuba Tandem Accelerator Complex (UTTAC), 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8577 (Japan)

    2015-12-07

    Synthesis of mid- to late-transition metal oxynitrides is generally difficult by conventional thermal ammonolysis because of thermal instability. In this letter, we synthesized epitaxial thin films of AX-type phase-pure cobalt oxynitrides (CoO{sub x}N{sub y}) by using nitrogen-plasma-assisted pulsed laser deposition and investigated their structural, electrical, and magnetic properties. The CoO{sub x}N{sub y} thin films with 0 ≤ y/(x + y) ≤ 0.63 grown on MgO (100) substrates showed a structural phase transition from rock salt (RS) to zinc blend at the nitrogen content y/(x + y) ∼ 0.5. As the nitrogen content increased, the room-temperature electrical resistivity of the CoO{sub x}N{sub y} thin films monotonically decreased from the order of 10{sup 5} Ω cm to 10{sup −4} Ω cm. Furthermore, we observed an insulator-to-metal transition at y/(x + y) ∼ 0.34 in the RS-CoO{sub x}N{sub y} phase, which has not yet been reported in Co{sup 2+}/Co{sup 3+} mixed-valence cobalt oxides with octahedral coordination. The low resistivity in the RS-CoO{sub x}N{sub y} phase, on the 10{sup −3} Ω cm order, may have originated from the intermediate spin state of Co{sup 3+} stabilized by the lowered crystal field symmetry of the CoO{sub 6−n}N{sub n} octahedra (n = 1, 2,…5). Magnetization measurements suggested that a magnetic phase transition occurred in the RS-CoO{sub x}N{sub y} films during the insulator-to-metal transition. These results demonstrate that low-temperature epitaxial growth is a promising approach for exploring novel electronic functionalities in oxynitrides.

  19. Resolving the chicken-and-egg problem in VO2: a new paradigm for the Mott transition

    Science.gov (United States)

    Najera, Oscar; Civelli, Marcello; Dobrosavljevi, Vladimir; Rozenberg, Marcelo

    We consider a minimal model to investigate the metal-insulator transition in VO2. We adopt a Hubbard model with two orbital per unit cell, which captures the competition between Mott and singlet-dimer localization. We solve the model within Dynamical Mean Field Theory, characterizing in detail the metal-insulator transition and finding new features in the electronic states. We compare our results with available experimental data obtaining good agreement in the relevant model parameter range. Crucially, we can account for puzzling optical conductivity data obtained within the hysteresis region, which we associate to a novel metallic state characterized by a split heavy quasiparticle band. Our results show that the thermal-driven insulator-to-metal transition in VO2 is entirely compatible with a Mott electronic mechanism, solving a long standing ''chicken-and-egg'' debate and calling for further research of ``Mottronics'' applications of this system. This work was partially supported by public Grants from the French National Research Agency (ANR), project LACUNES No ANR-13-BS04-0006-01, the NSF DMR-1005751 and DMR-1410132.

  20. A theory for the anisotropic interaction between two substitutional magnetic impurities and the magnetic anisotropic effect in dilute magnetic alloys

    International Nuclear Information System (INIS)

    Satter, M.A.

    1990-08-01

    In this paper, a formalism for studying the anisotropic interaction between two substitutional magnetic impurities and the magnetic anisotropic effect in a dilute noble metal- transition metal magnetic alloy has been developed from relativistic scattering theory. The theoretical development and the computational techniques of this formalism are based on relativistic spin-polarized scattering theory and relativistic band structure frameworks. For studying the magnetic anisotropic effect a convenient ''working'' frame of reference with its axes oriented along the fcc crystal axes is set up. This formalism is applied to study the situation for two Fe impurities in paramagnetic Au hosts. For AuFe dilute alloy, the two impurity site interaction as a function of separation is not oscillatory and the anisotropic effect is found to be less than the two site interaction itself only by an order of magnitude. Apart from the anisotropic coupling of the two impurity spins to the separation vector, for the first time, another weak anisotropic coupling to the crystal axes is also contained in the two site interaction. These anisotropic effects are the results of the relativistic spin-orbit interaction which are incorporated into the formalism. (author). 22 refs, 5 figs

  1. Reducing the Schottky barrier between few-layer MoTe2 and gold

    Science.gov (United States)

    Qi, Dianyu; Wang, Qixing; Han, Cheng; Jiang, Jizhou; Zheng, Yujie; Chen, Wei; Zhang, Wenjing; Thye Shen Wee, Andrew

    2017-12-01

    Schottky barriers greatly influence the performance of optoelectronic devices. Schottky barriers can be reduced by harnessing the polymorphism of 2D metal transition dichalcogenides, since both semiconducting and metallic phases exist. However, high energy, high temperature or chemicals are normally required for phase transformation, or the processes are complex. In this work, stable low-resistance contacts between few layer MoTe2 flakes and gold electrodes are achieved by a simple thermal annealing treatment at low temperature (200-400 °C). The resulting Schottky barrier height of the annealed MoTe2/Au interface is low (~23 meV). A new Raman A g mode of the 1T‧ metallic phase of MoTe2 on gold electrode is observed, indicating that the low-resistance contact is due to the phase transition of 2H-MoTe2. The gold substrate plays an important role in the transformation, and a higher gold surface roughness increases the transformation rate. With this method, the mobility and ON-state current of the MoTe2 transistor increase by ~3-4 orders of magnitude, the photocurrent of vertically stacked graphene/MoTe2/Au device increases ~300%, and the response time decreases by ~20%.

  2. Computer predictions on Rh-based double perovskites with unusual electronic and magnetic properties

    Science.gov (United States)

    Halder, Anita; Nafday, Dhani; Sanyal, Prabuddha; Saha-Dasgupta, Tanusri

    2018-03-01

    In search for new magnetic materials, we make computer prediction of structural, electronic and magnetic properties of yet-to-be synthesized Rh-based double perovskite compounds, Sr(Ca)2BRhO6 (B=Cr, Mn, Fe). We use combination of evolutionary algorithm, density functional theory, and statistical-mechanical tool for this purpose. We find that the unusual valence of Rh5+ may be stabilized in these compounds through formation of oxygen ligand hole. Interestingly, while the Cr-Rh and Mn-Rh compounds are predicted to be ferromagnetic half-metals, the Fe-Rh compounds are found to be rare examples of antiferromagnetic and metallic transition-metal oxide with three-dimensional electronic structure. The computed magnetic transition temperatures of the predicted compounds, obtained from finite temperature Monte Carlo study of the first principles-derived model Hamiltonian, are found to be reasonably high. The prediction of favorable growth condition of the compounds, reported in our study, obtained through extensive thermodynamic analysis should be useful for future synthesize of this interesting class of materials with intriguing properties.

  3. Origin of spin-polarization in edge boron doped zigzag graphene nanoribbon: a potential spin filter.

    Science.gov (United States)

    Chakrabarty, Soubhik; Wasey, A H M Abdul; Thapa, Ranjit; Das, Gour Prasad

    2018-06-04

    To realize the graphene based spintronic device the prime challenge is to control the electronic structure of edges. In this work we find the origin of spin filtering property in edge boron doped zigzag graphene nanoribbon (ZGNRs) and provide a guide to prepare the graphene based next generation spin filter based device. Here we unveil the role of orbital (p-electron) to tune the electronic, magnetic and transport properties of the edge B doped ZGNRs. When all the edge carbon atoms at one of the edges of ZGNRs are replaced by B (100% edge B-doping), the system undergoes semiconductor to metal transition. The role of passivation of the edge with single/double atomic hydrogen on the electronic properties and its relation with the p electron is correlated in-depth. 50% edge B-doped ZGNRs (50% of the edge C atoms at one of the edges are replaced by B) also shows half-metallicity when the doped edge is left unpassivated. The half-metallic systems show 100% spin-filtering efficiency for a wide range of bias voltages. Zero bias transmission function of the other configurations shows asymmetric behavior for the up and down spin channels, thereby indicating their possible application potential in nano-spintronics. © 2018 IOP Publishing Ltd.

  4. Dynamic Compression Experiments on Hydrogen and Deuterium in the Warm Dense Liquid.

    Science.gov (United States)

    Desjarlais, Michael; McCoy, Chad; Cochrane, Kyle; Mattsson, Thomas; Knudson, Marcus; Redmer, Ronald

    2017-06-01

    Recently a shock-ramp platform has been developed on the Z Accelerator to access off-Hugoniot states in liquids. The accelerator delivers a two-step current pulse; the first accelerates the electrode to a constant velocity, which upon impact with the sample cell creates a well-defined shock, the subsequent current rise produces ramp compression from the initially shocked state producing relatively cool (1-2 kK), high pressure (>300 GPa), high compression (10 to 15-fold compression) states. This technique allows experimental access to the region of phase space where hydrogen is predicted to undergo a first-order phase transition from an insulating molecular-like to a conducting atomic-like liquid. Here we discuss the experimental platform, survey various theoretical predictions for the liquid-liquid, insulator-to-metal transition in hydrogen, and present results of experiments on both deuterium and hydrogen that clearly show an abrupt transition to a metallic state. We also present results from recent experiments at higher temperatures (3-4 kK) and compare the observations to both first-principles theory and previous step-wise loading experiments that exhibited a minimum metallic conductivity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  5. Pressure-induced structural and semiconductor-semiconductor transitions in C o0.5M g0.5C r2O4

    Science.gov (United States)

    Rahman, S.; Saqib, Hajra; Zhang, Jinbo; Errandonea, D.; Menéndez, C.; Cazorla, C.; Samanta, Sudeshna; Li, Xiaodong; Lu, Junling; Wang, Lin

    2018-05-01

    The effect of pressure on the structural, vibrational, and electronic properties of Mg-doped Cr bearing spinel C o0.5M g0.5C r2O4 was studied up to 55 GPa at room-temperature using x-ray diffraction, Raman spectroscopy, electrical transport measurements, and ab initio calculations. We found that the ambient-pressure phase is cubic (spinel-type, F d 3 ¯m ) and underwent a pressure-induced structural transition to a tetragonal phase (space group I 4 ¯m 2 ) above 28 GPa. The ab initio calculation confirmed this first-order phase transition. The resistivity of the sample decreased at low pressures with the existence of a low-pressure (LP) phase and started to increase with the emergence of a high-pressure (HP) phase. The temperature dependent resistivity experiments at different pressures illustrated the wide band gap semiconducting nature of both the LP and HP phases with different activation energies, suggesting a semiconductor-semiconductor transition at HP. No evidence of chemical decomposition or a semiconductor-metal transition was observed in our studies.

  6. Evaluation of ΔGsub(f) values for unstable compounds: a Fortran program for the calculation of ternary phase equilibria

    International Nuclear Information System (INIS)

    Throop, G.J.; Rogl, P.; Rudy, E.

    1978-01-01

    A Fortran IV program was set up for the calculation of phase equilibria and tieline distributions in ternary systems of the type: transition metal-transition metal-nonmetal (interstitial type of solid solutions). The method offers the possibility of determining the thermodynamic values for unstable compounds through their influence upon ternary phase equilibria. The variation of the free enthalpy of formation of ternary solid solutions is calculated as a function of nonmetal content, thus describing the actual curvature of the phase boundaries. The integral and partial molar free enthalpies of formation of binary nonstoichiometric compounds and of phase solutions are expressed as analytical functions of the nonmetal content within their homogeneity range. The coefficient of these analytical expressions are obtained by the use either of the Wagner-Schottky vacancy model or polynomials second order in composition (parabolic approach). The free energy of formation, ΔGsub(f) has been calculated for the systems Ti-C, Zr-C, and Ta-C. Calculations of the ternary phase equilibria yielded the values for ΔGsub(f) for the unstable compounds Ti 2 C at 1500 0 C and Zr 2 C at 1775 0 C of -22.3 and 22.7 kcal g atom metal respectively. These values were used for the calculation of isothermal sections within the ternary systems Ti-Ta-C (at 1500 0 C) and Zr-Ta-C (at 1775 0 C). The ideal case of ternary phase solutions is extended to regular solutions. (author)

  7. Ultrafast photo-induced hidden phases in strained manganite thin films

    Science.gov (United States)

    Zhang, Jingdi; McLeod, A. S.; Zhang, Gu-Feng; Stoica, Vladimir; Jin, Feng; Gu, Mingqiang; Gopalan, Venkatraman; Freeland, John W.; Wu, Wenbin; Rondinelli, James; Wen, Haidan; Basov, D. N.; Averitt, R. D.

    Correlated transition metal oxides (TMOs) are particularly sensitive to external control because of energy degeneracy in a complex energy landscape that promote a plethora of metastable states. However, it remains a grand challenge to actively control and fully explore the rich landscape of TMOs. Dynamic control with pulsed photons can overcome energetic barriers, enabling access to transient or metastable states that are not thermally accessible. In the past, we have demonstrated that mode-selective single-laser-pulse excitation of a strained manganite thin film La2/3Ca1/3MnO3 initiates a persistent phase transition from an emergent antiferromagnetic insulating ground state to a ferromagnetic metallic metastable state. Beyond the photo-induced insulator to metal transition, we recently discovered a new peculiar photo-induced hidden phase, identified by an experimental approach that combines ultrafast pump-probe spectroscopy, THz spectroscopy, X-ray diffraction, cryogenic near-field spectroscopy and SHG probe. This work is funded by the DOE, Office of Science, Office of Basic Energy Science under Award Numbers DE-SC0012375 and DE-SC0012592.

  8. Molecular Dynamics Simulations of Liquid Phosphorus at High Temperature and Pressure

    International Nuclear Information System (INIS)

    Wu Yanning; Zhao Gang; Liu Changsong; Zhu Zhengang

    2008-01-01

    By performing ab initio molecular dynamics simulations, we have investigated the microstructure, dynamical and electronic properties of liquid phosphorus (P) under high temperature and pressure. In our simulations, the calculated coordination number (CN) changes discontinuously with density, and seems to increase rapidly after liquid P is compressed to 2.5 g/cm 3 . Under compression, liquid P shows the first-order liquid-liquid phase transition from the molecular liquid composed of the tetrahedral P 4 molecules to complex polymeric form with three-dimensional network structure, accompanied by the nonmetal to metal transition of the electronic structure. The order parameters Q 6 and Q 4 are sensitive to the microstructural change of liquid P. By calculating diffusion coefficients, we show the dynamical anomaly of liquid P by compression. At lower temperatures, a maximum exists at the diffusion coefficients as a function of density; at higher temperatures, the anomalous behavior is weakened. The excess entropy shows the same phenomena as the diffusion coefficients. By analysis of the angle distribution functions and angular limited triplet correlation functions, we can clearly find that the Peierls distortion in polymeric form of liquid P is reduced by further compression

  9. Equations of state for hydrogen and deuterium.

    Energy Technology Data Exchange (ETDEWEB)

    Kerley, Gerald Irwin (Kerley Technical Services, Appomattox, VA)

    2003-12-01

    This report describes the complete revision of a deuterium equation of state (EOS) model published in 1972. It uses the same general approach as the 1972 EOS, i.e., the so-called 'chemical model,' but incorporates a number of theoretical advances that have taken place during the past thirty years. Three phases are included: a molecular solid, an atomic solid, and a fluid phase consisting of both molecular and atomic species. Ionization and the insulator-metal transition are also included. The most important improvements are in the liquid perturbation theory, the treatment of molecular vibrations and rotations, and the ionization equilibrium and mixture models. In addition, new experimental data and theoretical calculations are used to calibrate certain model parameters, notably the zero-Kelvin isotherms for the molecular and atomic solids, and the quantum corrections to the liquid phase. The report gives a general overview of the model, followed by detailed discussions of the most important theoretical issues and extensive comparisons with the many experimental data that have been obtained during the last thirty years. Questions about the validity of the chemical model are also considered. Implications for modeling the 'giant planets' are also discussed.

  10. Electronic properties of high Tc superconductors. Propiedades electronicas de los superconductores de alta temperatura critica

    Energy Technology Data Exchange (ETDEWEB)

    Rojo, A G

    1989-01-01

    Using analytical and numerical methods, the electronic properties of the copper-oxygen plane in the normal phase of high Tc superconductors are described. Using the slave-boson technique in the saddle point, a theory of the metal insulator transition which generalizes the notions of a Mott insulator to the case of more than a single band for those planes is presented. A phase-diagram is obtained in the parameter space and effective masses, optical gaps and metallization are calculated as a function of the number of carriers. Based on the experimental evidence, the theory permits classification of superconducting compounds as charge transfer insulators in the stoichiometric case. The insulator state is characterized by a non-zero optical gap and a divergent effective mass which corresponds to the breakage of a Fermi-liquid scheme. The results obtained are applicable to metal-transition-oxides whose behaviour has been traditionally controversial and it is concluded that it is necessary to broaden the meaning of a Mott insulator to the case of more than a single band to better understand them. Based on the ideas of group renormalization in a real space, a lattice approximation is presented, which allows: a) To complement the treatment of slave-bosons in phase diagrams and optical gaps; b) Identification of an attraction mechanism between carriers originating from purely repulsive interactions. Numerical calculations in small clusters show the existence of a pairing mechanism showing a superconducting instability from a charge transfer insulator. (Author).

  11. New pathway for the formation of metallic cubic phase Ge-Sb-Te compounds induced by an electric current.

    Science.gov (United States)

    Park, Yong-Jin; Cho, Ju-Young; Jeong, Min-Woo; Na, Sekwon; Joo, Young-Chang

    2016-02-23

    The novel discovery of a current-induced transition from insulator to metal in the crystalline phase of Ge2Sb2Te5 and GeSb4Te7 have been studied by means of a model using line-patterned samples. The resistivity of cubic phase Ge-Sb-Te compound was reduced by an electrical current (~1 MA/cm(2)), and the final resistivity was determined based on the stress current density, regardless of the initial resistivity and temperature, which indicates that the conductivity of Ge-Sb-Te compound can be modulated by an electrical current. The minimum resistivity of Ge-Sb-Te materials can be achieved at high kinetic rates by applying an electrical current, and the material properties change from insulating to metallic behavior without a phase transition. The current-induced metal transition is more effective in GeSb4Te7 than Ge2Sb2Te5, which depends on the intrinsic vacancy of materials. Electromigration, which is the migration of atoms induced by a momentum transfer from charge carriers, can easily promote the rearrangement of vacancies in the cubic phase of Ge-Sb-Te compound. This behavior differs significantly from thermal annealing, which accompanies a phase transition to the hexagonal phase. This result suggests a new pathway for modulating the electrical conductivity and material properties of chalcogenide materials by applying an electrical current.

  12. Size-dependent single electron transfer and semi-metal-to-insulator transitions in molecular metal oxide electronics.

    Science.gov (United States)

    Balliou, Angelika; Bouroushian, Mirtat; Douvas, Antonios M; Skoulatakis, George; Kennou, Stella; Glezos, Nikos

    2018-07-06

    All-inorganic self-arranged molecular transition metal oxide hyperstructures based on polyoxometalate molecules (POMs) are fabricated and tested as electronically tunable components in emerging electronic devices. POM hyperstructures reveal great potential as charging nodes of tunable charging level for molecular memories and as enhancers of interfacial electron/hole injection for photovoltaic stacks. STM, UPS, UV-vis spectroscopy and AFM measurements show that this functionality stems from the films' ability to structurally tune their HOMO-LUMO levels and electron localization length at room temperature. By adapting POM nanocluster size in solution, self-doping and current modulation of four orders of magnitude is monitored on a single nanocluster on SiO 2 at voltages as low as 3 Volt. Structurally driven insulator-to-semi-metal transitions and size-dependent current regulation through single electron tunneling are demonstrated and examined with respect to the stereochemical and electronic structure of the molecular entities. This extends the value of self-assembly as a tool for correlation length and electronic properties tuning and demonstrate POM hyperstructures' plausibility for on-chip molecular electronics operative at room temperature.

  13. Porous silicon-VO{sub 2} based hybrids as possible optical temperature sensor: Wavelength-dependent optical switching from visible to near-infrared range

    Energy Technology Data Exchange (ETDEWEB)

    Antunez, E. E.; Salazar-Kuri, U.; Estevez, J. O.; Basurto, M. A.; Agarwal, V., E-mail: vagarwal@uaem.mx [Centro de Investigación en Ingeniería y Ciencias Aplicadas, Instituto de Investigación en Ciencias Básicas y Aplicadas, UAEM, Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Mor. 62209 (Mexico); Campos, J. [Instituto de Energías Renovables, UNAM, Priv. Xochicalco S/N, Temixco, Mor. 62580 (Mexico); Jiménez Sandoval, S. [Laboratorio de Investigación en Materiales, Centro de Investigación y estudios Avanzados del Instituto Politécnico Nacional, Unidad Querétaro, Qro. 76001 (Mexico)

    2015-10-07

    Morphological properties of thermochromic VO{sub 2}—porous silicon based hybrids reveal the growth of well-crystalized nanometer-scale features of VO{sub 2} as compared with typical submicron granular structure obtained in thin films deposited on flat substrates. Structural characterization performed as a function of temperature via grazing incidence X-ray diffraction and micro-Raman demonstrate reversible semiconductor-metal transition of the hybrid, changing from a low-temperature monoclinic VO{sub 2}(M) to a high-temperature tetragonal rutile VO{sub 2}(R) crystalline structure, coupled with a decrease in phase transition temperature. Effective optical response studied in terms of red/blue shift of the reflectance spectra results in a wavelength-dependent optical switching with temperature. As compared to VO{sub 2} film over crystalline silicon substrate, the hybrid structure is found to demonstrate up to 3-fold increase in the change of reflectivity with temperature, an enlarged hysteresis loop and a wider operational window for its potential application as an optical temperature sensor. Such silicon based hybrids represent an exciting class of functional materials to display thermally triggered optical switching culminated by the characteristics of each of the constituent blocks as well as device compatibility with standard integrated circuit technology.

  14. Fission of Polyanionic Metal Clusters

    Science.gov (United States)

    König, S.; Jankowski, A.; Marx, G.; Schweikhard, L.; Wolfram, M.

    2018-04-01

    Size-selected dianionic lead clusters Pbn2 -, n =34 - 56 , are stored in a Penning trap and studied with respect to their decay products upon photoexcitation. Contrary to the decay of other dianionic metal clusters, these lead clusters show a variety of decay channels. The mass spectra of the fragments are compared to the corresponding spectra of the monoanionic precursors. This comparison leads to the conclusion that, in the cluster size region below about n =48 , the fission reaction Pbn2 -→Pbn-10 -+Pb10- is the major decay process. Its disappearance at larger cluster sizes may be an indication of a nonmetal to metal transition. Recently, the pair of Pb10- and Pbn-10 - were observed as pronounced fragments in electron-attachment studies [S. König et al., Int. J. Mass Spectrom. 421, 129 (2017), 10.1016/j.ijms.2017.06.009]. The present findings suggest that this combination is the fingerprint of the decay of doubly charged lead clusters. With this assumption, the dianion clusters have been traced down to Pb212 -, whereas the smallest size for the direct observation was as high as n =28 .

  15. Transport properties of finite carbon nanotubes under electric and magnetic fields

    International Nuclear Information System (INIS)

    Li, T S; Lin, M F

    2006-01-01

    Electronic and transport properties of finite carbon nanotubes subject to the influences of a transverse electric field and a magnetic field with varying polar angles are studied by the tight-binding model. The external fields will modify the state energies, destroy the state degeneracy, and modulate the energy gap. Both the state energy and the energy gap exhibit rich dependence on the field strength, the magnetic field direction, and the types of carbon nanotubes. The semiconductor-metal transition would be allowed for certain field strengths and magnetic field directions. The variations of state energies with the external fields will also be reflected in the electrical and thermal conductance. The number, the heights, and the positions of the conductance peaks are strongly dependent on the external fields. The heights of the electrical and thermal conductance peaks display a quantized behaviour, while that of the Peltier coefficient does not. Finally, it is found that the validity of the Wiedemann-Franz law depends upon the temperature, the field strength, the electronic structure, and the chemical potential

  16. Microstructure and thermochromic properties of VOX-WOX-VOX ceramic thin films

    International Nuclear Information System (INIS)

    Khamseh, S.; Ghahari, M.; Araghi, H.; Faghihi Sani, M.A.

    2016-01-01

    W-doped VO 2 films have been synthesized via oxygen annealing of V-W-V (vanadium-tungsten-vanadium) multilayered films. The effects of middle layer's thickness of V-W-V multilayered film on structure and properties of VO X -WO X -VO X ceramic thin films were investigated. The as-deposited V-W-V multilayered film showed amorphous-like structure when mixed structure of VO 2 (M) and VO 2 (B) was formed in VO X -WO X -VO X ceramic thin films. Tungsten content of VO X -WO X -VO X ceramic thin films increased with increasing middle layer's thickness. With increasing middle layer's thickness, room temperature square resistance (R sq ) of VO X -WO X -VO X ceramic thin films increased from 65 to 86 kΩ/sq. The VO X -WO X -VO X ceramic thin film with the thinnest middle layer showed significant SMT (semiconductor-metal transition) when SMT became negligible on increasing middle layer's thickness. (orig.)

  17. Microstructure and thermochromic properties of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films

    Energy Technology Data Exchange (ETDEWEB)

    Khamseh, S.; Ghahari, M. [Institute for Color Science and Technology, Department of Nanomaterial and Nanocoatings, Tehran (Iran, Islamic Republic of); Araghi, H. [Islamic Azad University, Department of Materials Engineering, Science and Research Branch, Tehran (Iran, Islamic Republic of); Faghihi Sani, M.A. [Sharif University of Technology, Department of Materials Science and Engineering, Tehran (Iran, Islamic Republic of)

    2016-03-15

    W-doped VO{sub 2} films have been synthesized via oxygen annealing of V-W-V (vanadium-tungsten-vanadium) multilayered films. The effects of middle layer's thickness of V-W-V multilayered film on structure and properties of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films were investigated. The as-deposited V-W-V multilayered film showed amorphous-like structure when mixed structure of VO{sub 2} (M) and VO{sub 2} (B) was formed in VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films. Tungsten content of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films increased with increasing middle layer's thickness. With increasing middle layer's thickness, room temperature square resistance (R{sub sq}) of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films increased from 65 to 86 kΩ/sq. The VO{sub X}-WO{sub X}-VO{sub X} ceramic thin film with the thinnest middle layer showed significant SMT (semiconductor-metal transition) when SMT became negligible on increasing middle layer's thickness. (orig.)

  18. Active terahertz metamaterials based on the phase transition of VO{sub 2} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kim, H., E-mail: heungsoo.kim@nrl.navy.mil [Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375 (United States); Charipar, N. [Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375 (United States); Breckenfeld, E. [National Research Council Fellow at the Naval Research Laboratory, Washington, DC 20375 (United States); Rosenberg, A. [NOVA Research, Inc., Alexandria, VA 22308 (United States); Piqué, A. [Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375 (United States)

    2015-12-01

    Vanadium dioxide (VO{sub 2}) thin films were prepared on single crystal sapphire substrates by pulsed laser deposition. VO{sub 2} films exhibited a significant resistivity drop (> 10{sup 4} Ω-cm) and large optical transmittance change (> 60%) in the near-infrared region across their semiconductor-to-metal transition. Hybrid metamaterial devices designed for the THz frequency regime were fabricated by combining double split-ring resonators (SRRs) with phase changing VO{sub 2} films. By changing the conductivity of VO{sub 2} via temperature, the behavior of the SRR gap was adjusted from capacitive to resistive in order to modulate the THz beam transmission at their resonance frequencies. A modulation efficiency greater than 50% was achieved at the magnetic resonance frequencies (0.3 THz and 0.7 THz) in these hybrid SRR–VO{sub 2} metamaterial devices. - Highlights: • Pulsed laser deposition of phase changing VO{sub 2} thin films • Hybrid metamaterial devices composed of split-ring resonators and phase changing VO{sub 2} • Tunable THz transmission with a modulation efficiency over 50%.

  19. The strength of electron electron correlation in Cs3C60

    Science.gov (United States)

    Baldassarre, L.; Perucchi, A.; Mitrano, M.; Nicoletti, D.; Marini, C.; Pontiroli, D.; Mazzani, M.; Aramini, M.; Riccó, M.; Giovannetti, G.; Capone, M.; Lupi, S.

    2015-10-01

    Cs3C60 is an antiferromagnetic insulator that under pressure (P) becomes metallic and superconducting below Tc = 38 K. The superconducting dome present in the T - P phase diagram close to a magnetic state reminds what found in superconducting cuprates and pnictides, strongly suggesting that superconductivity is not of the conventional Bardeen-Cooper-Schrieffer (BCS) type We investigate the insulator to metal transition induced by pressure in Cs3C60 by means of infrared spectroscopy supplemented by Dynamical Mean-Field Theory calculations. The insulating compound is driven towards a metallic-like behaviour, while strong correlations survive in the investigated pressure range. The metallization process is accompanied by an enhancement of the Jahn-Teller effect. This shows that electronic correlations are crucial in determining the insulating behaviour at ambient pressure and the bad metallic nature for increasing pressure. On the other hand, the relevance of the Jahn-Teller coupling in the metallic state confirms that phonon coupling survives in the presence of strong correlations.

  20. Raman spectroscopy on simple molecular systems at very high density

    International Nuclear Information System (INIS)

    Schiferl, D.; LeSar, R.S.; Moore, D.S.

    1988-01-01

    We present an overview of how Raman spectroscopy is done on simple molecular substances at high pressures. Raman spectroscopy is one of the most powerful tools for studying these substances. It is often the quickest means to explore changes in crystal and molecular structures, changes in bond strength, and the formation of new chemical species. Raman measurements have been made at pressures up to 200 GPa (2 Mbar). Even more astonishing is the range of temperatures (4-5200/degree/K) achieved in various static and dynamic (shock-wave) pressure experiments. One point we particularly wish to emphasize is the need for a good theoretical understanding to properly interpret and use experimental results. This is particularly true at ultra-high pressures, where strong crystal field effects can be misinterpreted as incipient insulator-metal transitions. We have tried to point out apparatus, techniques, and results that we feel are particularly noteworthy. We have also included some of the /open quotes/oral tradition/close quotes/ of high pressure Raman spectroscopy -- useful little things that rarely or never appear in print. Because this field is rapidly expanding, we discuss a number of exciting new techniques that have been informally communicated to us, especially those that seem to open new possibilities. 58 refs., 18 figs

  1. Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chunyu, E-mail: licy@hpstar.ac.cn, E-mail: yanhao@hpstar.ac.cn; Ke, Feng; Yu, Zhenhai; Chen, Zhiqiang; Yan, Hao, E-mail: licy@hpstar.ac.cn, E-mail: yanhao@hpstar.ac.cn [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 (China); Hu, Qingyang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Zhao, Jinggeng [Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China)

    2016-04-07

    Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr{sub 2}S{sub 3}) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr{sub 2}S{sub 3} near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7–15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr{sub 2}S{sub 3} based applications under extreme conditions.

  2. Epitaxial growth of higher transition-temperature VO2 films on AlN/Si

    Directory of Open Access Journals (Sweden)

    Tetiana Slusar

    2016-02-01

    Full Text Available We report the epitaxial growth and the mechanism of a higher temperature insulator-to-metal-transition (IMT of vanadium dioxide (VO2 thin films synthesized on aluminum nitride (AlN/Si (111 substrates by a pulsed-laser-deposition method; the IMT temperature is TIMT ≈ 350 K. X-ray diffractometer and high resolution transmission electron microscope data show that the epitaxial relationship of VO2 and AlN is VO2 (010 ‖ AlN (0001 with VO2 [101] ‖   AlN   [ 2 1 ̄ 1 ̄ 0 ] zone axes, which results in a substrate-induced tensile strain along the in-plane a and c axes of the insulating monoclinic VO2. This strain stabilizes the insulating phase of VO2 and raises TIMT for 10 K higher than TIMT single crystal ≈ 340 K in a bulk VO2 single crystal. Near TIMT, a resistance change of about four orders is observed in a thick film of ∼130 nm. The VO2/AlN/Si heterostructures are promising for the development of integrated IMT-Si technology, including thermal switchers, transistors, and other applications.

  3. Vanadium Dioxide as a Natural Disordered Metamaterial: Perfect Thermal Emission and Large Broadband Negative Differential Thermal Emittance

    Directory of Open Access Journals (Sweden)

    Mikhail A. Kats

    2013-10-01

    Full Text Available We experimentally demonstrate that a thin (approximately 150-nm film of vanadium dioxide (VO_{2} deposited on sapphire has an anomalous thermal emittance profile when heated, which arises because of the optical interaction between the film and the substrate when the VO_{2} is at an intermediate state of its insulator-metal transition (IMT. Within the IMT region, the VO_{2} film comprises nanoscale islands of the metal and dielectric phases and can thus be viewed as a natural, disordered metamaterial. This structure displays “perfect” blackbodylike thermal emissivity over a narrow wavelength range (approximately 40  cm^{-1}, surpassing the emissivity of our black-soot reference. We observe large broadband negative differential thermal emittance over a >10 °C range: Upon heating, the VO_{2}-sapphire structure emits less thermal radiation and appears colder on an infrared camera. Our experimental approach allows for a direct measurement and extraction of wavelength- and temperature-dependent thermal emittance. We anticipate that emissivity engineering with thin-film geometries comprising VO_{2} and other thermochromic materials will find applications in infrared camouflage, thermal regulation, and infrared tagging and labeling.

  4. Electronic properties of high Tc superconductors

    International Nuclear Information System (INIS)

    Rojo, A.G.

    1989-01-01

    Using analytical and numerical methods, the electronic properties of the copper-oxygen plane in the normal phase of high Tc superconductors are described. Using the slave-boson technique in the saddle point, a theory of the metal insulator transition which generalizes the notions of a Mott insulator to the case of more than a single band for those planes is presented. A phase-diagram is obtained in the parameter space and effective masses, optical gaps and metallization are calculated as a function of the number of carriers. Based on the experimental evidence, the theory permits classification of superconducting compounds as charge transfer insulators in the stoichiometric case. The insulator state is characterized by a non-zero optical gap and a divergent effective mass which corresponds to the breakage of a Fermi-liquid scheme. The results obtained are applicable to metal-transition-oxides whose behaviour has been traditionally controversial and it is concluded that it is necessary to broaden the meaning of a Mott insulator to the case of more than a single band to better understand them. Based on the ideas of group renormalization in a real space, a lattice approximation is presented, which allows: a) To complement the treatment of slave-bosons in phase diagrams and optical gaps; b) Identification of an attraction mechanism between carriers originating from purely repulsive interactions. Numerical calculations in small clusters show the existence of a pairing mechanism showing a superconducting instability from a charge transfer insulator. (Author) [es

  5. Peculiarities of the electrontransport properties of polyimide films implanted with copper and cobalt ions

    International Nuclear Information System (INIS)

    Nazhim, F.A.; Odzhaev, V.B.; Lukashevich, M.G.; Nuzhdin, V.I.; Khajbullin, R.I.

    2010-01-01

    Thin polyimide foils were implanted with 40 keV Co + and Cu + ions at fluencies of 2,5·1016-1,251017 cm 2 and at ion current densities of 4, 8 and 12 mA cm 2 . Surface dc electric resistance of the implanted polymer samples have been measured in the temperature range 40-300 K. Metal implantation results in decreasing polymer resistance with the dose and current density increasing for the both kinds of metal ions. The decrease of dc electric resistance is caused by radiation-induced carbonization and metal nanoparticle formation in the implanted region of polymer. The transition from the insulating to metallic regime of conductivity is observed in cobalt implanted samples for critical doses above Dc = 1,25?1017 cm 2 at an ion current density of 8 mA cm 2 . In the contrary, high-fluence implantation in the polymer with Cu + ions for the same regimes does not result in the transition. The dominating mechanisms of charge carrier transport and the origin of insulator-to-metal transition in the metal implanted polymer are discussed. (authors)

  6. Structural Dynamics and Activity of Nanocatalysts Inside Fuel Cells by in-operando Atomic Pair Distribution Studies

    Science.gov (United States)

    Prasai, Binay

    We present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). Using in-operando high-energy X-ray diffraction we tracked the evolution of the atomic structure and activity of noble metal-transition metal(NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Data were analyzed in terms of atomic pair distribution functions and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore, we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation.

  7. Photon science 2008. Highlights and HASYLAB annual report

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2009-07-01

    The following topics are dealt with: A femtosecond X-ray/optical cross-correlator, ultrafast movies of nanoscale dynamics, massively parallel X-ray holography, clusters in super intense FLASH pulses, a chemical driven insulator-metal transition, tough silk, insight into the reactivity, the many faces of molecular assemblies in electronic devices, cooperative or self-centred electrons, visualizing a lost painting by Vincent van Gogh, metal contaminations in small water fleas, small-angle X-ray scattering as complement of crystallography, mapping the protein world, how metallic iron eats its own native oxide, hard X-ray diffraction imaging, the centre for free-electron laser science CFEL, the Hamburg EMBL unit, the Max-Planck unit for structural molecular biology, the GKSS Research Centre Geesthacht, the GFZ Helmholtz Centre Potsdam, the University of Hamburg on the DESY site, the light sources DORIS III, FLASH, PETRA III, and the European XFEL project, beamline enhancements and photon diagnostics at FLASH, undulator development for the European XFEL, special X-ray monochromators for PETRA III, high-power photon slits and shutters, the generation of brilliant beams, undulator demagnetization in LINAC based FELs, the control of experiments, advanced detection. (HSI)

  8. Semi-metallic, strong and stretchable wet-spun conjugated polymer microfibers

    KAUST Repository

    Zhou, Jian

    2015-01-21

    A dramatic improvement in electrical conductivity is necessary to make conductive polymer fibers viable candidates in applications such as flexible electrodes, conductive textiles, and fast-response sensors and actuators. In this study, high-performance poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) conjugated polymer microfibers were fabricated via wet-spinning followed by hot-drawing. Due to the combined effects of the vertical hot-drawing process and doping/de-doping the microfibers with ethylene glycol (EG), we achieved a record electrical conductivity of 2804 S cm−1. This is, to the best of our knowledge, a six-fold improvement over the best previously reported value for PEDOT/PSS fibers (467 S cm−1) and a two-fold improvement over the best values for conductive polymer films treated by EG de-doping (1418 S cm−1). Moreover, we found that these highly conductive fibers experience a semiconductor–metal transition at 313 K. They also have superior mechanical properties with a Young\\'s modulus up to 8.3 GPa, a tensile strength reaching 409.8 MPa and a large elongation before failure (21%). The most conductive fiber also demonstrates an extraordinary electrical performance during stretching/unstretching: the conductivity increased by 25% before the fiber rupture point with a maximum strain up to 21%. Simple fabrication of the semi-metallic, strong and stretchable wet-spun PEDOT/PSS microfibers described here could make them available for conductive smart electronics.

  9. Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films.

    Science.gov (United States)

    Mihailescu, Cristian N; Symeou, Elli; Svoukis, Efthymios; Negrea, Raluca F; Ghica, Corneliu; Teodorescu, Valentin; Tanase, Liviu C; Negrila, Catalin; Giapintzakis, John

    2018-04-25

    Controlling the semiconductor-to-metal transition temperature in epitaxial VO 2 thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO 2 epitaxial thin films grown on TiO 2 substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V 4+ -V 4+ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO 2 /TiO 2 multilayer structures.

  10. Thermal properties of rare earth cobalt oxides and of La1- x Gd x CoO3 solid solutions

    Science.gov (United States)

    Orlov, Yu. S.; Dudnikov, V. A.; Gorev, M. V.; Vereshchagin, S. N.; Solov'ev, L. A.; Ovchinnikov, S. G.

    2016-05-01

    Powder X-ray diffraction data for the crystal structure, phase composition, and molar specific heat for La1‒ x Gd x CoO3 cobaltites in the temperature range of 300-1000 K have been analyzed. The behavior of the volume thermal expansion coefficient in cobaltites with isovalent doping in the temperature range of 100-1000 K is studied. It is found that the β( T) curve exhibits two peaks at some doping levels. The rate of the change in the occupation number for the high-spin state of cobalt ions is calculated for the compounds under study taking into account the spin-orbit interaction. With the Birch-Murnaghan equation of state, it is demonstrated that the low-temperature peak in the thermal expansion shifts with the growth of the pressure toward higher temperatures and at pressure P ˜ 7 GPa coincides with the second peak. The similarity in the behavior of the thermal expansion coefficient in the La1- x Gd x CoO3 compounds with the isovalent substitution and the undoped LnCoO3 compound (Ln is a lanthanide) is considered. For the whole series of rare earth cobalt oxides, the nature of two specific features in the temperature dependence of the specific heat and thermal expansion is revealed and their relation to the occupation number for the high-spin state of cobalt ions and to the insulator-metal transition is established.

  11. First-principles study of mechanical, exchange interactions and the robustness in Co{sub 2}MnSi full Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Akriche, A., E-mail: akricheahmed@gmail.com [Laboratoire de Microscope Electronique et Sciences des Matériaux, Université d’Oran des Sciences et de la Technologie-USTO, Mohamed Boudiaf, Faculté de physique, Département de Génie Physique, Oran (Algeria); Bouafia, H. [Laboratoire de Génie Physique, Université Ibn-Khaldoun, Tiaret 14000 (Algeria); Hiadsi, S. [Laboratoire de Microscope Electronique et Sciences des Matériaux, Université d’Oran des Sciences et de la Technologie-USTO, Mohamed Boudiaf, Faculté de physique, Département de Génie Physique, Oran (Algeria); Abidri, B. [Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes (Algeria); Sahli, B. [Laboratoire de Génie Physique, Université Ibn-Khaldoun, Tiaret 14000 (Algeria); Elchikh, M.; Timaoui, M.A.; Djebour, B. [Laboratoire de Microscope Electronique et Sciences des Matériaux, Université d’Oran des Sciences et de la Technologie-USTO, Mohamed Boudiaf, Faculté de physique, Département de Génie Physique, Oran (Algeria)

    2017-01-15

    In this work we report the results of ab-initio studies of structural, mechanical, electronic and magnetic properties of Co based Co{sub 2}MnSi Heusler compound in stoichiometric composition. All of which are accurately calculated by the full-potential (FP-LMTO) program combined with the spin polarized generalized gradient approximation in the density functional formalism (DFT). The total energy calculations clearly favor the ferromagnetic ground state. The lattice parameter, elastic constants and their related parameters were also evaluated and compared to experimental and theoretical values whenever possible. In this paper, the electronic properties are treated with GGA+U approach. The magnetic exchange constants temperature has been calculated using a mean field-approximation (MFA). The half-metal to metal transition was observed around 40 GPa. Increasing pressure has no impact on the total magnetic moment or the overall shape of the band structure that indicates the robustness of the electronic structure of this system. - Highlights: • In this work, we have studied some physical properties of Co{sub 2}MnSi Heusler compound. • The exchange-correlation energy is treated within GGA and (GGA+U) approximation. • The electronic band structure shows that Co{sub 2}MnSi is a half-metallic compound.

  12. Influence of Mn site doping on electrical resistivity of polycrystalline La1-yAyMn1-xBxO3 (A=Ba, Sr; B=Cu, Cr, Co Manganites

    Directory of Open Access Journals (Sweden)

    Paunović N.

    2008-01-01

    Full Text Available We have the measured electrical resistivity of La1-yBayMn1-xCuxO3 (0.17≤y≤0.30; 0.04≤x≤0.10, La1-ySryMn1-xCrxO3 and La1-ySryMn1-xCoxO3 (0.270≤y≤0.294; 0.02≤x≤0.10 polycrystalline samples in the 25-325 K temperature range. The increase of Mn site doping concentration leads to an increase of the electrical resistivity of the samples and the appearance of a “double-peak” structure in the electrical resistivity versus temperature graphs. The first peak represents the insulator-metal transition in vicinity of the paramagnetic-ferromagnetic transition (TC. We have found that the intensity of the second peak increases with an increase of concentration of Mn substituents, due to the hole scattering by the random potential of the Mn site impurities.

  13. Non-volatile resistive switching in the Mott insulator (V1-xCrx)2O3

    Science.gov (United States)

    Querré, M.; Tranchant, J.; Corraze, B.; Cordier, S.; Bouquet, V.; Députier, S.; Guilloux-Viry, M.; Besland, M.-P.; Janod, E.; Cario, L.

    2018-05-01

    The discovery of non-volatile resistive switching in Mott insulators related to an electric-field-induced insulator to metal transition (IMT) has paved the way for their use in a new type of non-volatile memories, the Mott memories. While most of the previous studies were dedicated to uncover the resistive switching mechanism and explore the memory potential of chalcogenide Mott insulators, we present here a comprehensive study of resistive switching in the canonical oxide Mott insulator (V1-xCrx)2O3. Our work demonstrates that this compound undergoes a non-volatile resistive switching under electric field. This resistive switching is induced by a Mott transition at the local scale which creates metallic domains closely related to existing phases of the temperature-pressure phase diagram of (V1-xCrx)2O3. Our work demonstrates also reversible resistive switching in (V1-xCrx)2O3 crystals and thin film devices. Preliminary performances obtained on 880 nm thick layers with 500 nm electrodes show the strong potential of Mott memories based on the Mott insulator (V1-xCrx)2O3.

  14. A structural transformation and its effect on the physical properties of the V-substituted Bi sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub 1 sub 0 sub + sub y system

    CERN Document Server

    Yakinci, M E

    1997-01-01

    Systematic substitution of V in the Bi sub 2 sub - subdelta V subdelta Sr sub 2 Ca sub 2 Cu sub 3 O sub 1 sub 0 sub + sub y system (delta=0, 0.2, 0.4, 0.6, 0.8 and 1) was carried out in order to determine the effect of V ions on the phase formation and on the physical properties of the BSCCO 2223 system. The most interesting observation was structural transformation of the system from tetragonal to orthorhombic after delta=0.6. A solid solubility limit for V was also found to exist. Resistivity and susceptibility studies have shown that high-T sub c superconductivity exists up to delta=0.6 and that the semiconducting-to-metallic transition or fully semiconducting behaviour occurs after this limit. A fractionally small but very-high-T sub c transition at around 210 K was also observed, but it was not reproducible. Among the V-substituted samples the best electrical properties were obtained for delta=0.2; T sub c and T sub o were found to be 112 K and 92 K, respectively, the calculated value of J sub c was foun...

  15. Beyond benzyl grignards: facile generation of benzyl carbanions from styrenes.

    Science.gov (United States)

    Grigg, R David; Rigoli, Jared W; Van Hoveln, Ryan; Neale, Samuel; Schomaker, Jennifer M

    2012-07-23

    Benzylic functionalization is a convenient approach towards the conversion of readily available aromatic hydrocarbon feedstocks into more useful molecules. However, the formation of carbanionic benzyl species from benzyl halides or similar precursors is far from trivial. An alternative approach is the direct reaction of a styrene with a suitable coupling partner, but these reactions often involve the use of precious-metal transition-metal catalysts. Herein, we report the facile and convenient generation of reactive benzyl anionic species from styrenes. A Cu(I)-catalyzed Markovnikov hydroboration of the styrenic double bond by using a bulky pinacol borane source is followed by treatment with KOtBu to facilitate a sterically induced cleavage of the C-B bond to produce a benzylic carbanion. Quenching this intermediate with a variety of electrophiles, including CO(2), CS(2), isocyanates, and isothiocyanates, promotes C-C bond formation at the benzylic carbon atom. The utility of this methodology was demonstrated in a three-step, two-pot synthesis of the nonsteroidal anti-inflammatory drug (±)-flurbiprofen. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Size-dependent single electron transfer and semi-metal-to-insulator transitions in molecular metal oxide electronics

    Science.gov (United States)

    Balliou, Angelika; Bouroushian, Mirtat; Douvas, Antonios M.; Skoulatakis, George; Kennou, Stella; Glezos, Nikos

    2018-07-01

    All-inorganic self-arranged molecular transition metal oxide hyperstructures based on polyoxometalate molecules (POMs) are fabricated and tested as electronically tunable components in emerging electronic devices. POM hyperstructures reveal great potential as charging nodes of tunable charging level for molecular memories and as enhancers of interfacial electron/hole injection for photovoltaic stacks. STM, UPS, UV–vis spectroscopy and AFM measurements show that this functionality stems from the films’ ability to structurally tune their HOMO–LUMO levels and electron localization length at room temperature. By adapting POM nanocluster size in solution, self-doping and current modulation of four orders of magnitude is monitored on a single nanocluster on SiO2 at voltages as low as 3 Volt. Structurally driven insulator-to-semi-metal transitions and size-dependent current regulation through single electron tunneling are demonstrated and examined with respect to the stereochemical and electronic structure of the molecular entities. This extends the value of self-assembly as a tool for correlation length and electronic properties tuning and demonstrate POM hyperstructures’ plausibility for on-chip molecular electronics operative at room temperature.

  17. Photoelectron spectroscopy and Auger electron spectroscopy of solids and surfaces

    International Nuclear Information System (INIS)

    Kowalczyk, S.P.

    1976-01-01

    The use of photoelectron spectroscopy, primarily x-ray photoelectron spectroscopy, to obtain information on the electronic structure of a wide variety of solids (especially the bulk electronic structure of solids) is covered. Both valence band and core-level spectra, as well as a few cases of photon excited Auger electron spectroscopy, are employed in the investigations to derive information on N(E). The effect of several modulations inherent in the measured I(E)'s, such as final state band structure, cross section, and relaxation, is discussed. Examples of many-electron interactions in PES are given. Some experimental aspects of PES and AES studies are given with emphasis on sample preparation techniques. Multiple splitting of core levels is examined using the Mn levels in MnF 2 as a detailed case study. Core level splittings in transition metals, rare earth metals, transition metal halides and several alloys are also reported. The application of PES to the study of the chemical bond in some crystalline semiconductors and insulators, A/sup N/B/sup 8-N/ and A/sup N/B/sup 10-N/ compounds is treated, and a spectroscopic scale of ionicity for these compounds is developed from the measured ''s-band'' splitting in the valence band density of states

  18. Pressure-induced colossal piezoresistance effect and the collapse of the polaronic state in the bilayer manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7

    International Nuclear Information System (INIS)

    Thiyagarajan, R; Manivannan, N; Arumugam, S; Esakki Muthu, S; Tamilselvan, N R; Yoshino, H; Murata, K; Sekar, C; Apostu, M O; Suryanarayanan, R; Revcolevschi, A

    2012-01-01

    We have investigated the effect of hydrostatic pressure as a function of temperature on the resistivity of a single crystal of the bilayer manganite (La 0.4 Pr 0.6 ) 1.2 Sr 1.8 Mn 2 O 7 . Whereas a strong insulating behaviour is observed at all temperatures at ambient pressure, a clear transition into a metallic-like behaviour is induced when the sample is subjected to a pressure (P) of ∼1.0 GPa at T 6 in the low temperature region at moderate pressures is observed. When the pressure is increased further (5.5 GPa), the high temperature polaronic state disappears and a metallic behaviour is observed. The insulator to metal transition temperature exponentially increases with pressure and the distinct peak in the resistivity that is observed at 1.0 GPa almost vanishes for P > 7.0 GPa. A modification in the orbital occupation of the e g electron between 3d x 2 -y 2 and 3d z 2 -r 2 states, as proposed earlier, leading to a ferromagnetic double-exchange phenomenon, can qualitatively account for our data. (paper)

  19. Chip-carrier thermal barrier and its impact on lateral thermal lens profile and beam parameter product in high power broad area lasers

    Science.gov (United States)

    Rieprich, J.; Winterfeldt, M.; Kernke, R.; Tomm, J. W.; Crump, P.

    2018-03-01

    High power broad area diode lasers with high optical power density in a small focus spot are in strong commercial demand. For this purpose, the beam quality, quantified via the beam parameter product (BPP), has to be improved. Previous studies have shown that the BPP is strongly affected by current-induced heating and the associated thermal lens formed within the laser stripe. However, the chip structure and module-assembly related factors that regulate the size and the shape of the thermal lens are not well known. An experimental infrared thermographic technique is used to quantify the thermal lens profile in diode lasers operating at an emission wavelength of 910 nm, and the results are compared with finite element method simulations. The analysis indicates that the measured thermal profiles can best be explained when a thermal barrier is introduced between the chip and the carrier, which is shown to have a substantial impact on the BPP and the thermal resistance. Comparable results are observed in further measurements of samples from multiple vendors, and the barrier is only observed for junction-down (p-down) mounting, consistent with the barrier being associated with the GaAs-metal transition.

  20. Spectroscopic study of native defects in the semiconductor to metal phase transition in V2O5 nanostructure

    Science.gov (United States)

    Basu, Raktima; Dhara, Sandip

    2018-04-01

    Vanadium is a transition metal with multiple oxidation states and V2O5 is the most stable form among them. Besides catalysis, chemical sensing, and photo-chromatic applications, V2O5 is also reported to exhibit a semiconductor to metal transition (SMT) at a temperature range of 530-560 K. Even though there are debates in using the term "SMT" for V2O5, the metallic behavior above the transition temperature and its origin are of great interest in the scientific community. In this study, V2O5 nanostructures were deposited on a SiO2/Si substrate by the vapour transport method using Au as a catalyst. Temperature dependent electrical measurement confirms the SMT in V2O5 without any structural change. Temperature dependent photoluminescence analysis proves the appearance of oxygen vacancy related peaks due to reduction of V2O5 above the transition temperature, as also inferred from temperature dependent Raman spectroscopic studies. The newly evolved defect levels in the V2O5 electronic structure with increasing temperature are also understood from the downward shift of the bottom most split-off conduction bands due to breakdown of pdπ bonds leading to metallic behavior in V2O5 above the transition temperature.

  1. Photochemical Hydrogen Doping Induced Embedded Two-Dimensional Metallic Channel Formation in InGaZnO at Room Temperature.

    Science.gov (United States)

    Kim, Myeong-Ho; Lee, Young-Ahn; Kim, Jinseo; Park, Jucheol; Ahn, Seungbae; Jeon, Ki-Joon; Kim, Jeong Won; Choi, Duck-Kyun; Seo, Hyungtak

    2015-10-27

    The photochemical tunability of the charge-transport mechanism in metal-oxide semiconductors is of great interest since it may offer a facile but effective semiconductor-to-metal transition, which results from photochemically modified electronic structures for various oxide-based device applications. This might provide a feasible hydrogen (H)-radical doping to realize the effectively H-doped metal oxides, which has not been achieved by thermal and ion-implantation technique in a reliable and controllable way. In this study, we report a photochemical conversion of InGaZnO (IGZO) semiconductor to a transparent conductor via hydrogen doping to the local nanocrystallites formed at the IGZO/glass interface at room temperature. In contrast to thermal or ionic hydrogen doping, ultraviolet exposure of the IGZO surface promotes a photochemical reaction with H radical incorporation to surface metal-OH layer formation and bulk H-doping which acts as a tunable and stable highly doped n-type doping channel and turns IGZO to a transparent conductor. This results in the total conversion of carrier conduction property to the level of metallic conduction with sheet resistance of ∼16 Ω/□, room temperature Hall mobility of 11.8 cm(2) V(-1) sec(-1), the carrier concentration at ∼10(20) cm(-3) without any loss of optical transparency. We demonstrated successful applications of photochemically highly n-doped metal oxide via optical dose control to transparent conductor with excellent chemical and optical doping stability.

  2. VO2-based radiative thermal transistor with a semi-transparent base

    Science.gov (United States)

    Prod'homme, Hugo; Ordonez-Miranda, Jose; Ezzahri, Younès; Drévillon, Jérémie; Joulain, Karl

    2018-05-01

    We study a radiative thermal transistor analogous to an electronic one made of a VO2 base placed between two silica semi-infinite plates playing the roles of the transistor collector and emitter. The fact that VO2 exhibits an insulator to metal transition is exploited to modulate and/or amplify heat fluxes between the emitter and the collector, by applying a thermal current on the VO2 base. We extend the work of precedent studies considering the case where the base can be semi-transparent so that heat can be exchanged directly between the collector and the emitter. Both near and far field cases are considered leading to 4 typical regimes resulting from the fact that the emitter-base and base-collector separation distances can be larger or smaller than the thermal wavelength for a VO2 layer opaque or semi-transparent. Thermal currents variations with the base temperatures are calculated and analyzed. It is found that the transistor can operate in an amplification mode as already stated in [1] or in a switching mode as seen in [2]. An optimum configuration for the base thickness and separation distance maximizing the thermal transistor modulation factor is found.

  3. Upgrading of heavy crude oil with supported and unsupported transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Nares, H.R.; Schacht-Hernandez, P.; Cabrera-Reyes, M.C.; Ramirez-Garnica, M.; Cazarez-Candia, O. [Instituto Mexicano del Petroleo, Atepehuacan (Mexico)

    2006-07-01

    Heavy crude oil presents many problems such as difficulty in transportation, low processing capacity in refineries, and low mobility through the reservoir due to high viscosity which affects the index of productivity of the wells. Because of these challenges, it is necessary to enhance heavy crude oil, both aboveground and underground. The effects of several metallic oxides used to upgrade heavy crude oil properties were examined in order to increase the mobility of reservoir oil by reducing viscosity and improving the quality of the oil. This can be accomplished by reducing the asphaltene and sulfur contents and increasing the American Petroleum Institute (API) gravity using transition metal supported in alumina and unsupported from transition metals derived from either acetylacetonate or alkylhexanoate in liquid phase homogeneously mixed with heavy crude oil as well as metal transition supported in alumina. KU-H heavy crude oil from the Golf of Mexico was studied. The results were obtained by Simulated Distillation and True Boiling Point (TBP). It was concluded that the use of crude oil thermal hydrocracking allowed the API gravity to increase and considerably reduce the viscosity. As a result, the productivity index in wells was increased. However there is a high formation of coke that could damage the conductivity of the rock and then reduce the potential of oil recovery. 27 refs., 3 tabs., 5 figs.

  4. Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites.

    Science.gov (United States)

    Lee, J H; Choi, Woo Seok; Jeen, H; Lee, H-J; Seo, J H; Nam, J; Yeom, M S; Lee, H N

    2017-11-22

    The topotactic phase transition in SrCoO x (x = 2.5-3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO 2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO 3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO 2.5 , however, it has been conjectured that the magnetic transition is decoupled to the electronic phase transition, i.e., the AFM-to-FM transition occurs before the insulator-to-metal transition (IMT), which is still controversial. Here, we bridge the gap between the two-phase transitions by density-functional theory calculations combined with optical spectroscopy. We confirm that the IMT actually occurs concomitantly with the FM transition near the oxygen content x = 2.75. Strong charge-spin coupling drives the concurrent IMT and AFM-to-FM transition, which fosters the near room-T magnetic transition characteristic. Ultimately, our study demonstrates that SrCoO x is an intriguingly rare candidate for inducing coupled magnetic and electronic transition via fast and reversible redox reactions.

  5. Synthesis, structure and superconductivity in Ba1-xKxBiO3

    International Nuclear Information System (INIS)

    Hinks, D.G.

    1989-01-01

    Ba 1-x K x BiO 3 (with x = 0.4) has the highest T c (30 K) of any copperless compound. The superconducting transition temperature of this material is expected to be at the limit of conventional electron-phonon coupling. Since this material is much simpler than the copper containing high-T c superconductors (it is cubic in its superconducting state and only sp electrons are involved in the transport properties), it should be much easier to unravel the nature of the superconducting pairing mechanism in this system. Understanding this system may help explain superconductivity in the more complex copper-oxide materials. In this paper, the authors report on the development of a synthesis method which allows the preparation of stoichiometric, single-phase materials with x between 0.0 and 0.5. The structural phase diagram was determined using powder neutron diffraction as a function of both composition and temperature. Superconductivity only occurs in the cubic perovskite phase which is stable for x larger than 0.3. At a x = 0.3 composition the material undergoes a semiconductor to metal transition with a maximum value for T c . As the K content is further increased, T c is reduced

  6. High pressure phase transitions in Europous oxide

    International Nuclear Information System (INIS)

    Kremser, D.T.

    1982-01-01

    The pressure-volume relationship for EuO was investigated to 630 kilobars at room temperature with a diamond-anvil, high-pressure cell. Volumes were determined by x-ray diffraction; pressures were determined by the ruby R 1 fluorescence method. The preferred interpretation involves normal compression behavior for EuO, initially in the B1 (NaCl-type) structure, to about 280 kilobars. Between approx. =280 and approx. =350 kilobars a region of anomalous compressibility in which the volume drops continuously by approximately 2% is observed. A second-order electronic transition is proposed with the 6s band overlapping with the 4f levels, thereby reducing the volume of EuO without changing the structure. This is not a semiconductor-to-metal transition. In reflected light, this transition is correlated with a subtle and continuous change in color from brown-black to a light brown. The collapsed B1 phase (postelectronic transition) is stable between approx. =350 and approx. =400 kilobars. At about 400 kilobars the collapsed B1 structure transforms to the B2 (CsCl-type) structure, with a zero pressure-volume change of approximately 12 +/- 1.5%

  7. Outline of work under way at the Central Electricity Research Laboratories, Leatherhead (GB))

    International Nuclear Information System (INIS)

    Horton, C.A.P.

    1977-01-01

    At CERL the properties of structural materials suitable for primary sodium circuits of fast reactors are covered by a number of jobs, many of which are concerned with mechanical properties of steels in air. These include the measurement of creep and rupture behaviours, the identification of grain boundary deformation and damage processes and crack growth in creep and/or fatigue. The work covers the candidate fast reactor steels AISI 316, Alloy 800, 12CrMoV, 9CR1Mo, 24Cr1Mo and includes 316-9Cr1Mo and 316-24 Cr1Mo transition joints. One job is concerned specifically with the influence of liquid sodium on material properties and involves the use of high flow rate sodium loops. Details of the relevant projects are given: corrosion of steels in flowing sodium; creep and fatigue of steels in flowing sodium; small scale experiments in liquid sodium; creep, creep crack growth and fatigue of AISI 316 in air and vacuum; ageing studies of AISI 316 and 9Cr1Mo base and weld metals; dissimilar metal transition joints

  8. Electronic and magnetic properties of pristine and hydrogenated borophene nanoribbons

    Science.gov (United States)

    Meng, Fanchen; Chen, Xiangnan; Sun, Songsong; He, Jian

    2017-07-01

    The groundbreaking works in graphene and graphene nanoribbons (GNRs) over the past decade, and the very recent discovery of borophene naturally draw attention to the yet-to-be-explored borophene nanoribbons (BNRs). We herein report a density functional theory (DFT) study of the electronic and magnetic properties of BNRs. The foci are the impact of orientation (denoted as BxNRs and ByNRs with their respective periodic orientations along x- and y-axis), ribbon width (Nx, Ny=4-15), and hydrogenation effects on the geometric, electronic and magnetic properties of BNRs. We found that the anisotropic quasi-planar geometric structure of BNR and the edge states largely govern its electronic and magnetic properties. In particular, pristine ByNRs adopt a magnetic ground state, either anti-ferromagnetic (AFM) or ferromagnetic (FM) depending on the ribbon width, while pristine BxNRs are non-magnetic (NM). Upon hydrogenation, all BNRs exhibit NM. Interestingly, both pristine and hydrogenated ByNRs undergo a metal-semiconductor-metal transition at Ny=7, while all BxNRs remain metallic.

  9. On the localisation of charge carriers and suppression of superconductivity by praseodymium in systems derived from YBa2Cu3O7-d

    International Nuclear Information System (INIS)

    Infante, C.; El Mously, M.K.; Dayal, R.; Husain, M.; Siddiqi, S.A.; Ganguly, P.

    1990-04-01

    The effect of Pr substitution in suppressing T c in LaCaBaCu 3 O 7-d and Y 0.8 Ca 0.2 Ba 2 Cu 3 O 6+d has been studied. Infra-red spectroscopy and a model based on ionic radii considerations were used to examine the location of Pr ions and the influence of Pr and Ca ions on hole localisation on chains and planes. For this purpose the series PrBa 2-x Ca x Cu 3 O 7-d was also studied. The main conclusions are that Pr ions play a role in suppressing T c by exchange scattering and to some extent by the hole filling mechanism involving the formation of Pr 4+ . The Pr ions in La 1-x Pr x CaBaCu 3 O 7-d exist in both the Y and Ba sites. The magnitude of the resistivity at the insulator-metal transition for the polycrystalline samples is consistent with an anisotropic superconductor in which superconductivity accompanies metallization. The rate of suppression of T c is similar as in Y 1-x Pr x Ba 2 Cu 3 O 7d but it is suggested that a percolation model may explain the results more adequately than the Abrikosov-Gorkov theory. (author). 48 refs, 10 figs, 1 tab

  10. Reliability of the one-crossing approximation in describing the Mott transition

    International Nuclear Information System (INIS)

    Vildosola, V; Roura-Bas, P; Pourovskii, L V; Manuel, L O

    2015-01-01

    We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal–insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed. (paper)

  11. Reliability of the one-crossing approximation in describing the Mott transition

    Science.gov (United States)

    Vildosola, V.; Pourovskii, L. V.; Manuel, L. O.; Roura-Bas, P.

    2015-12-01

    We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed.

  12. Factors Controlling the Redox Activity of Oxygen in Perovskites: From Theory to Application for Catalytic Reactions

    Directory of Open Access Journals (Sweden)

    Chunzhen Yang

    2017-05-01

    Full Text Available Triggering the redox reaction of oxygens has become essential for the development of (electro catalytic properties of transition metal oxides, especially for perovskite materials that have been envisaged for a variety of applications such as the oxygen evolution or reduction reactions (OER and ORR, respectively, CO or hydrocarbons oxidation, NO reduction and others. While the formation of ligand hole for perovskites is well-known for solid state physicists and/or chemists and has been widely studied for the understanding of important electronic properties such as superconductivity, insulator-metal transitions, magnetoresistance, ferroelectrics, redox properties etc., oxygen electrocatalysis in aqueous media at low temperature barely scratches the surface of the concept of oxygen ions oxidation. In this review, we briefly explain the electronic structure of perovskite materials and go through a few important parameters such as the ionization potential, Madelung potential, and charge transfer energy that govern the oxidation of oxygen ions. We then describe the surface reactivity that can be induced by the redox activity of the oxygen network and the formation of highly reactive surface oxygen species before describing their participation in catalytic reactions and providing mechanistic insights and strategies for designing new (electro catalysts. Finally, we give a brief overview of the different techniques that can be employed to detect the formation of such transient oxygen species.

  13. Realization of a Hole-Doped Mott Insulator on a Triangular Silicon Lattice

    Science.gov (United States)

    Ming, Fangfei; Johnston, Steve; Mulugeta, Daniel; Smith, Tyler S.; Vilmercati, Paolo; Lee, Geunseop; Maier, Thomas A.; Snijders, Paul C.; Weitering, Hanno H.

    2017-12-01

    The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magnetoresistance, and high-temperature superconductivity in layered perovskite compounds. Advances in this field would greatly benefit from the availability of new material systems with a similar richness of physical phenomena but with fewer chemical and structural complications in comparison to oxides. Using scanning tunneling microscopy and spectroscopy, we show that such a system can be realized on a silicon platform. The adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half filled dangling bond orbitals. Modulation hole doping of these dangling bonds unveils clear hallmarks of Mott physics, such as spectral weight transfer and the formation of quasiparticle states at the Fermi level, well-defined Fermi contour segments, and a sharp singularity in the density of states. These observations are remarkably similar to those made in complex oxide materials, including high-temperature superconductors, but highly extraordinary within the realm of conventional s p -bonded semiconductor materials. It suggests that exotic quantum matter phases can be realized and engineered on silicon-based materials platforms.

  14. Superconductivity in MBE grown InN

    Energy Technology Data Exchange (ETDEWEB)

    Gunes, M.; Balkan, N. [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, CO4 3SQ, Colchester (United Kingdom); Tiras, E.; Ardali, S. [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, 26470, Eskisehir (Turkey); Ajagunna, A.O.; Iliopoulos, E.; Georgakilas, A. [Microelectronics Research Group, IESL, FORTH and Physics Department, University of Crete, P.O. Box 1385, 71110 Heraklion, Crete (Greece)

    2011-05-15

    We present the experimental investigation of superconductivity in unintentionally doped MBE grown InN samples with various InN film thicknesses. A significant change in resistivity was observed at 3.82 K, for an 1080 nm InN layer with carrier concentration n{sub 3D}=1.185x10{sup 19} cm{sup -3}. However, no significant resistance change was observed in the case of InN samples with carrier density of 1.024x10{sup 19} cm{sup -3}, 1.38x10{sup 19} cm{sup -3}, and thicknesses of 2070 and 4700 nm, respectively. The carrier density of all investigated samples was within the range of values between the Mott transition (2x10{sup 17} cm{sup -3}) and the superconductivity to metal transition (7x10{sup 20} cm{sup -3}). We believe that at lower temperatures ({sup 3}He) which we cannot achieve with our set-up, the phase transition in other samples is likely to be observed. The origin of the observed anisotropic type-II superconductivity is discussed (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. X-ray absorption experiments on rare earth and uranium compounds under high pressure

    International Nuclear Information System (INIS)

    Schmiester, G.

    1987-01-01

    After an introduction into the phenomenon of the mixed valency and the method of measuring the microstructures by X-ray absorption spectroscopy in the area of the L edges under pressure, the results of investigations at selected substitutes of the chalcogenides and puictides of the rare earths and the uranium were given. Thus, pressure-induced valency transitions in YbS and YbTe, instabilities in valency and structural phase transitions in EUS and SmTe as well as the change in the electron structure in USb under pressure were investigated in order to answer questions of solid state physics (e.g. semiconductor-metal transitions, correlation between valency and structural phase transitions). Hybridization effects in L III spectra of formally tetravalent Ca are analyzed at CeF 4 and CeO 2 (insulators) and the role of final state effects in the L III spectra are analyzed at EuP 2 P 2 and TmSe-TmTe (semiconductor systems). (RB) [de

  16. Structural, electronic and magnetic properties of carbon doped boron nitride nanowire: Ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Jalilian, Jaafar, E-mail: JaafarJalilian@gmail.com [Young Researchers and Elite Club, Kermanshah Br anch, Islamic Azad University, P.O. Box: 6718997551, Kermanshah (Iran, Islamic Republic of); Kanjouri, Faramarz, E-mail: kanjouri@khu.ac.ir [Physics Department, Faculty of Science, Kharazmi University, University Square, P.O. Box: 3197937551, Karaj (Iran, Islamic Republic of)

    2016-11-15

    Using spin-polarized density functional theory calculations, we demonstrated that carbon doped boron nitride nanowire (C-doped BNNW) has diverse electronic and magnetic properties depending on position of carbon atoms and their percentages. Our results show that only when one carbon atom is situated on the edge of the nanowire, C-doped BNNW is transformed into half-metal. The calculated electronic structure of the C-doped BNNW suggests that doping carbon can induce localized edge states around the Fermi level, and the interaction among localized edge states leads to semiconductor to half-metal transition. Overall, the bond reconstruction causes of appearance of different electronic behavior such as semiconducting, half-metallicity, nonmagnetic metallic, and ferromagnetic metallic characters. The formation energy of the system shows that when a C atom is doped on surface boron site, system is more stable than the other positions of carbon impurity. Our calculations show that C-doped BNNW may offer unique opportunities for developing nanoscale spintronic materials.

  17. Multimodal backside imaging of a microcontroller using confocal laser scanning and optical-beam-induced current imaging

    Science.gov (United States)

    Finkeldey, Markus; Göring, Lena; Schellenberg, Falk; Brenner, Carsten; Gerhardt, Nils C.; Hofmann, Martin

    2017-02-01

    Microscopy imaging with a single technology is usually restricted to a single contrast mechanism. Multimodal imaging is a promising technique to improve the structural information that could be obtained about a device under test (DUT). Due to the different contrast mechanisms of laser scanning microscopy (LSM), confocal laser scanning microscopy (CLSM) and optical beam induced current microscopy (OBICM), a combination could improve the detection of structures in integrated circuits (ICs) and helps to reveal their layout. While OBIC imaging is sensitive to the changes between differently doped areas and to semiconductor-metal transitions, CLSM imaging is mostly sensitive to changes in absorption and reflection. In this work we present the implementation of OBIC imaging into a CLSM. We show first results using industry standard Atmel microcontrollers (MCUs) with a feature size of about 250nm as DUTs. Analyzing these types of microcontrollers helps to improve in the field of side-channel attacks to find hardware Trojans, possible spots for laser fault attacks and for reverse engineering. For the experimental results the DUT is placed on a custom circuit board that allows us to measure the current while imaging it in our in-house built stage scanning microscope using a near infrared (NIR) laser diode as light source. The DUT is thinned and polished, allowing backside imaging through the Si-substrate. We demonstrate the possibilities using this optical setup by evaluating OBIC, LSM and CLSM images above and below the threshold of the laser source.

  18. Metallic hydrogen research

    International Nuclear Information System (INIS)

    Burgess, T.J.; Hawke, R.S.

    1978-01-01

    Theoretical studies predict that molecular hydrogen can be converted to the metallic phase at very high density and pressure. These conditions were achieved by subjecting liquid hydrogen to isentropic compression in a magnetic-flux compression device. Hydrogen became electrically conducting at a density of about 1.06 g/cm 3 and a calculated pressure of about 2 Mbar. In the experimental device, a cylindrical liner, on implosion by high explosive, compresses a magnetic flux which in turn isentropically compresses a hydrogen sample; coaxial conical anvils prevent escape of the sample during compression. One anvil contains a coaxial cable that uses alumina ceramic as an insulator; this probe allows continuous measurement of the electrical conductivity of the hydrogen. A flash x-ray radiograph exposed during the experiment records the location of the sample-tube boundaries and permits calculation of the sample density. The theoretical underpinnings of the metallic transition of hydrogen are briefly summarized, and the experimental apparatus and technique, analytical methods, and results are described. 9 figures

  19. Structural phases arising from reconstructive and isostructural transitions in high-melting-point oxides under hydrostatic pressure: A first-principles study

    Science.gov (United States)

    Tian, Hao; Kuang, Xiao-Yu; Mao, Ai-Jie; Yang, Yurong; Xu, Changsong; Sayedaghaee, S. Omid; Bellaiche, L.

    2018-01-01

    High-melting-point oxides of chemical formula A B O3 with A =Ca , Sr, Ba and B =Zr , Hf are investigated as a function of hydrostatic pressure up to 200 GPa by combining first-principles calculations with a particle swarm optimization method. Ca- and Sr-based systems: (1) first undergo a reconstructive phase transition from a perovskite state to a novel structure that belongs to the post-post-perovskite family and (2) then experience an isostructural transition to a second, also new post-post-perovskite state at higher pressures, via the sudden formation of a specific out-of-plane B -O bond. In contrast, the studied Ba compounds evolve from a perovskite phase to a third novel post-post-perovskite structure via another reconstructive phase transition. The original characteristics of these three different post-post-perovskite states are emphasized. Unusual electronic properties, including significant piezochromic effects and an insulator-metal transition, are also reported and explained.

  20. Fermi surface study of organic conductors using a magneto-optical measurement under high magnetic fields

    International Nuclear Information System (INIS)

    Kimata, M; Ohta, H; Koyama, K; Motokawa, M; Kondo, R; Kagoshima, S; Tanaka, H; Tokumoto, M; Kobayashi, H; Kobayashi, A

    2006-01-01

    Magneto-optical measurements have been performed in organic conductors β''-(BEDT-TTF) 2 CsCd(SCN) 4 and λ-(BETS) 2 FeCl 4 . Although the zero magnetic field ground state of β''-(BEDT-TTF) 2 CsCd(SCN) 4 is considered as the density wave state, periodic orbit resonances (POR's) attributed to quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) Fermi surfaces (FS's) have been observed above 6 T. The existence of these FS's are predicted by the band calculation based on room temperature lattice parameters. This result may suggest the destruction of the density wave state at 6 T, and the primal metallic state revives in the high field phase above 6 T. In the case of λ-(BETS) 2 FeCl 4 , large changes of the transmission intensity of electromagnetic waves around 10 T, which correspond to the insulator-metal transition, have been observed. However, no POR-like resonance has been observed. This may be due to the restriction of the observed frequency-field region

  1. Application of polyhydroxybutyrate-b-polyethyleneglycol (a block co-polymer) for solid phase extraction of lead and copper in different food samples

    International Nuclear Information System (INIS)

    Kazi, T.G.; Afridi, H.I.; Tuzen, M.; Naeemullah, A.

    2014-01-01

    In present work, a new adsorbent, polyhydroxybutyrate-b-polyethyleneglycol (block copolymer) was used for the preconcentration and separation of copper (Cu) and lead (Pb) ions without consuming expensive complexing reagent. The influence of various parameters like pH, adsorbent amount, and rates of flow of eluent, sample and sample volumes has been investigated. The polymer does not interact with alkaline earth metals, transition metals, alkaline, and few anions. The enrichment factor 50 was achieved in this method. The detection limit of method was found to be 0.36 micro g L/sup 1/ and 1.93 micro g L/sup 1/ for copper and lead, respectively. The recovery values of both analytes were found >96% and relative standard deviations (RSD) for all experiments were found less than 5%. The present method was validated by the analysis of Cu and Pb contents in various related certified reference materials (CRM) like; NIST SRM 1515 Apple leaves, IAEA -336 Lichen and GBW-07605 Tea. Found results and CRM values were precise and accurate. This developed method was then successfully applied for analysis of Cu and Pb in tap and bottled mineral water and real food samples. (author)

  2. Pressure-induced irreversible metallization accompanying the phase transitions in S b2S3

    Science.gov (United States)

    Dai, Lidong; Liu, Kaixiang; Li, Heping; Wu, Lei; Hu, Haiying; Zhuang, Yukai; Yang, Linfei; Pu, Chang; Liu, Pengfei

    2018-01-01

    We have revealed S b2S3 to have two phase transitions and to undergo metallization using a diamond anvil cell at around 5.0, 15.0, and 34.0 GPa, respectively. These results were obtained on the basis of high-pressure Raman spectroscopy, temperature-dependent conductivity measurements, atomic force microscopy, high-resolution transmission electron microscopy, and first-principles calculations. The first phase transition at ˜5.0 GPa is an isostructural phase transition, which is manifested in noticeable changes in five Raman-active modes and the slope of the conductivity because of a change in the electronic structure. The second pressure-induced phase transition was characterized by a discontinuous change in the slope of conductivity and a new low-intensity Raman mode at ˜15.0 GPa . Furthermore, a semiconductor-to-metal transition was found at ˜34.0 GPa , which was accompanied by irreversible metallization, and it could be attributed to the permanently plastic deformation of the interlayer spacing. This high-pressure behavior of S b2S3 will help us to understand the universal crystal structure evolution and electrical characteristics for A2B3 -type compounds, and to facilitate their application in electronic devices.

  3. Stability and Electronic Properties of Hydrogenated Zigzag Carbon Nanotube Focused on Stone-Wales Defect

    International Nuclear Information System (INIS)

    Pan Li-Jun; Zhang Jie; Chen Wei-Guang; Tang Ya-Nan

    2015-01-01

    We present a first-principles study of the chemisorption of hydrogen on a Stone-Wales (SW) defective carbon nanotube (10,0). The investigated configurations include four configurations covering single defects and double defects. One hydrogen dimer adsorption is energetically favored on bonds shared by carbon heptagon-heptagon for configurations with the defect parallel to the tube axis compared with the carbon pentagon-hexagon sites for ones with a slanted defect. This different behavior is also demonstrated for hydrogen dimer chain adsorption, the favored site for the former ones is through the defect, which is the nearest neighbor site to defect for the latter ones. It is found that the energy band gaps of hydrogenated configurations may be enlarged or decreased by altering the adsorption site or defect position. The semiconductor-to-metal transition may occur for configurations with the defect or defects parallel to the tube axis due to low electronic localization. Our results highlight the interest of the interaction of multi-factor system by providing a detailed bond and position picture of a hydrogenated defective carbon nanotube (10,0). (paper)

  4. Monolayer CS as a metal-free photocatalyst with high carrier mobility and tunable band structure: a first-principles study

    Science.gov (United States)

    Yang, Xiao-Le; Ye, Xiao-Juan; Liu, Chun-Sheng; Yan, Xiao-Hong

    2018-02-01

    Producing hydrogen fuel using suitable photocatalysts from water splitting is a feasible method to harvest solar energy. A desired photocatalyst is expected to have suitable band gap, moderate band edge position, and high carrier mobility. By employing first-principles calculations, we explore a α-CS monolayer as a metal-free efficient photocatalyst. The α-CS monolayer shows good energetic, dynamic, and thermal stabilities and is insoluble in water, suggesting its experimental practicability. Monolayer and bilayer α-CS present not only appropriate band gaps for visible and ultraviolet light absorption but also moderate band alignments with water redox potentials in pH neutral water. Remarkably, the α-CS monolayer exhibits high (up to 8453.19 cm2 V-1s-1 for hole) and anisotropic carrier mobility, which is favorable to the migration and separation of photogenerated carriers. In addition, monolayer α-CS experiences an interesting semiconductor-metal transition by applying uniaxial strain and external electric field. Moreover, α-CS under certain strain and electric field is still dynamically stable with the absence of imaginary frequencies. Furthermore, we demonstrate that the graphite (0 0 1) surface is a potential substrate for the α-CS growth with the intrinsic properties of α-CS maintaining. Therefore, our results could pave the way for the application of α-CS as a promising photocatalyst.

  5. Crossover from itinerant-electron to localized-electron behavior in Sr{sub 1-x}Ca{sub x}CrO{sub 3} perovskite solid solution

    Energy Technology Data Exchange (ETDEWEB)

    Long Youwen; Yang Liuxiang; Lv Yuxi; Liu Qingqing; Jin Changqing [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Zhou Jianshi; Goodenough, John B, E-mail: ywlong@iphy.ac.cn, E-mail: Jin@iphy.ac.cn [Texas Materials Institute, University of Texas, 1 University Station, C2200, Austin, TX 78712 (United States)

    2011-09-07

    Polycrystalline samples of the perovskite family Sr{sub 1-x}Ca{sub x}CrO{sub 3} have been prepared at high pressure and temperature in steps of 1/6 over the range 0{<=}x{<=}1. Rietveld analysis shows a series of structural phase transitions from cubic to tetragonal to orthorhombic with increasing x. The cubic samples have no long-range magnetic order; the other samples become antiferromagnetically ordered below a T{sub N} that increases with x. At ambient pressure, the electric transport properties of the cubic and tetragonal phases are semiconducting with a small (meV range) activation energy that increases with x; the orthorhombic phase exhibits variable-range hopping rather than the small-polaron behavior typically found for mixed-valent, localized-electron configurations. Above a pressure P = P{sub C}, a smooth insulator-metal transition is found at a T{sub IM} that decreases with increasing P for a fixed x; P{sub C} increases with x. These phenomena are rationalized qualitatively with a {pi}*-band model having a width W{sub {pi}} that approaches crossover from itinerant-electron to localized-electron behavior as W{sub {pi}} decreases with increasing x. The smaller size of the Ca{sup 2+} ion induces the structural changes and the greater acidity of the Ca{sup 2+} ion is primarily responsible for narrowing W{sub {pi}} as x increases. (paper)

  6. A comparative study of low-field magnetoresistance for La sub 2 sub / sub 3 Ca sub 1 sub / sub 3 Mn sub 1 sub - sub x Cu sub x O sub 3 (x = 0% and 4%) synthesized at different temperatures

    CERN Document Server

    Yuan, S L; Xia, Z C; Zhao, L F; Liu, L; Chen, W; Zhang, G H; Zhang, L J; Feng, W; Zhong, Q H; Liu, S

    2003-01-01

    Polycrystalline samples of nominal La sub 2 sub / sub 3 Ca sub 1 sub / sub 3 Mn sub 1 sub - sub x Cu sub x O sub 3 (x 0% and 4%) were fabricated by a sol-gel method following sintering treatments at temperature T sub s ranging between 1000 deg. C and 1300 deg. C. Experiments indicate that doping Cu does not cause a change in crystalline structure, but strongly affects transport and magnetoresistance (MR) properties. For lower T sub s , when a low magnetic field of H = 0.3 T, is applied, the x = 0 samples show typical intergrain MR behaviour with a monotonic increase in MR sub 0 (ident to DELTA rho/rho(H = 0)) on cooling; while for the x = 4% samples, in addition to intergrain MR, a characteristic feature similar to colossal MR (CMR) is observed near the insulator-metal transition. The maximum MR with a value approx 80% of that for H = 0.3 T is obtained in the sample prepared at 1100 deg. C, which is comparable to the intrinsic CMR response usually observed in large fields of the order of several teslas.

  7. Ferroelectric polymer dielectrics: Emerging materials for future electrostatic energy storage applications

    Science.gov (United States)

    Panda, Maheswar

    2018-05-01

    In this manuscript, the dielectric behavior of a variety of ferroelectric polymer dielectrics (FPD), which may bethe materials for future electrostatic energy storage application shave been discussed. The variety of polymer dielectrics, comprising of ferroelectric polymer[polyvinylidene fluoride (PVDF)]/non-polarpolymer [low density polyethylene (LDPE)] and different sizes of metal particles (Ni, quasicrystal of Al-Cu-Fe) as filler, were prepared through different process conditions (cold press/hot press) and are investigated experimentally. Very high values of effective dielectric constants (ɛeff) with low loss tangent (Tan δ) were observed forall the prepared FPD at their respective percolation thresholds (fc). The enhancement of ɛeff and Tan δ at the insulator to metal transition (IMT) is explained through the boundary layer capacitor effect and the percolation theory respectively. The non-universal fc/critical exponents across the IMT have been explained through percolation theory andis attributed to the fillerparticle size& shape, interaction between the components, method of their preparation, adhesiveness, connectivity and homogeneity, etc. of the samples. Recent results on developed FPD with high ɛeff and low Tan δ prepared through cold press have proven themselves to be the better candidates for low frequency and static dielectric applications.

  8. Improved electrical properties of La{sub 2/3}Ba{sub 1/3}MnO{sub 3}:Ag{sub 0.04} thin films by thermal annealing

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiang; Yin, Xue-Peng; Chen, Qing-Ming; Zhang, Hui; Zhang, Shao-Chun [Kunming University of Science and Technology, Faculty of Material Science and Engineering, Kunming, Yunnan (China)

    2014-09-15

    La{sub 2/3}Ba{sub 1/3}MnO{sub 3}:Ag{sub 0.04} (LBMO:Ag{sub 0.04}) thin films were prepared on single crystalline (001)-orientated LaAlO{sub 3} substrates by pulsed laser deposition technique. Thermal annealing with temperatures of 780, 800 and 820 C has been investigated to improve electrical properties of the films. All the samples are shown along the (00l) orientation in rhombohedral structure with R anti 3c space group. With thermal annealing temperature increasing, insulator-metal transition temperature (T{sub p}) and resistivity at T{sub p} (ρ{sub T{sub p}}) of the epilayer reach optimal value of 288 K and 0.03 Ω.cm, respectively. The electrical properties improvement of the LBMO:Ag{sub 0.04} films is due to an improved film crystallization, oxygen balance and photon scattering suppression. The fitting curves show that the region of ferro-magnetic metallic (FM, T < T{sub p}) is fitted with grain/domain boundary, electron-electron and magnon scattering mechanism, as well as the region of para-magnetic insulating (PI, T > T{sub p}) is fitted with adiabatic small polaron hopping mechanism. (orig.)

  9. Study on the electrical transport properties of La{sub 2/3}Ba{sub 1/3}MnO{sub 3}:Ag{sub 0.04}/LaAlO{sub 3} (001) films

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiang, E-mail: lxjim@126.com; Zhao, Shuang; Zhang, Shao-Chun

    2017-01-01

    La{sub 2/3}Ba{sub 1/3}MnO{sub 3}: wt%Ag{sub x} (LBMO:Ag{sub x}, x=0.04) films were prepared on single crystalline (001)-orientated LaAlO{sub 3} substrates by pulsed laser deposition technique. All the samples show along the (00l) orientation in rhombohedral structure with R3c space group. The surface roughness (Ra), insulator-metal transition temperature (Tp) and resistivity at Tp (ρ{sub Tp}) of the LBMO:Ag{sub 0.04} films reached optimal values of 3.29 nm, 288 K and 0.033 Ω cm at 740 °C, respectively. The improvement of electrical transport properties in the films are attributed to the optimal growth temperature and Ag-doping improve the microstructure of the surfaces, grain boundaries (GBs) in connectivity and better crystallization. In addition, the electrical conduction behaviors can be well fitted with the grain/domain boundary, electron–electron and magnon scattering mechanisms in the ferromagnetic metallic region (TTp).

  10. Photon science 2008. Highlights and HASYLAB annual report

    International Nuclear Information System (INIS)

    2009-01-01

    The following topics are dealt with: A femtosecond X-ray/optical cross-correlator, ultrafast movies of nanoscale dynamics, massively parallel X-ray holography, clusters in super intense FLASH pulses, a chemical driven insulator-metal transition, tough silk, insight into the reactivity, the many faces of molecular assemblies in electronic devices, cooperative or self-centred electrons, visualizing a lost painting by Vincent van Gogh, metal contaminations in small water fleas, small-angle X-ray scattering as complement of crystallography, mapping the protein world, how metallic iron eats its own native oxide, hard X-ray diffraction imaging, the centre for free-electron laser science CFEL, the Hamburg EMBL unit, the Max-Planck unit for structural molecular biology, the GKSS Research Centre Geesthacht, the GFZ Helmholtz Centre Potsdam, the University of Hamburg on the DESY site, the light sources DORIS III, FLASH, PETRA III, and the European XFEL project, beamline enhancements and photon diagnostics at FLASH, undulator development for the European XFEL, special X-ray monochromators for PETRA III, high-power photon slits and shutters, the generation of brilliant beams, undulator demagnetization in LINAC based FELs, the control of experiments, advanced detection. (HSI)

  11. Interplay of magnetism and superconductivity in the compressed Fe-ladder compound BaFe2Se3

    Energy Technology Data Exchange (ETDEWEB)

    Ying, Jianjun; Lei, Hechang; Petrovic, Cedomir; Xiao, Yuming; Struzhkin, Viktor V. (BNL); (CIW)

    2017-06-01

    High pressure resistance, susceptibility, and Fe K β x-ray emission spectroscopy measurements were performed on Fe-ladder compound BaFe 2 Se 3 . Pressure-induced superconductivity was observed which is similar to the previously reported superconductivity in the BaFe 2 S 3 samples. The slope of local magnetic moment versus pressure shows an anomaly across the insulator-metal transition pressure in the BaFe 2 Se 3 samples. The local magnetic moment is continuously decreasing with increasing pressure, and the superconductivity appears only when the local magnetic moment value is comparable to the one in the iron-pnictide superconductors. Our results indicate that the compressed BaFe 2 C h 3 ( C h = S , Se) is a new family of iron-based superconductors. Despite the crystal structures completely different from the known iron-based superconducting materials, the magnetism in this Fe-ladder material plays a critical role in superconductivity. This behavior is similar to the other members of iron-based superconducting materials.

  12. Two-dimensional tantalum disulfide: controlling structure and properties via synthesis

    Science.gov (United States)

    Zhao, Rui; Grisafe, Benjamin; Krishna Ghosh, Ram; Holoviak, Stephen; Wang, Baoming; Wang, Ke; Briggs, Natalie; Haque, Aman; Datta, Suman; Robinson, Joshua

    2018-04-01

    Tantalum disulfide (TaS2) is a transition metal dichalcogenide (TMD) that exhibits phase transition induced electronic property modulation at low temperature. However, the appropriate phase must be grown to enable the semiconductor/metal transition that is of interest for next generation electronic applications. In this work, we demonstrate direct and controllable synthesis of ultra-thin 1T-TaS2 and 2H-TaS2 on a variety of substrates (sapphire, SiO2/Si, and graphene) via powder vapor deposition. The synthesis process leads to single crystal domains ranging from 20 to 200 nm thick and 1-10 µm on a side. The TaS2 phase (1T or 2H) is controlled by synthesis temperature, which subsequently is shown to control the electronic properties. Furthermore, this work constitutes the first demonstration of a metal-insulator phase transition in directly synthesized 1T-TaS2 films and domains by electronic means.

  13. Magnetotransport properties of La0.67Ca0.33MnO3 with different grain sizes

    International Nuclear Information System (INIS)

    Ewe, L.S.; Hamadneh, I.; Salama, H.; Halim, S.A.; Hamid, N.A.; Abd-Shukor, R.

    2009-01-01

    The magnetotransport and magnetoresistive (MR) properties of manganese-based La 0.67 Ca 0.33 MnO 3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature in magnetic fields of 0.5 and 1 T. The insulator-metal transition temperature, T IM , shifted to a higher temperature with the application of the magnetic field. In zero field, T IM is almost constant (∝271 K) for all samples except for the sample with the largest grain size, where T IM =265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E F ), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The ρ-T 2 curves are nearly linear in the metallic regime, but the ρ-T 2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data well in the high-temperature region, indicating the existence of the Jahn-Teller distortion that localizes the charge carriers. MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling effect. (orig.)

  14. Study of the effect of ZnO film on some properties of clear and color window glass

    Science.gov (United States)

    Hamead, Alaa A. Abdul; Ahmed, Sura S.; Khdheer, Mena F.

    2018-05-01

    In the current research, a samples of transparent color and colorless window glass were prepared, (includes metal transition oxides) for construction applications. A nano-film layer of zinc oxide ZnO was deposited by spray pyrolysis technique for use in sustainability applications prepared. Structural properties (x-ray diffraction XRD, scanning electron microscopy SEM and atomic force microscopy AFM), and thermal properties, as well as optical properties and the effect of weathering conditions on applied film on clear and colored glass were examined. The results showed that the deposition film had a thickness of less than 90nm and that it was crystallized with high optical transparently, that was not significantly affected after deposited the ZnO nano film. While thermal insulation decreased significantly after deposition, and the effect of the weather conditions was very low as the ZnO coating was not affected, as the thermal insulation did not change after exposure to accelerated air conditions. Make it suitable in glass applications for buildings in vertical construction.

  15. Evolving Structural Diversity and Metallicity in Compressed Lithium Azide

    KAUST Repository

    Prasad, Dasari L. V. K.

    2013-10-10

    In pursuit of new stable nitrogen-rich phases and of a possible insulator-metal transition, the ground-state electronic structure of lithium azide, LiN3, is investigated from 1 atm to 300 GPa (∼2-fold compression) using evolutionary crystal structure exploration methods coupled with density functional theoretical calculations. Two new LiN3 phases, containing slightly reduced and well-separated N2 units, are found to be enthalpically competitive with the known lithium azide crystal structure at 1 atm. At pressures above 36 GPa nitrogen-rich assemblies begin to evolve. These incorporate NN bond formation beyond that in N2 or N3 -. N6 rings and infinite one-dimensional linear nitrogen chains (structural analogues to polyacetylene) appear. Above 200 GPa quasi-one- and two-dimensional extended puckered hexagonal and decagonal nitrogen layers emerge. The high-pressure phase featuring linear chains may be quenchable to P = 1 atm. With increasing pressure the progression in electrical conductivity is from insulator to metal. © 2013 American Chemical Society.

  16. Brillouin spectroscopy with surface acoustic waves on intermediate valent, doped SmS

    International Nuclear Information System (INIS)

    Schaerer, U.; Jung, A.; Wachter, P.

    1998-01-01

    Brillouin scattering on surface acoustic waves is a very powerful tool to determine the elastic constants of intermediate valent crystals, since the method is non-destructive and no mechanical contact is needed. A strong evidence for intermediate valence is a negative value of Poisson's ratio, which describes the behavior of the volume under uniaxial pressure. SmS by itself makes a semiconductor-metal transition at a pressure of more than 6.5 kbar. When substituting the divalent Sm by a trivalent cation, like Y, La or Tm, SmS can become - depending on the doping concentration - intermediate valent without any applied, external pressure. In this work, we will present measurements of the velocities of the surface acoustic waves and the calculation of the elastic constants of La- and Tm-doped SmS compounds. We found a clear dependence of Poisson's ratio on the doping concentration and on the valence of the materials. Furthermore, we will discuss the mechanism leading to intermediate valence when substituting Sm. Besides the internal, chemical pressure, which is produced by the built in trivalent cations with their smaller ionic radii, we have clear evidence, that the free electrons in the 5d band, induced by the substituting atoms, also play an important role in making doped SmS intermediate valent. (orig.)

  17. First principles study of the electronic properties and band gap modulation of two-dimensional phosphorene monolayer: Effect of strain engineering

    Science.gov (United States)

    Phuc, Huynh V.; Hieu, Nguyen N.; Ilyasov, Victor V.; Phuong, Le T. T.; Nguyen, Chuong V.

    2018-06-01

    The effect of strain on the structural and electronic properties of monolayer phosphorene is studied by using first-principle calculations based on the density functional theory. The intra- and inter-bond length and bond angle for monolayer phosphorene is also evaluated. The intra- and inter-bond length and the bond angle for phosphorene show an opposite tendency under different directions of the applied strain. At the equilibrium state, monolayer phosphorene is a semiconductor with a direct band gap at the Γ-point of 0.91 eV. A direct-indirect band gap transition is found in monolayer phosphorene when both the compression and tensile strain are simultaneously applied along both zigzag and armchair directions. Under the applied compression strain, a semiconductor-metal transition for monolayer phosphorene is observed at -13% and -10% along armchair and zigzag direction, respectively. The direct-indirect and phase transition will largely constrain application of monolayer phosphorene to electronic and optical devices.

  18. Uncovering edge states and electrical inhomogeneity in MoS2 field-effect transistors.

    Science.gov (United States)

    Wu, Di; Li, Xiao; Luan, Lan; Wu, Xiaoyu; Li, Wei; Yogeesh, Maruthi N; Ghosh, Rudresh; Chu, Zhaodong; Akinwande, Deji; Niu, Qian; Lai, Keji

    2016-08-02

    The understanding of various types of disorders in atomically thin transition metal dichalcogenides (TMDs), including dangling bonds at the edges, chalcogen deficiencies in the bulk, and charges in the substrate, is of fundamental importance for TMD applications in electronics and photonics. Because of the imperfections, electrons moving on these 2D crystals experience a spatially nonuniform Coulomb environment, whose effect on the charge transport has not been microscopically studied. Here, we report the mesoscopic conductance mapping in monolayer and few-layer MoS2 field-effect transistors by microwave impedance microscopy (MIM). The spatial evolution of the insulator-to-metal transition is clearly resolved. Interestingly, as the transistors are gradually turned on, electrical conduction emerges initially at the edges before appearing in the bulk of MoS2 flakes, which can be explained by our first-principles calculations. The results unambiguously confirm that the contribution of edge states to the channel conductance is significant under the threshold voltage but negligible once the bulk of the TMD device becomes conductive. Strong conductance inhomogeneity, which is associated with the fluctuations of disorder potential in the 2D sheets, is also observed in the MIM images, providing a guideline for future improvement of the device performance.

  19. Wet chemical deposition of single crystalline epitaxial manganite thin films with atomically flat surface

    International Nuclear Information System (INIS)

    Mishra, Amita; Dutta, Anirban; Samaddar, Sayanti; Gupta, Anjan K.

    2013-01-01

    We report the wet chemical deposition of single crystalline epitaxial thin films of the colossal magneto-resistive manganite La 0.67 Sr 0.33 MnO 3 on the lattice-matched (001)-face of a La 0.3 Sr 0.7 Al 0.65 Ta 0.35 O 3 substrate. Topographic images of these films taken with a scanning tunneling microscope show atomically flat terraces separated by steps of monatomic height. The resistivity of these films shows an insulator-metal transition at 310 K, nearly coincident with the Curie temperature of 340 K, found from magnetization measurements. The films show a magnetoresistance of 7% at 300 K and 1.2 T. Their saturation magnetization value at low temperatures is consistent with that of the bulk. - Highlights: ► Wet chemical deposition of La 0.67 Sr 0.33 MnO 3 (LSMO) on a lattice-matched substrate. ► Single crystalline epitaxial LSMO films obtained. ► Flat terraces separated by monatomic steps observed by scanning tunneling microscope

  20. Photolithographically Patterned TiO2 Films for Electrolyte-Gated Transistors.

    Science.gov (United States)

    Valitova, Irina; Kumar, Prajwal; Meng, Xiang; Soavi, Francesca; Santato, Clara; Cicoira, Fabio

    2016-06-15

    Metal oxides constitute a class of materials whose properties cover the entire range from insulators to semiconductors to metals. Most metal oxides are abundant and accessible at moderate cost. Metal oxides are widely investigated as channel materials in transistors, including electrolyte-gated transistors, where the charge carrier density can be modulated by orders of magnitude upon application of relatively low electrical bias (2 V). Electrolyte gating offers the opportunity to envisage new applications in flexible and printed electronics as well as to improve our current understanding of fundamental processes in electronic materials, e.g. insulator/metal transitions. In this work, we employ photolithographically patterned TiO2 films as channels for electrolyte-gated transistors. TiO2 stands out for its biocompatibility and wide use in sensing, electrochromics, photovoltaics and photocatalysis. We fabricated TiO2 electrolyte-gated transistors using an original unconventional parylene-based patterning technique. By using a combination of electrochemical and charge carrier transport measurements we demonstrated that patterning improves the performance of electrolyte-gated TiO2 transistors with respect to their unpatterned counterparts. Patterned electrolyte-gated (EG) TiO2 transistors show threshold voltages of about 0.9 V, ON/OFF ratios as high as 1 × 10(5), and electron mobility above 1 cm(2)/(V s).

  1. Magnetostructural, mechanical and electronic properties of manganese tetraboride

    Directory of Open Access Journals (Sweden)

    Yongcheng Liang

    2015-11-01

    Full Text Available Magnetostructural stabilities, mechanical behaviors and electronic structures of various phases of manganese tetraboride (MnB4 have been investigated systematically by density functional theory (DFT based first-principles methods. It is found that MnB4 undergoes temperature-induced phase transitions from the nonmagnetic (NM monoclinic mP20 structure to the ferromagnetic (FM orthorhombic oP10 structure at 438 K, then to the antiferromagnetic (AFM orthorhombic oP10 structure at 824 K. We reveal that the NM insulating mP20 phase stabilizes by the Peierls distortion breaking the structural degeneracy, while the FM and AFM metallic oP10 phases stabilize by the Stoner magnetism lifting the spin degeneracy. Furthermore, the calculated mechanical properties show that the NM mP20, FM oP10, and AFM oP10 phases exhibit low compressibility and high hardness, which originate from their three-dimensional covalent boron networks. Therefore, this unique temperature-assisted insulator-metal transition, strong stiffness and high hardness suggest that MnB4 may find promising technological applications as thermoelectric switches and field effect transistors at the extreme conditions.

  2. Ultrafast and directional diffusion of lithium in phosphorene for high-performance lithium-ion battery.

    Science.gov (United States)

    Li, Weifeng; Yang, Yanmei; Zhang, Gang; Zhang, Yong-Wei

    2015-03-11

    Density functional theory calculations have been performed to investigate the binding and diffusion behavior of Li in phosphorene. Our studies reveal the following findings: (1) Li atom forms strong binding with phosphorus atoms and exists in the cationic state; (2) the shallow energy barrier (0.08 eV) of Li diffusion on monolayer phosphorene along zigzag direction leads to an ultrahigh diffusivity, which is estimated to be 10(2) (10(4)) times faster than that on MoS2 (graphene) at room temperature; (3) the large energy barrier (0.68 eV) along armchair direction results in a nearly forbidden diffusion, and such strong diffusion anisotropy is absent in graphene and MoS2; (4) a remarkably large average voltage of 2.9 V is predicted in the phosphorene-based Li-ion battery; and (5) a semiconducting to metallic transition induced by Li intercalation of phosphorene gives rise to a good electrical conductivity, ideal for use as an electrode. Given these advantages, it is expected that phosphorene will present abundant opportunities for applications in novel electronic device and lithium-ion battery with a high rate capability and high charging voltage.

  3. Unexpected Magnetic Semiconductor Behavior in Zigzag Phosphorene Nanoribbons Driven by Half-Filled One Dimensional Band

    Science.gov (United States)

    Du, Yongping; Liu, Huimei; Xu, Bo; Sheng, Li; Yin, Jiang; Duan, Chun-Gang; Wan, Xiangang

    2015-01-01

    Phosphorene, as a novel two-dimensional material, has attracted a great interest due to its novel electronic structure. The pursuit of controlled magnetism in Phosphorene in particular has been persisting goal in this area. In this paper, an antiferromagnetic insulating state has been found in the zigzag phosphorene nanoribbons (ZPNRs) from the comprehensive density functional theory calculations. Comparing with other one-dimensional systems, the magnetism in ZPNRs display several surprising characteristics: (i) the magnetic moments are antiparallel arranged at each zigzag edge; (ii) the magnetism is quite stable in energy (about 29 meV/magnetic-ion) and the band gap is big (about 0.7 eV); (iii) the electronic and magnetic properties is almost independent on the width of nanoribbons; (iv) a moderate compressive strain will induce a magnetic to nonmagnetic as well as semiconductor to metal transition. All of these phenomena arise naturally due to one unique mechanism, namely the electronic instability induced by the half-filled one-dimensional bands which cross the Fermi level at around π/2a. The unusual electronic and magnetic properties in ZPNRs endow them possible potential for the applications in nanoelectronic devices. PMID:25747727

  4. Phosphorene as an anode material for Na-ion batteries: a first-principles study.

    Science.gov (United States)

    Kulish, Vadym V; Malyi, Oleksandr I; Persson, Clas; Wu, Ping

    2015-06-07

    We systematically investigate a novel two-dimensional nanomaterial, phosphorene, as an anode for Na-ion batteries. Using first-principles calculations, we determine the Na adsorption energy, specific capacity and Na diffusion barriers on monolayer phosphorene. We examine the main trends in the electronic structure and mechanical properties as a function of Na concentration. We find a favorable Na-phosphorene interaction with a high theoretical Na storage capacity. We find that Na-phosphorene undergoes semiconductor-metal transition at high Na concentration. Our results show that Na diffusion on phosphorene is fast and anisotropic with an energy barrier of only 0.04 eV. Owing to its high capacity, good stability, excellent electrical conductivity and high Na mobility, monolayer phosphorene is a very promising anode material for Na-ion batteries. The calculated performance in terms of specific capacity and diffusion barriers is compared to other layered 2D electrode materials, such as graphene, MoS2, and polysilane.

  5. The giant Stark effect in armchair-edge phosphorene nanoribbons under a transverse electric field

    Science.gov (United States)

    Zhou, Benliang; Zhou, Benhu; Liu, Pu; Zhou, Guanghui

    2018-01-01

    We study the variation of electronic properties for armchair-edge phosphorene nanoribbons (APNRs) modulated by a transverse electric field. Within the tight-binding model Hamiltonian, and by solving the differential Schrödinger equation, we find that a band gap closure appears at the critical field due to the giant Stark effect for an APNR. The gap closure has no field polarity, and the gap varies quadratically for small fields but becomes linear for larger ones. We attribute the giant Stark effect to the broken edge degeneracy, i.e., the charge redistributions of the conduction band minimum and valence band maximum states localized at opposite edges induced by the field. By combined with the Green's function approach, it is shown that in the presence of the critical field a gap of density of states (DOS) disappears and a high value DOS turns up at the energy position of the band gap closure. Finally, as the field increases, we find the band gap decreases more rapidly and the gap closure occurs at smaller fields for wider ribbons. Both the band gap and DOS variations with the field show an insulator-metal transition induced by a transverse electric field for the APNR. Our results show that wider APNRs are more appreciable to design field-effect transistors.

  6. Electrostatic doping of a Mott insulator in an oxide heterostructure: the case of LaVO{sub 3}/SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Andreas; Pfaff, Florian; Sing, Michael; Claessen, Ralph [Physikalisches Insititut and Roentgen Research Center for Complex Material Systems, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Boschker, Hans; Kamp, Martin; Koster, Gertjan; Rijnders, Guus [Faculty of Science and Technology and MESA-plus Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands)

    2012-07-01

    The discovery of a quasi-two-dimensional electron system at the interface between the two band insulators LaAlO{sub 3} and SrTiO{sub 3} has triggered intense investigations of oxide heterostructures with other material combinations. The hope is that by combining a polar overlayer with a non-polar substrate electronic reconstruction will lead to highly mobile interface charge carriers with special properties. The formation of a conducting interface layer in epitaxial LaVO{sub 3}/SrTiO{sub 3}, where LaVO{sub 3} is a Mott insulator, is studied by transport measurements and hard X-ray photoelectron spectroscopy. We identify an insulator-to-metal transition above a critical LaVO{sub 3} thickness with transport properties similar to those recently reported for LaAlO{sub 3}/SrTiO{sub 3} interfaces. Interestingly, our photoemission measurements give evidence that electronic charge is transferred exclusively to the LaVO{sub 3}-side of the interface caused by an electronic reconstruction within the film itself. This opens the opportunity to study a band-filling controlled Mott transition induced by a purely electrostatic mechanism.

  7. Synthesis and electrical transport properties of the LaVO{sub 3}/SrTiO{sub 3} interface

    Energy Technology Data Exchange (ETDEWEB)

    Hentrich, Richard; Schultz, Ludwig; Huehne, Ruben [IFW Dresden (Germany); Haenisch, Jens [IFW Dresden (Germany); ITEP, Karlsruhe Institute of Technology (KIT) (Germany)

    2015-07-01

    We have investigated the two dimensional electron gas at the interface of band gap insulator SrTiO{sub 3} and mott insulator LaVO{sub 3} in comparison to the well-known, purely band insulating LaAlO{sub 3}/SrTiO{sub 3} system. Thin films of LaVO{sub 3} were grown epitaxially on TiO{sub 2} terminated SrTiO{sub 3} single crystal substrates using RHEED-monitored pulsed laser deposition. Optimal process parameters for layer-by-layer growth were found resulting in the growth of atomically smooth films of well-defined thickness. Electrical transport measurements revealed an insulator-metal transition at a film thickness of six unit cells, which is different to previously reported values. Conducting samples showed metallic behavior in a wide temperature range, with their conductivity showing little to no dependence on layer thickness. This led to the conclusion of the metallic behavior being a merely interface driven effect.

  8. DFT+DMFT study of strain and interface effects in LaTiO{sub 3} and LaVO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Dymkowski, Krzysztof; Sclauzero, Gabriele; Ederer, Claude [Materials Theory, ETH Zurich (Switzerland)

    2015-07-01

    Metal-insulator transitions in thin films of early transition metal correlated oxides are linked to both epitaxial strain and electronic reconstruction at the film/substrate interface. We separately address these two key factors for LaTiO{sub 3} and LaVO{sub 3} through density functional theory plus dynamical mean-field theory (DFT+DMFT). We find that mere epitaxial strain suffices to induce an insulator-to-metal transition in LaTiO{sub 3}, but not in LaVO{sub 3}, in agreement with recent experiments. We show that this difference can be explained by the combined effect of strain-induced changes in the crystal field splitting of t{sub 2g} orbitals and different orbital filling in these two materials. The role of the interface is investigated through DFT+DMFT simulations of LaVO{sub 3}/SrTiO{sub 3} heterostructures with varying superlattice periodicities and substrate terminations. Our aim is to assess whether the metallicity observed at the LaVO3/SrTiO3 interface could be driven by pure electronic reconstruction effects, rather than structural or stoichiometric reasons (such as, e.g., O-related defects).

  9. Design, Fabrication and Characterization of Thin Film Structures through Oxidation Kinetics

    Science.gov (United States)

    Diaz Leon, Juan Jose

    Materials science and engineering is devoted to the understanding of the physics and chemistry of materials at the mesoscale and to applying that knowledge into real-life applications. In this work, different oxide materials and different oxidation methods are studied from a materials science point of view and for specific applications. First, the deposition of complex metal oxides is explored for solar energy concentration. This requires a number of multi-cation oxide structures such as thin-film dielectric barriers, low loss waveguides or the use of continuously graded composition oxides for antireflection coatings and light concentration. Then, oxidation via Joule heating is used for the self-alignment of a selector on top of a memristor structure on a nanovia. Simulations are used to explore the necessary voltage for the insulator-to-metal transition temperature of NbO2 using finite element analysis, followed by the fabrication and the characterization of such a device. Finally, long-term copper oxidation at room temperature and pressure is studied using optical techniques. Alternative characterization techniques are used to confirm the growth rate and phase change, and an application of copper oxide as a volatile conductive bridge is shown. All these examples show how the combination of novel simulation, fabrication and characterization techniques can be used to understand physical mechanisms and enable disruptive technologies in fields such as solar cells, light emitting diodes, photodetectors or memory devices.

  10. Temperature Dependent Electron Transport Properties of Gold Nanoparticles and Composites: Scanning Tunneling Spectroscopy Investigations.

    Science.gov (United States)

    Patil, Sumati; Datar, Suwarna; Dharmadhikari, C V

    2018-03-01

    Scanning tunneling spectroscopy (STS) is used for investigating variations in electronic properties of gold nanoparticles (AuNPs) and its composite with urethane-methacrylate comb polymer (UMCP) as function of temperature. Films are prepared by drop casting AuNPs and UMCP in desired manner on silicon substrates. Samples are further analyzed for morphology under scanning electron microscopy (SEM) and atomic force microscopy (AFM). STS measurements performed in temperature range of 33 °C to 142 °C show systematic variation in current versus voltage (I-V) curves, exhibiting semiconducting to metallic transition/Schottky behavior for different samples, depending upon preparation method and as function of temperature. During current versus time (I-t) measurement for AuNPs, random telegraphic noise is observed at room temperature. Random switching of tunneling current between two discrete levels is observed for this sample. Power spectra derived from I-t show 1/f2 dependence. Statistical analysis of fluctuations shows exponential behavior with time width τ ≈ 7 ms. Local density of states (LDOS) plots derived from I-V curves of each sample show systematic shift in valance/conduction band edge towards/away from Fermi level, with respect to increase in temperature. Schottky emission is best fitted electron emission mechanism for all samples over certain range of bias voltage. Schottky plots are used to calculate barrier heights and temperature dependent measurements helped in measuring activation energies for electron transport in all samples.

  11. Tuning the electrical and optical properties of Gd_1_-_xCa_xBaCo_2O_5_+_δ (x = 0–0.5) using solar energy

    International Nuclear Information System (INIS)

    Lu, Yi; Zhang, Rong; Wei, Ling; Lu, Chunhua; Fang, Zhenggang; Ni, Yaru; Xu, Zhongzi; Tao, Shunyan

    2016-01-01

    This study reveals that the use of a Ca dopant can increase the solar absorption of GdBaCo_2O_5_+_δ, with an optimal composition of Gd_0_._8Ca_0_._2BaCo_2O_5 achieving 85% solar absorptance. Electrical conductivity measurements revealed that this composition allows for faster insulator-metal transition and higher conductivity, with the observed variation in conductivity with 0.8 W/cm"2 of solar illumination explained in terms of a first-order spin-state transition. Thermal radiation imaging confirmed that regions of different radiative temperature are related to a change in free carriers that promote scattering, and therefore, cause an increase in infrared reflection. This rapid electrical conductivity transition and the low infrared radiation properties at high temperatures strongly suggest that Gd_0_._8Ca_0_._2BaCo_2O_5 could be used in a variety of potential fields, such as high-temperature thermosensitive or thermal storage materials. - Highlights: • The solar absorption properties of GdBaCo_2O_5_+_δ can be improved by Ca doping. • Gd_0_._8Ca_0_._2BaCo_2O_5 shows ultrafast conductivity transition induced by solar energy. • Gd_0_._8Ca_0_._2BaCo_2O_5 exhibits low thermal radiative properties at high temperature.

  12. Microchip power compensated calorimetry applied to metal hydride characterization

    Energy Technology Data Exchange (ETDEWEB)

    Sepulveda, A.; Lopeandia, A.F.; Domenech-Ferrer, R.; Garcia, G.; Pi, F.; Rodriguez-Viejo, J. [Nanomaterials and Microsystems Group, Physics Department, Universitat Autonoma de Barcelona, 08193 Bellaterra (Spain); Munoz, F.J. [Instituto de Microelectronica de Barcelona, Centro Nacional de Microelectronica, Campus UAB, 08193 Bellaterra (Spain)

    2008-06-15

    In this work, we show the suitability of the thin film membrane-based calorimetric technique to measure kinetically limited phase transitions such as the dehydrogenation of metallic hydrides. Different compounds such as Mg, Mg/Al and Mg{sub 80}Ti{sub 20} have been deposited over the active area of the microchip by electron beam evaporation. After several hydrogenation treatments at different temperatures to induce the hydride formation, calorimetric measurements on the dehydrogenation process of those thin films, either in vacuum or in air, are performed at a heating rate of 10 C/min. We observe a significant reduction in the onset of dehydrogenation for Mg{sub 80}Ti{sub 20} compared with pure Mg or Mg/Al layers, which confirms the beneficial effect of Ti on dehydrogenation. We also show the suitability of the membrane-based nanocalorimeters to be used in parallel with optical methods. Quantification of the energy released during hydrogen desorption remains elusive due to the semi-insulating to metallic transition of the film which affects the calorimetric trace. (author)

  13. Magneto-transport and thermoelectric properties of epitaxial FeSb{sub 2} thin film on MgO substrate

    Energy Technology Data Exchange (ETDEWEB)

    Duong, Anh Tuan; Rhim, S. H., E-mail: sonny@ulsan.ac.kr; Shin, Yooleemi; Nguyen, Van Quang; Cho, Sunglae, E-mail: slcho@ulsan.ac.kr [Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749 (Korea, Republic of)

    2015-01-19

    We report magneto-transport and thermoelectric properties of FeSb{sub 2} thin film epitaxially grown on the MgO substrate using molecular beam epitaxy. The film exhibits compressive strain of 1.74% owing to large lattice mismatch, whose physical consequences are nontrivial. Magnetic phase has been changed from diamagnetic in bulk, as evidenced by anomalous Hall effect (AHE) and negative magneto-resistance (MR). The FeSb{sub 2} film is semiconducting without any metallic transition unlike the bulk counterpart. In particular, hysteresis in MR with distinct feature of AHE is evident with coercive field of 500 and 110 Oe for T = 20 and 50 K, respectively. Furthermore, from the Seebeck coefficients and temperature dependence of the resistivity, it is evident that the film is semiconducting with small band gap: 3.76 meV for T < 40 K and 13.48 meV for T > 40 K, respectively, where maximum thermoelectric power factor of 12 μV/cm·K at T = 50 K.

  14. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y. -D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-16

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  15. Effects of swift heavy ion irradiation on La0.5Pr0.2Sr0.3MnO3 epitaxial thin films grown by pulsed laser deposition

    International Nuclear Information System (INIS)

    Markna, J.H.; Parmar, R.N.; Rana, D.S.; Ravi Kumar; Misra, P.; Kukreja, L.M.; Kuberkar, D.G.; Malik, S.K.

    2007-01-01

    We report the observation of room temperature insulator to metal transition and magnetoresistance characteristics of Swift Heavy Ions (SHIs) irradiated La 0.5 Pr 0.2 Sr 0.3 MnO 3 (LPSMO) epitaxial thin films grown on single crystal (1 0 0) SrTiO 3 substrates using Pulsed Laser Deposition. The epitaxial nature and crystallanity of the films was confirmed from the structural and magnetoresistance characteristics. Irradiation with the 200 MeV Ag 15+ ions at a fluence of about 5 x 10 11 ions/cm 2 showed suppression in the resistivity by ∼68% and 31% for the films with 50 nm and 100 nm thickness respectively. The possible reasons for this suppression could be either release of strain in the films in the dead layer at the interface of film-substrate or Swift Heavy Ions induced annealing which in turn affects the Mn-O-Mn bond angle thereby favoring the Zener double exchange. Field Coefficient of Resistance (FCR) values for both films, determined from R-H data and magnetoresistance data, showed a marginal enhancement after irradiation

  16. Effect of thickness on magnetic phase coexistence and electrical transport in Nd0.51Sr0.49MnO3 films

    International Nuclear Information System (INIS)

    Prasad, R.; Singh, M.P.; Fournier, P.; Siwach, P.K.; Singh, H.K.; Kaur, A.

    2010-01-01

    We present the impact of the film thickness on the coexistence of various magnetic phases and its link to the magnetoresistance of Nd 0.51 Sr 0.49 MnO 3 thin films. These epitaxial films are deposited on LaAlO 3 (001) substrates by DC magnetron sputtering. Films with thicknesses of approximately 30 nm are found to be under full compressive strain while those with thicknesses ∝100 nm and beyond exhibit the presence of both strained and relaxed phases, as evidenced from X-ray diffraction studies. Both films exhibit multiple magnetic transitions controlled by strong electron correlations and phase coexistence. These films also display insulator-metal transitions (IMT) and colossal magnetoresistance (CMR) under moderate magnetic fields. Among the two set of films, only the 30-nm films show a weak signature of charge ordering at T∼50 K. Even at temperatures much lower than the IMT, the 30-nm films show huge magnetoresistance (MR) ∝80%. This suggests presence of softened charge-ordered insulating (COI) clusters that are transformed into ferromagnetic metallic (FMM) ones by the external magnetic field. In the 100-nm films, the corresponding MR is suppressed to less than 20%. Our study demonstrates that the softening of the COI phase is induced by the combined effect of the in-plane compressive strain and a slight reduction in Sr concentration. (orig.)

  17. Thermoelectric power measurements in Fe doped La sub 0 sub . sub 6 sub 5 Ca sub 0 sub . sub 3 sub 5 MnO sub 3

    CERN Document Server

    Aslam, A; Zubair, M; Akhtar, M J; Nadeem, M

    2002-01-01

    We report measurements of the thermoelectric power (TEP) on the La sub 0 sub . sub 6 sub 5 Ca sub 0 sub . sub 3 sub 5 Mn sub 1 sub - sub x Fe sub x O sub 3 system for 0.00 <= x <= 0.07. The ferromagnetic and metallic transition temperatures are lowered and the TEP shows an increasingly positive trend with the addition of Fe. We also observe a clear magnetic contribution that manifests itself as a peak in the TEP close to the critical temperature. The activation energies determined from the TEP are seen to be insensitive to the Fe content. The data are interpreted firstly as showing a decrease in the density of active holes, i.e. holes that can participate in the hopping process, with increasing Fe content. Secondly the data suggest the role of magnetic scattering due to the clusters formed by the antiferromagnetically coupled Fe. Abrupt changes in the variation of the TEP are observed at the concentration region x approx 0.04 consistent with the hole density variation and with previously reported transp...

  18. Theoretical study of the localization-delocalization transition in amorphous molybdenum-germanium alloys

    International Nuclear Information System (INIS)

    Ding, K.; Andersen, H.C.

    1987-01-01

    Electronic structure calculations were performed for amorphous germanium and amorphous alloys of molybdenum and germanium. The calculations used Harrison's universal linear-combination-of-atomic-orbitals parameters to generate one-electron Hamiltonians for structural configurations obtained from molecular-dynamics simulations. The density of states calculated for a model of a-Ge showed a distinct pseudogap, although with an appreciable density of states at the minimum. The states in the pseudogap are localized. As the concentration of Mo atoms increases, the pseudogap of the density of states is gradually filled up. The density of states at the Fermi energy calculated for our model of the alloys agrees quite well with that experimentally determined by Yoshizumi, Geballe, and co-workers. The localization index for the states at the Fermi energy is a decreasing function of Mo concentration in the range of 2--14 at. % Mo and the localization length is an increasing function of molybdenum concentration. These results are consistent with the experimental observation of an insulator-metal transition at about 10 at. % Mo

  19. Synthesis of Mg2FeH6 containing as additives transition metal and transition metal fluorides or carbon

    International Nuclear Information System (INIS)

    Zepon, G.; Leiva, D.R.; Botta, W.J.

    2010-01-01

    The Mg 2 FeH 6 is a promising way of storing hydrogen in solid form, composed by elements that have low cost and, at the same time, high volumetric storage density: 150 kg H 2 /m 3 . However, this complex hydride is not easily synthesized as a single phase material. The hydrogen sorption high temperature and slow kinetics are the major limitations for the practical application of the Mg 2 FeH 6 as a hydrogen storage material. Little is known about the effects of additives in Mg 2 FeH 6 based nanocomposites in this work were synthesized by MAE under hydrogen atmosphere nanocomposites based on Mg 2 FeH 6 containing additives as transition metals, transition metals fluorides of transition metals or carbon, in order to obtain information on the effects of the selected additives. To this end, we used characterization techniques such as XRD, SEM and TEM, thermal analysis by DSC and curves made in apparatus PCT.(author)

  20. Strain and electric field induced metallization in the GaX (X = N, P, As & Sb) monolayer

    Science.gov (United States)

    Bahuguna, Bhagwati Prasad; Saini, L. K.; Sharma, Rajesh O.; Tiwari, Brajesh

    2018-05-01

    We investigate the strain and electric field dependent electronic properties of two dimensional Ga-based group III-V monolayer from the first-principles approach within density functional theory. The energy bandgap of GaX monolayer increases upto the certain value of compressive strain and then decreases. On the other hand, the energy bandgap of GaX monolayer is monotonically decreased with increasing tensile strain and become metallic at the higher value. Furthermore, the perpendicular electric field decreases the energy band gap of unstrained GaX monolayer and shows semiconductor to metal transition. These results suggest that the nature of energy bands and value of energy bandgap in GaX monolayer can be tuned by the biaxial mechanical strain or perpendicular electrical field. Additionally, we have also studied the optical response of unstrained GaX monolayer in term of optical conductivity. These findings may provide valuable information to develop the Ga-based optoelectronic devices and further the understanding of the GaX monolayer.

  1. Experimental and theoretical study of electronic structure of aluminum in extreme conditions with X-ray absorption spectroscopy

    International Nuclear Information System (INIS)

    Festa, Floriane

    2013-01-01

    Matter in extreme conditions belongs to Warm Dense Matter regime which lays between dense plasma regime and condensed matter. This regime is still not well known, indeed it is very complex to generate such plasma in the laboratory to get experimental data and validate models. The goal of this thesis is to study electronic structure of aluminum in extreme conditions with X-ray absorption spectroscopy. Experimentally aluminum has reached high densities and high temperatures, up to now unexplored. An X-ray source has also been generated to probe highly compressed aluminum. Two spectrometers have recorded aluminum absorption spectra and aluminum density and temperature conditions have been deduced thanks to optical diagnostics. Experimental spectra have been compared to ab initio spectra, calculated in the same conditions. The theoretical goal was to validate the calculation method in high densities and high temperatures regime with the study of K-edge absorption modifications. We also used absorption spectra to study the metal-non metal transition which takes place at low density (density ≤ solid density). This transition could be study with electronic structure modifications of the system. (author) [fr

  2. Synthesis of Mg{sub 2}FeH{sub 6} containing as additives transition metal and transition metal fluorides or carbon; Sintese de Mg{sub 2}FeH{sub 6} contando como aditivos metais de transicao e fluoretos de metais de transicao ou carbono

    Energy Technology Data Exchange (ETDEWEB)

    Zepon, G.; Leiva, D.R.; Botta, W.J., E-mail: guizepon@yahoo.com.b [Universidade Federal de Sao Carlos (DEMa/UFSCar), SP (Brazil). Dept. de Engenharia de Materiais

    2010-07-01

    The Mg{sub 2}FeH{sub 6} is a promising way of storing hydrogen in solid form, composed by elements that have low cost and, at the same time, high volumetric storage density: 150 kg H{sub 2}/m{sup 3}. However, this complex hydride is not easily synthesized as a single phase material. The hydrogen sorption high temperature and slow kinetics are the major limitations for the practical application of the Mg{sub 2}FeH{sub 6} as a hydrogen storage material. Little is known about the effects of additives in Mg{sub 2}FeH{sub 6} based nanocomposites in this work were synthesized by MAE under hydrogen atmosphere nanocomposites based on Mg{sub 2}FeH{sub 6} containing additives as transition metals, transition metals fluorides of transition metals or carbon, in order to obtain information on the effects of the selected additives. To this end, we used characterization techniques such as XRD, SEM and TEM, thermal analysis by DSC and curves made in apparatus PCT.(author)

  3. Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds

    Science.gov (United States)

    Su, Ching-Hua; Zhu, Shen; Li, Chao; Scripa, R.; Lehoczky, Sandra L.; Kim, Y. W.; Baird, J. K.; Lin, B.; Ban, Heng; Benmore, Chris

    2003-01-01

    The objectives of the project are to conduct ground-based experimental and theoretical research on the structural fluctuations and thermophysical properties of molten II-VI compounds to enhance the basic understanding of the existing flight experiments in microgravity materials science programs as well as to study the fundamental heterophase fluctuation phenomena in these melts by: 1) conducting neutron scattering analysis and measuring quantitatively the relevant thermophysical properties of the II-VI melts (such as viscosity, electrical conductivity, thermal diffusivity and density) as well as the relaxation characteristics of these properties to advance the understanding of the structural properties and the relaxation phenomena in these melts and 2) performing theoretical analyses on the melt systems to interpret the experimental results. All the facilities required for the experimental measurements have been procured, installed and tested. It has long been recognized that liquid Te presents a unique case having properties between those of metals and semiconductors. The electrical conductivity for Te melt increases rapidly at melting point, indicating a semiconductor-metal transition. Te melts comprise two features, which are usually considered to be incompatible with each other: covalently bound atoms and metallic-like behavior. Why do Te liquids show metallic behavior? is one of the long-standing issues in liquid metal physics. Since thermophysical properties are very sensitive to the structural variations of a melt, we have conducted extensive thermophysical measurements on Te melt.

  4. Bandstructure modulation for Si-h and Si-g nanotubes in a transverse electric field: Tight binding approach

    Science.gov (United States)

    Chegel, Raad; Behzad, Somayeh

    2013-11-01

    We have investigated the electronic properties of SiNTs, under the external electric field, using Tight Binding (TB) approximation. It was found that the energy levels, energy gaps, and density of states (DOS) strongly depend on the electric field strength. The large electric strength leads to coupling the neighbor subbands and induce destruction of subband degeneracy, increase of low-energy states, and strong modulation of energy gap which these effects reflect in the DOS spectrum. It has been shown that, the band gap reduction of Si g-NTs is linearly proportional to the electric field strength. The band gap variation for Si h-NTs increases first and later decreases (Metallic) or first remains constant and then decreases (semiconductor). Also we show that the larger diameter tubes are more sensitive to the field strength than smaller ones. The semiconducting metallic transition or vice versa can be achieved through an increasing of applied fields. Number and position of peaks in DOS spectrum are dependent on electric field strength.

  5. Manganite/Cuprate Superlattice as Artificial Reentrant Spin Glass

    KAUST Repository

    Ding, Junfeng

    2016-05-04

    Emerging physical phenomena at the unit-cell-controlled interfaces of transition-metal oxides have attracted lots of interest because of the rich physics and application opportunities. This work reports a reentrant spin glass behavior with strong magnetic memory effect discovered in oxide heterostructures composed of ultrathin manganite La0.7Sr0.3MnO3 (LSMO) and cuprate La2CuO4 (LCO) layers. These heterostructures are featured with enhanced ferromagnetism before entering the spin glass state: a Curie temperature of 246 K is observed in the superlattice with six-unit-cell LSMO layers, while the reference LSMO film with the same thickness shows much weaker magnetism. Furthermore, an insulator-metal transition emerges at the Curie temperature, and below the freezing temperature the superlattices can be considered as a glassy ferromagnetic insulator. These experimental results are closely related to the interfacial spin reconstruction revealed by the first-principles calculations, and the dependence of the reentrant spin glass behavior on the LSMO layer thickness is in line with the general phase diagram of a spin system derived from the infinite-range SK model. The results of this work underscore the manganite/cuprate superlattices as a versatile platform of creating artificial materials with tailored interfacial spin coupling and physical properties. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Effect of conducting polypyrrole on the transport properties of carbon nanotube yarn

    International Nuclear Information System (INIS)

    Foroughi, Javad; Kimiaghalam, Bahram; Ghorbani, Shaban Reza; Safaei, Farzad; Abolhasan, Mehran

    2012-01-01

    Experiments were conducted to measure the electrical conductivity in three types of pristine and carbon nanotube-polypyrrole (CNT-PPy) composite yarns and its dependence on over a wide temperature range. The experimental results fit well with the analytical models developed. The effective energy separation between localized states of the pristine CNT yarn is larger than that for both the electrochemically and chemically prepared CNT-PPy yarns. It was found that all samples are in the critical regime in the insulator–metal transition, or close to the metallic regime at low temperature. The electrical conductivity results are in good agreement with a Three Dimensional Variable Range Hopping model at low temperatures, which provides a strong indication that electron hopping is the main means of current transfer in CNT yarns at T < 100 K. We found that the two shell model accurately describes the electronic properties of CNT and CNT-PPy composite yarns in the temperature range of 5–350 K. - Highlights: ► We developed hybrid carbon nanotube conducting polypyrrole composite yarns. ► The main current transfer scheme in yarn is via three dimensional electrons hopping. ► Two shell model describes well electronic properties of yarns in range of 5-350 K.

  7. Minor Actinide Burning in Thermal Reactors. A Report by the Working Party on Scientific Issues of Reactor Systems

    International Nuclear Information System (INIS)

    Hesketh, K.; Porsch, D.; Rimpault, G.; Taiwo, T.; Worrall, A.

    2013-01-01

    The actinides (or actinoids) are those elements in the periodic table from actinium upwards. Uranium (U) and plutonium (Pu) are two of the principal elements in nuclear fuel that could be classed as major actinides. The minor actinides are normally taken to be the triad of neptunium (Np), americium (Am) and curium (Cm). The combined masses of the remaining actinides (i.e. actinium, thorium, protactinium, berkelium, californium, einsteinium and fermium) are small enough to be regarded as very minor trace contaminants in nuclear fuel. Those elements above uranium in the periodic table are known collectively as the transuranics (TRUs). The operation of a nuclear reactor produces large quantities of irradiated fuel (sometimes referred to as spent fuel), which is either stored prior to eventual deep geological disposal or reprocessed to enable actinide recycling. A modern light water reactor (LWR) of 1 GWe capacity will typically discharge about 20-25 tonnes of irradiated fuel per year of operation. About 93-94% of the mass of uranium oxide irradiated fuel is comprised of uranium (mostly 238 U), with about 4-5% fission products and ∼1% plutonium. About 0.1-0.2% of the mass is comprised of neptunium, americium and curium. These latter elements accumulate in nuclear fuel because of neutron captures, and they contribute significantly to decay heat loading and neutron output, as well as to the overall radio-toxic hazard of spent fuel. Although the total minor actinide mass is relatively small - approximately 20-25 kg per year from a 1 GWe LWR - it has a disproportionate impact on spent fuel disposal, and thus the longstanding interest in transmuting these actinides either by fission (to fission products) or neutron capture in order to reduce their impact on the back end of the fuel cycle. The combined masses of the trace actinides actinium, thorium, protactinium, berkelium and californium in irradiated LWR fuel are only about 2 parts per billion, which is far too low for

  8. The intriguing electronic and optical properties modulation of hydrogen and fluorine codecorated silicene layers

    International Nuclear Information System (INIS)

    Yang, Qun; Tan, Chunjian; Meng, Ruishen; Jiang, Junke; Liang, Qiuhua; Sun, Xiang; Yang, Daoguo; Chen, Xianping

    2017-01-01

    Highlights: • The HSiF bilayer is very stable due to the high binding energy even larger than the ones of bilayer graphene. • The HSiF bilayer exhibits a moderate direct band gap of 0.296 eV much lower than that of HSiF monolayer. • All the HSiF layers have a direct band gap nature, irrespective of stacking pattern, thickness and external electric fields, which is an advantage over MoS 2 layers. Besides, it is advantageous to the application of HSiF layers in the field of optical devices. • The external electric field can effectively tune the band gaps of HSiF layers. Especially, even a semiconductor–metal transition occurs. • After the formation of HSiF bilayer, the complete electron-hole separation enhances the photocatalytic efficiency of HSiF bilayer and it exhibits a significantly improved visible light adsorption peak. - Abstract: First-principles calculations based on density-functional theory reveal some superior physical properties of hydrogen and fluorine co-decorated silicene (HSiF) monolayer and bilayer. Our simulated results reveal that the HSiF monolayer is a large direct band gap semiconductor greatly differing from the gapless semi-metallic silicene. There exists strong interlayer coupling in HSiF bilayer, leading to the good stabilities of HSiF bilayer even beyond bilayer graphene. The proposed HSiF bilayer exhibits a moderate direct band gap of 0.296 eV which is much lower than that of HSiF monolayer. Encouragingly, HSiF layers all have a direct band gap nature, irrespective of stacking pattern, thickness and external electric fields, which is an advantage over MoS 2 layers. Furthermore, an out-of-plane electric field has an evident impact on the band structures of the HSiF monolayer and bilayer. Especially, the band gap of HSiF bilayer can be effectively tuned by external electric field, even a semiconductor–metal transition occurs. More importantly, the HSiF bilayer exhibits a significant improved visible light adsorption peak with

  9. The intriguing electronic and optical properties modulation of hydrogen and fluorine codecorated silicene layers

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Qun; Tan, Chunjian [Faculty of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, 541004 Guilin (China); Key Laboratory of Optoelectronic Technology & Systems, Education Ministry of China, Chongqing University and College of Opto-Electronic Engineering, Chongqing University, 400044 Chongqing (China); Meng, Ruishen; Jiang, Junke; Liang, Qiuhua; Sun, Xiang [Key Laboratory of Optoelectronic Technology & Systems, Education Ministry of China, Chongqing University and College of Opto-Electronic Engineering, Chongqing University, 400044 Chongqing (China); Yang, Daoguo [Faculty of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, 541004 Guilin (China); Chen, Xianping, E-mail: xianpingchen@cqu.edu.cn [Faculty of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, 541004 Guilin (China); Key Laboratory of Optoelectronic Technology & Systems, Education Ministry of China, Chongqing University and College of Opto-Electronic Engineering, Chongqing University, 400044 Chongqing (China)

    2017-03-15

    Highlights: • The HSiF bilayer is very stable due to the high binding energy even larger than the ones of bilayer graphene. • The HSiF bilayer exhibits a moderate direct band gap of 0.296 eV much lower than that of HSiF monolayer. • All the HSiF layers have a direct band gap nature, irrespective of stacking pattern, thickness and external electric fields, which is an advantage over MoS{sub 2} layers. Besides, it is advantageous to the application of HSiF layers in the field of optical devices. • The external electric field can effectively tune the band gaps of HSiF layers. Especially, even a semiconductor–metal transition occurs. • After the formation of HSiF bilayer, the complete electron-hole separation enhances the photocatalytic efficiency of HSiF bilayer and it exhibits a significantly improved visible light adsorption peak. - Abstract: First-principles calculations based on density-functional theory reveal some superior physical properties of hydrogen and fluorine co-decorated silicene (HSiF) monolayer and bilayer. Our simulated results reveal that the HSiF monolayer is a large direct band gap semiconductor greatly differing from the gapless semi-metallic silicene. There exists strong interlayer coupling in HSiF bilayer, leading to the good stabilities of HSiF bilayer even beyond bilayer graphene. The proposed HSiF bilayer exhibits a moderate direct band gap of 0.296 eV which is much lower than that of HSiF monolayer. Encouragingly, HSiF layers all have a direct band gap nature, irrespective of stacking pattern, thickness and external electric fields, which is an advantage over MoS{sub 2} layers. Furthermore, an out-of-plane electric field has an evident impact on the band structures of the HSiF monolayer and bilayer. Especially, the band gap of HSiF bilayer can be effectively tuned by external electric field, even a semiconductor–metal transition occurs. More importantly, the HSiF bilayer exhibits a significant improved visible light adsorption

  10. Resistive switching phenomena of extended defects in Nb-doped SrTiO3 under influence of external gradients

    International Nuclear Information System (INIS)

    Rodenbuecher, Christian

    2014-01-01

    Redox-based memristive materials have attracted much attention in the last decade owing to their ability to change the resistance upon application of an electric field making them promising candidates for future non-volatile memories. However, a fundamental understanding of the nature of the resistive switching effect, which is indispensable for designing future technological applications,is still lacking. As a prototype material of a memristive oxide, strontium titanate (SrTiO 3 ) has been investigated intensively and it was revealed that the valence change of a Ti ''d'' electron plays an important role during resistive switching related to insulator-to-metal transition. Such a transition can be induced by electrical gradients, by chemical gradients, by a combination of these gradients or by donor doping. Hence, SrTiO 3 doped with the donor Nb should have metallic properties and is used commonly as a conducting substrate for the growth of functional oxide thin films. Nevertheless,the resistive switching effect has also be observed in Nb-doped SrTiO 3 . This paradoxical situation offers a unique opportunity to gain an insight into the processes during the insulator-to metal transition. In this thesis, a comprehensive study of the influence of external gradients on SrTiO 3 :Nb single crystals is presented. The focus is especially set on the investigation of the crystallographic structure, the chemical composition, the electronic structure, the lattice dynamics and the electronic transport phenomena using surface-sensitive methods on the macro- and nanoscale. On the as-received epi-polished single crystals, the evolution of a surface layer having a slight excess of strontium and - in contrast to the bulk of the material - semiconducting properties are observed. Hence, the key for understanding of the resistive switching effect is the knowledge of the nature of the surface layer. On the basis of systematic studies of the influence of external

  11. Theoretical aspects of positrons in imperfect solids

    International Nuclear Information System (INIS)

    Puska, M.J.

    1987-01-01

    The efficient use of positron annihilation in defect studies requires a deep understanding of the basic processes of positron-imperfect solid interaction. Three stages, i.e. thermalization, trapping by a defect, and the annihilation can be separated during the evolution of the interaction. The last two processes are the most relevant ones for the positron lifetime spectroscopy and they will be discussed in detail in this review. The complete solution of the problem of a localized positron interacting with the electrons around a defect requires the simultaneous self-consistent calculation of the electronic structure and the positron state. This is in principle possible in the two component density functional theory. However, the approximation, in which the electronic structure without the positron influence is used and the electron-positron correlation effects are described by local enhancement factors, has turned out to be feasible in practice and also accurate enough in predicting positron annihilation characteristics. Moreover, a non-self-consistent electron structure is sufficient in many cases. This enables an efficient calculation method in which the positron wave function can be solved in three dimensions for arbitrary defect geometries. Enhancement models for simple metals, transition metals, and semiconductors are represented. Thereafter, applications to vacancies, vacancy clusters, and vacancy-impurity complexes are shown. The positron trapping by defects is mediated by the transfer of the positron binding energy to the solid in the form of electron-hole pairs and phonons. The trapping phenomenon is discussed in the case of metals and semiconductors. Semiconductors are especially challenging because the existence of the energy gap makes the low energy electron-hole excitations impossible and because the defects have different charge states effecting strongly on the trapping rate. (author)

  12. Creating Two-Dimensional Electron Gas in Nonpolar/Nonpolar Oxide Interface via Polarization Discontinuity: First-Principles Analysis of CaZrO3/SrTiO3 Heterostructure.

    Science.gov (United States)

    Nazir, Safdar; Cheng, Jianli; Yang, Kesong

    2016-01-13

    We studied strain-induced polarization and resulting conductivity in the nonpolar/nonpolar CaZrO3/SrTiO3 (CZO/STO) heterostructure (HS) system by means of first-principles electronic structure calculations. By modeling four types of CZO/STO HS-based slab systems, i.e., TiO2/CaO and SrO/ZrO2 interface models with CaO and ZrO2 surface terminations in each model separately, we found that the lattice-mismatch-induced compressive strain leads to a strong polarization in the CZO film and that as the CZO film thickness increases there exists an insulator-to-metal transition. The polarization direction and critical thickness of the CZO film for forming interfacial metallic states depend on the surface termination of CZO film in both types of interface models. In the TiO2/CaO and SrO/ZrO2 interface models with CaO surface termination, the strong polarization drives the charge transfer from the CZO film to the first few TiO2 layers in the STO substrate, leading to the formation of two-dimensional electron gas (2DEG) at the interface. In the HS models with ZrO2 surface termination, two polarization domains with opposite directions are in the CZO film, which results in the charge transfer from the middle CZO layer to the interface and surface, respectively, leading to the coexistence of the 2DEG on the interface and the two-dimensional hole gas (2DHG) at the middle CZO layer. These findings open a new avenue to achieve 2DEG (2DHG) in perovskite-based HS systems via polarization discontinuity.

  13. Variation of crystallinity and stoichiometry in films of gallium oxide, gallium nitride and barium zirconate prepared by means of PLD

    International Nuclear Information System (INIS)

    Brendt, Jochen

    2011-01-01

    Pulsed Laser Deposition (PLD) is an ablation technique for thin film preparation of many materials. The film properties can be well controlled by the process parameters. Therefore, in many cases a given material can be deposited with different properties by changing one or more process parameters. In this thesis thin films of gallium oxide, gallium nitride and barium zirconate were deposited with a large variation in structure and stoichiometry by means of Pulsed Laser Deposition. The characterization of the film crystallinity, phase purity and short range structural order was completed by means of X-ray diffraction and X-ray absorption spectroscopy. The stoichiometry was investigated using electron probe microanalysis. For analyzing the correlation between the structure and stoichiometry with the optical and electrical properties, optical absorption and electrical conductivity measurements were carried out. The investigation of all three material systems showed that very unique properties can be realized when combining an amorphous structure and a non-stoichiometric composition. For example, in amorphous and oxygen deficient gallium oxide an insulator-metal-transition can be induced by partial crystallization of the as prepared phase accomplished by annealing at about 400 C in argon atmosphere (as shown in literature). Furthermore, amorphous and highly non-stoichiometric barium zirconate has the ability to split water molecules to hydrogen and oxygen at room temperature. A detailed analysis of both phenomena has been performed by means of photoemission and transmission electron microscopy in the case of gallium oxide and via X-ray absorption spectroscopy and gas chromatography in the case of barium zirconate.

  14. Synthesis and magnetotransport studies of CrO2 films grown on TiO2 nanotube arrays by chemical vapor deposition

    Science.gov (United States)

    Wang, Xiaoling; Zhang, Caiping; Wang, Lu; Lin, Tao; Wen, Gehui

    2018-04-01

    The CrO2 films have been prepared on the TiO2 nanotube array template via atmospheric pressure chemical vapor deposition method. And the growth procedure was studied. In the beginning of the deposition process, the CrO2 grows on the cross section of the TiO2 nanotubes wall, forms a nanonet-like layer. And the grain size of CrO2 is very small. With the increase of the deposition time, the grain size of CrO2 also increases, and the nanonet-like layer changes into porous film. With the further increase of the deposition time, all the nanotubes are covered by CrO2 grains and the surface structure becomes polycrystalline film. The average grain size on the surface of the CrO2 films deposited for 1 h, 2 h and 5 h is about 190 nm, 300 nm and 470 nm. The X-ray diffraction pattern reveals that the rutile CrO2 film has been synthesized on the TiO2 nanotube array template. The CrO2 films show large magnetoresistance (MR) at low temperature, which should originate from spin-dependent tunneling through grain boundaries between CrO2 grains. And the tunneling mechanism of the CrO2 films can be well described by the fluctuation-induced tunneling (FIT) model. The CrO2 film deposited for 2 h shows insulator behavior from 5 k to 300 K, but the CrO2 film deposited for 5 h shows insulator-metal transition around 140 K. The reason is briefly discussed.

  15. Probing the spin-orbit Mott state in Sr3Ir2O7 by electron doping

    Science.gov (United States)

    Hogan, Thomas C.

    Iridium-based members of the Ruddlesden-Popper family of oxide compounds are characterized by a unique combination of energetically comparable effects: crystal-field splitting, spin-orbit coupling, and electron-electron interactions are all present, and the combine to produce a Jeff = 1/2 ground state. In the bilayer member of this series, Sr3Ir2O7, this state manifests as electrically insulating, with unpaired Ir4+ spins aligned along the long axis of the unit cell to produce a G-type antiferromagnet with an ordered moment of 0.36 uB. In this work, this Mott state is destabilized by electron doping via La3+ substitution on the Sr-site to produce (Sr1-x Lax)3Ir2O7. The introduction of carriers initially causes nano-scale phase-separated regions to develop before driving a global insulator-to-metal transition at x=0.04. Coinciding with this transition is the disappearance of evidence of magnetic order in the system in either bulk magnetization or magnetic scattering experiments. The doping also enhances a structural order parameter observed in the parent compound at forbidden reciprocal lattice vectors. A more complete structural solution is proposed to account for this previously unresolved distortion, and also offers an explanation as to the anomalous net ferromagnetism seen prior in bulk measurements. Finally, spin dynamics are probed via a resonant x-ray technique to reveal evidence of spin-dimer-like behavior dominated by inter-plane interactions. This result supports a bond-operator treatment of the interaction Hamiltonian, and also explains the doping dependence of high temperature magnetic susceptibility.

  16. Effect of different concentrations of cadmium growth and morphological changes in basil (ocimum basilicum)

    International Nuclear Information System (INIS)

    Nazarian, M.; Amouzgar, D.; Sedghianzadeh, H.

    2016-01-01

    This study was conducted on four treatments (0, 3, 5 and 10 milligrams per liter of cadmium nitrate solution) and three replications in a completely randomized design. The morphological characteristics including fresh weight, dry weight, stem length, root length, leaf weight ratio, measuring index of the imposed stress, specific leaf area and water availability per unit leaf area, and the amount of cadmium in stems and roots were measured. By increasing cadmium treatment at 10 ppm concentration, the root growth varied between 3.47 and 1.93 cm and the lowest root growth belonged to the treatment at 10 ppm concentration measured 1.93 ± 0.4 cm. The rising stem growth was also indicated. Fresh and dry weight analysis indicates their descending growth. The growth reduction was observed by increasing cadmium treatment at 10 ppm concentration in the study of the trait of weight and specific leaf area. Relative water content (RWC) of the leaves varies between 81 to 89 percent which represents the greatest amount of stress in the treatment at 10 ppm concentration. A notable decline in transport from the root to stem and a significant reduction in plant tolerance index were observed through the analysis of transfer factor and tolerance index in plants. The process of reducing metal transition from the root to stem has become slower by increasing the substance concentration. Basil can absorb and accumulate cadmium and its root is able to accumulate more quantity of the metal than its stem. The morphological signs of cadmium toxicity are remarkable through discolored roots, shortening the distance between nodes, creating an amorphous spots on the leaves, reducing the leaves extent and a slight pallor of the leaves. (author)

  17. Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

    Directory of Open Access Journals (Sweden)

    P. A. Bhobe

    2015-10-01

    Full Text Available Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K_{2}Cr_{8}O_{16}, which exhibits a temperature-dependent (T-dependent paramagnetic-to-ferromagnetic-metal transition at T_{C}=180  K and transforms into a ferromagnetic insulator below T_{MI}=95  K. We observe clear T-dependent dynamic valence (charge fluctuations from above T_{C} to T_{MI}, which effectively get pinned to an average nominal valence of Cr^{+3.75} (Cr^{4+}∶Cr^{3+} states in a 3∶1 ratio in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0∼3.5(k_{B}T_{MI}∼35  meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U∼4  eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr and the half-metallic ferromagnetism in the t_{2g} up-spin band favor a low-energy Peierls metal-insulator transition.

  18. Raman dispersion spectroscopy on the highly saddled nickel(II)-octaethyltetraphenylporphyrin reveals the symmetry of nonplanar distortions and the vibronic coupling strength of normal modes

    International Nuclear Information System (INIS)

    Schweitzer-Stenner, R.; Stichternath, A.; Dreybrodt, W.; Jentzen, W.; Song, X.; Shelnutt, J.A.; Nielsen, O.F.; Medforth, C.J.; Smith, K.M.

    1997-01-01

    We have measured the polarized Raman cross sections and depolarization ratios of 16 fundamental modes of nickel octaethyltetraphenylporphyrin in a CS 2 solution for 16 fundamental modes, i.e., the A 1g -type vibrations ν 1 , ν 2 , ν 3 , ν 4 , ν 5 , and φ 8 , the B 1g vibrations ν 11 and ν 14 , the B 2g vibrations ν 28 , ν 29 , and ν 30 and the antisymmetric A 2g modes ν 19 , ν 20 , ν 22 , and ν 23 as function of the excitation wavelength. The data cover the entire resonant regions of the Q- and B-bands. They were analyzed by use of a theory which describes intra- and intermolecular coupling in terms of a time-independent nonadiabatic perturbation theory [E. Unger, U. Bobinger, W. Dreybrodt, and R. Schweitzer-Stenner, J. Phys. Chem. 97, 9956 (1993)]. This approach explicitly accounts in a self-consistent way for multimode mixing with all Raman modes investigated. The vibronic coupling parameters obtained from this procedure were then used to successfully fit the vibronic side bands of the absorption spectrum and to calculate the resonance excitation profiles in absolute units. Our results show that the porphyrin macrocycle is subject to B 2u -(saddling) and B 1u -(ruffling) distortions which lower its symmetry to S 4 . Thus, evidence is provided that the porphyrin molecule maintains the nonplanar structure of its crystal phase in an organic solvent. The vibronic coupling parameters indicate a breakdown of the four-orbital model. This notion is corroborated by (ZINDO/S) calculations which reveal that significant configurational interaction occurs between the electronic transitions into |Q right-angle- and |1B right-angle-states and various porphyrin→porphyrin, metal→porphyrin, and porphyrin→metal transitions. (Abstract Truncated)

  19. Time-dependent density functional theory study of the luminescence properties of gold phosphine thiolate complexes.

    Science.gov (United States)

    Guidez, Emilie B; Aikens, Christine M

    2015-04-09

    The origin of the emission of the gold phosphine thiolate complex (TPA)AuSCH(CH3)2 (TPA = 1,3,5-triaza-7-phosphaadamantanetriylphosphine) is investigated using time-dependent density functional theory (TDDFT). This system absorbs light at 3.6 eV, which corresponds mostly to a ligand-to-metal transition with some interligand character. The P-Au-S angle decreases upon relaxation in the S1 and T1 states. Our calculations show that these two states are strongly spin-orbit coupled at the ground state geometry. Ligand effects on the optical properties of this complex are also discussed by looking at the simple AuP(CH3)3SCH3 complex. The excitation energies differ by several tenths of an electronvolt. Excited state optimizations show that the excited singlet and triplet of the (TPA)AuSCH(CH3)2 complex are bent. On the other hand, the Au-S bond breaks in the excited state for the simple complex, and TDDFT is no longer an adequate method. The excited state energy landscape of gold phosphine thiolate systems is very complex, with several state crossings. This study also shows that the formation of the [(TPA)AuSCH(CH3)2]2 dimer is favorable in the ground state. The inclusion of dispersion interactions in the calculations affects the optimized geometries of both ground and excited states. Upon excitation, the formation of a Au-Au bond occurs, which results in an increase in energy of the low energy excited states in comparison to the monomer. The experimentally observed emission of the (TPA)AuSCH(CH3)2 complex at 1.86 eV cannot be unambiguously assigned and may originate from several excited states.

  20. Colossal change in thermopower with temperature-driven p-n-type conduction switching in La x Sr2-x TiFeO6 double perovskites

    Science.gov (United States)

    Roy, Pinku; Maiti, Tanmoy

    2018-02-01

    Double perovskite materials have been studied in detail by many researchers, as their magnetic and electronic properties can be controlled by the substitution of alkaline earth metals or lanthanides in the A site and transition metals in the B site. Here we report the temperature-driven, p-n-type conduction switching assisted, large change in thermopower in La3+-doped Sr2TiFeO6-based double perovskites. Stoichiometric compositions of La x Sr2-x TiFeO6 (LSTF) with 0  ⩽  x  ⩽  0.25 were synthesized by the solid-state reaction method. Rietveld refinement of room-temperature XRD data confirmed a single-phase solid solution with cubic crystal structure and Pm\\bar{3}m space group. From temperature-dependent electrical conductivity and Seebeck coefficient (S) studies it is evident that all the compositions underwent an intermediate semiconductor-to-metal transition before the semiconductor phase reappeared at higher temperature. In the process of semiconductor-metal-semiconductor transition, LSTF compositions demonstrated temperature-driven p-n-type conduction switching behavior. The electronic restructuring which occurs due to the intermediate metallic phase between semiconductor phases leads to the colossal change in S for LSTF oxides. The maximum drop in thermopower (ΔS ~ 2516 µV K-1) was observed for LSTF with x  =  0.1 composition. Owing to their enormous change in thermopower of the order of millivolts per kelvin, integrated with p-n-type resistance switching, these double perovskites can be used for various high-temperature multifunctional device applications such as diodes, sensors, switches, thermistors, thyristors, thermal runaway monitors etc. Furthermore, the conduction mechanisms of these oxides were explained by the small polaron hopping model.

  1. Structural, electrical and magnetic properties of Sb-doped Pr2/3Ba1/3MnO3 perovskite manganites

    International Nuclear Information System (INIS)

    Sen, Vikram; Panwar, Neeraj; Bhalla, G.L.; Agarwal, S.K.

    2007-01-01

    We report here the electrical, magnetic and micro-structural features of the Sb-doped (nominally at Mn-sites) Pr 2/3 Ba 1/3 MnO 3 perovskite manganites. Pristine material shows two insulator-metal (I-M) like transitions in the resistivity-temperature (ρ-T) behaviour. While the higher temperature transition (T P1 ) at ∼195 K is reminiscent of the usual metal-insulator transition, the lower temperature transition (T P2 ) at ∼160 K has been ascribed to the grain boundary (GB) effects arising out of the ionic size mismatch between the ions present at the rare-earth site (Pr and Ba). With Sb doping at the Mn-site, both the resistivity peaks are seen to shift to lower temperatures. Room temperature resistivity and the peak values are also successively increasing with Sb doping. Scanning electron micrographs of the samples indicate a gradual increase in their grain sizes with Sb which indicates a gradual decrease in the GB density. The higher temperature insulator-metal transition (T P1 ) shift is explained on the basis of a competition between double-exchange and super-exchange mechanisms. The observed overall resistivity increase and the shift in the resistivity hump (T P2 ) with Sb are found related to the gradually decreasing GB density and the ensuing lattice strain increase at the grain boundaries. The intrinsic MR gets suppressed and the extrinsic MR gets enhanced with Sb doping. The observed low temperature resistivity upturn related to the localization of carriers, is also seen to increase with Sb

  2. Semi-metallic, strong conductive polymer microfiber, method and fast response rate actuators and heating textiles

    KAUST Repository

    Zhou, Jian; Li, Er Qiang; Lubineau, Gilles; Thoroddsen, Sigurdur T; Mulle, Matthieu

    2016-01-01

    A method comprising: providing at least one first composition comprising at least one conjugated polymer and at least one solvent, wet spinning the at least one first composition to form at least one first fiber material, hot-drawing the at least one fiber to form at least one second fiber material. In lead embodiments, high-performance poly(3,4-ethylenedioxy- thiophene)/poly(styrenesulfonate) (PEDOT/PSS) conjugated polymer microfibers were fabricated via wet- spinning followed by hot-drawing. In these lead embodiments, due to the combined effects of the vertical hot-drawing process and doping/de-doping the microfibers with ethylene glycol (EG), a record electrical conductivity of 2804 S · cm-1 was achieved. This is believed to be a six-fold improvement over the best previously reported value for PEDOT/PSS fibers (467 S · cm-1) and a twofold improvement over the best values for conductive polymer films treated by EG de-doping (1418 S · cm-1). Moreover, these lead, highly conductive fibers experience a semiconductor-metal transition at 313 K. They also have superior mechanical properties with a Young's modulus up to 8.3 GPa, a tensile strength reaching 409.8 MPa and a large elongation before failure (21%). The most conductive fiber also demonstrates an extraordinary electrical performance during stretching/unstretching: the conductivity increased by 25% before the fiber rupture point with a maximum strain up to 21%. Simple fabrication of the semi-metallic, strong and stretchable wet-spun PEDOT/PSS microfibers can make them available for conductive smart electronics. A dramatic improvement in electrical conductivity is needed to make conductive polymer fibers viable candidates in applications such as flexible electrodes, conductive textiles, and fast-response sensors and actuators.

  3. Shock Compression of Liquid Noble Gases to Multi-Mbar Pressures

    Science.gov (United States)

    Root, Seth

    2011-10-01

    The high pressure - high temperature behavior of noble gases is of considerable interest because of their use in z-pinch liners for fusion studies and for understanding astrophysical and planetary evolution. However, our understanding of the equation of state (EOS) of the noble gases at extreme conditions is limited. A prime example of this is the liquid xenon Hugoniot. Previous EOS models rapidly diverged on the Hugoniot above 1 Mbar because of differences in the treatment of the electronic contribution to the free energy. Similar divergences are observed for krypton EOS. Combining shock compression experiments and density functional theory (DFT) simulations, we can determine the thermo-physical behavior of matter under extreme conditions. The experimental and DFT results have been instrumental to recent developments in planetary astrophysics and inertial confinement fusion. Shock compression experiments are performed using Sandia's Z-Accelerator to determine the Hugoniot of liquid xenon and krypton in the Mbar regime. Under strong pressure, krypton and xenon undergo an insulator to metal transition. In the metallic state, the shock front becomes reflective allowing for a direct measurement of the sample's shock velocity using laser interferometry. The Hugoniot state is determined using a Monte Carlo analysis method that accounts for systematic error in the standards and for correlations. DFT simulations at these extreme conditions show good agreement with the experimental data - demonstrating the attention to detail required for dealing with elements with relativistic core states and d-state electrons. The results from shock compression experiments and DFT simulations are presented for liquid xenon to 840 GPa and for liquid krypton to 800 GPa, decidedly increasing the range of known behavior of both gases. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company

  4. Room temperature ferromagnetism and absorption red-shift in nitrogen-doped TiO2 nanoparticles

    International Nuclear Information System (INIS)

    Gómez-Polo, C.; Larumbe, S.; Monge, M.

    2014-01-01

    Highlights: • N-doped TiO 2 anatase nanoparticles were obtained by sol–gel. • The nanoparticle size, controlled by the N doping, determines lattice parameters. • Correlation between room temperature ferromagnetism and absorption red-shift. • Oxygen vacancies reinforce both phenomena. • Metal transition impurities contribute to the room temperature ferromagnetism. - Abstract: In this work, room-temperature ferromagnetism and the red-shift of the optical absorption is analyzed in nitrogen doped TiO 2 semiconductor nanoparticles. The nanoparticles were synthesized by the sol–gel method using urea as the nitrogen source. Titanium Tetraisopropoxide (TTIP) was employed as the alkoxyde precursor and dissolved in ethanol. The as prepared gels were dried and calcined in air at 300 °C. Additionally, post-annealing treatments under vacuum atmosphere were performed to modify the oxygen stoichiometry of the samples. The anatase lattice parameters, analyzed by means of powder X-ray diffractometry, depend on the nanometer grain size of the nanoparticles (increase and decrease, respectively, of the tetragonal a and c lattice parameters with respect to the bulk values). The diffuse reflectance ultraviolet–visible (UV–Vis) absorbance spectra show a clear red-shift as consequence of the nitrogen and the occurrence of intragap energy levels. The samples display ferromagnetic features at room temperature that are reinforced with the nitrogen content and after the post annealings in vacuum. The results indicate a clear correlation between the room temperature ferromagnetism and the shift of the absorbance spectrum. In both phenomena, oxygen vacancies (either induced by the nitrogen doping or by the post vacuum annealings) play a dominant role. However, we conclude the existence of very low concentration of diluted transition metal impurities that determine the room ferromagnetic response (bound magnetic polaron BMP model). The contraction of the c soft axis of the

  5. Room temperature ferromagnetism and absorption red-shift in nitrogen-doped TiO{sub 2} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Gómez-Polo, C., E-mail: gpolo@unavarra.es [Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadia, 31006 Pamplona (Spain); Larumbe, S. [Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadia, 31006 Pamplona (Spain); Monge, M. [Departamento de Química, Universidad de la Rioja, Centro de Investigación en Síntesis Química (CISQ), Complejo Científico Tecnológico, 26006 Logroño (Spain)

    2014-11-05

    Highlights: • N-doped TiO{sub 2} anatase nanoparticles were obtained by sol–gel. • The nanoparticle size, controlled by the N doping, determines lattice parameters. • Correlation between room temperature ferromagnetism and absorption red-shift. • Oxygen vacancies reinforce both phenomena. • Metal transition impurities contribute to the room temperature ferromagnetism. - Abstract: In this work, room-temperature ferromagnetism and the red-shift of the optical absorption is analyzed in nitrogen doped TiO{sub 2} semiconductor nanoparticles. The nanoparticles were synthesized by the sol–gel method using urea as the nitrogen source. Titanium Tetraisopropoxide (TTIP) was employed as the alkoxyde precursor and dissolved in ethanol. The as prepared gels were dried and calcined in air at 300 °C. Additionally, post-annealing treatments under vacuum atmosphere were performed to modify the oxygen stoichiometry of the samples. The anatase lattice parameters, analyzed by means of powder X-ray diffractometry, depend on the nanometer grain size of the nanoparticles (increase and decrease, respectively, of the tetragonal a and c lattice parameters with respect to the bulk values). The diffuse reflectance ultraviolet–visible (UV–Vis) absorbance spectra show a clear red-shift as consequence of the nitrogen and the occurrence of intragap energy levels. The samples display ferromagnetic features at room temperature that are reinforced with the nitrogen content and after the post annealings in vacuum. The results indicate a clear correlation between the room temperature ferromagnetism and the shift of the absorbance spectrum. In both phenomena, oxygen vacancies (either induced by the nitrogen doping or by the post vacuum annealings) play a dominant role. However, we conclude the existence of very low concentration of diluted transition metal impurities that determine the room ferromagnetic response (bound magnetic polaron BMP model). The contraction of the c soft axis

  6. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.

    Science.gov (United States)

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-19

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.

  7. RESEARCH OF FRUIT CONSERVES’ CORROSIVE AGGRESSIVENESS

    Directory of Open Access Journals (Sweden)

    I. Kuznecova

    2017-10-01

    Full Text Available Corrosion of metal canning containers is one of the obstacles in spreading its application for packing of food. Particularly aggressive to the metal container is fruit canned medium, containing organic acids.The basic material for the production of metal canning container is white tinplate. The main advantage of white tinplate is the tin compounds are harmless to human organism. For this reason, a white badge is used widely, usually used for production of canning containers, packaging beverages. Despite the fact that recently often used containers made of aluminum badge (foil, the basic material for manufacturing metal canning containers is steel white tinplate.Now applied for coating paints and varnishes do not provide anti-corrosion protection of inner surface of metal containers during storage. Preserving of canned fruit quality in metal containers is largely defined corrosion resistance of the containers. This is due to the fact that the metal transition to canned fruit in due courses of corrosion processes is lowering the nutritional value and deterioration taste of the product, and while allocation of hydrogen is accompanied by swelling and destruction of metal containers.We have investigated a number of anti-corrosion coatings based on Fe-Cr and Fe-Sn-Ti of their behavior in aggressive mediums canned fruit. For the purpose of modeling such mediums the solutions of most widespread organic acids were used. The research allowed conclude, that in surface solid solutions Fe-Sn-Ti increase the corrosion resistance of carbon steel in aqueous solutions of malic, citric and tartaric acids. This implies that the surface solid solutions’ formation can significantly improve corrosion resistance in aggressive canning mediums.

  8. Infrared reflectivity of the solid solutions LaNi1-xFexO3 (0.00≤x≤1.00)

    International Nuclear Information System (INIS)

    Massa, N.E.; Falcon, H.; Salva, H.; Carbonio, R.E.

    1997-01-01

    We report temperature-dependent far- and midinfrared reflectivity spectra of LaNi (1-x) Fe x O 3 solid solutions that span the passage from LaFeO 3 , a room-temperature antiferromagnetic insulator, to LaNiO 3 , a known metal oxide. Light Ni doping creates defects that induce extra bands assigned to electronic transitions within the insulating gap. An incipient Drude term emerges in the reflectivity spectrum of LaNi 0.39 Fe 0.61 O 3 together with subbands that contribute to the electronic background. At these concentrations the dielectric response shows a picture in which the spectral weigh switches over toward far-infrared frequencies while phonon features develop strong antiresonances near longitudinal-optical modes. Further increment of carriers produces phonon screening and the development of a reflectivity tail that extends beyond 1 eV. We assign extra-non-Drude terms in the 700 endash 4000cm -1 frequency region to transitions due to intrinsic defects. While the increment in reflectivity at far-infrared frequencies is evident for Fe concentrations well above the insulator-metal transition (x∼0.30), the spectral features of a metal oxide, with phonons mostly screened, are found for x=0.23. These metallic spectra show an absorption dip at ∼650cm -1 that is traced to the perovskite symmetric stretching longitudinal mode. Electron-phonon interactions are thus present in solid solutions even when the numbers of effective carriers are those of a metal. This characterization is also supported by the observation of weak reflectivity dips in LaNiO 3 that have a direct correspondence to longitudinal-optical mode frequencies of the insulating phases of our series. We infer that strong electron-phonon interactions play a role in the conductivity of those solid solutions and are likely related to polaron formation and carrier phonon-assisted hopping motion. (Abstract Truncated)

  9. Structural and electronic properties of the V-V compounds isoelectronic to GaN and isostructural to gray arsenic

    Science.gov (United States)

    Yang, Zhao; Han, Dan; Chen, Guohong; Chen, Shiyou

    2018-03-01

    The III-V binary compound semiconductors such as GaN, GaP, InN and InP have extensive applications in various optoelectronic, microwave and power-electronic devices. Using first-principles calculation, we systematically studied the structural and electronic properties of the V-V binary compounds (BiN, BiP, SbN and SbP) that are isoelectronic to GaN, GaP, InN and InP if Bi and Sb are in the +3 valence state. Interestingly, we found that the ground-state structures of BiP, SbN and SbP have the R-3m symmetry and are isostructural to the layered structure of gray arsenic, whereas BiN prefers a different ground-state structure with the C2 symmetry. Electronic structure calculations showed that the bulk BiN is a narrow bandgap semiconductor for its bandgap is about 0.2 eV. In contrast, BiP, SbN and SbP are metallic. The layered ground-state structure of the V-V binary compounds motivates us to study the electronic properties of their few-layer structures. As the structure becomes monolayer, their bandgaps increase significantly and are all in the range from about 1 eV to 1.7 eV, which are comparative to the bandgap of the monolayer gray arsenic. The monolayer BiP, SbN and SbP have indirect bandgaps, and they show a semiconductor-metal transition as the number of layers increase. Interestingly, the monolayer BiP has the largest splitting (350 meV) of the CBM valley, and thus may have potential application in novel spintronics and valleytronics devices.

  10. Decoupling of magnetism and electric transport in single-crystal (Sr1‑x A x )2IrO4 (A  =  Ca or Ba)

    Science.gov (United States)

    Zhao, H. D.; Terzic, J.; Zheng, H.; Ni, Y. F.; Zhang, Y.; Ye, Feng; Schlottmann, P.; Cao, G.

    2018-06-01

    We report a systematical structural, transport and magnetic study of Ca or Ba doped Sr2IrO4 single crystals. Isoelectronically substituting Ca2+ (up to 15%) or Ba2+ (up to 4%) ion for the Sr2+ ion provides no additional charge carriers but effectively changes the lattice parameters in Sr2IrO4. In particular, 15% Ca doping considerably reduces the c-axis and the unit cell by nearly 0.45% and 1.00%, respectively. These significant, anisotropic compressions in the lattice parameters conspicuously cause no change in the Néel temperature which remains at 240 K, but drastically reduces the electrical resistivity by up to five orders of magnitude or even precipitates a sharp insulator-to-metal transition at lower temperatures, i.e. the vanishing insulating state accompanies an unchanged Néel temperature in (Sr1‑x A x )2IrO4. This observation brings to light an intriguing difference between chemical pressure and applied pressure, the latter of which does suppress the long-range magnetic order in Sr2IrO4. This difference reveals the importance of the Ir1–O2–Ir1 bond angle and homogenous volume compression in determining the magnetic ground state. All results, along with a comparison drawn with results of Tb and La doped Sr2IrO4, underscore that the magnetic transition plays a nonessential role in the formation of the charge gap in the spin–orbit-tuned iridate.

  11. Magneto-electric properties and magnetic entropy change in perovskite La{sub 0.7}Sr{sub 0.3}Mn{sub 1−x}Ti{sub x}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Bau, Le Viet, E-mail: levietbau@hdu.edu.vn; An, Nguyen Manh

    2016-12-15

    The ceramic samples of La{sub 0.7}Sr{sub 0.3}Mn{sub 1−x}Ti{sub x}O{sub 3}(x=0; 0.05; 0.1; 0.2 and 0.3) were synthesized by the conventional solid state reaction method. Their electric, magnetic and magnetocaloric properties have been investigated. The transition temperature declines and a significant influence on the width of the ferro-paramagnetic phase transition is observed as increasing Ti concentration. Moreover, the sign of spin-glass is expected to exist in the high concentration samples. For fully replacing Ti{sup 4+} for Mn{sup 4+}, the canted spin state is formed. The substitution Ti for Mn increases resistivity quickly and the insulating–metallic transition temperature shifts toward lower temperature. For x>0.1 samples, the insulating state is observed even in ferromagnetic phase. The substitution Ti shifts the CME to room temperature while almost persists the value of entropy change. Although the maximum value of CME reduces slightly, the temperature range happening MCE is expended and then improves the relative cooling power. These properties could be explained in term of DE interaction and phase separation phenomenon. - Highlights: • Electro-magnetic properties and CME of La{sub 0.7}Sr{sub 0.3}Mn{sub 1-x}Ti{sub x}O{sub 3} have been investigated. • T{sub C} declines and the width of the F-M phase transition is observed as increasing Ti concentration. • For fully replacing Ti{sup 4+} for Mn{sup 4+}, the canted spin state is formed. • The substitution Ti for Mn increases resistivity quickly and T{sub P} shifts toward lower temperature. • The substitution Ti shifts CME to 300 K while almost persists the value of entropy change. • Relative cooling power (RCP) increases with substitution 5% Ti for Mn.

  12. Variation of crystallinity and stoichiometry in films of gallium oxide, gallium nitride and barium zirconate prepared by means of PLD; Variation von Kristallinitaet und Stoechiometrie in mittels PLD hergestellten Schichten aus Galliumoxid, Galliumnitrid und Bariumzirkonat

    Energy Technology Data Exchange (ETDEWEB)

    Brendt, Jochen

    2011-08-05

    Pulsed Laser Deposition (PLD) is an ablation technique for thin film preparation of many materials. The film properties can be well controlled by the process parameters. Therefore, in many cases a given material can be deposited with different properties by changing one or more process parameters. In this thesis thin films of gallium oxide, gallium nitride and barium zirconate were deposited with a large variation in structure and stoichiometry by means of Pulsed Laser Deposition. The characterization of the film crystallinity, phase purity and short range structural order was completed by means of X-ray diffraction and X-ray absorption spectroscopy. The stoichiometry was investigated using electron probe microanalysis. For analyzing the correlation between the structure and stoichiometry with the optical and electrical properties, optical absorption and electrical conductivity measurements were carried out. The investigation of all three material systems showed that very unique properties can be realized when combining an amorphous structure and a non-stoichiometric composition. For example, in amorphous and oxygen deficient gallium oxide an insulator-metal-transition can be induced by partial crystallization of the as prepared phase accomplished by annealing at about 400 C in argon atmosphere (as shown in literature). Furthermore, amorphous and highly non-stoichiometric barium zirconate has the ability to split water molecules to hydrogen and oxygen at room temperature. A detailed analysis of both phenomena has been performed by means of photoemission and transmission electron microscopy in the case of gallium oxide and via X-ray absorption spectroscopy and gas chromatography in the case of barium zirconate.

  13. Tuning the electrical and optical properties of Gd{sub 1-x}Ca{sub x}BaCo{sub 2}O{sub 5+δ} (x = 0–0.5) using solar energy

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Yi; Zhang, Rong; Wei, Ling [State Key Laboratory of Materials-Orient Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009 (China); Lu, Chunhua, E-mail: chhlu@njtech.edu.cn [State Key Laboratory of Materials-Orient Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009 (China); Fang, Zhenggang; Ni, Yaru [State Key Laboratory of Materials-Orient Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009 (China); Xu, Zhongzi, E-mail: zzxu@njtech.edu.cn [State Key Laboratory of Materials-Orient Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009 (China); Tao, Shunyan [Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 200050 (China)

    2016-06-15

    This study reveals that the use of a Ca dopant can increase the solar absorption of GdBaCo{sub 2}O{sub 5+δ}, with an optimal composition of Gd{sub 0.8}Ca{sub 0.2}BaCo{sub 2}O{sub 5} achieving 85% solar absorptance. Electrical conductivity measurements revealed that this composition allows for faster insulator-metal transition and higher conductivity, with the observed variation in conductivity with 0.8 W/cm{sup 2} of solar illumination explained in terms of a first-order spin-state transition. Thermal radiation imaging confirmed that regions of different radiative temperature are related to a change in free carriers that promote scattering, and therefore, cause an increase in infrared reflection. This rapid electrical conductivity transition and the low infrared radiation properties at high temperatures strongly suggest that Gd{sub 0.8}Ca{sub 0.2}BaCo{sub 2}O{sub 5} could be used in a variety of potential fields, such as high-temperature thermosensitive or thermal storage materials. - Highlights: • The solar absorption properties of GdBaCo{sub 2}O{sub 5+δ} can be improved by Ca doping. • Gd{sub 0.8}Ca{sub 0.2}BaCo{sub 2}O{sub 5} shows ultrafast conductivity transition induced by solar energy. • Gd{sub 0.8}Ca{sub 0.2}BaCo{sub 2}O{sub 5} exhibits low thermal radiative properties at high temperature.

  14. [Ag67(SPhMe2)32(PPh3)8]3+: Synthesis, Total Structure, and Optical Properties of a Large Box-Shaped Silver Nanocluster

    KAUST Repository

    Alhilaly, Mohammad J.; Bootharaju, Megalamane Siddaramappa; Joshi, Chakra Prasad; Besong, Tabot M.D.; Emwas, Abdul-Hamid M.; Juarez-Mosqueda, Rosalba; Kaappa, Sami; Malola, Sami; Adil, Karim; Shkurenko, Aleksander; Hakkinen, Hannu; Eddaoudi, Mohamed; Bakr, Osman

    2016-01-01

    Engineering the surface ligands of metal nanoparticles is critical in designing unique arrangements of metal atoms. Here, we report the synthesis and total structure determination of a large box-shaped Ag-67 nanocluster (NC) protected by a mixed shell of thiolate (2,4-dimethylbenzenethiolate, SPhMe2) and phosphine (triphenylphosphine, PPh3) ligands. Single crystal X-ray diffraction (SCXRD) and electrospray ionization mass spectrometry (ESI-MS) revealed the cluster formula to be [Ag-67(SPhMe2)(32)(PPh3)(8)](3+). The crystal structure shows an Ag-23 metal core covered by a layer of Ag44S32P8 arranged in the shape of a box. The Ag-13, core was formed through an unprecedented centered cuboctahedron, i.e., Ag-13, unlike the common centered Ag-13 icosahedron geometry. Two types of ligand motifs, eight AgS3P and eight bridging thiols, were found to stabilize the whole cluster. The optical spectrum of this NC displayed highly structured multiple absorption peaks. The electronic structure and optical spectrum of Ag-67 were computed using time-dependent density functional theory (TDDFT) for both the full cluster [Ag-67(SPhMe2)(32)(PPh3)(8)](3+) and a reduced model [Ag-67(SH)(32)(PH3)(8)](3+). The lowest metal-to-metal transitions in the range 500-800 nm could be explained by considering the reduced model that shows almost identical electronic states to 32 free electrons in a jellium box. The successful synthesis of the large box-shaped Ag-67 NC facilitated by the combined use of phosphine and thiol paves the way for synthesizing other metal clusters with unprecedented shapes by judicious choice of thiols and phosphines.

  15. Excitonic metal-insulator phase transition of the Mott type in compressed calcium

    Science.gov (United States)

    Voronkova, T. O.; Sarry, A. M.; Sarry, M. F.; Skidan, S. G.

    2017-05-01

    It has been experimentally found that, under the static compression of a calcium crystal at room temperature, it undergoes a series of structural phase transitions: face-centered cubic lattice → body-centered cubic lattice → simple cubic lattice. It has been decided to investigate precisely the simple cubic lattice (because it is an alternative lattice) with the aim of elucidating the possibility of the existence of other (nonstructural) phase transitions in it by using for this purpose the Hubbard model for electrons with half-filled ns-bands and preliminarily transforming the initial electronic system into an electron-hole system by means of the known Shiba operators (applicable only to alternative lattices). This transformation leads to the fact that, in the new system of fermions, instead of the former repulsion, there is an attraction between electrons and holes. Elementary excitations of this new system are bound boson pairs—excitons. This system of fermions has been quantitatively analyzed by jointly using the equation-of-motion method and the direct algebraic method. The numerical integration of the analytically exact transcendental equations derived from the first principles for alternative (one-, two-, and three-dimensional) lattices has demonstrated that, in systems of two-species (electrons + hole) fermions, temperature-induced metal-insulator phase transitions of the Mott type are actually possible. Moreover, all these crystals are in fact excitonic insulators. This conclusion is in complete agreement with the analytically exact calculations of the ground state of a one-dimensional crystal (with half-filled bands), which were performed by Lieb and Wu with the aim to find out the Mott insulator-metal transition of another type.

  16. Metal induced crystallization of silicon germanium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Gjukic, M.

    2007-05-15

    In the framework of this thesis the applicability of the aluminium-induced layer exchange on binary silicon germanium alloys was studied. It is here for the first time shown that polycrstalline silicon-germanium layers can be fabricated over the whole composition range by the aluminium-induced layer exchange. The experimental results prove thet the resulting material exhibits a polycrystalline character with typocal grain sizes of 10-100 {mu}m. Raman measurements confirm that the structural properties of the resulting layers are because of the large crystallites more comparable with monocrystalline than with nano- or microcrystalline silicon-germanium. The alloy ratio of the polycrystalline layer correspondes to the chemical composition of the amorphous starting layer. The polycrystalline silicon-germanium layers possess in the range of the interband transitions a reflection spectrum, as it is otherwise only known from monocrystalline reference layers. The improvement of the absorption in the photovoltaically relevant spectral range aimed by the application of silicon-germanium could be also proved by absorption measurments. Strongly correlated with the structural properties of the polycrystalline layers and the electronic band structure resulting from this are beside the optical properties also the electrical properties of the material, especially the charge-carrier mobility and the doping concentration. For binary silicon-germanium layers the hole concentration of about 2 x 10{sup 18} cm{sup -3} for pure silicon increrases to about 5 x 10{sup 20} cm{sub -3} for pure germanium. Temperature-resolved measurements were applied in order to detect doping levels respectively semiconductor-metal transitions. In the last part of the thesis the hydrogen passivation of polycrystalline thin silicon-germanium layers, which were fabricated by means of aluminium-induced layer exchange, is treated.

  17. Transmission of reactive pulsed laser deposited VO{sub 2} films in the THz domain

    Energy Technology Data Exchange (ETDEWEB)

    Émond, Nicolas; Hendaoui, Ali; Ibrahim, Akram; Al-Naib, Ibraheem; Ozaki, Tsuneyuki; Chaker, Mohamed, E-mail: chaker@emt.inrs.ca

    2016-08-30

    Highlights: • Synthesis of vanadium dioxide (VO{sub 2}) thin films as a function of oxygen pressure (2–25 mTorr) using Reactive Pulsed Laser Deposition (RPLD). • Characterization of RPLD-grown VO{sub 2} thin films in the THz frequency range. • THz switches and/or sensors require VO{sub 2} films deposited at low oxygen pressure (i.e. low transition temperature, large amplitude contrast of THz transmission, narrow hysteresis width). • THz optical memory applications require VO{sub 2} films deposited at high oxygen pressure (broad hysteresis width). - Abstract: This work reports on the characteristics of the insulator-to-metal transition (IMT) of reactive pulsed laser deposited vanadium dioxide (VO{sub 2}) films in the terahertz (THz) frequency range, namely the transition temperature T{sub IMT}, the amplitude contrast of the THz transmission over the IMT ΔA, the transition sharpness ΔT and the hysteresis width ΔH. XRD analysis shows the sole formation of VO{sub 2} monoclinic structure with an enhancement of (011) preferential orientation when varying the O{sub 2} pressure (P{sub O2}) during the deposition process from 2 to 25 mTorr. THz transmission measurements as a function of temperature reveal that VO{sub 2} films obtained at low P{sub O2} exhibit low T{sub IMT}, large ΔA, and narrow ΔH. Increasing P{sub O2} results in VO{sub 2} films with higher T{sub IMT}, smaller ΔA, broader ΔH and asymmetric hysteresis loop. The good control of the VO{sub 2} IMT features in the THz domain could be further exploited for the development of advanced smart devices, such as ultrafast switches, modulators, memories and sensors.

  18. Thickness dependent structural, magnetic and magneto-transport properties of epitaxial Nd{sub 0.50}Sr{sub 0.50}MnO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Pawan, E-mail: p.kumar@krmangalam.edu.in [School of Basic and Applied Sciences, K. R. Mangalam University, Sohna Road, Gurgaon, Haryana 122103 (India); Singh, Hari Krishna, E-mail: hks65@nplindia.org [CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India)

    2016-05-06

    We report the thickness-dependent structural, magnetic and magneto-transport properties in epitaxial Nd{sub 0.50}Sr{sub 0.50}MnO{sub 3} thin films (10 to 300nm) prepared by DC magnetron sputtering technique on single crystalline (001) oriented substrate LaAlO{sub 3}. X-ray diffraction pattern reveals the epitaxial growth of all the films and the out-of-plane lattice parameter of films were found to increase with thickness. As thickness of the film increases the paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature (T{sub C}), charge ordered transition temperature (T{sub CO}) and magnetic moment were found to increase with a strong bifurcation in ZFC-FC magnetization. The asymmetry in the coercivity seen in field dependent magnetization loops (M-H loops) suggests the presence of exchange bias (EB) effect. While temperature dependent resistivity of films show the semiconducting nature for thickness 10-200nm in temperature range from 5-300K, the film of thickness 300nm shows the insulator to metal transition with transition temperature (T{sub IM}) at 175K. Temperature dependent low field magnetoresistance (LFMR) measured at 4kOe found to decrease with thickness and for high field magnetoresistance (HFMR) at 40kOe and 60kOe also show similar dependence and a crossover at intermediate temperature range in the magnitude of MR between 10nm and 200nm films at constant field. Colossal increase in magnetoresistance observed for 10nm film at low temperature.

  19. Optimization of mobile analysis of radionuclides

    International Nuclear Information System (INIS)

    Labaska, M.

    2016-01-01

    This thesis is focused on optimization of separation and determination of radionuclides which can be used in mobile or field analysis. Mentioned methods are part of procedures and methods of mobile radiometric laboratory which is being developed for Slovak Armed forces. The main principle of these methods is the separation of analytes using high performance liquid chromatography using both reverse phase liquid chromatography and ion exchange chromatography. Chromatography columns such as Dionex IonPack"("R") CS5A, Dionex IonPack"("R") CS3 and Hypersil"("R") BDS C18 have been used. For detection of stabile nuclides, conductivity detection and UV/VIS detection have been employed. Separation of alkali and alkali earth metals. transition metals and lanthanides has been optimized. Combination of chromatographic separation and flow scintillation analysis has been also studied. Radioactive isotopes "5"5Fe, "2"1"0Pb, "6"0Co, "8"5Sr and "1"3"4Cs have been chosen as analytes for nuclear detection techniques. Utilization of well-type and planar NaI(Tl) detector has been investigated together with cloud point extraction. For micelle mediated extraction two possible ligands have been studied - 8-hydroxyquinoline and ammonium pyrolidinedithiocarbamate. Recoveries of cloud point extraction were in range between 80 to 90%. This thesis is also focused on possible application of liquid scintillation analysis with cloud point extraction of analytes. Radioactive standard containing "5"5Fe, "2"1"0Pb, "6"0Co, "8"5Sr and "1"3"4Cs has been separated using liquid chromatography and fractions of individual isotopes have been collected, extracted using cloud point extraction and measured using liquid scintillation analysis. Finally, cloud point extraction coupled with ICP-MS have been studied. (author)

  20. Optical switching and photoluminescence in erbium-implanted vanadium dioxide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Herianto, E-mail: mail@heriantolim.com; Stavrias, Nikolas; Johnson, Brett C.; McCallum, Jeffrey C. [School of Physics, University of Melbourne, Parkville, Victoria 3010 (Australia); Marvel, Robert E.; Haglund, Richard F. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37240 (United States)

    2014-03-07

    Vanadium dioxide (VO{sub 2}) is under intensive consideration for optical switching due to its reversible phase transition, which features a drastic and rapid shift in infrared reflectivity. Classified as an insulator–to–metal transition, the phase transition in VO{sub 2} can be induced thermally, electrically, and optically. When induced optically, the transition can occur on sub-picosecond time scales. It is interesting to dope VO{sub 2} with erbium ions (Er{sup 3+}) and observe their combined properties. The first excited-state luminescence of Er{sup 3+} lies within the wavelength window of minimal transmission-loss in silicon and has been widely utilized for signal amplification and generation in silicon photonics. The incorporation of Er{sup 3+} into VO{sub 2} could therefore result in a novel photonic material capable of simultaneous optical switching and amplification. In this work, we investigate the optical switching and photoluminescence in Er-implanted VO{sub 2} thin films. Thermally driven optical switching is demonstrated in the Er-implanted VO{sub 2} by infrared reflectometry. Photoluminescence is observed in the thin films annealed at ∼800 °C or above. In addition, Raman spectroscopy and a statistical analysis of switching hysteresis are carried out to assess the effects of the ion implantation on the VO{sub 2} thin films. We conclude that Er-implanted VO{sub 2} can function as an optical switch and amplifier, but with reduced switching quality compared to pure VO{sub 2}.

  1. Electronic structure of metal clusters

    International Nuclear Information System (INIS)

    Wertheim, G.K.

    1989-01-01

    Photoemission spectra of valence electrons in metal clusters, together with threshold ionization potential measurements, provide a coherent picture of the development of the electronic structure from the isolated atom to the large metallic cluster. An insulator-metal transition occurs at an intermediate cluster size, which serves to define the boundary between small and large clusters. Although the outer electrons may be delocalized over the entire cluster, a small cluster remains insulating until the density of states near the Fermi level exceeds 1/kT. In large clusters, with increasing cluster size, the band structure approaches that of the bulk metal. However, the bands remain significantly narrowed even in a 1000-atom cluster, giving an indication of the importance of long-range order. The core-electron binding-energy shifts of supported metal clusters depend on changes in the band structure in the initial state, as well as on various final-state effects, including changes in core hole screening and the coulomb energy of the final-state charge. For cluster supported on amorphous carbon, this macroscopic coulomb shift is often dominant, as evidenced by the parallel shifts of the core-electron binding energy and the Fermi edge. Auger data confirm that final-state effects dominate in cluster of Sn and some other metals. Surface atom core-level shifts provide a valuable guide to the contributions of initial-state changes in band structure to cluster core-electron binding energy shifts, especially for Au and Pt. The available data indicate that the shift observed in supported, metallic clusters arise largely from the charge left on the cluster by photoemission. As the metal-insulator transition is approached from above, metallic screening is suppressed and the shift is determined by the local environment. (orig.)

  2. Electrically driven hybrid photonic metamaterials for multifunctional control

    Science.gov (United States)

    Kang, Lei; Liu, Liu; Campbell, Sawyer D.; Yue, Taiwei; Ren, Qiang; Mayer, Theresa S.; Werner, Douglas H.

    2017-08-01

    The unique light-matter interaction in metamaterials, a type of artificial medium in which the geometrical features of subunits dominate their optical responses, have been utilized to achieve exotic material properties that are rare or nonexistent in natural materials. Furthermore, to extend their behaviors, active materials have been introduced into metamaterial systems to advance tunability, switchability and nonlinearity. Nevertheless, practical examples of versatile photonic metamaterials remain exceedingly rare for two main reasons. On the one hand, in sharp contrast to the broad material options available at lower frequencies, it is less common to find active media in the optical regime that can provide pronounced dielectric property changes under external stimuli, such as electric and magnetic fields. Vanadium dioxide (VO2), offering a large refractive index variation over a broad frequency range due to its near room temperature insulator-to-metal transition (IMT), has been favored in recent studies on tunable metamaterials. On the other hand, it turns out that regulating responses of hybrid metamaterials to external forces in an integrated manner is not a straightforward task. Recently, metamaterial-enabled devices (i.e., metadevices) with `self-sufficient' or `self-contained' electrical and optical properties have enabled complex functionalities. Here, we present a design methodology along with the associated experimental validation of a VO2 thin film integrated optical metamaterial absorber as a hybrid photonic platform for electrically driven multifunctional control, including reflectance switching, a rewritable memory process and manageable localized camouflage. The nanoengineered topologically continuous metal structure simultaneously supports the optical resonance and electrical functionality that actuates the phase transition in VO2 through the process of Joule heating. This work provides a universal approach to creating self-sufficient and highly

  3. Semi-metallic, strong conductive polymer microfiber, method and fast response rate actuators and heating textiles

    KAUST Repository

    Zhou, Jian

    2016-06-09

    A method comprising: providing at least one first composition comprising at least one conjugated polymer and at least one solvent, wet spinning the at least one first composition to form at least one first fiber material, hot-drawing the at least one fiber to form at least one second fiber material. In lead embodiments, high-performance poly(3,4-ethylenedioxy- thiophene)/poly(styrenesulfonate) (PEDOT/PSS) conjugated polymer microfibers were fabricated via wet- spinning followed by hot-drawing. In these lead embodiments, due to the combined effects of the vertical hot-drawing process and doping/de-doping the microfibers with ethylene glycol (EG), a record electrical conductivity of 2804 S · cm-1 was achieved. This is believed to be a six-fold improvement over the best previously reported value for PEDOT/PSS fibers (467 S · cm-1) and a twofold improvement over the best values for conductive polymer films treated by EG de-doping (1418 S · cm-1). Moreover, these lead, highly conductive fibers experience a semiconductor-metal transition at 313 K. They also have superior mechanical properties with a Young\\'s modulus up to 8.3 GPa, a tensile strength reaching 409.8 MPa and a large elongation before failure (21%). The most conductive fiber also demonstrates an extraordinary electrical performance during stretching/unstretching: the conductivity increased by 25% before the fiber rupture point with a maximum strain up to 21%. Simple fabrication of the semi-metallic, strong and stretchable wet-spun PEDOT/PSS microfibers can make them available for conductive smart electronics. A dramatic improvement in electrical conductivity is needed to make conductive polymer fibers viable candidates in applications such as flexible electrodes, conductive textiles, and fast-response sensors and actuators.

  4. Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

    Directory of Open Access Journals (Sweden)

    Manoj K. Srivastava

    2013-05-01

    Full Text Available Highly oriented polycrystalline Sm0.55Sr0.45MnO3 thin films (thickness ∼100 nm deposited on LaAlO3 (LAO, (001, SrTiO3 (STO, (001 and (La0.18Sr0.82 (Al0.59Ta0.41O3 (LSAT, (001 single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The out of plane lattice parameter (OPLP of the film on LAO is slightly larger than that of the corresponding bulk. In contrast, the OPLP of the films on STO and LSAT are slightly smaller than the corresponding bulk value. This suggests that the film on LAO is under compressive strain while LSAT and STO are under tensile strain. The films on LAO and LSAT show simultaneous paramagnetic-ferromagnetic (PM–FM and insulator-metal transition (IMT temperature at TC/TIM ∼ 165 K and 130 K, respectively. The PM–FM and IM transition occur at TC ∼ 120 K and TIM ∼ 105 K, respectively in the film on STO substrate. At T 99 % over a very wide temperature range of ∼40 K centred on TC/TIM. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signature of metamagnetic transitions. The observed results have been explained in terms of the variation of the relative fractions of the coexisting FM and AFM–CO phases as a function of the substrate induced strain and oxygen vacancy induced quenched disorder.

  5. Effects of strain on the magnetic and transport properties of the epitaxial La0.5Ca0.5MnO3 thin films

    Science.gov (United States)

    Zarifi, M.; Kameli, P.; Ehsani, M. H.; Ahmadvand, H.; Salamati, H.

    2016-12-01

    The epitaxial strain can considerably modify the physical properties of thin films compared to the bulk. This paper reports the effects of substrate-induced strain on La0.5Ca0.5MnO3 (LCMO) thin films, grown on (100) SrTiO3 (STO) and LaAlO3 (LAO) substrates by pulsed laser deposition technique. Transport and magnetic properties were found to be strongly dependent on strain type. It is also shown that compressive (tensile) strain leads to the increase (decrease) in the magnetization of the films. Moreover, it was observed that all LCMO films deposited on both LAO and STO substrates behave as an insulator, but LCMO/LAO thin films with compressive strain have lower resistivity than LCMO/STO thin films with tensile strain. Applying magnetic field to LCMO/STO thin films with thickness of 25 and 50 nm leads to very small change in the resistivity, while the effects of magnetic field on the sample with thickness of 125 nm leads to an insulator-metal transition. For LCMO/LAO thin films, the magnetic field has a strong impact on the resistivity of samples. The results show that the magnetoresistance (MR) is enhanced by increasing film thickness for LCMO/LAO samples, due to the relatively stronger phase separation. For LCMO/STO thin films MR is drastically decreased by reduction of film thickness, which is attributed to the enhancement of the charge-orbital order (CO-O) accompanying the complex spin order (the so-called CE type). The changes of the antiferromagnetic structure from the CE to C type and the enhancement of the CE type could be attributed to the in-plane compressive and tensile strain, respectively.

  6. Hole doping and pressure effects on the II-II-V-based diluted magnetic semiconductor (Ba1-xKx)(Zn1-yMny)2As2

    International Nuclear Information System (INIS)

    Sun, F.; Zhao, G. Q.; Escanhoela, C. A. Jr.

    2017-01-01

    We investigate doping- and pressure-induced changes in the electronic state of Mn 3d and As 4p orbitals in II-II-V based diluted magnetic semiconductor (Ba_1_-_x,K_x)(Zn_1_-_y,Mn_y)_2As_2 to shed light into the mechanism of indirect exchange interactions leading to high ferromagnetic ordering temperature (T_c = 230 K in optimally doped samples). A suite of x-ray spectroscopy experiments (emission, absorption and dichroism) show that the emergence, and further enhancement of ferromagnetic interactions with increased hole doping into the As 4p band is accompanied by a decrease in local 3d spin density at Mn sites. This is a result of increasing Mn 3d - As 4p hybridization with hole doping which enhances indirect exchange interactions between Mn dopants and gives rise to induced magnetic polarization in As 4p states. On the contrary, application of pressure suppresses exchange interactions. While Mn Kβ emission spectra show a weak response of 3d state to pressure, clear As 4p band broadening (hole delocalization) is observed under pressure ultimately leading to loss of ferromagnetism concomitant with a semiconductor to metal transition. The pressure response of As 4p and Mn 3d states is intimately connected with the evolution of the As-As interlayer distance and the geometry of the MnAs_4 tetrahedral units, which we probed with X-ray diffraction. Our results indicate that hole doping increases the degree of covalency between the anion (As) p states and cation (Mn) d states in the MnA_s_4 tetrahedron, a crucial ingredient to promote indirect exchange interactions between Mn dopants and high T_c ferromagnetism. As a result, the instability of ferromagnetism and semiconducting state against pressure is mainly dictated by delocalization of anion p states.

  7. Magnetic and electrical studies on La{sub 0.4}Sm{sub 0.1}Ca{sub 0.5}MnO{sub 3} charge ordered manganite

    Energy Technology Data Exchange (ETDEWEB)

    Krichene, A., E-mail: akramkri@hotmail.fr [Laboratoire de Physique des Matériaux, Faculté des Sciences de Sfax, Université de Sfax, B. P. 1171, 3000 Sfax (Tunisia); Solanki, P.S. [Department of Physics, Saurashtra University, Rajkot 360005 (India); Venkateshwarlu, D. [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017 (India); Rayaprol, S. [UGC-DAE Consortium for Scientific Research, Mumbai Centre, B.A.R.C. Campus, Mumbai 400085 (India); Ganesan, V. [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017 (India); Boujelben, W. [Laboratoire de Physique des Matériaux, Faculté des Sciences de Sfax, Université de Sfax, B. P. 1171, 3000 Sfax (Tunisia); Kuberkar, D.G. [Department of Physics, Saurashtra University, Rajkot 360005 (India)

    2015-05-01

    We have reported in this work the effect of the partial substitution of lanthanum by samarium on the structural, electrical and magnetic properties of La{sub 0.5}Ca{sub 0.5}MnO{sub 3}. The magnetic study indicated that substitution promotes charge ordering and weakens ferromagnetism. Below T{sub C}=123 K, the compound La{sub 0.4}Sm{sub 0.1}Ca{sub 0.5}MnO{sub 3} is a mixture of ferromagnetic and charge ordered antiferromagnetic domains. Between T{sub C} and T{sub CO}=215 K, the structure is paramagnetic with the presence of antiferromagnetic domains. The fractions of the coexisting magnetic phases are highly dependent on the applied magnetic field value. Resistivity measurements reveal the presence of an insulating-metal transition at T{sub ρ}=123 K. The equality between T{sub C} and T{sub ρ} indicates the presence of a correlation between magnetization and resistivity. For only 1 T applied field, we have reported a colossal value of magnetoresistance reaching 73% around T{sub C}. The origin of this high value is attributed to phase separation phenomenon. - Highlights: • Sm doping enhances charge ordering and weakens ferromagnetism in La{sub 0.5}Ca{sub 0.5}MnO{sub 3.} • Colossal magnetoresistance (73%) is recorded at 123 K for only 1 T applied field. • Phase separation is responsible for the magnetic and the magnetoresistive behavior.

  8. Charge transfer in gold--alkali-metal systems

    International Nuclear Information System (INIS)

    Watson, R.E.; Weinert, M.

    1994-01-01

    Based on conventional electronegativity arguments, gold--alkali-metal compounds are expected to be among the most ''ionic'' of metallic compounds. The concepts of ionicity and charge transfer are difficult to quantify. However, the changes in bonding in the 50/50 Au--alkali-metal systems between the elemental metals and the compounds are so severe that observations can readily be made concerning their character. The results, as obtained from self-consistent electronic-structure calculations, lead to the apparently odd observation that the electron density at the alkali-metal sites in the compound increases significantly and this involves high l componennts in the charge density. This increase, however, can be attributed to Au-like orbitals spatially overlapping the alkali-metal sites. In a chemical sense, it is reasonable to consider the alkali-metal transferring charge to these Au orbitals. While normally the difference in heats of formation between muffin-tin and full-potential calculations for transition-metal--transition-metal and transition-metal--main-group (e.g., Al) compounds having high site symmetry are small, for the gold--alkali-metal systems, the changes in bonding in the compounds cause differences of ∼0.5 eV/atom between the two classes of potential. Any serious estimate of the electronic structure in these systems must account for these aspherical bonding charges. The origin of the semiconducting behavior of the heavy-alkali-metal Au compounds is shown to arise from a combination of the Au-Au separations and the ionic character of the compounds; the light-alkali-metal Au compounds, with their smaller Au-Au separations, do not have a semiconducting gap. Core-level shifts and isomer shifts are also briefly discussed

  9. [Ag67(SPhMe2)32(PPh3)8]3+: Synthesis, Total Structure, and Optical Properties of a Large Box-Shaped Silver Nanocluster

    KAUST Repository

    Alhilaly, Mohammad J.

    2016-10-13

    Engineering the surface ligands of metal nanoparticles is critical in designing unique arrangements of metal atoms. Here, we report the synthesis and total structure determination of a large box-shaped Ag-67 nanocluster (NC) protected by a mixed shell of thiolate (2,4-dimethylbenzenethiolate, SPhMe2) and phosphine (triphenylphosphine, PPh3) ligands. Single crystal X-ray diffraction (SCXRD) and electrospray ionization mass spectrometry (ESI-MS) revealed the cluster formula to be [Ag-67(SPhMe2)(32)(PPh3)(8)](3+). The crystal structure shows an Ag-23 metal core covered by a layer of Ag44S32P8 arranged in the shape of a box. The Ag-13, core was formed through an unprecedented centered cuboctahedron, i.e., Ag-13, unlike the common centered Ag-13 icosahedron geometry. Two types of ligand motifs, eight AgS3P and eight bridging thiols, were found to stabilize the whole cluster. The optical spectrum of this NC displayed highly structured multiple absorption peaks. The electronic structure and optical spectrum of Ag-67 were computed using time-dependent density functional theory (TDDFT) for both the full cluster [Ag-67(SPhMe2)(32)(PPh3)(8)](3+) and a reduced model [Ag-67(SH)(32)(PH3)(8)](3+). The lowest metal-to-metal transitions in the range 500-800 nm could be explained by considering the reduced model that shows almost identical electronic states to 32 free electrons in a jellium box. The successful synthesis of the large box-shaped Ag-67 NC facilitated by the combined use of phosphine and thiol paves the way for synthesizing other metal clusters with unprecedented shapes by judicious choice of thiols and phosphines.

  10. Anomalous Hall effect

    Science.gov (United States)

    Nagaosa, Naoto; Sinova, Jairo; Onoda, Shigeki; MacDonald, A. H.; Ong, N. P.

    2010-04-01

    The anomalous Hall effect (AHE) occurs in solids with broken time-reversal symmetry, typically in a ferromagnetic phase, as a consequence of spin-orbit coupling. Experimental and theoretical studies of the AHE are reviewed, focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical works, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of the Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors have established systematic trends. These two developments, in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of the Berry-phase curvatures and it is therefore an intrinsic quantum-mechanical property of a perfect crystal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. The full modern semiclassical treatment of the AHE is reviewed which incorporates an anomalous contribution to wave-packet group velocity due to momentum-space Berry curvatures and correctly combines the roles of intrinsic and extrinsic (skew-scattering and side-jump) scattering-related mechanisms. In addition, more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms are reviewed, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Building on results from recent experiment and theory, a

  11. Eight joint BER II and BESSY II users meeting. Abstracts

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2016-07-01

    The following topics were dealt with: Accelerator operation and projecs, photon science and instrumentation at BESSY II, status of energy materials in-situ Lab at BESSY II, high resolution spectrometer PEAXIS at BESSY II, sample environment at BESSY II, molecular control mechanisms in the Brr2 RNA helicase for efficient and regulated splicing, the Li conversion reaction of 4CoFe{sub 2}O{sub 4} nanoparticles, buried interfaces in lithium ion batteries probed with HAXPES, ARPES studies of the STO(001) 2DEG, all-in/all-out magnetic order in rare earth iridates, oxygen reduction reaction on graphene in Li-air batteries, electronic order in high-T{sub c} superconductors, in-siu observation of novel switching phenomena in highly porous metal-organic frameworks, photoinduced demagnetization and insulator-to-metal transition in ferromagnetic insulating BaFeO{sub 3} thin films, ARPES measurement of the ferroelectric bulk Rashba system GeTe, bisphenol A on Cu(111) and Ag(111), reverse water-gas shift or Sabathier methanation on N(110), structural studies of molecular machines, multi-MHz time-of-flight electronic band-structure imaging of graphene on Ir(111), diffusion pathways in ion conductors, ground-state potential energy surfaces around selected atoms from resonant inelastic X-ray scattering, solar energy in an emerging country, in-situ neutron analysis of electrode materials for electrochemical energy storage, structure and transport properties in thermoelectric skutterudites, investigation of the interphase formation on solid lithium-ion conductors by neutron reflectometry, load partitin and damage characterization of cast AlSi{sub 12}CuMgNi alloy with ceramic reinforcement, methane adsorption in highly porous metal-organics, structure and magnetic interactions in dimer system Ba{sub (3-x)}Sr{sub x}Cr{sub 2}O{sub 8}, distribution of S in C-S nanocomposites, current status of HFM-EXED FACITIY; SPIN NEAMTICITY IN s=1/2 frustrated zigzag chaIN β-TeVO{sub 4}, electronic

  12. Quantitative Near-field Microscopy of Heterogeneous and Correlated Electron Oxides

    Science.gov (United States)

    McLeod, Alexander Swinton

    suitable for the investigation of nano-scale physics in correlated electron matter at cryogenic temperatures, thus vastly expanding the scope of applications for infrared SNOM. Performance of the microscope is demonstrated through quanttiative exploration of the canonical insulator-metal transition occuring in the correlated electron insulator V2O3. The methodology established for this investigation provides a model for ongoing and future nano-optical studies of phase transitions and phase coexistence in correlated electron oxides.

  13. Atomic layer deposition of VO{sub 2} films with Tetrakis-dimethyl-amino vanadium (IV) as vanadium precursor

    Energy Technology Data Exchange (ETDEWEB)

    Lv, Xinrui [Key Laboratory of Inorganic Coating Materials CAS, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Cao, Yunzhen, E-mail: yzhcao@mail.sic.ac.cn [Key Laboratory of Inorganic Coating Materials CAS, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800 (China); Yan, Lu; Li, Ying; Song, Lixin [Key Laboratory of Inorganic Coating Materials CAS, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800 (China)

    2017-02-28

    Highlights: • VO{sub 2} film was easily deposited by ALD using novel vanadium precursor V(NMe{sub 2}){sub 4}. • Deposition and annealing condition were systematically investigated. • Comparable transition properties of VO{sub 2} film on resistance and spectral transmittance were studied. - Abstract: VO{sub 2} thin films have been grown on Si(100) (VO{sub 2}/Si) and fused silica substrates (VO{sub 2}/SiO{sub 2}) by atomic layer deposition (ALD) using tetrakis-dimethyl-amino vanadium (IV) (TDMAV) as a novel vanadium precursor and water as reactant gas. The quartz crystal microbalance (QCM) measurement was performed to study the ALD process of VO{sub 2} thin film deposition, and a constant growth rate of about 0.95 Å/cycle was obtained at the temperature range of 150–200 °C. XRD measurement was performed to study the influence of deposition temperature and post-annealing condition on the crystallization of VO{sub 2} films, which indicated that the films deposited between 150 and 200 °C showed well crystallinity after annealing at 475 °C for 100 min in Ar atmosphere. XPS measurement verified that the vanadium oxidation state was 4+ for both as-deposited film and post-annealed VO{sub 2}/Si film. AFM was applied to study the surface morphology of VO{sub 2}/Si films, which showed a dense polycrystalline film with roughness of about 1 nm. The resistance of VO{sub 2}/Si films deposited between 150 °C and 200 °C as a function of temperature showed similar semiconductor-to-metal transition (SMT) characters with the transition temperature for heating branch (T{sub c,h}) of about 72 °C, a hysteresis width of about 10 °C and the resistance change of two orders of magnitude. The increase of T{sub c,h} compared with the bulk VO{sub 2} (68 °C) may be attributed to the tensile stress along the c-axis in the film. Transmittance measurement of VO{sub 2}/SiO{sub 2} films showed typical thermochromic property with a NIR switching efficiency of above 50% at 2 μm across

  14. Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy

    Science.gov (United States)

    Avella, Adolfo; Oleś, Andrzej M.; Horsch, Peter

    2018-04-01

    We explore the effects of disordered charged defects on the electronic excitations observed in the photoemission spectra of doped transition metal oxides in the Mott insulating regime by the example of the R1 -xCaxVO3 perovskites, where R = La, ⋯, Lu. A fundamental characteristic of these vanadium d2 compounds with partly filled t2 g valence orbitals is the persistence of spin and orbital order up to high doping, in contrast to the loss of magnetic order in high-Tc cuprates at low defect concentration. We study the disordered electronic structure of such doped Mott-Hubbard insulators within the unrestricted Hartree-Fock approximation and, as a result, manage to explain the spectral features that occur in photoemission and inverse photoemission. In particular, (i) the atomic multiplet excitations in the inverse photoemission spectra and the various defect-related states and satellites are qualitatively well reproduced, (ii) a robust Mott gap survives up to large doping, and (iii) we show that the defect states inside the Mott gap develop a soft gap at the Fermi energy. The soft defect-states gap, which separates the highest occupied from the lowest unoccupied states, can be characterized by a shape and a scale parameter extracted from a Weibull statistical sampling of the density of states near the chemical potential. These parameters provide a criterion and a comprehensive schematization for the insulator-metal transition in disordered systems. Our results provide clear indications that doped holes are bound to charged defects and form small spin-orbital polarons whose internal kinetic energy is responsible for the opening of the soft defect-states gap. We show that this kinetic gap survives disorder fluctuations of defects and is amplified by the long-range electron-electron interactions, whereas we observe a Coulomb singularity in the atomic limit. The small size of spin-orbital polarons is inferred by an analysis of the inverse participation ratio and by

  15. Investigations of inorganic and hybrid inorganic-organic nanostructures

    Science.gov (United States)

    Kam, Kinson Chihang

    This thesis focuses on the exploratory synthesis and characterization of inorganic and hybrid inorganic-organic nanomaterials. In particular, nanostructures of semiconducting nitrides and oxides, and hybrid systems of nanowire-polymer composites and framework materials, are investigated. These materials are characterized by a variety of techniques for structure, composition, morphology, surface area, optical properties, and electrical properties. In the study of inorganic nanomaterials, gallium nitride (GaN), indium oxide (In2O3), and vanadium dioxide (VO2) nanostructures were synthesized using different strategies and their physical properties were examined. GaN nanostructures were obtained from various synthetic routes. Solid-state ammonolysis of metastable gamma-Ga2O 3 nanoparticles was found to be particularly successful; they achieved high surface areas and photoluminescent study showed a blue shift in emission as a result of surface and size defects. Similarly, In2O3 nanostructures were obtained by carbon-assisted solid-state syntheses. The sub-oxidic species, which are generated via a self-catalyzed vapor-liquid-solid mechanism, resulted in 1D nanostructures including nanowires, nanotrees, and nanobouquets upon oxidation. On the other hand, hydrothermal methods were used to obtain VO2 nanorods. After post-thermal treatment, infrared spectroscopy demonstrated that these nanorods exhibit a thermochromic transition with temperature that is higher by ˜10°C compared to the parent material. The thermochromic behavior indicated a semiconductor-to-metal transition associated with a structural transformation from monoclinic to rutile. The hybrid systems, on the other hand, enabled their properties to be tunable. In nanowire-polymer composites, zinc oxide (ZnO) and silver (Ag) nanowires were synthesized and incorporated into polyaniline (PANI) and polypyrrole (PPy) via in-situ and ex-situ polymerization method. The electrical properties of these composites are

  16. Nonequilibrium emergent phenomena in organic molecular solids

    Energy Technology Data Exchange (ETDEWEB)

    Mitrano, Matteo

    2015-07-15

    The manipulation of matter with ultrashort laser pulses is a relevant research field from both a fundamental and an applied perspective, owing to the efficient coupling to the electronic degrees of freedom on femtosecond timescales and the ability to induce transient phases that cannot be realized in equilibrium scenarios. Strongly correlated materials are a natural environment for the observation of such novel and emergent out-of-equilibrium physics because small modifications to the electron-electron interactions can induce transitions between remarkably different macroscopic phases. One of the most effective means of modifying the effective electron-electron interactions is to perturb the crystal structure through pressure, strain or even light. However, it remains largely unexplored how perturbing the structural degrees of freedom affects the electron dynamics of the transiently driven states and how the interplay of correlations and electron-lattice interactions determine the intrinsic timescales of these nonequilibrium states. This thesis investigates how to control the light-induced nonequilibrium electronic properties in strongly correlated organics, that are highly tunable with moderate variations of external parameters, by perturbing their structural degrees of freedom, either via static pressures or vibrational excitation. We study the role of correlations in determining the relaxation rate of holes (holons) and double occupancies (doublons) in a solid state Mott insulator, the ET-F{sub 2}TCNQ, driven across a transient insulator-to-metal transition. By mapping holon-doublon lifetimes onto the ground-state electronic interactions, we found that the decay rate of the photoinjected quasiparticles depends on the degree of correlation between carriers and is affected by the presence of a competition between local recombination and delocalization of holon-doublon pairs. By optically controlling the effective correlations in organic molecular crystals through

  17. Valence, magnetism and conduction in the intermediate valence compounds: the case SmB6

    International Nuclear Information System (INIS)

    Derr, J.

    2006-09-01

    In some rare earth based compounds, the 4f level is situated so close to the Fermi level that the valence of the compound can become intermediate between two integer values. The so called 'intermediate valence' compound of Samarium hexaboride (SmB 6 ) is one typical example of the exciting physics which can result from this quantum equilibrium between two valence configurations. The first configuration (Sm 2+ ) corresponds to an insulating and non magnetic state whereas the second one (Sm 3+ ) would theoretically give a magnetic and metallic ground state. This dissertation deals with the influence of pressure on this equilibrium. Specific heat measurements under pressure evidenced a new long range magnetic ordering for pressures higher than p c ∼ 10 GPa. On another hand, transport measurements measured for the first time in good conditions of hydrostatics found a reliable and reproducible critical pressure for the insulator to metal transition equal to p c . The phase diagram of SmB 6 is now well known and the observation for the first time of a magnetic anomaly in the high pressure resistivity curves certifies that the onset of the magnetic phase really coincide with the closure of the gap. This change at the critical pressure p c is discussed in a general frame taking into account the Kondo lattice temperature as a key parameter for the renormalization of the wavefunction from one integer configuration to the other whereas the valence itself is still intermediate. This general idea seems to be valid also for other systems studied in this dissertation like SmS or TmSe and could even be valid for more general cases (Ytterbium, Cerium). In the same time, resistivity measurements under uniaxial stress were undertaken. The result is a strong anisotropy effect observed on the pressure dependence of the residual resistivity in the compound SmB 6 . The comparison with the transport under hydrostatic conditions enables us to consider a new idea for the nature of the gap

  18. An Angle Resolved Photoemission Study of a Mott Insulator and Its Evolution to a High Temperature Superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Ronning, Filip

    2002-03-19

    One of the most remarkable facts about the high temperature superconductors is their close proximity to an antiferromagnetically ordered Mott insulating phase. This fact suggests that to understand superconductivity in the cuprates we must first understand the insulating regime. Due to material properties the technique of angle resolved photoemission is ideally suited to study the electronic structure in the cuprates. Thus, a natural starting place to unlocking the secrets of high Tc would appears to be with a photoemission investigation of insulating cuprates. This dissertation presents the results of precisely such a study. In particular, we have focused on the compound Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}. With increasing Na content this system goes from an antiferromagnetic Mott insulator with a Neel transition of 256K to a superconductor with an optimal transition temperature of 28K. At half filling we have found an asymmetry in the integrated spectral weight, which can be related to the occupation probability, n(k). This has led us to identify a d-wave-like dispersion in the insulator, which in turn implies that the high energy pseudogap as seen by photoemission is a remnant property of the insulator. These results are robust features of the insulator which we found in many different compounds and experimental conditions. By adding Na we were able to study the evolution of the electronic structure across the insulator to metal transition. We found that the chemical potential shifts as holes are doped into the system. This picture is in sharp contrast to the case of La{sub 2-x}Sr{sub x}CuO{sub 4} where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca{sub 1.9}Na{sub 0.1}CuO{sub 2}Cl{sub 2} is most well described as a Fermi arc, although the high binding energy features reveal the presence of shadow bands. Thus, the results in this dissertation provide a

  19. Correlated effective field theory in transition metal compounds

    International Nuclear Information System (INIS)

    Mukhopadhyay, Subhasis; Chatterjee, Ibha

    2004-01-01

    Mean field theory is good enough to study the physical properties at higher temperatures and in higher dimensions. It explains the critical phenomena in a restricted sense. Near the critical temperatures, when fluctuations become important, it may not give the correct results. Similarly in low dimensions, the correlations become important and the mean field theory seems to be inadequate to explain the physical phenomena. At low-temperatures too, the quantum correlations become important and these effects are to be treated in an appropriate way. In 1974, Prof. M.E. Lines of Bell Laboratories, developed a theory which goes beyond the mean field theory and is known as the correlated effective field (CEF) theory. It takes into account the fluctuations in a semiempirical way. Lines and his collaborators used this theory to explain the short-range correlations and their anisotropy in the paramagnetic phase. Later Suzuki et al., Chatterjee and Desai, Mukhopadhyay and Chatterjee applied this theory to the magnetically ordered phase and a tremendous success of the theory has been found in real systems. The success of the CEF theory is discussed in this review. In order to highlight the success of this theory, earlier effective field theories and their improvements over mean field theories e.g., Bethe-Peierls-Weiss method, reaction field approximation, etc., are also discussed in this review for completeness. The beauty of the CEF theory is that it is mean field-like, but captures the essential physics of real systems to a great extent. However, this is a weak correlated theory and as a result is inappropriate for the metallic phase when strong correlations become important. In recent times, transition metal oxides become important due to the discovery of the high-temperature superconductivity and the colossal magnetoresistance phenomena. These oxides seem to be Mott insulators and undergo an insulator to metal transition by applying magnetic field, pressure and by changing

  20. Structural response in FeCl2 (iron chloride) to pressure-induced electro-magnetic transitions

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, R D [Los Alamos National Laboratory; Rozenberg, G Kh [TEL AVIV UNIV; Pasternak, M P [TEL AVIV UNIV; Gorodetsky, P [TEL AVIV UNIV; Xu, W M [TEL AVIV UNIV; Dubrovinsky, L S [UNIV OF BAYREUTH; Le Bihan, T L [FRANCE

    2009-01-01

    High pressure (HP) synchrotron x-ray diffraction studies were carried out in FeCl{sub 2} together with resistivity (R) studies, at various temperatures and pressures to 65 GPa using diamond anvil cells. This work follows a previous HP {sup 57}Fe Mossbauer study in which two pressure-induced (PI) electronic transitions were found interpreted as: (i) quenching of the orbital-term contribution to the hyperfine field concurring with a tilting of the magnetic moment by 55 degrees and (ii) collapse of the magnetism concurring with a sharp decrease of the isomer shift (IS). The R(P,T) studies affirm that the cause the collapse of the magnetism is a PI p-d correlation breakdown, leading to an insulator-metal transition at {approx}45 GPa and is not due to a spi-Ir,crossover (S=2 {yields} S=0). The structure response to the pressure evolution of the two electronic phase transitions starting at low pressures (LP), through an intermediate phase (IP) 30-57 GPa, and culminating in a high-pressure phase (HP), P >32 GPa, can clearly be quantified. The IP-HP phases coexist through the 32-57 GPa range in which the HP abundance increases monotonically at the expense of the IP phase. At the LP-IP interface no volume change is detected, yet the c-axis increases and the a-axis shrinks by 0.21 Angstroms and 0.13 Angstroms, respectively. The fit of the equation of state of the combined LP-IP phases yields a bulk modulus K{sub 0} = 35.3(1.8) GPa. The intralayer CI-CI distances increases, but no change is observed in Fe-CI bond-length nor are there substantial changes in the interlayer spacing. The pressure-induced electronic IP-HP transition leads to a first-order structural phase transition characterized by a decrease in Fe-CI bond length and an abrupt drop in V(P) by {approx}3.5% accompanying the correlation breakdown. In this transition no symmetry change is detected,and the XRD data could be satisfactorily fitted with the CdI{sub 2} structure. The bulk modulus of the HP phase is

  1. Eight joint BER II and BESSY II users meeting. Abstracts

    International Nuclear Information System (INIS)

    2016-01-01

    The following topics were dealt with: Accelerator operation and projecs, photon science and instrumentation at BESSY II, status of energy materials in-situ Lab at BESSY II, high resolution spectrometer PEAXIS at BESSY II, sample environment at BESSY II, molecular control mechanisms in the Brr2 RNA helicase for efficient and regulated splicing, the Li conversion reaction of 4CoFe_2O_4 nanoparticles, buried interfaces in lithium ion batteries probed with HAXPES, ARPES studies of the STO(001) 2DEG, all-in/all-out magnetic order in rare earth iridates, oxygen reduction reaction on graphene in Li-air batteries, electronic order in high-T_c superconductors, in-siu observation of novel switching phenomena in highly porous metal-organic frameworks, photoinduced demagnetization and insulator-to-metal transition in ferromagnetic insulating BaFeO_3 thin films, ARPES measurement of the ferroelectric bulk Rashba system GeTe, bisphenol A on Cu(111) and Ag(111), reverse water-gas shift or Sabathier methanation on N(110), structural studies of molecular machines, multi-MHz time-of-flight electronic band-structure imaging of graphene on Ir(111), diffusion pathways in ion conductors, ground-state potential energy surfaces around selected atoms from resonant inelastic X-ray scattering, solar energy in an emerging country, in-situ neutron analysis of electrode materials for electrochemical energy storage, structure and transport properties in thermoelectric skutterudites, investigation of the interphase formation on solid lithium-ion conductors by neutron reflectometry, load partitin and damage characterization of cast AlSi_1_2CuMgNi alloy with ceramic reinforcement, methane adsorption in highly porous metal-organics, structure and magnetic interactions in dimer system Ba_(_3_-_x_)Sr_xCr_2O_8, distribution of S in C-S nanocomposites, current status of HFM-EXED FACITIY; SPIN NEAMTICITY IN s=1/2 frustrated zigzag chaIN β-TeVO_4, electronic properties of U(Ru_0_._9_2Rh_0_._0_8)_2Si_2 in

  2. Chemically Conjugated Carbon Nanotubes and Graphene for Carrier Modulation.

    Science.gov (United States)

    Kim, Ki Kang; Kim, Soo Min; Lee, Young Hee

    2016-03-15

    Nanocarbons such as fullerene and carbon nanotubes (CNT) in late 20th century have blossomed nanoscience and nanotechnology in 21st century, which have been further proliferated by the new finding of graphene and have indeed opened a new carbon era. Several new branches of research, for example, zero-dimensional nanoparticles, one-dimensional nanowires, and two-dimensional insulating hexagonal boron nitride, and semiconducting and metallic transition metal dichalcogenides including the recently emerging black phosphorus, have been explored and numerous unprecedented quantum mechanical features have been revealed, that have been hardly accessible otherwise. Extensive research has been done on devices and applications related to such materials. Many experimental instruments have been developed with high sensitivity and improved spatial and temporal resolution to detect such tiny objects. The need for multidisciplinary research has been growing stronger than ever, which will be the tradition in the next few decades. In this Account, we will demonstrate an example of multidisciplinary effort of utilizing CNTs and graphene for electronics by modulating electronic structures. While there are several methods of modifying electronic structures of nanocarbons such as gate bias, contact metal, and conventional substitutional doping, we focus on chemical doping approaches here. We first introduce the concept of chemical doping on CNTs and graphene in terms of electronegativity of molecules and electrochemical potential of CNTs and graphene. To understand the relationship of electrochemical potential of CNTs and graphene to electronegativity of molecules, we propose a simple water bucket model: how to fill or drain water (electrons in CNTs or graphene) in the bucket (density of states) by the chemical dopants. The doping concept is then demonstrated experimentally by tracking the absorption spectroscopy, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy

  3. Growth, electrical, structural, and magnetic properties of half-Heusler CoT i1 -xF exSb

    Science.gov (United States)

    Harrington, S. D.; Rice, A. D.; Brown-Heft, T. L.; Bonef, B.; Sharan, A.; McFadden, A. P.; Logan, J. A.; Pendharkar, M.; Feldman, M. M.; Mercan, O.; Petukhov, A. G.; Janotti, A.; Colakerol Arslan, L.; Palmstrøm, C. J.

    2018-01-01

    Epitaxial thin films of the substitutionally alloyed half-Heusler series CoT i1 -xF exSb were grown by molecular beam epitaxy on InAlAs/InP(001) substrates for concentrations 0.0 ≤x ≤1.0 . The influence of Fe on the structural, electronic, and magnetic properties was studied and compared to that expected from density functional theory. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and x-ray diffraction. Using in situ x-ray photoelectron spectroscopy, only small changes in the valence band are detected for x ≤0.5 . For films with x ≥0.05 , ferromagnetism is observed in SQUID magnetometry with a saturation magnetization that scales linearly with Fe content. A dramatic decrease in the magnetic moment per formula unit occurs when the Fe is substitutionally alloyed on the Co site indicating a strong dependence on the magnetic moment with site occupancy. A crossover from both in-plane and out-of-plane magnetic moments to only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic resonance indicates a transition from weak to strong interaction with a reduction in inhomogeneous broadening as Fe content is increased. Temperature-dependent transport reveals a semiconductor to metal transition with thermally activated behavior for x ≤0.5 . Anomalous Hall effect and large negative magnetoresistance (up to -18.5% at 100 kOe for x =0.3 ) are observed for higher Fe content films. Evidence of superparamagnetism for x =0.3 and 0.2 suggests, for moderate levels of Fe, that demixing of the CoT i1 -xF exSb films into Fe-rich and Fe-deficient regions may be present. Atom probe tomography is used to examine the Fe distribution in an x =0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe atoms throughout the film, which is used to explain the observed magnetic and electrical behavior.

  4. Electrical transport in crystalline phase change materials

    International Nuclear Information System (INIS)

    Woda, Michael

    2012-01-01

    , profilometry, ellipsometry, FTIR spectroscopy, van der Pauw,Hall, and phase change optical and electrical switching techniques which are used to obtain the results. The latter chapter is split into two parts. In the first one thematerial class of doped Sb 2 Te is investigated with respect to structural, kinetic, optical and electrical properties. The second part covers the study of the systematic variation of the resistivity of pseudo-binary GeTe-Sb 2 Te 3 alloys upon thermal annealing. This variation is discussed in the framework of an insulator to metal transition with the help of results from a combined van der Pauw, XRD, Hall, STM and FTIR study.

  5. Electrical transport in crystalline phase change materials

    Energy Technology Data Exchange (ETDEWEB)

    Woda, Michael

    2012-01-06

    , profilometry, ellipsometry, FTIR spectroscopy, van der Pauw,Hall, and phase change optical and electrical switching techniques which are used to obtain the results. The latter chapter is split into two parts. In the first one thematerial class of doped Sb{sub 2}Te is investigated with respect to structural, kinetic, optical and electrical properties. The second part covers the study of the systematic variation of the resistivity of pseudo-binary GeTe-Sb{sub 2}Te{sub 3} alloys upon thermal annealing. This variation is discussed in the framework of an insulator to metal transition with the help of results from a combined van der Pauw, XRD, Hall, STM and FTIR study.

  6. Nonlinear phononics and structural control of strongly correlated materials

    Energy Technology Data Exchange (ETDEWEB)

    Mankowsky, Roman

    2016-01-20

    Mid-infrared light pulses can be used to resonantly excite infrared-active vibrational modes for the phase control of strongly correlated materials on subpicosecond timescales. As the energy is transferred directly into atomic motions, dissipation into the electronic system is reduced, allowing for the emergence of unusual low energy collective properties. Light-induced superconductivity, insulator-metal transitions and melting of magnetic order demonstrate the potential of this method. An understanding of the mechanism, by which these transitions are driven, is however missing. The aim of this work is to uncover this process by investigating the nonlinear lattice dynamics induced by the excitation and to elucidate their contribution to the modulation of collective properties of strongly correlated materials. The first signature of nonlinear lattice dynamics was reported in the observation of coherent phonon oscillations, resonant with the excitation of an infrared-active phonon mode in a manganite. This nonlinear phononic coupling can be described within a model, which predicts not only oscillatory coherent phonons dynamics but also directional atomic displacements along the coupled modes on average, which could cause the previously observed transitions. We verified this directional response and quantified the anharmonic coupling constant by tracing the atomic motions in a time-resolved hard X-ray diffraction experiment with sub-picometer spatial and femtosecond temporal resolution. In a subsequent study, we investigated the role of nonlinear lattice dynamics in the emergence of superconductivity far above the equilibrium transition temperature, an intriguing effect found to follow lattice excitation of YBa{sub 2}Cu{sub 3}O{sub 6+x}. By combining density functional theory (DFT) calculations of the anharmonic coupling constants with time-resolved X-ray diffraction experiments, we identified a structural rearrangement, which appears and decays with the same temporal

  7. Magnetism of Nanographene-Based Microporous Carbon and Its Applications: Interplay of Edge Geometry and Chemistry Details in the Edge State

    Science.gov (United States)

    Enoki, Toshiaki; Kiguchi, Manabu

    2018-03-01

    This paper is a contribution to the Physical Review Applied collection in memory of Mildred S. Dresselhaus. Nanographenes have important edge geometry dependence in their electronic structures. In armchair edges, electron wave interference works to contribute to energetic stability. Meanwhile, zigzag edges possess an edge-localized and spin-polarized nonbonding edge state, which causes electronic, magnetic, and chemical activities. In addition to the geometry dependence, the electronic structures are seriously affected by edge chemistry details. The edge chemistry dependence together with edge geometries on the electronic structures are discussed with samples of randomly networked nanographenes (microporous activated carbon fibers) in pristine state and under high-temperature annealing. In the pristine sample with the edges oxidized in ambient atmospheric conditions, the edge state, which is otherwise unstable, can be stabilized because of the charge transfer from nanographene to terminating oxygen. Nanographene, whose edges consist of a combination of magnetic zigzag edges and nonmagnetic armchair edges, is found to be ferrimagnetic with a nonzero net magnetic moment created under the interplay between a strong intrazigzag-edge ferromagnetic interaction and intermediate-strength interzigzag-edge antiferromagnetic-ferromagnetic interaction. At heat-treatment temperatures just below the fusion start (approximately 1500 K), the edge-terminating structure is changed from oxygen-containing groups to hydrogen in the nanographene network. Additionally, hydrogen-terminated zigzag edges, which are present as the majority and chemically unstable, play a triggering role in fusion above 1500 K. The fusion start brings about an insulator-to-metal transition at TI -M˜1500 K . Local fusions taking place percolatively between nanographenes work to expand the π -bond network, eventually resulting in the development of antiferromagnetic short-range order toward spin glass in the

  8. Effects of strain on the magnetic and transport properties of the epitaxial La0.5Ca0.5MnO3 thin films

    International Nuclear Information System (INIS)

    Zarifi, M.; Kameli, P.; Ehsani, M.H.; Ahmadvand, H.; Salamati, H.

    2016-01-01

    The epitaxial strain can considerably modify the physical properties of thin films compared to the bulk. This paper reports the effects of substrate-induced strain on La 0.5 Ca 0.5 MnO 3 (LCMO) thin films, grown on (100) SrTiO 3 (STO) and LaAlO 3 (LAO) substrates by pulsed laser deposition technique. Transport and magnetic properties were found to be strongly dependent on strain type. It is also shown that compressive (tensile) strain leads to the increase (decrease) in the magnetization of the films. Moreover, it was observed that all LCMO films deposited on both LAO and STO substrates behave as an insulator, but LCMO/LAO thin films with compressive strain have lower resistivity than LCMO/STO thin films with tensile strain. Applying magnetic field to LCMO/STO thin films with thickness of 25 and 50 nm leads to very small change in the resistivity, while the effects of magnetic field on the sample with thickness of 125 nm leads to an insulator–metal transition. For LCMO/LAO thin films, the magnetic field has a strong impact on the resistivity of samples. The results show that the magnetoresistance (MR) is enhanced by increasing film thickness for LCMO/LAO samples, due to the relatively stronger phase separation. For LCMO/STO thin films MR is drastically decreased by reduction of film thickness, which is attributed to the enhancement of the charge–orbital order (CO–O) accompanying the complex spin order (the so-called CE type). The changes of the antiferromagnetic structure from the CE to C type and the enhancement of the CE type could be attributed to the in-plane compressive and tensile strain, respectively. - Highlights: • Epitaxial La 0.5 Ca 0.5 MnO 3 thin films, grown on (100) SrTiO 3 and LaAlO 3 substrates. • The compressive strain leads to the increase in the magnetization of the films. • The tensile strain leads to the decrease in the magnetization of the films. • The magnetoresistance is enhanced by increasing film thickness.

  9. Electronic structure and metallization of cubic GdH{sub 3} under pressure: Ab initio many-body GW calculations

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Bo, E-mail: kong79@yeah.net, E-mail: yachao.zhang@pku.edu.cn [School of Physics and Electronic Sciences, Guizhou Education University, Guiyang 550018 (China); Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Education University, Guiyang 550018 (China); Zhang, Yachao, E-mail: kong79@yeah.net, E-mail: yachao.zhang@pku.edu.cn [Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Education University, Guiyang 550018 (China)

    2016-07-07

    The electronic structures of the cubic GdH{sub 3} are extensively investigated using the ab initio many-body GW calculations treating the Gd 4f electrons either in the core (4f-core) or in the valence states (4f-val). Different degrees of quasiparticle (QP) self-consistent calculations with the different starting points are used to correct the failures of the GGA/GGA + U/HSE03 calculations. In the 4f-core case, GGA + G{sub 0}W{sub 0} calculations give a fundamental band gap of 1.72 eV, while GGA+ GW{sub 0} or GGA + GW calculations present a larger band gap. In the 4f-val case, the nonlocal exchange-correlation (xc) functional HSE03 can account much better for the strong localization of the 4f states than the semilocal or Hubbard U corrected xc functional in the Kohn–Sham equation. We show that the fundamental gap of the antiferromagnetic (AFM) or ferromagnetic (FM) GdH{sub 3} can be opened up by solving the QP equation with improved starting point of eigenvalues and wave functions given by HSE03. The HSE03 + G{sub 0}W{sub 0} calculations present a fundamental band gap of 2.73 eV in the AFM configuration, and the results of the corresponding GW{sub 0} and GW calculations are 2.89 and 3.03 eV, respectively. In general, for the cubic structure, the fundamental gap from G{sub 0}W{sub 0} calculations in the 4f-core case is the closest to the real result. By G{sub 0}W{sub 0} calculations in the 4f-core case, we find that H or Gd defects can strongly affect the band structure, especially the H defects. We explain the mechanism in terms of the possible electron correlation on the hydrogen site. Under compression, the insulator-to-metal transition in the cubic GdH{sub 3} occurs around 40 GPa, which might be a satisfied prediction.

  10. Electronic self-organization in layered transition metal dichalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Ritschel, Tobias

    2015-10-30

    The interplay between different self-organized electronically ordered states and their relation to unconventional electronic properties like superconductivity constitutes one of the most exciting challenges of modern condensed matter physics. In the present thesis this issue is thoroughly investigated for the prototypical layered material 1T-TaS{sub 2} both experimentally and theoretically. At first the static charge density wave order in 1T-TaS{sub 2} is investigated as a function of pressure and temperature by means of X-ray diffraction. These data indeed reveal that the superconductivity in this material coexists with an inhomogeneous charge density wave on a macroscopic scale in real space. This result is fundamentally different from a previously proposed separation of superconducting and insulating regions in real space. Furthermore, the X-ray diffraction data uncover the important role of interlayer correlations in 1T-TaS{sub 2}. Based on the detailed insights into the charge density wave structure obtained by the X-ray diffraction experiments, density functional theory models are deduced in order to describe the electronic structure of 1T-TaS{sub 2} in the second part of this thesis. As opposed to most previous studies, these calculations take the three-dimensional character of the charge density wave into account. Indeed the electronic structure calculations uncover complex orbital textures, which are interwoven with the charge density wave order and cause dramatic differences in the electronic structure depending on the alignment of the orbitals between neighboring layers. Furthermore, it is demonstrated that these orbital-mediated effects provide a route to drive semiconductor-to-metal transitions with technologically pertinent gaps and on ultrafast timescales. These results are particularly relevant for the ongoing development of novel, miniaturized and ultrafast devices based on layered transition metal dichalcogenides. The discovery of orbital textures

  11. Effects of strain on the magnetic and transport properties of the epitaxial La{sub 0.5}Ca{sub 0.5}MnO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Zarifi, M. [Department of Physics, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kameli, P., E-mail: kameli@cc.iut.ac.ir [Department of Physics, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Ehsani, M.H. [Department of Physics, Semnan University, Semnan 35195-363 (Iran, Islamic Republic of); Ahmadvand, H.; Salamati, H. [Department of Physics, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)

    2016-12-15

    The epitaxial strain can considerably modify the physical properties of thin films compared to the bulk. This paper reports the effects of substrate-induced strain on La{sub 0.5}Ca{sub 0.5}MnO{sub 3} (LCMO) thin films, grown on (100) SrTiO{sub 3} (STO) and LaAlO{sub 3} (LAO) substrates by pulsed laser deposition technique. Transport and magnetic properties were found to be strongly dependent on strain type. It is also shown that compressive (tensile) strain leads to the increase (decrease) in the magnetization of the films. Moreover, it was observed that all LCMO films deposited on both LAO and STO substrates behave as an insulator, but LCMO/LAO thin films with compressive strain have lower resistivity than LCMO/STO thin films with tensile strain. Applying magnetic field to LCMO/STO thin films with thickness of 25 and 50 nm leads to very small change in the resistivity, while the effects of magnetic field on the sample with thickness of 125 nm leads to an insulator–metal transition. For LCMO/LAO thin films, the magnetic field has a strong impact on the resistivity of samples. The results show that the magnetoresistance (MR) is enhanced by increasing film thickness for LCMO/LAO samples, due to the relatively stronger phase separation. For LCMO/STO thin films MR is drastically decreased by reduction of film thickness, which is attributed to the enhancement of the charge–orbital order (CO–O) accompanying the complex spin order (the so-called CE type). The changes of the antiferromagnetic structure from the CE to C type and the enhancement of the CE type could be attributed to the in-plane compressive and tensile strain, respectively. - Highlights: • Epitaxial La{sub 0.5}Ca{sub 0.5}MnO{sub 3} thin films, grown on (100) SrTiO{sub 3} and LaAlO{sub 3} substrates. • The compressive strain leads to the increase in the magnetization of the films. • The tensile strain leads to the decrease in the magnetization of the films. • The magnetoresistance is enhanced by

  12. Stability of iron-rich magnesiowüstite in Earth's lower mantle

    Science.gov (United States)

    Ohta, K.; Fujino, K.; Kuwayama, Y.; Kondo, T.; Shimizu, K.; Ohishi, Y.

    2012-12-01

    At ambient conditions, MgO periclase and FeO wüstite form a solid solution (Mg1-xFex)O, named ferropericlase (x ≤ 0.5) and magnesiowüstite (x > 0.5). (Mg1-xFex)O ferropericlase is considered to be a major component of Earth's lower mantle, and may play an important role for its structure and dynamics. Iron-rich magnesiowüstite also needs to be considered because of possible iron enrichment at the core-mantle boundary region [e.g., Nomura et al., 2011]. Recent laser-heated diamond anvil cell experiments on FeO revealed that NaCl-type (B1) structured FeO underwent an insulator-metal transition at about 70 GPa and 1800 K without any structural transformation [Fischer et al., 2011; Ohta et al., 2012]. These results imply that the metallic B1 FeO would require a two-phase field for the MgO-FeO binary system due to different chemical bonding between insulating MgO and metallic FeO. We performed simultaneous electrical conductivity and x-ray diffraction measurements on (Mg0.20Fe0.80)O and (Mg0.05Fe0.95)O magnesiowüstite up to 140 GPa and 2100 K, and then examined recovered samples by using analytical transmission electron microprobe. We obtained some evidences for the dissociation of (Mg0.05Fe0.95)O into lighter and heavier phases than starting material occurring above 70 GPa and 1900 K, which is most likely due to the metallization of FeO component. On the other hand, we did not observe such dissociation and metallization in (Mg0.20Fe0.80)O. Observed dissociation in (Mg0.05Fe0.95)O might contribute to the heterogeneity in seismic wave and electrical conductivity at the Earth's core-mantle boundary region.

  13. Unraveling the Role of Structural Order in the Transformation of Electrical Conductivity in Ca2FeCoO6-δ, CaSrFeCoO6-δ, and Sr2FeCoO6-δ.

    Science.gov (United States)

    Hona, Ram Krishna; Huq, Ashfia; Ramezanipour, Farshid

    2017-12-04

    The ability to control the electrical conductivity of solid-state oxides using structural parameters has been demonstrated. A correlation has been established between the electrical conductivity and structural order in a series of oxygen-deficient perovskites using X-ray and neutron diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and electrical conductivity studies at a wide temperature range, 25-800 °C. The crystal structure of CaSrFeCoO 6-δ has been determined, and its stark contrast to Ca 2 FeCoO 6-δ and Sr 2 FeCoO 6-δ has been demonstrated. The Fe/Co distribution over tetrahedral and octahedral sites has been determined using neutron diffraction. There is a systematic increase in the structural order in progression from Sr 2 FeCoO 6-δ (δ = 0.5) to CaSrFeCoO 6-δ (δ = 0.8) and Ca 2 FeCoO 6-δ (δ = 0.9) . The oxygen contents of these materials were determined using iodometric titration and TGA. At room temperature, there is an inverse correlation between the electrical conductivity and structural order. The ordered Ca 2 and CaSr compounds are semiconductors, while the disordered Sr 2 compund shows metallic behavior. The metallic nature of the Sr 2 material persists up to 1073 K (800 °C), while the Ca 2 and CaSr compounds undergo a semiconductor-to-metal transition above 500 and 300 °C, respectively, highlighting another important impact of the structural order. At high temperature, the CaSr compound has the highest conductivity compared to the Ca 2 and Sr 2 materials. There appears to be an optimum degree of structural order that leads to the highest conductivity at high temperature. Another consequence of the structural order is the observation of mixed ionic-electronic conductivity in CaSr and Ca 2 compounds, as is evident from the hysteresis in the conductivity data obtained during heating and cooling cycles. The average ionic radius required for each structural transition was

  14. NTP Toxicity Study Report on the atmospheric characterization, particle size, chemical composition, and workplace exposure assessment of cellulose insulation (CELLULOSEINS).

    Science.gov (United States)

    Morgan, Daniel L

    2006-08-01

    samples for each day of CI activities were collected from the installer and hopper operator. Bulk CI samples were collected and analyzed for metal, boron, and sulfate content. Real-time and video exposure monitoring was conducted to further characterize the CI dust and workers' exposures. The exposure assessment also included a medical component. Investigators collected 175 personal breathing zone (PBZ) total dust, 106 area total dust, and 90 area respirable dust air samples during CI-related activities at the 10 contractor sites. Twenty-six employees' total dust 8-hour time-weighted averages (TWAs) exceeded the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 15 mg/m3, and 42 exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) threshold-limit value (TLV) of 10 mg/m3. Respirable dust air sampling and real-time monitoring with particle size discrimination indicated low levels of respirable dust generation. The SEM analyses revealed that fibers were an average 28 mum in length and ranged from 5 mum to 150 mum. CI installers' PBZ total dust, area total dust, and area respirable dust air samples were all significantly higher during dry attic applications than wet attic applications (Papplications than dry wall and ceiling applications (P=0.02). Analyses of variance tests revealed that exposure concentrations in total dust air samples collected in the PBZ of all CI workers, including installers working in attics, installers during wall applications, hopper operators during attic applications, and hopper operators during wall and ceiling applications, varied significantly during dry applications (Papplications, and hopper areas during wall and ceiling applications also differed significantly during dry applications (P=0.03). Twenty-three workers participated in the medical phase of the investigation. The workers completed medical and work history questionnaires, performed serial peak flow tests, and completed

  15. Role of Defects and Adsorbed Water Film in Influencing the Electrical, Optical and Catalytic Properties of Transition Metal Oxides

    Science.gov (United States)

    Wang, Qi

    obtain a mechanistic understanding of the charge transfer process. We have developed a spectroscopic technique for studying vacancy defects in TMOs using near-infrared photoluminescence (NIR-PL) spectroscopy and showed that this technique is uniquely suited for studying defect-adsorbate interactions. In this work, a series of studies were carried out to elucidate the underlying structure-defect-property correlations of TMOs and their role in catalyzing electrical and electrochemical properties. In the first study, we report a new type of electrical phase transition in p-type, non-stoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete change of conductivity from p- to n-type at room temperature induced by electrochemical Li+ intercalation. Direct observation of vacancy-ion interactions using in-situ NIR-PL show that the transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. X-ray photoemission spectroscopy studies performed to examine the changes in the oxidation states of nickel due to defect interactions support the above conclusions. In the second study, main effects of oxygen vacancy defects on the electronic and optical properties of V2O5 nanowires were studied using in-situ Raman, photoluminescence, absorption, and photoemission spectroscopy. We show that both thermal reduction and electrochemical reduction via Li+ insertion results in the creation of oxygen vacancy defects in the crystal that leads to band filling and an increase in the optical band gap of V2O5 from 1.95 eV to 2.45 eV, an effect known as the Burstein-Moss effect. In the third study, we report a new type of semiconductor-adsorbed water interaction in metal oxides known as "electrochemical surface transfer doping," a phenomenon that has been previously been observed on hydrogen-terminated diamond, carbon nanotube

  16. Unexpected Nonlinear Effects in Superconducting Transition-Edge Sensors

    Science.gov (United States)

    Sadleir, John

    2016-01-01

    When a normal metal transitions into the superconducting state the DC resistance drops from a finite value to zero over some finite transition width in temperature, current, and magnetic field. Superconducting transition-edge sensors (TESs) operate within this transition region and uses resistive changes to measure deposited thermal energy. This resistive transition is not perfectly smooth and a wide range of TES designs and materials show sub-structure in the resistive transition (as seen in smooth nonmonotonic behavior, jump discontinuities, and hysteresis in the devices current-voltage relation and derivatives of the resistance with respect to temperature, bias current, and magnetic field). TES technology has advanced to the point where for many applications this structure is the limiting factor in performance and optimization consists of finding operating points away from these structures. For example, operating at or near this structure can lead to nonlinearity in the detectors response and gain scale, limit the spectral range of the detector by limiting the usable resistive range, and degrade energy resolution. The origin of much of this substructure is unknown. This presentation investigates a number of possible sources in turn. First we model the TES as a superconducting weak-link and solve for the characteristic differential equations current and voltage time dependence. We find:(1) measured DC biased current-voltage relationship is the time-average of a much higher frequency limit cycle solution.(2) We calculate the fundamental frequency and estimate the power radiated from the TES treating the bias leads as an antennae.(3) The solution for a set of circuit parameters becomes multivalued leading to current transitions between levels.(4)The circuit parameters can change the measure resistance and mask the true critical current. As a consequence the TES resistance surface is not just a function of temperature, current, and magnetic field but is also a

  17. Phase structure and critical properties of an abelian gauge theory

    Energy Technology Data Exchange (ETDEWEB)

    Mo, Sjur

    2001-12-01

    . We also discuss the connection between the values of {eta} and D{sub H}, and the possibility of having a thermodynamic transition in finite background field. Paper III is about ''The order of the metal to superconductor transition''. Here we present results from large-scale Monte Carlo simulations on the full Ginzburg-Landau model, including fluctuations in the amplitude and the phase of the matter-field, as well as fluctuations of the non-compact gauge-field of the theory. From this we obtain a precise critical value of the Ginzburg-Landau parameter {kappa}{sub tri} separating a first order metal to superconductor transition from a second order one, {kappa}{sub trj} = (0.76 {+-} 0.04)/{radical}2. This agrees remarkably well with earlier analytical results based on a disorder theory of the superconductor to metal transition, where the value {kappa}{sub tri} = 0.798/{radical}2 was obtained. To achieve this, we have done careful infinite volume and continuum limit extrapolations. We argue that {kappa}{sub tri} is also the value that separates type-I from type-Il behavior. (author)

  18. Strain-dependent magnetism and electrical conductivity of La1-xSrxCoO3

    International Nuclear Information System (INIS)

    Zeneli, Orkidia

    2011-01-01

    thickness effect, the Curie temperature, the magnetic moment and the (rather large) coercivity of the films have been investigated in two electrically controlled strain states for a film on PMN-PT. Non-cracked, sufficiently thick x=0.18 films show metallic behaviour with large magnetoresistance. The crack-free x=0.3 films on LSAT undergo an insulator-to-metal transition with increasing thickness and also show large magnetoresistance, both consistent with a percolative transport behaviour. The spin state of the Co ions appears to remain unchanged in the investigated doping range. (orig.)

  19. Theory of novel normal and superconducting states in doped oxide high-Tc superconductors

    International Nuclear Information System (INIS)

    Dzhumanov, S.

    2001-10-01

    A consistent and complete theory of the novel normal and superconducting (SC) states of doped high-T c superconductors (HTSC) is developed by combining the continuum model of carrier self-trapping, the tight-binding model and the novel Fermi-Bose-liquid (FBL) model. The ground-state energy of carriers in lightly doped HTSC is calculated within the continuum model and adiabatic approximation using the variational method. The destruction of the long-range antiferromagnetic (AF) order at low doping x≥ x cl ≅0.015, the formation of the in-gap states or bands and novel (bi)polaronic insulating phases at x c2 ≅0.06-0.08, and the new metal- insulator transition at x≅x c2 in HTSC are studied within the continuum model of impurity (defect) centers and large (bi)polarons by using the appropriate tight-binding approximations. It is found that the three-dimensional (3d) large (bi)polarons are formed at ε ∞ /ε 0 ≤0.1 and become itinerant when the (bi)polaronic insulator-to-(bi)polaronic metal transitions occur at x x c2 . We show that the novel pseudogapped metallic and SC states in HTSC are formed at x c2 ≤x≤x p ≅0.20-0.24. We demonstrate that the large polaronic and small BCS-like pairing pseudogaps opening in the excitation spectrum of underdoped (x c2 BCS =0.125), optimally doped (x BCS o ≅0.20) and overdoped (x>x o ) HTSC above T c are unrelated to superconductivity and they are responsible for the observed anomalous optical, transport, magnetic and other properties of these HTSC. We develop the original two-stage FBL model of novel superconductivity describing the combined novel BCS-like pairing scenario of fermions and true superfluid (SF) condensation scenario of composite bosons (i.e. bipolarons and cooperons) in any Fermi-systems, where the SF condensate gap Δ B and the BCS-like pairing pseudogap Δ F have different origins. The pair and single particle condensations of attracting 3d and two- dimensional (2d) composite bosons are responsible for

  20. Effects of Structural and Electronic Disorder in Topological Insulator Sb2Te3 Thin Films

    Science.gov (United States)

    Korzhovska, Inna

    Topological quantum matter is a unique and potentially transformative protectorate against disorder-induced backscattering. The ultimate disorder limits to the topological state, however, are still not known - understanding these limits is critical to potential applications in the fields of spintronics and information processing. In topological insulators spin-orbit interaction and time-reversal-symmetry invariance guarantees - at least up to a certain disorder strength - that charge transport through 2D gapless Dirac surface states is robust against backscattering by non-magnetic disorder. Strong disorder may destroy topological protection and gap out Dirac surface states, although recent theories predict that under severe electronic disorder a quantized topological conductance might yet reemerge. Very strong electronic disorder, however, is not trivial to install and quantify, and topological matter under such conditions thus far has not been experimentally tested. This thesis addresses the behavior of three-dimensional (3D) topological insulator (TI) films in a wide range of structural and electronic disorder. We establish strong positional disorder in thin (20-50 nm) Sb2Te 3 films, free of extrinsic magnetic dopants. Sb 2Te3 is a known 2nd generation topological insulator in the low-disorder crystalline state. It is also a known phase-change material that undergoes insulator-to-metal transition with the concurrent orders of magnitude resistive drop, where a huge range of disorder could be controllably explored. In this work we show that even in the absence of magnetic dopants, disorder may induce spin correlations detrimental to the topological state. Chapter 1 contains a brief introduction to the topological matter and describes the role played by disorder. This is followed by theory considerations and a survey of prior experimental work. Next we describe the motivation for our experiments and explain the choice of the material. Chapter 2 describes deposition

  1. EDITORIAL: Nanotechnology in vivo Nanotechnology in vivo

    Science.gov (United States)

    Demming, Anna

    2010-04-01

    -imaging labels [4]. A surface hydroxyl group renders silicon quantum dots soluble in water and the photoluminescence can be made stable with oxygen-passivation. In addition, researchers in Japan have demonstrated how the initially modest yield in the preparation of silicon quantum dots can be improved to tens of milligrams per batch, thus further promoting their application in bio-imaging [5]. In the search for non-toxic quantum dots, researchers at the Amrita Centre for Nanoscience in India have prepared heavy metal-free quantum dot bio-probes based on single phase ZnS [6]. The quantum dots are selectively doped with metals, transition metals and halides to provide tuneable luminescence properties, and they are surface conjugated with folic acid for cancer targeting. The quantum dots were demonstrated to be water-soluble, non-toxic in normal and cancer cell lines, and have bright, tuneable luminescence. So far most of the quantum dots developed for bio-imaging have had excitation and emission wavelengths in the visible spectrum, which is highly absorbed by tissue. This limits imaging with these quantum dots to superficial tissues. This week, researchers in China and the US reported work developing functionalized dots for in vivo tumour vasculature in the infrared part of the spectrum [7]. In addition the quantum dots were functionalised with glycine-aspartic acid (RGD) peptides, which target the vasculature of almost all types of growing tumours, unlike antibody- or aptamer-mediated targeting strategies that are specific to a particular cancer type. In this issue, researchers in China and the US demonstrate a novel type of contrast agent for ultrasonic tumour imaging [8]. Contrast-enhanced ultrasonic tumour imaging extends the diagnostic and imaging capabilities of traditional techniques. The use of nanoparticles as ultrasound contrast agents exploits the presence of open pores in the range of 380 to 780 nm in tumour blood vessels, which enhance the permeability and retention

  2. HISTORICAL MEMOIR: The play of light in crystals

    Science.gov (United States)

    Zakharchenya, Boris Petrovitch

    2008-11-01

    important for modern microelectronics. Here I will mention just one: the discovery of trions, where a hole interacts with not one but two electrons. It is on the existence of trions that the hopes of creating quantum computers depend. I cannot count myself among the ardent followers of this idea, but who knows? Exciton spectra have been observed not only in semiconductors but also in ionic crystals (e.g. rock-salt, NaCl), molecular crystals, rare-earth and actinoid salt crystals, and in polymers (biological ones included). Nevertheless, it was only after the works of Gross and his colleagues that experimentalists became aware that those are the spectra of the quasiparticle exciton. That is strange, since the theory of such excitons was developed at the end of the 1940s by A Davydov who had been working in Kiev alongside experimentalists who were struggling to comprehend his ideas. Concluding my brief account of excitons, I would like to recall Gross once more. He taught me to love not only science, but music and art as well. Most of all, in painting he valued innovation and quest. He was attracted by avant-gardism as was Don Quixote by windmills. When I happen to visit New York, I always go to the Museum of Modern Art and often appreciate, as if with Gross' eyes, the unlooked-for 'moves' and 'tricks' of the avant-gardists. I've always been amazed that, sometime no later than 1920, our Alexander Rodchenko created a composition entitled Planes reflecting light. This is a three-dimensional piece made of copper and cardboard strips rendering our notion of the planetary model of the atom from which quanta of light fly out like Nabokov's butterflies. Bohr and Sommerfeld had suggested the planetary atomic model only in 1916, so how could the artist perceive the structure of microcosm before the majority of physicists did? As Shakespeare knew long ago, the world of human knowledge is full of wonders.

  3. Çan Yöresi Geçiş Dönemi Uygulamalarından Olan Evlenme Ritüelleri Üzerine On the Marriage Rituals of Transition Period Traditions in Çan District

    Directory of Open Access Journals (Sweden)

    Hamdi GÜLEÇ

    2012-09-01

    Full Text Available Çan is one of the most developed districts of Çanakkale province. The exact date of the district’s foundation has not been determined. Ruins belonging to ancient age have been found in the district and around. Çan region was called Sergis in Roman period. This region was annexed to Ottoman in XIV century. At first, it was a sub-district center dependent to Biga sanjak, and then in 1945 it was separated from Biga and became a district center dependent to Çanakkale. The district land has a rugged terrain. 62% of district square is forest, 32% is agricultural land, and 3% is pasture land and settlement. The ground of Çan district is formed from volcanic and sedimentary. District has a very rich source of metal. Transition climate, between Mediterranean and Black-sea climates, usually dominates the district. It generally rains in fall, winter and spring (Briefing report of Çan administrative district within a province – Türker, 2010. As a result of rapid population, growth depending on industrialization, migrations to the district center have been occurred especially from the neighbor villages and other settlements. As the traditional cultural structure dominates to the district, people have a life style shaped by the religion and social customs. Charity activity of village is carried out in the months of spring and summer in the region. Everybody in the village participates in this organization, which is also called farmers’ holiday (Güleç and Türker 2012, 1334.Native population is called as Manav in district center and villages. And also, the people who immigrated from the Balkans and settled there are called muhajir. Some ethnics groups such as Pomak and Kırcali also exists in the region. People living in mountains and high regions are known as Yoruk (Briefing report of Çan administrative district within a province – Türker, 2010. Çan, the district of Çanakkale, is very rich and productive in Folklore. It has an important