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Sample records for high o3 conditions

  1. La-doped Al2O3 supported Au nanoparticles: highly active and selective catalysts for PROX under PEMFC operation conditions.

    Lin, Qingquan; Qiao, Botao; Huang, Yanqiang; Li, Lin; Lin, Jian; Liu, Xiao Yan; Wang, Aiqin; Li, Wen-Cui; Zhang, Tao

    2014-03-14

    La-doped γ-Al2O3 supported Au catalysts show high activity and selectivity for the PROX reaction under PEMFC operation conditions. The superior performance is attributed to the formation of LaAlO3, which suppresses H2 oxidation and strengthens CO adsorption on Au sites, thereby improving competitive oxidation of CO at elevated temperature.

  2. B2O3/Al2O3 as a new, highly efficient and reusable heterogeneous catalyst for the selective synthesis of β-enamino ketones and esters under solvent-free conditions

    Chen, Jiu-Xi; Gao, Wen-Xia; Jin, Hui-Le; Ding, Jin-Chang; Wu, Hua-Yue

    2010-01-01

    Boron oxide adsorbed on alumina (B 2 O 3 /Al 2 O 3 ) has been found to be a new and highly efficient heterogeneous catalyst for the synthesis of β-enamino ketones and esters by the enamination of various primary and secondary amines with β-dicarbonyl compounds under solvent-free conditions. The important features of this methodology are broad substrate scope, high yield, no requirement of metal catalysts, high regio- and chemoselectivity and environmental friendliness. In addition, the catalyst could be recovered easily after the reactions and reused without evident loss of reactivity. (author)

  3. High-pressure crystal structure of elastically isotropic CaTiO3 perovskite under hydrostatic and non-hydrostatic conditions.

    Zhao, Jing; Ross, Nancy L; Wang, Di; Angel, Ross J

    2011-11-16

    The structural evolution of orthorhombic CaTiO3 perovskite has been studied using high-pressure single-crystal x-ray diffraction under hydrostatic conditions up to 8.1 GPa and under a non-hydrostatic stress field formed in a diamond anvil cell (DAC) up to 4.7 GPa. Under hydrostatic conditions, the TiO6 octahedra become more tilted and distorted with increasing pressure, similar to other 2:4 perovskites. Under non-hydrostatic conditions, the experiments do not show any apparent difference in the internal structural variation from hydrostatic conditions and no additional tilts and distortions in the TiO6 octahedra are observed, even though the lattice itself becomes distorted due to the non-hydrostatic stress. The similarity between the hydrostatic and non-hydrostatic cases can be ascribed to the fact that CaTiO3 perovskite is nearly elastically isotropic and, as a consequence, its deviatoric unit-cell volume strain produced by the non-hydrostatic stress is very small; in other words, the additional octahedral tilts relevant to the extra unit-cell volume associated with the deviatoric unit-cell volume strain may be totally neglected. This study further addresses the role that three factors--the elastic properties, the crystal orientation and the pressure medium--have on the structural evolution of an orthorhombic perovskite loaded in a DAC under non-hydrostatic conditions. The influence of these factors can be clearly visualized by plotting the three-dimensional distribution of the deviatoric unit-cell volume strain in relation to the cylindrical axis of the DAC and indicates that, if the elasticity of a perovskite is nearly isotropic as it is for CaTiO3, the other two factors become relatively insignificant.

  4. High-pressure crystal structure of elastically isotropic CaTiO3 perovskite under hydrostatic and non-hydrostatic conditions

    Zhao Jing; Ross, Nancy L; Wang, Di; Angel, Ross J

    2011-01-01

    The structural evolution of orthorhombic CaTiO 3 perovskite has been studied using high-pressure single-crystal x-ray diffraction under hydrostatic conditions up to 8.1 GPa and under a non-hydrostatic stress field formed in a diamond anvil cell (DAC) up to 4.7 GPa. Under hydrostatic conditions, the TiO 6 octahedra become more tilted and distorted with increasing pressure, similar to other 2:4 perovskites. Under non-hydrostatic conditions, the experiments do not show any apparent difference in the internal structural variation from hydrostatic conditions and no additional tilts and distortions in the TiO 6 octahedra are observed, even though the lattice itself becomes distorted due to the non-hydrostatic stress. The similarity between the hydrostatic and non-hydrostatic cases can be ascribed to the fact that CaTiO 3 perovskite is nearly elastically isotropic and, as a consequence, its deviatoric unit-cell volume strain produced by the non-hydrostatic stress is very small; in other words, the additional octahedral tilts relevant to the extra unit-cell volume associated with the deviatoric unit-cell volume strain may be totally neglected. This study further addresses the role that three factors-the elastic properties, the crystal orientation and the pressure medium-have on the structural evolution of an orthorhombic perovskite loaded in a DAC under non-hydrostatic conditions. The influence of these factors can be clearly visualized by plotting the three-dimensional distribution of the deviatoric unit-cell volume strain in relation to the cylindrical axis of the DAC and indicates that, if the elasticity of a perovskite is nearly isotropic as it is for CaTiO 3 , the other two factors become relatively insignificant. (paper)

  5. High frequency time modulation of neutrons by LiNbO3 crystals with surface acoustic waves excited under the diffraction condition

    Takahashi, Toshio; Granzer, E.; Kikuta, Seishi; Tomimitsu, Hiroshi; Doi, Kenji.

    1985-01-01

    High frequency time modulation of neutrons was investigated by using Y-cut LiNbO 3 crystals with surface acoustic waves excited. A double crystal arrangement of (+, -) parallel setting was used for 030 symmetric Bragg-case reflections. Synchronized standing waves with a resonance frequency of 14.26 MHz were excited on the both crystals. Variation of the diffracted intensity with phase difference between two standing waves was studied. The result showed an intensity change of diffracted neutrons with twice the resonance frequency. (author)

  6. High quality TbMnO3 films deposited on YAlO3

    Glavic, Artur; Voigt, Joerg; Persson, Joerg; Su, Yixi; Schubert, Juergen; Groot, Joost de; Zande, Willi; Brueckel, Thomas

    2011-01-01

    Research highlights: → We found a good substrate and suitable deposition parameters to create untwinned, epitaxial thin films of TbMnO 3 . → Laboratory experiments prove the crystalline quality of the films. → We were able to measure the micro magnetic structure in the films by polarized neutron diffraction (to our knowledge the first neutron investigations on TbMnO 3 thin films). - Abstract: High quality thin films of TbMnO 3 were grown by pulsed laser deposition on orthorhombicYAlO 3 (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04 o and 0.2 o for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO 3 .

  7. High-pressure phase transition in Ho2O3

    Lonappan, Dayana; Shekar, N.V. Chandra; Ravindran, T.R.; Sahu, P. Ch.

    2010-01-01

    High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho 2 O 3 ) have been carried out up to a pressure of ∼17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16 GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370 cm -1 disappears around the similar transition pressure. The bulk modulus of the parent phase is reported.

  8. O3, CH4, CO2, CO, NO2 and NMHC aircraft measurements in the Uinta Basin oil and gas region under low and high ozone conditions in winter 2012 and 2013

    S. J. Oltmans

    2016-10-01

    Full Text Available Abstract Instrumented aircraft measuring air composition in the Uinta Basin, Utah, during February 2012 and January-February 2013 documented dramatically different atmospheric ozone (O3 mole fractions. In 2012 O3 remained near levels of ∼40 ppb in a well-mixed 500–1000 m deep boundary layer while in 2013, O3 mole fractions >140 ppb were measured in a shallow (∼200 m boundary layer. In contrast to 2012 when mole fractions of emissions from oil and gas production such as methane (CH4, non-methane hydrocarbons (NMHCs and combustion products such as carbon dioxide (CO2 were moderately elevated, in winter 2013 very high mole fractions were observed. Snow cover in 2013 helped produce and maintain strong temperature inversions that capped a shallow cold pool layer. In 2012, O3 and CH4 and associated NMHCs mole fractions were not closely related. In 2013, O3 mole fractions were correlated with CH4 and a suite of NMHCs identifying the gas field as the primary source of the O3 precursor NMHC emissions. In 2013 there was a strong positive correlation between CH4 and CO2 suggesting combustion from oil and natural gas processing activities. The presence of O3 precursor NMHCs through the depth of the boundary layer in 2013 led to O3 production throughout the layer. In 2013, O3 mole fractions increased over the course of the week-long episodes indicating O3 photochemical production was larger than dilution and deposition rates, while CH4 mole fractions began to level off after 3 days indicative of some air being mixed out of the boundary layer. The plume of a coal-fired power plant located east of the main gas field was not an important contributor to O3 or O3 precursors in the boundary layer in 2013.

  9. Highly conductive homoepitaxial Si-doped Ga2O3 films on (010) β-Ga2O3 by pulsed laser deposition

    Leedy, Kevin D.; Chabak, Kelson D.; Vasilyev, Vladimir; Look, David C.; Boeckl, John J.; Brown, Jeff L.; Tetlak, Stephen E.; Green, Andrew J.; Moser, Neil A.; Crespo, Antonio; Thomson, Darren B.; Fitch, Robert C.; McCandless, Jonathan P.; Jessen, Gregg H.

    2017-07-01

    Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O3 and (0001) Al2O3 substrates. Films deposited on β-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline β-Ga2O3 with a preferred (20 1 ¯ ) orientation. An average conductivity of 732 S cm-1 with a mobility of 26.5 cm2 V-1 s-1 and a carrier concentration of 1.74 × 1020 cm-3 was achieved for films deposited at 550 °C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices.

  10. Leaching of Al2O3 in simulated repository conditions

    Svensson, B.-M.; Dahl, L.

    1978-06-01

    Al 2 O 3 material has been leached at 90 deg C in: simulated ground water at pH 8.5, embedded in bentonite + silica sand saturated with the same water, and in simulated ground water at pH 6 and pH 10. Leaching periods varied from 30 days to 300 days. We observed slight weight increments in all cases from deposits on samples from the environment. These mask weight losses from Al 2 O 3 that may have occurred. (author)

  11. Polymorphous GdScO3 as high permittivity dielectric

    Schäfer, A.; Rahmanizadeh, K.; Bihlmayer, G.; Luysberg, M.; Wendt, F.; Besmehn, A.; Fox, A.

    2015-01-01

    Four different polymorphs of GdScO 3 are assessed theoretically and experimentally with respect to their suitability as a dielectric. The calculations carried out by density functional theory reveal lattice constants, band gaps and the energies of formation of three crystal phases. Experimentally all three crystal phases and the amorphous phase can be realized as thin films by pulsed laser deposition using various growth templates. Their respective crystal structures are confirmed by X-ray diffraction and transmission electron microscopy reflecting the calculated lattice constants. X-ray photoelectron spectroscopy unveils the band gaps of the different polymorphs of GdScO 3 which are above 5 eV for all films demonstrating good insulating properties. From capacitance voltage measurements, high permittivities of up to 27 for hexagonal GdScO 3 are deduced. - Highlights: • Different epitaxial polymorph phases of GdScO 3 were grown by pulsed laser deposition. • The cubic phase of GdScO 3 is reported for the first time. • All phases are proven to be useful for the use in silicon based and III–V based microelectronic devices.

  12. The high temperature behavior of In2O3

    Wit, J.H.W. de

    The electrical conductivity of In2O3 has been measured up to 1400°C in air. The temperature dependence of the conductivity at high temperatures yields an activation energy of 1.5 ± 0.1 eV. This activation energy is interpreted in terms of a nonstoichiometric decomposition of the compound. This

  13. High-pressure synthesis and structural, physical properties of CaIr1-xPtxO3 and CaIr1-xRhxO3

    Hirai, S.; Bromiley, G. D.; Klemme, S.; Irifune, T.; Ohfuji, H.; Attfield, P.; Nishiyama, N.

    2010-12-01

    Since the discovery of the perovskite to post-perovskite transition in MgSiO3 in a laser-heated DAC, wide attention has been focussed on the post-perovskite phase of MgSiO3. This is because the post-perovskite phase is likely to play a key role in Earth’s lowermost mantle, and because the perovskite to post-perovskite transition can explain many features of the D” seismic discontinuity. While it is meaningful to conduct further studies of MgSiO3, the post-perovskite phase of MgSiO3 cannot be quenched to ambient pressure/temperature conditions. Thus, further studies must be conducted using analogue compounds of MgSiO3 post-perovskite, which are quenchable to ambient pressure/temperature conditions. The post-perovskite phase of MgSiO3 crystallizes in a layered structure with CaIrO3-structure. Therefore, it is useful to investigate compounds with CaIrO3-structure. There are only four quenchable oxides with CaIrO3-structure reported to date: CaIrO3, CaPtO3, CaRhO3 and CaRuO3. CaIrO3 can be synthesized at ambient pressure, whilst the other three oxides can only be obtained at high pressure/temperature conditions using a multi-anvil apparatus. Further studies on these materials have revealed structural phase transitions at high P-T and a metal-insulator transition by hole doping. In the case of CaIrO3, The post-perovskite phase of CaIrO3 synthesized at 2GPa, 1373K transforms into a perovskite phase at 2GPa, 1673K. In other words, the perovskite phase can be synthesized at temperatures higher than those needed for synthesizing the post-perovskite phase. This is also the case for CaRhO3 (6GPa, 1873K) and CaRuO3 (23GPa, 1343K), while CaPtO3 remained post-perovskite at higher temperatures. We have succeeded in synthesizing solid solutions between CaIrO3, CaPtO3 and CaRhO3. We have found the systematic change in structural and physical properties of post-perovskite oxides, with composition and P-T, which broadens the future opportunity for studying post-perovskite systems

  14. Synthesis and electrical properties of BaBiO3 and high resistivity BaTiO3–BaBiO3 ceramics

    Nitish Kumar

    2016-12-01

    Full Text Available Ceramics of the composition BaBiO3 (BB were sintered in oxygen to obtain a single phase with monoclinic I2/m symmetry as suggested by high-resolution X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states — 3+ and 5+. Optical spectroscopy showed presence of a direct bandgap at ∼ 2.2eV and a possible indirect bandgap at ∼ 0.9eV. This combined with determination of the activation energy for conduction of 0.25eV, as obtained from ac impedance spectroscopy, suggested that a polaron-mediated conduction mechanism was prevalent in BB. The BB ceramics were crushed, mixed with BaTiO3 (BT, and sintered to obtain BT–BB solid solutions. All the ceramics had tetragonal symmetry and exhibited a normal ferroelectric-like dielectric response. Using ac impedance and optical spectroscopy, it was shown that resistivity values of BT–BB were orders of magnitude higher than BT or BB alone, indicating a change in the fundamental defect equilibrium conditions. A shift in the site occupancy of Bi to the A-site is proposed to be the mechanism for the increased electrical resistivity.

  15. Highly flexible, conductive and transparent MoO3/Ag/MoO3 multilayer electrode for organic photovoltaic cells

    Abachi, T.; Cattin, L.; Louarn, G.; Lare, Y.; Bou, A.; Makha, M.; Torchio, P.

    2013-01-01

    MoO 3 /Ag/MoO 3 (MAM) multilayer structures were deposited by vacuum evaporation on polyethylene terephthalate (PET) substrate. We demonstrate that, as in the case of glass substrate, the sheet resistance of such structures depends significantly on the Ag film deposition rate. When it is deposited between 0.2 and 0.4 nm/s, an Ag thickness of 11 nm allows achieving sheet resistance of 13 Ω/sq and an averaged transmission of 74%. A study of the influence of the PET substrate on the optimum MoO 3 thicknesses was done. A good qualitative agreement between the theoretical calculations of the variation of the optical transmittance of the MoO 3 /Ag/MoO 3 structures is obtained. The optimum MAM structures MoO 3 (17.5 nm)/Ag (11 nm)/MoO 3 (35 nm) has a factor of merit F M = 4.21 10 −3 (Ω/sq) −1 . Proven by the scotch test the MAM structures exhibit a good adhesion to the PET substrates. The MAM structures were also submitted to bending tests. For outer bending, the samples exhibit no variation of their resistance value, while for inner bending there is a small increase of the resistance of the MAM structures. However this increasing is smaller than that exhibited by Indium Tin Oxide. When the PET/MAM structures are used as anode in organic photovoltaic cells, it is shown that the need to use thicker Ag films inside the multilayer and to cover the MAM with Au to obtain promising Current density vs Voltage characteristics is due to the heating of the PET substrate during the deposition process. - Highlights: • MoO 3 /Ag/MoO 3 structures deposited on polyethylene terephthalate substrate. • MoO 3 /Ag/MoO 3 structures deposited by vacuum evaporation. • The Ag deposition rate influences the properties of the structures. • The MoO 3 /Ag/MoO 3 optimum structure has a factor of merit F M = 4.21 10 −3 (Ω/sq) −1 . • The MoO 3 /Ag/MoO 3 structures exhibit a high flexibility

  16. High temperature oxidation-sulfidation behavior of Cr-Al2O3 and Nb-Al2O3 composites densified by spark plasma sintering

    Saucedo-Acuna, R.A.; Monreal-Romero, H.; Martinez-Villafane, A.; Chacon-Nava, J.G.; Arce-Colunga, U.; Gaona-Tiburcio, C.; De la Torre, S.D.

    2007-01-01

    The high temperature oxidation-sulfidation behavior of Cr-Al 2 O 3 and Nb-Al 2 O 3 composites prepared by mechanical alloying (MA) and spark plasma sintering (SPS) has been studied. These composite powders have a particular metal-ceramic interpenetrating network and excellent mechanical properties. Oxidation-sulfidation tests were carried out at 900 deg. C, in a 2.5%SO 2 + 3.6%O 2 + N 2 (balance) atmosphere for 48 h. The results revealed the influence of the sintering conditions on the specimens corrosion resistance, i.e. the Cr-Al 2 O 3 and Nb-Al 2 O 3 composite sintered at 1310 deg. C/4 min showed better corrosion resistance (lower weight gains) compared with those found for the 1440 deg. C/5 min conditions. For the former composite, a protective Cr 2 O 3 layer immediately forms upon heating, whereas for the later pest disintegration was noted. Thus, under the same sintering conditions the Nb-Al 2 O 3 composites showed the highest weight gains. The oxidation products were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy

  17. Lifetime laser damage performance of β-Ga2O3 for high power applications

    Jae-Hyuck Yoo

    2018-03-01

    Full Text Available Gallium oxide (Ga2O3 is an emerging wide bandgap semiconductor with potential applications in power electronics and high power optical systems where gallium nitride and silicon carbide have already demonstrated unique advantages compared to gallium arsenide and silicon-based devices. Establishing the stability and breakdown conditions of these next-generation materials is critical to assessing their potential performance in devices subjected to large electric fields. Here, using systematic laser damage performance tests, we establish that β-Ga2O3 has the highest lifetime optical damage performance of any conductive material measured to date, above 10 J/cm2 (1.4 GW/cm2. This has direct implications for its use as an active component in high power laser systems and may give insight into its utility for high-power switching applications. Both heteroepitaxial and bulk β-Ga2O3 samples were benchmarked against a heteroepitaxial gallium nitride sample, revealing an order of magnitude higher optical lifetime damage threshold for β-Ga2O3. Photoluminescence and Raman spectroscopy results suggest that the exceptional damage performance of β-Ga2O3 is due to lower absorptive defect concentrations and reduced epitaxial stress.

  18. Lifetime laser damage performance of β -Ga2O3 for high power applications

    Yoo, Jae-Hyuck; Rafique, Subrina; Lange, Andrew; Zhao, Hongping; Elhadj, Selim

    2018-03-01

    Gallium oxide (Ga2O3) is an emerging wide bandgap semiconductor with potential applications in power electronics and high power optical systems where gallium nitride and silicon carbide have already demonstrated unique advantages compared to gallium arsenide and silicon-based devices. Establishing the stability and breakdown conditions of these next-generation materials is critical to assessing their potential performance in devices subjected to large electric fields. Here, using systematic laser damage performance tests, we establish that β-Ga2O3 has the highest lifetime optical damage performance of any conductive material measured to date, above 10 J/cm2 (1.4 GW/cm2). This has direct implications for its use as an active component in high power laser systems and may give insight into its utility for high-power switching applications. Both heteroepitaxial and bulk β-Ga2O3 samples were benchmarked against a heteroepitaxial gallium nitride sample, revealing an order of magnitude higher optical lifetime damage threshold for β-Ga2O3. Photoluminescence and Raman spectroscopy results suggest that the exceptional damage performance of β-Ga2O3 is due to lower absorptive defect concentrations and reduced epitaxial stress.

  19. The behavior of ZrO_2/20%Y_2O_3 and Al_2O_3 coatings deposited on aluminum alloys at high temperature regime

    Pintilei, G.L.; Crismaru, V.I.; Abrudeanu, M.; Munteanu, C.; Baciu, E.R.; Istrate, B.; Basescu, N.

    2015-01-01

    Highlights: • In both the ZrO_2/20%Y_2O_3 and Al_2O_3 coatings the high temperature caused a decrease of pores volume and a lower thickness of the interface between successive splats. • The NiCr bond layer in the sample with a ZrO_2/20%Y_2O_3 suffered a fragmentation due to high temperature exposure and thermal expansion which can lead to coating exfoliation. • The NiCr bond layer in the sample with an Al_2O_3 coating showed an increase of pore volume due to high temperature. - Abstract: Aluminum alloy present numerous advantages like lightness, high specific strength and diversity which recommend them to a high number of applications from different fields. In extreme environments the protection of aluminum alloys is difficult and requires a high number of requirements like high temperature resistance, thermal fatigue resistance, corrosion fatigue resistance and galvanic corrosion resistance. To obtain these characteristics coatings can be applied to the surfaces so they can enhance the mechanical and chemical properties of the parts. In this paper two coatings were considered for deposition on an AA2024 aluminum alloy, ZrO_2/20%Y_2O_3 and Al_2O_3. To obtain a better adherence of the coating to the base material an additional bond layer of NiCr is used. Both the coatings and bond layer were deposited by atmospheric plasma spraying on the samples. The samples were subjected to a temperature of 500 °C and after that slowly cooled to room temperature. The samples were analyzed by electron microscopy and X-ray diffraction to determine the morphological and phase changes that occurred during the temperature exposure. To determine the stress level in the parts due to thermal expansion a finite element analysis was performed in the same conditions as the tests.

  20. High mobility of the strongly confined hole gas in AgTaO3/SrTiO3

    Nazir, Safdar

    2012-05-18

    A theoretical study of the two-dimensional hole gas at the (AgO)−/(TiO2)0 p-type interface in the AgTaO3/SrTiO3 (001) heterostructure is presented. The Ag 4d states strongly hybridize with the O 2p states and contribute to the hole gas. It is demonstrated that the holes are confined to an ultra thin layer (∼4.9Å) with a considerable carrier density of ∼1014cm−2. We estimate a hole mobility of 18.6 cm2 V−1 s−1, which is high enough to enable device applications.

  1. High charge carrier density at the NaTaO3/SrTiO3 hetero-interface

    Nazir, Safdar

    2011-08-05

    The formation of a (quasi) two-dimensional electron gas between the band insulators NaTaO3 and SrTiO3 is studied by means of the full-potential linearized augmented plane-wave method of density functional theory. Optimization of the atomic positions points to only small changes in the chemical bonding at the interface. Both the p-type (NaO)−/(TiO2)0 and n-type (TaO2)+/(SrO)0 interfaces are found to be metallic with high charge carrier densities. The effects of O vacancies are discussed. Spin-polarized calculations point to the formation of isolated O 2pmagnetic moments, located in the metallic region of the p-type interface.

  2. High mobility of the strongly confined hole gas in AgTaO3/SrTiO3

    Nazir, Safdar; Schwingenschlö gl, Udo; Upadhyay Kahaly, M.

    2012-01-01

    A theoretical study of the two-dimensional hole gas at the (AgO)−/(TiO2)0 p-type interface in the AgTaO3/SrTiO3 (001) heterostructure is presented. The Ag 4d states strongly hybridize with the O 2p states and contribute to the hole gas. It is demonstrated that the holes are confined to an ultra thin layer (∼4.9Å) with a considerable carrier density of ∼1014cm−2. We estimate a hole mobility of 18.6 cm2 V−1 s−1, which is high enough to enable device applications.

  3. Perovskite Nanoparticle-Sensitized Ga2O3 Nanorod Arrays for CO Detection at High Temperature.

    Lin, Hui-Jan; Baltrus, John P; Gao, Haiyong; Ding, Yong; Nam, Chang-Yong; Ohodnicki, Paul; Gao, Pu-Xian

    2016-04-13

    Noble metal nanoparticles are extensively used for sensitizing metal oxide chemical sensors through the catalytic spillover mechanism. However, due to earth-scarcity and high cost of noble metals, finding replacements presents a great economic benefit. Besides, high temperature and harsh environment sensor applications demand material stability under conditions approaching thermal and chemical stability limits of noble metals. In this study, we employed thermally stable perovskite-type La(0.8)Sr(0.2)FeO3 (LSFO) nanoparticle surface decoration on Ga2O3 nanorod array gas sensors and discovered an order of magnitude enhanced sensitivity to carbon monoxide at 500 °C. The LSFO nanoparticle catalysts was of comparable performance to that achieved by Pt nanoparticles, with a much lower weight loading than Pt. Detailed electron microscopy and X-ray photoelectron spectroscopy studies suggested the LSFO nanoparticle sensitization effect is attributed to a spillover-like effect associated with the gas-LSFO-Ga2O3 triple-interfaces that spread the negatively charged surface oxygen ions from LSFO nanoparticles surfaces over to β-Ga2O3 nanorod surfaces with faster surface CO oxidation reactions.

  4. High troposphere O3 filament at mid-latitude: a BORTAS campaign case study

    Aruffo, Eleonora; Peterson, David; Di Carlo, Piero; Biancofiore, Fabio; Busilacchio, Marcella; Dari Salisburgo, Cesare; Giammaria, Franco; Bauguitte, Stephane; Lee, James; Moller, Sarah; Hopkins, James; Punjabi, Shalini; Lewis, Alistair C.; Palmer, Paul; Hyer, Edward

    2016-04-01

    During a flight (B625, 24 July 2011) of the BORTAS campaign (BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites, Nova Scotia, Canada, July-August 2011), an increase in the ozone (O3) concentrations has been observed at high altitude (about 7.5 Km a.s.l.) correlated with a significant growth of total peroxy nitrates (∑PNs), CO, NO2, NOy, black carbon (BC), isoprene and other species. We will illustrate the data analysis, the Hysplit back trajectories calculation and the analysis of the meteorological/physical conditions occurred during this case study in order to demonstrate that the O3 filament measured at high altitude over the Atlantic Ocean (between Nova Scotia and the Gulf of St. Lawrence) is a consequence of boreal biomass burning fires.

  5. Interface properties of SrTiO3-based heterostructures studied by spectroscopy and high-resolution microscopy

    Pfaff, Florian Georg

    2017-01-01

    Oxide heterostructures can exhibit a variety of unexpected electronic and magnetic phenomena at their interfaces. A prominent example is the interface in LaAlO 3 /SrTiO 3 heterostructures where a two-dimensional electron system (2DES) forms if the LaAlO 3 thickness equals or exceeds a critical thickness of four unit cells. Similar to LaAlO 3 /SrTiO 3 an interface 2DES above a critical overlayer thickness has been observed in γ-Al 2 O 3 /SrTiO 3 . However, the electron mobility as well as the sheet carrier density exceed those of LaAlO 3 /SrTiO 3 heterostructures by more than one order of magnitude. This thesis is concerned with the growth and the characterization of these two types of interface systems with the main focus on the analysis of the physical properties at the interface and the understanding of their leading mechanisms. In regard to the sample fabrication it is demonstrated in the present thesis that the hitherto established growth routine of LaAlO 3 /SrTiO 3 by pulsed laser deposition has to be altered and optimized for the growth of γ-Al 2 O 3 . It is shown that growth monitoring by analyzing reflection high energy electron diffraction (RHEED) intensity oscillations is hindered by the formation of surface wave resonances. In order to avoid this effect, a modified growth geometry has to be used whereby also in this heterostructure systems monitoring of the layer-by-layer growth of γ-Al 2 O 3 /SrTiO 3 heterostructures by electron diffraction can be achieved. A so-called electronic reconstruction is discussed as the possible driving mechanism for the 2DES formation in LaAlO 3 /SrTiO 3 . In this scenario, the built-up potential within the polar LaAlO 3 overlayer is compensated by a charge transfer from the sample surface to the top most layers of the non-polar SrTiO 3 substrate. Furthermore, the properties of these heterostructures strongly depend on the used growth conditions. In the present work, for instance, a significant increase in the charge

  6. Improvement of High-Temperature Stability of Al2O3/Pt/ZnO/Al2O3 Film Electrode for SAW Devices by Using Al2O3 Barrier Layer

    Xingpeng Liu

    2017-12-01

    Full Text Available In order to develop film electrodes for the surface acoustic wave (SAW devices operating in harsh high-temperature environments, novel Al2O3/Pt/ZnO/Al2O3 multilayered film electrodes were prepared by laser molecular beam epitaxy (LMBE at 150 °C. The first Al2O3 layer was used as a barrier layer to prevent the diffusion of Ga, La, and Si atoms from the La3Ga5SiO14 (LGS substrate to the film electrode and thus improved the crystalline quality of ZnO and Pt films. It was found that the resistance of the Al2O3/Pt/ZnO/Al2O3 electrode did not vary up to a temperature of 1150 °C, suggesting a high reliability of electrode under harsh high-temperature environments. The mechanism of the stable resistance of the Al2O3/Pt/ZnO/Al2O3 film electrodes at high temperature was investigated by analyzing its microstructure. The proposed Al2O3/Pt/ZnO/Al2O3 film electrode has great potential for application in high-temperature SAW devices.

  7. High charge carrier density at the NaTaO3/SrTiO3 hetero-interface

    Nazir, Safdar; Schwingenschlö gl, Udo

    2011-01-01

    The formation of a (quasi) two-dimensional electron gas between the band insulators NaTaO3 and SrTiO3 is studied by means of the full-potential linearized augmented plane-wave method of density functional theory. Optimization of the atomic positions

  8. Post-perovskite transitions in CaB4+O3 at high pressure

    Akaogi, M; Shirako, Y; Kojitani, H; Takamori, S; Yamaura, K; Takayama-Muromachi, E

    2010-01-01

    High-pressure phase transitions in CaRhO 3 were examined using a multianvil apparatus up to 27 GPa and 1930 o C. CaRhO 3 perovskite transforms to post-perovskite via a monoclinic intermediate phase with increasing pressure. Volume changes for the transitions of perovskite - intermediate phase and of intermediate phase - post-perovskite are -1.1 and -0.7 %, respectively. CaRhO 3 post-perovskite is the fourth quenchable post-perovskite oxide found so far. By high-temperature calorimetric experiments, enthalpy of the perovskite - post-perovskite transition in CaRuO 3 was measured as 15.2±3.3 kJ/mol. Combining the datum with those of CaIrO 3 , it is shown that CaIrO 3 perovskite is energetically less stable than CaRuO 3 perovskite. This is consistent with the fact that orthorhombic distortion of CaIrO 3 perovskite is larger than CaRuO 3 , as indicated with the tilt-angle of octahedral framework of perovskite structure. The transition pressure from perovskite to post-perovskite in CaBO 3 (B = Ru, Rh, Ir) increases almost linearly with decreasing the tilt-angle, suggesting that the perovskite - post-perovskite transition may result from instability of the perovskite structure with pressure.

  9. High Power Ga2O3-based Schottky Diode, Phase I

    National Aeronautics and Space Administration — This SBIR Program will develop a new generation of radiation hard high-power high-voltage Ga2O3-based Schottky diode, which is suitable for applications in the space...

  10. Demonstration of high mobility and quantum transport in modulation-doped β-(AlxGa1-x)2O3/Ga2O3 heterostructures

    Zhang, Yuewei; Neal, Adam; Xia, Zhanbo; Joishi, Chandan; Johnson, Jared M.; Zheng, Yuanhua; Bajaj, Sanyam; Brenner, Mark; Dorsey, Donald; Chabak, Kelson; Jessen, Gregg; Hwang, Jinwoo; Mou, Shin; Heremans, Joseph P.; Rajan, Siddharth

    2018-04-01

    In this work, we demonstrate a high mobility two-dimensional electron gas (2DEG) formed at the β-(AlxGa1-x)2O3/Ga2O3 interface through modulation doping. Shubnikov-de Haas (SdH) oscillations were observed in the modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure, indicating a high-quality electron channel formed at the heterojunction interface. The formation of the 2DEG channel was further confirmed by the weak temperature dependence of the carrier density, and the peak low temperature mobility was found to be 2790 cm2/Vs, which is significantly higher than that achieved in bulk-doped Beta-phase Gallium Oxide (β-Ga2O3). The observed SdH oscillations allowed for the extraction of the electron effective mass in the (010) plane to be 0.313 ± 0.015 m0 and the quantum scattering time to be 0.33 ps at 3.5 K. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure lays the foundation for future exploration of quantum physical phenomena and semiconductor device technologies based on the β-Ga2O3 material system.

  11. Synthesis, Characterization, and NIR Reflectance of Highly Dispersed NiTiO3 and NiTiO3/TiO2 Composite Pigments

    Yuping Tong

    2016-01-01

    Full Text Available The highly dispersed nanostructured NiTiO3 pigments and NiTiO3/TiO2 composite pigments can be synthesized at relative low temperature. The activation energy of crystal growth of NiTiO3 during calcinations via salt-assistant combustion method is 9.35 kJ/mol. The UV-vis spectra results revealed that the absorbance decreased with the increasing of calcinations temperature due to small size effect of nanometer particles. The optical data of NiTiO3 nanocrystals were analyzed at the near-absorption edge. SEM showed that the obtained NiTiO3 nanocrystals and NiTiO3/TiO2 nanocomposite were composed of highly dispersed spherical-like and spherical particles with uniform size distribution, respectively. The chromatic properties and diffuse reflectance of samples were investigated. The obtained NiTiO3/TiO2 composite samples have higher NIR reflectance than NiTiO3 pigments.

  12. The behavior of ZrO2/20%Y2O3 and Al2O3 coatings deposited on aluminum alloys at high temperature regime

    Pintilei, G. L.; Crismaru, V. I.; Abrudeanu, M.; Munteanu, C.; Baciu, E. R.; Istrate, B.; Basescu, N.

    2015-10-01

    Aluminum alloy present numerous advantages like lightness, high specific strength and diversity which recommend them to a high number of applications from different fields. In extreme environments the protection of aluminum alloys is difficult and requires a high number of requirements like high temperature resistance, thermal fatigue resistance, corrosion fatigue resistance and galvanic corrosion resistance. To obtain these characteristics coatings can be applied to the surfaces so they can enhance the mechanical and chemical properties of the parts. In this paper two coatings were considered for deposition on an AA2024 aluminum alloy, ZrO2/20%Y2O3 and Al2O3. To obtain a better adherence of the coating to the base material an additional bond layer of NiCr is used. Both the coatings and bond layer were deposited by atmospheric plasma spraying on the samples. The samples were subjected to a temperature of 500 °C and after that slowly cooled to room temperature. The samples were analyzed by electron microscopy and X-ray diffraction to determine the morphological and phase changes that occurred during the temperature exposure. To determine the stress level in the parts due to thermal expansion a finite element analysis was performed in the same conditions as the tests.

  13. Microwave-Hydrothermal Synthesis and Characterization of High-Purity Nb Doped BaTiO3 Nanocrystals

    A. Khanfekr

    2014-01-01

    Full Text Available The synthesis of Nb doped BaTiO3 has been investigated under Microwave-Hydrothermal (MH conditions in the temperature of 150°C for only 2 h using C16H36O4Ti, BaH2O2.8H2O and NbCl5 as Ba, Ti and  Nb sources, respectively.  Typical experiments performed on MH processing have not yet reported for Nb doped BaTiO3.  In the MH process, the formation of high purity nano tetragonal Nb-BaTiO3 was strongly enhanced. New hydrothermal method was used instead of the previous solid state reaction for the BaTiO3±Nb2O3 system. The new method uses high pressure to create nano dimension particles in a lower time and temperature. In case of the phase evolution studies, the XRD pattern measurements and Raman spectroscopy were performed. TEM and FE-SEM images were taken for the detailed analysis of the particle size, surface and morphology.  Synthesis of Nb doped BaTiO3 with the Microwave-hydrothermal provides an advantage of fast crystallization and reduced crystal size when compared to existing methods.

  14. Preparation and encapsulation performance of Al_2O_3-SiO_2-B_2O_3 glass-ceramic for high temperature thermal storage

    Li, Ruguang; Zhu, Jiaoqun; Zhou, Weibing; Cheng, Xiaomin; Liu, Fengli

    2017-01-01

    Highlights: • Al_2O_3-B_2O_3-SiO_2 has good chemical durability, corrosion resistance and dense structure. • The material rarely used in high temperature thermal storage. • The material was prepared and characterized in the paper. - Abstract: In this paper, Al_2O_3-SiO_2-B_2O_3 glass-ceramic was prepared and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), further, the porosity was detected by Archimedes principle, thermo physical properties were investigated by differential scanning calorimeter (DSC), respectively. The phase composition was detected by XRD, and the morphology was observed by SEM. The results indicated that the thermal conductivities of the Al_2O_3-SiO_2-B_2O_3 glass-ceramic were between 1.3 and 1.5 W·(m·K)"−"1, and the material had good thermal stability in the range of 300–900 °C. The porosity and apparent density were increased with the temperature. The porosity of Al_2O_3-SiO_2-B_2O_3 glass-ceramic in ranging from 1.2 to 9.6%, the apparent density were between 2.12 and 2.67 g·cm"−"3, and heat capacities were between 0.64 and 0.79 kJ/(kg·K). All the results indicated that the Al_2O_3-SiO_2-B_2O_3 glass-ceramic can be applied as encapsulation material in high temperature latent thermal energy storage.

  15. Enhanced Energy-Storage Density and High Efficiency of Lead-Free CaTiO3-BiScO3 Linear Dielectric Ceramics.

    Luo, Bingcheng; Wang, Xiaohui; Tian, Enke; Song, Hongzhou; Wang, Hongxian; Li, Longtu

    2017-06-14

    A novel lead-free (1 - x)CaTiO 3 -xBiScO 3 linear dielectric ceramic with enhanced energy-storage density was fabricated. With the composition of BiScO 3 increasing, the dielectric constant of (1 - x)CaTiO 3 -xBiScO 3 ceramics first increased and then decreased after the composition x > 0.1, while the dielectric loss decreased first and increased. For the composition x = 0.1, the polarization was increased into 12.36 μC/cm 2 , 4.6 times higher than that of the pure CaTiO 3 . The energy density of 0.9CaTiO 3 -0.1BiScO 3 ceramic was 1.55 J/cm 3 with the energy-storage efficiency of 90.4% at the breakdown strength of 270 kV/cm, and the power density was 1.79 MW/cm 3 . Comparison with other lead-free dielectric ceramics confirmed the superior potential of CaTiO 3 -BiScO 3 ceramics for the design of ceramics capacitors for energy-storage applications. First-principles calculations revealed that Sc subsitution of Ti-site induced the atomic displacement of Ti ions in the whole crystal lattice, and lattice expansion was caused by variation of the bond angles and lenghths. Strong hybridization between O 2p and Ti 3d was observed in both valence band and conduction band; the hybridization between O 2p and Sc 3d at high conduction band was found to enlarge the band gap, and the static dielectric tensors were increased, which was the essential for the enhancement of polarization and dielectric properties.

  16. Design consideration of high voltage Ga2O3 vertical Schottky barrier diode with field plate

    Choi, J.-H.; Cho, C.-H.; Cha, H.-Y.

    2018-06-01

    Gallium oxide (Ga2O3) based vertical Schottky barrier diodes (SBDs) were designed for high voltage switching applications. Since p-type Ga2O3 epitaxy growth or p-type ion implantation technique has not been developed yet, a field plate structure was employed in this study to maximize the breakdown voltage by suppressing the electric field at the anode edge. TCAD simulation was used for the physical analysis of Ga2O3 SBDs from which it was found that careful attention must be paid to the insulator under the field plate. Due to the extremely high breakdown field property of Ga2O3, an insulator with both high permittivity and high breakdown field must be used for the field plate formation.

  17. Factors influencing formation of highly dispersed BaTiO3 nanospheres with uniform sizes in static hydrothermal synthesis

    Gao, Jiabing; Shi, Haiyue; Dong, Huina; Zhang, Rui; Chen, Deliang

    2015-01-01

    Highly dispersed BaTiO 3 nanospheres with uniform sizes have important applications in micro/nanoscale functional devices. To achieve well-dispersed spherical BaTiO 3 nanocrystals, we carried out as reported in this paper the systematic investigation on the factors that influence the formation of BaTiO 3 nanospheres by the static hydrothermal process, including the NaOH concentrations [NaOH], molar Ba/Ti ratios (R Ba/Ti ), hydrothermal temperatures, and durations, with an emphasis on understanding the related mechanisms. Barium nitrate and TiO 2 sols derived from tetrabutyl titanate were used as the starting materials. The as-synthesized BaTiO 3 samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, thermogravimetry, differential thermal analysis, and FT-IR spectra. The highly dispersed BaTiO 3 nanospheres (76 ± 13 nm) were achieved under the optimum hydrothermal conditions at 200 °C for 10 h: [NaOH] = 2.0 mol L −1 and R Ba/Ti  = 1.5. Higher NaOH concentrations, higher Ba/Ti ratios, higher hydrothermal temperatures, and longer hydrothermal durations are favorable in forming BaTiO 3 nanospheres with larger fractions of tetragonal phase and higher yields; but too long hydrothermal durations resulted in abnormal growth and reduced the uniformity in particle sizes. The possible formation mechanisms for BaTiO 3 nanocrystals under the static hydrothermal conditions were investigated

  18. Structural phase transition of BaZrO3 under high pressure

    Yang, Xue; Li, Quanjun; Liu, Ran; Liu, Bo; Zhang, Huafang; Jiang, Shuqing; Zou, Bo; Cui, Tian; Liu, Bingbing; Liu, Jing

    2014-01-01

    We studied the phase transition behavior of cubic BaZrO 3 perovskite by in situ high pressure synchrotron X-ray diffraction experiments up to 46.4 GPa at room temperature. The phase transition from cubic phase to tetragonal phase was observed in BaZrO 3 for the first time, which takes place at 17.2 GPa. A bulk modulus 189 (26) GPa for cubic BaZrO 3 is derived from the pressure–volume data. Upon decompression, the high pressure phase transforms into the initial cubic phase. It is suggested that the unstable phonon mode caused by the rotation of oxygen octahedra plays a crucial role in the high pressure phase transition behavior of BaZrO 3

  19. High breakdown electric field in β-Ga2O3/graphene vertical barristor heterostructure

    Yan, Xiaodong; Esqueda, Ivan S.; Ma, Jiahui; Tice, Jesse; Wang, Han

    2018-01-01

    In this work, we study the high critical breakdown field in β-Ga2O3 perpendicular to its (100) crystal plane using a β-Ga2O3/graphene vertical heterostructure. Measurements indicate a record breakdown field of 5.2 MV/cm perpendicular to the (100) plane that is significantly larger than the previously reported values on lateral β-Ga2O3 field-effect-transistors (FETs). This result is compared with the critical field typically measured within the (100) crystal plane, and the observed anisotropy is explained through a combined theoretical and experimental analysis.

  20. A new high-κ Al2O3 based metal-insulator-metal antifuse

    Tian, Min; Zhong, Huicai; Li, Li; Wang, Zhigang

    2018-06-01

    In this paper, a new metal-insulator-metal (MIM) antifuse was fabricated with the high κ Al2O3 deposited by atomic layer deposition (ALD) as the dielectric. On this high κ antifuse structure, the very low on-state resistance was obtained under certain programming conditions. It is the first time that the antifuse on-state resistance has been found decreasing along with the increase of dielectric film thickness, which is attributed to a large current overshoot during breakdown. For the device with a dielectric thickness of 12 nm, very large overshoot current (∼60 mA) was observed and extremely low on-state resistance (∼10 Ω) was achieved.

  1. Photochemical smog pollution in the Bangkok Metropolitan Region of Thailand in relation to O 3 precursor concentrations and meteorological conditions

    Zhang, B.-N.; Kim Oanh, N. T.

    Analysis of photochemical pollution was done using the available 5-yr monitoring data (1996-2000) from 11 monitoring stations in Bangkok and 5 stations in other surrounding provinces, i.e. the Bangkok Metropolitan Region (BMR). Status and trend of O 3 as well as the monthly and diurnal variations were analyzed in relation to the local meteorological conditions as well as the regional transport of pollutants associated with the monsoon. The O 3 in Bangkok was found to be typical for the polluted urban areas with a lower concentration in the city center, especially at curbside stations, and higher concentration at the downwind locations. O 3 pollution was highest in 1997 with the maximum hourly average of 370 ppbv and the total hours exceeding the national hourly O 3 standard (100 ppbv) of 314 h, which is most likely related to the strong El Niño and the forest fire in Southeast Asia in this year. Meteorology-unadjusted trend shows a slight increase in O 3 from 1998 to 2000. Local emission and photochemistry are mainly responsible for O 3 episodes in the BMR. Seasonal fluctuations of O 3, however, were found to relate to the regional transport associated with the Asian monsoon. Highest O 3 pollution was found in the period from January to April (winter and local summer) and lowest during mid-rainy season, August. The O 3 increase isopleth diagram was constructed which shows that O 3 production in BMR is effective when the NO x/NMHC ratio is in the range of 0.04-0.15 with optimum ratio of around 0.07. Seasonal variations in NO x/NMHC ratios are consistent with the O 3 variations, i.e., optimum in summer (0.07), followed by winter (0.05), and the lowest in rainy season (0.03).

  2. All-perovskite transparent high mobility field effect using epitaxial BaSnO3 and LaInO3

    Useong Kim

    2015-03-01

    Full Text Available We demonstrate an all-perovskite transparent heterojunction field effect transistor made of two lattice-matched perovskite oxides: BaSnO3 and LaInO3. We have developed epitaxial LaInO3 as the gate oxide on top of BaSnO3, which were recently reported to possess high thermal stability and electron mobility when doped with La. We measured the dielectric properties of the epitaxial LaInO3 films, such as the band gap, dielectric constant, and the dielectric breakdown field. Using the LaInO3 as a gate dielectric and the La-doped BaSnO3 as a channel layer, we fabricated field effect device structure. The field effect mobility of such device was higher than 90 cm2 V−1 s−1, the on/off ratio was larger than 107, and the subthreshold swing was 0.65 V dec−1. We discuss the possible origins for such device performance and the future directions for further improvement.

  3. Stabilization of the high coercivity ε-Fe2O3 phase in the CeO2–Fe2O3/SiO2 nanocomposites

    Mantlikova, A.; Poltierova Vejpravova, J.; Bittova, B.; Burianova, S.; Niznansky, D.; Ardu, A.; Cannas, C.

    2012-01-01

    We have investigated the processes leading to the formation of the Fe 2 O 3 and CeO 2 nanoparticles in the SiO 2 matrix in order to stabilize the ε-Fe 2 O 3 as the major phase. The samples with two different concentrations of the Fe were prepared by sol–gel method, subsequently annealed at different temperatures up to 1100 °C, and characterized by the Mössbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe 2 O 3 phases under various conditions of preparation was investigated, starting with the preferential appearance of the γ-Fe 2 O 3 phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major ε-Fe 2 O 3 phase for high Fe concentration and high annealing temperature, coexisting with the most stable α-Fe 2 O 3 phase. A continuous increase of the particle size of the CeO 2 nanocrystals with increasing annealing temperature was also observed. - Graphical abstract: The graphical abstract displays the most important results of our work. The significant change of the phase composition due to the variation of preparation conditions is demonstrated. As a result, significant change of the magnetic properties from superparamagnetic γ-Fe 2 O 3 phase with negligible coercivity to the high coercivity ε-Fe 2 O 3 phase has been observed. Highlights: ► Research of the stabilization of the high coercivity ε-Fe 2 O 3 in CeO 2 –Fe 2 O 3 /SiO 2 . ► Samples with two different concentrations of Fe and three annealing temperatures. ► Phase transition γ→ε→(β)→α with increasing annealing temperature and particle size. ► Elimination of the superparamagnetic phases in samples with higher content of Fe. ► Best conditions for high coercivity ε-Fe 2 O 3 —higher Fe content and T A =1100°C.

  4. High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

    Cossu, Fabrizio

    2013-01-28

    First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

  5. High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

    Cossu, Fabrizio; Schwingenschlö gl, Udo; Singh, Nirpendra

    2013-01-01

    First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

  6. Mobility Optimization in LaxBa1-xSnO3 Thin Films Deposited via High Pressure Oxygen Sputtering

    Postiglione, William Michael

    BaSnO3 (BSO) is one of the most promising semiconducting oxides currently being explored for use in future electronic applications. BSO possesses a unique combination of high room temperature mobility (even at very high carrier concentrations, > 1019 cm-3), wide band gap, and high temperature stability, making it a potentially useful material for myriad applications. Significant challenges remain however in optimizing the properties and processing of epitaxial BSO, a critical step towards industrial applications. In this study we investigate the viability of using high pressure oxygen sputtering to produce high mobility La-doped BSO thin films. In the first part of our investigation we synthesized, using solid state reaction, phase-pure stoichiometric polycrystalline 2% La-doped BaSnO 3 for use as a target material in our sputtering system. We verified the experimental bulk lattice constant, 4.117 A, to be in good agreement with literature values. Next, we set out to optimize the growth conditions for DC sputtering of La doped BaSnO3. We found that mobility for all our films increased monotonically with deposition temperature, suggesting the optimum temperature for deposition is > 900 °C and implicating a likely improvement in transport properties with post-growth thermal anneal. We then preformed systematic studies aimed at probing the effects of varying thickness and deposition rate to optimize the structural and electronic transport properties in unbuffered BSO films. In this report we demonstrate the ability to grow 2% La BSO thin films with an effective dopant activation of essentially 100%. Our films showed fully relaxed (bulk), out-of-plane lattice parameter values when deposited on LaAlO3, MgO, and (LaAlO3)0.3(Sr2 TaAlO6)0.7 substrates, and slightly expanded out-of-plane lattice parameters for films deposited on SrTiO3, GdScO3, and PrScO3 substrates. The surface roughness's of our films were measured via AFM, and determined to be on the nm scale or better

  7. Wet routes of high purity BaTiO3 nanopowders

    Wang Liqiu; Liu Liang; Xue Dongfeng; Kang Hongmin; Liu Changhou

    2007-01-01

    High purity BaTiO 3 nanopowders were prepared in wet routes through stearic acid gel (SAG) and acetic acid gel (AAG) techniques, respectively. BaTiO 3 samples were characterized by X-ray diffraction, transmission electron microscope, Fourier transform infrared spectrometry, X-ray fluorescence spectrometry, and thermal gravimetric analysis. The present results indicate that both methods have a similar reaction process during calcination, while BaTiO 3 crystallites were initially formed at 550 deg. C by SAG and 800 deg. C by AAG. Both methods could produce BaTiO 3 powders with a cubic perovskite structure, while they had different grain size distributions within 25-50 nm for SAG and 50-80 nm for AAG. BaTiO 3 samples prepared by SAG had a lower agglomeration than those by AAG. SAG has shown many distinctive advantages in the preparation of high purity BaTiO 3 nanopowders, without Ba and Ti losses and hazardous wastes

  8. Hydrothermal growth of highly textured BaTiO3 films composed of nanowires

    Zhou Zhi; Tang Haixiong; Sodano, Henry A; Lin Yirong

    2013-01-01

    Textured barium titanate (BaTiO 3 ) films are attracting immense research interest due to their lead-free composition and excellent piezoelectric and dielectric properties. Most synthesis methods for these films require a high temperature, leading to the formation of a secondary phase and an overall decrease in the electrical properties of the ceramic. In order to alleviate these issues, a novel fabrication method is introduced by transferring oriented rutile TiO 2 nanowires to a textured BaTiO 3 film at temperatures below 160 °C. The microstructure and thickness of the fabricated BaTiO 3 films were characterized by scanning electron microscopy, and the crystal structure and degree of orientation were evaluated by x-ray diffraction patterns using the Lotgering method. It is shown that the thickness of the BaTiO 3 film can be controlled by the length of TiO 2 nanowire array template, and the degree of orientation of the textured BaTiO 3 films is highly dependent on the film thickness; the crystallographic orientation has been measured to reach up to 87%. The relative dielectric constant (ε r = 1300) and ferroelectric properties (P r = 2.7 μC cm −2 , E c = 4.0 kV mm −1 ) of the textured BaTiO 3 films were also characterized to demonstrate their potential application in sensors, random access memory, and micro-electromechanical systems. (paper)

  9. Forecasting and analyzing high O3 time series in educational area through an improved chaotic approach

    Hamid, Nor Zila Abd; Adenan, Nur Hamiza; Noorani, Mohd Salmi Md

    2017-08-01

    Forecasting and analyzing the ozone (O3) concentration time series is important because the pollutant is harmful to health. This study is a pilot study for forecasting and analyzing the O3 time series in one of Malaysian educational area namely Shah Alam using chaotic approach. Through this approach, the observed hourly scalar time series is reconstructed into a multi-dimensional phase space, which is then used to forecast the future time series through the local linear approximation method. The main purpose is to forecast the high O3 concentrations. The original method performed poorly but the improved method addressed the weakness thereby enabling the high concentrations to be successfully forecast. The correlation coefficient between the observed and forecasted time series through the improved method is 0.9159 and both the mean absolute error and root mean squared error are low. Thus, the improved method is advantageous. The time series analysis by means of the phase space plot and Cao method identified the presence of low-dimensional chaotic dynamics in the observed O3 time series. Results showed that at least seven factors affect the studied O3 time series, which is consistent with the listed factors from the diurnal variations investigation and the sensitivity analysis from past studies. In conclusion, chaotic approach has been successfully forecast and analyzes the O3 time series in educational area of Shah Alam. These findings are expected to help stakeholders such as Ministry of Education and Department of Environment in having a better air pollution management.

  10. Formation of high oxide ion conductive phases in the sintered oxides of the system Bi2O3-Ln2O3 (Ln = La-Yb)

    Iwahara, H.; Esaka, T.; Sato, T.; Takahashi, T.

    1981-01-01

    The electrical conduction in various phases of the system Bi 2 O 3 -Ln 2 O 3 (Ln = La, Nd, Sm, Dy, Er, or Yb) was investigated by measuring ac conductivity and the emf of the oxygen gas concentration cell. High-oxide-ion conduction was observed in the rhombohedral and face-centered cubic (fcc) phase in these systems. The fcc phase could be stabilized over a wide range of temperature by adding a certain amount of Ln 2 O 3 . In these cases, the larger the atomic number of Ln, the lower the content of Ln 2 O 3 required to form the fcc solid solution, except in the case of Yb 2 O 3 . The oxide ion conductivity of this phase decreased with increasing content of Ln 2 O 3 . Maximum conductivity was obtained at the lower limit of the fcc solid solution formation range in each system, which was more than one order of magnitude higher than those of conventional stabilized zirconias. Lattice parameters of the fcc phase were calculated from the x-ray diffraction patterns. The relationship between the oxide ion conductivity and the lattice parameter was also discussed

  11. Synthesis and high (pressure, temperature) stability of ZnTiO3 polymorphs studied by Raman spectroscopy

    Bernert, T.; Ruiz-Fuertes, J.; Bayarjargal, L.; Winkler, B.

    2015-05-01

    The phase-purity of ilmenite-type ZnTiO3 prepared by the ceramic method was investigated in dependence of the conditions during ball milling. The previously proposed addition of 2 ml ethanol to the starting materials led to a significant contamination of the product phase after a subsequent sintering process at 1073 K. However, by omitting ethanol this synthesis route led to a phase-pure sample of ZnTiO3 as confirmed by X-ray powder diffraction and Raman spectroscopy. High-temperature high-pressure experiments gave an ilmenite-type to perovskite-type phase boundary with a slope of dT/dP∼-135 K GPa-1 crossing ambient temperature conditions at ∼ 24 GPa in good agreement with previous calculations. Room-temperature high-pressure Raman spectroscopy experiments have shown the stability of the ilmenite-type phase up to a pressure of at least 38.5 GPa, the highest pressure applied in this study, indicating the presence of a kinetic barrier in this phase transition. The synthesis of ferroelectric LiNbO3-type ZnTiO3 was confirmed by second harmonic generation.

  12. Influence of deposition conditions on the nature of epitaxial SrIrO3 on STO (001)

    Bhat, Shwetha G.; Sebastian, Nirmal K.; Kumar, P. S. Anil

    2018-05-01

    SrIrO3 (SIO) is one of the materials known to exhibit a high spin-orbit coupling with correlated semi-metallic ground state, along with the topological states, as proven in recent times. In this regard, the SIO thin films grown by us on SrTiO3 (001) at certain deposition conditions, exhibit a low temperature magneto-transport behavior which is analogous to the materials with topological states. Further, we have explored various deposition conditions of SIO such as partial pressure of O2 and different temperatures of growth for different thickness of SIO. In addition, from the electrical transport properties, SIO thin films found to exhibit semi-metallic nature with either insulating-like or a crossover from metal-like to insulating-like behavior based on the conditions chosen for the growth. Moreover, the magneto-transport data of various SIO thin films are found to be obeying the usual B2 (Lorentzian) behavior in majority of the cases. At the same time, we have also observed the weak-localization and weak-antilocalization effects; along with a linear magneto-resistance at low temperature ranges. Thus, from our extensive measurements, it becomes clear that SIO thin films can exhibit wide varieties of magneto-transport properties based on the deposition conditions. Plethora of interesting properties exhibited by the highly spin-orbit coupled SIO epitaxial thin films at lower temperatures in the presence of magnetic field makes the material to be promising for the future applications in the field of spintronics.

  13. Characterization of Al2O3-Co ceramic composite obtained by high energy mill

    Souza, J.L.; Assis, R.B. de; Carlos, E.M.; Oliveira, T.P.; Costa, F.A. da

    2014-01-01

    This work aims to characterize the ceramic composite Al 2 O3-Co obtained by high energy grinding. The composites were obtained by milling Al 2 O 3 and Co in a high energy mill at a speed of 400 rpm, in proportions of 5 to 20% Cobalt (Co). Ceramic composites with 5 and 20% cobalt were sintered at 1200 and 1300 ° C, with a 60-minute plateau and a heating rate of 10 ° C / min. The samples were characterized by X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG / DSC) and scanning electron microscopy (SEM). The results show the significant effect of cobalt percentage and high energy grinding on the final properties of the Al 2 O 3 - Co ceramic composite, presenting satisfactory values for the composite with a 20% cobalt percentage, showing to be a promising material for application in cutting tools

  14. Ceramic synthesis of 0.08BiGaO3-0.90BaTiO3-0.02LiNbO3 under high pressure and high temperature

    Hui, Jin; Yong, Li; Mou-Sheng, Song; Lin, Chen; Xiao-Peng, Jia; Hong-An, Ma

    2016-07-01

    In this paper, the preparation of 0.08BiGaO3-0.90BaTiO3-0.02LiNbO3 is investigated at pressure 3.8 GPa and temperature 1100-1200 °C. Experimental results indicate that not only is the sintered rate more effective, but also the sintered temperature is lower under high pressure and high temperature than those of under normal pressure. It is thought that the adscititious pressure plays the key role in this process, which is discussed in detail. The composition and the structure of the as-prepared samples are recorded by XRD patterns. The result shows that the phases of BaTiO3, BaBiO2.77, and Ba2Bi4Ti5O18 with piezoelectric ceramic performance generate in the sintered samples. Furthermore, the surface morphology characteristics of the typical samples are also investigated using a scanning electron microscope. It indicates that the grain size and surface structure of the samples are closely related to the sintering temperature and sintering time. It is hoped that this study can provide a new train of thought for the preparation of lead-free piezoelectric ceramics with excellent performance. Project supported by the National Natural Science Foundation of China (Grant No. 51172089), the Natural Science Foundation of Education Department of Guizhou Province, China (Grant Nos. KY [2013]183 and LH [2015]7232), and the Research Fund for the Doctoral Program of Tongren University, China (Grant No. DS1302).

  15. Facile Synthesis of Porous ZnMnO3 Spherulites with a High Lithium Storage Capability

    Liu, Xinru; Zhao, Chenhao; Zhang, He; Shen, Qiang

    2015-01-01

    Graphical abstract: Porous ZnMnO 3 spherulites show an enhanced high lithium storage capability when potentially applied as a lithium-ion battery anode for the first time. - Highlights: • Composite Zn 0.5 Mn 0.5 CO 3 microspheres are facilely co-precipitated. • Porous ZnMnO 3 spherulites can be used as a lithium-ion battery anode. • Porous ZnMnO 3 spherulites show superior electrochemical properties. • A synergistic effect of Zn-O and Mn-O components in cubic ZnMnO 3 is proposed. - Abstract: In this paper, pure-phase ZnMnO 3 porous spherulites are uniquely synthesized through the thermal decomposition of Zn-Mn binary carbonate precursors facilely co-precipitated at room temperature, possessing an average diameter of 1.2 ± 0.3 μm and acquiring porosity with a specific surface area of 24.3 m 2 g −1 . When tentatively applied as lithium-ion battery anodes for the first time, these porous spherulites deliver an initial discharge capacity of 1294 mAh g −1 at 500 mA g −1 and retain an reversible value of 879 mAh g −1 over 150 cycles. By comparison, the equimolar powder mixture of nano-sized ZnO and MnO 2 synergistically shows a higher lithium storage capability than the two unary transition metal oxides, but lower than anode material ZnMnO 3 . Aside from its nanostructured characteristics, an inner atomic synergistic effect within the cubic lattices may account for the superior electrochemical performance of well-crystallized ZnMnO 3

  16. Structural, dielectric and ferroelectric properties of (Bi,Na)TiO3–BaTiO3 system studied by high throughput screening

    Hayden, Brian E.; Yakovlev, Sergey

    2016-01-01

    Thin-film materials libraries of the Bi 2 O 3 –Na 2 O–TiO 2 –BaO system in a broad composition range have been deposited in ultra-high vacuum from elemental evaporation sources and an oxygen plasma source. A high throughput approach was used for systematic compositional and structural characterization and the screening of the dielectric and ferroelectric properties. The perovskite (Bi,Na)TiO 3 –BaTiO 3 phase with a Ba concentration near the morphotropic phase boundary (ca. 6 at.%) exhibited a relative dielectric permittivity of 180, a loss tangent of 0.04 and remnant polarization of 19 μC/cm 2 . Compared to published data, observed remnant polarization is close to that known for epitaxially grown films but higher than the values reported for polycrystalline films. The high throughput methodology and systematic nature of the study allowed us to establish the composition boundaries of the phase with optimal dielectric and ferroelectric characteristics. - Highlights: • Bi 2 O 3 –Na 2 O–TiO 2 –BaO high throughput materials library was deposited using PVD method. • Materials were processed from individual molecular beam epitaxy sources of elements. • High throughput approach was used for structural, dielectric and ferroelectric study. • Composition boundaries of perovskite compounds with optimum properties are reported.

  17. Relationship between tolerance factor and temperature coefficient of permittivity of temperature-stable high permittivity BaTiO3–Bi(MeO3 compounds

    Natthaphon Raengthon

    2016-03-01

    Full Text Available The temperature coefficient of permittivity (TCε of BaTiO3–Bi(MeO3 solid solutions were investigated. It was determined that as the tolerance factor was decreased with the addition of Bi(MeO3, the TCε shifted from large negative values to TCε values approaching zero. It is proposed that the different bonding nature of the dopant cation affects the magnitude and temperature stability of the permittivity. This study suggests that the relationship between tolerance factor and TCε can be used as a guide to design new dielectric compounds exhibiting temperature-stable high permittivity characteristics, which is similar to past research on perovskite and pyrochlore-based microwave dielectrics.

  18. Coexistence of weak ferromagnetism and ferroelectricity in the high pressure LiNbO3-type phase of FeTiO3.

    Varga, T; Kumar, A; Vlahos, E; Denev, S; Park, M; Hong, S; Sanehira, T; Wang, Y; Fennie, C J; Streiffer, S K; Ke, X; Schiffer, P; Gopalan, V; Mitchell, J F

    2009-07-24

    We report the magnetic and electrical characteristics of polycrystalline FeTiO_{3} synthesized at high pressure that is isostructural with acentric LiNbO_{3} (LBO). Piezoresponse force microscopy, optical second harmonic generation, and magnetometry demonstrate ferroelectricity at and below room temperature and weak ferromagnetism below approximately 120 K. These results validate symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LBO structure.

  19. Suppressed carrier density for the patterned high mobility two-dimensional electron gas at γ-Al2O3/SrTiO3 heterointerfaces

    Niu, Wei; Gan, Yulin; Christensen, Dennis Valbjørn

    2017-01-01

    The two-dimensional electron gas (2DEG) at the non-isostructural interface between spinel γ-Al2O3 and perovskite SrTiO3 is featured by a record electron mobility among complex oxide interfaces in addition to a high carrier density up to the order of 1015 cm-2. Herein, we report on the patterning...... is found to be approximately 3×1013 cm-2, much lower than that of the unpatterned sample (~1015 cm-2). Remarkably, a high electron mobility of approximately 3,600 cm2V-1s-1 was obtained at low temperatures for the patterned 2DEG at a carrier density of ~ 7×1012 cm-2, which exhibits clear Shubnikov-de Hass...... quantum oscillations. The patterned high-mobility 2DEG at the γ-Al2O3/SrTiO3 interface paves the way for the design and application of spinel/perovskite interfaces for high-mobility all-oxide electronic devic...

  20. Synthesis and characterization of high volume fraction Al-Al2O3 nanocomposite powders by high-energy milling

    Prabhu, B.; Suryanarayana, C.; An, L.; Vaidyanathan, R.

    2006-01-01

    Al-Al 2 O 3 metal matrix composite (MMC) powders with volume fractions of 20, 30, and 50% Al 2 O 3 were synthesized by high-energy milling of the blended component powders. The particle sizes of Al 2 O 3 studied were 50 nm, 150 nm, and 5 μm. A uniform distribution of the Al 2 O 3 reinforcement in the Al matrix was successfully obtained after milling the powders for a period of 20 h at a ball-to-powder ratio of 10:1 in a SPEX mill. The uniform distribution of Al 2 O 3 in the Al matrix was confirmed by characterizing these nanocomposite powders by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray mapping, and X-ray diffraction (XRD) techniques

  1. Phosphine Plasma Activation of α-Fe 2 O 3 for High Energy Asymmetric Supercapacitors

    Liang, Hanfeng; Xia, Chuan; Emwas, Abdul-Hamid M.; Anjum, Dalaver H.; Miao, Xiaohe; Alshareef, Husam N.

    2018-01-01

    , the asymmetric supercapacitor devices based on plasma-activated Fe2O3 anodes and electrodeposited MnO2 cathodes can achieve a high stack energy density of 0.42 mWh cm-3 at a stack power density of 10.3 mW cm-3 along with good stability (88% capacitance retention

  2. FoxO3a Serves as a Biomarker of Oxidative Stress in Human Lens Epithelial Cells under Conditions of Hyperglycemia.

    Ilangovan Raju

    Full Text Available Forkhead box 'O' transcription factors (FoxOs are implicated in the pathogenesis of type2 diabetes and other metabolic diseases. Abnormal activity of FoxOs was reported in the glucose and insulin metabolism. Expression of FoxO proteins was reported in ocular tissues; however their function under hyperglycemic conditions was not examined.Human lens epithelial cell line was used to study the function of FoxO proteins. Immunofluorescence, flow cytometry and Western blotting were employed to detect the FoxO proteins under the conditions of hyperglycemia.In this study we examined the role of FoxO3a in hyperglycemia-induced oxidative stress in human lens epithelial cells. FoxO3a protein expression was elevated in a dose- and time-dependent fashion after high glucose treatment. Anti-oxidant defense mechanisms of the lens epithelial cells were diminished as evidenced from loss of mitochondrial membrane integrity and lowered MnSOD after 72 h treatment with high glucose. Taken together, FoxO3a acts as a sensitive indicator of oxidative stress and cell homeostasis in human lens epithelial cells during diabetic conditions.FoxO3a is an early stress response protein to glucose toxicity in diabetic conditions.

  3. High-temperature mechanical relaxation in glass-like B2O3

    Lomovskoj, V.A.

    1987-01-01

    The study of high-temperature mechanical relaxation in glass-like B 2 O 3 was carried out at the temperatures from 470 to 620 K using the method of internal friction at freely damped tortional vibrations (frequency range is 0.05 - 10 Hz) and forced torsional vibrations (frequency range is 0.1 -0.00001 Hz). Possible mechanisms of high-temperature mechanical relaxation are considered. It is shown that several possible mechanisms of high-temperature mechanical relaxation in glass-like B 2 O 3 can be singled out. Switching of B-O bridge bond between two boroxol cycles of boroxol grouping for oxygen vacancy in spatial structure of glass-like B 2 O 3 , formed as a result of thermal breaking of one out of three B-O bonds, according to diffusion theory of glass viscosity. The slip of one layer boroxol groupings as to another one in the presence of only tricoordinated boron atoms in the structure of glass-like B 2 O 3

  4. Spectroscopic studies on (Ba,Ca)(Ti,Zr)O3 ferroelectric ceramics with high piezoelectric coefficients

    Archana Kumar; Sreenivas, K.

    2013-01-01

    In recent year non lead-based multi component ceramics consisting Ba(Ti 0.8 Zr 0.2 )O 3- (Ba 0.7 Ca 0.3 )TiO 3 have been found to exhibit high piezoelectric coefficients comparable to those of PZT, and there is a lot interest to understand nature of phase transition in these novel compositions. In the present study 0.5Ba(Ti 0.8 Zr 0.2 )O 3- 0.5(Ba 0.7 Ca 0.3 )TiO 3 ceramic composition calcinated and sintered at different temperatures has been investigated. The ceramics are prepared from the raw powders and reacted by a solid state reaction method. Spectroscopic methods including DTA/TGA, FTIR and Raman spectroscopy been used to understand the changes occurring in the chemical and structural properties during processing. The nature of polymorphic phase transition has been studied through the temperature dependent Raman spectroscopy. The de-poling characteristics with temperature have been studied to assess their usefulness for high temperature transducer applications, and their ferroelectric properties have been studied. This new composition exhibits high piezoelectric (d 33 ), and the transition temperature is low around 120℃. (author)

  5. Review on α-Fe2O3 based negative electrode for high performance supercapacitors

    Nithya, V. D.; Arul, N. Sabari

    2016-09-01

    Supercapacitor is an electrochemical energy storage device which has drawn attention of the researchers in recent years due to its high power density and long cycle life. Recently, an enormous effort has been imposed to improve the energy density of supercapacitor and might be attained through asymmetric cell configuration that offer wider potential window. Until now, a significant advancement has been achieved in the fabrication of positive electrodes for asymmetric cell. Nevertheless, the electrochemical performance of negative electrode materials is less explored, especially Hematite (α-Fe2O3). The α-Fe2O3 has been proved to be a promising negative electrode in supercapacitor application due to its wide operating potential, high redox activity, low cost, abundant availability and eco-friendliness. In this review, we have chosen α-Fe2O3 as the negative electrode and discussed its latest research progress with emphasis on various surface engineering synthesis strategies such as, carbon, polymer, metal-metal oxide, and ternary based α-Fe2O3 composites for supercapacitor. Besides, the importance of their synergistic effects over the supercapacitive performance in terms of specific capacitance, energy density, power density, cycling life and rate capability are highlighted. Also, an extensive analysis of the literature about its symmetric/asymmetric cell performance is explored.

  6. Phosphine Plasma Activation of α-Fe 2 O 3 for High Energy Asymmetric Supercapacitors

    Liang, Hanfeng

    2018-04-12

    We report a phosphine (PH3) plasma activation strategy for significantly boosting the electrochemical performance of supercapacitor electrodes. Using Fe2O3 as a demonstration, we show that the plasma activation simultaneously improves the conductivity, creates atomic-scale vacancies (defects), as well as increases active surface area, and thus leading to a greatly enhanced performance with a high areal capacitance of 340 mF cm-2 at 1 mA cm-2, compared to 66 mF cm-2 of pristine Fe2O3. Moreover, the asymmetric supercapacitor devices based on plasma-activated Fe2O3 anodes and electrodeposited MnO2 cathodes can achieve a high stack energy density of 0.42 mWh cm-3 at a stack power density of 10.3 mW cm-3 along with good stability (88% capacitance retention after 9000 cycles at 10 mA cm-2). Our work provides a simple yet effective strategy to greatly enhance the electrochemical performance of Fe2O3 anodes and to further promote their application in asymmetric supercapacitors.

  7. Dual-porosity Mn2O3 cubes for highly efficient dye adsorption.

    Shao, Yongjiu; Ren, Bin; Jiang, Hanmei; Zhou, Bingjie; Lv, Liping; Ren, Jingzheng; Dong, Lichun; Li, Jing; Liu, Zhenfa

    2017-07-05

    Dual-porosity materials containing both macropores and mesopores are highly desired in many fields. In this work, we prepared dual-porosity Mn 2 O 3 cube materials with large-pore mesopores, in which, macropores are made by using carbon spheres as the hard templates, while the mesopores are produced via a template-free route. The attained dual-porosity Mn 2 O 3 materials have 24nm of large-pore mesopores and 700nm of macropores. Besides, the achieved materials own cubic morphologies with particle sizes as large as 6.0μm, making them separable in the solution by a facile natural sedimentation. Dye adsorption measurements reveal that the dual-porosity materials possess a very high maximum adsorption capacity of 125.6mg/g, much larger than many reported materials. Particularly, the adsorbents can be recycled and the dye removal efficiency can be well maintained at 98% after four cycles. Adsorption isotherm and kinetics show that the Langmuir model and the pseudo-second-order kinetics model can well describe the adsorption process of Congo Red on the dual-porosity Mn 2 O 3 cube materials. In brief, the reported dual-porosity Mn 2 O 3 demonstrates a good example for controlled preparation of dual-porosity materials with large-pore mesopores, and the macropore-mesopore dual-porosity distribution is good for mass transfer in dye adsorption application. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Ferroelectric and magnetic properties in high-pressure synthesized BiFeO3 compound

    Zhai, L.; Shi, Y.G.; Gao, J.L.; Tang, S.L.; Du, Y.W.

    2011-01-01

    Highlights: → A high-density polycrystalline BiFeO 3 compound was synthesized by high-pressure annealing method. → The sample showed weak ferromagnetic at room temperature, which could be attributed to the lattice distortion induced by the high-pressure annealing. → Irregular domains were observed on the surface of the sample by piezoresponse force microscopy, and a typical hysteresis loop was obtained. - Abstract: High-density polycrystalline BiFeO 3 compound was synthesized by high-pressure annealing. Measurements of crystal structure, magnetic, and ferroelectric properties were made on the sample. It was found that the sample was almost single phase with a distorted R3c structure. The results of the X-ray photoelectron spectra demonstrate that the oxidation state of Fe in the sample is Fe 3+ . The room-temperature field dependence of magnetization for BiFeO 3 exhibits a hysteretic behavior. The observed weak ferromagnetism could be ascribed to the lattice distortion induced by the high-pressure annealing. In addition, the local ferroelectric performance of the sample was studied by piezoresponse force microscopy.

  9. Fe-Al2O3 nanocomposites prepared by high-energy ball milling

    Linderoth, Søren; Pedersen, M.S.

    1994-01-01

    Nanocomposites of alpha-Fe and alpha-Al2O3, prepared by high-energy ball milling, exhibit coercivities which are enhanced by about two orders of magnitude with respect to the bulk value. The degree of enhancement depends on the volume fraction (x(upsilon)) of Fe, with a maximum for x(upsilon) alm......Nanocomposites of alpha-Fe and alpha-Al2O3, prepared by high-energy ball milling, exhibit coercivities which are enhanced by about two orders of magnitude with respect to the bulk value. The degree of enhancement depends on the volume fraction (x(upsilon)) of Fe, with a maximum for x...

  10. Intense multimicrojoule high-order harmonics generated from neutral atoms of In2O3 nanoparticles

    Elouga Bom, L. B.; Abdul-Hadi, J.; Vidal, F.; Ozaki, T.; Ganeev, R. A.

    2009-01-01

    We studied high-order harmonic generation from plasma that contains an abundance of indium oxide nanoparticles. We found that harmonics from nanoparticle-containing plasma are considerably more intense than from plasma produced on the In 2 O 3 bulk target, with high-order harmonic energy ranging from 6 μJ (for the ninth harmonic) to 1 μJ (for the 17th harmonic) in the former case. The harmonic cutoff from nanoparticles was at the 21st order, which is lower than that observed using indium oxide solid target. By comparing the harmonic spectra obtained from solid and nanoparticle indium oxide targets, we concluded that intense harmonics in the latter case are dominantly generated from neutral atoms of the In 2 O 3 nanoparticles

  11. Aqueous supercapacitors of high energy density based on MoO3 nanoplates as anode material.

    Tang, Wei; Liu, Lili; Tian, Shu; Li, Lei; Yue, Yunbo; Wu, Yuping; Zhu, Kai

    2011-09-28

    MoO(3) nanoplates were prepared as anode material for aqueous supercapacitors. They can deliver a high energy density of 45 W h kg(-1) at 450 W kg(-1) and even maintain 29 W h kg(-1) at 2 kW kg(-1) in 0.5 M Li(2)SO(4) aqueous electrolyte. These results present a new direction to explore non-carbon anode materials.

  12. Growth from the melt of high-quality In2O3 and Ga2O3 single crystals

    Fornari, Roberto; Galazka, Zbigniew; Uecker, Reinhard; Irmscher, Klaus [Leibniz Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin (Germany)

    2013-07-01

    Because of their interesting properties semiconducting oxides, in particular Ga{sub 2}O{sub 3} In{sub 2}O{sub 3}, have recently received much attention. However, as they were deposited as films on hetero-substrates their quality was quite poor. The growth of high-quality bulk Ga{sub 2}O{sub 3} and In{sub 2}O{sub 3} and manufacture of the corresponding substrates can allow the deposition of high-quality epilayers with lower residual carrier density and fewer extended defects. For this reason IKZ has undertaken an effort to grow large single crystals of these oxide compounds from the melt. Transparent semiconducting Ga{sub 2}O{sub 3} single crystals with diameter of about 20 mm and 50-60 mm long were grown by the Czochralski method along the b-axis, using an Iridium crucible and a dynamic protective atmosphere to minimize the dissociation of Ga{sub 2}O{sub 3} melt and ingot. In the case of In{sub 2}O{sub 3} the Czochralski technique is not applicable and it was necessary to develop a novel melt growth method. This new method indeed supplied crystals from which oriented substrates could be prepared. In this presentation the melt growth of Ga{sub 2}O{sub 3} and In{sub 2}O{sub 3} single crystals will be reviewed. An important feature of both materials is given by their strong sensitivity to thermal processing: the free carrier concentration and the absorption spectra drastically vary as a function of annealing temperature, duration and ambient. The possible causes are discussed.

  13. High-Performance Ga2O3 Anode for Lithium-Ion Batteries.

    Tang, Xun; Huang, Xin; Huang, Yongmin; Gou, Yong; Pastore, James; Yang, Yao; Xiong, Yin; Qian, Jiangfeng; Brock, Joel D; Lu, Juntao; Xiao, Li; Abruña, Héctor D; Zhuang, Lin

    2018-02-14

    There is a great deal of interest in developing battery systems that can exhibit self-healing behavior, thus enhancing cyclability and stability. Given that gallium (Ga) is a metal that melts near room temperature, we wanted to test if it could be employed as a self-healing anode material for lithium-ion batteries (LIBs). However, Ga nanoparticles (NPs), when directly applied, tended to aggregate upon charge/discharge cycling. To address this issue, we employed carbon-coated Ga 2 O 3 NPs as an alternative. By controlling the pH of the precursor solution, highly dispersed and ultrafine Ga 2 O 3 NPs, embedded in carbon shells, could be synthesized through a hydrothermal carbonization method. The particle size of the Ga 2 O 3 NPs was 2.6 nm, with an extremely narrow size distribution, as determined by high-resolution transmission electron microscopy and Brunauer-Emmett-Teller measurements. A lithium-ion battery anode based on this material exhibited stable charging and discharging, with a capacity of 721 mAh/g after 200 cycles. The high cyclability is due to not only the protective effects of the carbon shell but also the formation of Ga 0 during the lithiation process, as indicated by operando X-ray absorption near-edge spectroscopy.

  14. Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity.

    Asmara, T C; Annadi, A; Santoso, I; Gogoi, P K; Kotlov, A; Omer, H M; Motapothula, M; Breese, M B H; Rübhausen, M; Venkatesan, T; Ariando; Rusydi, A

    2014-04-14

    In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e(-) from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥ 4 unit cells of LaAlO3) there is indeed a ~0.5e(-) transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤ 3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e(-) is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.

  15. Guiding of low-energy electrons by highly ordered Al2 O3 nanocapillaries

    Milosavljević, A.R.; Víkor, G.; Pešić, Z.D.

    2007-01-01

    We report an experimental study of guided transmission of low-energy (200-350 eV) electrons through highly ordered Al2 O3 nanocapillaries with large aspect ratio (140 nm diameter and 15 μm length). The nanochannel array was prepared using self-ordering phenomena during a two-step anodization...... process of a high-purity aluminum foil. The experimental results clearly show the existence of the guiding effect, as found for highly charged ions. The guiding of the electron beam was observed for tilt angles up to 12°. As seen for highly charged ions, the guiding efficiency increases with decreasing...

  16. Characterization of highly (110)- and (111)-oriented Pb(Zr,Ti)O3 films on BaPbO3 electrode using Ru conducting barrier

    Liang, C.-S.; Wu, J.-M.

    2005-01-01

    Highly non-(001)-oriented Pb(Zr,Ti)O 3 (PZT) films have been fabricated by rf-magnetron sputtering. The preferential (110)-oriented BaPbO 3 (BPO) deposited on Ru buffer layer induces the growth of (110)-oriented PZT film. With the aid of self-organized growth of PZT, the orientation of the film deposited on random-oriented BPO/Pt(111)/Ru(002) is (111)-preferred. The insertion of Pt layer between BPO and Ru changes the orientation of PZT from (110) to (111) and prevents the oxygen diffusion. These non-(001)-oriented PZT films possess more superior ferroelectric, fatigue, and retention properties than those of (001)-oriented PZT films

  17. Highly textured Sr, Nb co-doped BiFeO3 thin films grown on SrRuO3/Si substrates by rf- sputtering

    Ostos, C.; Raymond, O.; Siqueiros, J. M.; Suarez-Almodovar, N.; Bueno-Baques, D.; Mestres, L.

    2011-01-01

    In this study, (011)-highly oriented Sr, Nb co-doped BiFeO 3 (BFO) thin films were successfully grown on SrRuO 3 /Si substrates by rf-magnetron sputtering. The presence of parasite magnetic phases was ruled out based on the high resolution x-ray diffraction data. BFO films exhibited a columnar-like grain growth with rms surface roughness values of ≅5.3 nm and average grain sizes of ≅65-70 nm for samples with different thicknesses. Remanent polarization values (2P r ) of 54 μC cm -2 at room temperature were found for the BFO films with a ferroelectric behavior characteristic of an asymmetric device structure. Analysis of the leakage mechanisms for this structure in negative bias suggests Schottky injection and a dominant Poole-Frenkel trap-limited conduction at room temperature. Oxygen vacancies and Fe 3+ /Fe 2+ trap centers are consistent with the surface chemical bonding states analysis from x-ray photoelectron spectroscopy data. The (011)-BFO/SrRuO 3 /Si film structure exhibits a strong magnetic interaction at the interface between the multiferroic film and the substrate layer where an enhanced ferromagnetic response at 5 K was observed. Zero-field cooled (ZFC) and field cooled (FC) magnetization curves of this film system revealed a possible spin glass behavior at spin freezing temperatures below 30 K depending on the BFO film thickness.

  18. Bioinspired, Graphene/Al2O3 Doubly Reinforced Aluminum Composites with High Strength and Toughness.

    Zhang, Yunya; Li, Xiaodong

    2017-11-08

    Nacre, commonly referred to as nature's armor, has served as a blueprint for engineering stronger and tougher bioinspired materials. Nature organizes a brick-and-mortar-like architecture in nacre, with hard bricks of aragonite sandwiched with soft biopolymer layers. However, cloning nacre's entire reinforcing mechanisms in engineered materials remains a challenge. In this study, we employed hybrid graphene/Al 2 O 3 platelets with surface nanointerlocks as hard bricks for primary load bearer and mechanical interlocking, along with aluminum laminates as soft mortar for load distribution and energy dissipation, to replicate nacre's architecture and reinforcing effects in aluminum composites. Compared with aluminum, the bioinspired, graphene/Al 2 O 3 doubly reinforced aluminum composite demonstrated an exceptional, joint improvement in hardness (210%), strength (223%), stiffness (78%), and toughness (30%), which are even superior over nacre. This design strategy and model material system should guide the synthesis of bioinspired materials to achieve exceptionally high strength and toughness.

  19. Structural transitions and multiferroic properties of high Ni-doped BiFeO3

    Betancourt-Cantera, L. G.; Bolarín-Miró, A. M.; Cortés-Escobedo, C. A.; Hernández-Cruz, L. E.; Sánchez-De Jesús, F.

    2018-06-01

    Nickel doped bismuth ferrite powders, BiFe1-x NixO3 (0 ≤ x ≤ 0.5), were synthesized by high-energy ball milling followed by an annealing at 700 °C. A detailed study about the substitution of Fe3+ by Ni2+ on the crystal structure and multiferroic properties is presented. The X-ray diffraction patterns reveal the formation of rhombohedral structure with small amounts of Bi2Fe4O9 as a secondary phase for x behavior indicates the frustration of the G-antiferromagnetic order typical of the un-doped BiFeO3, caused by the presence of small amounts of Ni2+ (x Behavior modifications of electrical conductivity, permittivity and dielectric loss versus frequency are related with crystal structure transformations, when nickel concentration is increased.

  20. High resolution photoemission study of Nd1-xSrxMnO3

    Togashi, T.; Osawa, H.; Shin, S.; Tanaka, K.; Isozumi, Y.; Iwazumi, T.; Nozawa, S.

    2004-01-01

    Full text:Nd 1-x SrxMnO 3 shows the negative colossal magnetoresistance and various electronic phases. In order to reveal their states, we have performed a high- resolution Mn 2p-3d resonance photoemission (RPES) study of Nd 1-x SrxMnO 3 with an energy resolution of 100 meV at BL25SU in SPring-8. Figure 1 shows the Mn 2p-3d RPES spectra of Nd 1-x SrxMnO 3 . It is found that the spectral line shape in the ground-state phases (GS) at low temperatures is closely related to the shape of MnO 6 octahedra depending on x due to a static Jahn- Teller (JT) effect while the line shape in the paramagnetic insulator (PI) phase near room temperature is qualitatively similar to each other irrespective of x. These results strongly suggest that the dynamical and static JT effects are responsible for the 3d electronic states at high and low temperatures, respectively

  1. Getting nanometric MoO3 through chemical synthesis and high energy milling

    Santos-Beltrán, M.; Paraguay-Delgado, F.; Santos-Beltrán, A.; Fuentes, L.

    2015-01-01

    The effects of high energy mechanical milling (HEMM) were studied on the microstructure and optical properties of MoO 3 for hexagonal and orthorhombic phases. Employing HEMM was possible change particle size as a function of mechanical milling time, as well as the small quantity transformation percentage from hexagonal to orthorhombic phase. The relationship between microstrain and optical properties generated was studied. The electronic structures were calculated using the Density Functional Theory (DFT); to determinate partial density of state (PDOS). Band gap structure calculations show a good correlation between experimental and simulated data. The approximated values of microstrain, particle size, lattice parameters and oxygen vacancies were obtained employing the Rietveld refinement of X-ray diffraction patterns. Samples were characterized by electron microscopy techniques, surface area analysis (BET), thermal-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and ultraviolet–visible spectroscopy (UV–Vis). It was possible, obtain particles with size below 40 nm by 30 min milling. - Graphical abstract: Orthorhombic phase, SEM image, SAED before milling, milling NPs, Particle size and band gap variation by milling time. - Highlights: • MoO 3 with hexagonal and orthorhombic structures was synthesized selectively. • By milling short time (30 m), it was possible get 40 nm diameter particles. • The band gap decrease for nanoparticles, then corroborated by simulation. • MoO 3 nanoparticles get high surface area for new technologic applications

  2. Al2O3 nanocrystals embedded in amorphous Lu2O3 high-k gate dielectric for floating gate memory application

    Yuan, C L; Chan, M Y; Lee, P S; Darmawan, P; Setiawan, Y

    2007-01-01

    The integration of nanoparticles has high potential in technological applications and opens up possibilities of the development of new devices. Compared to the conventional floating gate memory, a structure containing nanocrystals embedded in dielectrics shows high potential to produce a memory with high endurance, low operating voltage, fast write-erase speeds and better immunity to soft errors [S. Tiwari, F. Rana, H. Hanafi et al. 1996 Appl.Phys. Lett. 68, 1377]. A significant improvement on data retention [J. J. Lee, X. Wang et al. 2003 Proceedings of the VLSI Technol. Symposium, p33] can be observed when discrete nanodots are used instead of continuous floating gate as charge storage nodes because local defect related leakage can be reduced efficiently. Furthermore, using a high-k dielectric in place of the conventional SiO2 based dielectric, nanodots flash memory is able to achieve significantly improved programming efficiency and data retention [A. Thean and J. -P. Leburton, 2002 IEEE Potentials 21, 35; D. W. Kim, T. Kim and S. K. Banerjee, 2003 IEEE Trans. Electron Devices 50, 1823]. We have recently successfully developed a method to produce nanodots embedded in high-k gate dielectrics [C. L. Yuan, P. Darmawan, Y. Setiawan and P. S. Lee, 2006 Electrochemical and Solid-State Letters 9, F53; C. L. Yuan, P. Darmawan, Y. Setiawan and P. S. Lee, 2006 Europhys. Lett. 74, 177]. In this paper, we fabricated the memory structure of Al 2 O 3 nanocrystals embedded in amorphous Lu 2 O 3 high k dielectric using pulsed laser ablation. The mean size and density of the Al 2 O 3 nanocrystals are estimated to be about 5 nm and 7x1011 cm -2 , respectively. Good electrical performances in terms of large memory window and good data retention were observed. Our preparation method is simple, fast and economical

  3. AuRu/meso-Mn2O3: A Highly Active and Stable Catalyst for Methane Combustion

    Han, Z.; Fang, J. Y.; Xie, S. H.; Deng, J. G.; Liu, Y. X.; Dai, H. X.

    2018-05-01

    Three-dimensionally ordered mesoporous Mn2O3 (meso-Mn2O3) and its supported Au, Ru, and AuRu alloy (0.49 wt% Au/meso-Mn2O3, 0.48 wt% Ru/meso-Mn2O3, and 0.97 wt% AuRu/meso-Mn2O3 (Au/Ru molar ratio = 0.98)) nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous techniques, and their catalytic activities were evaluated for the combustion of methane. It is found that among all of the samples, 0.48 wt% Ru/meso-Mn 2O3 and 0.97 wt% AuRu/meso-Mn2O3 performed the best (the reaction temperature (T90% ) at 90% methane conversion was 530-540°C), but the latter showed a better thermal stability than the former. The partial deactivation of 0.97 wt% AuRu/meso-Mn2O3 due to H2O or CO2 introduction was reversible. It is concluded that the good catalytic activity and thermal stability of 0.97 wt% AuRu/meso-Mn2O3 was associated with the high dispersion of AuRu alloy NPs (2-5 nm) on the surface of meso-Mn2O3 and good low-temperature reducibility.

  4. High-pressure synthesis, crystal structure, and magnetic properties of KSbO3-type 5d oxides K0.84OsO3 and Bi2.93Os3O11

    Yuan, Yahua; Feng, Hai L.; Shi, Youguo; Tsujimoto, Yoshihiro; Belik, Alexei A.; Matsushita, Yoshitaka; Arai, Masao; He, Jianfeng; Tanaka, Masahiko; Yamaura, Kazunari

    2014-12-01

    5d Solid-state oxides K0.84OsO3 (Os5.16+; 5d 2.84) and Bi2.93Os3O11 (Os4.40+; 5d 3.60) were synthesized under high-pressure and high-temperature conditions (6 GPa and 1500-1700 °C). Their crystal structures were determined by synchrotron x-ray diffraction and their 5d electronic properties and tunnel-like structure motifs were investigated. A KSbO3-type structure with a space group of Im-3 and Pn-3 was determined for K0.84OsO3 and Bi2.93Os3O11, respectively. The magnetic and electronic transport properties of the polycrystalline compounds were compared with those obtained theoretically. It was revealed that the 5d tunnel-like structures are paramagnetic with metallic charge conduction at temperatures above 2 K. This was similar to what was observed for structurally relevant 5d oxides, including Bi3Re3O11 (Re4.33+; 5d 2.66) and Ba2Ir3O9 (Ir4.66+; 5d 4.33). The absence of long-range magnetic order seems to be common among 5d KSbO3-like oxides, regardless of the number of 5d electrons (between 2.6 and 4.3 per 5d atom).

  5. Anomalous perovskite PbRuO3 stabilized under high pressure

    Cheng, J.-G.; Kweon, K. E.; Zhou, J.-S.; Alonso, J. A.; Kong, P.-P.; Liu, Y.; Jin, Changqing; Wu, Junjie; Lin, Jung-Fu; Larregola, S. A.; Yang, Wenge; Shen, Guoyin; MacDonald, A. H.; Manthiram, Arumugam; Hwang, G. S.; Goodenough, John B.

    2013-01-01

    Perovskite oxides ABO3 are important materials used as components in electronic devices. The highly compact crystal structure consists of a framework of corner-shared BO6 octahedra enclosing the A-site cations. Because of these structural features, forming a strong bond between A and B cations is highly unlikely and has not been reported in the literature. Here we report a pressure-induced first-order transition in PbRuO3 from a common orthorhombic phase (Pbnm) to an orthorhombic phase (Pbn21) at 32 GPa by using synchrotron X-ray diffraction. This transition has been further verified with resistivity measurements and Raman spectra under high pressure. In contrast to most well-studied perovskites under high pressure, the Pbn21 phase of PbRuO3 stabilized at high pressure is a polar perovskite. More interestingly, the Pbn21 phase has the most distorted octahedra and a shortest Pb—Ru bond length relative to the average Pb—Ru bond length that has ever been reported in a perovskite structure. We have also simulated the behavior of the PbRuO3 perovskite under high pressure by first principles calculations. The calculated critical pressure for the phase transition and evolution of lattice parameters under pressure match the experimental results quantitatively. Our calculations also reveal that the hybridization between a Ru:t2g orbital and an sp hybrid on Pb increases dramatically in the Pbnm phase under pressure. This pressure-induced change destabilizes the Pbnm phase to give a phase transition to the Pbn21 phase where electrons in the overlapping orbitals form bonding and antibonding states along the shortest Ru—Pb direction at P > Pc. PMID:24277807

  6. Unsuppressed fermion-number violation at high temperature: An O(3) model

    Mottola, E.; Wipf, A.

    1989-01-01

    The O(3) nonlinear σ model in 1+1 dimensions, modified by an explicit symmetry-breaking term, is presented as a model for baryon- and lepton-number violation in the standard electroweak theory. Although arguments based on the Atiyah-Singer index theorem and instanton physics apply to the model, we show by explicit calculations that the rate of chiral fermion-number violation due to the axial anomaly is entirely unsuppressed at sufficiently high temperatures. Our results apply to unbroken gauge theories as well and may require reevaluation of the role of instantons in high-temperature QCD

  7. Colour change in biferroic YCrO_3 under high pressure: a combined experimental and density functional theory investigation

    Chakraborty, Brahmananda; Mall, Ashish Kumar; Gupta, Rajeev; Chitnis, Abhishek; Garg, Nandini; Ramaniah, Lavanya M.; Sharma, Surinder M.

    2016-01-01

    Biferroic materials find potential applications in various technological fields due to their simultaneous ferroelectric and ferromagnetic ordering. Yttrium chromite (YCrO_3) is found to be a biferroic having orthorhombic structure with Pnma space group. Combining both experiment and density functional theory (DFT), we have investigated the high pressure behaviour of YCrO_3 up to 100 GPa. We have observed a colour change in YCrO_3 from yellow-green to red at pressures larger than 40 GPa, which can be correlated with reduction in band gap under pressure. Present experimental data seems to suggest no structural transition upto 100 GPa. All the calculations are carried out using the DFT based projector augmented wave (PAW) method as implemented in the VASP code. As DFT has a limitation in predicting the correct band gap, we have employed the GGA+U method to compute the band gap. The computed band gap of 2.33 eV in ambient condition is close to the experimental value of 2.4 eV. The X-ray diffraction experiments were carried out in an indigenously designed diamond anvil cell

  8. O3 Nanoparticles

    Wang, Juan; Li, Yangyang; Deng, Lin; Wei, Nini; Weng, Yakui; Dong, Shuai; Qi, Dianpeng; Qiu, Jun; Chen, Xiaodong; Wu, Tao

    2016-01-01

    Ti2O3 nanoparticles with high performance of photothermal conversion are demonstrated for the first time. Benefiting from the nanosize and narrow-bandgap features, the Ti2O3 nanoparticles possess strong light absorption and nearly 100% internal

  9. High temperature dielectric and ferroelectric properties of La-modified PbTiO3 nanoceramics

    Shukla, Archana; Shukla, Namrata; Choudhary, R.N.P.

    2016-01-01

    Ferroelectric materials with high Curie temperature (higher than 300 °C) are highly desirable to construct transducers for high-temperature piezoelectric applications. Among the ferroelectric materials, PbTiO 3 (PT) is considered to be one of the most promising materials. However, the fabrication of high density pure PT ceramics is very difficult because of the highly anisotropy, which limited the use in piezoelectric transducers. Usually, substitutions towards A or B-site of PT may reduce the high anisotropy. The present work reports the experimental investigations on the effect of lanthanum (La 3+ ) substitution on the structural, dielectric and piezoelectric properties of lead titanate (PT) ceramic at high-temperature (RT ∼ 600°C)

  10. Core-shell structured MnSiO3 supported with CNTs as a high capacity anode for lithium-ion batteries.

    Feng, Jing; Li, Qin; Wang, Huijun; Zhang, Min; Yang, Xia; Yuan, Ruo; Chai, Yaqin

    2018-04-17

    Metal silicates are good candidates for use in lithium ion batteries (LIBs), however, their electrochemical performance is hindered by their poor electrical conductivity and volume expansion during Li+ insertion/desertion. In this work, one-dimensional core-shell structured MnSiO3 supported with carbon nanotubes (CNTs) (referred to as CNT@MnSiO3) with good conductivity and electrochemical performance has been successfully synthesized using a solvothermal process under moderate conditions. In contrast to traditional composites of CNTs and nanoparticles, the CNT@MnSiO3 composite in this work is made up of CNTs with a layer of MnSiO3 on the surface. The one-dimensional CNT@MnSiO3 nanotubes provide a useful channel for transferring Li+ ions during the discharge/charge process, which accelerates the Li+ diffusion speed. The CNTs inside the structure not only enhance the conductivity of the composite, but also prevent volume expansion. A high reversible capacity (920 mA h g-1 at 500 mA g-1 over 650 cycles) and good rate performance were obtained for CNT@MnSiO3, showing that this strategy of synthesizing coaxial CNT@MnSiO3 nanotubes offers a promising method for preparing other silicates for LIBs or other applications.

  11. Compensation mechanisms at high temperature in Y-doped BaTiO3

    Paredes-Olguín, M.; Lira-Hernández, I.A.; Gómez-Yáñez, C.; Espino-Cortés, F.P.

    2013-01-01

    Samples of BaTiO 3 with different concentrations of Y were synthesized from powders. The mixtures of powders were pressed and sintered at 1500 °C for 1 h. Two groups of samples were processed, one satisfying Ba/(Ti+Y) 3+ occupies the Ti 4+ lattice sites. The conductivity behavior as a function of Y concentration suggests that the compensation mechanisms are hole and oxygen vacancies. Due to the presence of charge carriers in the material, high values for the dielectric constant and dielectric loss were observed. Analysis of the microstructure showed that the average grain size decreases as the Y concentration is increased.

  12. Thermal stability of multilayered Pt-Al2O3 nanocoatings for high temperature CSP systems

    Nuru, ZY

    2015-10-01

    Full Text Available B), 115-120 Thermal stability of multilayered Pt-Al2O3 nanocoatings for high temperature CSP systems Z.Y. Nuru a, b, *, L. Kotsedi a, b, C.J. Arendse c, D. Motaung d, B. Mwakikunga d, K. Roro d, e, M. Maaza a, b a UNESCO-UNISA Africa Chair... Pretoria, South Africa e R&D Core-Energy, Council for Scientific and Industrial Research, P O Box 395, 0001 Pretoria, South Africa Abstract This contribution reports on the effect of thermal annealing on sputtered Pt–Al(sub2)O(sub3) multilayered...

  13. High mobility In2O3:H transparent conductive oxides prepared by atomic layer deposition and solid phase crystallization

    Macco, B.; Wu, Y.; Vanhemel, D.; Kessels, W.M.M.

    2014-01-01

    The preparation of high-quality In2O3:H, as transparent conductive oxide (TCO), is demonstrated at low temperatures. Amorphous In2O3:H films were deposited by atomic layer deposition at 100 °C, after which they underwent solid phase crystallization by a short anneal at 200 °C. TEM analysis has shown

  14. High performance Bi0.5Na0.5TiO3-BiAlO3-K0.5Na0.5NbO3 lead-free pyroelectric ceramics for thermal detectors

    Liu, Zhen; Ren, Weijun; Peng, Ping; Guo, Shaobo; Lu, Teng; Liu, Yun; Dong, Xianlin; Wang, Genshui

    2018-04-01

    Both high pyroelectric properties and good temperature stability of ferroelectric materials are desirable when used for applications in infrared thermal detectors. In this work, we report lead-free ternary 0.97(0.99Bi0.5Na0.5TiO3-0.01BiAlO3)-0.03K0.5Na0.5NbO3 (BNT-BA-KNN) ceramics, which not only exhibits a large pyroelectric coefficient (p ˜ 3.7 × 10-8 C cm-2 K-1) and figures of merit (Fi, Fv, and Fd) but also shows excellent thermal stable properties. At room temperature, Fi, Fv, and Fd are determined as high as 1.32 × 10-10 m/V, 2.89 × 10-2 m2/C, and 1.15 × 10-5 Pa-1/2 at 1 kHz and 1.32 × 10-10 m/V, 2.70 × 10-2 m2/C, and 1.09 × 10-5 Pa-1/2 at 20 Hz, respectively. During the temperature range of RT to 85 °C, the achieved p, Fi, Fv, and Fd do not vary too much. The high depolarization temperature and the undispersed ferroelectric-ergodic relaxor phase transition with a sharp pyroelectric coefficient peak value of ˜400 × 10-8 C cm-2 K-1 are suggested to be responsible for this thermal stability, which ensures reliable actual operation. The results reveal the BNT-BA-KNN ceramics as promising lead-free candidates for infrared thermal detector applications.

  15. Five-dimensional visualization of phase transition in BiNiO3 under high pressure

    Liu, Yijin; Wang, Junyue; Yang, Wenge; Azuma, Masaki; Mao, Wendy L.

    2014-01-01

    Colossal negative thermal expansion was recently discovered in BiNiO 3 associated with a low density to high density phase transition under high pressure. The varying proportion of co-existing phases plays a key role in the macroscopic behavior of this material. Here, we utilize a recently developed X-ray Absorption Near Edge Spectroscopy Tomography method and resolve the mixture of high/low pressure phases as a function of pressure at tens of nanometer resolution taking advantage of the charge transfer during the transition. This five-dimensional (X, Y, Z, energy, and pressure) visualization of the phase boundary provides a high resolution method to study the interface dynamics of high/low pressure phase

  16. High-field Transport in Low Symmetry β-Ga2O3 Crystal

    Ghosh, Krishnendu; Singisetti, Uttam

    High-field carrier transport plays an important role in many disciplines of electronics. Conventional transport theories work well on high-symmetry materials but lacks insight as the crystal symmetry goes down. Newly emerging materials, many of which possess low symmetry, demand more rigorous treatment of charge transport. We will present a comprehensive study of high-field transport using ab initio electron-phonon interaction (EPI) elements in a full-band Monte Carlo (FBMC) algorithm. We use monoclinic β-Ga2O3 as a benchmark low-symmetry material which is also an emerging wide-bandgap semiconductor. β-Ga2O3 has a C2m space group and a 10 atom primitive cell. In this work the EPIs are calculated under density-functional perturbation theory framework. We will focus on the computational challenges arising from many phonon modes and low crystal symmetry. Significant insights will be presented on the details of energy relaxation by the hot electrons mediated by different phonon modes. We will also show the velocity-field curves of electrons in different crystal directions. The authors acknowledge the support from the National Science Foundation Grant (ECCS 1607833). The authors also acknowledge the computing support provided by the Center for Computational Research at the University at Buffalo.

  17. Twin-cuvette measurement technique for investigation of dry deposition of O3 and PAN to plant leaves under controlled humidity conditions

    Sun, Shang; Moravek, Alexander; von der Heyden, Lisa; Held, Andreas; Sörgel, Matthias; Kesselmeier, Jürgen

    2016-02-01

    We present a dynamic twin-cuvette system for quantifying the trace-gas exchange fluxes between plants and the atmosphere under controlled temperature, light, and humidity conditions. Compared with a single-cuvette system, the twin-cuvette system is insensitive to disturbing background effects such as wall deposition. In combination with a climate chamber, we can perform flux measurements under constant and controllable environmental conditions. With an Automatic Temperature Regulated Air Humidification System (ATRAHS), we are able to regulate the relative humidity inside both cuvettes between 40 and 90 % with a high precision of 0.3 %. Thus, we could demonstrate that for a cuvette system operated with a high flow rate (> 20 L min-1), a temperature-regulated humidification system such as ATRAHS is an accurate method for air humidification of the flushing air. Furthermore, the fully automatic progressive fill-up of ATRAHS based on a floating valve improved the performance of the entire measurement system and prevented data gaps. Two reactive gas species, ozone (O3) and peroxyacetyl nitrate (PAN), were used to demonstrate the quality and performance of the twin-cuvette system. O3 and PAN exchange with Quercus ilex was investigated over a 14 day measurement period under controlled climate chamber conditions. By using O3 mixing ratios between 32 and 105 ppb and PAN mixing ratios between 100 and 350 ppt, a linear dependency of the O3 flux as well as the PAN flux in relation to its ambient mixing ratio could be observed. At relative humidity (RH) of 40 %, the deposition velocity ratio of O3 and PAN was determined to be 0.45. At that humidity, the deposition of O3 to the plant leaves was found to be only controlled by the leaf stomata. For PAN, an additional resistance inhibited the uptake of PAN by the leaves. Furthermore, the formation of water films on the leaf surface of plants inside the chamber could be continuously tracked with our custom built leaf wetness sensors

  18. O3 Nanoparticles

    Wang, Juan

    2016-11-16

    Ti2O3 nanoparticles with high performance of photothermal conversion are demonstrated for the first time. Benefiting from the nanosize and narrow-bandgap features, the Ti2O3 nanoparticles possess strong light absorption and nearly 100% internal solar–thermal conversion efficiency. Furthermore, Ti2O3 nanoparticle-based thin film shows potential use in seawater desalination and purification.

  19. Synthesis and Structural Study of Sr2CuO3+δ Superconductor under High Pressure

    Qing-Qing, Liu; Fu-Ren, Wang; Feng-Ying, Li; Liang-Chen, Chen; Ri-Cheng, Yu; Chang-Qing, Jin; Yan-Chun, Li; Jing, Liu

    2008-01-01

    A single-phase Sr 2 CuO 3+δ superconductor is synthesized under high temperature and high pressure, in which oxygen atoms only partially occupy the apical sites next to the CuO 2 planes and act as hole-dopants. The superconducting transition temperature with T c max = 75 K is achieved in the material. Structure analysis from x-ray powder diffraction data show that this material crystallizes into a K 2 NiF 4 structure with tetragonal unit cell of a = 3. 795(3) Å and c = 12. 507(1) Å. Energy-dispersive synchrotron x-ray-diffraction studies at ambient are performed on powder samples of Sr 2 CuO 3+δ in a diamond-anvil cell at pressure up to 35 GPa. Anisotropic compressibility is found. Pressure-induced isostructural phase transition might exist as revealed by the discontinuous change of crystal cell volume V with pressure. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  20. High output power of differently cut Nd:MgO:LiTaO3 CW lasers

    Sun, D. H.; Liu, S. D.; Wang, D. Z.; Sang, Y. H.; Kang, X. L.; Liu, H.; Bi, Y.; Yan, B. X.; He, J. L.; Wang, J. Y.

    2013-04-01

    A high-quality Nd3+ and Mg2+ co-doped LiTaO3 (Nd:MgO:LT) crystal was grown by the Czochralski method. The polarized absorption spectra and fluorescence spectra were studied, and the absorption cross section was calculated by Judd-Ofelt (J-O) theory. The laser performance with different sample cuts of the crystal was investigated for the first time, and it was found that Nd:MgO:LT crystal with different cutting directions (a and c) exhibits different laser properties. By optimizing a partial reflectivity mirror in the laser experimental setting, a high continuous wave output power of 3.58 W was obtained at 1092 and 1076 nm with an optical-to-optical conversion efficiency of 22.78% and slope efficiency of 26.06%. The results indicate that Nd:MgO:LT crystal is a promising candidate for the manufacture of Nd3+ doped periodically poled MgO:LiTaO3 crystal (Nd:PPMgOLT), which should have considerable applications in self-frequency doubling and optical parametric oscillation laser devices.

  1. High output power of differently cut Nd:MgO:LiTaO3 CW lasers

    Sun, D H; Liu, S D; Wang, D Z; Sang, Y H; Kang, X L; Liu, H; He, J L; Wang, J Y; Bi, Y; Yan, B X

    2013-01-01

    A high-quality Nd 3+ and Mg 2+ co-doped LiTaO 3 (Nd:MgO:LT) crystal was grown by the Czochralski method. The polarized absorption spectra and fluorescence spectra were studied, and the absorption cross section was calculated by Judd–Ofelt (J–O) theory. The laser performance with different sample cuts of the crystal was investigated for the first time, and it was found that Nd:MgO:LT crystal with different cutting directions (a and c) exhibits different laser properties. By optimizing a partial reflectivity mirror in the laser experimental setting, a high continuous wave output power of 3.58 W was obtained at 1092 and 1076 nm with an optical-to-optical conversion efficiency of 22.78% and slope efficiency of 26.06%. The results indicate that Nd:MgO:LT crystal is a promising candidate for the manufacture of Nd 3+ doped periodically poled MgO:LiTaO 3 crystal (Nd:PPMgOLT), which should have considerable applications in self-frequency doubling and optical parametric oscillation laser devices. (paper)

  2. Ab initio study of properties of BaBiO3 at high pressure

    Martoňák, Roman; Ceresoli, Davide; Kagayama, Tomoko; Tosatti, Erio

    BaBiO3 is a mixed-valence perovskite which escapes metallic state by creating a Bi-O bond disproportionation or CDW pattern, resulting in a Peierls semiconductor with gap of nearly 1 eV at zero pressure. Evolution of structural and electronic properties at high pressure is, however, largely unknown. Pressure, it might be natural to expect, could reduce the bond-disproportionation and bring the system closer to metalicity or even superconductivity. We address this question by ab initio DFT methods based on GGA and hybrid functionals in combination with crystal structure prediction techniques based on genetic algorithms. We analyze the pressure evolution of bond disproportionation as well as other order parameters related to octahedra rotation for various phases in connection with corresponding evolution of the electronic structure. Results indicate that BaBiO3 continues to resist metalization also under pressure, through structural phase transitions which sustain and in fact increase the diversity of length of Bi-O bonds for neighboring Bi ions, in agreement with preliminary high pressure resistivity data. R.M. Slovak Research and Development Agency Contract APVV-15-0496, VEGA project No. 1-0904-15; E.T. ERC MODPHYSFRICT Advanced Grant No. 320796.

  3. High-pressure behavior of beta-Ga2O3 nanocrystals

    Wang, H.; He, Y.; Chen, W.

    2010-01-01

    that nanocrystalline monoclinic beta-Ga2O3 underwent a phase transition to rhombohedral alpha-Ga2O3. It was found that beta- to alpha-Ga2O3 transition began at about 13.6-16.4 GPa, and extended up to 39.2 GPa. At the highest pressure used, only alpha-Ga2O3 was present, which remained after pressure release. A Birch......-Murnaghan fit to the P-V data yielded a zero-pressure bulk modulus at fixed B-0(')=4: B-0=228(9) GPa and B-0=333(19) GPa for beta-Ga2O3 and alpha-Ga2O3 phases, respectively. We compared our results with bulk beta-Ga2O3, and concluded that the phase-transition pressure and bulk modulus of nanocrystalline beta...

  4. Possibilities and limitations of parametric Rietveld refinement on high pressure data. The case study of LaFeO3

    Etter, Martin; Mueller, Melanie; Dinnebier, Robert E.; Hanfland, Michael

    2014-01-01

    Parametric Rietveld refinement is a powerful technique to apply directly physical or empirical equations to the refinement of in situ powder diffraction data. In order to investigate the possibilities and limitations of parametric Rietveld refinements for high pressure data four competitive crystallographic approaches were used to carry out a full structural investigation of the orthoferrite LaFeO 3 (Pbnm at ambient conditions) under high pressure up to 47 GPa. Approach A with traditional Rietveld refinement using atomic coordinates, Approach B where the Rietveld refinement was done by using the rigid body method, Approach C where symmetry modes were used and Approach D where the newly developed method of the rotational symmetry mode description for a rigid body was used. For all approaches sequential as well as parametric refinements were carried out, confirming a second order phase transition of LaFeO 3 to a higher symmetric phase (space group Ibmm) at around 21.1?GPa and an isostructural first order phase transition at around 38 GPa. Limitations due to non-hydrostatic conditions as well as the possibilities of a direct modeling of phase transitions with parametric Rietveld refinement are discussed in detail. (orig.)

  5. Silver-incorporated composites of Fe2O3 carbon nanofibers as anodes for high-performance lithium batteries

    Zou, Mingzhong; Li, Jiaxin; Wen, WeiWei; Chen, Luzhuo; Guan, Lunhui; Lai, Heng; Huang, Zhigao

    2014-12-01

    Composites of Ag-incorporated carbon nanofibers (CNFs) confined with Fe2O3 nanoparticles (Ag-Fe2O3/CNFs) have been synthesized through an electrospinning method and evaluated as anodes for lithium batteries (LIBs). The obtained Ag-Fe2O3/CNF anodes show good LIB performance with a capacity of 630 mAh g-1 tested at 800 mA g-1 after 150 cycles with almost no capacity loss and superb rate performance. The obtained properties for Ag-Fe2O3/CNF anodes are much better than Fe2O3/CNF anodes without Ag-incorporating. In addition, the low-temperature LIB performances for Ag-Fe2O3/CNF anodes have been investigated for revealing the enhanced mechanism of Ag-incorporating. The superior electrochemical performances of the Ag-Fe2O3/CNFs are associated with a synergistic effect of the CNF matrix and the highly conducting Ag incorporating. This unique configuration not only facilitates electron conduction especially at a relative temperature, but also maintains the structural integrity of active materials. Meanwhile, the related analysis of the AC impedance spectroscopy and the corresponding hypothesis for DC impedance confirm that such configuration can effectively enhance the charge-transfer efficiency and the lithium diffusion coefficient. Therefore, CNF-supported coupled with Ag incorporating synthesis supplied a promising route to obtain Fe2O3 based anodes with high-performance LIBs especially at low temperature.

  6. Pentacene based thin film transistors with high-k dielectric Nd2O3 as a gate insulator

    Sarma, R.; Saikia, D.

    2010-01-01

    We have investigated the pentacene based Organic Thin Film Transistors (OTFTs) with high-k dielectric Nd 2 O 3 . Use of high dielectric constant (high-k) gate insulator Nd 2 O 3 reduces the threshold voltage and sub threshold swing of the OTFTs. The calculated threshold voltage -2.2V and sub-threshold swing 1V/decade, current ON-OFF ratio is 1.7 X 10 4 and mobility is 0.13cm 2 /V.s. Pentacene film is deposited on Nd 2 O 3 surface using two step deposition method. Deposited pentacene film is found poly crystalline in nature. (author)

  7. Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al2O3 under a Gaseous-Phase Condition

    Fengyuan Zhang

    2018-03-01

    Full Text Available Tetrahydropyran (THP represents an O-containing hetero-cyclic compound that can be used as a promising solvent or monomer for polymer synthesis. In this work, Cu–ZnO/Al2O3 catalysts have been prepared by a facile precipitation–extrusion method and used for the synthesis of THP through gaseous-phase hydrogenolysis of tetrahydrofurfuryl alcohol (THFA. The effect of the molar ratio of Cu/Zn/Al, reaction temperature, and hydrogen pressure was investigated. An 89.4% selectivity of THP was achieved at 270 °C and 1.0 MPa H2. Meanwhile, the optimum molar ratio of Cu/Zn/Al was determined to be 4:1:10. The Cu–ZnO/Al2O3 catalyst exhibited high catalytic activity and stability for 205 h on-stream. A possible reaction mechanism involving several consecutive reactions was proposed: THFA was firstly rearranged to 2-hydroxytetrahydropyran (2-HTHP, followed by the dehydration of 2-HTHP to 3,4-2H-dihydropyran (DHP over acid sites; finally, the DHP was hydrogenated to THP. The synergy of acid sites and metal sites of Cu–ZnO/Al2O3 played an important role during the production of THP.

  8. Characteristics of Cu–Al2O3 composites of various starting particle size obtained by high-energy milling

    VIŠESLAVA RAJKOVIĆ

    2009-05-01

    Full Text Available The powder Cu– Al2O3 composites were produced by high-energy milling. Various combinations of particle size and mixtures and approximately constant amount of Al2O3 were used as the starting materials. These powders were separately milled in air for up to 20 h in a planetary ball mill. The copper matrix was reinforced by internal oxidation and mechanical alloying. During the milling, internal oxidation of pre-alloyed Cu-2 mass %-Al powder generated 3.7 mass % Al2O3 nano-sized particles finely dispersed in the copper matrix. The effect of different size of the starting copper and Al2O3 powder particles on the lattice parameter, lattice distortion and grain size, as well as on the size, morphology and microstructure of the Cu– Al2O3 composite powder particles was studied.

  9. High-temperature thermoelectric properties of La-doped BaSnO3 ceramics

    Yasukawa, Masahiro; Kono, Toshio; Ueda, Kazushige; Yanagi, Hiroshi; Hosono, Hideo

    2010-01-01

    To elucidate the thermoelectric properties at high temperatures, perovskite-type La-doped BaSnO 3 ceramics were fabricated by a polymerized complex (PC) method and subsequent spark plasma sintering (SPS) technique. Fine powders of Ba 1-x La x SnO 3 (x = 0.00-0.07) were prepared by the PC method using citrate complexes, and SPS treatment converted the powders into dense ceramics with relative densities of 93-97%. The La content dependence of the lattice parameter suggested that the solubility of La for Ba sites was approximately x = 0.03. The temperature dependence of the electrical conductivity σ and Seebeck coefficient S showed that each La-doped ceramic was an n-type degenerate semiconductor in the measured temperature range of 373-1073 K. The La content dependence of the S values indicated that the electron carrier concentration increased successively up to x = 0.03, which was the solubility limit of the La atoms. The thermoelectric power factors S 2 σ increased drastically with La doping, and reached a maximum for x = 0.01 with values of 0.8 x 10 -4 W m -1 K -2 at 373 K to 2.8 x 10 -4 W m -1 K -2 at 1073 K.

  10. Surface Passivation of MoO3 Nanorods by Atomic Layer Deposition Towards High Rate Durable Li Ion Battery Anodes

    Ahmed, Bilal

    2015-06-03

    We demonstrate an effective strategy to overcome the degradation of MoO3 nanorod anodes in Lithium (Li) ion batteries at high rate cycling. This is achieved by conformal nanoscale surface passivation of the MoO3 nanorods by HfO2 using atomic layer deposition (ALD). At high current density such as 1500 mA/g, the specific capacity of HfO2 coated MoO3 electrodes is 68% higher than bare MoO3 electrodes after 50 charge/discharge cycles. After 50 charge/discharge cycles, HfO2 coated MoO3 electrodes exhibited specific capacity of 657 mAh/g, on the other hand, bare MoO3 showed only 460 mAh/g. Furthermore, we observed that HfO2 coated MoO3 electrodes tend to stabilize faster than bare MoO3 electrodes because nanoscale HfO2 layer prevents structural degradation of MoO3 nanorods. Additionally, the growth temperature of MoO3 nanorods and the effect of HfO2 layer thickness was studied and found to be important parameters for optimum battery performance. The growth temperature defines the microstructural features and HfO2 layer thickness defines the diffusion coefficient of Li–ions through the passivation layer to the active material. Furthermore, ex–situ HRTEM, X–ray photoelectron spectroscopy (XPS), Raman spectroscopy and X–ray diffraction was carried out to explain the capacity retention mechanism after HfO2 coating.

  11. Surface Passivation of MoO3 Nanorods by Atomic Layer Deposition Towards High Rate Durable Li Ion Battery Anodes

    Ahmed, Bilal; Shahid, Muhammad; Nagaraju, Doddahalli H.; Anjum, Dalaver H.; Hedhili, Mohamed N.; Alshareef, Husam N.

    2015-01-01

    We demonstrate an effective strategy to overcome the degradation of MoO3 nanorod anodes in Lithium (Li) ion batteries at high rate cycling. This is achieved by conformal nanoscale surface passivation of the MoO3 nanorods by HfO2 using atomic layer deposition (ALD). At high current density such as 1500 mA/g, the specific capacity of HfO2 coated MoO3 electrodes is 68% higher than bare MoO3 electrodes after 50 charge/discharge cycles. After 50 charge/discharge cycles, HfO2 coated MoO3 electrodes exhibited specific capacity of 657 mAh/g, on the other hand, bare MoO3 showed only 460 mAh/g. Furthermore, we observed that HfO2 coated MoO3 electrodes tend to stabilize faster than bare MoO3 electrodes because nanoscale HfO2 layer prevents structural degradation of MoO3 nanorods. Additionally, the growth temperature of MoO3 nanorods and the effect of HfO2 layer thickness was studied and found to be important parameters for optimum battery performance. The growth temperature defines the microstructural features and HfO2 layer thickness defines the diffusion coefficient of Li–ions through the passivation layer to the active material. Furthermore, ex–situ HRTEM, X–ray photoelectron spectroscopy (XPS), Raman spectroscopy and X–ray diffraction was carried out to explain the capacity retention mechanism after HfO2 coating.

  12. Dosimetry of Al2O3 optically stimulated luminescent dosimeter at high energy photons and electrons

    Yusof, M. F. Mohd; Joohari, N. A.; Abdullah, R.; Shukor, N. S. Abd; Kadir, A. B. Abd; Isa, N. Mohd

    2018-01-01

    The linearity of Al2O3 OSL dosimeters (OSLD) were evaluated for dosimetry works in clinical photons and electrons. The measurements were made at a reference depth of Zref according to IAEA TRS 398:2000 codes of practice at 6 and 10 MV photons and 6 and 9 MeV electrons. The measured dose was compared to the thermoluminescence dosimeters (TLD) and ionization chamber commonly used for dosimetry works for higher energy photons and electrons. The results showed that the measured dose in OSL dosimeters were in good agreement with the reported by the ionization chamber in both high energy photons and electrons. A reproducibility test also reported excellent consistency of readings with the OSL at similar energy levels. The overall results confirmed the suitability of OSL dosimeters for dosimetry works involving high energy photons and electrons in radiotherapy.

  13. Routes to High-Temperature Superconductivity: A Lesson from FeSe/SrTiO3

    Lee, Dung-Hai

    2018-03-01

    Raising the superconducting transition temperature to a point where applications are practical is one of the most important challenges in science. In this review, we aim at gaining insights on the Tc controlling factors for a particular high-temperature superconductor family - the FeSe-based superconductors. In particular, we discuss the mechanisms by which the Cooper pairing temperature is enhanced from ˜8 K in bulk FeSe to ˜80 K in the interface between an atomic layer of FeSe and SrTiO3. This includes the experimental hints and the theoretical simulation of the involved mechanisms. We end by applying these insights to suggest some possible high-temperature superconducting systems.

  14. Pressure response of vacancy ordered maghemite (γ-Fe2O3) and high pressure transformed hematite (α-Fe2O3)

    Hearne, Giovanni; Pischedda, Vittoria

    2012-01-01

    Combined XRD and Mössbauer effect spectroscopy studies to high pressures of ∼30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13–16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to ∼15° over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite→hematite transformation. - Graphical abstract: Pressure instigated topotactic transformation of vacancy ordered γ-Fe 2 O 3 →α-Fe 2 O 3 . There is restricted spin (B hf ) reorientation in the new pressure transformed hematite due to entrapped vacancies. The change in direction of V zz signifies a distortion of the FeO 6 octahedral local environment. Highlights: ► Robust vacancy ordered superstructure in maghemite to high pressures. ► Pressure instigated topotactic transformation to hematite and subsequent texture. ► Defect trapping in the pressure transformed hematite. ► Entrapped defects restricts spin reorientation in pressure transformed hematite. ► Contrasting behavior with pressurized hematite starting material.

  15. Effect of thermal gab conductance for MoO3 ampoules irradiated in a high neutron flux

    Abdelhady, Amr

    2010-01-01

    During the irradiation process of MoO 3 powder with in a high neutron flux, energy deposited in the powder must be released to avoid energy accumulation. The temperature increasing in the powder due to energy accumulation may cause powder phase change and under certain conditions the temperature may reach the melting point. An analytical model was developed to study the effect of gap conductance on the temperature distribution in the powder during the irradiation process. The gap conductance model was studied for helium and nitrogen gases at different pressures to obtain the optimum conditions verifying the safety in heat transfer point of view. It was found that the gap conductance is a function of gas pressure. The model provided the optimum conductivity for the gap filled with helium gas at 1 atm pressure. (orig.)

  16. Water Adsorption on a-Fe2O3(0001) at Near Ambient Conditions

    Yamamoto, Susumu

    2011-08-19

    We have investigated hydroxylation and water adsorption on {alpha}-Fe{sub 2}O{sub 3}(0001) at water vapor pressures up to 2 Torr and temperatures ranging from 277 to 647 K (relative humidity (RH) {le} 34%) using ambient-pressure X-ray photoelectron spectroscopy (XPS). Hydroxylation occurs at the very low RH of 1 x 10{sup -7} % and precedes the adsorption of molecular water. With increasing RH, the OH coverage increases up to one monolayer (ML) without any distinct threshold pressure. Depth profiling measurements showed that hydroxylation occurs only at the topmost surface under our experimental conditions. The onset of molecular water adsorption varies from {approx}2 x 10{sup -5} to {approx} 4 x 10{sup -2} % RH depending on sample temperature and water vapor pressure. The coverage of water reaches 1 ML at {approx}15% RH and increases to 1.5 ML at 34% RH.

  17. High glucose induced oxidative stress and apoptosis in cardiac microvascular endothelial cells are regulated by FoxO3a.

    Chaoming Peng

    Full Text Available Cardiac microvascular endothelial cells (CMECs dysfunction contributes to cardiovascular complications in diabetes, whereas, the underlying mechanism is not fully clarified. FoxO transcription factors are involved in apoptosis and reactive oxygen species (ROS production. Therefore, the present study was designed to elucidate the potential role of FoxO3a on the CMECs injury induced by high glucose.CMECs were isolated from hearts of adult rats and cultured in normal or high glucose medium for 6 h, 12 h and 24 h respectively. To down-regulate FoxO3a expression, CMECs were transfected with FoxO3a siRNA. ROS accumulation and apoptosis in CMECs were assessed by dihydroethidine (DHE staining and TUNEL assay respectively. Moreover, the expressions of Akt, FoxO3a, Bim and BclxL in CMECs were assessed by Western blotting assay.ROS accumulation in CMECs was significantly increased after high glucose incubation for 6 to 24 h. Meanwhile, high glucose also increased apoptosis in CMECs, correlated with decreased the phosphorylation expressions of Akt and FoxO3a. Moreover, high glucose incubation increased the expression of Bim, whereas increased anti-apoptotic protein BclxL. Furthermore, siRNA target FoxO3a silencing enhanced the ROS accumulation, whereas suppressed apoptosis in CMECs. FoxO3a silencing also abolished the disturbance of Bcl-2 proteins induced by high glucose in CMECs.Our data provide evidence that high glucose induced FoxO3a activation which suppressed ROS accumulation, and in parallel, resulted in apoptosis of CMECs.

  18. Facilely synthesized Fe2O3–graphene nanocomposite as novel electrode materials for supercapacitors with high performance

    Wang, Zhuo; Ma, Chunyan; Wang, Hailin; Liu, Zonghuai; Hao, Zhengping

    2013-01-01

    Graphical abstract: Fe 2 O 3 Graphene nanocomposite was synthesized in a simple hydrothermal way by using urea to adjust the system pH value, by this method the reduction of graphite oxide and the formation of Fe 2 O 3 nanocomposite are finished in one step. The specific capacitance of the Fe 2 O 3 Graphene electrode reached 226 F/g at a discharge current density of 1 A g –1 . Highlights: ► The Fe 2 O 3 –graphene nanocomposite was obtained by friendly method with urea in one step. ► The addition of Fe 2 O 3 composites has positive effect on the electrical performance of the graphene nanosheets. ► The specific capacitance of the Fe 2 O 3 –graphene electrode was 226 F/g at a discharge current density of 1 A g −1 . -- Abstract: Fe 2 O 3 –graphene nanocomposite with high capacitive properties had been prepared friendly and facilely by hydrothermal method in one-step. The morphology and structure of the obtained material were examined by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and transmission electron microscope (TEM) techniques. It was revealed by TEM images that Fe 2 O 3 nanoparticles grow well on the surface of graphene and the formation of Fe 2 O 3 nanoparticles hinders the aggregation of graphene (reduced graphene oxide, namely, RGO). Electrochemical properties of the synthesized materials were characterized by serials of electrochemical measurements in 1 M Na 2 SO 4 electrolyte. Fe 2 O 3 –graphene nanocomposite electrode show higher specific capacitance than graphene, indicating an accelerative effect of Fe 2 O 3 and graphene on improving the electrochemical performance of the electrode. The specific capacitance of Fe 2 O 3 –graphene nanocomposite is 226 F/g at a current density of 1 A/g. These attractive results indicate it is possible to seek and develop the promising, environmentally benign and commercial electrodes material based on Fe 2 O 3 and graphene

  19. Influence of High-Energy Proton Irradiation on β-Ga2O3 Nanobelt Field-Effect Transistors.

    Yang, Gwangseok; Jang, Soohwan; Ren, Fan; Pearton, Stephen J; Kim, Jihyun

    2017-11-22

    The robust radiation resistance of wide-band gap materials is advantageous for space applications, where the high-energy particle irradiation deteriorates the performance of electronic devices. We report on the effects of proton irradiation of β-Ga 2 O 3 nanobelts, whose energy band gap is ∼4.85 eV at room temperature. Back-gated field-effect transistor (FET) based on exfoliated quasi-two-dimensional β-Ga 2 O 3 nanobelts were exposed to a 10 MeV proton beam. The proton-dose- and time-dependent characteristics of the radiation-damaged FETs were systematically analyzed. A 73% decrease in the field-effect mobility and a positive shift of the threshold voltage were observed after proton irradiation at a fluence of 2 × 10 15 cm -2 . Greater radiation-induced degradation occurs in the conductive channel of the β-Ga 2 O 3 nanobelt than at the contact between the metal and β-Ga 2 O 3 . The on/off ratio of the exfoliated β-Ga 2 O 3 FETs was maintained even after proton doses up to 2 × 10 15 cm -2 . The radiation-induced damage in the β-Ga 2 O 3 -based FETs was significantly recovered after rapid thermal annealing at 500 °C. The outstanding radiation durability of β-Ga 2 O 3 renders it a promising building block for space applications.

  20. High-capacity FeTiO3/C negative electrode for sodium-ion batteries with ultralong cycle life

    Ding, Changsheng; Nohira, Toshiyuki; Hagiwara, Rika

    2018-06-01

    The development of electrode materials which improve both the energy density and cycle life is one of the most challenging issues facing the practical application of sodium-ion batteries today. In this work, FeTiO3/C nanoparticles are synthesized as negative electrode materials for sodium-ion batteries. The electrochemical performance and charge-discharge mechanism of the FeTiO3/C negative electrode are investigated in an ionic liquid electrolyte at 90 °C. The FeTiO3/C negative electrode delivers a high reversible capacity of 403 mAh g-1 at a current rate of 10 mA g-1, and exhibits high rate capability and excellent cycling stability for up to 2000 cycles. The results indicate that FeTiO3/C is a promising negative electrode material for sodium-ion batteries.

  1. Low-temperature growth of highly crystalline β-Ga2O3 nanowires by solid-source chemical vapor deposition.

    Han, Ning; Wang, Fengyun; Yang, Zaixing; Yip, SenPo; Dong, Guofa; Lin, Hao; Fang, Ming; Hung, TakFu; Ho, Johnny C

    2014-01-01

    Growing Ga2O3 dielectric materials at a moderately low temperature is important for the further development of high-mobility III-V semiconductor-based nanoelectronics. Here, β-Ga2O3 nanowires are successfully synthesized at a relatively low temperature of 610°C by solid-source chemical vapor deposition employing GaAs powders as the source material, which is in a distinct contrast to the typical synthesis temperature of above 1,000°C as reported by other methods. In this work, the prepared β-Ga2O3 nanowires are mainly composed of Ga and O elements with an atomic ratio of approximately 2:3. Importantly, they are highly crystalline in the monoclinic structure with varied growth orientations in low-index planes. The bandgap of the β-Ga2O3 nanowires is determined to be 251 nm (approximately 4.94 eV), in good accordance with the literature. Also, electrical characterization reveals that the individual nanowire has a resistivity of up to 8.5 × 10(7) Ω cm, when fabricated in the configuration of parallel arrays, further indicating the promise of growing these highly insulating Ga2O3 materials in this III-V nanowire-compatible growth condition. 77.55.D; 61.46.Km; 78.40.Fy.

  2. A Highly Selective Room Temperature NH3 Gas Sensor based on Nanocrystalline a-Fe2O3

    Priyanka A. PATIL

    2017-05-01

    Full Text Available Nanocrystalline a-Fe2O3 powder was synthesized by simple, inexpensive sol-gel method. The obtained powder was calcined at 700 0C in air atmosphere for 2 hours. The structural and morphological properties of calcined powder were studied by X-ray diffraction (XRD and Field Emission Scanning Electron Microscopy (FESEM respectively. Thermal properties of dried gel were studied by Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC. The XRD pattern of the powder confirmed the a-Fe2O3 (hematite phase of iron oxide with average crystalline size of 30.87 nm calculated from Scherrer equation. The FESEM images showed uniform wormlike morphology of a-Fe2O3 powder. TGA result indicated that a-Fe2O3 is thermodynamically stable. Room temperature NH3 sensing characteristics of a-Fe2O3 were studied for various concentration levels (250-2500 ppm of NH3 at various humid conditions. The sensor based on a-Fe2O3 exhibited good selectivity and excellent sensitivity (S=92 towards 1000 ppm of NH3 with quick response of 4 sec and fast recovery of 9 sec. Room temperature sensing mechanism is also discussed.

  3. Protection of MoO3 high work function by organic thin film

    Wang, Chenggong; Irfan, Irfan; Gao, Yongli

    2014-01-01

    The effects of air exposure are investigated for molybdenum trioxide (MoO 3 ) covered with organic thin films using ultraviolet photoemission spectroscopy. It is found that the severe drop of the work function of MoO 3 by air exposure is substantially reduced by the organic thin films. Both CuPc and C 60 are used for the investigations. The results indicate that the MoO 3 surface can be passivated by approximately two monolayers of organic thin films against exposure to air

  4. High energy transmission of Al2O3 doped with light transition metals

    Schuster, Cosima

    2012-01-31

    The transmission of transparent colored ceramics based on Al2O3doped with light transition metals is measured in the visible and infrared range. To clarify the role of the dopands we perform ab initiocalculations. We discuss the electronic structure and present optical spectra obtained in the independent particle approximation. We argue that the gross spectral features of Co- and Ni-doped Al2O3 samples are described by our model, while the validity of the approach is limited for Cr-doped Al2O3.

  5. High energy transmission of Al2O3 doped with light transition metals

    Schuster, Cosima; Klimke, J.; Schwingenschlö gl, Udo

    2012-01-01

    The transmission of transparent colored ceramics based on Al2O3doped with light transition metals is measured in the visible and infrared range. To clarify the role of the dopands we perform ab initiocalculations. We discuss the electronic structure and present optical spectra obtained in the independent particle approximation. We argue that the gross spectral features of Co- and Ni-doped Al2O3 samples are described by our model, while the validity of the approach is limited for Cr-doped Al2O3.

  6. Conductivity and electrochemical characterization of PrFe1-xNixO3-δ at high temperature

    Hashimoto, Shin-Ichi; Kammer Hansen, Kent; Poulsen, Finn Willy

    2007-01-01

    PrFe(1-x)NixO(3)- (x=0.4-0.6) compounds were synthesized and characterized by powder XRD, electrical conductivity and electrochemical impedance spectroscopy on point electrodes on a Ce0.9Gd0.1O2-delta (CGO10) electrolyte. As a reference, the electrochemical performance of LaFe(0.4)AM(0.6)O(3-delta......) was also measured. The main phase in the PrFe1-xNixO3-delta series was perovskite-type structure and belonged to the orthorhombic crystal system. The conductivities are fairly high, e.g. around 220 S cm(-1) at 873 K for the x = 0.4 compound. The electrochemical performance of the PrFe(1-x)NixO(3-delta...

  7. Synthesis of highly efficient Mn2O3 catalysts for CO oxidation derived from Mn-MIL-100

    Zhang, Xiaodong; Li, Hongxin; Hou, Fulin; Yang, Yang; Dong, Han; Liu, Ning; Wang, Yuxin; Cui, Lifeng

    2017-07-01

    In this work, metal-organic frameworks (MOFs) Mn-MIL-100 were first prepared, which were next used as templates to obtain the irregular porous Mn2O3 cubes through calcination with air at different temperature. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), H2-temperature program reduction (H2-TPR) and X-ray photoelectron spectroscopic (XPS). The catalytic activity for CO oxidation over Mn2O3 catalysts was investigated. It was found that calcination temperature had a strong effect on the structure and catalytic activity of Mn2O3 catalyst. Mn2O3 catalyst obtained by calcined at 700 °C (Mn2O3-700) showed a smaller specific surface area, but displayed a high catalytic activity and excellent stability with a complete CO conversion temperature (T98) of 240 °C, which was attributed to the unique structure, a high quantity of surface active oxygen species, smaller particle size, oxygen vacancies and good low temperature reduction behavior. The effect of water vapor on catalytic activity was also examined. The introduction of water vapor to the feedstock induced a positive effect on CO oxidation over Mn2O3-700 catalyst. Furthermore, no obvious drop is observed in activity over catalysts even in the presence of water vapor during 48 h.

  8. High energy proton simulation of 14-MeV neutron damage in Al2O3

    Muir, D.W.; Bunch, J.M.

    1975-01-01

    High-energy protons are a potentially useful tool for simulating the radiation damage produced by 14-MeV neutrons in CTR materials. A comparison is given of calculations and measurements of the relative damage effectiveness of these two types of radiation in single-crystal Al 2 O 3 . The experiments make use of the prominent absorption band at 206 nm as an index to lattice damage, on the assumption that peak absorption is proportional to the concentration of lattice vacancies. The induced absorption is measured for incident proton energies ranging from 5 to 15 MeV and for 14-MeV neutrons. Recoil-energy spectra are calculated for elastic and inelastic scattering using published angular distributions. Recoil-energy spectra also are calculated for the secondary alpha particles and 12 C nuclei produced by (p,p'α) reactions on 16 O. The recoil spectra are converted to damage-energy spectra and then integrated to yield the damage-energy cross section at each proton energy and for 14 MeV neutrons. A comparison of the calculations with experimental results suggests that damage energy, at least at high energies, is a reasonable criterion for estimating this type of radiation damage. (auth)

  9. Ag-Modified In2O3 Nanoparticles for Highly Sensitive and Selective Ethanol Alarming

    Jinxiao Wang

    2017-09-01

    Full Text Available Pure In2O3 nanoparticles are prepared by a facile precipitation method and are further modified by Ag. The synthesized samples are characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Raman and UV-Vis spectra. The results show the successful heterojunction formation between Ag and In2O3. Gas sensing property measurements show that the 5 mol % Ag-modified In2O3 sensor has the response of 67 to 50 ppm ethanol, and fast response and recovery time of 22.3 and 11.7 s. The response is over one magnitude higher than that of pure In2O3, which can be attributed to the enhanced catalytic activity of Ag-modified In2O3 as compared with the pure one. The mechanism of the gas sensor can be explained by the spillover effect of Ag, which enhances the oxygen adsorption onto the surface of In2O3 and thus give rise to the higher activity and larger surface barrier height.

  10. Separation and recovery of high grade Dy2O3 by solvent extraction process with DEHPA in kerosene

    Mishra, S.L.; Thakur, N.V.; Koppiker, K.S.

    1993-01-01

    During the solvent extraction (SX) fractionation of rare earths chloride obtained from monazite, a heavy RE (HRE) fraction assaying 60% Y 2 O 3 is produced. This is purified further to 93% Y 2 O 3 by another SX cycle. During this step most of Dy and Tb get separated to yield a concentrate assaying >50% Dy 2 O 3 . An attempt has been made to process this Dy rich concentrate to obtain a high grade Dy 2 O 3 by a SX route using DEHPA in kerosene. The distribution data (D vs H i + ) of Dy have been generated experimentally at various metal concentrations and similar data for other metals present (Gd, Tb, Y, Er and Ho) have been derived using a mathematical expression developed in our laboratory. Based on this information mathematical models for extraction behaviour of these HRE have been derived and used in a computer program developed for multicomponent system. This program has been utilised to optimise the process parameters to obtain 95-97% pure Dy 2 O 3 at about 90% recovery. The parameters have been experimentally confirmed and Dy 2 O 3 95.5% pure w.r.t. Tb was obtained at about 90% recovery, thus confirming the validity of the program. This paper presents data obtained during these investigations. (author). 6 refs., 5 tabs

  11. Electrical Conduction of Ba(Ti0.99Fe0.01)O3-δ Ceramic at High Temperatures

    Yu, Zi-De; Chen, Xiao-Ming

    2018-03-01

    BaTiO3 and Ba(Ti0.99Fe0.01)O3-δ ceramics with dense microstructure have been synthesized by a solid-state reaction method, and their electrical conduction investigated by broadband electrical impedance spectroscopy at frequencies from 0.05 Hz to 3 × 106 Hz and temperatures from 200°C to 400°C. Compared with BaTiO3, the real part of the permittivity and the phase-transition temperature of Ba(Ti0.99Fe0.01)O3-δ decreased. Relaxation peaks appeared in the curves of the imaginary part of the permittivity as a function of frequency. With increase in frequency, the peaks gradually shifted towards higher frequency and their height increased. Conductivity was closely related to frequency and temperature. Frequency-dependent conductivity was analyzed using the Jonscher double power law. Compared with BaTO3, Ba(Ti0.99Fe0.01)O3-δ exhibited high impedance at given frequency and temperature. Impedance Cole-Cole plots displayed two semicircles, which could be well fit using two parallel RC equivalent circuit models. The conductivity activation energy was found to be around 1 eV. For Ba(Ti0.99Fe0.01)O3-δ , the electrical modulus curve versus frequency displayed two peaks.

  12. In-situ preparation of Fe2O3 hierarchical arrays on stainless steel substrate for high efficient catalysis

    Yang, Zeheng; Wang, Kun; Shao, Zongming; Tian, Yuan; Chen, Gongde; Wang, Kai; Chen, Zhangxian; Dou, Yan; Zhang, Weixin

    2017-01-01

    Hierarchical array catalysts with micro/nano structures on substrates not only possess high reactivity from large surface area and suitable interface, but intensify mass transfer through shortening the diffusion paths of both reactants and products for high catalytic efficiency. Herein, we first demonstrate fabrication of Fe 2 O 3 hierarchical arrays grown on stainless-steel substrates via in-situ hydrothermal chemical oxidation followed by heat treatment in N 2 atmosphere. As a Fenton-like catalyst, Fe 2 O 3 hierarchical arrays exhibit excellent catalytic activity and life cycle performance for methylene blue (MB) dye degradation in aqueous solution in the presence of H 2 O 2 . The Fe 2 O 3 catalyst with unique hierarchical structures and efficient transport channels, effectively activates H 2 O 2 to generate large quantity of • OH radicals and highly promotes reaction kinetics between MB and • OH radicals. Immobilization of hierarchical array catalysts on stainless-steel can prevent particles agglomeration, facilitate the recovery and reuse of the catalysts, which is expected promising applications in wastewater remediation. - Graphical abstract: The in-situ synthesis of Fe 2 O 3 hierarchical arrays on stainless-steel substrates was reported for the first time, which exhibit excellent catalytic activity performance for methylene blue (MB) dye degradation in aqueous solution in the presence of H 2 O 2 . - Highlights: • Fe 2 O 3 hierarchical arrays was prepared by in-situ hydrothermal chemical oxidation. • F − ions play an important role in the formation of the Fe 2 O 3 hierarchical arrays. • Fe 2 O 3 hierarchical arrays show high catalytic activity to methylene blue degradation.

  13. Incipient 2D Mott insulators in extreme high electron density, ultra-thin GdTiO3/SrTiO3/GdTiO3 quantum wells

    Allen, S. James; Ouellette, Daniel G.; Moetakef, Pouya; Cain, Tyler; Chen, Ru; Balents, Leon; Stemmer, Susanne

    2013-03-01

    By reducing the number of SrO planes in a GdTiO3 /SrTiO3/ GdTiO3 quantum well heterostructure, an electron gas with ~ fixed 2D electron density can be driven close to the Mott metal insulator transition - a quantum critical point at ~1 electron per unit cell. A single interface between the Mott insulator GdTiO3 and band insulator SrTiO3 has been shown to introduce ~ 1/2 electron per interface unit cell. Two interfaces produce a quantum well with ~ 7 1014 cm-2 electrons: at the limit of a single SrO layer it may produce a 2D magnetic Mott insulator. We use temperature and frequency dependent (DC - 3eV) conductivity and temperature dependent magneto-transport to understand the relative importance of electron-electron interactions, electron-phonon interactions, and surface roughness scattering as the electron gas is compressed toward the quantum critical point. Terahertz time-domain and FTIR spectroscopies, measure the frequency dependent carrier mass and scattering rate, and the mid-IR polaron absorption as a function of quantum well thickness. At the extreme limit of a single SrO plane, we observe insulating behavior with an optical gap substantially less than that of the surrounding GdTiO3, suggesting a novel 2D Mott insulator. MURI program of the Army Research Office - Grant No. W911-NF-09-1-0398

  14. Structure of high alumina content Al2O3-SiO2 composition glasses.

    Weber, Richard; Sen, Sabyasachi; Youngman, Randall E; Hart, Robert T; Benmore, Chris J

    2008-12-25

    The structure of binary aluminosilicate glasses containing 60-67 mol % Al2O3 were investigated using high-resolution 27Al NMR and X-ray and neutron diffraction. The glasses were made by aerodynamic levitation of molten oxides. The 67% alumina composition required a cooling rate of approximately 1600 degrees C s(1-) to form glass from submillimeter sized samples. NMR results show that the glasses contain aluminum in 4-, 5-, and 6-fold coordination in the approximate ratio 4:5:1. The average Al coordination increases from 4.57 to 4.73 as the fraction of octahedral Al increases with alumina content. The diffraction results on the 67% composition are consistent with a disordered Al framework with Al ions in a range of coordination environments that are substantially different from those found in the equilibrium crystalline phases. Analysis of the neutron and X-ray structure factors yields an average bond angle of 125 +/- 4 degrees between an Al ion and the adjoining cation via a bridging oxygen. We propose that the structure of the glass is a "transition state" between the alumina-rich liquid and the equilibrium mullite phase that are dominated by 4- and 6-coordinated aluminum ions, respectively.

  15. High definition surface micromachining of LiNbO 3 by ion implantation

    Chiarini, M.; Bentini, G. G.; Bianconi, M.; De Nicola, P.

    2010-10-01

    High Energy Ion Implantation (HEII) of both medium and light mass ions has been successfully applied for the surface micromachining of single crystal LiNbO 3 (LN) substrates. It has been demonstrated that the ion implantation process generates high differential etch rates in the LN implanted areas, when suitable implantation parameters, such as ion species, fluence and energy, are chosen. In particular, when traditional LN etching solutions are applied to suitably ion implanted regions, etch rates values up to three orders of magnitude higher than the typical etching rates of the virgin material, are registered. Further, the enhancement in the etching rate has been observed on x, y and z-cut single crystalline material, and, due to the physical nature of the implantation process, it is expected that it can be equivalently applied also to substrates with different crystallographic orientations. This technique, associated with standard photolithographic technologies, allows to generate in a fast and accurate way very high aspect ratio relief micrometric structures on LN single crystal surface. In this work a description of the developed technology is reported together with some examples of produced micromachined structures: in particular very precisely defined self sustaining suspended structures, such as beams and membranes, generated on LN substrates, are presented. The developed technology opens the way to actual three dimensional micromachining of LN single crystals substrates and, due to the peculiar properties characterising this material, (pyroelectric, electro-optic, acousto-optic, etc.), it allows the design and the production of complex integrated elements, characterised by micrometric features and suitable for the generation of advanced Micro Electro Optical Systems (MEOS).

  16. Controllable electrical properties of metal-doped In2O3 nanowires for high-performance enhancement-mode transistors.

    Zou, Xuming; Liu, Xingqiang; Wang, Chunlan; Jiang, Ying; Wang, Yong; Xiao, Xiangheng; Ho, Johnny C; Li, Jinchai; Jiang, Changzhong; Xiong, Qihua; Liao, Lei

    2013-01-22

    In recent years, In(2)O(3) nanowires (NWs) have been widely explored in many technological areas due to their excellent electrical and optical properties; however, most of these devices are based on In(2)O(3) NW field-effect transistors (FETs) operating in the depletion mode, which induces relatively higher power consumption and fancier circuit integration design. Here, n-type enhancement-mode In(2)O(3) NW FETs are successfully fabricated by doping different metal elements (Mg, Al, and Ga) in the NW channels. Importantly, the resulting threshold voltage can be effectively modulated through varying the metal (Mg, Ga, and Al) content in the NWs. A series of scaling effects in the mobility, transconductance, threshold voltage, and source-drain current with respect to the device channel length are also observed. Specifically, a small gate delay time (0.01 ns) and high on-current density (0.9 mA/μm) are obtained at 300 nm channel length. Furthermore, Mg-doped In(2)O(3) NWs are then employed to fabricate NW parallel array FETs with a high saturation current (0.5 mA), on/off ratio (>10(9)), and field-effect mobility (110 cm(2)/V·s), while the subthreshold slope and threshold voltage do not show any significant changes. All of these results indicate the great potency for metal-doped In(2)O(3) NWs used in the low-power, high-performance thin-film transistors.

  17. Highly piezoelectric BaTiO3 nanorod bundle arrays using epitaxially grown TiO2 nanomaterials

    Jang, Seon-Min; Yang, Su Chul

    2018-06-01

    Low-dimensional piezoelectric nanostructures such as nanoparticles, nanotubes, nanowires, nanoribbons and nanosheets have been developed for potential applications as energy harvesters, tunable sensors, functional transducers and low-power actuators. In this study, lead-free BaTiO 3 nanorod bundle arrays (NBA) with highly piezoelectric properties were successfully synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step process consisting of TiO2 epitaxial growth and BaTiO3 conversion. Through the TiO2 epitaxial growth on FTO substrate, (001) oriented TiO2 nanostructures formed vertically-aligned NBA with a bundle diameter of 80 nm and an aspect ratio of six. In particular, chemical etching of the TiO2 NBA was conducted to enlarge the surface area for effective Ba2+ ion diffusion during the perovskite conversion process from TiO2 to BaTiO3. The final structure of perovskite BaTiO3 NBA was found to exhibit a feasible piezoelectric response of 3.56 nm with a clear phase change of 180° from the single BaTiO3 bundle, by point piezoelectric forced microscopy (PFM) analysis. Consequently, highly piezoelectric NBA could be a promising nanostructure for various nanoscale electronic devices.

  18. Highly piezoelectric BaTiO3 nanorod bundle arrays using epitaxially grown TiO2 nanomaterials.

    Jang, Seon-Min; Yang, Su Chul

    2018-06-08

    Low-dimensional piezoelectric nanostructures such as nanoparticles, nanotubes, nanowires, nanoribbons and nanosheets have been developed for potential applications as energy harvesters, tunable sensors, functional transducers and low-power actuators. In this study, lead-free BaTiO 3 nanorod bundle arrays (NBA) with highly piezoelectric properties were successfully synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step process consisting of TiO 2 epitaxial growth and BaTiO 3 conversion. Through the TiO 2 epitaxial growth on FTO substrate, (001) oriented TiO 2 nanostructures formed vertically-aligned NBA with a bundle diameter of 80 nm and an aspect ratio of six. In particular, chemical etching of the TiO 2 NBA was conducted to enlarge the surface area for effective Ba 2+ ion diffusion during the perovskite conversion process from TiO 2 to BaTiO 3 . The final structure of perovskite BaTiO 3 NBA was found to exhibit a feasible piezoelectric response of 3.56 nm with a clear phase change of 180° from the single BaTiO 3 bundle, by point piezoelectric forced microscopy (PFM) analysis. Consequently, highly piezoelectric NBA could be a promising nanostructure for various nanoscale electronic devices.

  19. Surface damages of polycrystalline W and La2O3-doped W induced by high-flux He plasma irradiation

    Liu, Lu; Li, Shouzhe; Liu, Dongping; Benstetter, Günther; Zhang, Yang; Hong, Yi; Fan, Hongyu; Ni, Weiyuan; Yang, Qi; Wu, Yunfeng; Bi, Zhenhua

    2018-04-01

    In this study, polycrystalline tungsten (W) and three oxide dispersed strengthened W with 0.1 vol %, 1.0 vol % and 5.0 vol % lanthanum trioxide (La2O3) were irradiated with low-energy (200 eV) and high-flux (5.8 × 1021 or 1.4 × 1022 ions/m2ṡs) He+ ions at elevated temperature. After He+ irradiation at a fluence of 3.0 × 1025/m2, their surface damages were observed by scanning electron microscopy, energy dispersive spectroscopy, scanning electron microscopy-electron backscatter diffraction, and conductive atomic force microscopy. Micron-sized holes were formed on the surface of W alloys after He+ irradiation at 1100 K. Analysis shows that the La2O3 grains doped in W were sputtered preferentially by the high-flux He+ ions when compared with the W grains. For irradiation at 1550 K, W nano-fuzz was formed at the surfaces of both polycrystalline W and La2O3-doped W. The thickness of the fuzz layers formed at the surface of La2O3-doped W is 40% lower than the one of polycrystalline W. The presence of La2O3 could suppress the diffusion and coalescence of He atoms inside W, which plays an important role in the growth of nanostructures fuzz.

  20. High-Transparency Sputtered In2O3 and ITO Films Containing Zirconium (Presentation)

    Gessert, T. A.; Yoshida, Y.; Fesenmaier, C. C.; Coutts, T. J.

    2007-01-01

    Our recent investigations have identified a method to produce ITO-like films that are less sensitive to variations in the oxygen-containing deposition ambient. Specifically, we are studying the effect of adding small amounts of Zr to both In2O3 and ITO ceramic sputtering targets

  1. Novel ultrathin Bi2O3 nanowires for supercapacitor electrode materials with high performance

    Qiu, Yongfu; Fan, Hongbo; Chang, Xueyi; Dang, Haifeng; Luo, Qun; Cheng, Zhiyu

    2018-03-01

    In this paper, the ultrathin Bi2O3 nanowires are synthesized by an oxidative metal vapor transport deposition technique. Their diameters and length are about 10 nm and several tens of micrometers, the growth direction is along [101] and the specific surface area is about 7.34 m2 g-1. The galvanostatic charge-discharge measurement results show that the specific capacitances of the Bi2O3 nanowires-based electrodes increase with the decrease of the current densities. The maximum capacitance is 691.3 F g-1 at the current density of 2.0 A g-1. The Ragone plot shows that the Bi2O3 nanowires has excellent supercapacitive performance. Moreover, the cyclic stability is measured by the galvanostatic charge/discharge technique at a constant current density of 10.0 A g-1 in 6.0 M KOH electrolyte. The results show the excellent capacitance retention of 75.5% over 3000 cycles. In a word, the Bi2O3 nanowires should be the ideal potential electrode materials for low-costing and effective electrochemical supercapacitors.

  2. Is LaAlO3 a viable substrate for the deposition of high quality thin films of YBa2Cu3O7-δ?

    Koren, Gad; Polturak, Emil

    2002-01-01

    A systematic study of the surface morphology of epitaxial thin films of YBa 2 Cu 3 O 7-δ on (100) LaAlO 3 wafers is reported. The films were prepared by high pressure dc sputtering or laser ablation deposition, on wafers of 0.5-2.8 mm thickness and 2 or 3 inch diameter. Optical and atomic force microscopy (AFM) were used to characterize the surfaces, while transport was used to verify the high quality of the films. For films prepared under the same conditions, we found a systematic increase in size and number of extended defects in the films with wafer thickness. In some cases, a clear correlation was observed between the defect structure and the twin boundaries of the LaAlO 3 substrate. We specify the conditions for minimizing these defects. (author)

  3. An equation of state for high pressure-temperature liquids (RTpress) with application to MgSiO3 melt

    Wolf, Aaron S.; Bower, Dan J.

    2018-05-01

    The thermophysical properties of molten silicates at extreme conditions are crucial for understanding the early evolution of Earth and other massive rocky planets, which is marked by giant impacts capable of producing deep magma oceans. Cooling and crystallization of molten mantles are sensitive to the densities and adiabatic profiles of high-pressure molten silicates, demanding accurate Equation of State (EOS) models to predict the early evolution of planetary interiors. Unfortunately, EOS modeling for liquids at high P-T conditions is difficult due to constantly evolving liquid structure. The Rosenfeld-Tarazona (RT) model provides a physically sensible and accurate description of liquids but is limited to constant volume heating paths (Rosenfeld and Tarazona, 1998). We develop a high P-T EOS for liquids, called RTpress, which uses a generalized Rosenfeld-Tarazona model as a thermal perturbation to isothermal and adiabatic reference compression curves. This approach provides a thermodynamically consistent EOS which remains accurate over a large P-T range and depends on a limited number of physically meaningful parameters that can be determined empirically from either simulated or experimental datasets. As a first application, we model MgSiO3 melt representing a simplified rocky mantle chemistry. The model parameters are fitted to the MD simulations of both Spera et al. (2011) and de Koker and Stixrude (2009), recovering pressures, volumes, and internal energies to within 0.6 GPa, 0.1 Å3 , and 6 meV per atom on average (for the higher resolution data set), as well as accurately predicting liquid densities and temperatures from shock-wave experiments on MgSiO3 glass. The fitted EOS is used to determine adiabatic thermal profiles, revealing the approximate thermal structure of a fully molten magma ocean like that of the early Earth. These adiabats, which are in strong agreement for both fitted models, are shown to be sufficiently steep to produce either a center

  4. The role of mechanical boundary conditions in the soft mode dynamics of PbTiO3.

    McCash, Kevin; Mani, B K; Chang, C-M; Ponomareva, I

    2014-10-29

    The role of different mechanical boundary conditions in the soft mode dynamics of ferroelectric PbTiO3 is systematically investigated using first-principles-based simulations and analytical model. The change in the soft mode dynamics due to hydrostatic pressure, uniaxial and biaxial stresses and biaxial strains is studied in a wide temperature range. Our computations predict: (i) the existence of Curie-Weiss laws that relate the soft mode frequency to the stress or strain; (ii) a non-trivial temperature evolution of the associated Curie-Weiss constants; (iii) a qualitative difference between the soft mode response to stresses/strains and hydrostatic pressure. The latter finding implies that the Curie-Weiss pressure law commonly used for residual stress estimation may not apply for the cases of uniaxial and biaxial stresses and strains. On the other hand, our systematic study offers a way to eliminate this difficulty through the establishment of Curie-Weiss stress and strain laws. Implications of our predictions for some available experimental data are discussed.

  5. Enhanced flux pinning by BaZrO3 and (Gd,y)2O3 nano-structures in metal organic chemical vapor deposited GdYBCO high temperature superconductor tapes

    Chen, Y [SuperPower Incorporated, Schenectady, New York; Selvamanickam, V. [SuperPower Incorporated, Schenectady, New York; Paranthaman, Mariappan Parans [ORNL; Cantoni, Claudia [ORNL; Aytug, Tolga [ORNL; Goyal, Amit [ORNL; Lee, Dominic F [ORNL; Specht, Eliot D [ORNL; Zuev, Yuri L [ORNL; Zhang, Yifei [ORNL

    2009-01-01

    We have formed BaZrO3 nano-columns and (Gd,Y)2O3 nano-precipitates in reel-to-reel MOCVD processed (Gd,Y)Ba2Cu3O7-x coated conductors and increased the critical currents (Ic) of the conductors in applied magnetic fields to remarkable levels. A (Gd,Y)Ba2Cu3O7-x tape of 1m length with 6.5% Zr-additions and 30% composition rich in both Gd and Y showed Ic values of 813 A/cm-width at (self-field, 77K) and above 186 A/cm-width at (1T, 77K). The strongly enhanced flux pinning over a wide range of magnetic field orientations can be attributed to the bidirectionally aligned defect structures of BaZrO3 and (Gd,Y)2O3 created by optimized MOCVD conditions.

  6. Synthesis of single-crystal perovskite PbCrO3 through a new reaction route at high pressure

    Han, Yunxia; Wang, Shanmin; Liu, Yinjuan; Ma, Dejiang; He, Duanwei; Zhao, Yusheng

    2018-04-01

    As a new member in the family of Mott system, perovskite PbCrO3 has recently been uncovered to exhibit fantastic structural transition under pressure, coupled with magnetic, electronic, and ferromagnetic transitions, which provide many opportunities for understanding of correlated system. However, it is still challenging to synthesize high-quality single-crystal PbCrO3, leading to the limited exploration of this Mott compound. In this work, we formulate a new high-pressure reaction route for preparation of high-quality PbCrO3 crystals between PbCl2 and Na2CrO4 at high pressure of 5-10 GPa and at high temperature of 750-1500°C. Because of the formation of reaction byproduct NaCl, the final product can readily be separated by washing with water. The obtained sample is in the form of single crystal with crystallite size up to 200 μm. In addition, combined with X-ray diffraction measurement, a tentative pressure-temperature synthesis diagram of PbCrO3 is mapped out from the reaction between PbCl2 and Na2CrO4 and the reaction mechanism is also explored in detail.

  7. Synthesis, Tunable Multicolor Output, and High Pure Red Upconversion Emission of Lanthanide-Doped Lu2O3 Nanosheets

    Lingzhen Yin

    2013-01-01

    Full Text Available Yb3+ and Ln3+ (Ln = Er, Ho codoped Lu2O3 square nanocubic sheets were successfully synthesized via a facile hydrothermal method followed by a subsequent dehydration process. The crystal phase, morphology, and composition of hydroxide precursors and target oxides were characterized by X-ray diffraction (XRD, field emission scanning electron microscope (FE-SEM, and energy-dispersive X-ray spectroscope (EDS. Results present the as-prepared Lu2O3 crystallized in cubic phase, and the monodispersed square nanosheets were maintained both in hydroxide and oxides. Moreover, under 980 nm laser diode (LD excitation, multicolor output from red to yellow was realized by codoped different lanthanide ions in Lu2O3. It is noteworthy that high pure strong red upconversion emission with red to green ratio of 443.3 of Er-containing nanocrystals was obtained, which is beneficial for in vivo optical bioimaging.

  8. EFFECT OF La2O3 ON HIGH-TEMPERATURE OXIDATION RESISTANCE OF ELECTROSPARK DEPOSITED Ni-BASED COATINGS

    YUXIN GAO; JIAN YI; ZHIGANG FANG; HU CHENG

    2014-01-01

    The oxidation tests of electrospark deposited Ni-based coatings without and with 2.5 wt.% La2O3 were conducted at 960°C in air for 100 h. The oxidation kinetic of the coatings was studied by testing the weight gain. The phase structures and morphologies of the oxidized coatings were investigated by XRD and SEM. The experimental results show that the coatings with 2.5 wt.% La2O3 exhibits excellent high-temperature oxidation resistance including low oxidation rate and improved spallation resist...

  9. High performance GaN-based LEDs on patterned sapphire substrate with patterned composite SiO2/Al2O3 passivation layers and TiO2/Al2O3 DBR backside reflector.

    Guo, Hao; Zhang, Xiong; Chen, Hongjun; Zhang, Peiyuan; Liu, Honggang; Chang, Hudong; Zhao, Wei; Liao, Qinghua; Cui, Yiping

    2013-09-09

    GaN-based light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with patterned composite SiO(2)/Al(2)O(3) passivation layers and TiO(2)/Al(2)O(3) distributed Bragg reflector (DBR) backside reflector have been proposed and fabricated. Highly passivated Al(2)O(3) layer deposited on indium tin oxide (ITO) layer with excellent uniformity and quality has been achieved with atomic layer deposition (ALD) technology. With a 60 mA current injection, an enhancement of 21.6%, 59.7%, and 63.4% in the light output power (LOP) at 460 nm wavelength was realized for the LED with the patterned composite SiO(2)/Al(2)O(3) passivation layers, the LED with the patterned composite SiO(2)/Al(2)O(3) passivation layers and Ag mirror + 3-pair TiO(2)/SiO(2) DBR backside reflector, and the LED with the patterned composite SiO(2)/Al(2)O(3) passivation layer and Ag mirror + 3-pair ALD-grown TiO(2)/Al(2)O(3) DBR backside reflector as compared with the conventional LED only with a single SiO(2) passivation layer, respectively.

  10. Suppressing the Photocatalytic Activity of TiO2 Nanoparticles by Extremely Thin Al2O3 Films Grown by Gas-Phase Deposition at Ambient Conditions

    Jing Guo

    2018-01-01

    Full Text Available This work investigated the suppression of photocatalytic activity of titanium dioxide (TiO2 pigment powders by extremely thin aluminum oxide (Al2O3 films deposited via an atomic-layer-deposition-type process using trimethylaluminum (TMA and H2O as precursors. The deposition was performed on multiple grams of TiO2 powder at room temperature and atmospheric pressure in a fluidized bed reactor, resulting in the growth of uniform and conformal Al2O3 films with thickness control at sub-nanometer level. The as-deposited Al2O3 films exhibited excellent photocatalytic suppression ability. Accordingly, an Al2O3 layer with a thickness of 1 nm could efficiently suppress the photocatalytic activities of rutile, anatase, and P25 TiO2 nanoparticles without affecting their bulk optical properties. In addition, the influence of high-temperature annealing on the properties of the Al2O3 layers was investigated, revealing the possibility of achieving porous Al2O3 layers. Our approach demonstrated a fast, efficient, and simple route to coating Al2O3 films on TiO2 pigment powders at the multigram scale, and showed great potential for large-scale production development.

  11. Hierarchical Mn2O3 Microspheres In-Situ Coated with Carbon for Supercapacitors with Highly Enhanced Performances

    Gong, Feilong; Lu, Shuang; Peng, Lifang; Zhou, Jing; Kong, Jinming; Jia, Dianzeng; Li, Feng

    2017-01-01

    Porous Mn2O3 microspheres have been synthesized and in-situ coated with amorphous carbon to form hierarchical C@Mn2O3 microspheres by first producing MnCO3 microspheres in solvothermal reactions, and then annealing at 500 °C. The self-assembly growth of MnCO3 microspheres can generate hollow structures inside each of the particles, which can act as micro-reservoirs to store biomass-glycerol for generating amorphous carbon onto the surfaces of Mn2O3 nanorods consisting of microspheres. The C@Mn2O3 microspheres, prepared at 500 °C, exhibit highly enhanced pseudocapacitive performances when compared to the particles after annealed at 400 °C and 600 °C. Specifically, the C@Mn2O3 microspheres prepared at 500 °C show high specific capacitances of 383.87 F g−1 at current density of 0.5 A g−1, and excellent cycling stability of 90.47% of its initial value after cycling for 5000 times. The asymmetric supercapacitors assembled with C@Mn2O3 microspheres after annealed at 500 °C and activated carbon (AC) show an energy density of up to 77.8 Wh kg−1 at power density of 500.00 W kg−1, and a maximum power density of 20.14 kW kg−1 at energy density of 46.8 Wh kg−1. We can attribute the enhanced electrochemical performances of the materials to their three-dimensional (3D) hierarchical structure in-situ coated with carbon. PMID:29168756

  12. Hierarchical Mn2O3 Microspheres In-Situ Coated with Carbon for Supercapacitors with Highly Enhanced Performances

    Feilong Gong

    2017-11-01

    Full Text Available Porous Mn2O3 microspheres have been synthesized and in-situ coated with amorphous carbon to form hierarchical C@Mn2O3 microspheres by first producing MnCO3 microspheres in solvothermal reactions, and then annealing at 500 °C. The self-assembly growth of MnCO3 microspheres can generate hollow structures inside each of the particles, which can act as micro-reservoirs to store biomass-glycerol for generating amorphous carbon onto the surfaces of Mn2O3 nanorods consisting of microspheres. The C@Mn2O3 microspheres, prepared at 500 °C, exhibit highly enhanced pseudocapacitive performances when compared to the particles after annealed at 400 °C and 600 °C. Specifically, the C@Mn2O3 microspheres prepared at 500 °C show high specific capacitances of 383.87 F g−1 at current density of 0.5 A g−1, and excellent cycling stability of 90.47% of its initial value after cycling for 5000 times. The asymmetric supercapacitors assembled with C@Mn2O3 microspheres after annealed at 500 °C and activated carbon (AC show an energy density of up to 77.8 Wh kg−1 at power density of 500.00 W kg−1, and a maximum power density of 20.14 kW kg−1 at energy density of 46.8 Wh kg−1. We can attribute the enhanced electrochemical performances of the materials to their three-dimensional (3D hierarchical structure in-situ coated with carbon.

  13. Electrical performance of multilayer MoS2 transistors on high-κ Al2O3 coated Si substrates

    Tao Li

    2015-05-01

    Full Text Available The electrical performance of MoS2 can be engineered by introducing high-κ dielectrics, while the interactions between high-κ dielectrics and MoS2 need to be studied. In this study, multilayer MoS2 field-effect transistors (FETs with a back-gated configuration were fabricated on high-κ Al2O3 coated Si substrates. Compared with MoS2 FETs on SiO2, the field-effect mobility (μFE and subthreshold swing (SS were remarkably improved in MoS2/Al2O3/Si. The improved μFE was thought to result from the dielectric screening effect from high-κ Al2O3. When a HfO2 passivation layer was introduced on the top of MoS2/Al2O3/Si, the field-effect mobility was further enhanced, which was thought to be concerned with the decreased contact resistance between the metal and MoS2. Meanwhile, the interface trap density increased from 2.4×1012 eV−1cm−2 to 6.3×1012 eV−1cm−2. The increase of the off-state current and the negative shift of the threshold voltage may be related to the increase of interface traps.

  14. Critical thickness of high structural quality SrTiO3 films grown on orthorhombic (101) DyScO3

    Biegalski, M. D.; Trolier-McKinstry, S.; Schlom, D. G.; Fong, D. D.; Eastman, J. A.; Fuoss, P. H.; Streiffer, S. K.; Heeg, T.; Schubert, J.; Tian, W.; Nelson, C. T.; Pan, X. Q.; Hawley, M. E.; Bernhagen, M.; Reiche, P.; Uecker, R.

    2008-01-01

    Strained epitaxial SrTiO 3 films were grown on orthorhombic (101) DyScO 3 substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 A were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500 A. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.0018 deg.). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700 deg. C in 1 atm of oxygen. The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTiO 3 films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films

  15. High strength Al–Al2O3p composites: Optimization of extrusion parameters

    Luan, B.F.; Hansen, Niels; Godfrey, A.

    2011-01-01

    Composite aluminium alloys reinforced with Al2O3p particles have been produced by squeeze casting followed by hot extrusion and a precipitation hardening treatment. Good mechanical properties can be achieved, and in this paper we describe an optimization of the key processing parameters...... on an investigation of their mechanical properties and microstructure, as well as on the surface quality of the extruded samples. The evaluation shows that material with good strength, though with limited ductility, can be reliably obtained using a production route of squeeze casting, followed by hot extrusion....... The parameters investigated are the extrusion temperature, the extrusion rate and the extrusion ratio. The materials chosen are AA 2024 and AA 6061, each reinforced with 30vol.% Al2O3 particles of diameter typically in the range from 0.15 to 0.3μm. The extruded composites have been evaluated based...

  16. Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

    McDaniel, Martin D.; Ngo, Thong Q.; Ekerdt, John G.; Hu, Chengqing; Jiang, Aiting; Yu, Edward T.; Lu, Sirong; Smith, David J.; Posadas, Agham; Demkov, Alexander A.

    2015-01-01

    The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO 3 (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10 −5 A/cm 2 at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (D it ) is estimated to be as low as ∼2 × 10 12  cm −2  eV −1 under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased D it value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications

  17. Luteolin and fisetin suppress oxidative stress by modulating sirtuins and forkhead box O3a expression under in vitro diabetic conditions.

    Kim, Arang; Lee, Wooje; Yun, Jung-Mi

    2017-10-01

    Chronic hyperglycemia induces oxidative stress via accumulation of reactive oxygen species (ROS) and contributes to diabetic complications. Hyperglycemia induces mitochondrial superoxide anion production through the increased activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. This study aimed to determine whether fisetin and luteolin treatments suppress the oxidative stress by modulating the expression of sirtuins (SIRTs) and forkhead box O3a (FOXO3a) under hyperglycemic conditions in human monocytes. Human monocytic cells (THP-1) were cultured under osmotic control (14.5 mmol/L mannitol), normoglycemic (NG, 5.5 mmol/L glucose), or hyperglycemic (HG, 20 mmol/L glucose) conditions, in the absence or presence of fisetin and luteolin for 48 h. To determine the effect of fisetin and luteolin treatments on high glucose-induced oxidative stress, western blotting and intracellular staining were performed. Hyperglycemic conditions increased the ROS production, as compared to normoglycemic condition. However, fisetin and luteolin treatments inhibited ROS production under hyperglycemia. To obtain further insight into ROS production in hyperglycemic conditions, evaluation of p47phox expression revealed that fisetin and luteolin treatments inhibited p47phox expression under hyperglycemic conditions. Conversely, the expression levels of SIRT1, SIRT3, SIRT6, and FOXO3a were decreased under high glucose conditions compared to normal glucose conditions, but exposure to fisetin and luteolin induced the expression of SIRT1, SIRT3, SIRT6, and FOXO3a. The above findings suggest that fisetin and luteolin inhibited high glucose-induced ROS production in monocytes through the activation of SIRTs and FOXO3a. The results of our study supports current researches that state fisetin and luteolin as potential agents for the development of novel strategies for diabetes.

  18. The influence of high hydrostatic pressure on lattice parameters of a single crystal of BaTiO3

    Malinowski, M.; Lukaszewicz, K.; Asbrink, S.

    1986-01-01

    The lattice parameters of a single crystal of BaTiO 3 have been measured under high hydrostatic pressure up to 5 GPa using a diamond-anvil high-pressure cell of a new design. The lattice becomes cubic at 2.08(8) GPa and stays cubic at higher pressures. The pressure dependence of the tetragonal-cubic transition temperature is estimated to be -46 K GPa -1 . (orig.)

  19. High-resolution photoemission study of Nd1-xSrxMnO3

    Fujiwara, H.; Sekiyama, A.; Higashiya, A.; Konoike, K.; Tsunekawa, M.; Yamasaki, A.; Irizawa, A.; Imada, S.; Muro, T.; Noda, K.; Kuwahara, H.; Tokura, Y.; Suga, S.

    2005-01-01

    We have performed the bulk sensitive Mn 2p-3d resonant photoemission for Nd 1-x Sr x MnO 3 (x=0.40, 0.47, 0.50, 0.63) in order to reveal the Mn 3d electronic states. We will report the temperature and doping dependence of the Mn 3d spectral functions. The sudden spectral change for x=0.50 across the FM-COI transition shows the strong influence of the charge-ordering on the Mn 3d electronic states

  20. Heterojunction p-Cu2O/n-Ga2O3 diode with high breakdown voltage

    Watahiki, Tatsuro; Yuda, Yohei; Furukawa, Akihiko; Yamamuka, Mikio; Takiguchi, Yuki; Miyajima, Shinsuke

    2017-11-01

    Heterojunction p-Cu2O/n-β-Ga2O3 diodes were fabricated on an epitaxially grown β-Ga2O3(001) layer. The reverse breakdown voltage of these p-n diodes reached 1.49 kV with a specific on-resistance of 8.2 mΩ cm2. The leakage current of the p-n diodes was lower than that of the Schottky barrier diode due to the higher barrier height against the electron. The ideality factor of the p-n diode was 1.31. It indicated that some portion of the recombination current at the interface contributed to the forward current, but the diffusion current was the dominant. The forward current more than 100 A/cm2 indicated the lower conduction band offset at the hetero-interface between Cu2O and Ga2O3 layers than that predicted from the bulk properties, resulting in such a high forward current without limitation. These results open the possibility of advanced device structures for wide bandgap Ga2O3 to achieve higher breakdown voltage and lower on-resistance.

  1. Influences of Different Preparation Conditions on Catalytic Activity of Ag2O-Co3O4/γ-Al2O3 for Hydrogenation of Coal Pyrolysis

    Lei Zhang

    2014-01-01

    Full Text Available A series of catalysts of Ag2O-Co3O4/γ-Al2O3 was prepared by equivalent volume impregnation method. The effects of the metal loading, calcination time, and calcination temperatures of Ag and Co, respectively, on the catalytic activity were investigated. The optimum preparing condition of Ag2O-Co3O4/γ-Al2O3 was decided, and then the influence of different preparation conditions on catalytic activity of Ag2O-Co3O4/γ-Al2O3 was analyzed. The results showed the following: (1 at the same preparation condition, when silver loading was 8%, the Ag2O-Co3O4/γ-Al2O3 showed higher catalyst activity, (2 the catalyst activity had obviously improved when the cobalt loading was 8%, while it was weaker at loadings 5% and 10%, (3 the catalyst activity was influenced by different calcination temperatures of silver, but the influences were not marked, (4 the catalyst activity can be influenced by calcination time of silver, (5 different calcination times of cobalt can also influence the catalyst activity of Ag2O-Co3O4/γ-Al2O3, and (6 the best preparation conditions of the Ag2O-Co3O4/γ-Al2O3 were silver loading of 8%, calcination temperature of silver of 450°C, and calcinations time of silver of 4 h, while at the same time the cobalt loading was 8%, the calcination temperature of cobalt was 450°C, and calcination time of cobalt was 4 h.

  2. A Highly Thermostable In2O3/ITO Thin Film Thermocouple Prepared via Screen Printing for High Temperature Measurements

    Yantao Liu

    2018-03-01

    Full Text Available An In2O3/ITO thin film thermocouple was prepared via screen printing. Glass additives were added to improve the sintering process and to increase the density of the In2O3/ITO films. The surface and cross-sectional images indicate that both the grain size and densification of the ITO and In2O3 films increased with the increase in annealing time. The thermoelectric voltage of the In2O3/ITO thermocouple was 53.5 mV at 1270 °C at the hot junction. The average Seebeck coefficient of the thermocouple was calculated as 44.5 μV/°C. The drift rate of the In2O3/ITO thermocouple was 5.44 °C/h at a measuring time of 10 h at 1270 °C.

  3. The Study of Electrical Properties for Multilayer La2O3/Al2O3 Dielectric Stacks and LaAlO3 Dielectric Film Deposited by ALD.

    Feng, Xing-Yao; Liu, Hong-Xia; Wang, Xing; Zhao, Lu; Fei, Chen-Xi; Liu, He-Lei

    2017-12-01

    The capacitance and leakage current properties of multilayer La 2 O 3 /Al 2 O 3 dielectric stacks and LaAlO 3 dielectric film are investigated in this paper. A clear promotion of capacitance properties is observed for multilayer La 2 O 3 /Al 2 O 3 stacks after post-deposition annealing (PDA) at 800 °C compared with PDA at 600 °C, which indicated the recombination of defects and dangling bonds performs better at the high-k/Si substrate interface for a higher annealing temperature. For LaAlO 3 dielectric film, compared with multilayer La 2 O 3 /Al 2 O 3 dielectric stacks, a clear promotion of trapped charges density (N ot ) and a degradation of interface trap density (D it ) can be obtained simultaneously. In addition, a significant improvement about leakage current property is observed for LaAlO 3 dielectric film compared with multilayer La 2 O 3 /Al 2 O 3 stacks at the same annealing condition. We also noticed that a better breakdown behavior for multilayer La 2 O 3 /Al 2 O 3 stack is achieved after annealing at a higher temperature for its less defects.

  4. Plasma dynamic synthesis and obtaining ultrafine powders of iron oxides with high content of ε-Fe2O3

    Sivkov, Alexander; Naiden, Evgenii; Ivashutenko, Alexander; Shanenkov, Ivan

    2016-05-01

    The ultrafine iron oxide powders were successfully synthesized using the plasma dynamic synthesis method, based on the use of a coaxial magnetoplasma accelerator with the iron electrode system. The synthesis was implemented in the high-speed iron-containing plasma jet, flowing into the space of the sealed chamber, filled with the gaseous mixture of oxygen and argon at different ratios. The XRD investigations showed that the synthesized products were heterophase and consisted of three main phases such as magnetite Fe3O4, hematite α-Fe2O3 and ε-Fe2O3. The SEM data confirmed the presence of three particle types: the hollow spheroids with sizes about hundreds of micrometers (magnetite), the particles with sizes up to 100 μm from the porous material of sintered submicron particles (hematite), and nanoscale particles (ε-phase). We found that at the higher oxygen concentration the content of ε-Fe2O3 is increased up to 50% at the same time with decreasing the Fe3O4 phase. The magnetic properties of the products are mainly determined by magnetite characteristics and are significantly reduced with decreasing its content in the powder. In order to investigate the synthesized ε-Fe2O3 on the ability to absorb the electromagnetic radiation in the millimeter wavelength range, we separated the product with the higher ε-phase concentration. The fraction mainly, consisting of ε-Fe2O3, showed the occurrence of the natural resonance at frequencies of 8.3 GHz and 130 GHz.

  5. Solvothermal Synthesis of Fe2O3 Loaded Activated Carbon as Electrode Materials for High-performance Electrochemical Capacitors

    Li, Ying; Kang, Litao; Bai, Gailing; Li, Peiyang; Deng, Jiachun; Liu, Xuguang; Yang, Yongzhen; Gao, Feng; Liang, Wei

    2014-01-01

    This article describes a facile solvothermal synthesis method to prepare Fe 2 O 3 /AC composites for electrochemical capacitors from Iron (III) chloride hexahydrate (FeCl 3 ·6H 2 O), activated carbon (AC, from petroleum coke), and four different precipitants (i.e., NaOH, CH 3 COONa, HMT, CO(NH 2 ) 2 ). X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Thermogravimetric (TG) analysis show that the products consisted of nanosized α-Fe 2 O 3 (weight ratios: 48.1, 47.9, 44.2, 44.3%) loaded onto AC particles (∼ 20 μm). Significantly, both kind and dosage of precipitants exhibit effects on the specific capacitances of Fe 2 O 3 /AC composites. The highest specific capacitance reaches up to 240 F g −1 (at a current density of 1 A g −1 in 6 M KOH aqueous electrolyte) when the molar ratio of CH 3 COONa: FeCl 3 is 9. On the other hand, the sample prepared with NaOH: FeCl 3 molar ratio being 1.5 exhibits excellent rate capability with specific capacitance of 215 F g −1 at 1 A g −1 , and 89.3, 82.3, 78.1, 72.6 and 65.1% capacity retention at 2, 5, 10, 20, and 40 A g −1 , respectively. These electrochemical performances are superior to other materials consisted of Fe 2 O 3 /carbon nanotube (CNT), graphene oxide (GO) or reduced graphene oxide (rGO) composites, demonstrating the great potential of Fe 2 O 3 /AC composites in the development of high-performance electrode materials for electrochemical capacitors

  6. Growth and physical properties of highly oriented La-doped (K,Na)NbO3 ferroelectric thin films

    Vendrell, X.; Raymond, O.; Ochoa, D.A.; García, J.E.; Mestres, L.

    2015-01-01

    Lead-free (K,Na)NbO 3 (KNN) and La doped (K,Na)NbO 3 (KNN-La) thin films are grown on SrTiO 3 substrates using the chemical solution deposition method. The effect of adding different amounts of Na and K excess (0–20 mol%) is investigated. The results confirm the necessity of adding 20 mol% excess amounts of Na and K precursor solutions in order to avoid the formation of the secondary phase, K 4 Nb 6 O 17 , as confirmed by X-ray diffraction and Raman spectroscopy. Moreover, when adding a 20 mol% of alkaline metal excess, the thin films are highly textured with out-of-plane preferential orientation in the [100] direction of the [100] orientation of the substrate. Doping with lanthanum results in a decrease of the leakage current density at low electric field, and an increase in the dielectric permittivity across the whole temperature range (80–380 K). Although the (100)-oriented KNN and KNN-La films exhibited rounded hysteresis loops, at low temperatures the films show the typical ferroelectric hysteresis loops. - Highlights: • (K 0.5 Na 0.5 )NbO 3 and [(K 0.5 Na 0.5 ) 0.985 La 0.005 ]NbO 3 thin films have been prepared. • The obtained thin films show an excellent (100) preferred orientation. • Doping with lanthanum results in a decrease of the leakage current density. • The dielectric properties are enhanced when doping with lanthanum

  7. Topotactic oxidation pathway of ScTiO3 and high-temperature structure evolution of ScTiO3.5 and Sc4Ti3O12-type phases.

    Shafi, Shahid P; Hernden, Bradley C; Cranswick, Lachlan M D; Hansen, Thomas C; Bieringer, Mario

    2012-02-06

    The novel oxide defect fluorite phase ScTiO(3.5) is formed during the topotactic oxidation of ScTiO(3) bixbyite. We report the oxidation pathway of ScTiO(3) and structure evolution of ScTiO(3.5), Sc(4)Ti(3)O(12), and related scandium-deficient phases as well as high-temperature phase transitions between room temperature and 1300 °Cusing in-situ X-ray diffraction. We provide the first detailed powder neutron diffraction study for ScTiO(3). ScTiO(3) crystallizes in the cubic bixbyite structure in space group Ia3 (206) with a = 9.7099(4) Å. The topotactic oxidation product ScTiO(3.5) crystallizes in an oxide defect fluorite structure in space group Fm3m (225) with a = 4.89199(5) Å. Thermogravimetric and differential thermal analysis experiments combined with in-situ X-ray powder diffraction studies illustrate a complex sequence of a topotactic oxidation pathway, phase segregation, and ion ordering at high temperatures. The optimized bulk synthesis for phase pure ScTiO(3.5) is presented. In contrast to the vanadium-based defect fluorite phases AVO(3.5+x) (A = Sc, In) the novel titanium analogue ScTiO(3.5) is stable over a wide temperature range. Above 950 °C ScTiO(3.5) undergoes decomposition with the final products being Sc(4)Ti(3)O(12) and TiO(2). Simultaneous Rietveld refinements against powder X-ray and neutron diffraction data showed that Sc(4)Ti(3)O(12) also exists in the defect fluorite structure in space group Fm3m (225) with a = 4.90077(4) Å. Sc(4)Ti(3)O(12) undergoes partial reduction in CO/Ar atmosphere to form Sc(4)Ti(3)O(11.69(2)).

  8. Combined XRD and XANES studies of a Re-promoted Co/γ-Al2O3 catalyst at Fischer–Tropsch synthesis conditions

    Rønning, Magnus; Tsakoumis, Nikolaos E.; Voronov, Alexey

    2010-01-01

    A cobalt based Fischer–Tropsch catalyst was studied during the initial stages of the reaction at industrially relevant conditions. The catalyst consists of 20wt% cobalt supported on γ-Al2O3 and promoted by 1wt% of rhenium. X-ray diffraction (XRD) in combination with X-ray absorption near edge...

  9. Highly polarized single-c-domain single-crystal Pb(Mn,Nb)O(3)-PZT thin films.

    Wasa, Kiyotaka; Adachi, Hideaki; Nishida, Ken; Yamamoto, Takashi; Matsushima, Tomoaki; Kanno, Isaku; Kotera, Hidetoshi

    2012-01-01

    In-plane unstrained single-c-domain/single-crystal thin films of PZT-based ternary ferroelectric perovskite, ξPb(Mn,Nb)O3-(1 - ξ)PZT, were grown on SrRuO(3)/Pt/MgO substrates using magnetron sputtering followed by quenching. The sputtered unstrained thin films exhibit unique ferroelectric properties: high coercive field, Ec > 180 kV/cm, large remanent polarization, P(r) = 100 μC/cm(2), small relative dielectric constants, ε* = 100 to 150, high Curie temperature, Tc = ~600 °C, and bulk-like large transverse piezoelectric constants, e31,f = -12.0 C/m(2) for PZT(48/52) at ξ = 0.06. The unstrained thin films are an ideal structure to extract the bulk ferroelectric properties. Their micro-structures and ferroelectric properties are discussed in relation to the potential applications for piezoelectric MEMS. © 2012 IEEE

  10. Size Tunable Synthesis of Highly Crystalline BaTiO3 Nanoparticles using Salt-Assisted Spray Pyrolysis

    Itoh, Yoshifumi; Lenggoro, I. Wuled; Okuyama, Kikuo; Maedler, Lutz; Pratsinis, Sotiris E.

    2003-01-01

    Highly crystalline, dense BaTiO 3 nanoparticles in a size range from 30 to 360nm with a narrow size distribution (σ g = 1.2-1.4) were prepared at various synthesis temperatures using a salt-assisted spray pyrolysis (SASP) method without the need for post-annealing. The effect of synthesis temperature on particle size, crystallinity and surface morphology of the nanoparticles were characterized by X-ray diffraction and scanning/transmission electron microscopy. The nature of the crystalline structure was analyzed by Rietveld refinement and Raman spectroscopy. The particle size decreased with decreasing operation temperature. The crystal phase was transformed from tetragonal to cubic at a particles size of about 50nm at room temperature. SASP can be used to produce high weight fraction of tetragonal BaTiO 3 nanoparticles down to 64nm in a single step

  11. High resolution electron microscopy studies of interfaces between Al2O3 substrates and MBE grown Nb films

    Mayer, J.; Ruhle, M.; Dura, J.; Flynn, C.P.

    1991-01-01

    This paper reports on single crystal niobium films grown by Molecular Beam Epitaxy (MBE) on (001) S sapphire substrates. Cross-sectional specimens with thickness of 2 O 3 interface could be investigated by high resolution electron microscopy (HREM). The orientation relationship between the metal film and the ceramic substrate was verified by selected area diffraction: (111) Nb parallel (0001) S and [1 bar 10] Nb parallel [2 bar 1 bar 10] S . The atomistic structure of the interface was identified by HREM

  12. Synthesis, morphology and microstructure of pomegranate-like hematite (α-Fe2O3) superstructure with high coercivity

    Tadic, Marin; Citakovic, Nada; Panjan, Matjaz; Stanojevic, Boban; Markovic, Dragana; Jovanovic, Đorđe; Spasojevic, Vojislav

    2012-01-01

    Highlights: ► We found superior magnetic properties of the hematite (α-Fe 2 O 3 ). ► TEM and HRTEM images show a pomegranate-like superstructure. ► Magnetic measurements display high coercivity H C = 4350 Oe at the room temperature. - Abstract: We found novel and superior magnetic properties of the hematite (α-Fe 2 O 3 ) that originate from an internal microstructure of particles and strong inter-particle interactions between nanocrystal sub-units. The hematite particles were synthesized by thermal decomposition of iron (III) nitrate without any template or surfactant. The purity, size, crystallinity, morphology, microstructure and magnetic features of the as-prepared particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and SQUID magnetometry. An XRD study reveals a pure phase of α-Fe 2 O 3 whereas TEM shows α-Fe 2 O 3 spheres with a diameter of about 150 nm. RS also shows high quality and purity of the sample. Moreover, TEM and HRTEM images show a pomegranate-like superstructure and evidence that the spherical particles are composed of individual well-crystallized nanoparticle sub-units (self-assembled nanoparticles) with a size of about 20 nm. Magnetic measurements display hysteretic behavior at the room temperature with remanent magnetization M r = 0.731 emu/g, saturation magnetization M S = 6.83 emu/g and coercivity H C = 4350 Oe, as well as the Morin transition at T M = 261 K. These results and comparison with those in the literature reveal that the sample has extremely high coercivity. The magnetic properties of the sample are discussed in relation to morphology, internal microstructure, surface effects and exchange and dipole–dipole interactions.

  13. Fabrication of high aspect ratio TiO2 and Al2O3 nanogratings by atomic layer deposition

    Shkondin, Evgeniy; Takayama, Osamu; Michael-Lindhard, Jonas

    2016-01-01

    The authors report on the fabrication of TiO2 and Al2O3 nanostructured gratings with an aspect ratio of up to 50. The gratings were made by a combination of atomic layer deposition (ALD) and dry etch techniques. The workflow included fabrication of a Si template using deep reactive ion etching...... spectroscopy. The approach presented opens the possibility to fabricate high quality optical metamaterials and functional nanostructures....

  14. Ni2+ supported on hydroxyapatite-core@shell γ-Fe2O3 nanoparticles as new and green catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H-ones under solvent-free condition

    Eshagh Rezaee Nezhad

    2013-10-01

    Full Text Available The aim of this research is to study Ni2+ supported on hydroxyapatite-core-shell magnetic γ-Fe2O3 nanoparticles (γ-Fe2O3@HAp-Ni2+ as a green and recyclable catalyst for the Biginelli reaction under solvent-free conditions. One-pot multi-component condensation of 1,3-dicarbonyl compounds, urea and aldehydes at 80 oC affords the corresponding compounds in high yields and in short reaction times using γ-Fe2O3@HAp-Ni2+. The catalyst can be readily isolated using an external magnet and no obvious loss of activity was observed when the catalyst was reused in seven consecutive runs. The mean size and the surface morphology of the nanoparticles were characterized by transmission electron microscopy, scanning electron microscope, vibrating sample magnetometry, X-ray powder diffraction and Fourier transform infrared techniques.

  15. Theoretical study of thermopower behavior of LaFeO3 compound in high temperature region

    Singh, Saurabh; Shastri, Shivprasad S.; Pandey, Sudhir K.

    2018-04-01

    The electronic structure and thermopower (α) behavior of LaFeO3 compound were investigated by combining the ab-initio electronic structures and Boltzmann transport calculations. LSDA plus Hubbard U (U = 5 eV) calculation on G-type anti-ferromagnetic (AFM) configuration gives an energy gap of ˜2 eV, which is very close to the experimentally reported energy gap. The calculated values of effective mass of holes (mh*) in valance band (VB) are found ˜4 times that of the effective mass of electrons (me*) in conduction band (CB). The large effective masses of holes are responsible for the large and positive thermopower exhibited by this compound. The calculated values of α using BoltzTraP code are found to be large and positive in the 300-1200 K temperature range, which is in agreement with the experimentally reported data.

  16. The surface structure of SrTiO3 at high temperatures under influence of oxygen

    Hesselberth, M. B. S.; Molen, S. J. van der; Aarts, J.

    2014-01-01

    We use low energy electron microscopy to investigate the structure of the SrTiO 3 (001) surface at elevated temperatures and different oxygen pressures. Upon varying the temperature between 500 °C and 900 °C in oxygen pressures ranging from 10 −9 millibar to 10 −4 millibar, two surface transitions are found to be present. The lower temperature (1 × 1) → (2 × 1) transition that is known to occur in ultrahigh vacuum can be reversed by increasing the oxygen pressure. At higher temperatures, we observe a (2 × 1) → disordered (1 × 1) transition which is irreversible in the experimental parameter range. The observations are expected to have a strong bearing on the growth of interface structures

  17. Highly-Ordered Magnetic Nanostructures on Self-Assembled α-Al2O3 and Diblock Copolymer Templates

    Erb, Denise

    2015-08-01

    This thesis shows the preparation of nanostructured systems with a high degree of morphological uniformity and regularity employing exclusively selfassembly processes, and documents the investigation of these systems by means of atomic force microscopy (AFM), grazing incidence small angle X-ray scattering (GISAXS), and nuclear resonant scattering of synchrotron radiation (NRS). Whenever possible, the X-ray scattering methods are applied in-situ and simultaneously in order to monitor and correlate the evolution of structural and magnetic properties of the nanostructured systems. The following systems are discussed, where highly-ordered magnetic nanostructures are grown on α-Al 2 O 3 substrates with topographical surface patterning and on diblock copolymer templates with chemical surface patterning: - Nanofaceted surfaces of α-Al 2 O 3 - Magnetic nanostructures on nanofaceted α-Al 2 O 3 substrates - Thin films of microphase separated diblock copolymers - Magnetic nanostructures on diblock copolymer thin film templates The fact that the underlying self-assembly processes can be steered by external factors is utilized to optimize the degree of structural order in the nanostructured systems. The highly-ordered systems are well-suited for investigations with X-ray scattering methods, since due to their uniformity the inherently averaged scattered signal of a sample yields meaningful information on the properties of the contained nanostructures: By means of an in-situ GISAXS experiment at temperatures above 1000 C, details on the facet formation on α-Al 2 O 3 surfaces are determined. A novel method, merging in-situ GISAXS and NRS, shows the evolution of magnetic states in a system with correlated structural and magnetic inhomogeneity with lateral resolution. The temperature-dependence of the shape of Fe nanodots growing on diblock copolymer templates is revealed by in-situ GISAXS during sputter deposition of Fe. Combining in-situ GISAXS and NRS, the magnetization

  18. Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions

    George Karaiskakis

    2012-04-01

    Full Text Available O2 adsorption is a key process for further understanding the mechanism of selective CO oxidation (SCO on gold catalysts. Rate constants related to the elementary steps of O2 adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al2O3 catalyst, were determined by Reversed-Flow Inverse Gas Chromatography (RF-IGC. The present study, carried-out in a wide temperature range (50–300 °C, both in excess as well as in the absence of H2, resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H2, the rate of O2 binding, over Au/γ-Al2O3, drastically changes with rising temperature, indicating possible O2 dissociation at elevated temperatures. H2 facilitates stronger O2 bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H2 rich conditions, can be correlated to O2 dissociation after hydrogenation. Although, H2 enhances both selective CO reactant’s desorption, O2 desorption is more favored than that of CO, in agreement with the well-known mild bonding of SCO reactant’s at lower temperatures. The experimentally observed drastic change in the strength of CO and O2 binding is consistent both with well-known high activity of SCO at ambient temperatures, as well as with the loss of selectivity at higher temperatures.

  19. Self-propagating high-temperature synthesis of Sr-doped LaMnO3 perovskite as oxidation catalyst

    Hirano, T.; Purwanto, H.; Watanabe, T.; Akiyama, T.

    2007-01-01

    Sr-doped LaMnO 3 perovskite oxide has been focused on as one of the alternative catalysts to precious metals such as platinum that are used for cleaning automotive emission gas. The conventional Solid-state reaction method is a popular productive process for perovskite oxide, however, it is time and energy consuming process because it requires repeated prolonged heat treatment at high temperatures. Therefore, the purposes of this work are to produce Sr-doped LaMnO 3 perovskite by using Self-propagating high-temperature synthesis (SHS) and experimentally examine the oxidation catalytic activity of the product for cleaning automotive emission gas. In the SHS, powders of La 2 O 3 , SrCO 3 , Mn and NaClO 4 were well mixed at the desired ratio and poured in a graphite crucible, where at one end it was ignited by using an electrically heated carbon foil. The wave of exothermic reaction due to oxidation of manganese propagated to the other end in a short time. The obtained products were characterized by means of XRD, FE-SEM, BET and particle size distribution analysis and then evaluated via catalytic oxidation tests by using propane in a fixed bed reactor at several temperatures. From the XRD analysis, the products had the desired composition of La 1-x Sr x MnO 3 (x = 0, 0.1, 0.2 and 0.4) perovskite, in which the replacing ratio x of La and Sr in the products was easily controlled by changing the mixing ratio of raw materials. The catalytic activity test showed that the samples exhibited good catalytic activity for propane oxidation over 200 deg. C , although the products had a relatively small surface area. SHS showed the potential for the production of a relatively inexpensive catalytic converter

  20. Molecular Beam Epitaxy Growth of High Crystalline Quality LiNbO3

    Tellekamp, M. Brooks; Shank, Joshua C.; Goorsky, Mark S.; Doolittle, W. Alan

    2016-12-01

    Lithium niobate is a multi-functional material with wide reaching applications in acoustics, optics, and electronics. Commercial applications for lithium niobate require high crystalline quality currently limited to bulk and ion sliced material. Thin film lithium niobate is an attractive option for a variety of integrated devices, but the research effort has been stagnant due to poor material quality. Both lattice matched and mismatched lithium niobate are grown by molecular beam epitaxy and studied to understand the role of substrate and temperature on nucleation conditions and material quality. Growth on sapphire produces partially coalesced columnar grains with atomically flat plateaus and no twin planes. A symmetric rocking curve shows a narrow linewidth with a full width at half-maximum (FWHM) of 8.6 arcsec (0.0024°), which is comparable to the 5.8 arcsec rocking curve FWHM of the substrate, while the film asymmetric rocking curve is 510 arcsec FWHM. These values indicate that the individual grains are relatively free of long-range disorder detectable by x-ray diffraction with minimal measurable tilt and twist and represents the highest structural quality epitaxial material grown on lattice mismatched sapphire without twin planes. Lithium niobate is also grown on lithium tantalate producing high quality coalesced material without twin planes and with a symmetric rocking curve of 193 arcsec, which is nearly equal to the substrate rocking curve of 194 arcsec. The surface morphology of lithium niobate on lithium tantalate is shown to be atomically flat by atomic force microscopy.

  1. High efficient conversion of furfural to 2-methylfuran over Ni-Cu/Al2O3 catalyst with formic acid as a hydrogen donor

    Fu, Zhaolin; Wang, Ze; Lin, Weigang

    2017-01-01

    Conversion of furfural to 2-methylfuran over Cu/Al2O3, Ni/Al2O3 and Ni-Cu/Al2O3 catalysts were investigated with formic acid as a hydrogen donor. Ni/Al2O3 showed a high catalytic activity but a moderate selectivity to 2-methylfuran. Contrarily, Cu/Al2O3 showed a low catalytic activity but a high...... selectivity for carbonyl reduction. Over the bimetallic catalysts Ni-10%Cu/Al2O3, by increasing Ni content, more furfural was converted with the reduction of carbonyl primarily. The effect of reaction solvent and the fraction of formic acid were also studied. The result showed that isopropanol solvent could...

  2. Efficient optical Kerr gate of Bi2O3–B2O3–SiO2 glass for acquiring high contrast ballistic imaging in turbid medium

    Zhan, Pingping; Tan, Wenjiang; Wu, Bin; Si, Jinhai; Chen, Feng; Hou, Xun; Liu, Xin

    2013-01-01

    We investigated the ballistic imaging of a 1.41 line pair mm −1 section of a resolution test chart hidden behind a solution of polystyrene spheres with a femtosecond optical Kerr gate (OKG). A better transillumination image contrast could be acquired with an OKG of Bi 2 O 3 –B 2 O 3 –SiO 2 (BI) glass than that with an OKG of fused silica in a highly scattering media, which indicated that the BI glass was a better OKG medium due to its large nonlinear refractive index. (paper)

  3. Microscopic observation of ferroelectric domains in SrTiO3 using birefringence imaging techniques under high electric fields

    Manaka, Hirotaka; Nozaki, Hirofumi; Miura, Yoko

    2017-01-01

    Phase transitions in SrTiO 3 between quantum paraelectric, coherent paraelectric, and electric-field-induced ferroelectric states are governed by tetragonal domains with quantum fluctuations. However, their characteristics are still unclear. To observe the electric-field-induced ferroelectric state using birefringence imaging techniques, we developed a suitable sample holder to apply high electric fields of up to E ≃ 5 kV/cm and temperatures down to T = 20 K. From birefringence imaging measurements of the ferroelectric LiNbO 3 with varying electric field, distributions of the electric field in the sample stage were found to be negligible. In SrTiO 3 , a huge-retardance area corresponding to the ferroelectric domains appears at E > 2 kV/cm and T ≤ 60 K even though the paraelectric domains partially remain. Furthermore, the fast-axis direction rotates by 90° at the ferroelectric phase transition because of an electrostrictive effect in ferroelectrics. The phase diagram of the critical electric field and temperature agrees with previous reports obtained from dielectric and neutron scattering measurements. (author)

  4. Pt–Al2O3 dual layer atomic layer deposition coating in high aspect ratio nanopores

    Pardon, Gaspard; Gatty, Hithesh K; Stemme, Göran; Wijngaart, Wouter van der; Roxhed, Niclas

    2013-01-01

    Functional nanoporous materials are promising for a number of applications ranging from selective biofiltration to fuel cell electrodes. This work reports the functionalization of nanoporous membranes using atomic layer deposition (ALD). ALD is used to conformally deposit platinum (Pt) and aluminum oxide (Al 2 O 3 ) on Pt in nanopores to form a metal–insulator stack inside the nanopore. Deposition of these materials inside nanopores allows the addition of extra functionalities to nanoporous materials such as anodic aluminum oxide (AAO) membranes. Conformal deposition of Pt on such materials enables increased performances for electrochemical sensing applications or fuel cell electrodes. An additional conformal Al 2 O 3 layer on such a Pt film forms a metal–insulator–electrolyte system, enabling field effect control of the nanofluidic properties of the membrane. This opens novel possibilities in electrically controlled biofiltration. In this work, the deposition of these two materials on AAO membranes is investigated theoretically and experimentally. Successful process parameters are proposed for a reliable and cost-effective conformal deposition on high aspect ratio three-dimensional nanostructures. A device consisting of a silicon chip supporting an AAO membrane of 6 mm diameter and 1.3 μm thickness with 80 nm diameter pores is fabricated. The pore diameter is reduced to 40 nm by a conformal deposition of 11 nm Pt and 9 nm Al 2 O 3 using ALD. (paper)

  5. Ag-Modified In2O3/ZnO Nanobundles with High Formaldehyde Gas-Sensing Performance

    Fang Fang

    2015-08-01

    Full Text Available Ag-modified In2O3/ZnO bundles with micro/nano porous structures have been designed and synthesized with by hydrothermal method continuing with dehydration process. Each bundle consists of nanoparticles, where nanogaps of 10–30 nm are present between the nanoparticles, leading to a porous structure. This porous structure brings high surface area and fast gas diffusion, enhancing the gas sensitivity. Consequently, the HCHO gas-sensing performance of the Ag-modified In2O3/ZnO bundles have been tested, with the formaldehyde-detection limit of 100 ppb (parts per billion and the response and recover times as short as 6 s and 3 s, respectively, at 300 °C and the detection limit of 100 ppb, response time of 12 s and recover times of 6 s at 100 °C. The HCHO sensing detect limitation matches the health standard limitation on the concentration of formaldehyde for indoor air. Moreover, the strategy to synthesize the nanobundles is just two-step heating and easy to scale up. Therefore, the Ag-modified In2O3/ZnO bundles are ready for industrialization and practical applications.

  6. Ag-Modified In2O3/ZnO Nanobundles with High Formaldehyde Gas-Sensing Performance

    Fang, Fang; Bai, Lu; Song, Dongsheng; Yang, Hongping; Sun, Xiaoming; Sun, Hongyu; Zhu, Jing

    2015-01-01

    Ag-modified In2O3/ZnO bundles with micro/nano porous structures have been designed and synthesized with by hydrothermal method continuing with dehydration process. Each bundle consists of nanoparticles, where nanogaps of 10–30 nm are present between the nanoparticles, leading to a porous structure. This porous structure brings high surface area and fast gas diffusion, enhancing the gas sensitivity. Consequently, the HCHO gas-sensing performance of the Ag-modified In2O3/ZnO bundles have been tested, with the formaldehyde-detection limit of 100 ppb (parts per billion) and the response and recover times as short as 6 s and 3 s, respectively, at 300 °C and the detection limit of 100 ppb, response time of 12 s and recover times of 6 s at 100 °C. The HCHO sensing detect limitation matches the health standard limitation on the concentration of formaldehyde for indoor air. Moreover, the strategy to synthesize the nanobundles is just two-step heating and easy to scale up. Therefore, the Ag-modified In2O3/ZnO bundles are ready for industrialization and practical applications. PMID:26287205

  7. Pt-Al2O3 dual layer atomic layer deposition coating in high aspect ratio nanopores

    Pardon, Gaspard; Gatty, Hithesh K.; Stemme, Göran; van der Wijngaart, Wouter; Roxhed, Niclas

    2013-01-01

    Functional nanoporous materials are promising for a number of applications ranging from selective biofiltration to fuel cell electrodes. This work reports the functionalization of nanoporous membranes using atomic layer deposition (ALD). ALD is used to conformally deposit platinum (Pt) and aluminum oxide (Al2O3) on Pt in nanopores to form a metal-insulator stack inside the nanopore. Deposition of these materials inside nanopores allows the addition of extra functionalities to nanoporous materials such as anodic aluminum oxide (AAO) membranes. Conformal deposition of Pt on such materials enables increased performances for electrochemical sensing applications or fuel cell electrodes. An additional conformal Al2O3 layer on such a Pt film forms a metal-insulator-electrolyte system, enabling field effect control of the nanofluidic properties of the membrane. This opens novel possibilities in electrically controlled biofiltration. In this work, the deposition of these two materials on AAO membranes is investigated theoretically and experimentally. Successful process parameters are proposed for a reliable and cost-effective conformal deposition on high aspect ratio three-dimensional nanostructures. A device consisting of a silicon chip supporting an AAO membrane of 6 mm diameter and 1.3 μm thickness with 80 nm diameter pores is fabricated. The pore diameter is reduced to 40 nm by a conformal deposition of 11 nm Pt and 9 nm Al2O3 using ALD.

  8. Interconnected α-Fe2O3 nanosheet arrays as high-performance anode materials for lithium-ion batteries

    Cai, Dandan; Li, Dongdong; Ding, Liang-Xin; Wang, Suqing; Wang, Haihui

    2016-01-01

    The electrode materials with structure stability and binder-free are urgently required for improving the electrochemical performance of lithium-ion batteries. In this work, interconnected α-Fe 2 O 3 nanosheet arrays directly grown on Ti foil were fabricated via a facile galvanostatic electrodeposition method followed by thermal treatment. The as-prepared α-Fe 2 O 3 has an open network structure constituted of interconnected nanosheets and can be directly used as integrated electrodes for lithium-ion batteries. The α-Fe 2 O 3 nanosheet arrays exhibit a high reversible capacity of 986.3 mAh g −1 at a current density of 100 mA g −1 . Moreover, a reversible capacity of ca. 425.9 mAh g −1 is achieved even at a superhigh current density of 10 A g −1 , which is higher than the theoretical capacity of commercially used graphite. The excellent performance could be attributed to the efficient electron transport, the large electrode/electrolyte interfaces and the good accommodations for volume expansion from the interconnected nanosheet arrays structure.

  9. Conditions for the growth of smooth La0.7Sr0.3MnO3 thin films by pulsed electron ablation

    Graziosi, P.; Prezioso, M.; Gambardella, A.; Kitts, C.; Rakshit, R.K.; Riminucci, A.; Bergenti, I.; Borgatti, F.; Pernechele, C.; Solzi, M.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.A.

    2013-01-01

    We report on the optimisation of the growth conditions of manganite La 0.7 Sr 0.3 MnO 3 thin films prepared by Channel Spark Ablation (CSA). CSA belongs to pulsed electron deposition methods and its energetic and deposition parameters are quite similar to those of pulsed laser deposition. The method has been already proven to provide manganite films with good magnetic properties, but the films were generally relatively rough (a few nm coarseness). Here we show that increasing the oxygen deposition pressure with respect to previously used regimes, reduces the surface roughness down to unit cell size while maintaining a robust magnetism. We analyse in detail the effect of other deposition parameters, like accelerating voltage, discharging energy, chamber pressure and substrate temperature and provide on this basis a set of optimal conditions for the growth of atomically flat films. The thicknesses for which atomically flat surface was achieved is as high as about 10–20 nm, corresponding to films with room temperature magnetism. We believe such magnetic layers represent appealing and suitable electrodes for various spintronic devices. - Highlights: ► Atomically flat manganite thin films ► Robust ferromagnetism at room temperature ► Perovskite thin films deposited by channel spark ablation ► Magnetotransport and magnetometry comparison

  10. Certain physicochemical characteristics of Bi1.4Y0.6O3 prepared by the method of direct high-frequency fusion in cold crucible

    Poluyan, A.F.; Lashneva, V.V.; Vecher, A.A.; Voropaev, A.G.; Savitskij, A.A.; Tatarintsev, V.M.

    1988-01-01

    Electric properties and the nature of conductivity of Bi 1.4 V 0.6 O 3 solid solution prepared by the method of direct high-frequency melting in the cold crucible are studied. A sample of Bi 1.4 Y 0.6 O 3 composition synthesized by this technique has a higher electric conductivity value as compared with analogous polycrystal sample has a cubic face-centered structure of the τ-Bi 2 O 3 type. On the basis of experimental e.m.f. values temperature dependences of pressures of oxygen dissociation for Bi 2 O 3 and Bi 1.4 Y 0.6 O 3 are calculated. Bi 1.4 Y 0.6 O 3 solid solution has lower values of Po 2 dissociation pressure as compared with bismuth oxide. This expands the limits of its application

  11. Exfoliated β-Ga2O3 nano-belt field-effect transistors for air-stable high power and high temperature electronics.

    Kim, Janghyuk; Oh, Sooyeoun; Mastro, Michael A; Kim, Jihyun

    2016-06-21

    This study demonstrated the exfoliation of a two-dimensional (2D) β-Ga2O3 nano-belt and subsequent processing into a thin film transistor structure. This mechanical exfoliation and transfer method produces β-Ga2O3 nano-belts with a pristine surface as well as a continuous defect-free interface with the SiO2/Si substrate. This β-Ga2O3 nano-belt based transistor displayed an on/off ratio that increased from approximately 10(4) to 10(7) over the operating temperature range of 20 °C to 250 °C. No electrical breakdown was observed in our measurements up to VDS = +40 V and VGS = -60 V between 25 °C and 250 °C. Additionally, the electrical characteristics were not degraded after a month-long storage in ambient air. The demonstration of high-temperature/high-voltage operation of quasi-2D β-Ga2O3 nano-belts contrasts with traditional 2D materials such as transition metal dichalcogenides that intrinsically have limited temperature and power operational envelopes owing to their narrow bandgap. This work motivates the application of 2D β-Ga2O3 to high power nano-electronic devices for harsh environments such as high temperature chemical sensors and photodetectors as well as the miniaturization of power circuits and cooling systems in nano-electronics.

  12. Twin-cuvette measurement technique for investigation of dry deposition of O3 and PAN to plant leaves under controlled humidity conditions

    S. Sun

    2016-02-01

    with Quercus ilex was investigated over a 14 day measurement period under controlled climate chamber conditions. By using O3 mixing ratios between 32 and 105 ppb and PAN mixing ratios between 100 and 350 ppt, a linear dependency of the O3 flux as well as the PAN flux in relation to its ambient mixing ratio could be observed. At relative humidity (RH of 40 %, the deposition velocity ratio of O3 and PAN was determined to be 0.45. At that humidity, the deposition of O3 to the plant leaves was found to be only controlled by the leaf stomata. For PAN, an additional resistance inhibited the uptake of PAN by the leaves. Furthermore, the formation of water films on the leaf surface of plants inside the chamber could be continuously tracked with our custom built leaf wetness sensors. Using this modified leaf wetness sensor measuring the electrical surface conductance on the leaves, an exponential relationship between the ambient humidity and the electrical surface conductance could be determined.

  13. Subcooled film boiling heat transfer on a high temperature sphere in very dilute Al2O3 nano-fluids

    Hyun Sun Park; Dereje Shiferaw; Bal Raj Sehgal

    2005-01-01

    Full text of publication follows: nano-fluids, or conventional liquids, e.g., water, with small concentration of nano-particles uniformly suspended, have attracted attention as a new heat transport medium with enhanced thermo-physical properties. Up to the present, only exploratory experiments on nano-fluids have been reported. Das et al (Int. J. Heat Mass Transfer 43, pp 3701-3707, 2003) conducted boiling experiments with water containing 38 nm Al 2 O 3 nano-particles. They observed deterioration in the nucleate boiling heat transfer due to the deposition of nano-particles. Boiling experiments conducted by Vassallo et al (Int. J. Heat Mass Transfer 47, pp 407-411, 2004) using silica nano-fluid using 0.4 mm diameter NiCr wire showed three times higher critical heat flux (CHF) and the wire traversed the film boiling region before it failed. Another independent experiment performed on 1 cm 2 square plate with a very low concentration of nano-particles ranging from 0.01 to 0.05 g/liter and at under pressure (2.89 psia), nano-fluids resulted in drastic 2∼3 times enhancement of the CHF (You and Kim, Appl. Phys. Lett. 83. No 16, 2003). However in all the aforementioned studies no appropriate explanation of the CHF enhancement has been advanced. The measured 2-3 times higher critical heat flux for very dilute nano-fluids may have high significance if such nano-fluids could be employed in heat transport systems. Recently, we investigated the effect of nano-particles on film boiling, which governs heat transfer during accident conditions in a reactor plant, e.g., in coolability of a degraded core, or a particulate debris bed or a core melt, and in steam explosions. Our previous experiments performed on film boiling in nano-fluids having larger concentrations of 5, 10, and 20 g/liter than those in You's experiments showed that the nano-fluids lower the film boiling temperature, decrease the film boiling heat transfer and provide a much thicker and more stable film than

  14. Fabrication of Al2O3–20 vol.% Al nanocomposite powders using high energy milling and their sinterability

    Zawrah, M.F.; Abdel-kader, H.; Elbaly, N.E.

    2012-01-01

    Highlights: ► Al 2 O 3 /Al nanocomposite powders were prepared via high energy ball milling. After 20 h milling, the size of Al 2 O 3 –20 vol.% Al nanocomposite particles was in the range of 23–29 nm. A uniform distribution of nanosized Al reinforcement throughout the Al 2 O 3 matrix, coating the particles was successfully obtained. ► There was no any sign of phase changes during the milling. A competition between the cold welding mechanism and the fracturing mechanism were found during milling and finally the above two mechanisms reached an equilibrium. ► The highest value of relative density was obtained for the sintered bodies at 1500 °C. ► The harness of the sintered composite was decreased while the fracture toughness was improved after addition Al into alumina. -- Abstract: In this study, alumina-based matrix nanocomposite powders reinforced with Al particles were fabricated and investigated. The sinterability of the prepared nanocomposite powder at different firing temperature was also conducted. Their mechanical properties in terms of hardness and toughness were tested. Alumina and aluminum powder mixtures were milled in a planetary ball mill for various times up to 30 h in order to produce Al 2 O 3 –20% Al nanocomposite. The phase composition, morphological and microstructural changes during mechanical milling of the nanocomposite particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) techniques, respectively. The crystallite size and internal strain were evaluated by XRD patterns using Scherrer methods. A uniform distribution of the Al reinforcement in the Al 2 O 3 matrix was successfully obtained after milling the powders. The results revealed that there was no any sign of phase changes during the milling. The crystal size decreased with the prolongation of milling times, while the internal strain increased. A simple model is presented to illustrate the mechanical

  15. Hollow Amorphous MnSnO3 Nanohybrid with Nitrogen-Doped Graphene for High-Performance Lithium Storage

    Liu, Peng; Hao, Qingli; Xia, Xifeng; Lei, Wu; Xia, Hui; Chen, Ziyang; Wang, Xin

    2016-01-01

    Graphical abstract: A novel hybrid of hollow amorphous MnSnO 3 nanoparticles and nitrogen-doped reduced graphene oxide was fabricated. The unique structure and well-combination of both components account for the ultra long-term cyclic life with high reversible capacity of 610 mAh g −1 over 1000 cycles at 400 mA g −1 . - Highlights: • Novel hybrid of MnSnO 3 and nitrogen-doped reduced graphene oxide was fabricated. • The MnSnO 3 nanoparticles possess amorphous and hollow structure in the composite. • The excellent electrochemical performance benefits from unique nanostructure. • The reversible capacity of as-prepared hybrid is 610 mAh g −1 after 1000 cycles. • A long-term life with 97.3% capacity retention over 1000 cycles was obtained. - Abstract: Tin-based metal oxides usually suffer from severe capacity fading resulting from aggregation and considerable volume variation during the charge/discharge process in lithium ion batteries. In this work, a novel nanocomposite (MTO/N-RGO) of hollow amorphous MnSnO 3 (MTO) nanoparticles and nitrogen-doped reduced graphene oxide (N-RGO) has been designed and synthesized by a two-step method. Firstly, the nitrogen-doped graphene nanocomposite (MTO/N-RGO-P) with MnSn(OH) 6 crystal nanoparticles was synthesized by a facile solvothermal method. Subsequently, the MTO/N-RGO nanocomposite was obtained through the post heat treatment of MTO/N-RGO-P. The designed heterostructure and well-combination of the hollow amorphous MTO and N-RGO matrix can accelerate the ionic and electronic transport, and simultaneously accommodate the aggregation and volume variation of MTO nanoparticles during the lithiation–delithiation cycles. The as-prepared hybrid of MTO and N-RGO (MTO/N-RGO) exhibits a high reversible capacity of 707 mAh g −1 after 110 cycles at 200 mA g −1 , superior rate capability, and long-term cyclic life with high capacity of 610 mAh g −1 over 1000 cycles at 400 mA g −1 . Superior capacity retention of

  16. In situ enhancement of the blue photoluminescence of colloidal Ga2O3 nanocrystals by promotion of defect formation in reducing conditions.

    Wang, Ting; Radovanovic, Pavle V

    2011-07-07

    We demonstrate redox control of defect-based photoluminescence efficiency of colloidal γ-Ga(2)O(3) nanocrystals. Reducing environment leads to an increase in photoluminescence intensity by enhancing the concentration of oxygen vacancies, while the blue emission is suppressed in oxidative conditions. These results enable optimization of nanocrystal properties by in situ defect manipulation. This journal is © The Royal Society of Chemistry 2011

  17. Effect of Y2O3-Al2O3 ratio on inter-granular phases and films in tape-casting α-SiC with high toughness

    Huang Rong; Gu Hui; Zhang Jingxian; Jiang Dongliang

    2005-01-01

    Silicon carbide (SiC) ceramics prepared from liquid phase sintering after aqueous-tape-casting can yield high toughness when appropriate amount of Y 2 O 3 -Al 2 O 3 are added, even though no elongated grains are present. Grain boundaries (GB), second-phases and hetero-phase boundaries (HB) in 2 samples with additive mole ratios of 3:5 and 3:7 are investigated using high-resolution and analytical electron microscopy (HREM and AEM). The meta-stable YAlO 3 (YAP) was nucleated from SiC surfaces in the sample with Y/Al = 3:5 as revealed by crystallographic relations across the HB, whilst relatively thick amorphous films were found at GB. In contrary, the higher level of Al 2 O 3 additives decreases the GB film thickness in the sample with Y/Al = 3:7, and the homogeneous nucleation of Y 3 Al 5 O 12 (YAG) occurs at triple pockets accompanying with thick HB films. The strong variation of GB widths is a result of GB wetting in the sample with Y/Al = 3:5 and HB wetting in the sample of Y/Al = 3:7, both by liquid Al 2 O 3 . The energy of GB in the former sample is higher than the energy of HB as exhibited by the preferential nucleation of meta-stable YAP on SiC surfaces, which results in wetting of GB by the liquid; the situation is opposite in the latter sample as the wetting of HB occurs, leading to de-wetting of GB. The thermal mismatch between SiC and YAP or YAG as well as the presence of amorphous films facilitate the creation of micro-crack to promote inter-granular fracture and result in high toughness in both SiC ceramics

  18. Two New 1,1,3,3-Tetramethylguanidinium Halochromates (C5H14N3CrO3X (X: Cl, F: Efficient Reagents for Oxidation of Organic Substrates under Solvent-Free Conditions and Microwave Irradiation

    Kıvılcım Şendıl

    2016-01-01

    Full Text Available Two new mild oxidizing agents 1,1,3,3-tetramethylguanidinium fluorochromate (TMGFC and 1,1,3,3-tetramethylguanidinium chlorochromate (TMGCC were prepared in high yields by reacting tetramethylguanidine with CrO3 and related acid. These reagents are suitable to oxidize various primary and secondary alcohols and oximes to the corresponding carbonyl compounds under solvent-free conditions and microwave irradiation.

  19. The influence of carbon doping on the performance of Gd2O3 as high-k gate dielectric

    Shekhter, P.; Yehezkel, S.; Shriki, A.; Eizenberg, M.; Chaudhuri, A. R.; Osten, H. J.; Laha, A.

    2014-01-01

    One of the approaches for overcoming the issue of leakage current in modern metal-oxide-semiconductor devices is utilizing the high dielectric constants of lanthanide based oxides. We investigated the effect of carbon doping directly into Gd 2 O 3 layers on the performance of such devices. It was found that the amount of carbon introduced into the dielectric is above the solubility limit; carbon atoms enrich the oxide-semiconductor interface and cause a significant shift in the flat band voltage of the stack. Although the carbon atoms slightly degrade this interface, this method has a potential for tuning the flat band voltage of such structures

  20. Theoretical Modeling for the X-ray Spectroscopy of Iron-bearing MgSiO3 under High Pressure

    Wang, X.; Tsuchiya, T.

    2012-12-01

    The behaviors of iron (Fe) in MgSiO3 perovskite, including valence state, spin state, and chemical environments, at high pressures are of fundamental importance for more detailed understanding the properties of the Earth's lower mantle. The pressure induced spin transition of Fe-bearing MgO and MgSiO3 are detected often by using high-resolution K-edge X-ray emission spectroscopy (XES) [1,2,3] and confirmed by theoretical simulations. [4,5] Since the Fe K-edge XES is associated to the 3p orbital, which is far from the valence orbitals (3d and 4s), it provides no information about its coordination environments. However, the Fe L-edge XES and X-ray absorption spectroscopy (XAS) can directly present the distribution and intensity of Fe-3d character. To identify both the spin states and the coordination environments of iron-bearing MgSiO3, we systematically investigate the L-edge XAS, XES and X-ray photoelectron (XPS) spectroscopy of Fe2+- and Fe3+-bearing MgSiO3 under high pressure by using the first-principles density functional method combined with the slater-transition method. Our results show that Fe2+ and Fe3+ can be distinguished easily by taking the XPS spectra. The spin transition of Fe2+ and Fe3+ can also be clearly certified by XAS and XES. Interestingly, the broadness of L-edge XES of Fe changes depending on the iron position, meaning that its coordination environment might also be distinguishable by using high-resolution XES measurements. Research supported by the Ehime University G-COE program and KAKENHI. [1] James Badro, Guillaume Fiquet, FranÇois Guyot, Jean-Pascal Rueff, Viktor V. Struzhkin, György VankÓ, and Giulio Monaco. Science 300, 789 (2003), [2] James Badro, Jean-Pascal Rueff, György VankÓ, Giulio Monaco, Guillaume Fiquet, and FranÇois Guyot, Science 305, 383 (2004), [3] Jung-Fu Lin, Viktor V. Struzhkin, Steven D. Jacobsen, Michael Y. Hu, Paul Chow, Jennifer Kung, Haozhe Liu, Ho-kwang Mao, and Gussell J. Hemley, Nature 436, 377 (2005). [4

  1. Fabrication and characterization of 6Li-enriched Li2TiO3 pebbles for a high Li-burnup irradiation test

    Tsuchiya, Kunihiko; Kawamura, Hiroshi

    2006-10-01

    Lithium titanate (Li 2 TiO 3 ) pebbles are considered to be a candidate material of tritium breeders for fusion reactor from viewpoints of easy tritium release at low temperatures (about 300degC) and chemical stability. In the present study, trial fabrication tests of 6 Li-enriched Li 2 TiO 3 pebbles of 1mm in diameter were carried out by a wet process with a dehydration reaction, and characteristics of the 6 Li-enriched Li 2 TiO 3 pebbles were evaluated for preparation of a high Li-burnup test in a testing reactor. Powder of 96at% 6 Li-enriched Li 2 TiO 3 was prepared by a solid state reaction, and two kinds of 6 Li-enriched Li 2 TiO 3 pebbles, namely un-doped and TiO 2 -doped Li 2 TiO 3 pebbles, were fabricated by the wet process. Based on results of the pebble fabrication tests, two kinds of 6 Li-enriched Li 2 TiO 3 pebbles were successfully fabricated with target values (density: 80-85%T.D., grain size: 2 TiO 3 pebbles was a satisfying value of about 1.05. Contact strength of these pebbles was about 6300MPa, which was almost the same as that of the Li 2 TiO 3 pebbles with natural Li. (author)

  2. Study of the phase transformation of single particles of Ga2O3 by UV-Raman spectroscopy and high-resolution TEM.

    Wang, Xiang; Xu, Qian; Fan, Fengtao; Wang, Xiuli; Li, Mingrun; Feng, Zhaochi; Li, Can

    2013-09-01

    By taking advantage of UV-Raman spectroscopy and high-resolution TEM (HRTEM), combined with the focused ion beam (FIB) technique, the transformation from GaOOH into α-Ga2O3 and then into β-Ga2O3 was followed. We found that the stepwise transformations took place from the surface region before developing into the bulk of single particles without particle agglomeration and growth. During the transformation from GaOOH into α-Ga2O3, the elimination of water vapor through the dehydroxylation of GaOOH resulted in the formation of micropores in the single particles, whilst maintaining their particle size. For the phase transformation from α-Ga2O3 into β-Ga2O3, the nucleation of β-Ga2O3 was found to occur at the surface defects and this process could be retarded by occupying these defects with a small amount of La2O3. By finely controlling the process of the phase transformation, the β-Ga2O3 domains gradually developed from the surface into the bulk of the single particles without particle agglomeration. Therefore, the surface structure of the α-Ga2O3 single particles can be easily tuned and a particle with an α@β core-shell phase structure has been obtained. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Effects of MnO-Al2O3 on the grain growth and high-temperature deformation strain of UO2 fuel pellets

    Kang, Ki Won; Yang, Jae Ho; Kim, Jong Hun; Rhee, Young Woo; Kim, Dong Joo; Kim, Keon Sik; Song, Kun Woo

    2010-01-01

    The fabrication and high-temperature deformation strain of MnO-Al 2 O 3 -doped UO 2 pellets were studied. The effects of additive composition and amount on the microstructure evolution of a UO 2 pellet were investigated. The compressive creep behaviors of MnO-Al 2 O 3 -doped UO 2 pellets were examined. The results indicated that a MnO-Al 2 O 3 binary additive can effectively promote the grain growth of UO 2 pellets. In addition, the high-temperature deformation strain of the UO 2 pellet can be improved significantly with 1,000 ppm 95MnO-5Al 2 O 3 (mol%). The developed MnO-Al 2 O 3 -additive-containing UO 2 pellets can be a potential candidate for a high-burn-up fuel and a pellet-cladding interaction (PCI) remedy. (author)

  4. A Core-Shell Fe/Fe2 O3 Nanowire as a High-Performance Anode Material for Lithium-Ion Batteries.

    Na, Zhaolin; Huang, Gang; Liang, Fei; Yin, Dongming; Wang, Limin

    2016-08-16

    The preparation of novel one-dimensional core-shell Fe/Fe2 O3 nanowires as anodes for high-performance lithium-ion batteries (LIBs) is reported. The nanowires are prepared in a facile synthetic process in aqueous solution under ambient conditions with subsequent annealing treatment that could tune the capacity for lithium storage. When this hybrid is used as an anode material for LIBs, the outer Fe2 O3 shell can act as an electrochemically active material to store and release lithium ions, whereas the highly conductive and inactive Fe core functions as nothing more than an efficient electrical conducting pathway and a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium ions. The core-shell Fe/Fe2 O3 nanowire maintains an excellent reversible capacity of over 767 mA h g(-1) at 500 mA g(-1) after 200 cycles with a high average Coulombic efficiency of 98.6 %. Even at 2000 mA g(-1) , a stable capacity as high as 538 mA h g(-1) could be obtained. The unique composition and nanostructure of this electrode material contribute to this enhanced electrochemical performance. Due to the ease of large-scale fabrication and superior electrochemical performance, these hybrid nanowires are promising anode materials for the next generation of high-performance LIBs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Giant strain with ultra-low hysteresis and high temperature stability in grain oriented lead-free K0.5Bi0.5TiO3-BaTiO3-Na0.5Bi0.5TiO3 piezoelectric materials.

    Maurya, Deepam; Zhou, Yuan; Wang, Yaojin; Yan, Yongke; Li, Jiefang; Viehland, Dwight; Priya, Shashank

    2015-02-26

    We synthesized grain-oriented lead-free piezoelectric materials in (K0.5Bi0.5TiO3-BaTiO3-xNa0.5Bi0.5TiO3 (KBT-BT-NBT) system with high degree of texturing along the [001]c (c-cubic) crystallographic orientation. We demonstrate giant field induced strain (~0.48%) with an ultra-low hysteresis along with enhanced piezoelectric response (d33 ~ 190pC/N) and high temperature stability (~160°C). Transmission electron microscopy (TEM) and piezoresponse force microscopy (PFM) results demonstrate smaller size highly ordered domain structure in grain-oriented specimen relative to the conventional polycrystalline ceramics. The grain oriented specimens exhibited a high degree of non-180° domain switching, in comparison to the randomly axed ones. These results indicate the effective solution to the lead-free piezoelectric materials.

  6. Simultaneous achievement of high dielectric constant and low temperature dependence of capacitance in (111-oriented BaTiO3-Bi(Mg0.5Ti0.5O3-BiFeO3 solid solution thin films

    Junichi Kimura

    2016-01-01

    Full Text Available The temperature dependence of the capacitance of (111c-oriented (0.90–xBaTiO3-0.10Bi(Mg0.5Ti0.5O3-xBiFeO3 solid solution films is investigated. These films are prepared on (111cSrRuO3/(111Pt/TiO2/SiO2/(100Si substrates by the chemical solution deposition technique. All the films have perovskite structures and the crystal symmetry at room temperature varies with increasing x ratio, from pseudocubic when x = 0–0.30 to rhombohedral when x = 0.50–0.90. The pseudocubic phase shows a high relative dielectric constant (εr (ranging between 400 and 560 at room temperature and an operating frequency of 100 kHz and a low temperature dependence of capacitance up to 400°C, while maintaining a dielectric loss (tan δ value of less than 0.2 at 100 kHz. In contrast, εr for the rhombohedral phase increases monotonically with increasing temperature up to 250°C, and increasingly high tan δ values are recorded at higher temperatures. These results indicate that pseudocubic (0.90–xBaTiO3-0.10Bi(Mg0.5Ti0.5O3-xBiFeO3 solid solution films with (111 orientation are suitable candidates for high-temperature capacitor applications.

  7. Crystal Growth and Characterization of (Bi0.5Na0.5)TiO3-BaTiO3 Single Crystals Obtained by a Top-Seeded Solution Growth Method under High-Pressure Oxygen Atmosphere

    Onozuka, Hiroaki; Kitanaka, Yuuki; Noguchi, Yuji; Miyayama, Masaru

    2011-09-01

    A single crystal of ferroelectric 0.88(Bi,Na)TiO3-0.12BaTiO3 (BNT-BT) solid solution with tetragonal P4mm structure was grown by a top-seeded solution growth (TSSG) method at a high oxygen pressure (PO2 ) of 0.9 MPa. The crystals exhibited a large remanent polarization (Pr) of 54 µC/cm2, which leads to a spontaneous polarization estimated to be 54 µC/cm2. The large Pr compared with that of crystals grown at PO2 = 0.1 MPa is suggested to originate from a low oxygen vacancy concentration. The high-PO2 TSSG method is demonstrated to be effective for obtaining large-sized, high-quality BNT-BT crystals.

  8. Structural and Optical Properties of Ultra-high Pure Hot Water Processed Ga2O3 Thin Film

    Subramani SHANMUGAN

    2016-05-01

    Full Text Available Thin film based gas sensor is an advanced application of thin film especially Ga2O3 (GO thin film gas sensor is useful for high temperature gas sensor. The effect of moisture or environment on thin film properties has more influence on gas sensing properties. Radio Frequency sputtered Ga2O3 thin film was synthesized and processed in ultra-high pure hot water at 95 °C for different time durations. The structural properties were verified by the Xray Diffraction technique and the observed spectra revealed the formation of hydroxyl compound of Gallium (Gallium Oxide Dueterate – GOD on the surface of the thin film and evidenced for structural defects as an effect of moisture. Decreased crystallite size and increased dislocation density was showed the crystal defects of prepared film. From the Ultra Violet – Visible spectra, decreased optical transmittance was noticed for various processing time. The formation of needle like GOD was confirmed using Field Emission Secondary Electron Microscope (FESEM images.DOI: http://dx.doi.org/10.5755/j01.ms.22.2.7186

  9. Facile Synthesis of Graphene@NiO/MoO3 Composite Nanosheet Arrays for High-performance Supercapacitors

    Zeng, Wei; Zhang, Guanhua; Hou, Sucheng; Wang, Taihong; Duan, Huigao

    2015-01-01

    Graphene@NiO/MoO 3 composite nanosheet arrays (CSAs) were grown on the nickel foam via a one-step hydrothermal way. The composite of NiO and MoO 3 showed a promising synergistic effect for capacitors. Graphene had been integrated to the composite nanosheets to further enhance the electrochemical performance. The prepared samples were characterized by scanning electron microscopy and transmission electron microscopy, X-ray diffraction spectroscopy and Raman spectroscopy. A possible growth mechanism was proposed to explain the formation of the composite nanosheets by carrying out a series of time-dependent experiments. Benefiting from the improved electron conductivity and effective buffering of the volume variation induced by redox reactions, the composite exhibited a high area capacitance of 1.372 F cm −2 even at a high current density of 42 mA cm −2 , and showed excellent cycle stability (62.7% of the initial capacitance after 7500 cycles, while 87.9% remained in the latter 7000 cycles)

  10. On the high temperature phase transition in Ba(Zr0.20Ti0.80O3 ceramic

    K. P. Chandra

    2017-08-01

    Full Text Available Temperature dependent X-ray diffraction (XRD and dielectric properties of perovskite Ba(Zr0.2Ti0.8O3 ceramic prepared using a standard solid-state reaction process is presented. Along with phase transitions at low temperature, a new phase transition at high temperature (873∘C at 20Hz, diffusive in character has been found where the lattice structure changes from monoclinic (space group: P2∕m to hexagonal (space group: P6∕mmm. This result places present ceramic in the list of potential candidate for intended high temperature applications. The AC conductivity data followed hopping type charge conduction and supports jump relaxation model. The experimental value of d33=98pC/N was found. The dependence of polarization and strain on electric field at room temperature suggested that lead-free Ba(Zr0.2Ti0.8O3 is a promising material for electrostrictive applications.

  11. Optical properties and crystal structure of Eu3+ -doped Y2O3 crystals prepared under different conditions and with different methods

    Chung, Yong Hwa; Jang, Ki Wan; Kim, Il Gon; Kim Sang Su; Lee, Yong Ill; Park, Seong Tae; Seo, Hyo Jin

    2003-01-01

    The optical properties and the crystal structure of 6-mol% Eu 3+ -doped Y 2 O 3 powders prepared under different conditions and with different methods were studied through emission spectroscopy and X-ray powder diffraction. All samples exhibited the normal fluorescence spectrum of Eu 3+ -doped cubic Y 2 O 3 powders. The peak positions of the 5 D 0 → 7 F 0 transitions of Eu 3+ ions were shifted to the short-wavelength direction as the sintering temperature was lowered or the size of the host particle itself was decreased. The dynamic properties, such as the rise or the decay time of the 5 D 0 → 7 F 2 transition, depended on other factors than the size of the grain contained in each particle and the size of host particle itself. The morphologies of the studied samples were also observed by using a scanning electron microscope

  12. Highly constrained ferroelectric [BaTiO3](1−x)Λ/[BaZrO3]xΛ superlattices: X-ray diffraction and Raman spectroscopy

    Belhadi, J.; El Marssi, M.; Gagou, Y.; El Mendili, Y.; Bouyanfif, H.; Yuzyuk, Yu. I.; Raevski, I. P.; Wolfman, J.

    2014-01-01

    We report an x-ray diffraction (XRD) and a Raman-scattering investigation of ferroelectric/paraelectric superlattices [BaTiO 3 ] (1−x)Λ /[BaZrO 3 ] xΛ for which the composition varied, 0.15 ≤ x ≤ 0.85, while the superlattice (SL) modulation period Λ was kept constant at about 100 Å. The samples were epitaxially grown by pulsed laser deposition on MgO substrates buffered with La 0.5 Sr 0.5 CoO 3 . Based on the XRD analysis and on polarized Raman spectra, we have showed that the large strain in SLs induced ferroelectricity in BaZrO 3 (BZ) for all SLs, a material that is paraelectric in the bulk form at any temperature and in the single film. The induced polar axis in BZ layers is perpendicular to the plane of substrate while BaTiO 3 (BT) layers exhibit in-plane polar orientation. Raman spectroscopy revealed a lattice ordering in SLs due to the misfit strain generated by the large lattice mismatch between the alternating BZ and BT layers. This strain induced a huge upward frequency of the lowest E(1TO) soft mode from 60 cm −1 in the BT single film to 215 cm −1 in the SL with x = 0.85. These results show that in spite of relatively large periodicity of SLs, they are highly constrained and the variation of BZ ratio allowed modifying strains between layers. The temperature dependence of the Raman spectra for BT 0.3Λ /BZ 0.7Λ and BT 0.7Λ /BZ 0.3Λ samples revealed giant shift of the ferroelectric phase transition. The phase transition temperature was found to be upshifted by about 300 °C with respect to BT single crystal.

  13. Note: a high-sensitivity current sensor based on piezoelectric ceramic Pb(Zr,Ti)O3 and ferromagnetic materials.

    He, Wei; Li, Ping; Wen, Yumei; Zhang, Jitao; Yang, Aichao; Lu, Caijiang

    2014-02-01

    An electric current sensor using piezoelectric ceramic Pb(Zr,Ti)O3 (PZT) sandwiched between two high permeability cuboids and two NdFeB magnets is presented. The magnetic field originating from an electric wire is augmented by the high permeability cuboids. The PZT plate experiences an enhanced magnetic force and generates voltage output. When placed with a distance of d = 5.0 mm from the wire, the sensor shows a flat sensitivity of ∼5.7 mV/A in the frequency range of 30 Hz-80 Hz and an average sensitivity of 5.6 mV/A with highly linear behavior in the current range of 1 A-10 A at 50 Hz.

  14. A highly uniform ZnO/NaTaO3 nanocomposite: Enhanced self-sensitized degradation of colored pollutants under visible light

    Xing, Guanjie; Tang, Changhe; Zhang, Bo; Zhao, Lanxiao; Su, Yiguo; Wang, Xiaojing

    2015-01-01

    In this study, a highly uniform ZnO/NaTaO 3 composite was prepared via simple hydrothermal synthesis. XRD confirmed the composite was constructed by pure cubic phase of NaTaO 3 and hexagonal phase of ZnO. SEM analysis showed that as-prepared ZnO/NaTaO 3 shaped as an irregular ginger with an obviously smaller size than that of pure ZnO without obvious agglomeration. EDS mapping demonstrated that the four elements (Na, Ta, O, Zn) in the composite were very uniformly distributed. The photocatalytic behaviors of as-prepared composites were studied in the degradation of methylene blue both under UV and visible irradiation. The bare ZnO showed the highest activity with 99.8% methylene blue (MB) photodegraded in 70 min under UV light irradiation whereas 94% photodegraded rate was achieved for ZnO/NaTaO 3 . More importantly, the uniform composite of ZnO/NaTaO 3 exhibited effective degradation of methylene blue under visible light which can be attributed to the well dyes adsorption abilities and the high efficiency of electron separation, induced by the synergistic effect between ZnO and NaTaO 3 . It is confirmed the dye rather than a semiconductor is excited under visible light irradiation and a self-sensitized photocatalytic mechanism was then proposed based on the experimental results. - Graphical abstract: Visible light photocatalytic activity of ZnO/NaTaO 3 and proposed schematic of self-sensitization directed photogradation of MB. - Highlights: • Highly uniform ZnO/NaTaO 3 photocatalysts were fabricated by hydrothermal method. • ZnO/NaTaO 3 composite exhibited effective degradation of MB under visible light. • ZnO/NaTaO 3 composite effectively promoted dye adsorption and electrons separation. • A self-sensitized photocatalytic mechanism was proposed for the degradation of dye

  15. Solid phase epitaxial growth of high mobility La:BaSnO_3 thin films co-doped with interstitial hydrogen

    Niedermeier, Christian A.; Rhode, Sneha; Fearn, Sarah; Moram, Michelle A.; Ide, Keisuke; Hiramatsu, Hidenori; Hosono, Hideo; Kamiya, Toshio

    2016-01-01

    This work presents the solid phase epitaxial growth of high mobility La:BaSnO_3 thin films on SrTiO_3 single crystal substrates by crystallization through thermal annealing of nanocrystalline thin films prepared by pulsed laser deposition at room temperature. The La:BaSnO_3 thin films show high epitaxial quality and Hall mobilities up to 26 ± 1 cm"2/Vs. Secondary ion mass spectroscopy is used to determine the La concentration profile in the La:BaSnO_3 thin films, and a 9%–16% La doping activation efficiency is obtained. An investigation of H doping to BaSnO_3 thin films is presented employing H plasma treatment at room temperature. Carrier concentrations in previously insulating BaSnO_3 thin films were increased to 3 × 10"1"9" cm"−"3 and in La:BaSnO_3 thin films from 6 × 10"1"9" cm"−"3 to 1.5 × 10"2"0" cm"−"3, supporting a theoretical prediction that interstitial H serves as an excellent n-type dopant. An analysis of the free electron absorption by infrared spectroscopy yields a small (H,La):BaSnO_3 electron effective mass of 0.27 ± 0.05 m_0 and an optical mobility of 26 ± 7 cm"2/Vs. As compared to La:BaSnO_3 single crystals, the smaller electron mobility in epitaxial thin films grown on SrTiO_3 substrates is ascribed to threading dislocations as observed in high resolution transmission electron micrographs.

  16. Pressure response of vacancy ordered maghemite (γ-Fe2O3) and high pressure transformed hematite (α-Fe2O3)

    Hearne, Giovanni; Pischedda, Vittoria

    2012-03-01

    Combined XRD and Mössbauer effect spectroscopy studies to high pressures of ˜30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13-16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to ˜15° over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite→hematite transformation.

  17. A simple dissolved metals mixing method to produce high-purity MgTiO3 nanocrystals

    Pratapa, Suminar; Baqiya, Malik A.; Istianah,; Lestari, Rina; Angela, Riyan

    2014-01-01

    A simple dissolved metals mixing method has been effectively used to produce high-purity MgTiO 3 (MT) nanocrystals. The method involves the mixing of independently dissolved magnesium and titanium metal powders in hydrochloric acid followed by calcination. The phase purity and nanocrystallinity were determined by making use of laboratory x-ray diffraction data, to which Rietveld-based analyses were performed. Results showed that the method yielded only one type magnesium titanate powders, i.e. MgTiO 3 , with no Mg 2 TiO 4 or MgTi 2 O 5 phases. The presence of residual rutile or periclase was controlled by adding excessive Mg up to 5% (mol) in the stoichiometric mixing. The method also resulted in MT nanocrystals with estimated average crystallite size of 76±2 nm after calcination at 600°C and 150±4 nm (at 800°C). A transmission electron micrograph confirmed the formation of the nanocrystallites

  18. Comprehensive Study of Z-Cut Highly Integrated LiNbO3 Optical Modulator with Adjustable Chirp Parameters

    Palodiya, Vikram; Raghuwanshi, Sanjeev Kumar

    2017-12-01

    In this paper, the domain inversion is used in a simple fashion to improve the performance of a Z-cut highly integrated LiNbO3 optical modulator (LNOM). The Z-cut modulator having ≤ 3 V switching voltage and bandwidth of 15 GHz for an external modulator in which traveling-wave electrode length L_{m} imposed the modulating voltage, the product of V_π and L_{m} is fixed for a given electro-optic material (EOM). An investigation to achieve a low V_π by both magnitude of the electro-optic coefficient (EOC) for a wide variety of EOMs has been reported. The Sellmeier equation (SE) for the extraordinary index of congruent LiNbO3 is derived. The predictions related to phase matching are accurate between room temperature and 250 °C and wavelength ranging from 0.4 to 5 μm. The SE predicts more accurate refractive indices (RI) at long wavelengths. The different overlaps between the waveguides for the Z-cut structure are shown to yield a chirp parameter that can able to adjust 0-0.7. Theoretical results are perfectly verified by simulated results.

  19. Effect of preparation and processing conditions on UV absorbing properties of hydroxyapatite-Fe2O3 sunscreen.

    C Teixeira, M A; Piccirillo, C; Tobaldi, D M; Pullar, R C; Labrincha, J A; Ferreira, M O; L Castro, P M; E Pintado, M M

    2017-02-01

    The development of innovative, safe and non-photocatalytic sunscreens is urgently needed, as it is essential to have sunscreen filters offering appropriate UV protection without damaging the environment and/or generating free radicals when in contact with the skin. Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAp) when substituted with iron has UV protection properties and is not photocatalytic; HAp was used to make a sunscreen filter by treating cod fish bones in an iron-containing solution, and then calcining them at 700°C. Here we present a systematic and advanced study on this material, to obtain a sunscreen with improved UV absorbing properties. Bones were treated with three different iron salts - Fe(II) chloride, Fe(II) lactate and Fe(III) nitrate - under various pH conditions. Results showed that Fe(II) chloride in basic pH led to the most effective iron inclusion. High energy ball milling or ultrasound were investigated to increase surface area and corresponding UV absorption; high energy ball milling treatment led to the best optical properties. The optimum powders were used to formulate UV protection creams, which showed Sun Protection Factor (SPF) values significantly superior to the control cream (up to 4.1). Moreover the critical wavelength (λ crit ) was >370nm (388-389nm) and UVA/UVB ratios were very close to 1. With these properties these sunscreens can be classified as broad UV protectors. Results also showed that combining these powders with other sunscreens (i.e. titanium dioxide), a synergic effect between the different components was also observed. This investigation showed that HAp-based sunscreens of marine origin are a valid alternative to commercial products, safe for the health of the customers and, being non-photocatalytic, do not pose a threat to the environment. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Efficient degradation of Methylene Blue dye over highly reactive Cu doped strontium titanate (SrTiO3) nanoparticles photocatalyst under visible light.

    Rahman, Qazi Inamur; Ahmad, Musheer; Misra, Sunil Kumar; Lohani, Minaxi

    2012-09-01

    Visible light induced photocatalysts of Cu doped SrTiO3 (Cu/SrTiO3) nanoparticles with the size -60-75 nm were prepared via facile sol-gel method. The morphological, optical, crystalline properties and compositions of synthesized Cu/SrTiO3 nanoparticles were thoroughly characterized by field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD), ultra violet-visible spectroscopy (UV-Vis) and energy dispersive X-ray (EDX). A significant red shift in the UV-diffused reflectance spectrum was observed and the absorption edge shifted to visible region by the Cu doping. Surprisingly, the band gap of SrTiO3 was changed from 3.2 eV drop to 2.96 eV. The photocatalytic activity of the synthesized Cu/SrTiO3 nanoparticles was demonstrated for the degradation of Methylene Blue dye under visible light irradiation. The formation of new acceptor region in Cu/SrTiO3 was responsible for high photocatalytic activity of Cu/SrTiO3 nanoparticles. The results showed that the Methylene Blue dye was degraded by -66% within time span of 2 h over the Cu/SrTiO3 nanoparticles. This dye degradation reaction followed the Langmuir-Hinshelwood kinetics and also exhibited first order reaction rate. The calculated rate constant for the degradation reaction following first order kinetics was k = 0.0016 min(-1).

  1. Thermal Stability of Al2O3/Silicone Composites as High-Temperature Encapsulants

    Yao, Yiying

    Underwater gliders are robust and long endurance ocean sampling platforms that are increasingly being deployed in coastal regions. This new environment is characterized by shallow waters and significant currents that can challenge the mobility of these efficient (but traditionally slow moving) vehicles. This dissertation aims to improve the performance of shallow water underwater gliders through path planning. The path planning problem is formulated for a dynamic particle (or "kinematic car") model. The objective is to identify the path which satisfies specified boundary conditions and minimizes a particular cost. Several cost functions are considered. The problem is addressed using optimal control theory. The length scales of interest for path planning are within a few turn radii. First, an approach is developed for planning minimum-time paths, for a fixed speed glider, that are sub-optimal but are guaranteed to be feasible in the presence of unknown time-varying currents. Next the minimum-time problem for a glider with speed controls, that may vary between the stall speed and the maximum speed, is solved. Last, optimal paths that minimize change in depth (equivalently, maximize range) are investigated. Recognizing that path planning alone cannot overcome all of the challenges associated with significant currents and shallow waters, the design of a novel underwater glider with improved capabilities is explored. A glider with a pneumatic buoyancy engine (allowing large, rapid buoyancy changes) and a cylindrical moving mass mechanism (generating large pitch and roll moments) is designed, manufactured, and tested to demonstrate potential improvements in speed and maneuverability.

  2. Corrosion resistance properties of enamels with high B2O3-P2O5 content to molten aluminum

    Zhou, M.; Li, K.; Shu, D.; Sun, B.D.; Wang, J.

    2003-01-01

    Anticorrosive properties of borophosphate and boron-free enamels to molten aluminum were investigated using SEM and electron probe. Carbonates of alkali metal and alkaline earth metal were added in an appropriate weight ratio to achieve desired melting temperature of the enamels. SEM examination on the solidified interface between the enamels and aluminum alloy show that the enamels can spread slightly on aluminum alloy. For anticorrosive sample of borophosphate enamel, phosphorus was not detected by electron probe at the side of aluminum alloy near the interface, but silicon was detected in the silica-free enamels side. For the sample of boron-free enamels, however, phosphorus was found at the side of aluminum alloy near the interface. It was revealed that the enamels with high B 2 O 3 -P 2 O 5 content have high corrosion resistance to molten aluminum

  3. Multiferroic BiFeO3 thin films and nanodots grown on highly oriented pyrolytic graphite substrates

    Shin, Hyun Wook; Son, Jong Yeog

    2017-12-01

    Multiferroic BiFeO3 (BFO) thin films and nanodots are deposited on highly oriented pyrolytic graphite (HOPG) substrates via a pulsed laser deposition technique, where the HOPG surface has a honeycomb lattice structure made of carbon atoms, similar to graphene. A graphene/BFO/HOPG capacitor exhibited multiferroic properties, namely ferroelectricity (a residual polarization of 26.8 μC/cm2) and ferromagnetism (a residual magnetization of 1.1 × 10-5 emu). The BFO thin film had high domain wall energies and demonstrated switching time of approximately 82 ns. An 8-nm BFO nanodot showed a typical piezoelectric hysteresis loop with an effective residual piezoelectric constant of approximately 110 pm/V and exhibited two clearly separated current curves depending on the ferroelectric polarization direction.

  4. Influence of ruthenium ions on the precipitation of α-FeOOH, α-Fe2O3 and Fe3O4 in highly alkaline media

    Krehula, Stjepko; Music, Svetozar

    2006-01-01

    The influence of ruthenium ions on the precipitation of goethite (α-FeOOH), α-Fe 2 O 3 and Fe 3 O 4 in highly alkaline media was investigated by 57 Fe Moessbauer and FT-IR spectroscopies, thermal field emission scanning electron microscope (FE SEM) and EDS. The presence of Ru-dopant strongly affected the precipitation of α-FeOOH at highly alkaline pH, i.e. the formation of α-Fe 2 O 3 was also noticed. A decrease of hyperfine magnetic field (HMF) at RT from 35.1 T (undoped α-FeOOH) to 31.3 T for sample with [Ru]/([Ru] + [Fe]) = 0.0196 was assigned to the incorporation of ruthenium ions into the α-FeOOH structure. Moessbauer spectroscopy showed the formation of stoichiometric Fe 3 O 4 for [Ru]/([Ru] + [Fe]) = 0.0291-0.0909. α-Fe 2 O 3 and Fe 3 O 4 did not show a tendency to the formation of solid solutions with ruthenium ions. FE SEM observations of the samples showed that reference α-FeOOH sample contained acicular particles of good uniformity, which increased the length up to ∼5 times with increase of concentration of ruthenium ions. On the other hand, large octahedral Fe 3 O 4 crystals (particles) were associated with small particles of ruthenium (hydrous) oxide with a size in the range ∼100 nm or less. A possible catalytic action of ruthenium that created reduction conditions for Fe 3+ ions and formation of Fe 2+ ions for precipitation of Fe 3 O 4 was discussed

  5. High-sensitivity β-Ga_2O_3 solar-blind photodetector on high-temperature pretreated c-plane sapphire substrate

    Qian, Ling-Xuan

    2017-09-20

    Recently, monoclinic Ga2O3 (beta-Ga2O3) photodetectors (PDs) have been extensively studied for various commercial and military applications due to the merits of intrinsic solar rejection, high gain, and great compactness. In this work, c-plane sapphire substrates were annealed under different temperatures in a vacuum furnace prior to the molecular beam epitaxy (MBE) of beta-Ga2O3 thin film, which yielded a smoother surface and even a terraceand- step-like morphology on the substrate, resulting in improved crystallinity of the epitaxial film. Accordingly, both the dark and photo currents of beta-Ga2O3 metal-semiconductor-metal (MSM) PDs were increased by the enhanced carrier mobility (mu) of the more crystalline film. However, the substrate-annealing temperature must be sufficiently high to offset the rise of the dark current and thus achieve a remarkable improvement in the photodetection properties. As a result, the PD fabricated on the 1050 degrees C-annealed substrate exhibited extremely high sensitivity, for example, high responsivity (R) of 54.9 A/ W and large specific detectivity (D*) of 3.71 x 10(14) Jones. Both parameters were increased by one order of magnitude because of the combined effects of the dramatic increase in mu and the effective reduction in defect-related recombination centers. Nevertheless, the latter also prolonged the recovery time of the PD. These findings suggest another way to develop beta-Ga2O3 PD with extremely high sensitivity. (C) 2017 Optical Society of America

  6. High performance In2O3 thin film transistors using chemically derived aluminum oxide dielectric

    Nayak, Pradipta K.

    2013-07-18

    We report high performance solution-deposited indium oxide thin film transistors with field-effect mobility of 127 cm2/Vs and an Ion/Ioff ratio of 106. This excellent performance is achieved by controlling the hydroxyl group content in chemically derived aluminum oxide (AlOx) thin-film dielectrics. The AlOx films annealed in the temperature range of 250–350 °C showed higher amount of Al-OH groups compared to the films annealed at 500 °C, and correspondingly higher mobility. It is proposed that the presence of Al-OH groups at the AlOx surface facilitates unintentional Al-doping and efficient oxidation of the indium oxide channel layer, leading to improved device performance.

  7. High performance In2O3 thin film transistors using chemically derived aluminum oxide dielectric

    Nayak, Pradipta K.; Hedhili, Mohamed N.; Cha, Dong Kyu; Alshareef, Husam N.

    2013-01-01

    We report high performance solution-deposited indium oxide thin film transistors with field-effect mobility of 127 cm2/Vs and an Ion/Ioff ratio of 106. This excellent performance is achieved by controlling the hydroxyl group content in chemically derived aluminum oxide (AlOx) thin-film dielectrics. The AlOx films annealed in the temperature range of 250–350 °C showed higher amount of Al-OH groups compared to the films annealed at 500 °C, and correspondingly higher mobility. It is proposed that the presence of Al-OH groups at the AlOx surface facilitates unintentional Al-doping and efficient oxidation of the indium oxide channel layer, leading to improved device performance.

  8. Low operating voltage InGaZnO thin-film transistors based on Al2O3 high-k dielectrics fabricated using pulsed laser deposition

    Geng, G. Z.; Liu, G. X.; Zhang, Q.; Shan, F. K.; Lee, W. J.; Shin, B. C.; Cho, C. R.

    2014-01-01

    Low-voltage-driven amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) with an Al 2 O 3 dielectric were fabricated on a Si substrate by using pulsed laser deposition. Both Al 2 O 3 and IGZO thin films are amorphous, and the thin films have very smooth surfaces. The Al 2 O 3 gate dielectric exhibits a very low leakage current density of 1.3 x 10 -8 A/cm 2 at 5 V and a high capacitance density of 60.9 nF/cm 2 . The IGZO TFT with a structure of Ni/IGZO/Al 2 O 3 /Si exhibits high performance with a low threshold voltage of 1.18 V, a high field effect mobility of 20.25 cm 2 V -1 s -1 , an ultra small subthreshold swing of 87 mV/decade, and a high on/off current ratio of 3 x 10 7 .

  9. Note: High-power piezoelectric transformer fabricated with ternary relaxor ferroelectric Pb(Mg(1/3)Nb(2/3))O3-Pb(In(1/2)Nb(1/2))O3-PbTiO3 single crystal.

    Wang, Qing; Ma, Chuanguo; Wang, Feifei; Liu, Bao; Chen, Jianwei; Luo, Haosu; Wang, Tao; Shi, Wangzhou

    2016-03-01

    A plate-shaped piezoelectric transformer was designed and fabricated using ternary relaxor ferroelectric single crystal Pb(Mg(1/3)Nb(2/3))O3-Pb(In(1/2)Nb(1/2))O3-PbTiO3. Both the input and output sections utilized the transverse-extensional vibration mode. The frequency and load dependences of the electrical properties for the proposed transformer were systematically studied. Results indicated that under a matching load resistance of 14.9 kΩ, a maximum output power of 2.56 W was obtained with the temperature rise less than 5 °C. The corresponding power density reached up to 50 W/cm(3). This ternary single-crystal transformer had potential applications in compact-size converters requiring high power density.

  10. Non-linear thermal evolution of the crystal structure and phase transitions of LaFeO3 investigated by high temperature X-ray diffraction

    Selbach, Sverre M.; Tolchard, Julian R.; Fossdal, Anita; Grande, Tor

    2012-01-01

    The crystal structure, anisotropic thermal expansion and structural phase transition of the perovskite LaFeO 3 has been studied by high-temperature X-ray diffraction from room temperature to 1533 K. The structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R3 ¯ c structure of LaFeO 3 is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes. Non-linear lattice expansion across the antiferromagnetic to paramagnetic transition of LaFeO 3 at T N =735 K was compared to the corresponding behavior of the ferroelectric antiferromagnet BiFeO 3 to gain insight to the magnetoelectric coupling in BiFeO 3 , which is also multiferroic. The first order phase transition of LaFeO 3 from Pbnm to R3 ¯ c was observed at 1228±9 K, and a subsequent transition to Pm3 ¯ m was extrapolated to occur at 2140±30 K. The stability of the Pbnm and R3 ¯ c polymorphs of LaFeO 3 is discussed in terms of the competing enthalpy and entropy of the two crystal polymorphs and the thermal evolution of the polyhedral volume ratio V A /V B . - Graphical abstract: Aniostropic thermal evolution of the lattice parameters and phase transition of LaFeO 3 . Highlights: ► The crystal structure of LaFeO 3 is studied by HTXRD from RT to 1533 K. ► A non-linear expansion across the Néel temperature is observed for LaFeO 3 . ► The ratio V A /V B is used to rationalize the thermal evolution of the structure.

  11. High dielectric constant observed in (1 − x)Ba(Zr0.07Ti0.93)O3–xBa(Fe0.5Nb0.5)O3 binary solid-solution

    Kruea-In, Chatchai; Eitssayeam, Sukum; Pengpat, Kamonpan; Rujijanagul, Gobwute

    2012-01-01

    Binary solid-solutions of the (1 − x)Ba(Zr 0.07 Ti 0.93 )O 3 –xBa(Fe 0.5 Nb 0.5 O 3 ) system, with 0.1 ≤ x ≤ 0.9,were fabricated via a solid-state processing technique. X-ray diffraction analysis revealed that all samples exhibited a single perovskite phase. The BaFe 0.5 Nb 0.5 O 3 also promoted densification and grain growth of the system. Dielectric measurements showed that all samples displayed a relaxor like behavior. The x = 0.1 sample presented a dielectric-frequency and temperature with low loss tangent ( 0.2 samples, the dielectric data showed a broad dielectric constant–temperature curve with a giant dielectric characteristic. In addition, a high dielectric constant > 50,000 (at 10 kHz and temperature > 150 °C) was observed for the x = 0.9 sample.

  12. High dielectric permittivity in the microwave region of SrBi2Nb2O9 (SBN) added La2O3, PbO and Bi2O3, obtained by mechanical alloying

    Rocha, M. J. S.; Silva, P. M. O.; Theophilo, K. R. B.; Sancho, E. O.; Paula, P. V. L.; Silva, M. A. S.; Honorato, S. B.; Sombra, A. S. B.

    2012-08-01

    This paper presents the microwave dielectric properties and a structural study of SrBi2Nb2O9 (SBN) added La2O3, PbO or Bi2O3 obtained by a solid state procedure. High-energy mechanical milling was used to reduce the particle size, which allows for a better shaping of the green body and an increased reactivity. The mechanical milling activation process produced a reduced sintering temperature in the material, decreasing the loss of the volatile elements and controlling the growth of the grain that is produced when a high temperature is required to obtain dense ceramics. The incorporation of La3+, or Pb2+, or Bi3+ of different amounts (0, 3, 5, 10 and 15 wt%) was used to improve the densification without changing the crystal structure, since with a low doping content these ions can occupy the A site of the perovskite blocks; they can also occupy the Bi3+ sites in Bi2O3 layers. A single orthorhombic phase was formed after calcination at 800 °C for 2 h. X-ray diffraction, Fourier transformation, infrared and Raman spectroscopy have been carried out in order to investigate the effects of doping on SBN. The dielectric permittivity (ɛ‧r) and loss in the microwave region (2-4 GHz) of SBN ceramics with additions of Bi2O3, La2O3 and PbO were studied. Higher values of permittivity (ɛr‧ = 154.6) have been obtained for the SBN added La (15 wt%) a lower loss (tg δ = 0.01531) was also achieved in the SBN added La (15 wt%) sample with PVA and TEOS, respectively. The samples that showed the highest dielectric permittivities were all lanthanum doped, all with values of permittivity above 90. A comparative study associated with different types of binders was completed (with glycerin, PVA and TEOS). This procedure allowed us to obtain phases at lower temperatures than usually appear in the literature. The microwave dielectric properties (permittivity and loss) in the region 2-4 GHz, were studied for all samples. The structural and microwave dielectric properties of SBN show a

  13. Influence of reaction conditions on formation of ionic liquid-based nanostructured Bi2O3 as an efficient visible-light-driven photocatalyst

    Bagheri, Mozhgan; Heydari, Mojgan; Vaezi, Mohammad Reza

    2018-01-01

    In this study, nanostructured bismuth oxide was synthesized based on the chemical reaction of bismuth nitrate and NaOH in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) under ultrasonic irradiation. The effect of sodium hydroxide with a different molar ratio of NaOH to bismuth in the range of 3-10 was investigated. The results of fourier-transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD) showed that NaOH has a critical role in the formation of pure α-Bi2O3. So, at high concentrations of NaOH (NaOH:Bi ≥ 7.5), the chloride anion from the ionic liquid cannot be entered into the crystalline structure of bismuth oxide, which resulted in the formation of pure bismuth oxide, while at lower concentrations of NaOH (NaOH:Bi ≤ 5), Bi3O4Cl was formed with a layered structure. The XRD results revealed that the synthesized α-Bi2O3 has a monoclinic structure and scanning electron microscopy (SEM) images showed that the sample consists of needle like particles with an average thickness of 50 nm. The ionic liquid has an important role in the prevention of an agglomeration of particles in the Bi2O3 sample. The photocatalytic activity of the synthesized Bi2O3 was investigated to study the degradation of malachite green dye as a model pollutant under visible light. The effects of various parameters such as the pH, concentration of the dye, and the catalyst on the degradation of malachite green were also investigated.

  14. First-Principles Study of MoO3/Graphene Composite as Cathode Material for High-Performance Lithium-Ion Batteries

    Cui, Yanhua; Zhao, Yu; Chen, Hong; Wei, Kaiyuan; Ni, Shuang; Cui, Yixiu; Shi, Siqi

    2018-03-01

    Using first-principles calculations, we have systematically investigated the adsorption and diffusion behavior of Li in MoO3 bulk, on MoO3 (010) surface and in MoO3/graphene composite. Our results indicate that, in case of MoO3 bulk, Li diffusion barriers in the interlayer and intralayer spaces are 0.55 eV and 0.58 eV respectively, which are too high to warrant fast Lithium-ion charge/discharge processes. While on MoO3 (010) surface, Li exhibits a diffusion barrier as low as 0.07 eV which guarantees an extremely fast Li diffusion rate during charge/discharge cycling. However, in MoO3/graphene monolayer, Li diffusion barrier is at the same level as that on MoO3 (010) surface, which also ensures a very rapid Li charge/discharge rate. The rapid Li charge/discharge rate in this system originates from the removal of the upper dangling O1 atoms which hinder the Li diffusion on the lower MoO3 layer. Besides this, due to the interaction between Li and graphene, the Li average binding energy increases to 0.14 eV compared to its value on MoO3 (010) surface which contributes to a higher voltage. Additionally, the increased ratio of surface area provides more space for Li storage and the capacity of MoO3/graphene composite increases up to 279.2 mAhg-1. The last but not the least, due to the high conductivity of graphene, the conductivity of MoO3/graphene composite enhances greatly which is beneficial for electrode materials. In the light of present results, MoO3/graphene composite exhibits higher voltage, good conductivity, large Li capacity and very rapid Li charge/discharge rate, which prove it as a promising cathode material for high-performance lithium-ion batteries (LIBs).

  15. Optical properties and thermal stability of LaYbO3 ternary oxide for high-k dielectric application

    Su, Wei-tao; Yang, Li; Li, Bin

    2011-01-01

    A new ternary rare oxide dielectric LaYbO3 film had been prepared on silicon wafers and quartz substrates by reactive sputtering method using a La-Yb metal target. A range of analysis techniques was performed to determine the optical band gap, thermal stability, and electrical property of the deposited samples. It was found the band gap of LaYbO3 film was about 5.8 eV. And the crystallization temperature for rapid thermal annealing (20 s) was between 900 and 950 °C. X-ray photoelectron spectroscopy results indicate the formation of the SiO2 and silicate in the interface between silicon wafer and LaYbO3 film. The dielectric constant is about 23 from the calculation of capacitance-voltage curve, which is comparable higher than previously reported La2O3 or Yb2O3 film.

  16. Cube-like α-Fe2O3 supported on ordered multimodal porous carbon as high performance electrode material for supercapacitors.

    Chaudhari, Nitin K; Chaudhari, Sudeshna; Yu, Jong-Sung

    2014-11-01

    Well-dispersed cube-like iron oxide (α-Fe2O3) nanoparticles (NPs) supported on ordered multimodal porous carbon (OMPC) are synthesized for the first time by a facile and efficient glycine-assisted hydrothermal route. The effect of OPMC support on growth and formation mechanism of the Fe2O3 NPs is discussed. OMPC as a supporting material plays a pivotal role of controlling the shape, size, and dispersion of the Fe2O3 NPs. As-synthesized α-Fe2O3/OMPC composites reveal significant improvement in the performance as electrode material for supercapacitors. Compared to the bare Fe2O3 and OMPC, the composite exhibits excellent cycling stability, rate capability, and enhanced specific capacitances of 294 F g(-1) at 1.5 A g(-1), which is twice that of OMPC (145 F g(-1)) and about four times higher than that of bare Fe2O3 (85 F g(-1)). The improved electrochemical performance of the composite can be attributed to the well-defined structure, high conductivity, and hierarchical porosity of OMPC as well as the unique α-Fe2O3 NPs with cube-like morphology well-anchored on the OMPC support, which makes the composite a promising candidate for supercapacitors. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Three-dimensional core-shell Fe_2O_3 @ carbon/carbon cloth as binder-free anode for the high-performance lithium-ion batteries

    Wang, Xiaohua; Zhang, Miao; Liu, Enzuo; He, Fang; Shi, Chunsheng; He, Chunnian; Li, Jiajun; Zhao, Naiqin

    2016-01-01

    Highlights: • The 3D core-shell Fe_2O_3@C/CC structure is fabricated by simple hydrothermal route. • The composite connected 3D carbon networks consist of carbon cloth, Fe_2O_3 nanorods and outer carbon layer. • The Fe_2O_3@C/CC used as binder-free anode in LIBs, demonstrates excellent performances. - Abstract: A facile and scalable strategy is developed to fabricate three dimensional core-shell Fe_2O_3 @ carbon/carbon cloth structure by simple hydrothermal route as binder-free lithium-ion battery anode. In the unique structure, carbon coated Fe_2O_3 nanorods uniformly disperse on carbon cloth which forms the conductive carbon network. The hierarchical porous Fe_2O_3 nanorods in situ grown on the carbon cloth can effectively shorten the transfer paths of lithium ions and reduce the contact resistance. The carbon coating significantly inhibits pulverization of active materials during the repeated Li-ion insertion/extraction, as well as the direct exposure of Fe_2O_3 to the electrolyte. Benefiting from the structural integrity and flexibility, the nanocomposites used as binder-free anode for lithium-ion batteries, demonstrate high reversible capacity and excellent cyclability. Moreover, this kind of material represents an alternative promising candidate for flexible, cost-effective, and binder-free energy storage devices.

  18. The effects of particle size and content on the thermal conductivity and mechanical properties of Al2O3/high density polyethylene (HDPE composites

    2011-07-01

    Full Text Available The influences of filler size and content on the properties (thermal conductivity, impact strength and tensile strength of Al2O3/high density polyethylene (HDPE composites are studied. Thermal conductivity and tensile strength of the composites increase with the decrease of particle size. The dependence of impact strength on the particle size is more complicated. The SEM micrographs of the fracture surface show that Al2O3 with small particle size is generally more efficient for the enhancement of the impact strength, while the 100 nm particles prone to aggregation due to their high surface energy deteriorate the impact strength. Composite filled with Al2O3 of 0.5 µm at content of 25 vol% show the best synthetic properties. It is suggested that the addition of nano-Al2O3 to HDPE would lead to good performance once suitably dispersed.

  19. High optical and structural quality of GaN epilayers grown on ( 2¯01) β-Ga2O3

    Mumthaz Muhammed, Mufasila; Peres, M.; Yamashita, Y.; Morishima, Y.; Sato, S.; Franco, N.; Lorenz, K.; Kuramata, A.; Roqan, Iman S.

    2014-01-01

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2̄01) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2̄01) oriented β-Ga 2O3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼108cm-2. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2̄01) β-Ga2O3 with in-plane epitaxial orientation relationships between the β-Ga2O3 and the GaN thin film defined by (010) β-Ga2O3 || (112̄0) GaN and (2̄01) β-Ga2O3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high. © 2014 AIP Publishing LLC.

  20. High optical and structural quality of GaN epilayers grown on ( 2¯01) β-Ga2O3

    Mumthaz Muhammed, Mufasila

    2014-07-28

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2̄01) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2̄01) oriented β-Ga 2O3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼108cm-2. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2̄01) β-Ga2O3 with in-plane epitaxial orientation relationships between the β-Ga2O3 and the GaN thin film defined by (010) β-Ga2O3 || (112̄0) GaN and (2̄01) β-Ga2O3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high. © 2014 AIP Publishing LLC.

  1. Synthesis of graphene supported Li2SiO3 as a high performance anode material for lithium-ion batteries

    Yang, Shuai; Wang, Qiufen; Miao, Juan; Zhang, Jingyang; Zhang, Dafeng; Chen, Yumei; Yang, Hong

    2018-06-01

    The Li2SiO3-graphene composite is successfully synthesized through an easy hydrothermal method. The structures and morphologies of the produced samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrum, Brunauer-Emmett-Teller formalism, scanning electron microscope, transmission electron microscope, and electrochemistry methods. The result shows a well crystalline of the Li2SiO3-GE composite. The existence of graphene doesn't change the crystalline of Li2SiO3. In addition, the Li2SiO3 compound with an average diameter of 20 nm can be seen on the surface of graphene with uniform distribution. After the composite with graphene, the composite displays large surface area which ensures the well electrochemistry of the composite. Finally, the Li2SiO3-graphene composite delivers a high initial capacity of 878.3 mAh g-1 at 1C as well as a high recovery capacity of 400 mAh g-1 after 200 cycles. When charged and discharged at high rate, the Li2SiO3-doping graphene composite still exhibits a high specific capacity of 748.3 mAh g-1 (at 2C, and 576 mAh g-1 at 5C) and well cycling performance. The well synthesized composite possesses well structure and well electrochemistry performance.

  2. High breakdown voltage quasi-two-dimensional β-Ga2O3 field-effect transistors with a boron nitride field plate

    Bae, Jinho; Kim, Hyoung Woo; Kang, In Ho; Yang, Gwangseok; Kim, Jihyun

    2018-03-01

    We have demonstrated a β-Ga2O3 metal-semiconductor field-effect transistor (MESFET) with a high off-state breakdown voltage (344 V), based on a quasi-two-dimensional β-Ga2O3 field-plated with hexagonal boron nitride (h-BN). Both the β-Ga2O3 and h-BN were mechanically exfoliated from their respective crystal substrates, followed by dry-transfer onto a SiO2/Si substrate for integration into a high breakdown voltage quasi-two-dimensional β-Ga2O3 MESFETs. N-type conducting behavior was observed in the fabricated β-Ga2O3 MESFETs, along with a high on/off current ratio (>106) and excellent current saturation. A three-terminal off-state breakdown voltage of 344 V was obtained, with a threshold voltage of -7.3 V and a subthreshold swing of 84.6 mV/dec. The distribution of electric fields in the quasi-two-dimensional β-Ga2O3 MESFETs was simulated to analyze the role of the dielectric h-BN field plate in improving the off-state breakdown voltage. The stability of the field-plated β-Ga2O3 MESFET in air was confirmed after storing the MESFET in ambient air for one month. Our results pave the way for unlocking the full potential of β-Ga2O3 for use in a high-power nano-device with an ultrahigh breakdown voltage.

  3. Controlled High Filler Loading of Functionalized Al2O3-Filled Epoxy Composites for LED Thermal Management

    Permal, Anithambigai; Devarajan, Mutharasu; Hung, Huong Ling; Zahner, Thomas; Lacey, David; Ibrahim, Kamarulazizi

    2018-03-01

    Thermal management in light-emitting diode (LED) has been extensively researched recently. This study is intended to develop an effective thermally conductive epoxy composite as thermal interface material (TIM) for headlamp LEDs. Silane-functionalized aluminum oxide (Al2O3) powder of different average particle sizes (44 and 10 µm) was studied for its feasibility as filler at its maximum loading. A detailed comparison of three different methods of particle dispersions, hand-mix, speed-mix and calendaring process (3-roll mill), has been reported. The dispersion of Al2O3 particles, the thermal conductivity and thermal degradation characteristics of the composites were investigated and explained in detail. At 75 wt.% filler loading, 10 and 44 µm Al2O3 achieved composite thermal conductivities of 1.13 and 2.08 W/mK, respectively, which is approximately 528 and 1055% of enhancement with respect to neat epoxy. The package-level thermal performance of the LED employing the Al2O3-filled TIMs was carried out using thermal transient analysis. The experimental junction-to-ambient thermal resistances ( R thJ-A) achieved were 6.65, 7.24, and 8.63 K/W for Al2O3_44µm, Al2O3_10µm and neat epoxy, respectively. The results revealed that the Al2O3_44µm fillers-filled composite performed better in both material-level and package-level thermal characteristics.

  4. Structural properties and sensing characteristics of high-k Ho2O3 sensing film-based electrolyte-insulator-semiconductor

    Pan, Tung-Ming; Huang, Ming-De

    2011-01-01

    Highlights: → We report the structural properties and sensing characteristics of Ho 2 O 3 sensing membranes deposited on Si substrates by reactive sputtering. → We applied X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to study the structural and morphological features of these films after they had been subjected to annealing at various temperatures (700 deg. C, 800 deg. C, and 900 deg. C). → The Ho 2 O 3 electrolyte-insulator-semiconductor device annealed at 800 deg. C exhibited a higher sensitivity, a lower hysteresis voltage, and a smaller drift rate than other annealing temperatures. - Abstract: In this study, we report a Ho 2 O 3 electrolyte-insulator-semiconductor (EIS) device films deposited on Si substrates through reactive sputtering. The effect of thermal annealing (700, 800, and 900 deg. C) on the structural and surface properties of Ho 2 O 3 sensing film was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. We found that the EIS device with a Ho 2 O 3 sensing film annealed at 800 deg. C exhibited a higher sensitivity of ∼57 mV/pH, a lower hysteresis voltage of 2.68 mV, and a smaller drift rate of 2.83 mV h -1 compared to those at other annealing conditions. This improvement can be attributed to the well-crystallized Ho 2 O 3 structure and the large surface roughness.

  5. High-Density Near-Field Readout Using Solid Immersion Lens Made of KTaO3 Monocrystal

    Shinoda, Masataka; Saito, Kimihiro; Kondo, Takao; Furuki, Motohiro; Takeda, Minoru; Nakaoki, Ariyoshi; Sasaura, Masahiro; Fujiura, Kazuo

    2006-02-01

    We developed solid immersion lenses made of a KTaO3 monocrystal. The refractive index of KTaO3 is 2.382 at a wavelength of 405 nm. Using KTaO3 as the raw material of a solid immersion lens, we could design an effective numerical aperture of 2.20. We observed an eye pattern of a 150 GB capacity with a 130 nm track pitch and a 47.6 nm bit length. The areal density is 104.3 Gbit/in.2.

  6. Conditions for stability of different valence states of manganese impurity in α-Al2O3

    Kulagin, N.A.; Apanasenko, A.L.; Kazakov, N.A.

    1983-01-01

    The influence of crystal growth conditions on valence change of a Mn ion at γ-irradiation of corUndum has been studied. The results were obtained on an ESR-spectrome-- ter at 300 K. The crystals (except Mn ions) contained different impurities (Fe 3+ , Cr 3+ , Ti) and depending on the impurities on γ-irradiation, the transition of Mn 3+ both into Mn 3+ and Mn 4+ state or into one of them was observed. For several crystals (with Ti impOrity), the delta-like decrease of Csub(Mnsup(2+)) concentration is observed at 750+800 K and a full decrease of Csub(Mnsup(2+)) was obtained at 1100-1200 K.The results allow the conclusion of the possible mechanisms underlying the stabilization of Mn 2+ and Mn 4+ ions in corundum

  7. Physical and electrical characteristics of AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors with rare earth Er2O3 as a gate dielectric

    Lin, Ray-Ming; Chu, Fu-Chuan; Das, Atanu; Liao, Sheng-Yu; Chou, Shu-Tsun; Chang, Liann-Be

    2013-01-01

    In this study, the rare earth erbium oxide (Er 2 O 3 ) was deposited using an electron beam onto an AlGaN/GaN heterostructure to fabricate metal-oxide-semiconductor high-electron-mobility transistors (MOS–HEMTs) that exhibited device performance superior to that of a conventional HEMT. Under similar bias conditions, the gate leakage currents of these MOS–HEMT devices were four orders of magnitude lower than those of conventional Schottky gate HEMTs. The measured sub-threshold swing (SS) and the effective trap state density (N t ) of the MOS–HEMT were 125 mV/decade and 4.3 × 10 12 cm −2 , respectively. The dielectric constant of the Er 2 O 3 layer in this study was 14, as determined through capacitance–voltage measurements. In addition, the gate–source reverse breakdown voltage increased from –166 V for the conventional HEMT to –196 V for the Er 2 O 3 MOS–HEMT. - Highlights: ► GaN/AlGaN/Er 2 O 3 metal-oxide semiconductor high electron mobility transistor ► Physical and electrical characteristics are presented. ► Electron beam evaporated Er 2 O 3 with excellent surface roughness ► Device exhibits reduced gate leakage current and improved I ON /I OFF ratio

  8. Solar-Blind Photodetector with High Avalanche Gains and Bias-Tunable Detecting Functionality Based on Metastable Phase α-Ga2O3/ZnO Isotype Heterostructures.

    Chen, Xuanhu; Xu, Yang; Zhou, Dong; Yang, Sen; Ren, Fang-Fang; Lu, Hai; Tang, Kun; Gu, Shulin; Zhang, Rong; Zheng, Youdou; Ye, Jiandong

    2017-10-25

    The metastable α-phase Ga 2 O 3 is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga 2 O 3 remains challenging. To this end, single crystalline α-Ga 2 O 3 epilayers are achieved on nonpolar ZnO (112̅0) substrates for the first time and a high performance Au/α-Ga 2 O 3 /ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 10 3 and a detectivity of 9.66 × 10 12 cm Hz 1/2 W -1 . Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W -1 at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga 2 O 3 and Ga 2 O 3 /ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 10 3 and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 10 5 and a high responsivity of 1.10 × 10 4 A W -1 . Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.

  9. Size-dependent effects in supported highly dispersed Fe2O3 catalysts, doped with Pt and Pd

    Cherkezova-Zheleva, Zara; Shopska, Maya; Mitov, Ivan; Kadinov, Georgi

    2010-01-01

    Series of Fe and Fe–Me (Me = Pt or Pd) catalyst supported on γ-Al 2 O 3 , TiO 2 (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also.

  10. Performance and stability of (ZrO2)0.89(Y2O3)0.01(Sc2O3)0.10-LaCr0.85Cu0.10Ni0.05O3-δ oxygen transport membranes under conditions relevant for oxy-fuel combustion

    Pirou, Stéven; Bermudez, Jose M.; Tak Na, Beom

    2018-01-01

    Self-standing, planar dual-phase oxygen transport membranes consisting of 70 vol.% (ZrO2)0.89(Y2O3)0.01(Sc2O3)0.10 (10Sc1YSZ) and 30 vol.% LaCr0.85Cu0.10Ni0.05O3-δ (LCCN) were successfully developed and tested. The stability of the composite membrane was studied in simulated oxy-fuel power plant...

  11. Effects of fabrication conditions on mechanical properties and microstructure of duplex β″-Al2O3 solid electrolyte

    Canfield, Nathan L.; Kim, Jin Y.; Bonnett, Jeff F.; Pearson, R.L.; Sprenkle, Vincent L.; Jung, Keeyoung

    2015-01-01

    Highlights: • The concept of duplex BASEs is presented as a method to lower the ASR for NBBs. • Duplex BASEs consist of thin dense electrolyte and porous support. • Strength of converted BASEs shows a different trend from as-sintered samples. • Cell orientation gives significant impact on strength of duplex BASEs. - Abstract: Na-beta batteries are an attractive technology as a large-scale electrical energy storage for grid applications. However, additional improvements in performance and cost are needed for wide market penetration. To improve cell performance by minimizing polarizations, reduction of electrolyte thickness was attempted using a duplex structure consisting of a thin dense electrolyte layer and a porous support layer. In this paper, the effects of sintering conditions, dense electrolyte thickness, and cell orientation on the flexural strength of duplex BASEs fabricated using a vapor phase approach were investigated. It is shown that sintering at temperatures between 1500 and 1550 °C results in fine grained microstructures and the highest flexural strength after conversion. Increasing thickness of the dense electrolyte has a small impact on flexural strength, while the orientation of load such that the dense electrolyte is in tension instead of compression has major effects on strength for samples with a well-sintered dense electrolyte

  12. Dielectric properties of (K0.5Na0.5)NbO3-(Bi0.5Li0.5)ZrO3 lead-free ceramics as high-temperature ceramic capacitors

    Yan, Tianxiang; Han, Feifei; Ren, Shaokai; Ma, Xing; Fang, Liang; Liu, Laijun; Kuang, Xiaojun; Elouadi, Brahim

    2018-04-01

    (1 - x)K0.5Na0.5NbO3- x(Bi0.5Li0.5)ZrO3 (labeled as (1 - x)KNN- xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic-tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN-0.08BLZ ceramic exhibits a high and stable permittivity ( 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies.

  13. High-performance flexible resistive memory devices based on Al2O3:GeOx composite

    Behera, Bhagaban; Maity, Sarmistha; Katiyar, Ajit K.; Das, Samaresh

    2018-05-01

    In this study a resistive switching random access memory device using Al2O3:GeOx composite thin films on flexible substrate is presented. A bipolar switching characteristic was observed for the co-sputter deposited Al2O3:GeOx composite thin films. Al/Al2O3:GeOx/ITO/PET memory device shows excellent ON/OFF ratio (∼104) and endurance (>500 cycles). GeOx nanocrystals embedded in the Al2O3 matrix have been found to play a significant role in enhancing the switching characteristics by facilitating oxygen vacancy formation. Mechanical endurance was retained even after several bending. The conduction mechanism of the device was qualitatively discussed by considering Ohmic and SCLC conduction. This flexible device is a potential candidate for next-generation electronics device.

  14. Ferroelectric BiFeO3as an Oxide Dye in Highly Tunable Mesoporous All-Oxide Photovoltaic Heterojunctions

    Wang, Lingfei; Ma, He; Chang, Lei; Ma, Chun; Yuan, Guoliang; Wang, Junling; Wu, Tao

    2016-01-01

    As potential photovoltaic materials, transition-metal oxides such as BiFeO3 (BFO) are capable of absorbing a substantial portion of solar light and incorporating ferroic orders into solar cells with enhanced performance. But the photovoltaic

  15. Synthesis of a mesoporous single crystal Ga2O3 nanoplate with improved photoluminescence and high sensitivity in detecting CO.

    Yan, Shicheng; Wan, Lijuan; Li, Zhaosheng; Zhou, Yong; Zou, Zhigang

    2010-09-14

    A new approach is proposed to synthesize a mesoporous single crystal Ga(2)O(3) nanoplate by heating a single crystal nanoplate of GaOOH, which involves an ion exchange between KGaO(2) and CH(3)COOH at room temperature for the formation of GaOOH and pseudomorphic and topotactic phase transformation from GaOOH to Ga(2)O(3).

  16. Au plasmon enhanced high performance β-Ga2O3 solar-blind photo-detector

    Yuehua An

    2016-02-01

    Full Text Available Surface plasmon polariton (SPP is electro-magnetic wave coupled to free electron oscillations near the surface of metal, and has been used to improve the photoelectric properties in many optoelectronic devices. In the present study, the Au nanoparticles (NPs/β-Ga2O3 composite thin film was fabricated through depositing Au ultra-thin film on the β-Ga2O3 thin film followed by post-thermal treatment. Compared to bare β-Ga2O3 thin film, a significant absorption around 510 nm, which is attributed to SPP of Au NPs, was observed in the UV–vis spectrum of Au NPs/β-Ga2O3 composite thin film. The results showed that the photoresponse of Au NPs/Ga2O3 photodetector illuminated under 254 nm+532 nm light was much higher than that illuminated under 254 nm light, indicating an enhancement of photoelectric property for the solar-blind photodetector based on β-Ga2O3 thin film.

  17. Evolution mechanisms of MgO·Al2O3 inclusions by cerium in spring steel used in fasteners of high-speed railway

    Wang Lijun; Wang Qi; Chou Kuochih; Liu Yanqiang

    2015-01-01

    The effect of rare earth metal addition on the non-metallic inclusions in spring steel used in fastener of high speed railway was investigated by metallographic examination; SEM-EDS and component analysis, aiming at deform those harmful inclusions to improve service life of spring steel. MgO·Al 2 O 3 inclusions were found in present experimental steel, which is also confirmed by the stability diagram of MgO/MgO·Al 2 O 3 /Al 2 O 3 from thermodynamic consideration. After Ce addition, the evolution process of Al 2 O 3 ·MgO inclusions was determined through the surface and line scanning. The effects of time and Ce content on the evolution of Al 2 O 3 ·MgO inclusions were examined. It was indicated that Al 2 O 3 ·MgO inclusions were wrapped by rare earth inclusions to form a ring like shape Ce-riched band around the inclusion, which would be useful to improve fatigue and corrosion resistance of spring steel. It was found that diffusion of Ce 3+ , Al 3+ and Mg 2+ in inclusions core and intermediate layer would be the limited step during evolutions of inclusions. (author)

  18. Cast Aluminum Alloys for High Temperature Applications Using Nanoparticles Al2O3 and Al3-X Compounds (X = Ti, V, Zr)

    Lee, Jonathan A.

    2009-01-01

    In this paper, the effect of nanoparticles Al2O3 and Al3-X compounds (X = Ti, V, Zr) on the improvement of mechanical properties of aluminum alloys for elevated temperature applications is presented. These nanoparticles were selected based on their low cost, chemical stability and low diffusions rates in aluminum at high temperatures. The strengthening mechanism at high temperature for aluminum alloy is based on the mechanical blocking of dislocation movements by these nanoparticles. For Al2O3 nanoparticles, the test samples were prepared from special Al2O3 preforms, which were produced using ceramic injection molding process and then pressure infiltrated by molten aluminum. In another method, Al2O3 nanoparticles can also be homogeneously mixed with fine aluminum powder and consolidated into test samples through hot pressing and sintering. With the Al3-X nanoparticles, the test samples are produced as precipitates from in-situ reactions with molten aluminum using conventional permanent mold or die casting techniques. It is found that cast aluminum alloy using nanoparticles Al3-X is the most cost effective method to produce high strength aluminum alloys for high temperature applications in comparison to nanoparticles Al2O3. Furthermore, significant mechanical properties retention in high temperature environment could be achieved with Al3-X nanoparticles, resulting in tensile strength of nearly 3 times higher than most 300- series conventional cast aluminum alloys tested at 600 F.

  19. Dielectric and Ferroelectric Properties of SrTiO3-Bi0.5Na0.5TiO3-BaAl0.5Nb0.5O3 Lead-Free Ceramics for High-Energy-Storage Applications.

    Yan, Fei; Yang, Haibo; Lin, Ying; Wang, Tong

    2017-11-06

    Pulsed capacitors require high-recoverable energy-storage density (W rec ) and high energy-storage efficiency (η), which can be realized through the selection and adjustment of the composition. In this work, (1 - x)SrTiO 3 -x(0.95Bi 0.5 Na 0.5 TiO 3 -0.05BaAl 0.5 Nb 0.5 O 3 ) [(1 - x)ST-x(BNT-BAN)] ceramics were successfully prepared via the pressureless solid-state reaction method. The dielectric constant increases gradually with the introduction of BNT-BAN and obtains a maximum value of 3430 with the composition of 0.4ST-0.6(BNT-BAN) at 100 Hz, which is 10.39 times higher than that of the pure ST sample (∼330). Dispersive relaxor behaviors and ferroelectric performances can be enhanced with the introduction of BNT-BAN. The composition of 0.5ST-0.5(BNT-BAN) exhibits a high W rec of 1.89 J/cm 3 as well as a high η of 77%. Therefore, the (1 - x)ST-x(BNT-BAN) systems are candidate materials for pulsed capacitor applications.

  20. First assessment of Li2O-Bi2O3 ceramic oxides for high temperature carbon dioxide capture

    E.M.Briz-López; M.J.Ramírez-Moreno; I.C.Romero-Ibarra; C.Gómez-Yá(n)ez; H.Pfeiffer; J.Ortiz-Landeros

    2016-01-01

    The capacity to capture CO2 was determined in several stoichiometric compositions in the Li2O-Bi2O3 system.The compounds (Li7BiO6,Li5BiOs,Li3BiO4 and LiBiO2 phases) were synthesized via solid-state reaction and characterized by X-ray diffraction,scanning electron microscopy and N2 adsorption techniques.The samples were heat-treated at temperatures from 40 to 750 ℃ under the CO2 atmosphere to evaluate the carbonate formation,which is indicative of the capacity of CO2 capture.Moreover,Li7BiO6 shows an excellent CO2 capture capacity of 7.1 mmol/g,which is considerably higher than those of other previously reported ceramics.Li7BiO6 is able to react with CO2 from 240 ℃ to approximately 660 ℃ showing a high kinetic reaction even at CO2 partial pressure values as low as 0.05.

  1. First assessment of Li2O–Bi2O3 ceramic oxides for high temperature carbon dioxide capture简

    E.M.Briz-López; M.J.Ramírez-Moreno; I.C.Romero-Ibarra; C.Gómez-Yá?ez; H.Pfeiffer; J.Ortiz-Landeros

    2016-01-01

    The capacity to capture CO2 was determined in several stoichiometric compositions in the Li2O–Bi2O3 system. The compounds(Li7BiO6, Li5BiO5, Li3BiO4 and LiBiO2 phases) were synthesized via solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption techniques.The samples were heat-treated at temperatures from 40 to 750 °C under the CO2 atmosphere to evaluate the carbonate formation, which is indicative of the capacity of CO2 capture. Moreover, Li7BiO6 shows an excellent CO2 capture capacity of 7.1 mmol/g, which is considerably higher than those of other previously reported ceramics. Li7BiO6 is able to react with CO2 from 240 °C to approximately 660 °C showing a high kinetic reaction even at CO2 partial pressure values as low as 0.05.

  2. Ferroelectric BiFeO3as an Oxide Dye in Highly Tunable Mesoporous All-Oxide Photovoltaic Heterojunctions

    Wang, Lingfei

    2016-10-12

    As potential photovoltaic materials, transition-metal oxides such as BiFeO3 (BFO) are capable of absorbing a substantial portion of solar light and incorporating ferroic orders into solar cells with enhanced performance. But the photovoltaic application of BFO has been hindered by low energy-conversion efficiency due to poor carrier transport and collection. In this work, a new approach of utilizing BFO as a light-absorbing sensitizer is developed to interface with charge-transporting TiO2 nanoparticles. This mesoporous all-oxide architecture, similar to that of dye-sensitized solar cells, can effectively facilitate the extraction of photocarriers. Under the standard AM1.5 (100 mW cm−2) irradiation, the optimized cell shows an open-circuit voltage of 0.67 V, which can be enhanced to 1.0 V by tailoring the bias history. A fill factor of 55% is achieved, which is much higher than those in previous reports on BFO-based photovoltaic devices. The results provide here a new viable approach toward developing highly tunable and stable photovoltaic devices based on ferroelectric transition-metal oxides.

  3. Ferroelectric BiFeO3 as an Oxide Dye in Highly Tunable Mesoporous All-Oxide Photovoltaic Heterojunctions.

    Wang, Lingfei; Ma, He; Chang, Lei; Ma, Chun; Yuan, Guoliang; Wang, Junling; Wu, Tom

    2017-01-01

    As potential photovoltaic materials, transition-metal oxides such as BiFeO 3 (BFO) are capable of absorbing a substantial portion of solar light and incorporating ferroic orders into solar cells with enhanced performance. But the photovoltaic application of BFO has been hindered by low energy-conversion efficiency due to poor carrier transport and collection. In this work, a new approach of utilizing BFO as a light-absorbing sensitizer is developed to interface with charge-transporting TiO 2 nanoparticles. This mesoporous all-oxide architecture, similar to that of dye-sensitized solar cells, can effectively facilitate the extraction of photocarriers. Under the standard AM1.5 (100 mW cm -2 ) irradiation, the optimized cell shows an open-circuit voltage of 0.67 V, which can be enhanced to 1.0 V by tailoring the bias history. A fill factor of 55% is achieved, which is much higher than those in previous reports on BFO-based photovoltaic devices. The results provide here a new viable approach toward developing highly tunable and stable photovoltaic devices based on ferroelectric transition-metal oxides. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. High temperature X-ray diffraction studies on HfO2-Gd2O3 system

    Panneerselvam, G.; Antony, M.P.; Ananthasivan, K.; Joseph, M.

    2016-01-01

    High temperature X-ray diffraction (HTXRD) technique is an important experimental tool for measuring thermal expansion of materials of interest. A series of solid solutions containing GdO 1.5 in HfO 2 ,Hf 1-y Gd y )O 2 (y = 0.15, 0.2, 0.3, 0.41 and 0.505) were prepared by solid state method. Structural characterization and computation of lattice parameter was carried out by using room temperature X-ray diffraction measurements. The room temperature lattice parameter estimated for (Hf 1-y Gd y )O 2 (y=0.15, 0.2, 0.3, 0.41 and 0.505) are 0.51714 nm, 0.51929 nm, 0.52359nm, 0.52789nm and 0.53241 nm, respectively. Thermal expansion coefficients and percentage linear thermal expansion of the HfO 2 -Gd 2 O 3 solid solutions containing 20 and 41 mol% GdO 1.5 were determined using HTXRD in the temperature range 298 to 1673K. The mean linear thermal expansion coefficients of the solid solutions containing 20 and 41 mol. %Gd are 11.65 x 10 -6 K -1 and 12.07 x 10 -6 K -1 , respectively. (author)

  5. High-pressure versus isoelectronic doping effect on the honeycomb iridate Na2IrO3

    Hermann, V.; Ebad-Allah, J.; Freund, F.; Pietsch, I. M.; Jesche, A.; Tsirlin, A. A.; Deisenhofer, J.; Hanfland, M.; Gegenwart, P.; Kuntscher, C. A.

    2017-11-01

    We study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate Na2IrO3 by combining optical spectroscopy with synchrotron x-ray diffraction measurements on single crystals. The obtained optical conductivity of Na2IrO3 is discussed in terms of a Mott-insulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev interactions. With increasing Li content x , (Na1 -xLix )2IrO3 moves deeper into the Mott-insulating regime, and there are indications that up to a doping level of 24% the compound comes closer to the Kitaev limit. The optical conductivity spectrum of single-crystalline α -Li2IrO3 does not follow the trends observed for the series up to x =0.24 . There are strong indications that α -Li2IrO3 is not as close to the Kitaev limit as Na2IrO3 and lies closer to the quasimolecular orbital picture instead. Except for the pressure-induced hardening of the phonon modes, the optical properties of Na2IrO3 seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between x =0.24 and x =1 are given by comparing the pressure-induced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.

  6. Hydrothermal synthesis of Fe_2O_3/polypyrrole/graphene oxide composites as highly efficient electrocatalysts for oxygen reduction reaction in alkaline electrolyte

    Ren, Suzhen; Ma, Shaobo; Yang, Ying; Mao, Qing; Hao, Ce

    2015-01-01

    Graphical abstract: Fe_2O_3/polypyrrole/graphene oxide electrocatalysts for oxygen reduction reaction (ORR) are successfully prepared through one simple polypyrrole-assisted hydrothermal method and possess very high ORR activity and are able to selectively reduce O_2 to water through the four-electron transfer reaction mechanism in alkaline electrolyte. - Abstract: Advantages in low cost, and excellent catalytic activity of Fe-based nanomaterials dispersed on nitrogen-doped graphene supports render them to be good electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Here, Fe_2O_3/polypyrrole/graphene oxide (Fe_2O_3/Ppy/GO) composites with the Fe_2O_3 embedded in the Ppy modified GO are synthesized using hydrothermal method. With an optimal iron atom content ratio of 1.6% in graphene oxide and heat treatment at 800 °C, the Fe_2O_3/Ppy/GO exhibited enhanced catalytic performance for ORR with the onset potential of −0.1 V (vs SCE), cathodic potential of −0.24 V (vs SCE), an approximate 4e"− transfer process in O_2-saturated 0.1 M KOH, and superior stability that only reduced 5% catalytic activity after 5000 cycles. The decisive factors in improving the electrocatalytic and durable performance are the intimate and large contact interfaces between nanocrystallines of Fe_2O_3 and Ppy/GO, in addition to the high electron withdrawing/storing ability and the high conductivity of GO doped with nitrogen from Ppy during the hydrothermal reaction. The Fe_2O_3/Ppy/GO showed significantly improved ORR properties and confirmed that Fe-N-C-based electrocatalysts played a key role in fuel cells.

  7. Rambutan-like CNT-Al2O3 scaffolds for high-performance cathode catalyst layers of polymer electrolyte fuel cells

    Chang, KwangHyun; Cho, Seonghun; Lim, Eun Ja; Park, Seok-Hee; Yim, Sung-Dae

    2018-03-01

    Rambutan-like CNT-Al2O3 scaffolds are introduced as a potential candidate for CNT-based catalyst supports to overcome the CNT issues, such as the easy bundling in catalyst ink and the poor pore structure of the CNT-based catalyst layers, and to achieve high MEA performance in PEFCs. Non-porous α-phase Al2O3 balls are introduced to enable the growth of multiwalled CNTs, and Pt nanoparticles are loaded onto the CNT surfaces. In a half-cell, the Pt/CNT-Al2O3 catalyst shows much higher durability than those of a commercial Pt/C catalyst even though it shows lower oxygen reduction reaction (ORR) activity than Pt/C. After using the decal process for MEA formation, the Pt/CNT-Al2O3 shows comparable initial performance characteristics to Pt/C, overcoming the lower ORR activity, mainly due to the facile oxygen transport in the cathode catalyst layers fabricated with the CNT-Al2O3 scaffolds. The Pt/CNT-Al2O3 also exhibits much higher durability against carbon corrosion than Pt/C owing to the durable characteristics of CNTs. Systematic analysis of single cell performance for both initial and after degradation is provided to understand the origin of the high initial performance and durable behavior of Pt/CNT-Al2O3-based catalyst layers. This will provide insights into the design of electrocatalysts for high-performance MEAs in PEFCs.

  8. High performance of mesoporous γ-Fe2O3 nanoparticle/Ketjen Black composite as anode material for lithium ion batteries

    Dong, Hui; Xu, Yunlong; Ji, Mandi; Zhang, Huang; Zhao, Zhen; Zhao, Chongjun

    2015-01-01

    Highlights: • A mesoporous γ-Fe 2 O 3 /KB composite was synthesized via solvothermal method. • KB was used as a carbon template to improve electrochemical performance of γ-Fe 2 O 3 . • 3D network structure can relieve volume change and improve the ionic transport. • The composite exhibited an ultrahigh capacity and high rate performance. - Abstract: A type of γ-Fe 2 O 3 nanoparticle/Ketjen Black (KB) composite material is synthesized by a solvothermal method combined with precursor thermal transformation. The structure and morphology are characterized by XRD, raman spectra, TG, nitrogen sorption, SEM, TEM and EDS. The results show that the composite has a uniform nanoporous network and well-dispersed γ-Fe 2 O 3 particles with a size of ca. 5 nm are embedded in the mesopores of KB. The γ-Fe 2 O 3 /KB exhibits superior eletrochemical performances to the bare γ-Fe 2 O 3 , especially at high current rate. The discharge capacity of the composite is 1100 mAh·g −1 at the first cycle and remains 988.8 mAh·g −1 after 100 cycles at 0.2 C. Moreover, it also maintains a high discharge capacity of 697.8 mAh·g −1 at 2 C and 410.1 mAh·g −1 at 5 C after 100 cycles, respectively. Such improved electrochemical performances could be attributed to the superior conductivity and favorable structure of KB, which contributes to the improvement in electronic conductivity and structure stability of γ-Fe 2 O 3 during the lithium ion insertion/desertion process

  9. GWAS of Barley Phenotypes Established Under Future Climate Conditions of Elevated Temperature, CO2, O3 and Elevated Temperature and CO2 Combined

    Ingvordsen, Cathrine Heinz; Backes, G.; Lyngkjær, M. F.

    2015-01-01

    Climate change is likely to decrease crop yields worldwide. Developing climate resilient cultivars is one way to combat this production scarcity, however, little is known of crop response to future climate conditions and in particular the variability within crops.In Scandinavia, barley is widely...... cultivated, but yields have stagnated since the start of this century. In this study we cultivated 138 spring barley accessions in a climate phytotron under four treatments mimicking forecasted levels of temperature, carbon dioxide concentration ([CO2]) and ozone ([O3]) at the end of the 21st century1...... yield, grain protein concentration, grain protein harvested, number of grains, number of ears, aboveground vegetative biomass and harvest index. In addition, stability of the production was calculated over the applied treatments for the assessed parameters.In the climate scenario of elevated temperature...

  10. High electrochemical performance of RuO_2–Fe_2O_3 nanoparticles embedded ordered mesoporous carbon as a supercapacitor electrode material

    Xiang, Dong; Yin, Longwei; Wang, Chenxiang; Zhang, Luyuan

    2016-01-01

    The electrode materials RuO_2 or RuO_2–Fe_2O_3 nanoparticle embedded OMC (ordered mesoporous carbon) are prepared by the method of impregnation and heating in situ. The mesoporous structure optimized the electron and proton conducting pathways, leading to the enhanced capacitive performances of the composite materials. The average nanoparticle size of RuO_2 and RuO_2–Fe_2O_3 is 2.54 and 1.96 nm, respectively. The fine RuO_2–Fe_2O_3 nanoparticles are dispersed evenly in the pore channel wall of the two-dimensional mesoporous carbon without blocking the mesoporous channel, and they have a higher specific surface area, a larger pore volume, a proper pore size and a small charge transfer impedance value. The special electrochemical capacitance of RuO_2–Fe_2O_3/OMC tested in acid electrolyte (H_2SO_4) is measured to be as high as 1668 F g"−"1, which is higher than that of RuO_2/OMC. Meanwhile, the supercapacitor properties of the RuO_2–Fe_2O_3/OMC composites show a good cycling performance of 93% capacitance retention (3000 cycles), a better reversibility, a higher energy density (134 Wh kg"−"1) and power density (4000 W kg"−"1). The composite electrode of RuO_2–Fe_2O_3/OMC, which combines a double layer capacitance with pseudo-capacitance, is proved to be suitable for ideal high performance electrode material of a hybrid supercapacitor application. - Highlights: • The nanocomposites of RuO_2–Fe_2O_3/OMC are prepared by impregnation and heating in situ. • The fine RuO_2–Fe_2O_3 nanoparticles distribute in the pore channel wall of OMC. • We discuss a reversible redox reaction mechanism of RuO_2–Fe_2O_3/OMC in acid solutions. • RuO_2–Fe_2O_3 nanoparticles embedded OMC shows a higher supercapacitive performance.

  11. NaIrO3-A pentavalent post-perovskite

    Bremholm, M.; Dutton, S.E.; Stephens, P.W.; Cava, R.J.

    2011-01-01

    Sodium iridium (V) oxide, NaIrO 3, was synthesized by a high pressure solid state method and recovered to ambient conditions. It is found to be isostructural with CaIrO 3 , the much-studied structural analog of the high-pressure post-perovskite phase of MgSiO 3 . Among the oxide post-perovskites, NaIrO 3 is the first example with a pentavalent cation. The structure consists of layers of corner- and edge-sharing IrO 6 octahedra separated by layers of NaO 8 bicapped trigonal prisms. NaIrO 3 shows no magnetic ordering and resistivity measurements show non-metallic behavior. The crystal structure, electrical and magnetic properties are discussed and compared to known post-perovskites and pentavalent perovskite metal oxides. -- Graphical abstract: Sodium iridium(V) oxide, NaIrO 3 , synthesized by a high pressure solid state method and recovered to ambient conditions is found to crystallize as the post-perovskite structure and is the first example of a pentavalent ABO 3 post-perovskite. Research highlights: → NaIrO 3 post-perovskite stabilized by pressure. → First example of a pentavalent oxide post-perovskite. → Non-metallic and non-magnetic behavior of NaIrO 3 .

  12. Effects of thermal treatment conditions on the phase formation and the morphological changes of sol-gel derived 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 thin films

    Yang, Sun A; Han, Jin Kyu; Choi, Yong Chan; Bu, Sang Don

    2011-01-01

    We report the synthesis of Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) thin films and the effects of thermal conditions on their surface morphologies and phase formation behaviors. The PMN-PT thin films were prepared by spin-coating PMN-PT sol-gel solutions on Pt/Ti/SiO 2 /Si substrates and subsequent thermal treatments including pyrolysis, annealing, and additional pre-annealing. We found that the surface morphologies and the formation of the perovskite phase were strongly affected by the final annealing temperature. The grain size of perovskite phase and the amount of the perovskite phase increased as the annealing temperature was increased from 550 to 800 .deg. C. We also found that the voids started to form on the surface of the film at an annealing temperature of 650 .deg. C and that their areas increased with increasing in annealing temperature. The void formation was found to depend on the time period of pyrolysis and on the pre-annealing process between pyrolysis and final annealing. Dense PMN-PT films with relatively high amounts of the perovskite phase were obtained when additional pre-annealing at 750 .deg. C for 5 min was performed.

  13. A highly triflated rare-earth ion in [Eu(O_3SCF_3)_8]"5"-

    Bruns, Joern; Kluener, Thorsten; Kraeuter, Jessica; Wickleder, Mathias S.; Krueger, Sascha; Adlung, Matthias; Wickleder, Claudia; Niehaus, Oliver; Poettgen, Rainer

    2015-01-01

    The reaction of Eu_2O_3 with fuming nitric acid, trifluormethanesulfonic acid, and its anhydride in torch-sealed glass ampoules at 120 C gave the europium compound (NO)_5[Eu(O_3SCF_3)_8] (orthorhombic, Fddd, Z=16, a=1932.69(4), b=2878.44(7), c=2955.12(7) pm, V=16439.7(7) Aa"3). The compound exhibits the [Eu(O_3SCF_3)_8]"5"- anion showing for the first time a lanthanide ion that is exclusively coordinated by eight triflate anions. The anion has been further investigated by DFT calculations, which also allowed clear assignment of the vibrational spectra. Moreover, magnetochemical and luminescence measurements gave additional insight into the properties of this complex. The luminescence spectra revealed that the Eu"3"+ ions are in a pseudo D_4_d symmetric environment. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. modified BiFeO3–BaTiO3

    based perovskite structures lead- free BiFeO3–BaTiO3 solid solutions are popularly studied due to the high Curie temperature (TC). It was reported that the BiFeO3–BaTiO3 system possessed high piezoelectric. ∗. Author for correspondence ...

  15. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

    Scarisoreanu, N. D.; Craciun, F.; Birjega, R.; Ion, V.; Teodorescu, V. S.; Ghica, C.; Negrea, R.; Dinescu, M.

    2016-05-01

    BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε’ ∼2500) and low dielectric loss (tan δ priced target.

  16. Ablation Behavior of Plasma-Sprayed La1-xSrxTiO3+δ Coating Irradiated by High-Intensity Continuous Laser.

    Zhu, Jinpeng; Ma, Zhuang; Gao, Yinjun; Gao, Lihong; Pervak, Vladimir; Wang, Lijun; Wei, Chenghua; Wang, Fuchi

    2017-10-11

    Laser protection for optical components, particularly those in high-power laser systems, has been a major concern. La 1-x Sr x TiO 3+δ with its good optical and thermal properties can be potentially applied as a high-temperature optical protective coating or high-reflectivity material for optical components. However, the high-power laser ablation behavior of plasma-sprayed La 1-x Sr x TiO 3+δ (x = 0.1) coatings has rarely been investigated. Thus, in this study, laser irradiation experiments were performed to study the effect of high-intensity continuous laser on the ablation behavior of the La 1-x Sr x TiO 3+δ coating. The results show that the La 1-x Sr x TiO 3+δ coating undergoes three ablation stages during laser irradiation: coating oxidation, formation and growth of new structures (columnar and dendritic crystals), and mechanical failure. A finite-element simulation was also conducted to explore the mechanism of the ablation damage to the La 1-x Sr x TiO 3+δ coating and provided a good understanding of the ablation behavior. The apparent ablation characteristics are attributed to the different temperature gradients determined by the reflectivity and thermal diffusivity of the La 1-x Sr x TiO 3+δ coating material, which are critical factors for improving the antilaser ablation property. Now, the stainless steel substrate deposited by it can effectively work as a protective shield layer against ablation by laser irradiation.

  17. Preparation of three-dimensionally ordered macroporous perovskite-type lanthanum-iron-oxide LaFeO3 with tunable pore diameters: High porosity and photonic property

    Sadakane, Masahiro; Horiuchi, Toshitaka; Kato, Nobuyasu; Sasaki, Keisuke; Ueda, Wataru

    2010-01-01

    Three-dimensionally ordered macroporous (3DOM) lanthanum-iron-oxide (LaFeO 3 ) with different pore diameters was prepared using a colloidal crystal of polymer spheres with different diameters as templates. Ethylene glycol-methanol mixed solution of metal nitrates was infiltrated into the void of the colloidal crystal template of a monodispersed poly(methyl methacrylate) (PMMA) sphere. Heating of this PMMA-metal salt-ethylene glycol composite produced the desired well-ordered 3DOM LaFeO 3 with a high pore fraction, which was confirmed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), mercury (Hg) porosimetry, and ultraviolet-visible (UV-vis) diffuse reflectance spectra. 3DOM LaFeO 3 with pore diameters of 281 and 321 nm shows opalescent colors because of photonic stop band properties. Catalytic activity of the 3DOM LaFeO 3 for combustion of carbon particles was enhanced by a potassium cation, which was involved from K 2 S 2 O 8 used as a polymerization initiator. - Graphical abstract: Well-ordered three-dimensionally ordered macroporous LaFeO 3 materials with pore sizes ranging from 127 to 321 nm were obtained in a high pore fraction.

  18. Highly uniform bipolar resistive switching characteristics in TiO2/BaTiO3/TiO2 multilayer

    Ma, W. J.; Zhang, X. Y.; Wang, Ying; Zheng, Yue; Lin, S. P.; Luo, J. M.; Wang, B.; Li, Z. X.

    2013-01-01

    Nanoscale multilayer structure TiO 2 /BaTiO 3 /TiO 2 has been fabricated on Pt/Ti/SiO 2 /Si substrate by chemical solution deposition method. Highly uniform bipolar resistive switching (BRS) characteristics have been observed in Pt/TiO 2 /BaTiO 3 /TiO 2 /Pt cells. Analysis of the current-voltage relationship demonstrates that the space-charge-limited current conduction controlled by the localized oxygen vacancies should be important to the resistive switching behavior. X-ray photoelectron spectroscopy results indicated that oxygen vacancies in TiO 2 play a crucial role in the resistive switching phenomenon and the introduced TiO 2 /BaTiO 3 interfaces result in the high uniformity of bipolar resistive switching characteristics

  19. A flexible, high-performance magnetoelectric heterostructure of (001) oriented Pb(Zr0.52Ti0.48)O3 film grown on Ni foil

    Palneedi, Haribabu; Yeo, Hong Goo; Hwang, Geon-Tae; Annapureddy, Venkateswarlu; Kim, Jong-Woo; Choi, Jong-Jin; Trolier-McKinstry, Susan; Ryu, Jungho

    2017-09-01

    In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by depositing a (001) oriented Pb(Zr0.52Ti0.48)O3 (PZT) film on a thin, flexible Ni foil buffered with LaNiO3/HfO2. Excellent ferroelectric properties and large ME voltage coefficient of 3.2 V/cmṡOe were realized from the PZT/Ni heterostructure. The PZT/Ni composite's high performance was attributed to strong texturing of the PZT film, coupled with the compressive stress in the piezoelectric film. Besides, reduced substrate clamping in the PZT film due to the film on the foil structure and strong interfacial bonding in the PZT/LaNiO3/HfO2/Ni heterostructure could also have contributed to the high ME performance of PZT/Ni.

  20. High performance Li2MnO3/rGO composite cathode for lithium ion batteries

    Zhao, Wei; Xiong, Lilong; Xu, Youlong; Li, Houli; Ren, Zaihuang

    2017-05-01

    The novel composite Li2MnO3 (LMO)/reduced graphene oxide (rGO) has been synthesized successfully. Based on the scanning electron microscopy and transmission electron microscopy, LMO is found to distribute separately on the rGO sheets by forming a laminated structure, which is in favor of good electrical contact between the cathode active materials and the rGO matrix, and also facilitates the separation of LMO secondary particles with reduced size. Cyclic voltammetry and electrochemical impedance spectroscopy tests show that the charge transfer resistance decreases from 81.2 Ω for LMO to 29.6 Ω for LMO/rGO composite. The Li-ion diffusion coefficient of LMO/rGO composite is almost triple that of LMO. As a result, the LMO/rGO composite delivers an initial discharge capacity of 284.9 mAh g-1 with a capacity retention of 86.6% after 45 cycles at 0.1 C between 2.0 and 4.6 V. Cycle performance is even better at a higher current density 0.2 C while the retention ratio is up to 97.1% after 45 cycles. The rate capability is also significantly enhanced, and the LMO/rGO composite could exhibit a large discharge capacity of 123.7 mAh g-1 which is more than three times larger than that of LMO (40.8 mAh g-1) at a high rate of 8 C.

  1. Role of process conditions on the microstructure, stoichiometry and functional performance of atmospheric plasma sprayed La(Sr)MnO3 coatings

    Han, Su Jung; Chen, Yikai; Sampath, Sanjay

    2014-08-01

    Strontium doped lanthanum manganite (LSM) perovskite coatings were produced via atmospheric plasma spray technique to examine their applicability as electrically conductive coatings to protect chromium-poisoning of cathode side metallic interconnects in solid oxide fuel cells. Various plasma spray process conditions were manipulated including plasma power, total gas flow and content of H2 in the plasma gas in order to understand their effects on coating properties as well as efficacy as a protectant against Cr-poisoning. In-flight temperatures and velocities of spray particles were monitored for the various plasma spray conditions enabling assessment of thermal and kinetic energies of LSM particles. As anticipated, coating density improves with increasing thermal and/or kinetic energies of the LSM particles. However, the LSM particles also experienced significant phase decomposition at higher thermal exposure and longer residence time conditions. Due to preferential loss of oxygen and manganese, La2O3 phase is also formed under certain processing regimes. The resultant mixed-phase coating is ineffective both from electrical transport and as a protective coating for the metallic interconnect. Concomitantly, coatings with limited decomposition show excellent conductivity and protection characteristics demonstrating the need for mechanism driven process optimization for these functional oxide coatings.

  2. Mechanical wet-milling and subsequent consolidation of ultra-fine Al2O3-(ZrO2+3%Y2O3) bioceramics by using high-frequency induction heat sintering

    Khalil Abdelrazek KHALIL; Sug Won KIM

    2007-01-01

    Alumina/zirconia composites were synthesized by wet-milling technique and rapid consolidation with high frequency induction heat sintering(HFIHS). The starting materials were a mixture of alumina micro-powder (80%, volume fraction) and 3YSZ nano-powders (20%). The mixtures were optimized for good sintering behaviors and mechanical properties. Nano-crystalline grains are obtained after 24 h milling. The nano-structured powder compacts are then processed to full density at different temperatures by HFIHS. Effects of temperature on the mechanical and microstructure properties were studied. Al2O3-3YSZ composites with higher mechanical properties and small grain size are successfully developed at relatively low temperatures through this technique.

  3. Effects of heat-treatment conditions on electrical properties of sol-gel-derived ferroelectric Pb(Zr,Ti)O3 thin films

    Shim, Donghyun; Pak, Jaemoon; Nam, Kuangwoo; Park, Gwangseo

    2005-01-01

    Pb(Zr,Ti)O 3 (PZT) films with Zr/Ti ratio of 50 : 50 were prepared by spin-casting at 3000 rpm for 30 sec on Pt/Ti/SiO 2 /Si substrates. After standard processing procedure, three different methods of annealing were conducted at 600 .deg. C : a single-step process carried out in (a) air, and (b) O 2 ambient, and (c) a 2-step process carried out in air, followed by an O 2 annealing process. These films were highly oriented along the (111) direction with large remnant polarization and low coercive voltage values. The films treated in O 2 had relatively larger polarization values, but the 2-step-annealed films possessed lower coercive voltage. Fatigue measurements were conducted until 1 X 10 10 switching cycles, resulting in abnormal switching characteristics for these films. A comparative study on the ferroelectric and fatigue properties will be emphasized.

  4. MoO3–Au composite interfacial layer for high efficiency and air-stable organic solar cells

    Pan, Hongbin; Zuo, Lijian; Fu, Weifei

    2013-01-01

    Efficient and stable polymer bulk-heterojunction solar cells based on regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend active layer have been fabricated with a MoO3–Au co-evaporation composite film as the anode interfacial layer (AIL). The optical...

  5. Piezoelectric properties of PbTiO(3) thin films characterized with piezoresponse force and high resolution transmission electron microscopy

    Morelli, A.; Venkatesan, Sriram; Kooi, B. J.; Palasantzas, G.; De Hosson, J. Th. M.

    2009-01-01

    In this paper we investigate the piezoelectric properties of PbTiO(3) thin films grown by pulsed laser deposition with piezoresponse force microscopy and transmission electron microscopy. The as-grown films exhibit an upward polarization, inhomogeneous distribution of piezoelectric characteristics

  6. Facile and Low-Temperature Fabrication of Thermochromic Cr2O3/VO2 Smart Coatings: Enhanced Solar Modulation Ability, High Luminous Transmittance and UV-Shielding Function.

    Chang, Tianci; Cao, Xun; Li, Ning; Long, Shiwei; Gao, Xiang; Dedon, Liv R; Sun, Guangyao; Luo, Hongjie; Jin, Ping

    2017-08-09

    In the pursuit of energy efficient materials, vanadium dioxide (VO 2 ) based smart coatings have gained much attention in recent years. For smart window applications, VO 2 thin films should be fabricated at low temperature to reduce the cost in commercial fabrication and solve compatibility problems. Meanwhile, thermochromic performance with high luminous transmittance and solar modulation ability, as well as effective UV shielding function has become the most important developing strategy for ideal smart windows. In this work, facile Cr 2 O 3 /VO 2 bilayer coatings on quartz glasses were designed and fabricated by magnetron sputtering at low temperatures ranging from 250 to 350 °C as compared with typical high growth temperatures (>450 °C). The bottom Cr 2 O 3 layer not only provides a structural template for the growth of VO 2 (R), but also serves as an antireflection layer for improving the luminous transmittance. It was found that the deposition of Cr 2 O 3 layer resulted in a dramatic enhancement of the solar modulation ability (56.4%) and improvement of luminous transmittance (26.4%) when compared to single-layer VO 2 coating. According to optical measurements, the Cr 2 O 3 /VO 2 bilayer structure exhibits excellent optical performances with an enhanced solar modulation ability (ΔT sol = 12.2%) and a high luminous transmittance (T lum,lt = 46.0%), which makes a good balance between ΔT sol and T lum for smart windows applications. As for UV-shielding properties, more than 95.8% UV radiation (250-400 nm) can be blocked out by the Cr 2 O 3 /VO 2 structure. In addition, the visualized energy-efficient effect was modeled by heating a beaker of water using infrared imaging method with/without a Cr 2 O 3 /VO 2 coating glass.

  7. Electrostatic interactions for directed assembly of high performance nanostructured energetic materials of Al/Fe2O3/multi-walled carbon nanotube (MWCNT)

    Zhang, Tianfu; Ma, Zhuang; Li, Guoping; Wang, Zhen; Zhao, Benbo; Luo, Yunjun

    2016-01-01

    Electrostatic self-assembly in organic solvent without intensively oxidative or corrosive environments, was adopted to prepare Al/Fe 2 O 3 /MWCNT nanostructured energetic materials as an energy generating material. The negatively charged MWCNT was used as a glue-like agent to direct the self-assembly of the well dispersed positively charged Al (fuel) and Fe 2 O 3 (oxide) nanoparticles. This spontaneous assembly method without any surfactant chemistry or other chemical and biological moieties decreased the aggregation of the same nanoparticles largely, moreover, the poor interfacial contact between the Al (fuel) and Fe 2 O 3 (oxide) nanoparticles was improved significantly, which was the key characteristic of high performance nanostructured energetic materials. In addition, the assembly process was confirmed as Diffusion-Limited Aggregation. The assembled Al/Fe 2 O 3 /MWCNT nanostructured energetic materials showed excellent performance with heat release of 2400 J/g, peak pressure of 0.42 MPa and pressurization rate of 105.71 MPa/s, superior to that in the control group Al/Fe 2 O 3 nanostructured energetic materials prepared by sonication with heat release of 1326 J/g, peak pressure of 0.19 MPa and pressurization rate of 33.33 MPa/s. Therefore, the approach, which is facile, opens a promising route to the high performance nanostructured energetic materials. - Graphical abstract: The negatively charged MWCNT was used as a glue-like agent to direct the self-assembly of the well dispersed positively charged Al (fuel) and Fe 2 O 3 (oxide) nanoparticles. - Highlights: • A facile spontaneous electrostatic assembly strategy without surfactant was adopted. • The fuels and oxidizers assembled into densely packed nanostructured composites. • The assembled nanostructured energetic materials have excellent performance. • This high performance energetic material can be scaled up for practical application. • This strategy can be applied into other nanostructured

  8. Dielectric Performance of High Permitivity Nanocomposites: Impact of Polystyrene Grafting on BaTiO3 and TiO2

    2016-09-22

    prepared using high-shear mixing (Ultra-Turrax T18, IKA). All BaTiO3 nanocomposites were solution cast from DMF onto aluminum-coated glass substrates...coated from chlorobenzene onto aluminum-coated glass substrates. Figure 3 a Real dielectric permittivity ε′ measured at 1 kHz for PS@BaTiO3 HNPs... SiO2 nanocomposites, where 15% v/v PS  +  SiO2 blends exhibited degraded energy storage efficiencies when driven above 100 V/μm, while 18% v/v PS@ SiO2

  9. High frequency transducer for vessel imaging based on lead-free Mn-doped (K0.44Na0.56)NbO3 single crystal

    Ma, Jinpeng; Xue, Saidong; Zhao, Xiangyong; Wang, Feifei; Tang, Yanxue; Duan, Zhihua; Wang, Tao; Shi, Wangzhou; Yue, Qingwen; Zhou, Huifang; Luo, Haosu; Fang, Bijun

    2017-08-01

    We report a high frequency ultrasonic transducer up to 50 MHz for vessel imaging based on a lead-free (K0.44Na0.56)NbO3-0.5 mol. % Mn (Mn-KNN) single crystal, which has a high electromechanical coupling coefficient kt of 0.64 and a large thickness frequency constant Nt of 3210 kHz . mm. The Krimholtz, Leedom, and Mattaei (KLM) equivalent circuit model was utilized to simulate and optimize the pulse-echo response combined with PiezoCAD software. Theoretically, a high -6 dB bandwidth of 74.94% was obtained at a center frequency of 50.47 MHz and optimized matching conditions. The experimental results showed a center frequency of 51.8 MHz with a -6 dB bandwidth of 70.2%. The excellent global performance makes this lead-free single-crystal transducer quite potential in an environmentally friendly vessel imaging transducer.

  10. Highly Sensitive Ethanol Chemical Sensor Based on Novel Ag-Doped Mesoporous α-Fe2O3 Prepared by Modified Sol-Gel Process

    Alqahtani, Moteb M.; Ali, Atif M.; Harraz, Farid A.; Faisal, M.; Ismail, Adel A.; Sayed, Mahmoud A.; Al-Assiri, M. S.

    2018-05-01

    Mesoporous α-Fe2O3 has been synthesized via a simple sol-gel procedure in the presence of Pluronic (F-127) triblock copolymer as structure directing agent. Silver (Ag) nanoparticles were deposited onto α-Fe2O3 matrix by the photochemical reduction approach. Morphological analysis revealed the formation of Ag nanoparticles with small sizes < 20 nm onto the mesoporous structure of α-Fe2O3 possessing < 50 nm semi-spherical shape. The XRD, FTIR, Raman, UV-vis, PL, and N2 sorption isotherm studies confirmed the high crystallinity, mesoporosity, and optical characteristics of the synthesized product. The electrochemical sensing toward liquid ethanol has been performed using the current devolved Ag/α-Fe2O3-modified glassy carbon electrode (GCE) by cyclic voltammetry ( CV) and current potential ( I-V) techniques, and the obtained results were compared with bare GCE or pure α-Fe2O3. Mesoporous Ag/α-Fe2O3 was found to largely enhance the sensor sensitivity and it exhibited excellent sensing characteristics during the precision detection of low concentrations of ethanol. High and reproducible sensitivity of 41.27 μAmM- 1 cm- 2 at lower ethanol concentration region (0.05 to 0.8 mM) and 2.93 μAmM- 1 cm- 2 at higher concentration zone (0.8 to 15 mM), with a limit of detection (LOD) of 15.4 μM have been achieved. Investigation on reaction kinetics revealed a characteristic behavior of mixed surface and diffusion-controlled processes. Detailed sensing studies revealed also that the sensitivity toward ethanol was higher than that of methanol or isopropanol. With further effort in developing the synthesis and fabrication approaches, a proper utility for the current proposed protocol for fabricating a better sensor device performance is possible.

  11. Controlled reduction of LaFe xMn yMo zO3/Al2O3 composites to produce highly dispersed and stable Fe0 catalysts: a Mössbauer investigation

    Juliana Cristina Tristão

    2008-06-01

    Full Text Available In this work, controlled reduction of perovskites supported on Al2O3 was used to prepare thermally stable nanodispersed iron catalysts based on Fe0/La2O3/Al2O3. The perovskites composites LaFe0.90Mn0.08Mo0.02O3(25, 33 and 50 wt (% /Al2O3 and LaFe0.90Mn0.1O3(25 wt (% /Al2O3 were prepared and characterized by XRD, BET, TPR, SEM and Mössbauer spectroscopy. XRD for unsupported perovskite showed the formation of a single phase perovskite structure. The Mössbauer spectra of the perovskites were fitted with hyperfine field distribution model for the perovskite. Supported perovskites on Al2O3 showed a decrease of the hyperfine field in respect to unsupported perovskite, due to decrease of particle size and dispersion of the Fe3+ specimens on the support. Also showed broaden lines and relaxation effects due to the small particle size. To produce the Fe0 catalyst, the composite perovskite(25%/Al2O3 was reduced with H2 at 900, 1000 and 1100 °C for 1 hour. XRD data indicated the formation of Fe0 catalyst with particles sizes of ca. 35 nm. The Mössbauer spectrum showed the formation of metallic iron and doublets corresponding to species of octahedric Fe2+ and Fe3+ sites dispersed on Al2O3. These catalysts showed improved stability towards sintering even upon treatment at 1000 and 1100 °C under H2.

  12. Correlation of gas sensitivite properties with microstructure of Fe2O3-SnO2 ceramics prepared by high energy ball milling

    Jiang, Jianzhong; Lu, S.W.; Zhou, Y.X.

    1997-01-01

    A remarkable gas sensitivity to ethnaol gas has been observed in nanostructured Fe2O3-SnO2 materials with a composition of 6.4 mol% SnO2 prepared by high energy ball milling. The microstructure of the materials has been examined by x-ray diffraction (XRD) and Mossbauer spectroscopy. It was found...

  13. Epitaxial growth of metallic buffer layer structure and c-axis oriented Pb(Mn1/3,Nb2/3)O3-Pb(Zr,Ti)O3 thin film on Si for high performance piezoelectric micromachined ultrasonic transducer

    Thao, Pham Ngoc; Yoshida, Shinya; Tanaka, Shuji

    2017-12-01

    This paper reports on the development of a metallic buffer layer structure, (100) SrRuO3 (SRO)/(100) Pt/(100) Ir/(100) yttria-stabilized zirconia (YSZ) layers for the epitaxial growth of a c-axis oriented Pb(Mn1/3,Nb2/3)O3-Pb(Zr,Ti)O3 (PMnN-PZT) thin film on a (100) Si wafer for piezoelectric micro-electro mechanical systems (MEMS) application. The stacking layers were epitaxially grown on a Si substrate under the optimal deposition condition. A crack-free PMnN-PZT epitaxial thin films was obtained at a thickness up to at least 1.7 µm, which is enough for MEMS applications. The unimorph MEMS cantilevers based on the PMnN-PZT thin film were fabricated and characterized. As a result, the PMnN-PZT thin film exhibited -10 to -12 C/m2 as a piezoelectric coefficient e 31,f and ˜250 as a dielectric constants ɛr. The resultant FOM for piezoelectric micromachined ultrasonic transducer (pMUT) is higher than those of general PZT and AlN thin films. This structure has a potential to provide high-performance pMUTs.

  14. On the optimum processing conditions of Pb(Zr x Ti1-x )O3: revealing the mechanisms to increase the piezoelectric coefficients up to 1100 pm V-1

    Zeibekis, M.; Vertsioti, G.; Stamopoulos, D.

    2016-03-01

    The ferroelectric compound family Pb(Zr x Ti1-x )O3 (PZT) is one of the most investigated and widely used piezoelectric materials. Optimization of the piezoelectric coefficients is observed for x ~ 0.52 (Pb(Zr0.52Ti0.48)O3) and is further promoted by the increase of grain size (GS). However, in some cases the piezoelectric properties of Pb(Zr0.52Ti0.48)O3 deteriorate upon processing due to the decrease of density, ρ, that is mostly ascribed to the appearance of byproduct phases. In the present study we discuss the influence of the processing conditions on the piezoelectric properties for polycrystalline Pb(Zr0.52Ti0.48)O3, specifically focusing on the sintering temperature, 1100 °C  ⩽  T sin  ⩽  1250 °C. To this end, we use atomic force microscopy (AFM), Archimedes’ method, x-ray diffraction (XRD) and a newly introduced local technique, based on a conventional optical microscope, which is further developed here to accommodate non-clamped specimens. The data obtained via this technique in the regime of relatively high electric fields evidence that the absolute piezoelectric coefficients, |d zi | (i  =  x, y) show a non-monotonic behavior with an unexpectedly high maximum value |d zi | ~ 1100 pm V-1 at T sin  =  1180 °C. These features are accompanied by a progressive increase of coercivity, reaching maximum value E C,i ~ 4.5-5.0 kV cm-1 (i  =  x, y) at T sin  =  1250 °C. To explain these findings, the |d zi | coefficients are compared with the microstructure and compositional information, coming from AFM, Archimedes’ method and XRD data. We conclude that the significantly high |d zi | values observed for samples prepared at T sin  =  1180 °C are motivated by the increase of mean GS, , while for T sin  >  1180 °C the decrease of density, ρ, ascribed to the appearance of byproduct phases, dominates and deteriorates |d zi |. These experimental results on |d zi |(T sin) are reliably

  15. Flexible Fe2O3 and V2O5 nanofibers as binder-free electrodes for high-performance all-solid-state asymmetric supercapacitors.

    Jiang, He; Niu, Hao; Yang, Xue; Sun, Zhiqin; Li, Fuzhi; Wang, Qian; Qu, Fengyu

    2018-04-16

    Flexible highly porous Fe2O3 and V2O5 nanofibers are synthesized by a facile electrospinning method followed by calcination treatment and directly used as binder-free electrodes for high-performance supercapacitors. These Fe2O3 and V2O5 nanofibers interconnect with each other and construct three-dimensional hierarchical porous films with high specific surface area. Benefiting from the unique structural features, the intriguing binder-free Fe2O3 and V2O5 porous nanofiber electrodes possess high specific capacitance of 255 F g-1 and 256 F g-1 at 2 mV s-1 in 1 M Na2SO4 electrolyte, respectively. An all-solid-state asymmetric supercapacitor is fabricated using Fe2O3 and V2O5 nanofibers as negative and positive electrodes, respectively, and the all-solid-state asymmetric supercapacitor can be operated up to 1.8 V attributed to the wide and opposite potential window of both electrodes. The assembled all-solid-state asymmetric supercapacitor achieves a high energy density up to 32.2 Wh kg-1 at an average power density of 128.7 W kg-1 as well as excellent cycling stability and power capability. The effective and facile synthesis method and superior electrochemical performance provided in this work make electrospun Fe2O3 and V2O5 nanofibers promising electrode materials for high performance asymmetric supercapacitors. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. The Formation of High-Coercivity, Oriented, Nanophase Cobalt Precipitates in Al2O3 single cyrstals by ion implantation

    Honda, S.; Modine, F.A.; Haynes, T.E.; Meldrum, A.; Budai, J.D.; SOng, K.J.; Thompson, J.R.; Boatner, L.A.

    1999-01-01

    Ion-implantation and thermal-processing methods have been used to form nanophase magnetic precipitates of metallic cobalt that are embedded in the near-surface region of single crystals of Al 2 O 3 . The Co precipitates are isolated, single-crystal particles that are crystallographically oriented with respect to the host Al 2 O 3 lattice. Embedded nanophase Co precipitates were formed by the implantation of Co+ at an energy of 140 keV and a dose of 8 x l0 16 ions/cm 2 followed by annealing in a reducing atmosphere. The implanted/annealed Co depth profile, particle size distributions and shapes, and the orientational relationship between the nanophase precipitates and the host crystal lattice were determined using RBS/channeling, transmission electron microscopy, and x-ray diffraction

  17. Multi-modal TiO2-LaFeO3 composite films with high photocatalytic activity and hydrophilicity

    Gao Kun; Li Shudan

    2012-01-01

    In this paper, a series of multi-modal TiO 2 -LaFeO 3 composite films have been successfully synthesized through a two-step method. The resultant films were characterized in detail by several testing techniques, such as X-ray diffraction (XRD), ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and water contact angle measurements. The photocatalytic activity of different films was evaluated for degrading Methylene Blue (MB) aqueous solution. Hydrophilicity of the obtained TiO 2 -LaFeO 3 composite films was also investigated. The results show that TL film and LT film exhibited superior photocatalytic activity and hydrophilicity.

  18. Graphene/Fe2O3/SnO2 ternary nanocomposites as a high-performance anode for lithium ion batteries.

    Xia, Guofeng; Li, Ning; Li, Deyu; Liu, Ruiqing; Wang, Chen; Li, Qing; Lü, Xujie; Spendelow, Jacob S; Zhang, Junliang; Wu, Gang

    2013-09-11

    We report an rGO/Fe2O3/SnO2 ternary nanocomposite synthesized via homogeneous precipitation of Fe2O3 nanoparticles onto graphene oxide (GO) followed by reduction of GO with SnCl2. The reduction mechanism of GO with SnCl2 and the effects of reduction temperature and time were examined. Accompanying the reduction of GO, particles of SnO2 were deposited on the GO surface. In the graphene nanocomposite, Fe2O3 nanoparticles with a size of ∼20 nm were uniformly dispersed surrounded by SnO2 nanoparticles, as demonstrated by transmission electron microscopy analysis. Due to the different lithium insertion/extraction potentials, the major role of SnO2 nanoparticles is to prevent aggregation of Fe2O3 during the cycling. Graphene can serve as a matrix for Li+ and electron transport and is capable of relieving the stress that would otherwise accumulate in the Fe2O3 nanoparticles during Li uptake/release. In turn, the dispersion of nanoparticles on graphene can mitigate the restacking of graphene sheets. As a result, the electrochemical performance of rGO/Fe2O3/SnO2 ternary nanocomposite as an anode in Li ion batteries is significantly improved, showing high initial discharge and charge capacities of 1179 and 746 mAhg(-1), respectively. Importantly, nearly 100% discharge-charge efficiency is maintained during the subsequent 100 cycles with a specific capacity above 700 mAhg(-1).

  19. Hierarchical structured Sm2O3 modified CuO nanoflowers as electrode materials for high performance supercapacitors

    Zhang, Xiaojuan; He, Mingqian; He, Ping; Liu, Hongtao; Bai, Hongmei; Chen, Jingchao; He, Shaoying; Zhang, Xingquan; Dong, Faqing; Chen, Yang

    2017-12-01

    By a simple and cost effective chemical precipitation-hydrothermal method, novel hierarchical structured Sm2O3 modified CuO nanoflowers are prepared and investigated as electrode materials for supercapacitors. The physical properties of prepared materials are characterized by XRD, FE-SEM, EDX and FTIR techniques. Furthermore, electrochemical performances of prepared materials are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectrum in 1.0 M KOH electrolyte. The resulting Sm2O3 modified CuO based electrodes exhibit obviously enhanced capacitive properties owing to the unique nanostructures and strong synergistic effects. It is worth noting that the optimized SC-3 based electrode exhibits the best electrochemical performances in all prepared electrodes, including higher specific capacitance (383.4 F g-1 at 0.5 A g-1) and good rate capability (393.2 F g-1 and 246.3 F g-1 at 0.3 A g-1 and 3.0 A g-1, respectively), as well as excellent cycling stability (84.6% capacitance retention after 2000 cycles at 1.0 A g-1). The present results show that Sm2O3 is used as a promising modifier to change the morphology and improve electrochemical performances of CuO materials.

  20. Insights on the High-Temperature Operational Limits of ZrO2-Y2O3 TBCs Manufactured via Air Plasma Spray

    Lima, Rogerio S.; Marple, Basil R.

    2017-03-01

    The effective high-temperature operation limit of a ZrO2-7-8 wt.%Y2O3 (YSZ) thermal barrier coating (TBC) manufactured via air plasma spray (APS) is considered to be 1300 °C. This is related to the metastable tetragonal t'-phase formed during the rapid quenching of the YSZ particles during spraying. The t'-phase transforms into the equilibrium tetragonal and cubic phases at temperatures ≥ 1300 °C, which can lead to the formation of the monoclinic phase of YSZ upon cooling to room temperature. This formation of the monoclinic phase is accompanied by a volume expansion that leads to TBC failure due to extensive micro-cracking. To further investigate this limitation, an APS YSZ TBC was sprayed on a CMSX-4 substrate. By using a thermal (laser) gradient cyclic testing, a temperature gradient was generated across the TBC/substrate system. The YSZ T- front and substrate backside T- back temperature levels were 1500 and 1000 °C, respectively. In cycle conditions (5-min or 1-h hot and 2-min cool), no TBC failure has been observed. This behavior was partially attributed to the unexpected absence of the monoclinic phase of the YSZ in the cycled coatings. Although preliminary, these results are promising regarding increasing the effective high-temperature operational limits of APS YSZ TBCs.

  1. A highly stable and sensitive GO-XDA-Mn2O3 electrochemical sensor for simultaneous electrooxidation of paracetamol and ascorbic acid

    Ejaz, Ammara; Jeon, Seungwon

    2017-01-01

    Highlights: •π–π interaction of graphene oxide (GO) with 1,4-xylenediamine (XDA) was studied. •The synergistic effect of the Mn 2 O 3 nanospheres with GO-XDA was electrochemically studied in the detection of Paracetamol (PCT) and ascorbic acid (AA). •The GO-XDA-Mn 2 O 3 accurately detected PCT and AA with LOD of 5.6 × 10 −8 M and 6.0 × 10 −7 M respectively. •The GO-XDA-Mn 2 O 3 selectively detected PCT and AA simultaneously in the presence of DA, 5-HT and Glu with peak separation of 240 mV. -- Abstract: Highly stable electrochemical sensor based on strong π- π interactions between GO and XDA was fabricated for simultaneous as well as for individual detection of paracetamol (PCT) and ascorbic acid (AA). The oxidation potential of PCT and AA was greatly resolved with the decoration of Mn 2 O 3 nanospheres. We believe that, presence of metal oxide on the surface of GO-XDA will offer higher electrochemical performance with its large surface area and fast electron transfer ability. Therefore, a comparative study was executed in the presence and absence of Mn 2 O 3 nanospheres on the surface of GO-XDA. The GO-XDA-Mn 2 O 3 modified electrode showed electrocatalytic oxidation of PCT in a very wide linear range of 1 × 10 −6 –1 × 10 −3 M with limit of detection (LOD) and sensitivity of 5.6 × 10 −8 M, 527.04 μAmM −1 cm −2 respectively and AA with 1 × 10 −5 –8 × 10 −3 M linear range, LOD and sensitivity of 6.0 × 10 −7 M, 655.74 μAmM −1 cm −2 respectively. Furthermore, astonishing stability was found when GO-XDA-Mn 2 O 3 nanocomposite was stored for over a week. The proposed sensor displayed incredible selectivity, sensitivity and excellent recovery results for real samples with appreciable consistency and precision suggesting practical utility of the GO-XDA-Mn 2 O 3 as an effective and reliable electrochemical sensor for simultaneous as well as individual determination of PCT and AA.

  2. High Efficient Photo-Fenton Catalyst of α-Fe2O3/MoS2 Hierarchical Nanoheterostructures: Reutilization for Supercapacitors

    Yang, Xijia; Sun, Haiming; Zhang, Lishu; Zhao, Lijun; Lian, Jianshe; Jiang, Qing

    2016-08-01

    A novel three-dimensional (3D) α-Fe2O3/MoS2 hierarchical nanoheterostructure is effectively synthesized via a facile hydrothermal method. The zero-dimensional (0D) Fe2O3 nanoparticles guide the growth of two-dimensional (2D) MoS2 nanosheets and formed 3D flower-like structures, while MoS2 facilitates the good dispersion of porous Fe2O3 with abundant oxygen vacancies. This charming 3D-structure with perfect match of non-equal dimension exhibits high recyclable photo-Fenton catalytic activity for Methyl orange pollutant and nice specific capacity in reusing as supercapacitor after catalysis. The synergistic effect between Fe2O3 and MoS2, the intermediate nanointerfaces, the 3D porous structures, and the abundant oxygen vacancies both contribute to highly active catalysis, nice electrochemical performance and stable cycling. This strategy is simple, cheap, and feasible for maximizing the value of the materials, as well as eliminating the secondary pollution.

  3. Room temperature direct bonding of LiNbO3 crystal layers and its application to high-voltage optical sensing

    Tulli, D; Janner, D; Pruneri, V

    2011-01-01

    LiNbO 3 is a crystal widely used in photonics and acoustics, for example in electro-optic modulation, nonlinear optical frequency conversion, electric field sensing and surface acoustic wave filtering. It often needs to be combined with other materials and used in thin layers to achieve the adequate device performance. In this paper, we investigate direct bonding of LiNbO 3 crystals with other dielectric materials, such as Si and fused silica (SiO 2 ), and we show that specific surface chemical cleaning, together with Ar or O 2 plasma activation, can be used to increase the surface free energy and achieve effective bonding at room temperature. The resulting hybrid material bonding is very strong, making the dicing and grinding of LiNbO 3 layers as thin as 15 µm possible. To demonstrate the application potentials of the proposed bonding technique, we have fabricated and characterized a high-voltage field sensor with high sensitivity in a domain inverted and bonded LiNbO 3 waveguide substrate

  4. Self-assembled 3D ZnSnO3 hollow cubes@reduced graphene oxide aerogels as high capacity anode materials for lithium-ion batteries

    Wang, Yankun; Li, Dan; Liu, Yushan; Zhang, Jianmin

    2016-01-01

    Highlights: • 3D ZnSnO 3 hollow cubes@reducedgrapheneoxideaerogels(ZGAs) were fabricated. • The electrochemical properties of ZGAs were investigated for LIBs. • ZGAs demonstrated superior lithium storage performance. - Abstract: 3D ZnSnO 3 hollow cubes@reduced graphene oxide aerogels (ZGAs) were fabricated via a colloid electrostatic self-assembly method between the graphene oxide (GO) nanosheets and poly(diallyldimethylammonium chloride) (PDDA) modified ZnSnO 3 hollow cubes colloid, followed by hydrothermal and freeze-drying treatments. The unique porous architecture of ZnSnO 3 hollow cubes encapsulated by flexible reduced graphene oxide (rGO) sheets not only effectively retarded the huge volume expansion during repeated charge-discharge cycles, but also facilitated fast lithium ion and electron transport through 3D networks. The ZGAs exhibited significantly enhanced cycling stability (745.4 mAh g −1 after 100 cycles at a current of 100 mA g −1 ) and superior rate capability (as high as 552.6 mAh g −1 at 1200 mA g −1 ). The results indicate that the ZGAs are promising anode materials for high-performance lithium-ion batteries.

  5. Surface morphology of Al0.3Ga0.7N/Al2O3-high electron mobility transistor structure.

    Cörekçi, S; Usanmaz, D; Tekeli, Z; Cakmak, M; Ozçelik, S; Ozbay, E

    2008-02-01

    We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.

  6. Flux Growth of Highly Crystalline Photocatalytic BaTiO3 Particle Layers on Porous Titanium Sponge Substrate and Insights into the Formation Mechanism

    Wang, Q.; Li, B.

    2017-09-01

    A unique architecture of idiomorphic and highly crystalline BaTiO3 particle layers directly grown on a porous titanium sponge substrate was successfully achieved for the first time using a facile molten salt method at a relatively low temperature of 700 °C. Specifically, the low-melting KCl-NaCl eutectic salts and barium hydroxide octahydrate were employed as the reaction medium and barium source, respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectrophotometry were used to characterize the structure, morphology and optical property of the obtained samples. The results revealed that the flux-grown tetragonal BaTiO3 products had well-defined and uniform morphology with an average size of 300 nm and a band gap of ∼3.16 eV. Based on XRD, EDS, SEM, and TEM, the possible formation mechanism responsible for the well-developed architecture of BaTiO3 particle layers was proposed and discussed. Furthermore, the photocatalytic activity of the flux-grown BaTiO3 products for organic pollutant degradation under simulated sunlight irradiation was also investigated.

  7. Combinatorial processing libraries for bulk BiFeO3-PbTiO3 piezoelectric ceramics

    Hu, W.; Tan, X.; Rajan, K.

    2010-01-01

    A high throughput approach for generating combinatorial libraries with varying processing conditions for bulk ceramics has been developed. This approach utilized the linear temperature gradient in a tube furnace to screen a whole temperature range for optimized preparation. With this approach, the processing of 0.98[0.6BiFeO 3 -0.4PbTiO 3 ]-0.02Pb(Mg 1/3 Nb 2/3 )O 3 ceramic powders and pellets for high-temperature piezoelectric applications was demonstrated to identify the best synthesis conditions for phase purity. The dielectric property measurement on the as-processed solid solution ceramics confirmed the high Curie temperature and the improved loss tangent with the Pb(Mg 1/3 Nb 2/3 )O 3 doping. (orig.)

  8. Magneto-optical properties of α-Fe2O3@ZnO nanocomposites prepared by the high energy ball-milling technique

    Chaudhury, Chandana Roy; Roychowdhury, Anirban; Das, Anusree; Das, Dipankar

    2016-05-01

    Magnetic-fluorescent nanocomposites (NCs) with 10 wt% of α-Fe2O3 in ZnO have been prepared by the high energy ball-milling. The crystallite sizes of α-Fe2O3 and ZnO in the NCs are found to vary from 65 nm to 20 nm and 47 nm to 15 nm respectively as milling time is increased from 2 to 30 h. XRD analysis confirms presence of α-Fe2O3 and ZnO in pure form in all the NCs. UV-vis study of the NCs shows a continuous blue-shift of the absorption peak and a steady increase of band gap of ZnO with increasing milling duration that are assigned to decreasing particle size of ZnO in the NCs. Photoluminescence (PL) spectra of the NCs reveal three weak emission bands in the visible region at 421, 445 and 485 nm along with the strong near band edge emission at 391 nm. These weak emission bands are attributed to different defect - related energy levels e.g. Zn-vacancy, Zn interstitial and oxygen vacancy. Dc and ac magnetization measurements show presence of weakly interacting superparamagnetic (SPM) α-Fe2O3 particles in the NCs. 57Fe-Mössbauer study confirms presence of SPM hematite in the sample milled for 30 h. Positron annihilation lifetime measurements indicate presence of cation vacancies in ZnO nanostructures confirming results of PL studies.

  9. Ketoprofen removal by O3 and O3/UV processes: Kinetics, transformation products and ecotoxicity

    Illés, Erzsébet; Szabó, Emese; Takács, Erzsébet; Wojnárovits, László; Dombi, András; Gajda-Schrantz, Krisztina

    2014-01-01

    Ozonation (O 3 ) and its combination with ultraviolet radiation (O 3 /UV) were used to decompose ketoprofen (KET). Depending on the initial KET concentration, fourteen to fifty time's faster KET degradation was achieved using combined O 3 /UV method compared to simple ozonation. Using both methods, formation of four major aromatic transformation products were observed: 3-(1-hydroxyethyl)benzophenone, 3-(1-hydroperoxyethyl) benzophenone, 1-(3-benzoylphenyl) ethanone and 3-ethylbenzophenone. In the combined treatment the degradation was mainly due to the direct effect of UV light, however, towards the end of the treatment, O 3 highly contributed to the mineralization of small carboxylic acids. High (∼ 90%) mineralization degree was achieved using the O 3 /UV method. Toxicity tests performed using representatives of three trophic levels of the aquatic ecosystems (producers, consumers and decomposers) Pseudokirchneriella subcapitata green algae, Daphnia magna zooplanktons and Vibrio fischeri bacteria showed that under the used experimental conditions the transformation products have significantly higher toxicity towards all the test organisms, than KET itself. The bacteria and the zooplanktons showed higher tolerance to the formed products than algae. The measured toxicity correlates well with the concentration of the aromatic transformation products, therefore longer treatments than needed for complete degradation of KET are strongly suggested, in order to avoid possible impact of aromatic transformation products on the aquatic ecosystem. - Highlights: • Ketoprofen degradation is significantly faster using O 3 /UV compared to ozonation. • The presence of O 3 enhances the overall mineralization. • Formation of four major aromatic by-products was observed. • The main step in the decomposition is the decarboxylation. • Degradation products have higher toxicity than ketoprofen itself

  10. Fracture Resistances of Y_2O_3 Particle Dispersion Strengthened 9Cr Steel at Room Temperature and High Temperatures

    Yoon, Ji Hyun; Kang, Suk Hoon; Lee, Yongbok; Kim, Sung Soo

    2012-01-01

    The fracture resistance and tensile properties of Y_2O_3 oxide dispersion strengthened steel containing 9 wt% Cr (9Cr-ODS) were measured at various temperatures up to 700°C. The fracture characteristics were compared with those of commercial E911 ferritic/martensitic steel. The strength of 9Cr-ODS was at least 30% higher than that of E911 steel at the test temperatures below 500°C. The strength difference between the two materials was almost diminished at 700°C. 9Cr-ODS showed cleavage fracture behavior at room temperature and unstable crack growth behaviors at 300°C and 500°C. The J-R fracture resistance of 9Cr-ODS was much lower than that of E911 steel at all temperatures. It was deduced that the coarse Cr_2O_3 particles that were formed during the alloying process provided the crack initiation sites of cleavage fracture in 9Cr-ODS.

  11. Optical properties of highly crystalline Y2O3:Er,Yb nanoparticles prepared by laser ablation in water

    Nunokawa, Takashi; Odawara, Osamu; Wada, Hiroyuki

    2014-01-01

    Y 2 O 3 :Er,Yb nanoparticles were prepared by laser ablation in water. We investigated crystallinity, distribution of dopant, and optical properties of the prepared nanoparticles. The full-width half-maximum (FWHD) of the crystalline peak of nanoparticles measured by an x-ray diffractometer (XRD) barely changed. Further, using scanning transmission electron microscopy–energy dispersive x-ray spectroscopy (STEM–EDX), we confirmed the peaks of Y, Er, Yb, and O. Moreover, on the basis of the optical properties of the nanoparticles, the emission of red ( 2 F 9/2  →  4 I 15/2 ) and green ( 2 H 11/2 , 4 S 3/2  →  4 I 15/2 ) was confirmed. We also investigated the emission intensity as a function of the excitation power of 980 nm LD in the prepared nanoparticles. The photon avalanche effect was observed at the excitation power of 100 mW. These results confirmed that uniformly Er-Yb-doped Y 2 O 3 nanoparticles were successfully prepared by laser ablation in water. (paper)

  12. Cell characteristics of FePt nano-dot memories with a high-k Al2O3 blocking oxide

    Lee, Gae Hun; Lee, Jung Min; Yang, Hyung Jun; Song, Yun Heub; Bea, Ji Cheol; Tanaka, Testsu

    2012-01-01

    The cell characteristics of an alloy FePt nano-dot (ND) charge trapping memory with a high-k dielectric as a blocking oxide was investigated. Adoption of a high-k Al 2 O 3 material as a blocking oxide for the metal nano-dot memory provided a superior scaling of the operation voltage compared to silicon oxide under a similar gate leakage level. For the 40-nm-thick high-k (Al 2 O 3 ) blocking oxide, we confirmed an operation voltage reduction of ∼7 V under the same memory window on for silicon dioxide. Also, this device showed a large memory window of 7.8 V and a low leakage current under 10 -10 A in an area of Φ 0.25 mm. From these results, the use of a dielectric (Al 2 O 3 ) as a blocking oxide for a metal nano-dot device is essential, and a metal nano-dot memory with a high-k dielectric will be one of the candidates for a high-density non-volatile memory device.

  13. Ultrathin Epitaxial Ferromagneticγ-Fe2O3Layer as High Efficiency Spin Filtering Materials for Spintronics Device Based on Semiconductors

    Li, Peng

    2016-06-01

    In spintronics, identifying an effective technique for generating spin-polarized current has fundamental importance. The spin-filtering effect across a ferromagnetic insulating layer originates from unequal tunneling barrier heights for spin-up and spin-down electrons, which has shown great promise for use in different ferromagnetic materials. However, the low spin-filtering efficiency in some materials can be ascribed partially to the difficulty in fabricating high-quality thin film with high Curie temperature and/or partially to the improper model used to extract the spin-filtering efficiency. In this work, a new technique is successfully developed to fabricate high quality, ferrimagnetic insulating γ-Fe2O3 films as spin filter. To extract the spin-filtering effect of γ-Fe2O3 films more accurately, a new model is proposed based on Fowler–Nordheim tunneling and Zeeman effect to obtain the spin polarization of the tunneling currents. Spin polarization of the tunneled current can be as high as −94.3% at 2 K in γ-Fe2O3 layer with 6.5 nm thick, and the spin polarization decays monotonically with temperature. Although the spin-filter effect is not very high at room temperature, this work demonstrates that spinel ferrites are very promising materials for spin injection into semiconductors at low temperature, which is important for development of novel spintronics devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  14. Densification kinetics and structure formation during the high-pressure sintering of Al2O3-TiN powder systems

    Neshpor, V.S.; Barashkov, G.A.; Nikitiuk, A.F.

    1986-04-01

    Specimens of alumina of varying specific surface and a composite material containing 80 pct alpha-Al2O3 and 20 pct TiN were sintered at 5 GPa for 30-480 s in the temperature range 1650-1750 K. It is found that the densification process is particularly intensive during the first 30-60 s. Under the conditions investigated, alpha-Al2O3 powder exhibits higher densification rates and final density (100 percent) than the ultradisperse TiN powder, whose final density is 96 percent. The results of the study suggest that densification is achieved through particle fragmentation and slip. Noticeable grain growth is observed for alumina only when the sintering time exceeds 2 min. 7 references.

  15. Polycrystalline and Mesoporous 3-D Bi2O3 Nanostructured Negatrodes for High-Energy and Power-Asymmetric Supercapacitors: Superfast Room-Temperature Direct Wet Chemical Growth.

    Shinde, Nanasaheb M; Xia, Qi Xun; Yun, Je Moon; Mane, Rajaram S; Kim, Kwang Ho

    2018-04-04

    Superfast (≤10 min) room-temperature (300 K) chemical synthesis of three-dimensional (3-D) polycrystalline and mesoporous bismuth(III) oxide (Bi 2 O 3 ) nanostructured negatrode (as an abbreviation of negative electrode) materials, viz., coconut shell, marigold, honey nest cross section and rose with different surface areas, charge transfer resistances, and electrochemical performances essential for energy storage, harvesting, and even catalysis devices, are directly grown onto Ni foam without and with poly(ethylene glycol), ethylene glycol, and ammonium fluoride surfactants, respectively. Smaller diffusion lengths, caused by the involvement of irregular crevices, allow electrolyte ions to infiltrate deeply, increasing the utility of inner active sites for the following electrochemical performance. A marigold 3-D Bi 2 O 3 electrode of 58 m 2 ·g -1 surface area has demonstrated a specific capacitance of 447 F·g -1 at 2 A·g -1 and chemical stability of 85% even after 5000 redox cycles at 10 A·g -1 in a 6 M KOH electrolyte solution, which were higher than those of other morphology negatrode materials. An asymmetric supercapacitor (AS) device assembled with marigold Bi 2 O 3 negatrode and manganese(II) carbonate quantum dots/nickel hydrogen-manganese(II)-carbonate (MnCO 3 QDs/NiH-Mn-CO 3 ) positrode corroborates as high as 51 Wh·kg -1 energy at 1500 W·kg -1 power and nearly 81% cycling stability even after 5000 cycles. The obtained results were comparable or superior to the values reported previously for other Bi 2 O 3 morphologies. This AS assembly glowed a red-light-emitting diode for 20 min, demonstrating the scientific and industrial credentials of the developed superfast Bi 2 O 3 nanostructured negatrodes in assembling various energy storage devices.

  16. Molybdenum oxide supported on silica (MoO3/SiO2): an efficient and reusable catalyst for the synthesis of 1,8-dioxodecahydroacridines under solvent-free conditions

    Khojastehnezhad, A.; Vafaei, M.; Moeinpour, F.

    2014-01-01

    Silica supported molybdenum oxide (MoO 3 /SiO 2 ) was found to be and efficient, eco-friendly and heterogeneous catalyst for the multicomponent reaction of aromatic aldehydes, dimedone and ammonium acetate or aromatic amines under solvent-free conditions to afford the corresponding 1,8-dioxodecahydroacridines in high yields. The catalyst can be easily recovered and reused for several times without considerable loss of activity. Furthermore, the present method offers several advantages, such as an easy experimental and work-up procedures, short reaction times and good to excellent yields. For the characterization were used: Fourier transform infrared spectroscopy (Ft-IR), X-ray diffraction and scanning electron microscopy analyses. (Author)

  17. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

    Mumthaz Muhammed, Mufasila

    2016-07-14

    We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

  18. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer.

    Muhammed, M M; Roldan, M A; Yamashita, Y; Sahonta, S-L; Ajia, I A; Iizuka, K; Kuramata, A; Humphreys, C J; Roqan, I S

    2016-07-14

    We demonstrate the high structural and optical properties of InxGa1-xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 10(7) cm(-2)) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1-xN epilayers can be achieved with high optical quality of InxGa1-xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

  19. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

    Mumthaz Muhammed, Mufasila; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, Idris A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, Iman S.

    2016-01-01

    We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

  20. Characterization, integration and reliability of HfO2 and LaLuO3 high-κ/metal gate stacks for CMOS applications

    Nichau, Alexander

    2013-01-01

    The continued downscaling of MOSFET dimensions requires an equivalent oxide thickness (EOT) of the gate stack below 1 nm. An EOT below 1.4 nm is hereby enabled by the use of high-κ/metal gate stacks. LaLuO 3 and HfO 2 are investigated as two different high-κ oxides on silicon in conjunction with TiN as the metal electrode. LaLuO 3 and its temperature-dependent silicate formation are characterized by hard X-ray photoemission spectroscopy (HAXPES). The effective attenuation length of LaLuO 3 is determined between 7 and 13 keV to enable future interface and diffusion studies. In a first investigation of LaLuO 3 on germanium, germanate formation is shown. LaLuO 3 is further integrated in a high-temperature MOSFET process flow with varying thermal treatment. The devices feature drive currents up to 70μA/μm at 1μm gate length. Several optimization steps are presented. The effective device mobility is related to silicate formation and thermal budget. At high temperature the silicate formation leads to mobility degradation due to La-rich silicate formation. The integration of LaLuO 3 in high-T processes delicately connects with the optimization of the TiN metal electrode. Hereby, stoichiometric TiN yields the best results in terms of thermal stability with respect to Si-capping and high-κ oxide. Different approaches are presented for a further EOT reduction with LaLuO 3 and HfO 2 . Thereby the thermodynamic and kinetic predictions are employed to estimate the behavior on the nanoscale. Based on thermodynamics, excess oxygen in the gate stack, especially in oxidized metal electrodes, is identified to prevent EOT scaling below 1.2 nm. The equivalent oxide thickness of HfO 2 gate stacks is scalable below 1 nm by the use of thinned interfacial SiO 2 . The prevention of oxygen incorporation into the metal electrode by Si-capping maintains the EOT after high temperature annealing. Redox systems are employed within the gate electrode to decrease the EOT of HfO 2 gate stacks

  1. High pressure studies of magnetic, electronic, and local structure properties in the rare-earth orthoferrites RFeO3 (R = Nd, Lu)

    Gavriliuk, A.G.; Stepanov, G.N.; Lyubutin, I.S.; Stepin, A.S.; Trojan, I.A.; Sidorov, V.A.

    2000-01-01

    The high pressure modification of the electronic structure, magnetic properties, and local crystal structure have been studied in the rare-earth RFeO 3 (R=Nd, Lu) orthoferrites in both pure single crystals and polycrystalline samples doped with Sn. The pressure dependences of the unit cell parameters, Neel temperatures, supertransferred hyperfine magnetic fields at tin nuclei H Sn , and the optical absorption edge have been obtained. The relations of the obtained values with the geometry of exchange interactions were analyzed

  2. The behavior of lattice defects produced in Al2O3 irradiated by neutrons at high temperatures

    Atobe, K.; Koizumi, T.; Okada, M.

    2003-01-01

    Single crystals of α-Al 2 O 3 were irradiated by the two reactors, KUR and JMTR, at three different temperatures. Lattice defects produced by irradiation were studied by esr (electron spin resonance). Three kinds of esr spectram, which are denoted as A, B and C spectram, are observed. The spectram A was observed at three different irradiation temperatures and was ascribed to oxygen vacancies. The spectram B showed no angular dependence for the rotation of external magnetic field to the crystal axis, and the defect density of this spectram decreased with an increase of annealing temperature. When the specimen was annealed at 400 degC after irradiation at 200 degC, the spectram C was observed and was presumed to be due to Al-colloids. (Y. Kazumata)

  3. Effects of Sb-doping on the formation of (K, Na)(Nb, Sb)O3 solid solution under hydrothermal conditions

    Su Likui; Zhu Kongjun; Bai Lin; Qiu Jinhao; Ji Hongli

    2010-01-01

    (K, Na)(Nb, Sb)O 3 (KNNS) lead-free peizoceramic powders were successfully synthesized by hydrothermal treatment at 240 o C for 8 h using the KOH, NaOH, Nb 2 O 5 and Sb 2 O 3 as raw materials. Effects of Sb-doping on the crystal structure and morphology of the as-prepared powders were investigated by powder X-ray diffraction (XRD), Raman spectra (Raman), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The Sb element was successfully doped into the alkaline niobate perovskite structure to form crystalline (K 0.7 Na 0.3 )(Nb 0.95 Sb 0.05 )O 3 lead-free piezoelectric ceramic powder, which has a hexagonal morphology due to the aggregation growth of small grains. Phase and morphology evolutions with the reaction time were also studied, and a possible formation mechanism was proposed.

  4. Mechanical properties and thermal shock performance of W-Y2O3 composite prepared by high-energy-rate forging

    Lian, Youyun; Liu, Xiang; Feng, Fan; Song, Jiupeng; Yan, Binyou; Wang, Yingmin; Wang, Jianbao; Chen, Jiming

    2017-12-01

    The effects of the addition of Y2O3 and hot-deformation on the mechanical properties of tungsten (W) have been studied. The processing route comprises a doping technique for the distribution of Y2O3 particles in a tungsten matrix, conventional sintering in a hydrogen environment, and high-energy-rate forging (HERF). The microstructure of the composite was characterized by using transmission electron microscopy and electron backscattering diffraction imaging technique, and its mechanical properties were studied by means of tensile testing. The thermal shock response of the HERF processed W-Y2O3 was evaluated by applying edge-localized mode-like loads (100 pulses) with a pulse duration of 1 ms and an absorbed power density of up to 1 GW m-2 at various temperatures between room temperature and 200 °C. HERF processing has produced elongated W grains with preferred orientations and a high density of structure defects in the composite. The composite material exhibits high tensile strength and good ductility, and a thermal shock cracking threshold lower than 100 °C.

  5. O3 stars

    Walborn, N.R.

    1982-01-01

    A brief review of the 10 known objects in this earliest spectral class is presented. Two new members are included: HD 64568 in NGC 2467 (Puppis OB2), which provides the first example of an O3 V((f*)) spectrum; and Sk -67 0 22 in the Large Magellanic Cloud, which is intermediate between types O3 If* and WN6-A. In addition, the spectrum of HDE 269810 in the LMC is reclassified as the first of type O3 III (f*). The absolute visual magnitudes of these stars are rediscussed

  6. Color-tunable and highly thermal stable Sr_2MgAl_2_2O_3_6:Tb"3"+ phosphors

    Zhang, Haiming; Zhang, Haoran; Liu, Yingliang; Lei, Bingfu; Deng, Jiankun; Liu, Wei-Ren; Zeng, Yuan; Zheng, Lingling; Zhao, Minyi

    2017-01-01

    Tb"3"+ activated Sr_2MgAl_2_2O_3_6 phosphor was prepared by a high-temperature solid-state reaction route. The X-ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy were used to characterize the as-prepared samples. The Sr_2MgAl_2_2O_3_6:Tb"3"+ phosphors show intense green light emission under UV excitation. The phosphor exhibit two groups of emission lines from about 370 to 700 nm, which originating from the characteristic "5D_3-"7F_J and "5D_4-"7F_J transitions of the Tb"3"+ ion, respectively. The cross-relaxation mechanism between the "5D_3 and "5D_4 emission was investigated and discussed. The emission colors of these phosphors can be tuned from bluish-green to green by adjusting the Tb"3"+ doping concentration. Furthermore, the thermal quenching temperature (T_1_/_2) is higher than 500 K. The excellent thermal stability and color-tunable luminescent properties suggest that the developed material is a promising green-emitting phosphor candidate for optical devices. - Highlights: • A Color-tunable emitting phosphor Sr_2MgAl_2_2O_3_6:Tb"3"+ was prepared successfully via high-temperature solid-state reaction. • The photoluminescence of Sr_2MgAl_2_2O_3_6:Tb"3"+ shows highly thermal stable. • The cross-relaxation mechanism between the "5D_3 and "5D_4 emission was investigated and discussed.

  7. The thermal equation of state of FeTiO3 ilmenite based on in situ X-ray diffraction at high pressures and temperatures

    Tronche, E.J.; Van Kan Parker, M.; De Vries, J.; Wang, Y.; Sanehire, T.; Li, J.; Chen, B.; Gao, L.; Klemme, S.; McCammon, C.A.; Van Westerenen, W.

    2010-01-01

    We present in situ measurements of the unit-cell volume of a natural terrestrial ilmenite (Jagersfontein mine, South Africa) and a synthetic reduced ilmenite (FeTiO 3 ) at simultaneous high pressure and high temperature up to 16 GPa and 1273 K. Unit-cell volumes were determined using energy-dispersive synchrotron X-ray diffraction in a multi-anvil press. Moessbauer analyses show that the synthetic sample contained insignificant amounts of Fe 3+ both before and after the experiment. Results were fit to Birch-Murnaghan thermal equations of state, which reproduce the experimental data to within 0.5 and 0.7 GPa for the synthetic and natural samples, respectively. At ambient conditions, the unit-cell volume of the natural sample (V 0 = 314.75 ± 0.23 (1σ) (angstrom) 3 ) is significantly smaller than that of the synthetic sample (V 0 = 319.12 ± 0.26 (angstrom) 3 ). The difference can be attributed to the presence of impurities and Fe 3+ in the natural sample. The 1 bar isothermal bulk moduli K T0 for the reduced ilmenite is slightly larger than for the natural ilmenite (181 ± 7 and 165 ± 6 GPa, respectively), with pressure derivatives K(prime) 0 = 3 ± 1. Our results, combined with literature data, suggest that the unit-cell volume of reduced ilmenite is significantly larger than that of oxidized ilmenite, whereas their thermoelastic parameters are similar. Our data provide more appropriate input parameters for thermo-chemical models of lunar interior evolution, in which reduced ilmenite plays a critical role.

  8. Fe2O3/Reduced Graphene Oxide/Fe3O4 Composite in Situ Grown on Fe Foil for High-Performance Supercapacitors.

    Zhao, Chongjun; Shao, Xiaoxiao; Zhang, Yuxiao; Qian, Xiuzhen

    2016-11-09

    A Fe 2 O 3 /reduced graphene oxide (RGO)/Fe 3 O 4 nanocomposite in situ grown on Fe foil was synthesized via a simple one-step hydrothermal growth process, where the iron foil served as support, reductant of graphene oxide, Fe source of Fe 3 O 4 , and also the current collector of the electrode. When it directly acted as the electrode of a supercapacitor, as-synthesized Fe 2 O 3 /RGO/Fe 3 O 4 @Fe exhibited excellent electrochemical performance with a high capability of 337.5 mF/cm 2 at 20 mA/cm 2 and a superior cyclability with 2.3% capacity loss from the 600th to the 2000th cycle.

  9. High Resolution and Differential PIXE combined with RBS, EBS and AFM analysis of magnesium titanate (MgTiO3) multilayer structures

    Reis, M.A.; Alves, L.C.; Barradas, N.P.; Chaves, P.C.; Nunes, B.; Taborda, A.; Surendran, K.P.; Wu, A.; Vilarinho, P.M.; Alves, E.

    2010-01-01

    Thorough structural characterization of deep laying thin film, including the inference of interdiffusion profiles is frequently a complex problem. The use of RBS/PIXE holistic approaches, already shown to represent a powerful method, sometimes faces difficulties if standard experimental procedures are used. In this work, following a series of 4 He Rutherford backscattering and 1 H elastic backscattering experiments, carried out to study the influence of SrTiO 3 as a possible cladding layer between Pt/TiO 2 /SiO 2 /(1 0 0)Si substrates and MgTiO 3 films, a simple holistic RBS-PIXE is shown to be not enough for the solution of such a problem. Establishing of the Sr depth profile, was only possible after AFM, High-Resolution EDS PIXE and differential PIXE analysis were carried out. Results, problems faced and conclusions obtained are presented.

  10. Processing simulated high-level liquid waste by heat treatment with addition of TiN and AlN or Al2O3

    Uno, Masayoshi; Kinoshita, Hajime; Sakai, Etsuro; Ikeda, Akira; Matsumoto, Y.; Yamanaka, Shinsuke

    1999-01-01

    The present study aims to decrease the melting temperature of the oxide phase by the addition of the mixture of TiN and AlN or Al 2 O 3 for reduction of the treatment temperature of super high temperature method. The addition of the mixture of TiN and AlN or Al 2 O 3 with the atomic ratio of Al to Ti of 1:9 caused the melting of both the alloy phase and oxide phase at 1673 K. The measured values of density and hardness for thus obtained oxide phase were same as those for the oxide phase obtained at 1873 K without Al. Thus, above mentioned method is achieved at 1673 K without degradation of the properties of the oxide phase as an waste. (author)

  11. Demonstration of high-responsivity epitaxial β-Ga2O3/GaN metal–heterojunction-metal broadband UV-A/UV-C detector

    Kalra, Anisha; Vura, Sandeep; Rathkanthiwar, Shashwat; Muralidharan, Rangarajan; Raghavan, Srinivasan; Nath, Digbijoy N.

    2018-06-01

    We demonstrate epitaxial β-Ga2O3/GaN-based vertical metal–heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UV-to-visible rejection >103, and a photo-to-dark current ratio of ∼100. A small (large) conduction (valence) band offset at the heterojunction of pulsed laser deposition (PLD)-grown β-Ga2O3 on metal organic chemical vapor deposition (MOCVD)-grown GaN-on-silicon with epitaxial registry, as confirmed by X-ray diffraction (XRD) azimuthal scanning, is exploited to realize detectors with an asymmetric photoresponse and is explained with one-dimensional (1D) band diagram simulations. The demonstrated novel vertical MHM detectors on silicon are fully scalable and promising for enabling focal plane arrays for broadband ultraviolet sensing.

  12. Microstructural Investigations of Al2O3 Scale Formed on FeCrAl Steel during High Temperature Oxidation in SO2

    Homa, M.; Zurek, Z.; Morgiel, B.; Zieba, P.; Wojewoda, J.

    2008-01-01

    The results of microstructure observations of the Al 2 O 3 scale formed on a Fe-Cr-Al steel during high temperature oxidation in the SO 2 atmosphere are presented. Morphology of the scale has been studied by SEM and TEM techniques. Phase and chemical compositions have been studied by EDX and XRD techniques. The alumina oxide is a primary component of the scale. TEM observations showed that the scale was multilayer. The entire surface of the scale is covered with 'whiskers, which look like very thin platelets and have random orientation. The cross section of a sample shows, that the 'whiskers' are approximately 2 μm high, however the compact scale layer on which they reside is 0.2 μm thick. The scale layer was composed mainly of small equiaxial grains and a residual amount of small columnar grains. EDX analysis of the scale surface showed that the any sulfides were found in the formed outer and thin inner scale layer. A phase analysis of the scale formed revealed that it is composed mainly of the θ-Al 2 O 3 phase and a residual amount of α-Al 2 O 3

  13. Suppressing the Photocatalytic Activity of TiO2 Nanoparticles by Extremely Thin Al2O3 Films Grown by Gas-Phase Deposition at Ambient Conditions

    Guo, J.; Bui, H.V.; Valdesueiro Gonzalez, D.; Yuan, Shaojun; Liang, Bin; van Ommen, J.R.

    2018-01-01

    This work investigated the suppression of photocatalytic activity of titanium dioxide (TiO2) pigment powders by extremely thin aluminum oxide (Al2O3) films deposited via an atomic-layer-deposition-type process using trimethylaluminum (TMA) and H2O as precursors. The deposition was performed on

  14. Controlling Piezoelectric Responses in Pb(Zr0.52Ti0.48)O3 Films through Deposition Conditions and Nanosheet Buffer Layers on Glass

    Nguyen, Minh D.; Houwman, Evert P.; Yuan, Huiyu; Wylie- Van Eerd, Benjamin; Dekkers, Matthijn; Koster, Gertjan; Ten Elshof, Johan E.; Rijnders, Guus

    2017-01-01

    Nanosheet Ca2Nb3O10 (CNOns) layers were deposited on ultralow expansion glass substrates by the Langmuir-Blodgett method to obtain preferential (001)-oriented growth of Pb(Zr0.52Ti0.48)O3 (PZT) thin films using pulsed laser deposition (PLD) to enhance the ferroelectric and piezoelectric properties

  15. Hydrostatic pressing effect on some properties of Al2O3 and Sc2O3 base ceramics

    Artemova, K.K.; Rudenko, L.A.; Maslova, G.Ya.; Levkovich, N.A.; Orlova, L.A.

    1981-01-01

    Found is the effect of hydrostatic pressing pressure on some physico-mechanical properties of the ceramic on the Al 2 O 3 and Se 2 O 3 base. Mathematical models, describing dependences of the strength of materials made of Al 2 O 3 and Sc 2 O 3 on sintering conditions and on hydrostatic pressing pressure, are plotted. Production regimes on the Al 2 O 3 and Sc 2 O 3 base ceramics with improved properties are optimized [ru

  16. Structural and compositional characterization of X-cut LiNbO3 crystals implanted with high energy oxygen and carbon ions

    Bentini, G.G.; Bianconi, M.; Cerutti, A.; Chiarini, M.; Pennestri, G.; Sada, C.; Argiolas, N.; Bazzan, M.; Mazzoldi, P.; Guzzi, R.

    2005-01-01

    High energy implantation of medium-light elements such as oxygen and carbon was performed in X-cut LiNbO 3 single crystals in order to prepare high quality optical waveguides. The compositional and damage profiles, obtained by exploiting the secondary ion mass spectrometry and Rutherford back-scattering techniques respectively, were correlated to the structural properties measured by the high resolution X-ray diffraction. This study evidences the development of tensile strain induced by the ion implantation that can contribute to the decrease of the ordinary refractive index variation through the photo-elastic effect

  17. O3 Layers via Spray Pyrolysis at Low Temperatures and Their Application in High Electron Mobility Transistors

    Isakov, Ivan

    2017-04-06

    The growth mechanism of indium oxide (InO) layers processed via spray pyrolysis of an aqueous precursor solution in the temperature range of 100-300 °C and the impact on their electron transporting properties are studied. Analysis of the droplet impingement sites on the substrate\\'s surface as a function of its temperature reveals that Leidenfrost effect dominated boiling plays a crucial role in the growth of smooth, continuous, and highly crystalline InO layers via a vapor phase-like process. By careful optimization of the precursor formulation, deposition conditions, and choice of substrate, this effect is exploited and ultrathin and exceptionally smooth layers of InO are grown over large area substrates at temperatures as low as 252 °C. Thin-film transistors (TFTs) fabricated using these optimized InO layers exhibit superior electron transport characteristics with the electron mobility reaching up to 40 cm V s, a value amongst the highest reported to date for solution-processed InO TFTs. The present work contributes enormously to the basic understanding of spray pyrolysis and highlights its tremendous potential for large-volume manufacturing of high-performance metal oxide thin-film transistor electronics.

  18. O3 Layers via Spray Pyrolysis at Low Temperatures and Their Application in High Electron Mobility Transistors

    Isakov, Ivan; Faber, Hendrik; Grell, Max; Wyatt-Moon, Gwenhivir; Pliatsikas, Nikos; Kehagias, Thomas; Dimitrakopulos, George P.; Patsalas, Panos P.; Li, Ruipeng; Anthopoulos, Thomas D.

    2017-01-01

    The growth mechanism of indium oxide (InO) layers processed via spray pyrolysis of an aqueous precursor solution in the temperature range of 100-300 °C and the impact on their electron transporting properties are studied. Analysis of the droplet impingement sites on the substrate's surface as a function of its temperature reveals that Leidenfrost effect dominated boiling plays a crucial role in the growth of smooth, continuous, and highly crystalline InO layers via a vapor phase-like process. By careful optimization of the precursor formulation, deposition conditions, and choice of substrate, this effect is exploited and ultrathin and exceptionally smooth layers of InO are grown over large area substrates at temperatures as low as 252 °C. Thin-film transistors (TFTs) fabricated using these optimized InO layers exhibit superior electron transport characteristics with the electron mobility reaching up to 40 cm V s, a value amongst the highest reported to date for solution-processed InO TFTs. The present work contributes enormously to the basic understanding of spray pyrolysis and highlights its tremendous potential for large-volume manufacturing of high-performance metal oxide thin-film transistor electronics.

  19. Improved linearity and reliability in GaN metal-oxide-semiconductor high-electron-mobility transistors using nanolaminate La2O3/SiO2 gate dielectric

    Hsu, Ching-Hsiang; Shih, Wang-Cheng; Lin, Yueh-Chin; Hsu, Heng-Tung; Hsu, Hisang-Hua; Huang, Yu-Xiang; Lin, Tai-Wei; Wu, Chia-Hsun; Wu, Wen-Hao; Maa, Jer-Shen; Iwai, Hiroshi; Kakushima, Kuniyuki; Chang, Edward Yi

    2016-04-01

    Improved device performance to enable high-linearity power applications has been discussed in this study. We have compared the La2O3/SiO2 AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) with other La2O3-based (La2O3/HfO2, La2O3/CeO2 and single La2O3) MOS-HEMTs. It was found that forming lanthanum silicate films can not only improve the dielectric quality but also can improve the device characteristics. The improved gate insulation, reliability, and linearity of the 8 nm La2O3/SiO2 MOS-HEMT were demonstrated.

  20. A high selective methanol gas sensor based on molecular imprinted Ag-LaFeO3 fibers.

    Rong, Qian; Zhang, Yumin; Wang, Chao; Zhu, Zhongqi; Zhang, Jin; Liu, Qingju

    2017-09-21

    Ag-LaFeO 3 molecularly imprinted polymers (ALMIPs) were fabricated, which provided special recognition sites to methanol. Then ALMIPs fiber 1, fiber 2 and fiber 3 were prepared using filter paper, silk and carbon fibers template, respectively. Based on the observation of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and Nitrogen adsorption surface area analyzer (BET), the structure, morphology and surface area of the fibers were characterized. The ALMIPs fibers (fiber 1, fiber 2 and fiber 3) show excellent selectivity and good response to methanol. The responses to 5 ppm methanol and the optimal operating temperature of ALMIPs fibers are 23.5 and 175 °C (fiber 1), 19.67 and 125 °C (fiber 2), 17.59 and 125 °C (fiber 3), and a lower response (≤10, 3, 2) to other test gases including formaldehyde, acetone, ethanol, ammonia, gasoline and benzene was measured, respectively.

  1. Direct observation of low energy nuclear spin excitations in HoCrO3 by high resolution neutron spectroscopy.

    Chatterji, T; Jalarvo, N; Kumar, C M N; Xiao, Y; Brückel, Th

    2013-07-17

    We have investigated low energy nuclear spin excitations in the strongly correlated electron compound HoCrO3. We observe clear inelastic peaks at E = 22.18 ± 0.04 μeV in both energy loss and gain sides. The energy of the inelastic peaks remains constant in the temperature range 1.5-40 K at which they are observed. The intensity of the inelastic peak increases at first with increasing temperature and then decreases at higher temperatures. The temperature dependence of the energy and intensity of the inelastic peaks is very unusual compared to that observed in other Nd, Co, V and also simple Ho compounds. Huge quasielastic scattering appears at higher temperatures presumably due to the fluctuating electronic moments of the Ho ions that get increasingly disordered at higher temperatures. The strong quasielastic scattering may also originate in the first Ho crystal-field excitations at about 1.5 meV.

  2. Temperature-dependent high energy-resolution EELS of ferroelectric and paraelectric BaTiO3 phases

    Bugnet, Matthieu; Radtke, Guillaume; Woo, Steffi Y.; Zhu, Guo-zhen; Botton, Gianluigi A.

    2016-01-01

    Probing the ferroelectricity at the nanometer scale is of particular interest for a wide range of applications. In this Rapid Communication, the structural distortion of BaTiO3 (BTO) is studied in its ferroelectric (rhombohedral and tetragonal), and paraelectric phases from the O K near edge structures in electron energy loss spectroscopy. Modifications of the electronic structure are detected in the lowest energy fine structure (FS) of the O K edge in the ferroelectric phases, and are interpreted by core-hole valence-electron screening geometry. For the paraelectric phase, the lowest energy FS of the O K edge is comparable to the one obtained at room temperature, which is inconsistent with an expected cubic structure. The variations observed in the O K near edge structures, such as a broader and more asymmetric lowest energy FS at low temperature, suggest that the magnitude of the Ti+4 off-centering along increases in lower-temperature phases. These findings demonstrate the sensitivity of the O K near edge structures to the structural distortions of BTO polymorphs, and form a basis for further investigations on defective or strained BTO at the nanoscale.

  3. High-frequency Lamb wave device composed of MEMS structure using LiNbO3 thin film and air gap.

    Kadota, Michio; Ogami, Takashi; Yamamoto, Kansho; Tochishita, Hikari; Negoro, Yasuhiro

    2010-11-01

    High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.

  4. High-performance electrodes for reduced temperature solid oxide fuel cells with doped lanthanum gallate electrolyte. II. La(Sr)CoO 3 cathode

    Inagaki, Toru; Miura, Kazuhiro; Yoshida, Hiroyuki; Maric, Radenka; Ohara, Satoshi; Zhang, Xinge; Mukai, Kazuo; Fukui, Takehisa

    The reduced temperature solid oxide fuel cell (SOFC) with 0.5 mm thick La 0.9Sr 0.1Ga 0.8Mg 0.2O 3- α (LSGM) electrolyte, La 0.6Sr 0.4CoO 3- δ (LSCo) cathode, and Ni-(CeO 2) 0.8(SmO 1.5) 0.2 (SDC) cermet anode showed an excellent initial performance, and high maximum power density, 0.47 W/cm 2, at 800°C. The results were comparable to those for the conventional SOFC with yttria-stabilized zirconia (YSZ) electrolyte, La(Sr)MnO 3-YSZ cathode and Ni-YSZ cermet anode at 1000°C. Using an LSCo powder prepared by spray pyrolysis, and selecting appropriate sintering temperatures, the lowest cathodic polarization of about 25 mV at 300 mA/cm 2 was measured for a cathode prepared by sintering at 1000°C. Life time cell test results, however, showed that the polarization of the LSCo cathode increased with operating time. From EPMA results, this behavior was considered to be related to the interdiffusion of the elements at the cathode/electrolyte interface. Calcination of LSCo powder could be a possible way to suppress this interdiffusion at the interface.

  5. CoO-doped MgO-Al2O3-SiO2-colored transparent glass-ceramics with high crystallinity

    Tang, Wufu; Zhang, Qian; Luo, Zhiwei; Yu, Jingbo; Gao, Xianglong; Li, Yunxing; Lu, Anxian

    2018-02-01

    To obtain CoO-doped MgO-Al2O3-SiO2 (MAS)-colored transparent glass-ceramics with high crystallinity, the glass with the composition 21MgO-21Al2O3-54SiO2-4B2O3-0.2CoO (in mol %) was prepared by conventional melt quenching technique and subsequently thermal treated at several temperatures. The crystallization behavior of the glass, the precipitated crystalline phases and crystallinity were analyzed by X-ray diffraction (XRD). The microstructure of the glass-ceramics was characterized by field emission scanning electron microscopy (FSEM). The transmittance of glass-ceramic was measured by UV spectrophotometer. The results show that a large amount of α-cordierite (indianite) with nano-size was precipitated from the glass matrix after treatment at 1020 °C for 3 h. The crystallinity of the transparent glass-ceramic reached up to 97%. Meanwhile, the transmittance of the glass-ceramic was 74% at 400 nm with a complex absorption band from 450 nm to 700 nm. In addition, this colored transparent glass-ceramic possessed lower density (2.469 g/cm3), lower thermal expansion coefficient (1.822 × 10-6 /℃), higher Vickers hardness (9.1 GPa) and higher bending strength (198 MPa) than parent glass.

  6. Effects of Fuel to Synthesis of CaTiO3 by Solution Combustion Synthesis for High-Level Nuclear Waste Ceramics.

    Jung, Choong-Hwan; Kim, Yeon-Ku; Han, Young-Min; Lee, Sang-Jin

    2016-02-01

    A solution combustion process for the synthesis of perovskite (CaTiO3) powders is described. Perovskite is one of the crystalline host matrics for the disposal of high-level radioactive wastes (HLW) because it immobilizes Sr and Lns elements by forming solid solutions. Solution combustion synthesis, which is a self-sustaining oxi-reduction reaction between nitrate and organic fuel, the exothermic reaction, and the heat evolved convert the precursors into their corresponding oxide products above 1100 degrees C in air. To investigate the effects of amino acid on the combustion reaction, various types of fuels were used; a glycine, amine and carboxylic ligand mixture. Sr, La and Gd-nitrate with equivalent amounts of up to 20% of CaTiO3 were mixed with Ca and Ti nitrate and amino acid. X-ray diffraction analysis, SEM and TEM were conducted to confirm the formed phases and morphologies. While powders with an uncontrolled shape are obtained through a general oxide-route process, Ca(Sr, Lns)TiO3 powders with micro-sized soft agglomerates consisting of nano-sized primary particles can be prepared using this method.

  7. Dielectric and barrier thickness fluctuation scattering in Al2O3/AlGaN/GaN double heterojunction high-electron mobility transistors

    Ji, Dong; Lu, Yanwu; Liu, Bing; Liu, Guipeng; Zhu, Qinsheng; Wang, Zhanguo

    2013-01-01

    The two-dimensional electron gas (2DEG) mobility limited by dielectric and barrier thickness fluctuations (TF) scattering in Al 2 O 3 /AlGaN/GaN double heterojunction high-electron mobility transistors (HEMTs) is calculated. Calculation shows that thickness fluctuation scattering is the main limitation in Al 2 O 3 /AlGaN/GaN double heterojunction HEMTs with thin Al 2 O 3 layer thicknesses. In addition, a study of 2DEG mobility as a function of 2DEG density, n s , shows that TF scattering acts as the main limitation when n s exceeds 2 × 10 12 cm −2 . The results may be used to design HEMTs to obtain higher 2DEG mobilities by modulating the dielectric layer and barrier thicknesses or 2DEG density. - Highlights: • The mobility limited by thickness fluctuation (TF) scattering is studied. • Results show that thickness fluctuation scattering is the main limitation. • Two-dimensional electron gas (2DEG) mobility is a function of 2DEG density. • TF scattering is the main limitation when 2DEG density exceeds 2 × 10 12 cm −2

  8. Investigation of optical, electrical and magnetic properties of hexagonal NiTiO3 nanoparticles prepared via ultrasonic dispersion techniques for high power applications

    Karmakar, Subrata; Manna, Ashis Kumar; Varma, Shikha; Behera, Dhrubananda

    2018-05-01

    Nickel titanate (NiTiO3) nanoparticles were synthesized by ultrasonic dispersion techniques using ethylene glycol monoetheline ether as a solvent. The x-ray diffraction (XRD), Raman, transmission electron micrographs (TEM) exhibit pure phase formation, fine hexagonal nanostructure, agglomerated and inhomogeneous grain growth in nm range (26.5 nm) of as-prepared NiTiO3 nanoparticles. Raman studies on NiTiO3 nanoparticles exposed almost all the active vibrational modes (5Ag + 5Eg) of its crystalline structure. A wide optical band gap (3.02 eV) was observed from UV-DRS spectra which arises from the hybridized Ni- 3d and O- 2p orbitals to the Ti -3d orbitals. The characteristics vibration bands of M-O (Ni–O, and Ti–O) were also analyzed using Fourier Transform Infrared spectrum. The antiferromagnetic (AFM) properties were examined from M-H loop with coercive field 75.02 ± 0.05 Oe and saturation magnetization 0.418 ± 0.05 emu gm‑1. respectively. The dielectrics constant and loss decays with high frequency evaluation and Maxwell–Wagner type of polarization were responsible for its dielectric behavior. The total conductivity was explained using NNH and VRH hopping relaxation model and dc activation energy (0.81 eV) were calculated from Arrhenius plot.

  9. Growth of uniform lath-like α-(Fe,Al)OOH and disc-like α-(Fe,Al)2O3 nanoparticles in a highly alkaline medium

    Krehula, Stjepko; Music, Svetozar

    2010-01-01

    The effects of aluminium (Al 3+ )-dopant on the precipitation of uniform lath-like α-FeOOH particles, the obtention and growth of α-(Fe,Al)OOH and α-(Fe,Al) 2 O 3 solid solutions, particle size and shape were investigated using X-ray powder diffraction, Moessbauer and Fourier transform infrared spectroscopies, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Acicular α-FeOOH particles, precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH), were used as reference material. The influence of Al-dopant was investigated by adding varying amounts of Al 3+ ions to the initial FeCl 3 solution. In the presence of lower concentrations of aluminium ions (up to 11.11 mol%) α-(Fe,Al)OOH as a single phase was formed, whereas higher concentrations led to an additional obtention and growth of α-(Fe,Al) 2 O 3 . Al-for-Fe substitution in the α-FeOOH and α-Fe 2 O 3 structures was confirmed by a decrease in the unit-cell dimensions, a decrease in the hyperfine magnetic field and an increase in the wave number of the infrared absorption bands. The presence of lower concentrations of aluminium ions (up to 11.11 mol%) in the precipitation system did not affect the size and shape of the α-(Fe,Al)OOH particles, whereas higher concentrations influenced a decrease in the length and aspect ratio. In the presence of 42.86 mol% Al 3+ ions fairly uniform disc-shaped α-(Fe,Al) 2 O 3 were formed.

  10. Influence of hydroxybenzoic acids on the adsorption of Eu(III) onto α,γ-Al_2O_3 particles in mildly acidic conditions: A macroscopic and spectroscopic study

    Moreau, Pauline; Colette-Maatouk, Sonia; Gareil, Pierre; Reiller, Pascal E.

    2016-01-01

    The influence of hydroxybenzoic acids (HAH_n), namely p-hydroxybenzoic acid (4-hydroxybenzoic acid, HPhbH) and protocatechuic acid (3,4-dihydroxybenzoic acid, HProtoH_2), on the adsorption of europium(III) onto α,γ-Al_2O_3 particles is studied as a function of acid concentration. After measuring the adsorption edge of the Eu(III)/α,γ-Al_2O_3 binary system, and using the previously studied binary component system Eu(III)/HAH_n—Moreau et al. (2015) Inorg. Chim. Acta432, 81—, and HAH_n/α,γ-Al_2O_3—Moreau et al. (2013) Colloids Surf. A435, 97—, it is evidenced that HPhbH does not enhance Eu(III) adsorption onto α,γ-Al_2O_3 in the Eu(III)/HPhbH/α,γ-Al_2O_3 ternary system. Conversely, HProtoH_2 enhances Eu(III) adsorption onto α,γ-Al_2O_3 in the Eu(III)/HProtoH_2/α,γ-Al_2O_3 ternary system. Adsorption of the acids are also found higher in the Eu(III)/acid/α,γ-Al_2O_3 ternary systems as compared with the corresponding binary systems assessing synergetic effects. For high HPhbH concentrations, a ternary surface species involving ≡AlOH surface sites, Eu(III), and PhbH"– is evidenced by time-resolved luminescence spectroscopy (TRLS). However, in the Eu(III)/HProtoH_2/α,γ-Al_2O_3 ternary system, chemical environment of Eu(III) is found to be very close to that in the Eu(III)/HProtoH_2 binary system. Ternary surface species could not be evidenced in the Eu(III)/HProtoH_2/α,γ-Al_2O_3 ternary system with TRLS because of the very short decay time of Eu(III) in the presence of protocatechuic acid. - Highlights: • Adsorption in the Eu(III) – hydroxybenzoic acid – alumina system is studied. • Adsorption is quantified and luminescence parameters are obtained independently. • Synergistic effect of organic acids adsorption are evidenced in the ternary systems. • A ternary species is clearly shown for the p-hydrobenzoic acid.

  11. High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate.

    Muhammed, Mufasila M; Alwadai, Norah; Lopatin, Sergei; Kuramata, Akito; Roqan, Iman S

    2017-10-04

    We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga 2 O 3 ) substrate, obtained using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multiquantum well (MQW) grown on the masked β-Ga 2 O 3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ∼86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

  12. High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate

    Muhammed, Mufasila; Alwadai, Norah Mohammed Mosfer; Lopatin, Sergei; Kuramata, Akito; Roqan, Iman S.

    2017-01-01

    We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multi-quantum well (MQW) grown on the masked β-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ~ 86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

  13. High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate

    Muhammed, Mufasila

    2017-09-11

    We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multi-quantum well (MQW) grown on the masked β-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ~ 86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

  14. BaO-Nd2O3-CuOx subsolidus equilibria under carbonate-free conditions at pO2=100 Pa and at pO2=21 kPa

    Wong-Ng, W.; Cook, L.P.; Suh, J.; Coutts, R.; Stalick, J.K.; Levin, I.; Huang, Q.

    2003-01-01

    Subsolidus phase equilibria of the BaO-Nd 2 O 3 -CuO x system at pO 2 =100 Pa (0.1% O 2 volume fraction, 810 deg. C) and at pO 2 =21 kPa (21% O 2 volume fraction, 930 deg. C) have been investigated by applying controlled-atmosphere methods to minimize the presence of carbonate and CO 2 and H 2 O contamination. Under carbonate-free conditions, the BaO-Nd 2 O 3 -CuO x phase diagrams at pO 2 =100 Pa and at pO 2 =21 kPa are similar to one another except for differences in the extent of the solid solutions. Apart from the limiting binary phases, the ternary system consists of three solid solutions and one stoichiometric ternary compound. The first solid solution is the high T c series, Ba 2-x Nd 1+x Cu 3 O 6+z (0.3≥x≥0 at pO 2 =100 Pa; 0.95≥x≥ 0 at pO 2 =21 kPa). At pO 2 =21 kPa, a compositionally dependent phase change was detected, from tetragonal (0.7>x≥0) to orthorhombic (0.95≥x≥0.7). The second solid solution series, the 'brown-phase' Ba 1+x Nd 2-x CuO z , has a narrow homogeneity region (0.10>x≥0 at pO 2 =100 Pa; 0.15>x≥0 at pO 2 =21 kPa). In the high BaO part of the phase diagram, a third solid solution (Ba 2-x Nd x )CuO 3+z (x=0 to ∼ 0.3 at pO 2 =100 Pa; x=0-0.45 at pO 2 =21 kPa) was confirmed, as well as a nominally stoichiometric phase, Ba 4 Nd 2 Cu 2 O z . The latter phase is an insulator, with a structure comprised of unusual CuO 5 linear chains. A significant difference in tie line distribution involving the Ba 2-x Nd 1+x Cu 3 O 6+z superconductor was found under carbonate-free conditions relative to literature studies completed in air. Instead of the BaCuO 2+x -Ba 2+x Nd 4-x Cu 2 O z tie line normally encountered in air, a Ba 2-x Nd 1+x Cu 3 O 6+z -(Ba,Nd) 2 CuO 3+x tie line was established. This tie line substantially expands the field of stability of the Ba 2-x Nd 1+x Cu 3 O 6+z superconductor phase into the BaO-rich region of the phase diagram. Implications for the processing of materials based on the Ba 2-x Nd 1+x Cu 3 O 6+z

  15. Room-Temperature Fabrication of High-Performance Amorphous In-Ga-Zn-O/Al2O3 Thin-Film Transistors on Ultrasmooth and Clear Nanopaper.

    Ning, Honglong; Zeng, Yong; Kuang, Yudi; Zheng, Zeke; Zhou, Panpan; Yao, Rihui; Zhang, Hongke; Bao, Wenzhong; Chen, Gang; Fang, Zhiqiang; Peng, Junbiao

    2017-08-23

    Integrating biodegradable cellulose nanopaper into oxide thin-film transistors (TFTs) for next generation flexible and green flat panel displays has attracted great interest because it offers a viable solution to address the rapid increase of electronic waste that poses a growing ecological problem. However, a compromise between device performance and thermal annealing remains an obstacle for achieving high-performance nanopaper TFTs. In this study, a high-performance bottom-gate IGZO/Al 2 O 3 TFT with a dual-layer channel structure was initially fabricated on a highly transparent, clear, and ultrasmooth nanopaper substrate via conventional physical vapor deposition approaches, without further thermal annealing processing. Purified nanofibrillated cellulose with a width of approximately 3.7 nm was used to prepare nanopaper with excellent optical properties (92% transparency, 0.85% transmission haze) and superior surface roughness (Rq is 1.8 nm over a 5 × 5 μm 2 scanning area). More significantly, a bilayer channel structure (IGZO/Al 2 O 3 ) was adopted to fabricate high performance TFT on this nanopaper substrate without thermal annealing and the device exhibits a saturation mobility of 15.8 cm 2 /(Vs), an I on /I off ratio of 4.4 × 10 5 , a threshold voltage (V th ) of -0.42 V, and a subthreshold swing (SS) of 0.66 V/dec. The room-temperature fabrication of high-performance IGZO/Al 2 O 3 TFTs on such nanopaper substrate without thermal annealing treatment brings industry a step closer to realizing inexpensive, flexible, lightweight, and green paper displays.

  16. Surface passivation by Al2O3 and a-SiNx: H films deposited on wet-chemically conditioned Si surfaces

    Bordihn, S.; Mertens, V.; Engelhart, P.; Kersten, K.; Mandoc, M.M.; Müller, J.W.; Kessels, W.M.M.

    2012-01-01

    The surface passivation of p- and n-type silicon by different chemically grown SiO2 films (prepared by HNO3, H2SO4/H2O2 and HCl/H2O2 treatments) was investigated after PECVD of a-SiNx:H and ALD of Al2O3 capping films. The wet chemically grown SiO2 films were compared to thermally grown SiO2 and the

  17. Exceptionally High Piezoelectric Coefficient and Low Strain Hysteresis in Grain-Oriented (Ba, Ca)(Ti, Zr)O3 through Integrating Crystallographic Texture and Domain Engineering.

    Liu, Yingchun; Chang, Yunfei; Li, Fei; Yang, Bin; Sun, Yuan; Wu, Jie; Zhang, Shantao; Wang, Ruixue; Cao, Wenwu

    2017-09-06

    Both low strain hysteresis and high piezoelectric performance are required for practical applications in precisely controlled piezoelectric devices and systems. Unfortunately, enhanced piezoelectric properties were usually obtained with the presence of a large strain hysteresis in BaTiO 3 (BT)-based piezoceramics. In this work, we propose to integrate crystallographic texturing and domain engineering strategies into BT-based ceramics to resolve this challenge. [001] c grain-oriented (Ba 0.94 Ca 0.06 )(Ti 0.95 Zr 0.05 )O 3 (BCTZ) ceramics with a texture degree as high as 98.6% were synthesized by templated grain growth. A very high piezoelectric coefficient (d 33 ) of 755 pC/N, and an extremely large piezoelectric strain coefficient (d 33 * = 2027 pm/V) along with an ultralow strain hysteresis (H s ) of 4.1% were simultaneously achieved in BT-based systems for the first time, which are among the best values ever reported on both lead-free and lead-based piezoceramics. The exceptionally high piezoelectric response is mainly from the reversible contribution, and can be ascribed to the piezoelectric anisotropy, the favorable domain configuration, and the formation of smaller sized domains in the BCTZ textured ceramics. This study paves a new pathway to develop lead-free piezoelectrics with both low strain hysteresis and high piezoelectric coefficient. More importantly, it represents a very exciting discovery with potential application of BT-based ceramics in high-precision piezoelectric actuators.

  18. Isotope analysis of diamond-surface passivation effect of high-temperature H2O-grown atomic layer deposition-Al2O3 films

    Hiraiwa, Atsushi; Saito, Tatsuya; Matsumura, Daisuke; Kawarada, Hiroshi

    2015-01-01

    The Al 2 O 3 film formed using an atomic layer deposition (ALD) method with trimethylaluminum as Al precursor and H 2 O as oxidant at a high temperature (450 °C) effectively passivates the p-type surface conduction (SC) layer specific to a hydrogen-terminated diamond surface, leading to a successful operation of diamond SC field-effect transistors at 400 °C. In order to investigate this excellent passivation effect, we carried out an isotope analysis using D 2 O instead of H 2 O in the ALD and found that the Al 2 O 3 film formed at a conventional temperature (100 °C) incorporates 50 times more CH 3 groups than the high-temperature film. This CH 3 is supposed to dissociate from the film when heated afterwards at a higher temperature (550 °C) and causes peeling patterns on the H-terminated surface. The high-temperature film is free from this problem and has the largest mass density and dielectric constant among those investigated in this study. The isotope analysis also unveiled a relatively active H-exchange reaction between the diamond H-termination and H 2 O oxidant during the high-temperature ALD, the SC still being kept intact. This dynamic and yet steady H termination is realized by the suppressed oxidation due to the endothermic reaction with H 2 O. Additionally, we not only observed the kinetic isotope effect in the form of reduced growth rate of D 2 O-oxidant ALD but found that the mass density and dielectric constant of D 2 O-grown Al 2 O 3 films are smaller than those of H 2 O-grown films. This is a new type of isotope effect, which is not caused by the presence of isotopes in the films unlike the traditional isotope effects that originate from the presence of isotopes itself. Hence, the high-temperature ALD is very effective in forming Al 2 O 3 films as a passivation and/or gate-insulation layer of high-temperature-operation diamond SC devices, and the knowledge of the aforementioned new isotope effect will be a basis for further enhancing ALD

  19. Structural features and high-temperature transport in SrFe0.7Mo0.3O3

    Merkulov, O. V.; Markov, A. A.; Patrakeev, M. V.; Leonidov, I. A.; Shalaeva, E. V.; Tyutyunnik, A. P.; Kozhevnikov, V. L.

    2018-02-01

    The complex oxide SrFe0.7Mo0.3O3-δ was obtained by combustion of the organometallic precursor in air followed by annealing in an argon flow at 1350 °C, and characterized with the help of X-ray and electron diffraction methods. Oxygen nonstoichiometry and electrical conductivity data were collected in the oxygen partial pressure range from 10-19 to 0.5 atm at temperatures 750-950 °C. The as-prepared single phase oxide SrFe0.7Mo0.3O3-δ with the cubic double perovskite structure (SG Fm3m) is shown to undergo a structural transition to the tetragonal double perovskite phase (SG I4mmm) in the result of reducing treatment at pO2 = 10-12 atm and 950 °C. The ordered phases are characterized by a strong anti-site disordering of iron and molybdenum and nearly zero long-range ordering parameter. The maximal concentration of n-type carriers is about four times larger than of p-type carriers in the studied limits of oxygen pressure and temperature. The mobility of p-type carriers is found to vary within 0.02-0.03 cm2 V-1 s-1 with the migration energy of about 0.4 eV, while the n-type mobility being approximately twice higher does not practically depend on temperature. Such features as good electrical conductivity, which can rise up to 40 S cm-1 in reducing conditions and a considerable amount of oxygen vacancies favorable for fast oxygen ion transport are beneficial for application of SrFe0.7Mo0.3O3-δ as anode material in SOFCs and oxygen membrane for hydrogen generation by a water splitting.

  20. Growth of high phase-match temperature LiNbO3 single crystals. Annual report for period ending March 15, 1978

    Kway, W.L.; Feigelson, R.S.

    1978-09-01

    LiNbO 3 crystal with T/sub pm/ greater than or equal to 180 0 C together with excellent phase matching characteristics and a high degree of optical homogeneity can be grown by the Czochralski technique with the following set of growth parameters: a melt composition of .54 Li 2 O/.46 Nb 2 O 5 doped with 1.0 mole % MgO; a growth rate of 2 mm/hr or less; positive axial and radial temperature gradients; and a crystal rotation rate of 50 rpm or higher to provide for a planar solid-liquid growth interface

  1. Characteristics of surface O3 over Qinghai Lake area in Northeast Tibetan Plateau, China

    Shen, Zhenxing; Cao, Junji; Zhang, Leiming; Zhao, Zhuzi; Dong, Jungang; Wang, Linqing; Wang, Qiyuan; Li, Guohui; Liu, Suixin; Zhang, Qian

    2014-01-01

    Surface O 3 was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3200 m above sea level) in Qinghai Lake area (36°58′37″N, 99°53′56″E) in Northeast Tibetan Plateau, China. Daily average O 3 ranged from 21.8 ppbv to 65.3 ppbv with an annual average of 41.0 ppbv. Seasonal average of O 3 followed a decreasing order of summer > autumn > spring > winter. Diurnal variations of O 3 showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13–31, 2010 to investigate correlations between meteorological or chemical conditions and O 3 . It was found that O 3 was poorly correlated with solar radiation due to the insufficient NO x in the ambient air, thus limiting O 3 formation under strong solar radiation. In contrast, high O 3 levels always coincided with strong winds, suggesting that stratospheric O 3 and long range transport might be the main sources of O 3 in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions. - Highlights: • Surface O 3 was measured in Qinghai Lake area in Northeast Tibetan Plateau, China. • The O 3 chemical formation was under a strong NOx-limited in Qinghai Lake areas. • Stratospheric O 3 and transport might be the main sources of O 3 in this area

  2. Large piezoelectric strain with ultra-low strain hysteresis in highly c-axis oriented Pb(Zr0.52Ti0.48)O3 films with columnar growth on amorphous glass substrates

    Nguyen, Minh D.; Houwman, Evert P.; Rijnders, Guus

    2017-01-01

    Thin films of PbZr0.52Ti0.48O3 (PZT) with largely detached columnar grains, deposited by pulsed laser deposition (PLD) on amorphous glass substrates covered with Ca2Nb3O10 nanosheets as growth template and using LaNiO3 electrode layers, are shown to exhibit very high unipolar piezoelectric strain

  3. Highly Stable Sr-Free Cobaltite-Based Perovskite Cathodes Directly Assembled on a Barrier-Layer-Free Y2 O3 -ZrO2 Electrolyte of Solid Oxide Fuel Cells.

    Ai, Na; Li, Na; Rickard, William D A; Cheng, Yi; Chen, Kongfa; Jiang, San Ping

    2017-03-09

    Direct assembly is a newly developed technique in which a cobaltite-based perovskite (CBP) cathode can be directly applied to a barrier-layer-free Y 2 O 3 -ZrO 2 (YSZ) electrolyte with no high-temperature pre-sintering steps. Solid oxide fuel cells (SOFCs) based on directly assembled CBPs such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ show high performance initially but degrade rapidly under SOFC operation conditions at 750 °C owing to Sr segregation and accumulation at the electrode/electrolyte interface. Herein, the performance and interface of Sr-free CBPs such as LaCoO 3-δ (LC) and Sm 0.95 CoO 3-δ (SmC) and their composite cathodes directly assembled on YSZ electrolyte was studied systematically. The LC electrode underwent performance degradation, most likely owing to cation demixing and accumulation of La on the YSZ electrolyte under polarization at 500 mA cm -2 and 750 °C. However, the performance and stability of LC electrodes could be substantially enhanced by the formation of LC-gadolinium-doped ceria (GDC) composite cathodes. Replacement of La by Sm increased the cell stability, and doping of 5 % Pd to form Sm 0.95 Co 0.95 Pd 0.05 O 3-δ (SmCPd) significantly improved the electrode activity. An anode-supported YSZ-electrolyte cell with a directly assembled SmCPd-GDC composite electrode exhibited a peak power density of 1.4 W cm -2 at 750 °C, and an excellent stability at 750 °C for over 240 h. The higher stability of SmC as compared to that of LC is most likely a result of the lower reactivity of SmC with YSZ. This study demonstrates the new opportunities in the design and development of intermediate-temperature SOFCs based on the directly assembled high-performance and durable Sr-free CBP cathodes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Stability investigation of a high number density Pt1/Fe2O3 single-atom catalyst under different gas environments by HAADF-STEM

    Duan, Sibin; Wang, Rongming; Liu, Jingyue

    2018-05-01

    Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt1/Fe2O3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water–gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe2O3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H2O molecules to the CO or H2 significantly accelerates the sintering of the Fe2O3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal–support interaction.

  5. A Novel 2D Porous Print Fabric-like α-Fe_2O_3 Sheet with High Performance as the Anode Material for Lithium-ion Battery

    Zhang, Suyue; Zhang, Peigen; Xie, Anjian; Li, Shikuo; Huang, Fangzhi; Shen, Yuhua

    2016-01-01

    Anode materials are very crucial in lithium ion batteries. Exploring the simple and low cost production of anodes with excellent electrochemical performance remains a great challenge. Here, we used natural flower spikes of Typha orientalis as the bio-templates and organizers to prepare a novel two-dimensional (2D) porous print fabric-like α-Fe_2O_3 sheet with thickness of about 30 nm. The prepared large-area sheets were orderly assembled by many nanosheets or nanoparticles, and two kinds of pore structures, such as pores with average diameter of about 50 nm or pore channels with aspect ratio of ca. 4, presented between adjacent nanosheets. The pre-treatment by ammonium for flower spikes has a great effect on the microstructure and electrochemical performance of the products. As the anode material for lithium ion battery (LIB), the as-obtained porous print fabric-like α-Fe_2O_3 sheets show an initial discharge capacity of 2264 mA h g"−"1 and the specific capacity of 1028 mA h g"−"1 after 100 cycles at a current density of 500 mA g"−"1, which is higher than the theoretical capacity of α-Fe_2O_3 (1007 mA h g"−"1). This highly reversible capacity is attributed to the very thin large-area sheet structure, and many pores or pore channels among the interconnected nanosheets, which could increase lithium-ion mobility, facilitate the transport of electrons and shorten the distance for Li"+ diffusion, and also buffer large volume changes of the anodes during lithium insertion and extraction at the same time. The synthesis process is very simple, providing a low-cost production approach toward high-performance energy storage materials.

  6. Synthesis of α-Fe2O3 and Fe-Mn Oxide Foams with Highly Tunable Magnetic Properties by the Replication Method from Polyurethane Templates

    Yuping Feng

    2018-02-01

    Full Text Available Open cell foams consisting of Fe and Fe-Mn oxides are prepared from metallic Fe and Mn powder precursors by the replication method using porous polyurethane (PU templates. First, reticulated PU templates are coated by slurry impregnation. The templates are then thermally removed at 260 °C and the debinded powders are sintered at 1000 °C under N2 atmosphere. The morphology, structure, and magnetic properties are studied by scanning electron microscopy, X-ray diffraction and vibrating sample magnetometry, respectively. The obtained Fe and Fe-Mn oxide foams possess both high surface area and homogeneous open-cell structure. Hematite (α-Fe2O3 foams are obtained from the metallic iron slurry independently of the N2 flow. In contrast, the microstructure of the FeMn-based oxide foams can be tailored by adjusting the N2 flow. While the main phases for a N2 flow rate of 180 L/h are α-Fe2O3 and FeMnO3, the predominant phase for high N2 flow rates (e.g., 650 L/h is Fe2MnO4. Accordingly, a linear magnetization versus field behavior is observed for the hematite foams, while clear hysteresis loops are obtained for the Fe2MnO4 foams. Actually, the saturation magnetization of the foams containing Mn increases from 5 emu/g to 52 emu/g when the N2 flow rate (i.e., the amount of Fe2MnO4 is increased. The obtained foams are appealing for a wide range of applications, such as electromagnetic absorbers, catalysts supports, thermal and acoustic insulation systems or wirelessly magnetically-guided porous objects in fluids.

  7. Synthesis of α-Fe2O3 and Fe-Mn Oxide Foams with Highly Tunable Magnetic Properties by the Replication Method from Polyurethane Templates

    Feng, Yuping; Fornell, Jordina; Zhang, Huiyan; Solsona, Pau; Barό, Maria Dolors; Suriñach, Santiago; Sort, Jordi

    2018-01-01

    Open cell foams consisting of Fe and Fe-Mn oxides are prepared from metallic Fe and Mn powder precursors by the replication method using porous polyurethane (PU) templates. First, reticulated PU templates are coated by slurry impregnation. The templates are then thermally removed at 260 °C and the debinded powders are sintered at 1000 °C under N2 atmosphere. The morphology, structure, and magnetic properties are studied by scanning electron microscopy, X-ray diffraction and vibrating sample magnetometry, respectively. The obtained Fe and Fe-Mn oxide foams possess both high surface area and homogeneous open-cell structure. Hematite (α-Fe2O3) foams are obtained from the metallic iron slurry independently of the N2 flow. In contrast, the microstructure of the FeMn-based oxide foams can be tailored by adjusting the N2 flow. While the main phases for a N2 flow rate of 180 L/h are α-Fe2O3 and FeMnO3, the predominant phase for high N2 flow rates (e.g., 650 L/h) is Fe2MnO4. Accordingly, a linear magnetization versus field behavior is observed for the hematite foams, while clear hysteresis loops are obtained for the Fe2MnO4 foams. Actually, the saturation magnetization of the foams containing Mn increases from 5 emu/g to 52 emu/g when the N2 flow rate (i.e., the amount of Fe2MnO4) is increased. The obtained foams are appealing for a wide range of applications, such as electromagnetic absorbers, catalysts supports, thermal and acoustic insulation systems or wirelessly magnetically-guided porous objects in fluids. PMID:29439450

  8. Synchrotron radiation x-ray photoelectron spectroscopy study on the interface chemistry of high-k PrxAl2-xO3 (x=0-2) dielectrics on TiN for dynamic random access memory applications

    Schroeder, T.; Lupina, G.; Sohal, R.; Lippert, G.; Wenger, Ch.; Seifarth, O.; Tallarida, M.; Schmeisser, D.

    2007-07-01

    Engineered dielectrics combined with compatible metal electrodes are important materials science approaches to scale three-dimensional trench dynamic random access memory (DRAM) cells. Highly insulating dielectrics with high dielectric constants were engineered in this study on TiN metal electrodes by partly substituting Al in the wide band gap insulator Al2O3 by Pr cations. High quality PrAlO3 metal-insulator-metal capacitors were processed with a dielectric constant of 19, three times higher than in the case of Al2O3 reference cells. As a parasitic low dielectric constant interface layer between PrAlO3 and TiN limits the total performance gain, a systematic nondestructive synchrotron x-ray photoelectron spectroscopy study on the interface chemistry of PrxAl2-xO3 (x =0-2) dielectrics on TiN layers was applied to unveil its chemical origin. The interface layer results from the decreasing chemical reactivity of PrxAl2-xO3 dielectrics with increasing Pr content x to reduce native Ti oxide compounds present on unprotected TiN films. Accordingly, PrAlO3 based DRAM capacitors require strict control of the surface chemistry of the TiN electrode, a parameter furthermore of importance to engineer the band offsets of PrxAl2-xO3/TiN heterojunctions.

  9. Preparation and microstructure of ZrO2- and LaGaO3-based high-porosity ceramics

    Kaleva, G.M.; Golubko, N.V.; Suvorkin, S.V.; Kosarev, G.V.; Sukhareva, I.P.; Avetisov, A.K.; Politova, E.D.

    2006-01-01

    The morphology and concentration of pore formers are studied for their effect on the microstructure and gas permeability of porous zirconia- and lanthanum-gallate-based oxygen-ion-conducting ceramics. The results have been used to optimize the preparation conditions and composition of the ceramics. The resultant dense, fine-grained materials have porosities of up to ∼56% [ru

  10. Synthesis of high-surface-area γ-Al2O3 from aluminum scrap and its use for the adsorption of metals: Pb(II), Cd(II) and Zn(II)

    Asencios, Yvan J.O.; Sun-Kou, María R.

    2012-01-01

    Highlights: ► Aluminum hydroxide obtained from aluminum scrap led to the formation of gamma alumina. ► Acidic pH of precipitation favored the formation of small particles of high surface areas. ► Higher aging temperature favored the formation of large structures of large pore sizes. ► Higher aging temperature generated symmetrical solids of regular hexagonal prism forms. ► Aluminas of large pores adsorbed metals as following: Pb (1.75 Å) > Cd (1.54 Å) > Zn (1.38 Å). - Abstract: Several types of alumina were synthesized from sodium aluminate (NaAlO 2 ) by precipitation with sulfuric acid (H 2 SO 4 ) and subsequently calcination at 500 °C to obtain γ-Al 2 O 3 . The precursor aluminate was derived from aluminum scrap. The various γ-Al 2 O 3 synthesized were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), adsorption–desorption of N 2 (S BET ) and scanning electron microscopy (SEM). XRD revealed that distinct phases of Al 2 O 3 were formed during thermal treatment. Moreover, it was observed that conditions of synthesis (pH, aging time and temperature) strongly affect the physicochemical properties of the alumina. A high-surface-area alumina (371 m 2 g −1 ) was synthesized under mild conditions, from inexpensive raw materials. These aluminas were tested for the adsorption of Cd(II), Zn(II) and Pb(II) from aqueous solution at toxic metal concentrations, and isotherms were determined.

  11. Low sintering temperature and high piezoelectric properties of Li-doped (Ba,Ca)(Ti,Zr)O3 lead-free ceramics

    Chen, Xiaoming; Ruan, Xuezheng; Zhao, Kunyun; He, Xueqing; Zeng, Jiangtao; Li, Yongsheng; Zheng, Liaoying; Park, Chul Hong; Li, Guorong

    2015-01-01

    Highlights: • Li-doped Ba 0.85 Ca 0.15 Ti 0.9 Zr 0.1 O 3 (BCZT) lead-free piezoceramics were prepared by the two-step synthesis and solid-state reaction method. • Their sintering temperature decreases from about 1540 °C down to about 1400 °C. • With the proper addition of Li, the densities and grain sizes of ceramics increase. • The ceramics not only have the characteristics of hard piezoceramics but also possesses the features of soft piezoceramics at low sintering temperature. - Abstract: Li-doped Ba 0.85 Ca 0.15 Ti 0.9 Zr 0.1 O 3 (BCZT) lead-free piezoelectric ceramics were prepared by the two-step synthesis and the solid-state reaction method. The density and grain size of ceramics sufficiently increases by Li-doped sintering aid, and their sintering temperature decreases from about 1540 °C down to about 1400 °C. X-ray diffraction reveals that the phase structure of Li-doped BCTZ ceramics is changed with the sintering temperature, which is consistent with their phase transition observed by the temperature-dependent dielectric curves. The well-poled Li-doped BCZT ceramics show a high piezoelectric constant d 33 (512 pC/N) and a planar electromechanical coupling factor k p (0.49), which have the characteristics of soft Pb(Zr,Ti)O 3 (PZT) piezoceramic, on the other hand, the mechanical quality factor Q m is about 190, which possesses the features of hard PZT piezoceramics. The enhanced properties of the Li-doped BCZT are explained by the combination of Li-doped effect and sintering effect on the microstructure and the phase transition around room temperature

  12. Self-propagating high-temperature synthesis of La(Sr)Ga(Mg)O3-δ for electrolyte of solid oxide fuel cells

    Ishikawa, Hiroyuki; Enoki, Makiko; Ishihara, Tatsumi; Akiyama, Tomohiro

    2007-01-01

    This paper describes self-propagating high-temperature synthesis (SHS) of an electrolyte for solid oxide fuel (SOFC), in comparison to a conventional solid-state reaction method (SRM). Doped-lanthanum gallate: La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ (LSGM9182) and LSGM9173 as the SOFC electrolyte, was prepared by the SHS and sintered at different temperatures, for measuring the electrical conductivity of the sintered LSGM and the power generating performance at 1073 K, in comparison to the SRM. In the SHS, the LSGM powders with smaller size were obtained and easily sintered at the 100 K-lower temperature, 1673 K, than in the SRM. Most significantly, the electrical conductivity of the sintered LSGM9182 was as high as 0.11 S cm -1 and its maximum power density was a value of 245 mW cm -2 in the cell configuration of Ni/LSGM9182 (0.501 mm in thickness)/Sm 0.5 Sr 0.5 CoO 3 . The conclusion was that the proposed SHS-sintering method with many benefits of minimizing the energy requirement and the processing time in the production, easing temperature restriction for the sintering, and improving the electrolyte performance up to a conventional level is practicable for producing the LSGM-electrolyte of SOFC at an intermediate-temperature application

  13. Highly conformal SiO2/Al2O3 nanolaminate gas-diffusion barriers for large-area flexible electronics applications

    Choi, Jin-Hwan; Kim, Young-Min; Park, Young-Wook; Park, Tae-Hyun; Jeong, Jin-Wook; Choi, Hyun-Ju; Song, Eun-Ho; Ju, Byeong-Kwon; Lee, Jin-Woo; Kim, Cheol-Ho

    2010-01-01

    The present study demonstrates a flexible gas-diffusion barrier film, containing an SiO 2 /Al 2 O 3 nanolaminate on a plastic substrate. Highly uniform and conformal coatings can be made by alternating the exposure of a flexible polyethersulfone surface to vapors of SiO 2 and Al 2 O 3 , at nanoscale thickness cycles via RF-magnetron sputtering deposition. The calcium degradation test indicates that 24 cycles of a 10/10 nm inorganic bilayer, top-coated by UV-cured resin, greatly enhance the barrier performance, with a permeation rate of 3.79 x 10 -5 g m -2 day -1 based on the change in the ohmic behavior of the calcium sensor at 20 deg. C and 50% relative humidity. Also, the permeation rate for 30 cycles of an 8/8 nm inorganic bilayer coated with UV resin was beyond the limited measurable range of the Ca test at 60 deg. C and 95% relative humidity. It has been found that such laminate films can effectively suppress the void defects of a single inorganic layer, and are significantly less sensitive against moisture permeation. This nanostructure, fabricated by an RF-sputtering process at room temperature, is verified as being useful for highly water-sensitive organic electronics fabricated on plastic substrates.

  14. Current linearity and operation stability in Al2O3-gate AlGaN/GaN MOS high electron mobility transistors

    Nishiguchi, Kenya; Kaneki, Syota; Ozaki, Shiro; Hashizume, Tamotsu

    2017-10-01

    To investigate current linearity and operation stability of metal-oxide-semiconductor (MOS) AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated and characterized the Al2O3-gate MOS-HEMTs without and with a bias annealing in air at 300 °C. Compared with the as-fabricated (unannealed) MOS HEMTs, the bias-annealed devices showed improved linearity of I D-V G curves even in the forward bias regime, resulting in increased maximum drain current. Lower subthreshold slope was also observed after bias annealing. From the precise capacitance-voltage analysis on a MOS diode fabricated on the AlGaN/GaN heterostructure, it was found that the bias annealing effectively reduced the state density at the Al2O3/AlGaN interface. This led to efficient modulation of the AlGaN surface potential close to the conduction band edge, resulting in good gate control of two-dimensional electron gas density even at forward bias. In addition, the bias-annealed MOS HEMT showed small threshold voltage shift after applying forward bias stress and stable operation even at high temperatures.

  15. Properties of epitaxial Ba2YCu3O7-x films on LaAlO3(001) grown using optimized conditions

    Siegal, M.P.; Phillips, J.M.; van Dover, R.B.; Tiefel, T.H.; Marshall, J.H.; Carlson, D.J.

    1990-01-01

    The superconducting and structural properties of Ba 2 YCu 3 O 7-x (BYCO) films on LaAlO 3 (001) substrates can be improved by carefully optimizing the post-deposition annealing parameters. Films are grown by codeposition of BaF 2 , Y, and Cu in the correct stoichiometric ratio to within 1% of 2:1:3. Compositional deviations greater than ± 1% result in the degradation of film quality. Important annealing parameters include the ambient, annealing temperature, oxidation temperature, and duration of the anneal. Films are characterized for epitaxial quality (χ min ), morphology, critical temperature (T c ), sharpness of the superconducting transition (ΔT), and critical current density (J c ). The optimized films have relatively smooth morphology with χ min c > 90 K, ΔT c > 10 6 A/cm 2 in essentially zero magnetic field at 77 K

  16. pH sensor using AlGaN/GaN high electron mobility transistors with Sc2O3 in the gate region

    Kang, B. S.; Wang, H. T.; Ren, F.; Gila, B. P.; Abernathy, C. R.; Pearton, S. J.; Johnson, J. W.; Rajagopal, P.; Roberts, J. C.; Piner, E. L.; Linthicum, K. J.

    2007-01-01

    Ungated AlGaN/GaN high electron mobility transistors (HEMTs) exhibit large changes in current upon exposing the gate region to polar liquids. The polar nature of the electrolyte introduced leds to a change of surface charges, producing a change in surface potential at the semiconductor/liquid interface. The use of Sc 2 O 3 gate dielectric produced superior results to either a native oxide or UV ozone-induced oxide in the gate region. The ungated HEMTs with Sc 2 O 3 in the gate region exhibited a linear change in current between pH 3 and 10 of 37 μA/pH. The HEMT pH sensors show stable operation with a resolution of <0.1 pH over the entire pH range. The results indicate that the HEMTs may have application in monitoring pH solution changes between 7 and 8, the range of interest for testing human blood

  17. Multiferroic Double Perovskites ScFe1-xCrxO3 (1 /6 ≤x ≤5 /6 ) for Highly Efficient Photovoltaics and Spintronics

    Cai, Tian-Yi; Liu, Shi-Chen; Ju, Sheng; Liu, Cheng-You; Guo, Guang-Yu

    2017-09-01

    Ferroelectric oxides are attractive materials for constructing efficient solar cells. Nevertheless, a wide band gap of nearly 3.0 eV in these ferroelectric oxides would result in poor overall sunlight absorption and, hence, low energy conversion efficiency. Here, by systematic first-principles density-functional calculations, we demonstrate that double-perovskite semiconductors ScFe1-xCrxO3 (1 /6 ≤x ≤5 /6 ) with a narrow band gap of approximately 1.8 eV would simultaneously exhibit large ferroelectric polarization (100 μ C /cm2 ) and ferrimagnetic magnetization (170 emu/cm3 ). Within a Schottky-based model for a typical sandwich solar-cell structure, a power-conversion efficiency of 9.0% can be reached by neglecting all other sources of photovoltaicity in ferroelectric materials. This value is larger than the largest value of 8.1% observed in ferroelectric oxides. Furthermore, these double perovskites are found to be single-spin semiconductors, and the obtained photocurrent is fully spin polarized over almost the entire Sun spectrum. These fascinating advantages would make ScFex Cr1 -xO3 (1 /6 ≤x ≤5 /6 ) semiconductors promising candidates for highly efficient solar cells and spin photovoltaic devices.

  18. High performance Pd–Rh/YBaCo4O7/γ-Al2O3 three-way catalysts for gasoil engine

    Brou Albert Kouadio

    2017-11-01

    Full Text Available The evaluation of catalytic activity for Rh–Pd/YBa(Co1−xMx4O7/γ-Al2O3 (M = Al, Ce, Zr, and La showed that the efficiency of NOx reduction depends strongly on the nature of the OSMs. Among a series of oxygen storage materials, YBa(Co1−xMx4O7 (M = Ce, Zr, La, Ga and In studied for catalyst enhancement, only the catalyst with YBa(Co0.9Ce0.14O7 has better conversion efficiency respectively (85% of NO, 96% of CO and 92% of HC. After treatment at 1000 °C for 3 h, these fresh catalysts showed a substantial decrease of their catalytic activities, only Rh–Pd/YBa(Co0.9Ce0.14O7/γ-Al2O3 retains its high catalytic activity. Keywords: Chemical synthesis, X-ray diffraction, Oxygen storage and catalytic activity

  19. Artificial O3 formation during fireworks

    Fiedrich, M.; Kurtenbach, R.; Wiesen, P.; Kleffmann, J.

    2017-09-01

    In several previous studies emission of ozone (O3) during fireworks has been reported, which was attributed to either photolysis of molecular oxygen (O2) or nitrogen dioxide (NO2) by short/near UV radiation emitted during the high-temperature combustion of fireworks. In contrast, in the present study no O3 formation was observed using a selective O3-LOPAP instrument during the combustion of pyrotechnical material in the laboratory, while a standard O3 monitor using UV absorption showed extremely high O3 signals. The artificial O3 response of the standard O3 monitor was caused by known interferences associated with high levels of co-emitted VOCs and could also be confirmed in field measurements during New Year's Eve in the city of Wuppertal, Germany. The present results help to explain unreasonably high ozone levels documented during ambient fireworks, which are in contradiction to the fast titration of O3 by nitrogen monoxide (NO) in the night-time atmosphere.

  20. Effects of high vacancy concentrations on the magnetic properties of La1-xMn1-yO3 (0.02⩽x, y⩽0.13)

    de Silva, P. S. I. P. N.; Richards, F. M.; Cohen, L. F.; Alonso, J. A.; Martínez-Lope, M. J.; Casais, M. T.; Thomas, K. A.; MacManus-Driscoll, J. L.

    1998-01-01

    It has been found that the synthesis conditions and subsequent annealing treatments can significantly change the magnetic and transport behavior of the colossal magnetoresistive materials of the general formula La1-zAzMnO3, where A is a divalent ion. In order to clarify the role of vacancies within this structure, resistivity and magnetization measurements have been carried out on a series of samples derived from the parent compound LaMnO3, with La and Mn vacancies introduced by systematically varying the oxygen annealing conditions. Previous studies have shown that for a given carrier concentration, the Curie temperature of the paramagnetic to ferromagnetic transition (Tc) increases as the tolerance factor of the perovskite structure increases and then begins to decrease slowly for even higher tolerance factors. Generally, Tc also increases with the Mn4+ content, consistent with a double exchange mechanism responsible for ferromagnetism. In this study Tc was found to decrease as the vacancy concentration (and therefore the Mn4+ concentration) and tolerance factor both increase. The magnetic and transport data are discussed in the light of structural information obtained from neutron diffraction studies. In the present study it is found that La and Mn vacancies play a significant role in determining the physical properties of these materials: for high vacancy concentrations (x,y⩾0.080) the magnetic properties are analogous to those of spin glasses associated with disorder and frustration. Semiconductorlike resistivity was observed for all samples at all temperatures.

  1. Graphene oxide-Fe2O3 hybrid nanoparticles: a highly efficient sorbent for Am (III) from aqueous solutions

    Patre, D.K.; Gujar, R.B.; Mohapatra, P.K.; Gadly, T.; Ghosh, S.K.

    2016-01-01

    Recently, carbon nano materials such as carbon nano tubes and graphene oxide (GO) have been widely studied for the treatment of radioactive waste water. GO can be obtained after oxidization of graphene, and there are many oxygen containing surface functional groups such as epoxy (C-O-C), hydroxyl (OH) and carboxyl (COOH) groups on GO surfaces. As a result, GO showed high adsorption capacity for the removal of different kinds of metal ions and organic contaminants in practical applications. In addition to this, the existences of oxygen-containing functional groups make GO participate in various modifications, and thus lots of GO-based multifunctional materials have been prepared and used for the removal of environmental contaminants. The introduction of magnetic materials into GO can combine the high adsorption properties of GO and the separation convenience of magnetic materials. GO-based magnetic materials have caught more attentions in adsorption study due to their unique magnetic and structural characteristics. In this paper, the magnetic GO nanoparticles were used for the sorption of Am(III) from acidic feed solutions in the pH range of 1-6

  2. Remarkably high apparent quantum yield of the overall photocatalytic H2O splitting achieved by utilizing Zn ion added Ga2O3 prepared using dilute CaCl2 solution.

    Sakata, Yoshihisa; Hayashi, Takuya; Yasunaga, Ryō; Yanaga, Nobuyuki; Imamura, Hayao

    2015-08-21

    Remarkably high photocatalytic activity for the overall H2O splitting, where the activity was 32 mmol h(-1) for H2 production and 16 mmol h(-1) for O2 production under irradiation from a 450 W high-pressure Hg lamp and the apparent quantum yield (AQY) was 71% under irradiation at 254 nm, was achieved by utilizing a Rh(0.5)Cr(1.5)O3(Rh; 0.5 wt%)/Zn(3 mol%)-Ga2O3 photocatalyst when Ga2O3 was prepared using dilute CaCl2 aqueous solution having a concentration of 0.001 mol l(-1).

  3. Frictional properties of CeO$_{2}$-Al$_{2}$O$_{3}$-ZrO$_{2}$ plasma-sprayed film under mixed and boundary lubricating conditions

    Kita, H; Osumi, K; 10.2109/jcersj.112.615

    2004-01-01

    In order to find a counterpart for reducing the frictional coefficient of Al/sub 2/O/sub 3/-ZrO/sub 2/-CeO/sub 2/ plasma-sprayed film, the sliding properties in mixed and boundary lubricating conditions was investigated. It was found that combination of a CrN- coated cast iron pin and an Al/sub 2/O/sub 3/-ZrO/sub 2/-CeO/sub 2/ plasma sprayed plate provided the lowest frictional coefficient among several combinations chosen from practical materials. The coefficient of friction was much lower than that of the materials combination widely used for piston ring and cylinder liner. It was inferred that the combination of a pin made of hard materials with high density, a smooth surface such as CrN-coated cast iron and a porous plate can reduce the frictional coefficient because less sliding resistance is implemented and porosity retains oil.

  4. Pure and Y-substituted BaZrO3 ceramics. A possible support material for fabrication of YBa2Cu3O7-x high-Tc superconductors

    Wang Xiandong.

    1993-01-01

    This thesis concerns the preparation and characterization of cuprate based high-T c superconductors (Y-123 and Bi-2223) and especially development and testing of BaZrO 3 based materials. The formation of YBa 2 Cu 3 O y (Y-123) by a CO 2 -free route involving reaction sintering of stoichiometric mixtures of chemically prepared fine powders of Y 2 BaCuO 5 , BaCuO 2 and CuO have been studied by thermal and XRD analysis. The synthesis and sintering of BaZrO 3 powders prepared by the hydroxide-alkoxide-methanol sol-gel route have been studied. The phase relations in the system BaO-Y 2 O 3 -ZrO 2 have been studied to determine the solid solubility limits for the perovskite phase Ba X Y Y Zr Z O N (X+X+Z=3) at 1500 deg. C. In the binary system Y 2 O 3 -BaZrO 3 the solubility limit was found to be ≅19 mol% Y 2 O 3 , i.e. Ba 0.81 Y 0. 4 2 Zr 0.81 O 3 . along the joint BaYO 2.5 -Ba the boundary was determined to be at BaY 0.21 Zr 0 . 79 O 2.895 . evidence for a new solid solution series between Ba 3 Y 4 O 9 and ZrO 2 are given, and a partial 1500 deg. C phase diagram for the ternary system BaO-Y 2 O 3 -ZrO 2 is presented. The growth of BaZrO 3 single crystals have been attempted both by a laser zone floating technique and flux methods. The compatibility between YBa 2 Cu 3 O 7 -X and BaZrO 3 , Ba X Y Y Zr Z O 3-δ as well as BaHfO 3 have been studied at 950 deg. and 1050 deg. C. The results show the four most promising candidates as support materials for fabrication of YBa 2 Cu 3 O y to be BaHfO 3 , BaY 0.05 Zr 0.95 O 2.975 , , BaZrO 3 and BaY 0.1 Zr 0.9 O 2.95 . (EG)

  5. Li_2ZrO_3-coated Li_4Ti_5O_1_2 with nanoscale interface for high performance lithium-ion batteries

    Zhang, Han; Liu, Yang; Wang, Ting; Yang, Yang; Shi, Shaojun; Yang, Gang

    2016-01-01

    Graphical abstract: - Highlights: • Zr doped and Li_2ZrO_3 coated Li_4Ti_5O_1_2 are prepared by a solid-state method. • Zr-doping and LZO coating are positive in improving lithium diffusion ability. • Li_2ZrO_3 coated Li_4Ti_5O_1_2 deliver 168.1 mAh g"−"1 higher than 150.2 mAh g"−"1 of Li_4Ti_5O_1_2. • Li_2ZrO_3 coated Li_4Ti_5O_1_2 remains 162 mAh g"−"1 after 100 cycles. • The lowest D_L_i"+ is 5.97 × 10"−"1"7 and 1.85 × 10"−"1"5 cm"2 s"−"1 of Li_4Ti_5O_1_2 before and after coating. - Abstract: Zr doped sample of Li_4Ti_4_._9_9Zr_0_._0_1O_1_2 (LZTO) and Li_2ZrO_3 (LZO) coated Li_4Ti_5O_1_2 (LTO) are prepared by a solid-state method. The lattice structure of LTO is remained after doping element of Zr and coating layer of LZO. The crystal structure and electrochemical performance of the material are investigated by X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and charge-discharge tests, respectively. Zr-doping and LZO coating play the positive role in improving the diffusion ability of lithium cations. LZTO and LZO-LTO show much improved specific capacity and rate capability compared with pristine sample of LTO. LZO-LTO has the smallest voltage differential (ΔV) of the redox peaks because the coating of Li_2ZrO_3 is helpful for the diffusion ability of lithium ions during charge/discharge processes. LZTO and LZO-LTO as electrode deliver the initial capacities of 164.8, 168.1 mAh g"−"1, respectively, which are much higher than 150.2 mAh g"−"1 of intrinsic sample of LTO. Even at the current density of 2 A g"−"1, LTZO and LZO-LTO offer capacity of 96 and 106 mAh g"−"1, which are much higher than 33 mAh g"−"1 of LTO. The improved electrochemical performance is attributed to the improved diffusion ability of lithium. During the whole discharge process, the lowest value of LTO is 5.97 × 10"−"1"7 cm"2 s"−"1 that is

  6. Fabrication and EMI shielding effectiveness of Ag-decorated highly porous poly(vinyl alcohol)/Fe2O3 nanofibrous composites

    Kim, Hae-Rim; Kim, Byoung-Suhk; Kim, Ick-Soo

    2012-01-01

    The Ag-decorated poly(vinyl alcohol) (PVA) composite nanofibrous webs incorporating Fe 2 O 3 nanoparticles were fabricated by electrospinning and metal-deposition methods for electromagnetic interference (EMI) shielding applications. The Ag-decorated PVA/Fe 2 O 3 composite nanofiber webs with various Ag thicknesses and different amounts of Fe 2 O 3 nanoparticles were prepared and used for EMI shielding measurement. For the EMI SE measurement, a near-field antenna measurement system was used. The measurement of EMI SE was carried out at the frequency range from 0.5 to 18 GHz, and the electromagnetic parameters were measured. The morphologies and microstructures of the resultant PVA/Fe 2 O 3 composite nanofiber webs were characterized using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), respectively. The effects of surface morphologies and Fe 2 O 3 nanoparticles on the EMI shielding effectiveness of Ag-decorated PVA/Fe 2 O 3 composite nanofiber webs were investigated. -- Highlights: ► We prepare Ag-decorated poly(vinyl alcohol) nanowebs incorporating Fe 2 O 3 nanoparticles. ► Solvents will affect the fiber morphologies and Fe 2 O 3 nanoparticles dispersion. ► EMI shielding effectiveness depends on the metal thickness and Fe 2 O 3 nanoparticles dispersion.

  7. Synthesis of High Crystalline Al-Doped ZnO Nanopowders from Al2O3 and ZnO by Radio-Frequency Thermal Plasma

    Min-Kyeong Song

    2015-01-01

    Full Text Available High crystalline Al-doped ZnO (AZO nanopowders were prepared by in-flight treatment of ZnO and Al2O3 in Radio-Frequency (RF thermal plasma. Micron-sized (~1 μm ZnO and Al2O3 powders were mixed at Al/Zn ratios of 3.3 and 6.7 at.% and then injected into the RF thermal plasma torch along the centerline at a feeding rate of 6.6 g/min. The RF thermal plasma torch system was operated at the plate power level of ~140 kVA to evaporate the mixture oxides and the resultant vapor species were condensed into solid particles by the high flow rate of quenching gas (~7000 slpm. The FE-SEM images of the as-treated powders showed that the multipod shaped and the whisker type nanoparticles were mainly synthesized. In addition, these nanocrystalline structures were confirmed as the single phase AZO nanopowders with the hexagonal wurtzite ZnO structure by the XRD patterns and FE-TEM results with the SAED image. However, the composition changes of 0.3 and 1.0 at.% were checked for the as-synthesized AZO nanopowders at Al/Zn ratios of 3.3 and 6.7 at.%, respectively, by the XRF data, which can require the adjustment of Al/Zn in the mixture precursors for the applications of high Al doping concentrations.

  8. Nanoparticle Metamorphosis: An in Situ High-Temperature Transmission Electron Microscopy Study of the Structural Evolution of Heterogeneous Au:Fe 2 O 3 Nanoparticles

    Baumgardner, William J.

    2014-05-27

    High-temperature in situ electron microscopy and X-ray diffraction have revealed that Au and Fe2O3 particles fuse in a fluid fashion at temperatures far below their size-reduced melting points. With increasing temperature, the fused particles undergo a sequence of complex structural transformations from surface alloy to phase segregated and ultimately core-shell structures. The combination of in situ electron microscopy and spectroscopy provides insights into fundamental thermodynamic and kinetic aspects governing the formation of heterogeneous nanostructures. The observed structural transformations present an interesting analogy to thin film growth on the curved surface of a nanoparticle. Using single-particle observations, we constructed a phase diagram illustrating the complex relationships among composition, morphology, temperature, and particle size. © 2014 American Chemical Society.

  9. Nanoparticle Metamorphosis: An in Situ High-Temperature Transmission Electron Microscopy Study of the Structural Evolution of Heterogeneous Au:Fe 2 O 3 Nanoparticles

    Baumgardner, William J.; Yu, Yingchao; Hovden, Robert; Honrao, Shreyas; Hennig, Richard G.; Abruñ a, Hé ctor D.; Muller, David; Hanrath, Tobias

    2014-01-01

    High-temperature in situ electron microscopy and X-ray diffraction have revealed that Au and Fe2O3 particles fuse in a fluid fashion at temperatures far below their size-reduced melting points. With increasing temperature, the fused particles undergo a sequence of complex structural transformations from surface alloy to phase segregated and ultimately core-shell structures. The combination of in situ electron microscopy and spectroscopy provides insights into fundamental thermodynamic and kinetic aspects governing the formation of heterogeneous nanostructures. The observed structural transformations present an interesting analogy to thin film growth on the curved surface of a nanoparticle. Using single-particle observations, we constructed a phase diagram illustrating the complex relationships among composition, morphology, temperature, and particle size. © 2014 American Chemical Society.

  10. Microscale 1-3-Type (Na,K)NbO(3)-Based Pb-Free Piezocomposites for High-Frequency Ultrasonic Transducer Applications.

    Shen, Zong-Yang; Li, Jing-Feng; Chen, Ruimin; Zhou, Qifa; Shung, K Kirk

    2011-05-01

    Fine-grained Pb-free (Na(0.535)K(0.485))(0.95)Li(0.05)(Nb(0.8)Ta(0.2))O(3) (NKLNT) piezoceramics prepared by spark plasma sintering (SPS) technique was used to fabricate NKLNT/epoxy 1-3 composites with a modified dice-fill method. Because of its good machinability, SPSed NKLNT ceramic rods could be miniaturized to a lateral width of 50 µm. After lapping down to 56 µm in thickness, the composite was used to fabricate an ultrasonic transducer as the active piezoelectric element. This composite transducer showed a bandwidth at -6 dB nearly 90%at a center frequency of 29 MHz, demonstrating that this Pb-free composite thick film is very promising for the fabrication of high-frequency ultrasonic transducers in medical imaging applications.

  11. Mikrostruktur dan Karakterisasi Sifat Mekanik Lapisan Cr3C2-NiAl-Al2O3 Hasil Deposisi Dengan Menggunakan High Velocity Oxygen Fuel Thermal Spray Coating

    Edy Riyanto

    2012-03-01

    Full Text Available Surface coating processing of industrial component with thermal spray coatings have been applied in many industrial fields. Ceramic matrix composite coating which consists of Cr3C2-Al2O3-NiAl had been carried out to obtain layers of material that has superior mechanical properties to enhance component performance. Deposition of CMC with High Velocity Oxygen Fuel (HVOF thermal spray coating has been employed. This study aims to determine the effect of powder particle size on the microstructure, surface roughness and hardness of the layer, by varying the NiAl powder particle size. Test results show NiAl powder particle size has an influence on the mechanical properties of CMC coating. Hardness of coating increases and surface roughness values of coating decrease with smaller NiAl particle size.  

  12. High Temperature Oxidation of Nickel-based Cermet Coatings Composed of Al2O3 and TiO2 Nanosized Particles

    Farrokhzad, M. A.; Khan, T. I.

    2014-09-01

    New technological challenges in oil production require materials that can resist high temperature oxidation. In-Situ Combustion (ISC) oil production technique is a new method that uses injection of air and ignition techniques to reduce the viscosity of bitumen in a reservoir and as a result crude bitumen can be produced and extracted from the reservoir. During the in-situ combustion process, production pipes and other mechanical components can be exposed to air-like gaseous environments at extreme temperatures as high as 700 °C. To protect or reduce the surface degradation of pipes and mechanical components used in in-situ combustion, the use of nickel-based ceramic-metallic (cermet) coating produced by co-electrodeposition of nanosized Al2O3 and TiO2 have been suggested and earlier research on these coatings have shown promising oxidation resistance against atmospheric oxygen and combustion gases at elevated temperatures. Co-electrodeposition of nickel-based cermet coatings is a low-cost method that has the benefit of allowing both internal and external surfaces of pipes and components to be coated during a single electroplating process. Research has shown that the volume fraction of dispersed nanosized Al2O3 and TiO2 particles in the nickel matrix which affects the oxidation resistance of the coating can be controlled by the concentration of these particles in the electrolyte solution, as well as the applied current density during electrodeposition. This paper investigates the high temperature oxidation behaviour of novel nanostructured cermet coatings composed of two types of dispersed nanosized ceramic particles (Al2O3 and TiO2) in a nickel matrix and produced by coelectrodeposition technique as a function of the concentration of these particles in the electrolyte solution and applied current density. For this purpose, high temperature oxidation tests were conducted in dry air for 96 hours at 700 °C to obtain mass changes (per unit of area) at specific time

  13. Study of the Synchrotron Photoionization Oxidation of 2-Methylfuran Initiated by O(3P) under Low-Temperature Conditions at 550 and 650 K.

    Fathi, Yasmin; Meloni, Giovanni

    2017-09-21

    The O-( 3 P)-initiated oxidation of 2-methylfuran (2-MF) was investigated using vacuum-ultraviolet synchrotron radiation from the Advanced Light Source at Lawrence Berkeley National Laboratory. Reaction species were studied by multiplexed photoionization mass spectrometry at 550 and 650 K. The oxygen addition pathway is favored in this reaction, forming four triplet diradicals that undergo intersystem crossing into singlet epoxide species that lead to the formation of products at m/z 30 (formaldehyde), 42 (propene), 54 (1-butyne, 1,3-butadiene, and 2-butyne), and 70 (2-butenal, methyl vinyl ketone, and 3-butenal). Mass-to-charge ratios, photoionization spectra, and adiabatic ionization energies for each primary reaction species were obtained and used to characterize their identities. In addition, by means of electronic structure calculations, potential energy surface scans of the different species produced throughout the oxidation were examined to further validate the primary chemistry occurring. Branching fractions for the formation of the primary products were calculated at the two temperatures and contribute 81.0 ± 21.4% at 550 K and 92.1 ± 25.5% at 650 K.

  14. Embedding ultrafine ZnSnO3 nanoparticles into reduced graphene oxide composites as high-performance electrodes for lithium ion batteries

    Ma, Yuhang; Jiang, Ranran; Li, Dan; Dong, Yutao; Liu, Yushan; Zhang, Jianmin

    2018-05-01

    Ultrafine ZnSnO3 nanoparticles, with an average diameter of 45 nm, homogeneously grown on reduced graphene oxide (rGO) have been successfully fabricated via methods of low temperature coprecipitation, colloid electrostatic self-assembly, and hydrothermal treatment. The uniformly distributed ZnSnO3 nanocrystals could inhibit the restacking of rGO sheets. In turn, the existence of rGO could hinder the growth and aggregation of ZnSnO3 nanoparticles in the synthesis process, increase the conductivity of the composite, and buffer the volume expansion of the ZnSnO3 nanocrystals upon lithium ion insertion and extraction. The obtained ZnSnO3/rGO exhibited superior cycling stability with a discharge/charge capacity of 718/696 mA h g-1 after 100 cycles at a current density of 0.1 A g-1.

  15. Synthesis of rare-earth selenate and selenite materials under 'sol-gel' hydrothermal conditions: crystal structures and characterizations of La(HSeO3)(SeO4) and KNd(SeO4)2

    Liu Wei; Chen Haohong; Yang Xinxin; Li Mangrong; Zhao Jingtai

    2004-01-01

    Two rare-earth compounds containing selenium atoms, La(HSeO 3 )(SeO 4 ) with a new open framework structure and KNd(SeO 4 ) 2 with a layered structure, have been synthesized under ''sol-gel'' hydrothermal conditions for the first time. Single-crystals of La(HSeO 3 )(SeO 4 ) crystallize in the monoclinic system (P2 1 , a=8.5905(17)A, b=7.2459(14)A, c=9.5691(19)A, β=104.91(3) o , Z=2, RAll=0.032). The structure contains puckered polyhedral layers made of LaO x (x=9,10) and SeO 4 groups, which are connected via SeO 3 -uints to the 3D structure. The crytal structure of KNd(SeO 4 ) 2 (monoclinc, P2 1 /c, a=8.7182(17)A, b=7.3225(15)A, c=11.045(2)A, β=91.38(3) o , Z=4, RAll=0.051) contains honeycomb-like six-ring NdO 9 polyhedra forming layers which are further decorated with SeO 4 tetrahedra. The K + ions occupy the interspaces of these layers and provide the charge balance

  16. Structure and thermal expansion of Lu2O3 and Yb2O3 up to the melting points

    Pavlik, Alfred; Ushakov, Sergey V.; Navrotsky, Alexandra; Benmore, Chris J.; Weber, Richard J. K.

    2017-11-01

    Knowledge of thermal expansion and high temperature phase transformations is essential for prediction and interpretation of materials behavior under the extreme conditions of high temperature and intense radiation encountered in nuclear reactors. Structure and thermal expansion of Lu2O3 and Yb2O3 were studied in oxygen and argon atmospheres up to their melting temperatures using synchrotron X-ray diffraction on laser heated levitated samples. Both oxides retained the cubic bixbyite C-type structure in oxygen and argon to melting. In contrast to fluorite-type structures, the increase in the unit cell parameter of Yb2O3 and Lu2O3 with temperature is linear within experimental error from room temperature to the melting point, with mean thermal expansion coefficients (8.5 ± 0.6) · 10-6 K-1 and (7.7 ± 0.6) · 10-6 K-1, respectively. There is no indication of a superionic (Bredig) transition in the C-type structure or of a previously suggested Yb2O3 phase transformation to hexagonal phase prior to melting.

  17. Comparative analysis of the effects of tantalum doping and annealing on atomic layer deposited (Ta2O5)x(Al2O3)1−x as potential gate dielectrics for GaN/AlxGa1−xN/GaN high electron mobility transistors

    Partida-Manzanera, T.; Roberts, J. W.; Sedghi, N.; Potter, R. J.; Bhat, T. N.; Zhang, Z.; Tan, H. R.; Dolmanan, S. B.; Tripathy, S.

    2016-01-01

    This paper describes a method to optimally combine wide band gap Al 2 O 3 with high dielectric constant (high-κ) Ta 2 O 5 for gate dielectric applications. (Ta 2 O 5 ) x (Al 2 O 3 ) 1−x thin films deposited by thermal atomic layer deposition (ALD) on GaN-capped Al x Ga 1−x N/GaN high electron mobility transistor (HEMT) structures have been studied as a function of the Ta 2 O 5 molar fraction. X-ray photoelectron spectroscopy shows that the bandgap of the oxide films linearly decreases from 6.5 eV for pure Al 2 O 3 to 4.6 eV for pure Ta 2 O 5 . The dielectric constant calculated from capacitance-voltage measurements also increases linearly from 7.8 for Al 2 O 3 up to 25.6 for Ta 2 O 5 . The effect of post-deposition annealing in N 2 at 600 °C on the interfacial properties of undoped Al 2 O 3 and Ta-doped (Ta 2 O 5 ) 0.12 (Al 2 O 3 ) 0.88 films grown on GaN-HEMTs has been investigated. These conditions are analogous to the conditions used for source/drain contact formation in gate-first HEMT technology. A reduction of the Ga-O to Ga-N bond ratios at the oxide/HEMT interfaces is observed after annealing, which is attributed to a reduction of interstitial oxygen-related defects. As a result, the conduction band offsets (CBOs) of the Al 2 O 3 /GaN-HEMT and (Ta 2 O 5 ) 0.16 (Al 2 O 3 ) 0.84 /GaN-HEMT samples increased by ∼1.1 eV to 2.8 eV and 2.6 eV, respectively, which is advantageous for n-type HEMTs. The results demonstrate that ALD of Ta-doped Al 2 O 3 can be used to control the properties of the gate dielectric, allowing the κ-value to be increased, while still maintaining a sufficient CBO to the GaN-HEMT structure for low leakage currents

  18. Electrical properties and interfacial issues of high-k/Si MIS capacitors characterized by the thickness of Al2O3 interlayer

    Xing Wang

    2016-06-01

    Full Text Available A thin Al2O3 interlayer deposited between La2O3 layer and Si substrate was used to scavenge the interfacial layer (IL by blocking the out-diffusion of substrate Si. Some advantages and disadvantages of this method were discussed in detail. Evident IL reduction corroborated by the transmission electron microscopy results suggested the feasibility of this method in IL scavenging. Significant improvements in oxygen vacancy and leakage current characteristics were achieved as the thickness of Al2O3 interlayer increase. Meanwhile, some disadvantages such as the degradations in interface trap and oxide trapped charge characteristics were also observed.

  19. Capacitance and voltage matching between MnO2 nanoflake cathode and Fe2O3 nanoparticle anode for high-performance asymmetric micro-supercapacitors

    Zehua Liu; Xiaocong Tian; Xu Xu; Liang He; Mengyu Yan; Chunhua Han; Yan Li; Wei Yang; Liqiang Mai

    2017-01-01

    Planar micro-supercapacitors show great potential as the energy storage unit in miniaturized electronic devices.Asymmetric structures have been widely investigated in micro-supercapacitors,and carbon-based materials are commonly applied in the electrodes.To integrate different metal oxides in both electrodes in micro-supercapacitors,the critical challenge is the pairing of different faradic metal oxides.Herein,we propose a strategy of matching the voltage and capacitance of two faradic materials that are fully integrated into one high-performance asymmetric micro-supercapadtor by a fadle and controllable fabrication process.The fabricated micro-supercapacitors employ MnO2 as the positive active material and Fe2O3 as the negative active material,respectively.The planar asymmetric micro-supercapacitors possess a high capacitance of 60 F·cm-3,a high energy density of 12 mW·h·cm-3,and a broad operation voltage range up to 1.2 V.

  20. Optical Thin Film Coating Having High Damage Resistance in Near-Stoichiometric MgO-Doped LiTaO3

    Tateno, Ryo; Kashiwagi, Kunihiro

    2008-08-01

    Currently, High power and compact red, green, and blue (RGB) lasers are being considered for use in large screen laser televisions and reception-lobby projectors. Among these three laser sources, green semiconductor lasers are expensive and exhibit inferior performance in terms of the semiconductor material used, making it difficult to achieve a high output. In this study, we examined the use of our coating on MgO-doped LiTaO3, using a mirror coated with a multilayer film. Over a substrate, a Ta2O5 film was used to coat a high-refractive-index film layer, and a SiO2 film was used to coat a low-refractive-index film layer. To improve reflectivity, we designed the peak of the electric field intensity to be in the film layer with the low refractive index. As a result, the film endurance of 100 J/cm2 was obtained by one-on-one testing. With the nonlinear crystal material, the mirror without our coating exhibited a damage threshold of 33 J/cm2; however, after coating, this mirror demonstrated a higher damage threshold of 47 J/cm2. Thus, the film we fabricated using this technique is useful for improving the strength and durability of laser mirrors.

  1. Influence of deposition conditions on electrical and mechanical properties of Sm2O3-doped CeO2 thin films prepared by EB-PVD (+IBAD) methods. Part 1: Effective relative permittivity

    Hartmanová, Mária; Nádaždy, Vojtech; Kundracik, František; Mansilla, Catina

    2013-03-01

    Study is devoted to the effective relative permittivity ɛr of CeO2 + x. Sm2O3 thin films prepared by electron-beam physical vapour deposition and ionic beam-assisted deposition methods; ɛr was investigated by three independent ways from the bulk parallel capacitance Cp, impedance capacitance Cimp, and accumulation capacitance Cacc in dependence on the deposition conditions (deposition temperature, dopant amount x and Ar+ ion bombardment during the film deposition) used. Investigations were performed using impedance spectroscopy, capacitance-voltage and current-voltage characteristics as well as deep level transient spectroscopy. Results obtained are described and discussed.

  2. Complex structural hierarchies observed in Y2O3–Al2O3–SiO2 eutectic ceramics prepared by laser melting

    Dian-Zheng Wang

    2015-03-01

    Full Text Available Amorphous Y2O3–Al2O3–SiO2 beads were directly melted by a Nd:YAG laser. The structural features in multi-scale of the samples after solidification were investigated. The results showed that the cooling speed in the applied processing conditions was not high enough to retain the amorphous nature of ceramic beads into the consolidated bulks. In addition to an amorphous phase two crystalline phases, YAG and α-Al2O3, were formed yielding the formation of complex structural hierarchies.

  3. Comparative study of LaNiO$_3$/LaAlO$_3$ heterostructures grown by pulsed laser deposition and oxide molecular beam epitaxy

    Wrobel, F.; Mark, A. F.; Christiani, G.; Sigle, W.; Habermeier, H. -U.; van Aken, P. A.; Logvenov, G.; Keimer, B.; Benckiser, E.

    2017-01-01

    Variations in growth conditions associated with different deposition techniques can greatly affect the phase stability and defect structure of complex oxide heterostructures. We synthesized superlattices of the paramagnetic metal LaNiO3 and the large band gap insulator LaAlO3 by atomic layer-by-layer molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) and compared their crystallinity, microstructure as revealed by high-resolution transmission electron microscopy images and resistiv...

  4. Enhancement of the chemical stability in confined δ-Bi2O3

    Sanna, Simone; Esposito, Vincenzo; Andreasen, Jens Wenzel

    2015-01-01

    Bismuth-oxide-based materials are the building blocks for modern ferroelectrics1, multiferroics2, gas sensors3, light photocatalysts4 and fuel cells5,6. Although the cubic fluorite δ-phase of bismuth oxide (δ-Bi2O3) exhibits the highest conductivity of known solid-state oxygen ion conductors5, its...... instability prevents use at low temperature7–10. Here we demonstrate the possibility of stabilizing δ-Bi2O3 using highly coherent interfaces of alternating layers of Er2O3-stabilized δ-Bi2O3 and Gd2O3-doped CeO2. Remarkably, an exceptionally high chemical stability in reducing conditions and redox cycles...

  5. Interface-enhanced high-temperature superconductivity in single-unit-cell FeT e1 -xS ex films on SrTi O3

    Li, Fangsen; Ding, Hao; Tang, Chenjia; Peng, Junping; Zhang, Qinghua; Zhang, Wenhao; Zhou, Guanyu; Zhang, Ding; Song, Can-Li; He, Ke; Ji, Shuaihua; Chen, Xi; Gu, Lin; Wang, Lili; Ma, Xu-Cun; Xue, Qi-Kun

    2015-06-01

    Recently discovered high-temperature superconductivity in single-unit-cell (UC) FeSe films on SrTi O3 (STO) substrate has stimulated tremendous research interest, both experimental and theoretical. Whether this scenario could be extended to other superconductors is vital in both identifying the enhanced superconductivity mechanism and further raising the critical transition temperature (Tc). Here we successfully prepared single-UC FeT e1 -xS ex(0.1 ≤x ≤0.6 ) films on STO substrates by molecular beam epitaxy and observed U -shaped superconducting gaps (Δ ) up to ˜16.5 meV , nearly ten times the gap value (Δ ˜1.7 meV ) of the optimally doped bulk FeT e0 .6S e0 .4 single crystal (Tc˜14.5 K ). No superconducting gap has been observed on the second UC and thicker FeT e1 -xS ex films at 5.7 K, indicating the important role of the interface. This interface-enhanced high-temperature superconductivity is further confirmed by ex situ transport measurements, which revealed an onset superconducting transition temperature above 40 K, nearly two times higher than that of the optimally doped bulk FeT e0 .6S e0 .4 single crystal. This work demonstrates that interface engineering is a feasible way to discover alternative superconductors with higher Tc.

  6. Influence of High Magnetic Field and Zn Doping on Robust CO Phase of La0.5Ca0.5MnO3

    Jin, Z.; Xia, Z. C.; Wei, M.; Yang, F.; Huang, S.; Xiao, G. L.; Shang, C.; Cheng, H.; Wu, H.; Zhang, X. X.; Ouyang, Z. W.

    2017-08-01

    Magnetic and electrical transport properties of La0.5Ca0.5- x Zn x MnO3 ( x = 0, 0.1, 0.15) have been investigated in a wide magnetic field range from 0 T to 50 T. Experimental results show that doping of nonmagnetic Zn2+ ion at Ca site and application of high magnetic field had obvious tuning effects on the stability of the robust charge-order phase, inducing new magnetization and electrical transport behaviors. In particular, obvious temperature and field hysteresis was induced, leading to enhanced magnetoresistance at around room temperature. Based on the intricate interplay between the external magnetic field and chemical strain (lattice distortion) induced by the dopant, which changed the bond length and the angle of double exchange and partially destroyed the charge-order phase, a weak ferromagnetic phase formed. The hysteretic behavior and enhanced magnetoresistance can be understood based on the tuning effects of the high magnetic field and dopant on the stability of the charge-order phase.

  7. Ethanol Sensor of CdO/Al2O3/CeO2 Obtained from Ce-DOPED Layered Double Hydroxides with High Response and Selectivity

    Xu, Dongmei; Guan, Meiyu; Xu, Qinghong; Guo, Ying; Wang, Yao

    2013-04-01

    In this paper, Ce-doped CdAl layered double hydroxide (LDH) was first synthesized and the derivative CdO/Al2O3/CeO2 composite oxide was prepared by calcining Ce-doped CdAl LDH. The structure, morphology and chemical state of the Ce doped CdAl LDH and CdO/Al2O3/CeO2 were also investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), solid state nuclear magnetic resonance (SSNMR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The gas sensing properties of CdO/Al2O3/CeO2 to ethanol were further studied and compared with CdO/Al2O3 prepared from CdAl LDH, CeO2 powder as well as the calcined Ce salt. It turns out that CdO/Al2O3/CeO2 sensor shows best performance in ethanol response. Besides, CdO/Al2O3/CeO2 possesses short response/recovery time (12/72 s) as well as remarkable selectivity in ethanol sensing, which means composite oxides prepared from LDH are very promising in gas sensing application.

  8. ITO-free flexible organic photovoltaics with multilayer MoO3/LiF/MoO3/Ag/MoO3 as the transparent electrode

    Chen, Shilin; Dai, Yunjie; Zhang, Hongmei; Zhao, Dewei

    2016-01-01

    We present efficient flexible organic photovoltaics (OPVs) with multiple layers of molybdenum oxide (MoO 3 )/LiF/MoO 3 /Ag/MoO 3 as the transparent electrode, where the thin Ag layer yields high conductivity and the dielectric layer MoO 3 /LiF/MoO 3 has high transparency due to optical interference, leading to improved power conversion efficiency compared with indium tin oxide (ITO) based devices. The MoO 3 contacting organic active layer is used as a buffer layer for good hole extraction. Thus, the multilayer MoO 3 /LiF/MoO 3 /Ag/MoO 3 can improve light transmittance and also facilitate charge carrier extraction. Such an electrode shows excellent mechanical bendability with a 9% reduction of efficiency after 1000 cycles of bending due to the ductile nature of the thin metal layer and dielectric layer used. Our results suggest that the MoO 3 /LiF/MoO 3 /Ag/MoO 3 multilayer electrode is a promising alternative to ITO as an electrode in OPVs. (paper)

  9. Effects of high vacancy concentrations on the magnetic properties of La1-xMn1-yO3 (0.02≤x, y≤0.13)

    Silva, P.S. de; Richards, F.M.; Cohen, L.F.; Alonso, J.A.; Martinez-Lope, M.J.; Casais, M.T.; Thomas, K.A.; MacManus-Driscoll, J.L.

    1998-01-01

    It has been found that the synthesis conditions and subsequent annealing treatments can significantly change the magnetic and transport behavior of the colossal magnetoresistive materials of the general formula La 1-z A z MnO 3 , where A is a divalent ion. In order to clarify the role of vacancies within this structure, resistivity and magnetization measurements have been carried out on a series of samples derived from the parent compound LaMnO 3 , with La and Mn vacancies introduced by systematically varying the oxygen annealing conditions. Previous studies have shown that for a given carrier concentration, the Curie temperature of the paramagnetic to ferromagnetic transition (T c ) increases as the tolerance factor of the perovskite structure increases and then begins to decrease slowly for even higher tolerance factors. Generally, T c also increases with the Mn 4+ content, consistent with a double exchange mechanism responsible for ferromagnetism. In this study T c was found to decrease as the vacancy concentration (and therefore the Mn 4+ concentration) and tolerance factor both increase. The magnetic and transport data are discussed in the light of structural information obtained from neutron diffraction studies. In the present study it is found that La and Mn vacancies play a significant role in determining the physical properties of these materials: for high vacancy concentrations (x,y≥0.080) the magnetic properties are analogous to those of spin glasses associated with disorder and frustration. Semiconductorlike resistivity was observed for all samples at all temperatures. copyright 1998 American Institute of Physics

  10. Anisotropic phonon coupling in the relaxor ferroelectric (Na1/2Bi1/2)TiO3 near its high-temperature phase transition

    Cai, Ling; Toulouse, Jean; Luo, Haosu; Tian, Wei

    2014-08-01

    The lead free relaxor Na1/2Bi1/2TiO3 (NBT) undergoes a structural cubic-to-tetragonal transition near 800 K which is caused by the cooperative rotations of O6 octahedra. These rotations are also accompanied by the displacements of the cations and the formation of the polar nanodomains (PNDs) that are responsible for the characteristic dielectric dispersion of relaxor ferroelectrics. Because of their intrinsic properties, spontaneous polarization, and lack of inversion symmetry, these PNDs are also piezoelectric and can mediate an interaction between polarization and strain or couple the optic and acoustic phonons. Because PNDs introduce a local tetragonal symmetry, the phonon coupling they mediate is found to be anisotropic. In this paper we present inelastic neutron scattering results on coupled transverse acoustic (TA) and transverse optic (TO) phonons in the [110] and [001] directions and across the cubic-tetragonal phase transition at TC˜800 K. The phonon spectra are analyzed using a mode coupling model. In the [110] direction, as in other relaxors and some ferroelectric perovskites, a precipitous drop of the TO phonon into the TA branch or "waterfall" is observed at a certain qwf˜0.14 r.l.u. In the [001] direction, the highly overdamped line shape can be fitted with closely positioned bare mode energies which are largely overlapping along the dispersion curves. Two competing lattice coupling mechanism are proposed to explain these observations.

  11. High temperature spin-glass-like transition in La0.67Sr0.33MnO3 nanofibers near the Curie point.

    Lu, Ruie; Yang, Sen; Li, Yitong; Chen, Kaiyun; Jiang, Yun; Fu, Bi; Zhang, Yin; Zhou, Chao; Xu, Minwei; Zhou, Xuan

    2017-06-28

    The glassy transition of superparamagnetic (SPM) (r glass-like (SGL) behavior near the Curie point (T C ), i.e., T 0 = 330 K, in La 0.67 Sr 0.33 MnO 3 (LSMO) nanofibers (NFs) composed of nanoparticles beyond the SPM size (r ≫ r 0 ), resulting in a significant increase of the glass transition temperature. This SGL transition near the T C of bulk LSMO can be explained to be the scenario of locally ordered clusters embedded in a disordered host, in which the assembly of nanoparticles has a magnetic core-shell model driven by surface spin glass. The presence of a surface spin glass of nanoparticles was proved by the Almeida-Thouless line δT f ∝ H 2/3 , exchange bias, and reduced saturation magnetization of the NF system. Composite dynamics were found - that is, both the SPM and the super-spin-glass (SSG) behavior are found in such an NF system. The bifurcation of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization vs. temperature curves at the ZFC peak, and the flatness of FC magnetization involve SSG, while the frequency-dependent ac susceptibility anomaly follows the Vogel-Fulcher law that implies weak dipole interactions of the SPM model. This finding can help us to find a way to search for high temperature spin glass materials.

  12. Synthesis of core-shell hematite (α-Fe2O3) nanoplates: Quantitative analysis of the particle structure and shape, high coercivity and low cytotoxicity

    Tadic, Marin; Kopanja, Lazar; Panjan, Matjaz; Kralj, Slavko; Nikodinovic-Runic, Jasmina; Stojanovic, Zoran

    2017-05-01

    Hematite core-shell nanoparticles with plate-like morphology were synthesized using a one-step hydrothermal synthesis. An XRPD analysis indicates that the sample consist of single-phase α-Fe2O3 nanoparticles. SEM and TEM measurements show that the hematite sample is composed of uniform core-shell nanoplates with 10-20 nm thickness, 80-100 nm landscape dimensions (aspect ratio ∼5) and 3-4 nm thickness of the surface shells. We used computational methods for the quantitative analysis of the core-shell particle structure and circularity shape descriptor for the quantitative shape analysis of the nanoparticles from TEM micrographs. The calculated results indicated that a percentage of the shell area in the nanoparticle area (share [%]) is significant. The determined values of circularity in the perpendicular and oblique perspective clearly show shape anisotropy of the nanoplates. The magnetic properties revealed the ferromagnetic-like properties at room temperature with high coercivity HC = 2340 Oe, pointing to the shape and surface effects. These results signify core-shell hematite nanoparticles' for practical applications in magnetic devices. The synthesized hematite plate-like nanoparticles exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating the safe use of these nanoparticles for biomedical applications.

  13. High power density cell using nanostructured Sr-doped SmCoO3 and Sm-doped CeO2 composite powder synthesized by spray pyrolysis

    Shimada, Hiroyuki; Yamaguchi, Toshiaki; Suzuki, Toshio; Sumi, Hirofumi; Hamamoto, Koichi; Fujishiro, Yoshinobu

    2016-01-01

    High power density solid oxide electrochemical cells were developed using nanostructure-controlled composite powder consisting of Sr-doped SmCoO3 (SSC) and Sm-doped CeO2 (SDC) for electrode material. The SSC-SDC nano-composite powder, which was synthesized by spray pyrolysis, had a narrow particle size distribution (D10, D50, and D90 of 0.59, 0.71, and 0.94 μm, respectively), and individual particles were spherical, composing of nano-size SSC and SDC fragments (approximately 10-15 nm). The application of the powder to a cathode for an anode-supported solid oxide fuel cell (SOFC) realized extremely fine cathode microstructure and excellent cell performance. The anode-supported SOFC with the SSC-SDC cathode achieved maximum power density of 3.65, 2.44, 1.43, and 0.76 W cm-2 at 800, 750, 700, and 650 °C, respectively, using humidified H2 as fuel and air as oxidant. This result could be explained by the extended electrochemically active region in the cathode induced by controlling the structure of the starting powder at the nano-order level.

  14. High-rate deposition of high-quality Sn-doped In2O3 films by reactive magnetron sputtering using alloy targets

    Oka, Nobuto; Kawase, Yukari; Shigesato, Yuzo

    2012-01-01

    Sn-doped In 2 O 3 (ITO) films were deposited on heated (200 °C) fused silica glass substrates by reactive DC sputtering with mid-frequency pulsing (50 kHz) and a plasma control unit combined with a feedback system of the optical emission intensity for the atomic O* line at 777 nm. A planar In–Sn alloy target was connected to the switching unit, which was operated in the unipolar pulse mode. The power density on the target was maintained at 4.4 W cm −2 during deposition. The feedback system precisely controlled the oxidation of the target surface in “the transition region.” The ITO film with lowest resistivity (3.1 × 10 −4 Ω cm) was obtained with a deposition rate of 310 nm min −1 and transmittance in the visible region of approximately 80%. The deposition rate was about 6 times higher than that of ITO films deposited by conventional sputtering using an oxide target.

  15. Effect of the synthesis conditions on the magnetic and electrical properties of the BaFeO3-x oxide: A metamagnetic behavior

    Gil de Muro, Izaskun; Insausti, Maite; Lezama, Luis; Rojo, Teofilo

    2005-01-01

    The BaFeO 2.95 oxide has been obtained from thermal decomposition of the [BaFe(C 3 H 2 O 4 ) 2 (H 2 O) 4 ] metallo-organic precursor at 800 deg. C under atmospheric oxygen pressure as small and homogeneous particles. From electronic paramagnetic resonance data, a metallic behavior in the 230-130K temperature range has been observed. Magnetic measurements confirm the existence of a ferro-antiferromagnetic transition at 178K. The magnetic properties of the BaFeO 2.95 oxide are strongly dependent on both temperature and magnetic field with a metamagnetic behavior. The synthesis conditions play an important role on the morphology and the electrical and magnetic properties. The syntherization of the sample produces a dramatic change in the transport properties and the existence of conductivity disappears

  16. Macrodynamic study and catalytic reduction of NO by ammonia under mild conditions over Pt-La-Ce-O/Al2O3 catalysts

    Wang, Yanhui; Zhu, Jingli; Ma, Runyu

    2007-01-01

    Catalytic reduction of NO using ammonia upon series prepared catalysts under 423-573 K in a fixed bed reactor was investigated. Results showed that the performance of supported platinum catalyst could be improved by addition of La and Ce to it. Experimental studies indicated that the suitable molar ratio of Pt:La:Ce would be 1.0:3.78:3.56, Pt-La-Ce (c). Results also found Pt-La-Ce (c) catalyst had good stability and tolerance to certain amounts of sulfur compounds under the used experimental conditions. Characterization for the fresh and used catalysts showed the Pt-La-Ce (c) catalyst had a stable structure. In addition, based on experimental data and using a nonlinear regression algorithm method, an empirical macrodynamic equation was obtained in this study

  17. Characterization of optical and microstructure properties of ultraviolet Sc2O3 thin films and their damage mechanism at high laser power

    Liu Guanghui; Xue Chunrong; Jin Yunxia; Zhang Weili; Fang Ming; He Hongbo; Fan Zhengxiu

    2010-01-01

    The electron beam evaporation deposition method was employed to prepare scandium oxide (Sc 2 O 3 ) films with substrate temperatures varying from 50 to 350 degree C. A spectrophotometer, a glancing incidence X-ray diffraction spectrometer and a WYKO optical profilograph were employed to investigate the optical, microstructure properties and surface roughness of the Sc 2 O 3 films. The refractive index and the extinction coefficient were calculated from the transmittance and reflectance spectra with the help of the Essential Macleod. The laser induced damage threshold (LIDT) of the Sc 2 O 3 films was characterized by a pulsed Nd: YAG laser system at 355 nm with a pulse duration of 8 ns. A maximum value of 2.6 J/cm 2 was derived, and the LIDT results were found to vary in the opposite direction to the extinction coefficient, surface root mean square roughness and optical loss of the Sc 2 O 3 films. An optical microscope and a scanning electron microscope were used to characterize the damage morphology of the samples, and the development of damage with increasing laser energy density was recorded and discussed. The relationship between the LIDT and the deposition parameters of the Sc 2 O 3 thin films was analyzed, and the damage mechanism of the films under 355 nm laser irradiation was discussed. (authors)

  18. High Ic, YBa2Cu3O7-x films grown at very high rates by liquid assisted growth incorporating lightly Au-doped SrTiO3 buffers

    Kursumovic, A; Durrell, J H; Harrington, S; Wimbush, S; MacManus-Driscoll, J L; Maiorov, B; Zhou, H; Stan, L; Holesinger, T G; Wang, H

    2009-01-01

    YBa 2 Cu 3 O 7-x (YBCO) thick films were grown by hybrid liquid phase epitaxy (HLPE) on (001) SrTiO 3 (STO) substrates. In the presence of a 100 nm thick, 5 mol% Au-doped STO buffer, self-field critical current densities, J c sf , at 77 K of ∼2.4 MA cm -2 and critical currents, I c sf , up to 700 A (cm-width) -1 were achieved. The J c value is virtually independent of thickness and the growth rates are very high (∼1 μm min -1 ). From transmission electron microscopy (TEM), Y 2 O 3 nanocloud extended defects (∼100 nm in size) were identified as the pinning defects in the films. Enhanced random pinning was induced by the presence of Au in the buffer.

  19. Magnetic heating characteristics of La0.7SrxCa0.3-xMnO3 nanoparticles fabricated by a high energy mechanical milling method

    Do, Hung Manh; Pham, Hong Nam; Chien Nguyen, Van; Bich Hoa Phan, Thi; Tran, Dai Lam; Nguyen, Anh Tuan; Thong Phan, Quoc; Le, Van Hong; Phuc Nguyen, Xuan

    2011-09-01

    Magnetic inductive heating (MIH) of nanoparticles (NPs) attracts considerable research attention, first because of its application to hyperthermia in biological tissues. Most reports so far have dealt with magnetite NPs with a Curie temperature, TC, of as high as above 500 °C. In this paper, we present results of a MIH study in an ac field of frequency 219 and 236 kHz and strength of 40-100 Oe for several samples of La0.7SrxCa0.3-x MnO3 NPs of TC in the region of hyperthermia, that is some tens of degrees above human body temperature. The particle materials were fabricated by a high energy mechanical milling method combined with calcining at various temperatures in the range of 600-900 °C. The heating temperatures of the samples were observed to saturate at a field irradiating time of less than 10 min and at temperatures ranging from 40 to 75 °C depending on the strontium content, the NP concentration, c, and the field parameters. A sudden change in heating rate was clearly revealed in several heating curves for the case of low applied field and low c, which was considered to be related to the onset of a strong decrease in zero-field cooling (ZFC) magnetization of NPs. The initial temperature increase slope, dT/dt, and the saturation temperature, Ts will be analyzed as dependent on the NP concentration. Field dependences of the specific loss power will be analyzed and discussed for various concentrations, c. Evidence of fluid viscosity influence will also be noted.

  20. Magnetic heating characteristics of La0.7SrxCa0.3-xMnO3 nanoparticles fabricated by a high energy mechanical milling method

    Manh Do, Hung; Nam Pham, Hong; Chien Nguyen, Van; Bich Hoa Phan, Thi; Lam Tran, Dai; Tuan Nguyen, Anh; Hong Le, Van; Phuc Nguyen, Xuan; Thong Phan, Quoc

    2011-01-01

    Magnetic inductive heating (MIH) of nanoparticles (NPs) attracts considerable research attention, first because of its application to hyperthermia in biological tissues. Most reports so far have dealt with magnetite NPs with a Curie temperature, T C , of as high as above 500 °C. In this paper, we present results of a MIH study in an ac field of frequency 219 and 236 kHz and strength of 40–100 Oe for several samples of La 0.7 Sr x Ca 0.3−x MnO 3 NPs of T C in the region of hyperthermia, that is some tens of degrees above human body temperature. The particle materials were fabricated by a high energy mechanical milling method combined with calcining at various temperatures in the range of 600–900 °C. The heating temperatures of the samples were observed to saturate at a field irradiating time of less than 10 min and at temperatures ranging from 40 to 75 °C depending on the strontium content, the NP concentration, c, and the field parameters. A sudden change in heating rate was clearly revealed in several heating curves for the case of low applied field and low c, which was considered to be related to the onset of a strong decrease in zero-field cooling (ZFC) magnetization of NPs. The initial temperature increase slope, dT/dt, and the saturation temperature, T s will be analyzed as dependent on the NP concentration. Field dependences of the specific loss power will be analyzed and discussed for various concentrations, c. Evidence of fluid viscosity influence will also be noted

  1. Tribological investigation of novel HDPE-HAp-Al2O3 hybrid biocomposites against steel under dry and simulated body fluid condition.

    Nath, Shekhar; Bodhak, Subhadip; Basu, Bikramjit

    2007-10-01

    Among various biocompatible polymers, polyethylene based materials have received wider attention because of its excellent stability in body fluid, inertness, and easy formability. Attempts have been made to improve their physical properties (modulus/strength) to enable them to be used as load bearing hard tissue replacement applications. Among such attempts, high density polyethylene (HDPE)-hydroxyapatite (HAp) composite (HAPEX), has already been developed for total hip replacement (THR) acetabular cup and low load bearing bone tissue replacement. In the present work, alumina has been added as a partial replacement of HAp phase to improve the mechanical and tribological properties of the HAPEX composite. In an attempt to assess the suitability of the developed composite in THR application, the tribological properties against steel counterbody under both in air and simulated body fluid (SBF), have been investigated and efforts have been made to understand the wear mechanisms. The fretting wear study indicates the possibility of achieving extremely low COF (Coefficient of Friction approximately 0.09) as well as higher wear resistance (order of 10(-6) mm(3)/N m) with the newly developed composites in SBF. A low wear depth of approximately 4.6-5.3 microm is recorded, irrespective of fretting environment. The implication of the work is that optimal and combined addition of bioactive and bioinert ceramic filler to HDPE can provide a good opportunity to obtain hybrid biocomposites with better combination of physical properties (modulus, hardness) as well as low friction and high wear resistance.

  2. Gas-solids kinetics of CuO/Al2O3 as an oxygen carrier for high-pressure chemical looping processes : the influence of the total pressure

    San Pio Bordeje, M.A.; Gallucci, F.; Roghair, I.; van Sint Annaland, M.

    2017-01-01

    Copper oxide on alumina is often used as oxygen carrier for chemical looping combustion owing to its very high reduction rates at lower temperatures and its very good mechanical and chemical stability at not too high temperatures. In this work, the redox kinetics of CuO/Al2O3 have been studied at

  3. Diode-pumped high power 2.7 μm Er:Y2O3 ceramic laser at room temperature

    Wang, Li; Huang, Haitao; Shen, Deyuan; Zhang, Jian; Chen, Hao; Tang, Dingyuan

    2017-09-01

    Investigation of room temperature laser performance of the polycrystalline Er:Y2O3 ceramic at 2.7 μm with respect to dopant concentrations was conducted. With 7 at.% Er3+ concentration Er:Y2O3 ceramic as laser gain medium, over 2.05 W of CW output power at 2.7 μm was generated with a slope efficiency of 11.1% with respect to the absorbed LD pump power. The prospects for improvement in lasing efficiency and output power are considered.

  4. Synthesis of 0.64Pb(Mg1/3Nb2/3O3–0.36PbTiO3 ceramic near morphotropic phase boundary for high performance piezoelectric, ferroelectric and pyroelectric applications

    Abid Hussain

    2016-09-01

    Full Text Available A near MPB composition of 0.64PMN–0.36PT ceramic has been synthesized by solid-state reaction technique using columbite precursor. Sintering at 1030 °C resulted in a single perovskite phase with tetragonal structure having uniform and dense microstructure as revealed by powder XRD, Raman spectroscopy and FESEM analyses. An excellent dielectric response was obtained with room temperature dielectric permittivity value of 142 and high-phase transition temperature (Tm of 210 °C at 1 kHz. A huge value of piezoelectric charge coefficient (490 pC/N was obtained, which shows potential of PMN–PT for piezoelectric device applications. Well-shaped and fatigue-free P–E hysteresis loops over a wide temperature range of 30–230 °C were traced. A very large value of pyroelectric coefficient (p ∼ 2739.2 μC m−2 °C−1 was obtained.

  5. Ferromagnetic clusters in polycrystalline BaCoO3

    Botta, P.M.; Pardo, V.; Calle, C. de la; Baldomir, D.; Alonso, J.A.; Rivas, J.

    2007-01-01

    Polycrystalline BaCoO 3 was synthesized by a citrate technique using thermal treatments at high oxygen pressure. Magnetic susceptibility measurements on the compound were carried out under AC conditions. The magnetic properties of the material at low temperatures were found to be determined by the appearance of nanoscale ferromagnetic (FM) regions and not by a true magnetic phase transition. These clusters have a mean size of about 1 nm in diameter and obey an Arrhenius-like thermal relaxation

  6. Nanoblast synthesis and consolidation of (La0.8Sr0.2)(Ga0.9Mg0.1)O(3-delta) under Spark plasma sintering conditions.

    Vasylkiv, Oleg; Borodianska, Hanna; Badica, Petre; Zhen, Yongda; Tok, Alfred

    2009-01-01

    Four-cation nanograined strontium and magnesium doped lanthanum gallate (La0.8Sr0.2) (Ga0.9Mg0.1)O(3-delta) (LSGM) and its composite with 2 wt% of ceria (LSGM-Ce) were prepared. Morphologically homogeneous nanoreactors, i.e., complex intermediate metastable aggregates of desired composition were assembled by spray atomization technique, and subsequently loaded with nanoparticles of highly energetic C3H6N6O6. Rapid nanoblast calcination technique was applied and the final composition was synthesized within the preliminary localized volumes of each single nanoreactor on the first step of spark plasma treatment. Subsequent SPS consolidations of nanostructured extremely active LSGM and LSGM-Ce powders were achieved by rapid treatment under pressures of 90-110 MPa. This technique provided the heredity of the final structure of nanosize multimetal oxide, allowed the prevention of the uncontrolled agglomeration during multicomponent aggregates assembling, subsequent nanoblast calcination, and final ultra-rapid low-temperature SPS consolidation of nanostructured ceramics. LaSrGaMgCeO(3-delta) nanocrystalline powder consisting of approximately 11 nm crystallites was consolidated to LSGM-Ce nanoceramic with average grain size of approximately 14 nm by low-temperature SPS at 1250 degrees C. Our preliminary results indicate that nanostructured samples of (La0.8Sr0.2)(Ga0.9Mg0.1)O(3-delta) with 2 wt% of ceria composed of approximataley 14 nm grains can exhibit giant magnetoresistive effect in contrast to the usual paramagnetic properties measured on the samples with larger grain size.

  7. Epitaxial Gd2O3 on GaN and AlGaN: a potential candidate for metal oxide semiconductor based transistors on Si for high power application

    Ghosh, Kankat; Das, S.; Khiangte, K. R.; Choudhury, N.; Laha, Apurba

    2017-11-01

    We report structural and electrical properties of hexagonal Gd2O3 grown epitaxially on GaN/Si (1 1 1) and AlGaN/GaN/Si(1 1 1) virtual substrates. GaN and AlGaN/GaN heterostructures were grown on Si(1 1 1) substrates by plasma assisted molecular beam epitaxy (PA-MBE), whereas the Gd2O3 layer was grown by the pulsed laser ablation (PLA) technique. Initial structural characterizations show that Gd2O3 grown on III-nitride layers by PLA, exhibit a hexagonal structure with an epitaxial relationship as {{≤ft[ 0 0 0 1 \\right]}G{{d2}{{O}3}}}||{{≤ft[ 0 0 0 1 \\right]}GaN} and {{≤ft[ 1 \\bar{1} 0 0 \\right]}G{{d2}{{O}3}}}||{{≤ft[ 1 \\bar{1} 0 0 \\right]}GaN} . X-ray photoelectron measurements of the valence bands revealed that Gd2O3 exhibits band offsets of 0.97 eV and 0.4 eV, for GaN and Al0.3Ga0.7N, respectively. Electrical measurements such as capacitance-voltage and leakage current characteristics further confirm that epi-Gd2O3 on III-nitrides could be a potential candidate for future metal-oxide-semiconductor (MOS)-based transistors also for high power applications in radio frequency range.

  8. Nonstoichiometry of Epitaxial FeTiO(3+delta) Films

    2003-01-01

    nonstoichiometry of the FeTiO3 +8 films was probably produced by cation vacancies and disarrangement of Fe3+ and Ti4 ions, which randomly occupied both interstitial...and substitutional sites of the FeTiO 3 related structure. INTRODUCTION Solid solutions of ot-Fe20 3- FeTiO3 (hematite-ilmenite) series are known to...tried to confirm preparation conditions of stoichiometric FeTiO 3 films. According to a literature on bulk crystal growth of FeTiO3 [5], very low oxygen

  9. Effect of sintering condition on the microstructure and electrical properties of lead-free (Na0.5K0.5NbO3 - Bi0.5(Na0.83K0.170.5TiO3 ceramics

    Wang Chun Huy

    2017-01-01

    Full Text Available In this work, the piezoelectric ceramic system of the (1-x(Na0.5K0.5NbO3 - xBi(Na0.83K0.17TiO3 with composition close to the morphotropic phase boundary is studied. (Na0.5K0.5NbO3 with 0∼5 mole% Bi(Na0.83K0.17TiO3 has been prepared following the conventional mixed oxide process. The effect of sintering time on the properties of 0.97(Na0.5K0.5NbO3-0.03Bi(Na0.83K0.17TiO3 ceramics is discussed. For 0.97(Na0.5K0.5NbO3-0.03Bi(Na0.83K0.17TiO3 ceramics, the electromechanical coupling coefficients of the thickness mode kt and the piezoelectric constant d33 reach 0.46 and 155 p/CN, respectively, at the sintering of 1100 °C for 3 h. Dielectric and piezoelectric properties have maximum values at the sintering temperature of 1100 °C for 5 h. For 0.97(Na0.5K0.5NbO3 -0.03Bi(Na0.83K0.17TiO3 ceramics, the electromechanical coupling coefficients of the thickness mode kt and the piezoelectric constant d33 reach 0.56 and 190, respectively, at the sintering of 1100 °C for 5 h. The effect of prolonging the sintering time to the 0.97(Na0.5K0.5NbO3-0.03Bi(Na0.83K0.17TiO3 system is a helpful method on ceramic processing to improve densification and properties.

  10. High-temperature electrolysis of CO2-enriched mixtures by using fuel-electrode supported La0.6Sr0.4CoO3/YSZ/Ni-YSZ solid oxide cells

    Kim, Si-Won; Bae, Yonggyun; Yoon, Kyung Joong; Lee, Jong-Ho; Lee, Jong-Heun; Hong, Jongsup

    2018-02-01

    To mitigate CO2 emissions, its reduction by high-temperature electrolysis using solid oxide cells is extensively investigated, for which excessive steam supply is assumed. However, such condition may degrade its feasibility due to massive energy required for generating hot steam, implying the needs for lowering steam demand. In this study, high-temperature electrolysis of CO2-enriched mixtures by using fuel-electrode supported La0.6Sr0.4CoO3/YSZ/Ni-YSZ solid oxide cells is considered to satisfy such needs. The effect of internal and external steam supply on its electrochemical performance and gas productivity is elucidated. It is shown that the steam produced in-situ inside the fuel-electrode by a reverse water gas shift reaction may decrease significantly the electrochemical resistance of dry CO2-fed operations, attributed to self-sustaining positive thermo-electrochemical reaction loop. This mechanism is conspicuous at low current density, whereas it is no longer effective at high current density in which total reactant concentrations for electrolysis is critical. To overcome such limitations, a small amount of external steam supply to the CO2-enriched feed stream may be needed, but this lowers the CO2 conversion and CO/H2 selectivity. Based on these results, it is discussed that there can be minimum steam supply sufficient for guaranteeing both low electrochemical resistance and high gas productivity.

  11. A facile route to large-scale synthesis MoO2 and MoO3 as electrode materials for high-performance supercapacitors

    Xuan, H.C.; Du, Y.W.; Zhang, Y.Q.; Xu, Y.K.; Li, H.; Han, P.D.; Wang, D.H.

    2016-01-01

    MoO 3 and MoO 2 materials have been successfully synthesized by thermal decomposition of ammonium paramolybdate in air and a sealed quartz tube, respectively. The microstructure of as-synthesized MoO 3 is composed of irregular lamellar plates with a plate thickness around 100 nm and MoO 2 has the larger grain size with lamellar plates connected with each other. A maximum specific capacitance of 318 F/g at 0.5 A/g is obtained for MoO 2 prepared in a closed environment. On the other hand, the sample MoO 3 exhibits excellent rate capacity with specific capacitances of 218, 209, 196, 188, 176, and 160 F/g at current densities of 0.5, 1, 2, 3, 4, and 5 A/g, respectively. These results pave the way to consider MoO 3 and MoO 2 as prospective materials for energy-storage applications. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. High pressure study of low compressibility tetracalcium aluminum carbonate hydrates 3CaO·Al2O3·CaCO3·11H2O

    Moon, Juhyuk; Oh, Jae Eun; Balonis, Magdalena; Glasser, Fredrik P.; Clark, Simon M.; Monteiro, Paulo J.M.

    2012-01-01

    Synchrotron X-ray diffraction data was collected from a sample of monocarboaluminate 3CaO•Al2O3•CaCO 3•11H2O from ambient pressure to 4.3 GPa. The refined crystal structure at ambient pressure is triclinic with parameters a = 5.77(2) Å, b = 8

  13. New theory of effective work functions at metal/high-k dielectric interfaces : application to metal/high-k HfO2 and la2O 3 dielectric interfaces

    Shiraishi, Kenji; Nakayama, Takashi; Akasaka, Yasushi; Miyazaki, Seiichi; Nakaoka, Takashi; Ohmori, Kenji; Ahmet, Parhat; Torii, Kazuyoshi; Watanabe, Heiji; Chikyow, Toyohiro; Nara, Yasuo; Iwai, Hiroshi; Yamada, Keisaku

    2006-01-01

    We have constructed a universal theory of the work functions at metal/high-k HfO2 and La2O3 dielectric interfaces by introducing a new concept of generalized charge neutrality levels. Our theory systematically reproduces the experimentally observed work functions of various gate metals on Hf-based high-k dielectrics, including the hitherto unpredictable behaviors of the work functions of p-metals. Our new concept provides effective guiding principles to achieving near-bandedge work functions ...

  14. Fabrication and characterization of Al2O3 /Si composite nanodome structures for high efficiency crystalline Si thin film solar cells

    Ruiying Zhang

    2015-12-01

    Full Text Available We report on our fabrication and characterization of Al2O3/Si composite nanodome (CND structures, which is composed of Si nanodome structures with a conformal cladding Al2O3 layer to evaluate its optical and electrical performance when it is applied to thin film solar cells. It has been observed that by application of Al2O3thin film coating using atomic layer deposition (ALD to the Si nanodome structures, both optical and electrical performances are greatly improved. The reflectivity of less than 3% over the wavelength range of from 200 nm to 2000 nm at an incident angle from 0° to 45° is achieved when the Al2O3 film is 90 nm thick. The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively. Electrical characterization was made by using CND-decorated MOS devices to measure device’s leakage current and capacitance dispersion. It is found the electrical performance is sensitive to the thickness of the Al2O3 film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10−9 A/cm2 over voltage range of from -3 V to 3 V, is reduced by several orders of magnitude. C-V measurements also shows as small as 0.3% of variation in the capacitance over the frequency range from 10 kHz to 500 kHz, which is a strong indication of surface states being fully passivated. TEM examination of CND-decorated samples also reveals the occurrence of SiOx layer formed between the interface of Si and the Al2O3 film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al2O3 coated CND structures is a truly viable approach to achieving higher device efficiency.

  15. Mg shallow doping effects on the ac magnetic self-heating characteristics of γ-Fe2O3 superparamagnetic nanoparticles for highly efficient hyperthermia

    Jang, Jung-tak; Bae, Seongtae

    2017-10-01

    The effects of Mg doping on the magnetic and AC self-heating temperature rising characteristics of γ-Fe2O3 superparamagnetic nanoparticles (SPNPs) were investigated for hyperthermia applications in biomedicine. The doping concentration of nonmagnetic Mg2+ cation was systematically controlled from 0 to 0.15 at. % in Mgx-γFe2O3 SPNPs during chemically and thermally modified one-pot thermal decomposition synthesis under bubbling O2/Ar gas mixture. It was empirically observed that the saturation magnetization (Ms) and the out-of-phase magnetic susceptibility ( χm″)of Mgx-γFe2O3 SPNPs were increased by increasing the Mg2+ cation doping concentration from 0.05 to 0.13 at. %. Correspondingly, the AC magnetically induced self-heating temperature (Tac,max) in solid state and the intrinsic loss power in water were increased up to 184 °C and 14.2 nH m2 kg-1 (Mgx-γFe2O3, x = 0.13), respectively, at the biologically and physiologically safe range of AC magnetic field (Happl × fappl = 1.2 × 109 A m-1 s-1). All the chemically and physically analyzed results confirmed that the dramatically improved AC magnetic induction heating characteristics and the magnetic properties of Mgx-γFe2O3 SPNPs (x = 0.13) are primarily due to the significantly enhanced magnetic susceptibility (particularly, χm″) and the improved AC/DC magnetic softness (lower AC/DC magnetic anisotropy) resulting from the systematically controlled nonmagnetic Mg2+ cation concentrations and distributions (occupation ratio) in the Fe vacancy sites of γ-Fe2O3 (approximately 12% vacancy), instead of typically well-known Fe3O4 (no vacancy) SPNPs. The cell viability and biocompatibility with U87 MG cell lines demonstrated that Mgx-γFe2O3 SPNPs (x = 0.13) has promising bio-feasibility for hyperthermia agent applications.

  16. Growth mechanism of NaClO 3 and NaBrO 3 crystals from aqueous ...

    A study of growth rates of NaClO3 and NaBrO3 has been carried out using a small growth cell by in situ observation. Normal growth rates of {100} faces of NaClO3 and {111} faces of NaBrO3 along ⟨ 110 ⟩ direction are measured under relatively high supersaturation ranging from 3–8%. In the initial stages of growth, {100}, ...

  17. The influence of Cd-dopant on the properties of α-FeOOH and α-Fe2O3 particles precipitated in highly alkaline media

    Krehula, Stjepko; Music, Svetozar

    2007-01-01

    The effects of Cd-dopant on the phenomenology of the precipitation of α-(Fe, Cd)OOH and α-(Fe, Cd) 2 O 3 particles, the formation of solid solutions, particle size and their geometrical shapes were investigated using Moessbauer and Fourier transform infrared (FT-IR) spectroscopies, field emission scanning electron microscopy (FE SEM) and energy dispersive X-ray analysis (EDS). The formation of merely α-(Fe, Cd)OOH solid solutions was measured up to r = 0.0196, where r = [Cd]/([Cd] + [Fe]). The formation of two types of solid solutions, α-(Fe, Cd)OOH and α-(Fe, Cd) 2 O 3 was found at r between 0.0291 and 0.0698, whereas the formation of an α-(Fe, Cd) 2 O 3 solid solution alone was obtained at r = 0.0909. The incorporation of Cd-substitutions into α-FeOOH and α-Fe 2 O 3 structures decreased the hf > values of the corresponding hyperfine magnetic field. The IR band at 639 cm -1 , recorded for α-FeOOH, was found to be sensitive to Cd-substitutions. With an increased r value a gradual elongation of α-(Fe, Cd)OOH particles along the c-axis was observed, with the maximum elongation (∼600-700 nm) obtained at r = 0.0476. At the same time, particle width (b-axis direction) and thickness (a-axis direction) showed a gradual decrease. With a further increase in the r value the length of α-(Fe, Cd)OOH particles rapidly decreased. α-(Fe, Cd) 2 O 3 particles ∼100-200 nm in size were obtained at r = 0.0909

  18. O3 and NOx Exchange

    Loubet, B.; Castell, J.F.; Laville, P.; Personne, E.; Tuzet, A.; Ammann, C.; Emberson, L.; Ganzeveld, L.; Kowalski, A.S.; Merbold, L.; Stella, P.; Tuovinen, J.P.

    2015-01-01

    This discussion was based on the background document “Review on modelling atmosphere-biosphere exchange of Ozone and Nitrogen oxides”, which reviews the processes contributing to biosphere-atmosphere exchange of O3 and NOx, including stomatal and non-stomatal exchange of O3 and NO, NO2.

  19. Electromechanical behavior of [001]-textured Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics

    Yan, Yongke; Wang, Yu. U.; Priya, Shashank

    2012-05-01

    [001]-textured Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) ceramics were synthesized by using templated grain growth method. Significantly high [001] texture degree corresponding to 0.98 Lotgering factor was achieved at 1 vol. % BaTiO3 template. Electromechanical properties for [001]-textured PMN-PT ceramics with 1 vol. % BaTiO3 were found to be d33 = 1000 pC/N, d31 = 371 pC/N, ɛr = 2591, and tanδ = ˜0.6%. Elastoelectric composite based modeling results showed that higher volume fraction of template reduces the overall dielectric constant and thus has adverse effect on the piezoelectric response. Clamping effect was modeled by deriving the changes in free energy as a function of applied electric field and microstructural boundary condition.

  20. High index surfaces of Au-nanocrystals supported on one-dimensional MoO3-nanorod as a bi-functional electrocatalyst for ethanol oxidation and oxygen reduction

    Karuppasamy, L.; Chen, C.Y.; Anandan, S.; Wu, J.J.

    2017-01-01

    Highlights: •Synthesis of a new class of Au nanocrystals enclosed with high index surface supported on MoO 3 nanorods by ultrasonic probe method. •The role of supporting materials reduces the loading of Au and acts as a co-catalyst. •The as prepared electrocatalyst exhibits enhanced catalytic activity and stability towards both EOR and ORR. -- Abstract: The design of highly active electrocatalyst for ethanol electrooxidation (EOR) and oxygen reduction reaction (ORR) is of great significance for the improvement of efficient direct ethanol fuel cells (DEFCs). Therefore, creating high index facets nanocrystals with abundant catalytic active sites of stepped atoms is an effective way to enhance the electrocatalytic performance. In this article, we prepared the high index surface structures of Au nanocrystals supported on one-dimensional (1-D) MoO 3 nanorods by using two steps ultrasonic probe irradiation method. The size and physical properties of as electrocatalysts were studied by using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD) instrumentation. Besides, the catalytic activity of as Au-MoO 3 electrocatalyst was determined by using cyclic voltammetry (CV), chronoamperometric (CA), electrochemical impedance spectroscopy (EIS), CO-stripping, and linear sweep voltammetry-rotating disk electrode (LSV-RDE). As a consequence, the Au-MoO 3 nanocomposites has been considered as an effective electrocatalyst for both ethanol oxidation and oxygen reduction reaction.

  1. LaNiO3 buffer layers for high critical current density YBa2Cu3O7-δ and Tl2Ba2CaCu2O8-δ films

    Carlson, C.M.; Parilla, P.A.; Siegal, M.P.; Ginley, D.S.; Wang, Y.; Blaugher, R.D.; Price, J.C.; Overmyer, D.L.; Venturini, E.L.

    1999-01-01

    We demonstrate high critical current density superconducting films of YBa 2 Cu 3 O 7-δ (YBCO) and Tl 2 Ba 2 CaCu 2 O 8-δ (Tl-2212) using LaNiO 3 (LNO) buffer layers. YBCO films grown on an LNO buffer layer have only a slightly lower J c (5 K, H=0) than films grown directly on a bare LaAlO 3 substrate. YBCO films grown on LNO buffer layers exhibit minor microstructural disorder and enhanced flux pinning. LNO-buffered Tl-2212 samples show large reductions in J c at all temperatures and fields compared to those grown on bare LaAlO 3 , correlating to both a-axis grain and nonsuperconducting phase formation. LNO could be a promising buffer layer for both YBCO and Tl-based superconducting films in coated conductor applications. copyright 1999 American Institute of Physics

  2. LaNiO3 Buffer Layers for High Critical Current Density YBa2Cu3O7δ and Tl2Ba2CaCu2O8δ Films

    Carlson, C.M.; Parilla, P.A.; Siegal, M.P.; Ginley, D.S.; Wang, Y.-T.; Blaugher, R.D.; Price, J.C.; Overmyer, D.L.; Venturini, E.L.

    1999-01-01

    We demonstrate high critical current density superconducting films of YBa 2 Cu 3 O 7-δ (YBCO) and Tl 2 Ba 2 CaCu 2 O 8-δ (Tl-2212) using LaNiO 3 (LNO) buffer layers. YBCO films grown on an LNO buffer layer have only a slightly lower J c (5K, H=0) than films grown directly on a bare LaAlO 3 substrate. It is noteworthy that YBCO films grown on LNO buffer layers exhibit minor microstructural disorder and enhanced flux pinning. LNO-buffered Tl-2212 samples show large reductions in J c at all temperatures and fields compared to those grown on bare LaAlO 3 , correlating to both a-axis grain and nonsuperconducting phase formation. With additional optimization, LNO could be a promising buffer layer for both YBCO and Tl-based superconducting films, perhaps ideally suited for coated conductor applications

  3. Investigation of the structure and properties of (KxNa1-x)NbO3-based piezoelectric ceramics using both conventional and high-throughput experimentation (HTE) methods

    Mgbemere, Henry Ekene

    2012-01-01

    The structure and properties of (K x Na 1-x )NbO 3 lead-free piezoelectric ceramics was investigated in this work. Both the conventional mixed-oxide ceramics synthesis route and the high-throughput experimentation (HTE) approaches were employed for the synthesis. Structural characterization was carried out with synchrotron X-rays while the electrical properties were characterized with techniques (dielectric measurement, hysteresis measurements, impedance measurements etc). Both isovalent and aliovalent elements (Ta, Sb, Li) were used to dope (K x Na 1-x )NbO 3 ceramics in order to improve its piezoelectric properties and sinterability.

  4. Synthesis, characterization and photocatalysis enhancement of Eu2O3-ZnO mixed oxide nanoparticles

    Mohamed, W. S.; Abu-Dief, Ahmed M.

    2018-05-01

    Pure ZnO nanoparticles (NPs) and mixed Eu2O3 and ZnO NPs with different Eu2O3 ratios (5%, 10%, and 15%) were synthesized by a precipitation method under optimum conditions. The synthesized samples were characterized by means of X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and UV-vis diffuse reflectance spectroscopy. The as-synthesized ZnO NPs exhibit high phase purity and a highly crystalline wurtzite ZnO structure. The mixed Eu2O3 and ZnO NPs exhibit a Eu2O3 zinc blend phase in addition to the wurtzite phase of pure ZnO, confirming the high purity and good crystallinity of the as-synthesized samples. The high-purity formation of ZnO and Eu2O3 phases was confirmed by FTIR and Raman spectra. Microstructural analysis by SEM and TEM confirmed the sphere-like morphology with different particle sizes (29-40 nm) of the as-synthesized samples. The photocatalytic activities of pure ZnO NPs and mixed Eu2O3 and ZnO NPs for the degradation of methylene blue were evaluated under ultraviolet (UV) irradiation. The results show that Eu2O3 plays an important role in the enhancement of the photocatalytic properties of ZnO NPs. We found that mixed 5% Eu2O3 and ZnO NPs exhibit the highest photocatalytic activity (degradation efficiency of 96.5% after 180 min of UV irradiation) as compared with pure ZnO NPs (degradation efficiency of 80.3% after 180 min of UV irradiation). The increased photocatalytic activity of the optimum mixed Eu2O3 and ZnO NPs is due to the high crystallinity, high surface area with small particle size, and narrow energy gap.

  5. Effect of the thin Ga2O3 layer in n+-ZnO/n-Ga2O3/p-Cu2O heterojunction solar cells

    Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

    2013-01-01

    The influence of inserting a Ga 2 O 3 thin film as an n-type semiconductor layer on the obtainable photovoltaic properties in Cu 2 O-based heterojunction solar cells was investigated with a transparent conductive Al-doped ZnO (AZO) thin film/n-Ga 2 O 3 thin film/p-Cu 2 O sheet structure. It was found that this Ga 2 O 3 thin film can greatly improve the performance of Cu 2 O-based heterojunction solar cells fabricated using polycrystalline Cu 2 O sheets that had been prepared by a thermal oxidization of copper sheets. The obtained photovoltaic properties in the AZO/Ga 2 O 3 /Cu 2 O heterojunction solar cells were strongly dependent on the deposition conditions of the Ga 2 O 3 films. The external quantum efficiency obtained in AZO/Ga 2 O 3 /Cu 2 O heterojunction solar cells was found to be greater at wavelengths below approximately 500 nm than that obtained in AZO/Cu 2 O heterojunction solar cells (i.e., prepared without a Ga 2 O 3 layer) at equivalent wavelengths. This improvement of photovoltaic properties is mainly attributed to a decrease in the level of defects at the interface between the Ga 2 O 3 thin film and the Cu 2 O sheet. Conversion efficiencies over 5% were obtained in AZO/Ga 2 O 3 /Cu 2 O heterojunction solar cells fabricated using an n-Ga 2 O 3 thin-film layer prepared with a thickness of 40–80 nm at an O 2 gas pressure of approximately 1.7 Pa by a pulsed laser deposition. - Highlights: • We demonstrate high-efficiency Cu 2 O-based p-n heterojunction solar cells. • A non-doped Ga 2 O 3 thin film was used as an n-type semiconductor layer. • The Ga 2 O 3 thin film was prepared at a low temperature by a low damage deposition. • p-type Cu 2 O sheets prepared by thermal oxidization of copper sheets were used. • Conversion efficiencies over 5% were obtained in AZO/n-Ga 2 O 3 /p-Cu 2 O solar cells

  6. High-sensitivity β-Ga_2O_3 solar-blind photodetector on high-temperature pretreated c-plane sapphire substrate

    Qian, Ling-Xuan; Zhang, Hua-Fan; Lai, P. T.; Wu, Ze-Han; Liu, Xing-Zhao

    2017-01-01

    -annealing temperature must be sufficiently high to offset the rise of the dark current and thus achieve a remarkable improvement in the photodetection properties. As a result, the PD fabricated on the 1050 degrees C-annealed substrate exhibited extremely high

  7. Positron annihilation studies on the behaviour of vacancies in LaAlO3/SrTiO3 heterostructures

    Yuan, Guoliang; Li, Chen; Yin, Jiang; Liu, Zhiguo; Wu, Di; Uedono, Akira

    2012-11-01

    The formation and diffusion of vacancies are studied in LaAlO3/SrTiO3 heterostructures. Oxygen vacancies (VOS) appear easily in the SrTiO3 substrate during LaAlO3 film growth at 700 °C and 10-4 Pa oxygen pressure rather than at 10-3-10-1 Pa, thus the latter two-dimensional electron gas should come from the polarity discontinuity at the (LaO)+/(TiO2)0 interface. For SrTiO3-δ/LaAlO3/SrTiO3, high-density VOS of the SrTiO3-δ film can pass through the LaAlO3 film and then diffuse to 1.7 µm depth in the SrTiO3 substrate, suggesting that LaAlO3 has VOS at its middle-deep energy levels within the band gap. Moreover, high-density VOS may combine with a strontium/titanium vacancy (VSr/Ti) to form VSr/Ti-O complexes in the SrTiO3 substrate at 700 °C.

  8. Core-satellite Ag@BaTiO3 nanoassemblies for fabrication of polymer nanocomposites with high discharged energy density, high breakdown strength and low dielectric loss.

    Xie, Liyuan; Huang, Xingyi; Li, Bao-Wen; Zhi, Chunyi; Tanaka, Toshikatsu; Jiang, Pingkai

    2013-10-28

    Dielectric polymer nanocomposites with high dielectric constant have wide applications in high energy density electronic devices. The introduction of high dielectric constant ceramic nanoparticles into a polymer represents an important route to fabricate nanocomposites with high dielectric constant. However, the nanocomposites prepared by this method generally suffer from relatively low breakdown strength and high dielectric loss, which limit the further increase of energy density and energy efficiency of the nanocomposites. In this contribution, by using core-satellite structured ultra-small silver (Ag) decorated barium titanate (BT) nanoassemblies, we successfully fabricated high dielectric constant polymer nanocomposites with enhanced breakdown strength and lower dielectric loss in comparison with conventional polymer-ceramic particulate nanocomposites. The discharged energy density and energy efficiency are derived from the dielectric displacement-electric field loops of the polymer nanocomposites. It is found that, by using the core-satellite structured Ag@BT nanoassemblies as fillers, the polymer nanocomposites can not only have higher discharged energy density but also have high energy efficiency. The mechanism behind the improved electrical properties was attributed to the Coulomb blockade effect and the quantum confinement effect of the introduced ultra-small Ag nanoparticles. This study could serve as an inspiration to enhance the energy storage densities of dielectric polymer nanocomposites.

  9. High-power diode-pumped Nd:Lu2O3 crystal continuous-wave thin-disk laser at 1359 nm

    Li, J H; Liu, X H; Wu, J B; Zhang, X; Li, Y L

    2012-01-01

    We present for the first time, to the best of our knowledge, a 1359 nm continuous-wave (CW) Nd:Lu 2 O 3 laser based on the 4 F 5/2 – 4 F 13/2 transition. The use of a pump module with 16 passes through the crystal allowed the realization of a Nd:Lu 2 O 3 thin-disk laser with 3.52 W of CW output power. The slope efficiency with respect to the incident pump power was 21.4%, and the fluctuation of the output power was better than 3.55% in the given 2 hour. The beam quality factor M 2 is 1.14 and 1.18 for tangential direction and sagittal direction, respectively

  10. Isotopic labeling study of oxygen diffusion in amorphous LaScO3 high-κ films on Si(100) and its effects on the electrical characteristics

    Lopes, J.M.J.; Littmark, U.; Roeckerath, M.; Durgun Oezben, E.; Lenk, S.; Schubert, J.; Mantl, S.; Breuer, U.; Besmehn, A.; Staerk, A.; Grande, P.L.; Sortica, M.A.; Radtke, C.

    2009-01-01

    The influence of post-deposition oxygen anneals on the properties of amorphous LaScO 3 films on Si(100) is reported. The use of an isotopically ( 18 O 2 ) enriched atmosphere allowed to investigate the 16 O- 18 O exchange and the oxygen diffusion across the dielectric layer. Such effects are connected to the formation of an interfacial layer. Oxygen annealing leads to nearly ideal capacitance-voltage curves, lower leakage currents and interface trap densities, as well as to κ-values up to 33 for the LaScO 3 films. These results are attributed to the suppression of oxygen-related trap centers and the achievement of a stoichiometric oxygen content. (orig.)

  11. High-Efficiency Intracavity Continuous-Wave Green-Light Generation by Quasiphase Matching in a Bulk Periodically Poled MgO:LiNbO3 Crystal

    Shaowei Chu

    2008-01-01

    Full Text Available 908 mW of green light at 532 nm were generated by intracavity quasiphase matching in a bulk periodically poled MgO:LiNbO3 (PPMgLN crystal. A maximum optical-to-optical conversion efficiency of 33.5% was obtained from a 0.5 mm thick, 10 mm long, and 5 mol% MgO:LiNbO3 crystal with an end-pump power of 2.7 W at 808 nm. The temperature bandwidth between the intracavity and single-pass frequency doubling was found to be different for the PPMgLN. Reliability and stability of the green laser were evaluated. It was found that for continuous operation of 100 hours, the output stability was better than 97.5% and no optical damage was observed.

  12. Crossed Molecular Beams and Quasiclassical Trajectory Surface Hopping Studies of the Multichannel Nonadiabatic O((3)P) + Ethylene Reaction at High Collision Energy.

    Balucani, Nadia; Leonori, Francesca; Casavecchia, Piergiorgio; Fu, Bina; Bowman, Joel M

    2015-12-17

    The combustion relevant O((3)P) + C2H4 reaction stands out as a prototypical multichannel nonadiabatic reaction involving both triplet and singlet potential energy surfaces (PESs), which are strongly coupled. Crossed molecular beam (CMB) scattering experiments with universal soft electron ionization mass spectrometric detection have been used to characterize the dynamics of this reaction at the relatively high collision energy Ec of 13.7 kcal/mol, attained by crossing the reactant beams at an angle of 135°. This work is a full report of the data at the highest Ec investigated for this reaction. From laboratory product angular and velocity distribution measurements, angular and translational energy distributions in the center-of-mass system have been obtained for the five observed exothermic competing reaction channels leading to H + CH2CHO, H + CH3CO, CH3 + HCO, CH2 + H2CO, and H2 + CH2CO. The product branching ratios (BRs) have been derived. The elucidation of the reaction dynamics is assisted by synergic full-dimensional quasiclassical trajectory surface-hopping calculations of the reactive differential cross sections on coupled ab initio triplet/singlet PESs. This joint experimental/theoretical study extends and complements our previous combined CMB and theoretical work at the lower collision energy of 8.4 kcal/mol. The theoretically derived BRs and extent of intersystem crossing (ISC) are compared with experimental results. In particular, the predictions of the QCT results for the three main channels (those leading to vinoxy + H, methyl + HCO and methylene + H2CO formation) are compared directly with the experimental data in the laboratory frame. Good overall agreement is noted between theory and experiment, although some small, yet significant shortcomings of the theoretical differential cross section are noted. Both experiment and theory find almost an equal contribution from the triplet and singlet surfaces to the reaction, with a clear tendency of the

  13. Electrical characterization of ALD HfO2 high-k dielectrics on ( 2 ¯ 01) β-Ga2O3

    Shahin, David I.; Tadjer, Marko J.; Wheeler, Virginia D.; Koehler, Andrew D.; Anderson, Travis J.; Eddy, Charles R.; Christou, Aris

    2018-01-01

    The electrical quality of HfO2 dielectrics grown by thermal atomic layer deposition at 175 °C on n-type ( 2 ¯ 01) β-Ga2O3 has been studied through capacitance- and current-voltage measurements on metal-oxide-semiconductor capacitors. These capacitors exhibited excellent electrical characteristics, including dual-sweep capacitance-voltage curves with low hysteresis and stretch-out and a frequency-stable dielectric constant of k˜14 when measured between 10 kHz and 1 MHz. The C-V curves exhibited a uniform and repeatable +1.05 V shift relative to the ideal case when swept from 3.5 to -5 V, yielding positively measured flatband (+2.15 V) and threshold (+1.05 V) voltages that may be useful for normally off n-channel Ga2O3 devices. Using the Terman method, an average interface trap density of 1.3 × 1011 cm-2.eV-1 was obtained between 0.2 and 0.6 eV below the conduction band edge. The forward bias current-voltage characteristic was successfully fitted to the Fowler-Nordheim tunneling model at a field strength of 5 MV/cm, allowing an extraction of a 1.3 eV conduction band offset between HfO2 and Ga2O3, which matches the value previously determined from x-ray photoelectron spectroscopy. However, a temperature dependence in the leakage current was observed. These results suggest that HfO2 is an appealing dielectric for Ga2O3 device applications.

  14. High-temperature compressive creep behaviour of perovskite-type oxides SrTi1-xFexO3

    ten Donkelaar, S.F.P.; Stournari, V.; Malzbender, J.; Nijmeijer, Arian; Bouwmeester, Henricus J.M.

    2015-01-01

    Compressive creep tests have been performed on mixed ionic-electronic conducting perovskite-type oxides SrTi1-xFexO3- (STF, x = 0.3, 0.5 and 0.7). Observed activation energies and stress exponents, at 800–1000 ◦C and in the stress range 10 100 MPa, indicate that the steady-state creep rate of STF

  15. Preparation of a Ni-MgO-Al2O3 catalyst with high activity and resistance to potassium poisoning during direct internal reforming of methane in molten carbonate fuel cells

    Jang, Won-Jun; Jung, You-Shick; Shim, Jae-Oh; Roh, Hyun-Seog; Yoon, Wang Lai

    2018-02-01

    Steam reforming of methane (SRM) is conducted using a series of Ni-MgO-Al2O3 catalysts for direct internal reforming (DIR) in molten carbonate fuel cells (MCFCs). Ni-MgO-Al2O3 catalysts are prepared by the homogeneous precipitation method with a variety of MgO loading amounts ranging from 3 to 15 wt%. In addition, each precursor concentrations are systemically changed (Ni: 1.2-4.8 mol L-1; Mg: 0.3-1.2 mol L-1; Al: 0.4-1.6 mol L-1) at the optimized composition (10 wt% MgO). The effects of MgO loading and precursor concentration on the catalytic performance and resistance against poisoning of the catalyst by potassium (K) are investigated. The Ni-MgO-Al2O3 catalyst with 10 wt% MgO and the original precursor concentration (Ni: 1.2 mol L-1; Mg: 0.3 mol L-1; Al: 0.4 mol L-1) exhibits the highest CH4 conversion and resistance against K poisoning even at the extremely high gas space velocity (GHSV) of 1,512,000 h-1. Excellent SRM performance of the Ni-MgO-Al2O3 catalyst is attributed to strong metal (Ni) to alumina support interaction (SMSI) when magnesium oxide (MgO) is co-precipitated with the Ni-Al2O3. The enhanced interaction of the Ni with MgO-Al2O3 support is found to protect the active Ni species against K poisoning.

  16. High-temperature mass spectrometric study of the vaporization processes and thermodynamic properties of melts in the PbO-B2O3-SiO2 system.

    Stolyarova, V L; Lopatin, S I; Shilov, A L; Shugurov, S M

    2013-07-15

    The unique properties of the PbO-B2O3-SiO2 system, especially its extensive range of glass-forming compositions, make it valuable for various practical applications. The thermodynamic properties and vaporization of PbO-B2O3-SiO2 melts are not well established so far and the data obtained on these will be useful for optimization of technology and thermodynamic modeling of glasses. High-temperature Knudsen effusion mass spectrometry was used to study vaporization processes and to determine the partial pressures of components of the PbO-B2O3-SiO2 melts. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using two quartz effusion cells containing the sample under study and pure PbO (reference substance). Ions were produced by electron ionization at an energy of 25 eV. To facilitate interpretation of the mass spectra, the appearance energies of ions were also measured. Pb, PbO and O2 were found to be the main vapor species over the samples studied at 1100 K. The PbO activities as a function of the composition of the system were derived from the measured PbO partial pressures. The B2O3 and SiO2 activities, the Gibbs energy of formation, the excess Gibbs energy of formation and mass losses in the samples studied were calculated. Partial pressures of the vapor species over PbO-B2O3-SiO2 melts were measured at 1100 K in the wide range of compositions using the Knudsen mass spectrometric method. The data enabled the PbO, B2O3, and SiO2 activities in these melts to be derived and provided evidence of their negative deviations from ideal behavior. Copyright © 2013 John Wiley & Sons, Ltd.

  17. Microstructure and Magnetic Properties of Highly Ordered SBA-15 Nanocomposites Modified with Fe2O3 and Co3O4 Nanoparticles

    P. F. Wang

    2012-01-01

    Full Text Available Owing to the unique order mesopores, mesoporous SBA-15 could be used as the carrier of the magnetic nanoparticles. The magnetic nanoparticles in the frame and the mesopores lead to the exchange-coupling interaction or other interactions, which could improve the magnetic properties of SBA-15 nanocomposites. Mesoporous Fe/SBA-15 had been prepared via in situ anchoring Fe2O3 into the frame and the micropores of SBA-15 using the sol-gel and hydrothermal processes. Co3O4 nanoparticles had been impregnated into the mesopores of Fe/SBA-15 to form mesoporous Fe/SBA-15-Co3O4 nanocomposites. XRD, HRTEM, VSM, and N2 physisorption isotherms were used to characterize the mesostructure and magnetic properties of the SBA-15 nanocomposites, and all results indicated that the Fe2O3 nanoparticles presented into the frame and micropores, while the Co3O4 nanoparticles existed inside the mesopores of Fe/SBA-15. Furthermore, the magnetic properties of SBA-15 could be conveniently adjusted by the Fe2O3 and Co3O4 magnetic nanoparticles. Fe/SBA-15 exhibited ferromagnetic properties, while the impregnation of Co3O4 nanoparticles greatly improved the coercivity with a value of 1424.6 Oe, which was much higher than that of Fe/SBA-15.

  18. Porous Na2O-B2O3-Nd2O3 material

    De Villiers, D R; Res, M A; Richter, P W

    1986-12-01

    Substitution of SiO2 by Nd2O3 in the sodium borosilicate system produced glasses containing up to 50 mass% Nd2O3. Sodium borate was leached out of some of the materials to produce either a porous Nd2O3-rich glass or a porous glass-ceramic containing NdBO3, depending on the starting material. Surface areas of up to 190 mS g- were measured. Powder X-ray diffraction (XRD) revealed the NdBO3 to be the high-temperature form with low symmetry.

  19. DO3SE model applicability and O3 flux performance compared to AOT40 for an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma').

    Assis, Pedro I L S; Alonso, Rocío; Meirelles, Sérgio T; Moraes, Regina M

    2015-07-01

    Phytotoxic ozone (O3) levels have been recorded in the Metropolitan Region of São Paulo (MRSP). Flux-based critical levels for O3 through stomata have been adopted for some northern hemisphere species, showing better accuracy than with accumulated ozone exposure above a threshold of 40 ppb (AOT40). In Brazil, critical levels for vegetation protection against O3 adverse effects do not exist. The study aimed to investigate the applicability of O3 deposition model (Deposition of Ozone for Stomatal Exchange (DO3SE)) to an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma') under the MRSP environmental conditions, which are very unstable, and to assess the performance of O3 flux and AOT40 in relation to O3-induced leaf injuries. Stomatal conductance (g s) parameterization for 'Paluma' was carried out and used to calculate different rate thresholds (from 0 to 5 nmol O3 m(-2) projected leaf area (PLA) s(-1)) for the phytotoxic ozone dose (POD). The model performance was assessed through the relationship between the measured and modeled g sto. Leaf injuries were analyzed and associated with POD and AOT40. The model performance was satisfactory and significant (R (2) = 0.56; P < 0.0001; root-mean-square error (RMSE) = 116). As already expected, high AOT40 values did not result in high POD values. Although high POD values do not always account for more injuries, POD0 showed better performance than did AOT40 and other different rate thresholds for POD. Further investigation is necessary to improve our model and also to check if there is a critical level of ozone in which leaf injuries arise. The conclusion is that the DO3SE model for 'Paluma' is applicable in the MRSP as well as in temperate regions and may contribute to future directives.

  20. Anti-bombing insensitivity life of molybdenum cathode doped with La2O3 and Y2O3

    Wang Jinshu; Wang Yiman; Zhou Meiling

    2006-01-01

    Anti-bombing insensitivity of La 2 O 3 -Y 2 O 3 -Mo secondary emitter has been studied in this paper. The variation of maximum secondary emission coefficient δ max with time was measured. The cathode after life experiment was analyzed by means of HRM, SEM, EDS and XRD. The results showed that δ max of La 2 O 3 -Y 2 O 3 -Mo cathode operating at 1100 deg. C under continuous electron bombardment of 300 W/cm 2 was still about 2.5 after 1000 h operation, indicating that this kind of cathode had good anti-bombing insensitivity. In the internal part of the cathode, RE 2 O 3 (rare earth oxide) and molybdenum grains distributed alternately and there existed a certain relationship between crystallographic orientation of RE 2 O 3 and that of molybdenum. It was found that a RE 2 O 3 layer was formed on the surface after operation. The high δ max of La 2 O 3 -Y 2 O 3 -Mo cathode was related to the RE 2 O 3 layer on the surface and the amount of nanosized La 2 O 3 particles on the Y 2 O 3 layer

  1. Neutron irradiation damage in Al2O3 and Y2O3

    Clinard, F.W. Jr.; Bunch, J.M.; Ranken, W.A.

    1975-01-01

    Two ceramics under consideration for use in fusion reactors, Al 2 O 3 and Y 2 O 3 , were irradiated in the EBR-II fission reactor at 650, 875, and 1025 0 K to fluences between 2 and 6 x 10 21 n/cm 2 (E greater than 0.1 MeV). Samples evaluated include sapphire, Lucalox, alumina, Y 2 O 3 , and Y 2 O 3 -10 percent ZrO 2 (Yttralox). All Al 2 O 3 specimens swelled significantly (1 to 3 percent), with most of the growth observed in sapphire along the c-axis at the higher temperatures. Al 2 O 3 samples irradiated at 875 to 1025 0 K contained a high density of small aligned ''pores''. Irradiated Y 2 O 3 -based ceramics exhibited dimensional stability and a defect content consisting primarily of unresolved damage and/or dislocation loops. The behavior of these ceramics under irradiation is discussed, and the relevance of fission neutron damage studies to fusion reactor applications is considered. (auth)

  2. Nonvolatile Resistive Switching in Pt/LaAlO_{3}/SrTiO_{3} Heterostructures

    Shuxiang Wu

    2013-12-01

    Full Text Available Resistive switching heterojunctions, which are promising for nonvolatile memory applications, usually share a capacitorlike metal-oxide-metal configuration. Here, we report on the nonvolatile resistive switching in Pt/LaAlO_{3}/SrTiO_{3} heterostructures, where the conducting layer near the LaAlO_{3}/SrTiO_{3} interface serves as the “unconventional” bottom electrode although both oxides are band insulators. Interestingly, the switching between low-resistance and high-resistance states is accompanied by reversible transitions between tunneling and Ohmic characteristics in the current transport perpendicular to the planes of the heterojunctions. We propose that the observed resistive switching is likely caused by the electric-field-induced drift of charged oxygen vacancies across the LaAlO_{3}/SrTiO_{3} interface and the creation of defect-induced gap states within the ultrathin LaAlO_{3} layer. These metal-oxide-oxide heterojunctions with atomically smooth interfaces and defect-controlled transport provide a platform for the development of nonvolatile oxide nanoelectronics that integrate logic and memory devices.

  3. Improved Charge Transfer in a Mn2O3@Co1.2Ni1.8O4 Hybrid for Highly Stable Alkaline Direct Methanol Fuel Cells with Good Methanol Tolerance.

    Liu, Yan; Chen, Yuanzhen; Li, Sai; Shu, Chenyong; Fang, Yuan; Song, Bo

    2018-03-21

    A three-dimensional Mn 2 O 3 @Co 1.2 Ni 1.8 O 4 hybrid was synthesized via facile two-step processes and employed as a cathode catalyst in direct methanol fuel cells (DMFCs) for the first time. Because of the unique architecture with ultrathin and porous nanosheets of the Co 1.2 Ni 1.8 O 4 shell, this composite exhibits better electrochemical performance than the pristine Mn 2 O 3 . Remarkably, it shows excellent methanol tolerance, even in a high concentration solution. The DMFC was assembled with Mn 2 O 3 @Co 1.2 Ni 1.8 O 4 , polymer fiber membranes, and PtRu/C as the cathode, membrane, and anode, respectively. The power densities of 57.5 and 70.5 mW cm -2 were recorded at 18 and 28 °C, respectively, especially the former is the best result reported in the literature at such a low temperature. The stability of the Mn 2 O 3 @Co 1.2 Ni 1.8 O 4 catalyzed cathode was evaluated, and the results show that this compound possesses excellent stability in a high methanol concentration. The improved electrochemical activity could be attributed to the narrow band gap of the hybrid, which accelerates the electrons jumping from the valence band to the conduction band. Therefore, Mn III could be oxidized into Mn IV more easily, simultaneously providing an electron to the absorbed oxygen.

  4. Adhesion of Y2O3-Al2O3-SiO2 coatings to typical aerospace substrates

    Marraco-Borderas, C.; Nistal, A.; Garcia, E.; Sainz, M.A.; Martin de la Escalera, F.; Essa, Y.; Miranzo, P.

    2016-01-01

    High performance lightweight materials are required in the aerospace industry. Silicon carbide, carbon fiber reinforced carbon and slicon carbide composites comply with those requirements but they suffer from oxidation at the high temperature of the service conditions. One of the more effective approaches to prevent this problem is the use of protecting ceramic coatings, where the good adhesion between substrates and coatings are paramount to guarantee the optimal protection performance. In the present work, the adhesion between those substrates and glass coatings of the Y2O3-Al2O3-SiO2 system processed by oxyacetylene flame spraying is analyzed. Increasing load scratch tests are employed for determining the failure type, maximum load and their relation with the elastic and mechanical properties of the coatings. The results points to the good adhesion of the coatings to silicon carbide and carbon fibre reinforced silicon carbide while the carbon fiber reinforced carbon is not a suitable material to be coated. (Author)

  5. High resistance ratio of bipolar resistive switching in a multiferroic/high-K Bi(Fe0.95Cr0.05)O3/ZrO2/Pt heterostructure

    Dong, B. W.; Miao, Jun; Han, J. Z.; Shao, F.; Yuan, J.; Meng, K. K.; Wu, Y.; Xu, X. G.; Jiang, Y.

    2018-03-01

    An novel heterostructure composed of multiferroic Bi(Fe0.95Cr0.05)O3 (BFCO) and high-K ZrO2 (ZO) layers is investigated. Ferroelectric and electrical properties of the BFZO/ZO heterostructure have been investigated. A pronounced bipolar ferroelectric resistive switching characteristic was achieved in the heterostructure at room temperature. Interestingly, the BFCO/ZO structures exhibit a reproducible resistive switching with a high On/Off resistance ratio ∼2×103 and long retention time. The relationship between polarization and band structure at the interface of BFCO/ZO bilayer under the positive and negative sweepings has been discussed. As a result, the BFCO/ZO multiferroic/high-K heterostructure with high On/Off resistance ratio and long retention characterizes, exhibits a potential in future nonvolatile memory application.

  6. Decorating TiO2 Nanowires with BaTiO3 Nanoparticles: A New Approach Leading to Substantially Enhanced Energy Storage Capability of High-k Polymer Nanocomposites.

    Kang, Da; Wang, Guanyao; Huang, Yanhui; Jiang, Pingkai; Huang, Xingyi

    2018-01-31

    The urgent demand of high energy density and high power density devices has triggered significant interest in high dielectric constant (high-k) flexible nanocomposites comprising dielectric polymer and high-k inorganic nanofiller. However, the large electrical mismatch between polymer and nanofiller usually leads to earlier electric failure of the nanocomposites, resulting in an undesirable decrease of electrical energy storage capability. A few studies show that the introduction of moderate-k shell onto a high-k nanofiller surface can decrease the dielectric constant mismatch, and thus, the corresponding nanocomposites can withstand high electric field. Unfortunately, the low apparent dielectric enhancement of the nanocomposites and high electrical conductivity mismatch between matrix and nanofiller still result in low energy density and low efficiency. In this study, it is demonstrated that encapsulating moderate-k nanofiller with high-k but low electrical conductivity shell is effective to significantly enhance the energy storage capability of dielectric polymer nanocomposites. Specifically, using BaTiO 3 nanoparticles encapsulated TiO 2 (BaTiO 3 @TiO 2 ) core-shell nanowires as filler, the corresponding poly(vinylidene fluoride-co-hexafluoropylene) nanocomposites exhibit superior energy storage capability in comparison with the nanocomposites filled by either BaTiO 3 or TiO 2 nanowires. The nanocomposite film with 5 wt % BaTiO 3 @TiO 2 nanowires possesses an ultrahigh discharged energy density of 9.95 J cm -3 at 500 MV m -1 , much higher than that of commercial biaxial-oriented polypropylene (BOPP) (3.56 J cm -3 at 600 MV m -1 ). This new strategy and corresponding results presented here provide new insights into the design of dielectric polymer nanocomposites with high electrical energy storage capability.

  7. Synthesis, microstructure and properties of BiFeO3-based multiferroic materials: A review

    Bernardo, M. S.

    2014-02-01

    Full Text Available BiFeO3-based materials are currently one of the most studied multiferroics due to their possible applications at room temperature. However, among the large number of published papers there is much controversy. For example, possibility of synthesizing a pure BiFeO3 phase is still source of discussion in literature. Not even the nature of the binary Bi2O3-Fe2O3 diagram has been clarified yet. The difficulty in controlling the formation of parasite phases reaches the consolidation step. Accordingly, the sintering conditions must be carefully determined both to get dense materials and to avoid bismuth ferrite decomposition. However, the precise conditions to attain dense bismuth ferrite materials are frequently contradictory among different works. As a consequence, the reported properties habitually result opposed and highly irreproducible hampering the preparation of BiFeO3 materials suitable for practical applications. In this context, the purpose of the present review is to summarize the main researches regarding BiFeO3 synthesis, microstructure and properties in order to provide an easier understanding of these materials.Los materiales basados en BiFeO3 son en la actualidad uno de los multiferroicos más estudiados debido a sus posibles aplicaciones a temperatura ambiente. Sin embargo, entre la multitud de trabajos publicados referentes a estos materiales existe mucha controversia. Por ejemplo, la posibilidad de sintetizar una fase BiFeO3 pura es aún objeto de discusión en la bibliografía y la naturaleza de los diagramas de fases del sistema Bi2O3-Fe2O3 aún no está clara. La dificultad para controlar las fases parásitas se extiende al proceso de consolidación por lo que las condiciones de sinterización deben ser cuidadosamente controladas para obtener materiales densos y al mismo tiempo evitar la descomposición de la ferrita. No obstante, las condiciones precisas para obtener materiales densos de BiFeO3 son frecuentemente

  8. Apparent vanishing of ferroelectricity in nanostructured BiScO3PbTiO3

    Amorín , H; Jiménez , R; Ricote , J; Hungría , T; Castro , A; Algueró , M

    2010-01-01

    Abstract Nanostructured ceramics of high-temperature piezoelectric 0.375BiScO 3 -0.625PbTiO 3 were prepared by spark plasma sintering of nanocrystalline powders obtained by mechanosynthesis. The macroscopic electrical properties were characterized on dense ceramics with decreasing average grain size down to 28 nm. Results indicate that the electric field is screened by the electrically insulating grain boundaries at the nanoscale, which needs to be considered when discussing size effects i...

  9. Development of an automatic high-throughput assay for tetracycline determination by using Eu2O3 nanoparticles and dry-reagent technology.

    Aguilar-Vázquez, L; Aguilar-Caballos, M P; Gómez-Hens, A

    2014-02-01

    The usefulness of europium oxide nanoparticles (Eu2O3 NPs) as analytical reagent for the direct determination of organic compounds is described for the first time. Tetracycline, which forms a luminescent chelate with europium, has been chosen as a model analyte. Dry reagent chemistry is used in a 96-well format, which considerably speeds up the determination and contributes to its automation. The NPs are immobilized onto polystyrene wells by adding a volume of a Eu2O3 NP dispersion in 2-propanol to each well and drying in an oven until they dry completely. At the moment of analysis, a standard or sample volume (200 μL) in the appropriate medium is added, and the mixture shaken for 15 min at 37°C. The method allows the determination of tetracycline in the range 20-1000 ng mL(-1), with a detection limit of 8 ng mL(-1). The inter-assay and intra-assay precision, which were assayed at two different tetracycline concentrations and expressed as relative standard deviation, were in the ranges of 6.5-8.2% and 9.2-12.7%, respectively. The study of the selectivity of the system showed that the method is adequate for tetracycline determination in agri-food samples, since most of antibiotics assayed did not interfere the determination. Only other tetracycline antibiotics provided luminescent signal when reacting to Eu2O3 NPs. The method has been applied to the determination of tetracycline in calf urine and in honey samples obtaining recovery values in the ranges of 85.0-110.0% and 99.7-116.7%, respectively. © 2013 Published by Elsevier B.V.

  10. Effects of processing parameters on the synthesis of (K0.5Na0.5)NbO3 nanopowders by reactive high-energy ball milling method.

    Nguyen, Duc Van

    2014-01-01

    The effects of ball milling parameters, namely, the ball-to-powder mass ratio and milling speed, on the synthesis of (K0.5Na0.5)NbO3 nanopowders by high-energy ball milling method from a stoichiometric mixture containing Na2CO3, K2CO3, and Nb2O5 were investigated in this paper. The results indicated that the single crystalline phase of (K0.5Na0.5)NbO3 was received in as-milled samples synthesized using optimized ball-to-powder mass ratio of 35 : 1 and at a milling speed of 600 rpm for 5 h. In the optimized as-milled samples, no remaining alkali carbonates that can provide the volatilizable potassium-containing species were found and (K0.5Na0.5)NbO3 nanopowders were readily obtained via the formation of an intermediate carbonato complex. This complex was mostly transformed into (K0.5Na0.5)NbO3 at temperature as low as 350°C and its existence was no longer detected at spectroscopic level when calcination temperature crossed over 700°C.

  11. Production of biodiesel from non-edible Jatropha curcas oil via transesterification using Bi2O3–La2O3 catalyst

    Rabiah Nizah, M.F.; Taufiq-Yap, Y.H.; Rashid, Umer; Teo, Siow Hwa; Shajaratun Nur, Z.A.; Islam, Aminul

    2014-01-01

    Highlights: • Effects of methanol/oil molar ratio, catalyst amount, reaction temperature and reaction time were optimized. • High FAME conversion of 93% was achieved. • Bi 2 O 3 –La 2 O 3 catalysts were characterized using XRD, BET, TPD-CO 2 and TPD-NH 3 . • Effects of acidity and basicity of the catalyst have been correlated with the FAME conversion. • Bi 2 O 3 –La 2 O 3 catalyst can easy to recover and maintain 87% conversion after three times of successive reuse. - Abstract: The simultaneous esterification and transesterification of Jatropha curcas oil (JCO) was carried out in the presence of Bi 2 O 3 (1–7 wt.%) modified La 2 O 3 catalyst at atmospheric pressure. The catalyst were characterized by X-ray diffraction (XRD), BET surface area, desorption of CO 2 (TPD-CO 2 ) and NH 3 (TPD-NH 3 ). Under the optimal reaction condition of methanol/oil molar ratio of 15:1, 2 wt.% of catalyst amount and a reaction temperature of 150 °C for 4 h, the highest conversion of biodiesel obtained was 93%. This catalyst maintained 87% of FAME conversion after three times of successive reuse

  12. HRTEM analysis on nanocrystalline BaTiO3 and PbTiO3: size effects on ferroelectric phase transition temperature

    Bursill, L.A.; Jiang, B.; Peng, J.L.; Zhong, W.L.; Zhang, P.L.

    1997-01-01

    High-Resolution Transmission Electron Microscopic studies of nanocrystaline particles of BaTiO 3 and PbTiO 3 are reported. There are characteristic differences observed for BaTiO 3 prepared using sol gel (SG) and steric acid gel (SAG) methods. The former exhibit a critical size below which there is no paraelectric/ferroelectric phase transition, whereas BaTiO 3 prepared via the SAG route remained cubic for all conditions. The SAG preparations always showed chemical intergrowth defects whereas the SG preparations were single phase. Atomic resolution images of both varieties showed interesting surface steps and surface relaxations/reconstructions of some facets. Nanocrystalline PbTiO 3 prepared by the SG route remains tetragonal, albeit with decreasing c/a ratio, down to 25nm diameter. HRTEM observations of nanocrystalline PbTiO 3 are also presented. X-ray diffraction, dielectric and Raman scattering measurements also demonstrate pronounced size effects. The relationship between the observed nanostructures and size effects on the physical properties is discussed. 6 refs., 1 tab., 6 figs

  13. Trends in (LaMnO3)n/(SrTiO3)m superlattices with varying layer thicknesses

    Jilili, J.

    2015-09-01

    We investigate the thickness dependence of the structural, electronic, and magnetic properties of (LaMnO3)n/(SrTiO3)m (n, m = 2, 4, 6, 8) superlattices using density functional theory. The electronic structure turns out to be highly sensitive to the onsite Coulomb interaction. In contrast to bulk SrTiO3, strongly distorted O octahedra are observed in the SrTiO3 layers with a systematic off centering of the Ti atoms. The systems favour ferromagnetic spin ordering rather than the antiferromagnetic spin ordering of bulk LaMnO3 and all show half-metallicity, while a systematic reduction of the minority spin band gaps as a function of the LaMnO3 and SrTiO3 layer thicknesses originates from modifications of the Ti dxy states.

  14. X-ray diffraction measurements on CuGeO3 under high pressures to 81 GPa using synchrotron radiation and imaging plates

    Ming, L C; Eto, T; Takeda, K; Kobayashi, Y; Suzuki, E; Endo, S; Sharma, S K; Jayaraman, A; Kikegawa, T

    2002-01-01

    Angle-dispersive x-ray diffraction measurements using CuGeO 3 (I) and CuGeO 3 (III) as the starting materials were carried out to 81 and 31 GPa, respectively, at room temperature. Data for phase (I) show that phase transitions occur at ∼7, ∼14, and ∼22 GPa, respectively, corresponding to (I) → (II), (II) → (II'), and (II') → (VI) transitions, as reported previously. The tetragonal phase (VI) was found to be stable up to 81 GPa, the highest pressure determined in this study. The volume changes at the transition pressures are estimated to be of ∼5%, ∼0%, and ∼14% for (I) → (II), (II) → (II'), and (II') → (VI) transitions, respectively. Data from measurements where phase (III) was the starting material show that phase (III) first changes to phase (IV) at ∼7 GPa and then to (IV') at 13.5 GPa, and finally to phase (V) at ∼18 GPa, with volume changes of 1.5%, 0%, and 20%, respectively, at the transition pressure. The volume change of 20% at 18 GPa is consistent with the pyroxene-perovskite transition

  15. Characterization of Al2O3NP–Al2024 and AgCNP–Al2024 composites prepared by mechanical processing in a high energy ball mill

    Carreño-Gallardo, C.; Estrada-Guel, I.; Romero-Romo, M.; Cruz-García, R.; López-Meléndez, C.; Martínez-Sánchez, R.

    2012-01-01

    Graphical abstract: Mechanical alloying was used to produce two kinds of metal matrix composites based on 2024 aluminum alloy, the nanocomposites were reinforced with different percentages of Al 2 O 3 and Ag C nanoparticles. The content of nanoparticles has a role important on the mechanical properties of the nanocomposite. 10 h of milling time are enough to former the Al 2024 nanocomposites. The results obtained by differential scanning calorimeter show the temperatures of intermetallic precipitation, which were identified by X-ray diffraction. The results revealed that mechanical alloying is an excellent route to incorporate and distribute NP into Al 2024 . Highlights: ► Aluminum-based nanocomposites were synthesized bay milling process. ► An homogeneous nanoparticles dispersion was reached and mechanical properties were enhanced. ► Phase transformation during heating was characterized by XRD. - Abstract: Mechanical alloying was used to produce two kinds of metal matrix composites based on 2024 aluminum alloy. The nanocomposites were reinforced with different percentages of Al 2 O 3 and Ag C nanoparticles. The content of nanoparticles has an important role on the mechanical properties of the nanocomposites. A milling time of 10 h is enough to form the Al 2024 nanocomposites. The thermograms obtained by differential scanning calorimeter show the temperatures of phase precipitation, which were identified by X-ray diffraction. The results revealed that mechanical alloying is an excellent route for the incorporation and distribution of nanoparticles into Al 2024 .

  16. High-pressure BaCrO_3 polytypes and the 5H–BaCrO_2_._8 phase

    Arévalo-López, Angel M.; Paul Attfield, J.

    2015-01-01

    Polytypism of BaCrO_3 perovskites has been investigated at 900–1100 °C and pressures up to 22 GPa. Hexagonal 5H, 4H, and 6H perovskites are observed with increasing pressure, and the cubic 3C perovskite (a=3.99503(1) Å) is observed in bulk form for the first time at 19–22 GPa. An oxygen-deficient material with limiting composition 5H–BaCrO_2_._8 is synthesised at 1200 °C under ambient pressure. This contains double tetrahedral Cr"4"+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure. - Graphical abstract: Hexagonal 5H, 4H, and 6H perovskites polytypes of BaCrO_3 are observed with increasing pressure and the cubic 3C perovskite is stabilised in bulk form for the first time at 19–22 GPa. Oxygen-deficient 5H–BaCrO_2_._8 synthesised at ambient pressure contains double tetrahedral Cr"4"+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure.

  17. Self-Powered, High-Speed and Visible-Near Infrared Response of MoO(3-x)/n-Si Heterojunction Photodetector with Enhanced Performance by Interfacial Engineering.

    Zhao, Chuanxi; Liang, Zhimin; Su, Mingze; Liu, Pengyi; Mai, Wenjie; Xie, Weiguang

    2015-11-25

    Photodetectors with a wide spectrum response are important components for sensing, imaging, and other optoelectronic applications. A molybdenum oxide (MoO(3-x))/Si heterojunction has been applied as solar cells with great success, but its potential in photodetectors has not been explored yet. Herein, a self-powered, high-speed heterojunction photodetector fabricated by coating an n-type Si hierarchical structure with an ultrathin hole-selective layer of molybdenum oxide (MoO(3-x)) is first investigated. Excellent and stable photoresponse performance is obtained by using a methyl group passivated interface. The heterojunction photodetector demonstrated high sensitivity to a wide spectrum from 300 to 1100 nm. The self-powered photodetector shows a high detectivity of (∼6.29 × 10(12) cmHz(1/2) W(-1)) and fast response time (1.0 μs). The excellent photodetecting performance is attributed to the enhanced interfacial barrier height and three-dimensional geometry of Si nanostructures, which is beneficial for efficient photocarrier collection and transportation. Finally, our devices show excellent long-term stability in air for 6 months with negligible performance degradation. The thermal evaporation method for large-scale fabrication of MoO(3-x)/n-Si photodetectors makes it suitable for self-powered, multispectral, and high-speed response photodetecting applications.

  18. A novel highly efficient adsorbent {[Co4(L)2(μ3-OH)2(H2O)3(4,4‧-bipy)2]·(H2O)2}n: Synthesis, crystal structure, magnetic and arsenic (V) absorption capacity

    Zhang, Chong; Xiao, Yu; Qin, Yan; Sun, Quanchun; Zhang, Shuhua

    2018-05-01

    A novel highly efficient adsorbent-microporous tetranuclear Co(II)-based polymer, {[Co4(L)2(μ3-OH)2(H2O)3(4,4‧-bipy)2]·(H2O)2}n (1, H3L = 4-(N,N‧-bis(4-carboxybenzyl)amino) benzenesulfonic acid, 4,4‧-bipy = 4,4‧-bipyridine), was hydrothermally synthesized. The complex 1 is a metal-organic framework (MOF) material which was characterized by single-crystal X-ray diffraction, BET and platon software. Co-MOF (complex 1) reveals excellent adsorption property. The capacity of Co-MOF to remove arsenic As(V) from sodium arsenate aqueous solutions was investigated (The form of As(V) is AsO43-). The experimental results showed that Co-MOF had a higher stable and relatively high As(V) removal rate (> 98%) at pH 4-10. The adsorption kinetics followed a pseudo-second-order kinetic model, and the adsorption isotherm followed the Langmuir equation. Co-MOF exhibits a very high adsorption capacity of As(V) in aqueous solution (Qmax of 96.08 mg/g). Finally, the optimal adsorption conditions for the model were obtained through a Box-Behnken response surface experiment which was designed with adsorption time, dose, temperature and rotational speed of the shaker as the influencing factors to determine two-factor interaction effects. Co-MOF was further characterized using FTIR, PXRD, X-ray photoelectron spectroscopy before and after adsorption As (V). The magnetism of Co-MOF was also discussed.

  19. An internal magnetic field strategy to reuse pulverized active materials for high performance: a magnetic three-dimensional ordered macroporous TiO2/CoPt/α-Fe2O3 nanocomposite anode.

    Tang, Yiping; Hong, Liang; Li, Jiquan; Hou, Guangya; Cao, Huazhen; Wu, Liankui; Zheng, Guoqu; Wu, Qingliu

    2017-05-09

    A ferromagnetic three-dimensional ordered macroporous TiO 2 /CoPt/α-Fe 2 O 3 (3DOMTCF) nanocomposite was synthesized via a sol-gel approach templated by poly(methyl methacrylate) (PMMA) microspheres. After magnetization, it exhibited an extremely high reversible capacity and a long cycle life, which were ascribed to the internal magnetic field for reusing pulverized active materials and its unique structure.

  20. Synthesis, characterization and thermal properties of paraffin microcapsules modified with nano-Al2O3

    Jiang, Xiang; Luo, Ruilian; Peng, Feifei; Fang, Yutang; Akiyama, Tomohiro; Wang, Shuangfeng

    2015-01-01

    Highlights: • Novel MEPCM modified with nano-Al 2 O 3 was prepared via emulsion polymerization. • The paraffin microcapsules presented a well-defined microstructure. • The composite achieved high encapsulation efficiency. • The thermal conductivity of MEPCM was enhanced due to the nano-Al 2 O 3 particles. - Abstract: A sort of new microencapsulated phase change materials (MEPCM) based on paraffin wax core and poly(methyl methacrylate-co-methyl acrylate) shell with nano alumina (nano-Al 2 O 3 ) inlay was synthesized through emulsion polymerization. Various techniques were used to characterize the as-prepared products so as to investigate the effect of nano-Al 2 O 3 on morphology and thermal performance, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and thermal conductivity measurement. The results showed that the products achieved the best performance with 16% (monomer mass) nano-Al 2 O 3 added under the optimal preparation conditions. The DSC results indicated that the phase change temperature of the composite exhibited appropriate phase change temperature and achieved high encapsulation efficiency. The thermal conductivity of the paraffin microcapsules is also significantly improved owing to the presence of high thermal conductive nano-Al 2 O 3 . This synthetic technique can be a perspective way to prepare the MEPCM with enhanced thermal transfer and phase change properties for potential applications to energy-saving building materials

  1. Phase stability of iron germanate, FeGeO3, to 127 GPa

    Dutta, R.; Tracy, S. J.; Stan, C. V.; Prakapenka, V. B.; Cava, R. J.; Duffy, T. S.

    2018-04-01

    The high-pressure behavior of germanates is of interest as these compounds serve as analogs for silicates of the deep Earth. Current theoretical and experimental studies of iron germanate, FeGeO3, are limited. Here, we have examined the behavior of FeGeO3 to 127 GPa using the laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction. Upon compression at room temperature, the ambient-pressure clinopyroxene phase transforms to a disordered triclinic phase [FeGeO3 (II)] at 18 GPa in agreement with earlier studies. An additional phase transition to FeGeO3 (III) occurs above 54 GPa at room temperature. Laser-heating experiments ( 1200-2200 K) were conducted at three pressures (33, 54, and 123 GPa) chosen to cover the stability regions of different GeO2 polymorphs. In all cases, we observe that FeGeO3 dissociates into GeO2 + FeO at high pressure and temperature conditions. Neither the perovskite nor the post-perovskite phase was observed up to 127 GPa at ambient or high temperatures. The results are consistent with the behavior of FeSiO3, which also dissociates into a mixture of the oxides (FeO + SiO2) at least up to 149 GPa.

  2. Unimolecular fragrmentations of the radical cation of the high-valent organometal oxide CH3ReO3 and its reactivity with ethylene in the gas phase

    Schröder, Detlef; Herrmann, W. A.; Fischer, Richard W.; Schwarz, Helmut

    1992-12-01

    The unimolecular chemistry of CH3ReO[radical sign]+3 in the gas phase commences with a methyl migration to' generate CH3 OReO[radical sign]+2. This further undergoes multiple hydrogen migration to the metal centre to generate an intermediate which serves as a precursor for the elimination of both molecular hydrogen and of carbon monoxide. If CH3ReO[radical sign]+3 is reacted with ethylene, inter alia products are observed which point to a competition between an intramolecular metathesis reaction of the ethylene-inserted intermediate CH3CH2CH2ReO3[radical sign]+ and epoxidation of ethylene to generate c-C2H4O.

  3. Study of Phase Transformations on Nano-Crystalline (La,Sr)(Mn,Fe)O3 Systems by High-Pressure Moessbauer Spectroscopy

    Chandra, Usha; Mudgal, Prerana; Kumar, Manoj

    2006-01-01

    We report pressure-dependent 57Fe Moessbauer studies on a nano-crystalline perovskite La0.8Sr0.2(Mn0.8Fe0.2) O3 system up to 10 GPa using diamond anvil cell. At ambient pressure, iron is present as Fe3+ and Fe4+ in two different environments. Pressure seems to affect the higher symmetry site of Fe4+, while the octahedral site containing Fe3+ remains almost unaffected. Phase transformations are observed at pressures 0.52 GPa and 3.7 GPa respectively. A sudden increase in the isomer shift at 0.52 GPa is related to the reduction of Fe4+ ions while at 3.7 GPa, a structural transition is observed with sudden drop in isomer shift indicating Fe3+ ions in identical environment. Quadrupole splittings increase continuously with pressures up to 10 GPa

  4. Single-crystal X-ray diffraction study of SrGeO3 high-pressure perovskite phase at 100 K

    Nakatsuka, Akihiko; Arima, Hiroshi; Ohtaka, Osamu; Fujiwara, Keiko; Yoshiasa, Akira

    2017-10-01

    Single-crystal X-ray diffraction study of SrGeO3 perovskite (cubic; space group Pmɜ¯m) synthesized at 6 GPa and 1223 K was conducted at a low temperature of 100 K. The residual electron density revealed the presence of the bonding electron at the center of the Ge-O bond, in accordance with our previous conclusion that the Ge-O bond is strongly covalent. From comparison with our previous structure-refinement result at 296 K, the mean square displacement (MSD) of the O atom in the direction of the Ge-O bond is suggested to exhibit no significant temperature dependence, in contrast to that in the direction perpendicular to the bond. Thus, the strong covalency of the Ge-O bond can have a large influence on the temperature dependence of thermal vibration of the O atom.

  5. Flexible superior electrode architectures based on three-dimensional porous spinous α-Fe2O3 with a high performance as a supercapacitor.

    Nan, Honghong; Yu, Liutao; Ma, Wenqin; Geng, Baoyou; Zhang, Xiaojun

    2015-05-28

    Flexible supercapacitors have recently attracted increasing attention as they show unique promising advantages, such as flexibility and shape diversity, and they are light-weight and so on. Herein, we designed a series of 3D porous spinous iron oxide materials synthesized on a thin iron plate through a facile method under mild conditions. The unique nanostructural features endow them with excellent electrochemical performance. The electrochemical properties of the integrated electrodes as active electrode materials for supercapacitors have been investigated using different electrochemical techniques including cyclic voltammetry, and galvanostatic charge-discharge in Na2SO4 and LiPF6/EC : DEC electrolyte solutions. These integrated electrodes showed high specific capacitance (as high as 524.6 F g(-1) at the current density of 1 A g(-1)) in 1.0 M Na2SO4 (see Table S1). Moreover, the integrated electrodes also show high power densities and high energy densities in a LiPF6/EC : DEC electrolyte solution; for example, the energy densities were 319.3, 252.5, 152.1, 74.13 and 38.6 W h kg(-1) at different power densities of 8.81, 21.59, 56.65, 92.09 and 152.64 kW kg(-1), respectively. Additionally, the flexible superior electrode exhibited excellent stability with capacitance retention of 92.9% after 5000 cycles. Therefore, such flexible integrated devices might be used in smart and portable electronics.

  6. Study of phase equilibria in function of temperature in UO2-PuO2-Pu2O3 system for nuclear ceramics with high plutonium contents

    Truphemus, Thibaut

    2013-01-01

    In the UO 2 -PuO 2 -Pu 2 O 3 section, a monophasic (U 1-y ,Pu y )O 2-x domain is stable for y≤0,20 at 25 C and up to solid-liquid equilibrium. At higher Pu content, phase equilibria are more unclear with a phase separation process. The main objective of this work consisted in upgrading the representation of this system for 0,15≤y≤0,65 and 25≤T(C)≤1500. At 25 C, a miscibility gap composed by two different (U 1-y ,Pu y )O 2-x phases has been observed for y≤0,45, with one very closed to stoichiometric state (Oxygen/Metal=2) and one other very reduced. For the first time, a triphasic domain has been characterized at higher Pu contents, with two (U 1-y ,Pu y )O 2-x phases near y=0,45 and one (U 1-y ,Pu y ) 2 O 3 phase with a low U content inside. Concerning the study in function of temperature, we have demonstrated that phase separation temperature increase when Pu content grows. Several representations have been established. At 200 C, the representation is closed to that at 25 C. At 400 C, the phase separation have been specified at a lower Pu content than that of literature: y=0,35. At 600 C, our results have clarified the section, until then very unclear, with a phase separation appearing at y=0,60.The microstructural analysis has clearly demonstrated the significant impact of the phase separation on the material. Indeed many cracks have been observed in our samples, and quantity of these defects increases when Pu content grows. (author) [fr

  7. Strain induced optical properties of BaReO3

    Kumavat, Sandip R.; Kansara, Shivam; Gupta, Sanjeev K.; Sonvane, Yogesh

    2018-05-01

    Here, we have performed strain induce optical properties of BaReO3 by using density functional theory (DFT). We noticed that after applying intrinsic and extrinsic strain to the BaReO3, it shows the metallic behavior. We also studied optical properties, which show good activity in the ultraviolet region. The results show that after applying intrinsic and extrinsic strain to BaReO3 the absorption peaks are shifted towards the high UV region of the spectrum. Thus, we concluded that, BaReO3 material with extrinsic strain can be useful for high frequency UV device and optoelectronic devices.

  8. Electric Properties of Pb(Sb1/2Nb1/2)O3 PbTiO3 PbZrO3 Ceramics

    Kawamura, Yasushi; Ohuchi, Hiromu

    1994-09-01

    Solid-solution ceramics of ternary system xPb(Sb1/2Nb1/2)O3 yPbTiO3 zPbZrO3 were prepared by the solid-state reaction of powder materials. Ceramic, electric, dielectric and piezoelectric properties and crystal structures of the system were studied. Sintering of the system xPb(Sb1/2Nb1/2)O3 yPbTiO3 zPbZrO3 is much easier than that of each end composition, and well-sintered high-density ceramics were obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high relative dielectric constants, high radial coupling coefficient and low resonant resistance were obtained for the composition near the morphotropic transformation. The composition Pb(Sb1/2Nb1/2)0.075Ti0.45Zr0.475O3 showed the highest dielectric constant (ɛr=1690), and the composition Pb(Sb1/2Nb1/2)0.05Ti0.45Zr0.5O3 showed the highest radial coupling coefficient (kp=64%).

  9. Oxidation of GaAs substrates to enable β-Ga2O3 films for sensors and optoelectronic devices

    Mao, Howard; Alhalaili, Badriyah; Kaya, Ahmet; Dryden, Daniel M.; Woodall, Jerry M.; Islam, M. Saif

    2017-08-01

    A very simple and inexpensive method for growing β-Ga2O3 films by heating GaAs wafers at high temperature in a furnace was found to contribute to large-area, high-quality β-Ga2O3 nanoscale thin films as well as nanowires depending on the growth conditions. We present the material characterization results including the optical band gap, Schottky barrier height with metal (gold), field ionization and photoconductance of β-Ga2O3 film and nanowires.

  10. Nb and Pd co-doped La0.57Sr0.38Co0.19Fe0.665Nb0.095Pd0.05O3-δ as a stable, high performance electrode for barrier-layer-free Y2O3-ZrO2 electrolyte of solid oxide fuel cells

    Chen, Kongfa; He, Shuai; Li, Na; Cheng, Yi; Ai, Na; Chen, Minle; Rickard, William D. A.; Zhang, Teng; Jiang, San Ping

    2018-02-01

    La0.6Sr0.2Co0.2Fe0.8O3-δ (LSCF) is the most intensively investigated high performance cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs), but strontium segregation and migration at the electrode/electrolyte interface is a critical issue limiting the electrocatalytic activity and stability of LSCF based cathodes. Herein, we report a Nb and Pd co-doped LSCF (La0.57Sr0.38Co0.19Fe0.665Nb0.095Pd0.05O3-δ, LSCFNPd) perovskite as stable and active cathode on a barrier-layer-free anode-supported yttria-stabilized zirconia (YSZ) electrolyte cell using direct assembly method without pre-sintering at high temperatures. The cell exhibits a peak power density of 1.3 W cm-2 at 750 °C and excellent stability with no degradation during polarization at 500 mA cm-2 and 750 °C for 175 h. Microscopic and spectroscopic analysis show that the electrochemical polarization promotes the formation of electrode/electrolyte interface in operando and exsolution of Pd/PdO nanoparticles. The Nb doping in the B-site of LSCF significantly reduces the Sr surface segregation, enhancing the stability of the cathode, while the exsoluted Pd/PdO nanoparticles increases the electrocatalytic activity for the oxygen reduction reaction. The present study opens up a new route for the development of cobaltite-based perovskite cathodes with high activity and stability for barrier-layer-free YSZ electrolyte based IT-SOFCs.

  11. In situ formation of CA6 platelets in Al2O3 and Al2O3/ZrO2 matrices

    Belmonte , M.; SÁnchez-Herencia , A.; Moreno , R.; Miranzo , P.; Moya , J.; Tomsia , A.

    1993-01-01

    Al2O3 and Al2O3/ZrO2 compacts containing CaO as a dopant have been sintered under different conditions and atmospheres: air, high vacuum (> 10-6torr). SEM observations have been made on the polished surfaces of sintered and also of annealed samples. Only after the annealing treatment in air at temperatures ranging from 1400° to 1 500°C, a massive formation of CA6 platelets was detected in samples sintered in low oxygen partial pressure atmospheres.ln order to clarify the mechanism of formatio...

  12. Core-shell structured polystyrene/BaTiO3 hybrid nanodielectrics prepared by in situ RAFT polymerization: a route to high dielectric constant and low loss materials with weak frequency dependence.

    Yang, Ke; Huang, Xingyi; Xie, Liyuan; Wu, Chao; Jiang, Pingkai; Tanaka, Toshikatsu

    2012-11-23

    A novel route to prepare core-shell structured nanocomposites with excellent dielectric performance is reported. This approach involves the grafting of polystyrene (PS) from the surface of BaTiO(3) by an in situ RAFT polymerization. The core-shell structured PS/BaTiO(3) nanocomposites not only show significantly increased dielectric constant and very low dielectric loss, but also have a weak frequency dependence of dielectric properties over a wide range of frequencies. In addition, the dielectric constant of the nanocomposites can also be easily tuned by varying the thickness of the PS shell. Our method is very promising for preparing high-performance nanocomposites used in energy-storage devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Evidence of sharp and diffuse domain walls in BiFeO3 by means of unit-cell-wise strain and polarization maps obtained with high resolution scanning transmission electron microscopy.

    Lubk, A; Rossell, M D; Seidel, J; He, Q; Yang, S Y; Chu, Y H; Ramesh, R; Hÿtch, M J; Snoeck, E

    2012-07-27

    Domain walls (DWs) substantially influence a large number of applications involving ferroelectric materials due to their limited mobility when shifted during polarization switching. The discovery of greatly enhanced conduction at BiFeO(3) DWs has highlighted yet another role of DWs as a local material state with unique properties. However, the lack of precise information on the local atomic structure is still hampering microscopical understanding of DW properties. Here, we examine the atomic structure of BiFeO(3) 109° DWs with pm precision by a combination of high-angle annular dark-field scanning transmission electron microscopy and a dedicated structural analysis. By measuring simultaneously local polarization and strain, we provide direct experimental proof for the straight DW structure predicted by ab initio calculations as well as the recently proposed theory of diffuse DWs, thus resolving a long-standing discrepancy between experimentally measured and theoretically predicted DW mobilities.

  14. Realizing a facile and environmental-friendly fabrication of high-performance multi-crystalline silicon solar cells by employing ZnO nanostructures and an Al2O3 passivation layer

    Chen, Hong-Yan; Lu, Hong-Liang; Sun, Long; Ren, Qing-Hua; Zhang, Hao; Ji, Xin-Ming; Liu, Wen-Jun; Ding, Shi-Jin; Yang, Xiao-Feng; Zhang, David Wei

    2016-01-01

    Nowadays, the multi-crystalline silicon (mc-Si) solar cells dominate the photovoltaic industry. However, the current acid etching method on mc-Si surface used by firms can hardly suppress the average reflectance value below 25% in the visible light spectrum. Meanwhile, the nitric acid and the hydrofluoric contained in the etching solution is both environmental unfriendly and highly toxic to human. Here, a mc-Si solar cell based on ZnO nanostructures and an Al2O3 spacer layer is demonstrated. The eco-friendly fabrication is realized by low temperature atomic layer deposition of Al2O3 layer as well as ZnO seed layer. Moreover, the ZnO nanostructures are prepared by nontoxic and low cost hydro-thermal growth process. Results show that the best passivation quality of the n+ -type mc-Si surface can be achieved by balancing the Si dangling bond saturation level and the negative charge concentration in the Al2O3 film. Moreover, the average reflectance on cell surface can be suppressed to 8.2% in 400–900 nm range by controlling the thickness of ZnO seed layer. With these two combined refinements, a maximum solar cell efficiency of 15.8% is obtained eventually. This work offer a facile way to realize the environmental friendly fabrication of high performance mc-Si solar cells. PMID:27924911

  15. Highly oriented as-deposited superconducting laser ablated thin films of Y1Ba2Cu3O/sub 7-//sub δ/ on SrTiO3, zirconia, and Si substrates

    Koren, G.; Polturak, E.; Fisher, B.; Cohen, D.; Kimel, G.

    1988-01-01

    KrF excimer laser ablation of an Y 1 Ba 2 Cu 3 O/sub 7-//sub δ/ pellet in 0.1--0.2 Torr of O 2 ambient was used to deposit thin superconducting films onto SrTiO 3 , yttria-stabilized zirconia (YSZ), and silicon substrates at 600--700 0 C. The as-deposited 1-μm-thick films at 650--700 0 C substrate temperature were superconducting, without further high-temperature annealing. All films had a similar T/sub c/ onset of ∼92 K but different zero-resistance T/sub c/ of 90, 85, and 70 K for the films on SrTiO 3 , YSZ, and Si substrates, respectively. Angular x-ray diffraction analysis showed that all the films were highly oriented with the c axis perpendicular to their surface. Critical current densities at 77 K were about 40 000 and 10 000 A/cm 2 for the films on SrTiO 3 and YSZ, respectively. Smooth surface morphology was observed in all films, with occasional defects and cracks in the films on YSZ, which seems to explain the lower critical current in these films

  16. High field conditioning of cryogenic RF cavities

    Cole, M.; Debiak, T.; Lom, C.; Shephard, W.; Sredniawski, J.

    1993-01-01

    Space-based and other related accelerators have conditioning and operation requirements that are not found in most machines. The use of cryogenic copper, relatively poor vacuum, and limited power storage and operating time put unusual demands on the high-field conditioning process and present some concerns. Two CW cryogenic engineering model open-quotes sparkerclose quotes cavities have been fabricated and tested to fairly high field levels. Tests included initial and repeated conditioning as well as sustained RF operations. The two cavities were an engineering model TDL and an engineering model RFQ. Both cavities operated at 425 MHz. The DTL was conditioned to 46 MV/m at 100% duty factor (CW) at cryogenic temperature. This corresponds to a gap voltage of 433 kV and a real estate accelerating gradient (energy gain/total cavity length) of 6.97 MV/m. The authors believe this to be record performance for cryo CW operation. During cryo pulsed operation, the same cavity reached 48 MV/m with 200 μsec pulses at 0.5% DF. The RFQ was conditioned to 30 MV/m CW at cryo, 85 kV gap voltage. During a brief period of cryo pulsed operation, the RFQ operated at 46 MV/m, or 125 kV gap voltage. Reconditioning experiments were performed on both cavities and no problems were encountered. It should be noted that the vacuum levels were not very stringent during these tests and no special cleanliness or handling procedures were followed. The results of these tests indicate that cavities can run CW without difficulty at cryogenic temperatures at normal conservative field levels. Higher field operation may well be possible, and if better vacuums are used and more attention is pai