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Sample records for 0-5 cm layer

  1. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

  2. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    We present an ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer superlattices grown by MBE at low temperature (500 C), and compare our results with X-ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. We show that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. We also note that we do not observe any strain effect on the E1 critical point.

  3. Ga0.5In0.5P Barrier Layer for Wet Oxidation of AlAs

    NASA Astrophysics Data System (ADS)

    Lee, Shih-Chang; Lee, Wei-I

    2000-05-01

    We study the stability of Ga0.5In0.5P and Al0.4Ga0.6As barrier layers for wet thermal oxidation of AlAs on GaAs. Samples with a Ga0.5In0.5P or Al0.4Ga0.6As barrier layer are oxidized in a water vapor environment under various oxidation conditions. The results of photoluminescence and secondary-ion mass spectrometry (SIMS) depth profile measurements indicate that the Ga0.5In0.5P barrier layer is more stable than the Al0.4Ga0.6As layer at higher oxidation temperatures and longer periods of oxidation time.

  4. Epitaxial growth of AlN and Al0.5Ga0.5N layers on aluminum nitride substrates

    NASA Astrophysics Data System (ADS)

    Schowalter, L. J.; Shusterman, Y.; Wang, R.; Bhat, I.; Arunmozhi, G.; Slack, G. A.

    2000-02-01

    High quality epitaxial AlN and AlxGa1-xN layers have been grown by organo-metallic vapor-phase epitaxy on single crystal a-face AlN substrates. Here we report the characterization of these layers using Rutherford backscattering/ion channeling spectroscopy, atomic force microscopy, double crystal x-ray diffraction, and preliminary electrical results. Ion channeling along the [112¯0] axis gave a minimum yield of 1.5% for an AlN layer and 2.2% for an Al0.5Ga0.5N, indicating excellent crystal quality. A resistivity of 20 Ω cm and a mobility of 20 cm2/V s was measured in a Si-doped, 1-μm-thick Al0.5Ga0.5N grown epitaxially on the AlN substrates.

  5. Epitaxial growth of AlN and Al 0.5Ga 0.5N layers on aluminum nitride substrates

    NASA Astrophysics Data System (ADS)

    Schowalter, L. J.; Rojo, J. C.; Slack, G. A.; Shusterman, Y.; Wang, R.; Bhat, I.; Arunmozhi, G.

    2000-04-01

    High-quality epitaxial AlN and Al xGa 1- xN layers have been grown by organo-metallic vapor-phase epitaxy (OMVPE) on single-crystal AlN substrates. Here we report the characterization of these layers on a-face substrates using Rutherford backscattering/ion channeling spectroscopy (RBS), atomic force microscopy (AFM), double-crystal X-ray diffraction (XRD), and preliminary electrical results. Ion channeling along the [ 1 1 2¯ 0 ] axis gave a minimum yield of 1.5% for an AlN layer and 2.2% for an Al 0.5Ga 0.5N, indicating excellent crystal quality. A resistivity of 20 Ω cm and a mobility of 20 cm 2/V s was measured in a Si-doped, 1 μm-thick, epitaxial Al 0.5Ga 0.5N grown epitaxially on the AlN substrates.

  6. Defect distribution and compositional inhomogeneities in Al0.5Ga0.5N layers grown on stepped surfaces

    NASA Astrophysics Data System (ADS)

    Mogilatenko, A.; Knauer, A.; Zeimer, U.; Weyers, M.

    2016-02-01

    This study reports on defect distribution and compositional homogeneity of Al x Ga1-x N layers with a nominal composition x of 0.5 grown on AlN by metal organic vapor phase epitaxy. The AlN layers with a low threading dislocation density (TDD) of a few 108 cm-2 were obtained by ELO and showed periodic surface macrosteps. Al x Ga1-x N growth on these AlN surfaces results in inhomogeneous Ga distribution due to enhanced Ga incorporation on the macrostep sidewalls. Variation of AlGaN deposition rate strongly influences the Ga distribution as well as the defect structure in the layers. Low growth rates (0.2 μm h-1) result in an inhomogeneous TD distribution with formation of alternating stripes with lower and higher defect densities. Additionally, self-organized formation of additional Ga-rich areas at the top edge of the steps is observed. In contrast, at a higher growth rate of 1 μm h-1 the formation of additional Ga-rich areas can be completely suppressed, but the defect density increases. This leads to an optimum growth rate to minimize the TDD.

  7. High pressure Raman study of layered Mo0.5W0.5S2 ternary compound

    NASA Astrophysics Data System (ADS)

    Kim, Joon-Seok; Moran, Samuel T.; Nayak, Avinash P.; Pedahzur, Shahar; Ruiz, Itzel; Ponce, Gabriela; Rodriguez, Daniela; Henny, Joanna; Liu, Jin; Lin, Jung-Fu; Akinwande, Deji

    2016-06-01

    Ternary two-dimensional (2D) transition metal dichalcogenide compounds exhibit a tunable electronic structure allowing for control of the interlayer and the intralayer atomic displacement to efficiently tune their physical and electronic properties. Using a diamond anvil cell, hydrostatic pressure was applied to Mo0.5W0.5S2 up to 40 GPa in order to study the optical phonon vibrational modes. Analysis of the high-pressure Raman spectra shows that the two in-plane E2g modes resembling that of pristine MoS2 and WS2, as well as disorder-activated longitudinal acoustic phonon mode, are hardened and suppressed as pressure increases. The two A1g modes of the ternary compound that resemble the A1g modes of pristine MoS2 and WS2, displayed similar Raman shifts to the pristine compounds as pressure increases. A Raman peak at 470 cm-1 that is close to A1g peaks emerges at ˜8 GPa, which represents a disorder-activated pressure-induced out-of-plane Raman mode observed only in the ternary compound under high pressure. At pressures above ˜30 GPa, a Raman peak at approximately 340 cm-1 is observed, signifying additional disorder-activated vibration mode. Our results reveal the enhanced interactions in the structural and vibrational behavior of the MoS2 and WS2 domains in the Mo0.5W0.5S2 compound under hydrostatic pressure. These results could have implications in understanding the electronic, optical, and structural properties of the new 2D ternary compound materials under extreme mechanical conditions.

  8. Polynomial coefficients for calculating O2 Schumann-Runge cross sections at 0.5/cm resolution

    NASA Technical Reports Server (NTRS)

    Minschwaner, K.; Anderson, G. P.; Hall, L. A.; Yoshino, K.

    1992-01-01

    O2 cross sections from 49,000 to 57,000/cm have been fitted with temperature dependent polynomial expressions, providing an accurate and efficient means of determining Schumann-Runge band cross sections for temperatures between 130 and 500 K. The least squares fits were carried out on a 0.5/cm spectral grid, using cross sections obtained from a Schumann-Runge line-by-line model that incorporates the most recent spectroscopic data. The O2 cross sections do not include the underlying Herzberg continuum, but they do contain contributions from the temperature dependent Schumann-Runge continuum. The cross sections are suitable for use in UV transmission calculations at high spectral resolution. They should also prove useful for updating existing parameterizations of ultraviolet transmission and O2 photolysis.

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

    SciTech Connect

    Chen, Hungru; Umezawa, Naoto

    2015-02-07

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

  10. Growth of layered LiNi0.5Mn0.5O2 thin films by pulsed laser deposition for application in microbatteries

    NASA Astrophysics Data System (ADS)

    Xia, Hui; Lu, Li; Meng, Ying Shirley

    2008-01-01

    LiNi0.5Mn0.5O2 films were prepared by pulsed laser deposition on stainless steel (SS) and Au substrates. The substrate was found to play an important role in determining the growth of films. Although similar x-ray diffraction spectra were observed for both types of substrates, Raman spectra exhibited different features. The charge-discharge behavior of the film on the SS substrate indicates a spinel structure while the charge-discharge behavior of the film on the Au substrate indicates a layered structure. The secondary ion mass spectrometry depth-profiling results indicate interdiffusion between the film and the substrate, which inhibits the formation of pure layered LiNi0.5Mn0.5O2 phase.

  11. Optimization of exchange bias in Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} Heusler alloy layers

    SciTech Connect

    Hirohata, Atsufumi; Izumida, Keisuke; Ishizawa, Satoshi; Nakayama, Tadachika; Sagar, James

    2014-05-07

    We have fabricated and investigated IrMn{sub 3}/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} stacks to meet the criteria for future spintronic device applications which requires low-temperature crystallisation (<250 °C) and a large exchange bias H{sub ex} (>500 Oe). Such a system would form the pinned layer in spin-valve or tunnel junction applications. We have demonstrated that annealing at 300 °C which can achieve crystalline ordering in the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} layer giving ∼80% of the predicted saturation magnetisation. We have also induced an exchange bias of ∼240 Oe at the interface. These values are close to the above criteria and confirm the potential of using antiferromagnet/Heusler-alloy stacks in current Si-based processes.

  12. Electronic structure of a new layered bismuth oxyselenide superconductor: LaO0.5F0.5BiSe2.

    PubMed

    Xia, M; Jiang, J; Niu, X H; Liu, J Z; Wen, C H P; Lu, H Y; Lou, X; Pu, Y J; Huang, Z C; Zhu, Xiyu; Wen, H H; Xie, B P; Shen, D W; Feng, D L

    2015-07-22

    LaO(0.5)F(0.5)BiSe(2) is a new layered superconductor discovered recently, which shows the superconducting transition temperature of 3.5 K. With angle-resolved photoemission spectroscopy, we study the electronic structure of LaO(0.5)F(0.5)BiSe(2) comprehensively. Two electron-like bands are located around the X point of the Brillouin zone, and the outer pockets connect with each other and form large Fermi surface around Γ and M. These bands show negligible k(z) dispersion, indicating their two-dimensional nature. Based on the Luttinger theorem, the carrier concentration is about 0.53 e(-) per unit cell, close to its nominal value. Moreover, the photoemission data and the band structure calculations agree very well, and the renormalization factor is nearly 1.0, indicating the electron correlations in this material are rather weak. Our results suggest that LaO(0.5)F(0.5)BiSe(2) is a conventional BCS superconductor without strong electron correlations. PMID:26102451

  13. Substrate-free layer-number identification of two-dimensional materials: A case of Mo0.5W0.5S2 alloy

    NASA Astrophysics Data System (ADS)

    Qiao, Xiao-Fen; Li, Xiao-Li; Zhang, Xin; Shi, Wei; Wu, Jiang-Bin; Chen, Tao; Tan, Ping-Heng

    2015-06-01

    Any of two or more two-dimensional (2D) materials with similar properties can be alloyed into a new layered material, namely, 2D alloy. Individual monolayer in 2D alloys is kept together by van der Waals interactions. The property of multilayer alloys is a function of their layer number. Here, we studied the shear (C) and layer-breathing (LB) modes of Mo0.5W0.5S2 alloy flakes and their link to the layer number. The study reveals that the disorder effect is absent in the C and LB modes of 2D alloys, and the monatomic chain model can be used to estimate the frequencies of the C and LB modes. We demonstrated how to use the frequencies of C and LB modes to identify the layer number of alloy flakes deposited on different substrates. This technique is independent of the substrate, stoichiometry, monolayer thickness, and complex refractive index of 2D materials, offering a robust and substrate-free approach for layer-number identification of ultrathin flakes of 2D materials, such as 2D crystals and 2D alloys.

  14. Microstructural evaluation of Sb-adjusted Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer layer systems for IR applications

    SciTech Connect

    Chen, E.; Paine, D.C.; Uppal, P.; Ahearn, J.S.; Nichols, K.; Charache, G.W.

    1998-06-01

    The authors report on a transmission electron microscopy (TEM) study of Sb-adjusted quaternary Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBe at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} is successively increased in a series of 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60{degree} type and are distributed through out the interfaces of the buffer layer. When optimized, the authors have shown, using plan view and cross-sectional TEM, that this approach can reduce the threading defect density to below the detectability limit of TEM (< 10{sup 5}/cm{sup 2}) and preserve growth surface planarity. The Sb-graded approach was used to fabricate two 2.2 {micro}m power converter structures fabricated using InGaAs grown on Sb-based buffer layers on GaAs substrates. A microstructural and electrical characterization was performed on these device structures and the results are contrasted with a sample in which InP was selected as the substrate. Microstructure, defect density and device performance in these not-yet-optimized Sb-based buffer layers compares favorably to equivalent devices fabricated using InP substrates.

  15. BEHAVIORAL AND PHYSIOLOGICAL EFFECTS OF CHRONIC 2,450-MHZ MICROWAVE IRRADIATION OF THE RAT AT 0.5 MW/CM SQ

    EPA Science Inventory

    Adult male Long-Evans rats were intermittently exposed to 2450 MHz CW microwaves at an average power density of 0.5 mW/sq. cm. for 90 days. The resulting SAR was 0.14 W/kg (range 0.11 to 0.18 W/kg). The animals were exposed 7 h/day, 7 days/wk, for a total of 630 h in a monopole-a...

  16. PrBa0.5Sr0.5Co2O5+δ layered perovskite cathode for intermediate temperature solid oxide fuel cells

    SciTech Connect

    Ding, Hanping; Xue, Xingjian

    2010-02-06

    Layered perovskite oxides have ordered A-cations localizing oxygen vacancies, and may potentially improve oxygen ion diffusivity and surface exchange coefficient. The A-site-ordered layered perovskite PrBa0.5Sr0.5Co2O5+δ (PBSC) was evaluated as new cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The material was characterized using electrochemical impedance spectroscopy in a symmetrical cell system (PBSC/Ce0.9Sm0.1O1.9 (SDC)/PBSC), exhibiting excellent performance in the intermediate temperature range of 500–700 °C. An area-specific-resistance (ASR) of 0.23 Ω cm2 was achieved at 650 °C for cathode polarization. The low activation energy (Ea) 124 kJ mol-1 is comparable to that of La0.8Sr0.2CoO3-δ. A laboratory-scaled SDC-based tri-layer cell of Ni-SDC/SDC/PBSC was tested in intermediate temperature conditions of 550 to 700 °C. A maximum power density of 1045 mW cm-2 was achieved at 700 °C. The interfacial polarization resistance is as low as 0.285, 0.145, 0.09 and 0.05 Ω cm2 at 550, 600, 650 and 700 °C, respectively. Layered perovskite PBSC shows promising performance as cathode material for IT-SOFCs.

  17. The hierarchical structure of cubic K0.5La0.5TiO3 layers and enhanced photocatalytic hydrogen evolution after surface acidification.

    PubMed

    Zhao, Wenli; Zhu, Guilian; Zhao, Wei; Lin, Tianquan; Xu, Fangfang; Huang, Fuqiang

    2015-11-14

    Transition-metal perovskite oxides possess rich functionalities in the fields of ferroelectrics, piezoelectrics, superconductors, dielectrics, fuel cells and photocatalysis. Nano-facet control of the cubic ATiO3 (A: a divalent cation) phase, a typical perovskite oxide, may result in new properties or phenomena not observable in the bulk material. Herein, we first report a puzzle-like 3D hierarchical structure constructed with K0.5La0.5TiO3 nanosheets. Surprisingly, K0.5La0.5TiO3 has a cubic symmetry similar to a SrTiO3 perovskite. The unusual phase is synthesized by a simple one-pot hydrothermal strategy without using any structure-directing agent. After modest acidification, the assembled 3D hierarchical structure is etched into a core-shell nanostructure which consists of a crystalline K0.5La0.5TiO3 core and an amorphous TiO2 shell. The acid-treated sample exhibits remarkably enhanced photocatalytic H2 production, which is over 60 times higher than the pristine sample. PMID:26455735

  18. Structural, electrochemical and magnetic characterization of the layered-type PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+δ} perovskite

    SciTech Connect

    Azad, Abul K.; Kim, Jung H.; Irvine, John T.S.

    2014-05-01

    Structural, electrical and magnetic properties of the layered cobaltite PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+δ} have been investigated by means of neutron diffraction, electron diffraction, thermogravimetric analysis and SQUID magnetometry. Rietveld analysis of neutron diffraction data shows the ordered distribution of oxygen vacancies in [PrO{sub δ}] planes which doubles the lattice parameters from the simple perovskite cell parameter as a≈2a{sub p} and c≈2a{sub p} (a{sub p} is the cell parameter of the simple Perovskite) yielding tetragonal symmetry in the P4/mmm space group. On heating, above 573 K in air, structural rearrangement takes place and the structure can be defined as a≈a{sub p} and c≈2a{sub p} in the same space group. Oxygen occupancies have been determined as a function of temperature from neutron diffraction results. Initially (≥373 K), oxygen occupancy was increased and then decreased with increasing temperature. It was found that at 973 K the total oxygen loss is calculated about 0.265 oxygen/formula unit. Oxygen vacancy ordering was observed below 573 K, and the oxygen occupancy decreases as cell volume increases with increasing temperature. Area specific resistance (ASR) measurements show a resistance of 0.153 Ωcm{sup 2} and 0.286 Ωcm{sup 2} at 973 K and 923 K, respectively. On cooling, paramagnetic to ferromagnetic and an incomplete ferromagnetic to antiferromagnetic transition takes place. Different behaviours in field cooled and zero-field-cooled measurements leads to a coexistence of ferromagnetic and antiferromagnetic order. - Graphical abstract: Structural phase changes in PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+δ} at elevated temperatures determined by neutron powder diffraction. Depending on oxygen occupancy it form different phases at different temperatures. This pictures show the schematic 3D diagram of PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+δ} at 295 K (a), 373 K (b) and 573 K (c). Co atoms are inside the

  19. Enhancement of magnetoresistance by inserting thin NiAl layers at the interfaces in Co2FeGa0.5Ge0.5/Ag/Co2FeGa0.5Ge0.5 current-perpendicular-to-plane pseudo spin valves

    NASA Astrophysics Data System (ADS)

    Jung, J. W.; Sakuraba, Y.; Sasaki, T. T.; Miura, Y.; Hono, K.

    2016-03-01

    We have investigated the effects of insertion of a thin NiAl layer (≤0.63 nm) into a Co2FeGa0.5Ge0.5 (CFGG)/Ag interface on the magnetoresistive properties in CFGG/Ag/CFGG current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs). First-principles calculations of ballistic transmittance clarified that the interfacial band matching at the (001)-oriented NiAl/CFGG interface is better than that at the (001)-Ag/CFGG interface. The insertion of 0.21-nm-thick NiAl layers at the Co2FeGa0.5Ge0.5/Ag interfaces effectively improved the magnetoresistance (MR) output; the observed average and the highest MR ratio (ΔRA) are 62% (25 mΩ μm2) and 77% (31 mΩ μm2) at room temperature, respectively, which are much higher than those without NiAl insertion. Microstructural analysis using scanning transmission electron microscopy confirmed the existence of thin NiAl layers at the Ag interfaces with only modest interdiffusion even after annealing at 550 °C. The improvement of the interfacial spin-dependent scattering by very thin NiAl insertion can be a predominant reason for the enhancement of the MR output.

  20. Fabrication of 100-Oriented (Na0.5K0.5)NbO3-BaZrO3-(Bi0.5Li0.5)TiO3 Films on Si Substrate Using LaNiO3 Layer

    NASA Astrophysics Data System (ADS)

    Nakao, Tomohiro; Yamazoe, Seiji; Fukada, Masaki; Komaki, Kazuki; Noda, Toshinari; Adachi, Hideaki; Wada, Takahiro

    2012-09-01

    0.92(Na0.5K0.5)NbO3-0.06BaZrO3-0.02(Bi0.5Li0.5)TiO3 (NKN-BZ-BLT) thin films were fabricated by pulsed laser deposition (PLD) on a (100)Si substrate on which a 100-oriented LaNiO3 (LNO) bottom layer was fabricated by the chemical solution deposition method. The NKN-BZ-BLT films were characterized by X-ray diffraction (XRD) analysis, θ/2θ scan and ψ-2θ/ω scan, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The properties were compared with those of the NKN-BZ-BLT film deposited on the (111)Pt/Ti/SiO2/(100)Si substrate. We demonstrated that the LNO layer plays an important role in obtaining 100-oriented NKN-BZ-BLT films on the Si substrate. SEM surface and cross-sectional images showed that the NKN-BZ-BLT films fabricated at a substrate temperature of 800 °C had a high density and a relatively smooth surface. From the TEM image, this NKN-BZ-BLT film fabricated at 800 °C was composed of the columnar grains and some vertical-long pores could be observed. The energy dispersive X-ray (EDX) analysis showed that the LNO layer is decomposed to La2NiO4 by its reaction with Nb. The dielectric properties showed that the NKN-BZ-BLT film on the LNO electrode had a small dielectric constant of 82, compared with the NKN-BZ-BLT film (ɛr = 3127) on the (111)Pt/Ti/SiO2/(100)Si substrate. This difference is due to the polarization direction of the film and the polarization axis of the NKN-BZ-BLT film on the LNO electrode exists in a direction perpendicular to the surface of the substrate. However, the NKN-BZ-BLT film on LNO showed a small Pr value. This is due to the dispersion of Ni from the LNO layer.

  1. Fabrication of Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) catalysts with enhanced electrochemical performance by removing an inherent heterogeneous surface film layer.

    PubMed

    Jung, Jae-Il; Jeong, Hu Young; Kim, Min Gyu; Nam, Gyutae; Park, Joohyuk; Cho, Jaephil

    2015-01-14

    A heat-treatment approach for Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) (BSCF5582) is introduced as a way of enhancing the electrocatalytic performance of perovskite catalysts. The perovskite made by heat-treatment in oxygen atmosphere loses around 30 nm of spinel layer on the surface relative to the untreated version, and demonstrates enhanced oxygen reduction reaction and oxygen evolution reaction catalytic activities. PMID:25413252

  2. Effect of InxGa1-XAs Underlying Layer and Growth Mode on the Surface Morphology of In0.5Ga0.5As/GaAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ismail, A. K.; Aryanto, D.; Othaman, Z.; Ameruddin, A. S.

    2010-07-01

    Single layer of In0.5Ga0.5As quantum dots (QDs) was grown using self-assembled Stranski-Krastanow on a thin InxGa1-xAs underlying layer and on a reference GaAs wafer by metal-organic chemical vapour deposition (MOCVD). The effect of different indium composition in the underlying layer and the duration of arsine (AsH3) flow during cooling-down period of the growth process were investigated and characterized using atomic force microscopy (AFM). The growth of the thin underlying layer has significant influence on the formation of the QDs on the top surface. The dots density increases with increasing indium composition in the underlying layer. AsH3 flow during the period was found to influence the nucleation process of In0.5Ga0.5As QDs. A shorter period of AsH3 flow promotes smaller dots size and therefore increases the dots density.

  3. The effect of the thickness of tunneling layer on the memory properties of (Cu2O)0.5(Al2O3)0.5 high-k composite charge-trapping memory devices

    NASA Astrophysics Data System (ADS)

    Liu, Jinqiu; Lu, Jianxin; Yin, Jiang; Xu, Bo; Xia, Yidong; Liu, Zhiguo

    2016-06-01

    The charge-trapping memory devices namely Pt/Al2O3/(Al2O3)0.5(Cu2O)0.5/SiO2/p-Si with 2, 3 and 4 nm SiO2 tunneling layers were fabricated by using RF magnetron sputtering and atomic layer deposition techniques. At an applied voltage of ±11 V, the memory windows in the C-V curves of the memory devices with 2, 3 and 4 nm SiO2 tunneling layers were about 4.18, 9.91 and 11.33 V, respectively. The anomaly in memory properties among the three memory devices was ascribed to the different back tunneling probabilities of trapped electrons in the charge-trapping dielectric (Al2O3)0.5(Cu2O)0.5 due to the different thicknesses of SiO2 tunneling layer.

  4. Free and bound excitonic effects in Al0.5Ga0.5N/Al0.35Ga0.65N MQWs with different Si-doping levels in the well layers

    PubMed Central

    He, Chenguang; Qin, Zhixin; Xu, Fujun; Hou, Mengjun; Zhang, Shan; Zhang, Lisheng; Wang, Xinqiang; Ge, Weikun; Shen, Bo

    2015-01-01

    Free exciton (FX) and bound exciton (BX) in Al0.5Ga0.5N/Al0.35Ga0.65N multiple quantum wells (MQWs) with different Si-doping levels in the well layers are investigated by photoluminescence (PL) spectra. Low temperature (10 K) PL spectra identify a large binding energy of 87.4 meV for the BX in undoped sample, and 63.6 meV for the BX in Si-doped (2 × 1018 cm−3) sample. They are attributed to O-bound and Si-bound excitons, respectively. The large binding energies of BX are assumed to originate from the strong quantum confinement in the quantum wells, which also leads to a stronger FX PL peak intensity in comparison with BX at 10 K. Si-doping is found to suppress the FX quenching by reducing threading dislocation density (TDD) in the well layers, leading to a significant improvement of IQE from 33.7% to 45%. PMID:26267249

  5. Reduction of critical current density for out-of-plane mode oscillation in a mag-flip spin torque oscillator using highly spin-polarized Co2Fe(Ga0.5Ge0.5) spin injection layer

    NASA Astrophysics Data System (ADS)

    Bosu, S.; Sepehri-Amin, H.; Sakuraba, Y.; Hayashi, M.; Abert, C.; Suess, D.; Schrefl, T.; Hono, K.

    2016-02-01

    We study spin torque oscillators comprised of a perpendicular spin injection layer (SIL) and a planar field generating layer to reveal the influence of the spin polarization of SIL material on the critical current density, JC, to induce microwave oscillation. Two systems with different SIL are compared: one with a highly spin-polarized Heusler alloy, Co2Fe(Ga0.5Ge0.5) (CFGG), and the other a prototypical Fe2Co alloy. Cross sectional scanning transmission electron microscopy observations show the B2-ordered structure in a 3-nm-thick CFGG SIL, a prerequisite for obtaining half-metallic transport properties. Current induced microwave oscillations are found at frequencies of ˜15 GHz for both systems. However, the current needed to cause the oscillations is ˜50% smaller for films with the CFGG SIL compared to those of the Fe2Co SIL. These results are in accordance with micromagnetic simulations that include spin accumulation at the SIL.

  6. Crystal orientation dependence of current-perpendicular-to-plane giant magnetoresistance of pseudo spin-valves with epitaxial Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) Heusler alloy layers

    SciTech Connect

    Chen, Jiamin; Hono, K.; Li, Songtian; Furubayashi, T. Takahashi, Y. K.

    2014-06-21

    The magnetoresistive (MR) properties of Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) (CFGG) Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance pseudo-spin-valves (PSVs) are investigated. The PSV films are epitaxially grown on a sapphire (112{sup ¯}0) substrate with an Ag or Cu spacer layer, and their magnetoresistive properties are compared with those of PSV grown on MgO(001) substrates. For substrates with an Ag spacer, the PSV with the (001)[110]{sub CFGG}//(001)[010]{sub Ag} interface grown on MgO(001) exhibits a higher MR output compared with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Ag} interface grown on sapphire (112{sup ¯}0). In contrast, a higher MR output is obtained using a Cu spacer with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Cu} interface. These results demonstrate that the MR outputs depend upon the crystal orientation at the interface, and that interfaces with a small misfit tend to exhibit a larger MR output. This indicates the influence of crystal orientation as well as lattice mismatch upon the interfacial spin scattering asymmetry.

  7. ESR Studies of Layered-Perovskite Manganites R0.5Sr1.5MnO4 (R = La, Nd)

    NASA Astrophysics Data System (ADS)

    Marumoto, Kazuhiro; Soda, Kazuya; Kuroda, Shin-ichi; Moritomo, Yutaka

    2003-03-01

    ESR studies have been performed on single crystals of layered-perovskite manganites R0.5Sr1.5MnO4 (R = La, Nd). An anisotropic ESR signal with extremely broad linewidth is observed and ascribed to the single-ion-anisotropic D term. For La0.5Sr1.5MnO4, the spin susceptibility χs deviates from the Curie-Weiss-like behavior and the peak-to-peak linewidth Δ Hpp shows a broad maximum at the charge-ordering temperature Tco (≈ 217 K). With further decrease of temperature below 160 K, χs decreases and Δ Hpp increases rapidly due to the spin order at the Néel temperature TN (≈ 110 K). These anomalies are absent in Nd0.5Sr1.5MnO4, which does not show the charge-ordering nor the spin-ordering. On the basis of these experimental data, we will discuss the charge and spin order of La0.5Sr1.5MnO4.

  8. Intercalation of aliphatic amines into the layered structure of vanadyl(IV) hydrogen phosphate hemihydrate (VOHPO[sub 4][center dot]0. 5H[sub 2]O)

    SciTech Connect

    Guliants, V.V.; Benziger, J.B.; Sundaresan, S. )

    1994-04-01

    The vanadyl(IV) hydrogen phosphate hemihydrate, VOHPO[sub 4][center dot]0.5H[sub 2]O, is a pyrolytic precursor of the vanadyl(IV) pyrophosphate phase, (VO)[sub 2]P[sub 2]O[sub 7], generally believed to be the active phase in the selective oxidation of n-butane into maleic anhydride. Pyrolytic transformation into the pyrophosphate phase occurs with conservation of a morphology of the material. VOHPO[sub 4][center dot]0.5H[sub 2]O is a layered hydrogen phosphate, where -POH groups form interlayer hydrogen bonds with the water molecules shared by two face-linked vanadyl octahedra. The structure of the hemihydrate is similar to that of [alpha]-zirconium hydrogen phosphate ([alpha]-ZrP), where hydrogen bonds are within the same layer and -POH groups are also pointed into the interlayer space. In contrast to [alpha]-ZrP, where extensive data exist, intercalation chemistry of the layered vanadyl(IV) hydrogen phosphate hemihydrate at present is a terra incognita. This paper reports the results of the first systematic study of VOHPO[sub 4][center dot]0.5H[sub 2]O intercalation with aliphatic amines as a new route to novel vanadyl(IV) phosphate phases. N-Alkylamines have been commonly known as excellent intercalation agents for testing the intracrystalline reactivity of layered oxides. Intercalated alkylamines may also facilitate introduction of thermostable guest molecules, or [open quotes]pillars[close quotes], by ion exchange producing microporous materials which can modify catalytic and sorptive properties. 9 refs., 6 figs., 2 tabs.

  9. Synthesis and electrochemical properties of layered structure Li[Ni0.5Co0.25Mn0.25]O2 cathode material

    NASA Astrophysics Data System (ADS)

    Prathibha, G.; Rosaiah, P.; Reddy, B. Purusottam; Ganesh, K. Sivajee; Hussain, O. M.

    2015-06-01

    Lithium ion (Li-ion) batteries are currently the energy source of choice for cell phones, laptops, and other mobile electronic devices due to their balance of high energy density with high power density compared to other electrochemical energy carriers. In the present study, mixed hydroxide method is used to prepare Li[Ni0.5Co0.25Mn0.25]O2 from the precursors and analyze qualitatively and studied the electrochemical properties. The XRD spectrum exhibited predominant (003) orientation at 2θ =18.39o corresponding to hexagonal layered structure of R3m symmetry with evaluated lattice parameters are a= 2.84 Å, c= 14.43 Å. Raman measurements were performed to understand the microstructure and vibrational modes of the prepared sample. From the electrochemical (EC) studies an initial discharge capacity of about 140 mAhg-1 with good cyclic stability was observed for the prepared sample in the potential range 0.0 -1.0V in aqueous medium.

  10. Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

    SciTech Connect

    Krishnaprasad, P. S. E-mail: mkj@cusat.ac.in; Jayaraj, M. K. E-mail: mkj@cusat.ac.in; Antony, Aldrin; Rojas, Fredy

    2015-03-28

    Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BST thin films show significantly improved tunable performance over polycrystalline thin films.

  11. LIME 0.5

    SciTech Connect

    2011-01-14

    LIME 0.5 is an initial version of a Lightweight Integrating Multi-physics Environment for coupling codes. LIME by itself is not a code for doing multiphysics simulations. Instead, LIME provides the key high-level software, a flexible but defined approach, and interface requirements for a collection of (potentially disparate) physics codes to be combined with strong coupling (when needed) though non-linear solution methods (e.g. JFNK, fixed point), thus creating a new multi-physics simulation capability customized for a particular need. ! ! The approach taken is designed to! •! preserve and leverage any important specialized algorithms and/or functionality an existing application may provide,! •! minimize the requirements barrier for an application to participate,! •! work within advanced solver frameworks (e.g. as extensions to the Trilinos/NOX nonlinear solver libraries, PETSc, . . .),! Of note is that components/physics codes that can be coupled within LIME are NOT limited to:! •! components written in one particular language,! •! a particular numerical discretization approach ( e.g. Finite Element), or! •! physical models expressed as PDEʼs.!

  12. LIME 0.5

    2011-01-14

    LIME 0.5 is an initial version of a Lightweight Integrating Multi-physics Environment for coupling codes. LIME by itself is not a code for doing multiphysics simulations. Instead, LIME provides the key high-level software, a flexible but defined approach, and interface requirements for a collection of (potentially disparate) physics codes to be combined with strong coupling (when needed) though non-linear solution methods (e.g. JFNK, fixed point), thus creating a new multi-physics simulation capability customized for amore » particular need. ! ! The approach taken is designed to! •! preserve and leverage any important specialized algorithms and/or functionality an existing application may provide,! •! minimize the requirements barrier for an application to participate,! •! work within advanced solver frameworks (e.g. as extensions to the Trilinos/NOX nonlinear solver libraries, PETSc, . . .),! Of note is that components/physics codes that can be coupled within LIME are NOT limited to:! •! components written in one particular language,! •! a particular numerical discretization approach ( e.g. Finite Element), or! •! physical models expressed as PDEʼs.!« less

  13. A top-down strategy for the synthesis of mesoporous Ba0.5Sr0.5Co0.8Fe0.2O3-δ as a cathode precursor for buffer layer-free deposition on stabilized zirconia electrolyte with a superior electrochemical performance

    NASA Astrophysics Data System (ADS)

    Su, Chao; Xu, Xiaomin; Chen, Yubo; Liu, Yu; Tadé, Moses O.; Shao, Zongping

    2015-01-01

    We develop a facile and effective top-down method for the fabrication of mesoporous Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) oxide with a high specific surface area (∼25 m2 g-1). The original BSCF is first synthesized by the simple EDTA-citric acid complexing method, and then treated in H2O2 to obtain the mesoporous BSCF. The structure and morphology of as-prepared BSCF power is systematically characterized by N2 adsorption/desorption isotherms, XRD, TEM, SEM and ICP techniques. A possible mechanism for the creation of mesoporous BSCF is proposed, in which Ba2+ and Sr2+ dissolve selectively from partial BSCF particles during the catalytic decomposition of H2O2. The electrochemical properties are investigated by the EIS and I-V test in the symmetrical cell and integrated single cell configurations, respectively. The interfacial reaction between BSCF electrode and YSZ electrolyte was suppressed successfully by using the BSCF with high specific surface area to decrease the sintering temperature (800 °C), thus the electrode exhibits high oxygen reduction reaction activity. The solid oxide fuel cell (SOFC) achieves an exciting peak power density of ∼1800 mW cm-2 at 800 °C, signifying the mesoporous BSCF, together with the preparation method, has a good application prospect in the development of SOFCs.

  14. Ultrathin Hf0.5Zr0.5O2 Ferroelectric Films on Si.

    PubMed

    Chernikova, Anna; Kozodaev, Maksim; Markeev, Andrei; Negrov, Dmitrii; Spiridonov, Maksim; Zarubin, Sergei; Bak, Ohheum; Buragohain, Pratyush; Lu, Haidong; Suvorova, Elena; Gruverman, Alexei; Zenkevich, Andrei

    2016-03-23

    Because of their immense scalability and manufacturability potential, the HfO2-based ferroelectric films attract significant attention as strong candidates for application in ferroelectric memories and related electronic devices. Here, we report the ferroelectric behavior of ultrathin Hf0.5Zr0.5O2 films, with the thickness of just 2.5 nm, which makes them suitable for use in ferroelectric tunnel junctions, thereby further expanding the area of their practical application. Transmission electron microscopy and electron diffraction analysis of the films grown on highly doped Si substrates confirms formation of the fully crystalline non-centrosymmetric orthorhombic phase responsible for ferroelectricity in Hf0.5Zr0.5O2. Piezoresponse force microscopy and pulsed switching testing performed on the deposited top TiN electrodes provide further evidence of the ferroelectric behavior of the Hf0.5Zr0.5O2 films. The electronic band lineup at the top TiN/Hf0.5Zr0.5O2 interface and band bending at the adjacent n(+)-Si bottom layer attributed to the polarization charges in Hf0.5Zr0.5O2 have been determined using in situ X-ray photoelectron spectroscopy analysis. The obtained results represent a significant step toward the experimental implementation of Si-based ferroelectric tunnel junctions. PMID:26931409

  15. Ordering and disordering of doped Ga[sub 0. 5]In[sub 0. 5]P

    SciTech Connect

    Kurtz, S.R.; Olson, J.M.; Friedman, D.J.; Kibbler, A.E.; Asher, S. )

    1994-05-01

    The band gap of Ga[sub 0.5]In[sub 0.5]P is reported as a function of doping level and growth rate. The lowest band gaps are obtained for hole concentrations of about 2 x 10[sup 17] cm[sup [minus]3]. For samples doped p-type above 1 x 10[sup 18] cm[sup [minus]3], the band gap increases dramatically, regardless of growth rate. This effect is shown to be the result of disordering during growth rather than a change in the equilibrium surface structure with doping. The doping level dependence of the band gap of Ga[sub 0.5]In[sub 0.5]P samples grown at higher and lower growth rates differs for selenium and zinc doping even though the effects of high doping are the same for both dopants. 22 refs., 3 figs.

  16. Synthesis and electrochemical properties of layered structure Li[Ni{sub 0.5}Co{sub 0.25}Mn{sub 0.25}]O{sub 2} cathode material

    SciTech Connect

    Prathibha, G.; Rosaiah, P.; Reddy, B. Purusottam; Ganesh, K. Sivajee; Hussain, O. M.

    2015-06-24

    Lithium ion (Li-ion) batteries are currently the energy source of choice for cell phones, laptops, and other mobile electronic devices due to their balance of high energy density with high power density compared to other electrochemical energy carriers. In the present study, mixed hydroxide method is used to prepare Li[Ni{sub 0.5}Co{sub 0.25}Mn{sub 0.25}]O{sub 2} from the precursors and analyze qualitatively and studied the electrochemical properties. The XRD spectrum exhibited predominant (003) orientation at 2θ =18.39{sup o} corresponding to hexagonal layered structure of R3m symmetry with evaluated lattice parameters are a= 2.84 Å, c= 14.43 Å. Raman measurements were performed to understand the microstructure and vibrational modes of the prepared sample. From the electrochemical (EC) studies an initial discharge capacity of about 140 mAhg{sup −1} with good cyclic stability was observed for the prepared sample in the potential range 0.0 −1.0V in aqueous medium.

  17. Self-assembled In0.5Ga0.5As quantum dots on GaP

    NASA Astrophysics Data System (ADS)

    Song, Yuncheng; Simmonds, Paul J.; Lee, Minjoo Larry

    2010-11-01

    We demonstrate the growth and luminescence of coherently strained In0.5Ga0.5As self-assembled quantum dots on GaP. Cross-sectional and planar-view transmission electron microscopy confirmed the dislocation-free nature of the In0.5Ga0.5As quantum dots and GaP cap layers. Intense photoluminescence from the quantum dots was measured at 80 K and was visible to the unaided eye in ambient lighting. The photoluminescence results show that emission energy can be controlled by varying the In0.5Ga0.5As deposition thickness. In combination with recent advances in the growth of GaP on Si, the In0.5Ga0.5As quantum dots demonstrated here could enable monolithic optoelectronic integration on Si.

  18. Single layer fuel cell based on a composite of Ce0.8Sm0.2O2-δ-Na2CO3 and a mixed ionic and electronic conductor Sr2Fe1.5Mo0.5O6-δ

    NASA Astrophysics Data System (ADS)

    Dong, Xiao; Tian, Li; Li, Jiang; Zhao, Yicheng; Tian, Ye; Li, Yongdan

    2014-03-01

    A new kind of single layer fuel cell (SLFC) based on a composite material of Ce0.8Sm0.2O2-δ (SDC)-Na2CO3 and Sr2Fe1.5Mo0.5O6-δ (SFM) is successfully fabricated and characterized. As a mixed ionic and electronic conductor, SFM provides more reaction areas than the triple phase boundary provided by a simple mixture of ionic conductor and electronic conductor. SDC-Na2CO3 is used to adjust the ratio of ionic and electronic conductivities. The influence of the SFM content on the electrochemical performance of the SLFC is examined. The pellet made of 30 wt.% SFM and 70 wt.% SDC-Na2CO3 exhibits the highest open circuit voltage of 1.05 V and output of 360 mW cm-2 at 750 °C. Besides, by discussing influence factors of the OCV of the cell, the reason why the SLFC can give a similar OCV and output comparing with the conventional three-layer fuel cell, has been explained in detail.

  19. Copper uranyl phosphate and arsenate incorporating an organic ligand with a pillared layer structure: [Cu(4,4‧-bpy)(UO2)0.5(HPO4)(H2PO4)]·H2O and [Cu(4,4‧-bpy)(UO2)0.5(HAsO4)(H2AsO4)]·1.5H2O

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Min; Lii, Kwang-Hwa

    2013-01-01

    Two mixed-metal uranium compounds, [Cu(4,4'-bpy)(UO2)0.5(HPO4)(H2PO4)]·H2O (1) and [Cu(4,4'-bpy)(UO2)0.5(HAsO4)(H2AsO4)]·1.5H2O (2) have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction, fluorescence spectroscopy, and magnetic susceptibility. They are the first examples of mixed-metal uranium phosphate and arsenate incorporating an organic ligand. Their structures contain copper uranyl phosphate/arsenate layers which are covalently linked by 4,4'-bpy pillars to form a 3-D framework structure. The fluorescence spectrum of 1 shows the characteristic vibronic structure of the UO22+ moiety despite the presence of copper(II) ions in its structure. The two compounds are isostructural and crystallize in the monoclinic space group C2/c with a=20.184(4) Å, b=8.921(2) Å, c=19.095(3) Å, β=115.15(1)°, and R1=0.0244 for 1, and a=20.184(1) Å, b=9.0210(5) Å, c=19.714(1) Å, β=114.879(1)°, and R1=0.0399 for 2.

  20. Synthesis crystal structure and ionic conductivity of Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10

    NASA Astrophysics Data System (ADS)

    Porob, Digamber G.; Guru Row, T. N.

    2004-12-01

    Two new compounds Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10 have been synthesized in the ternary system: MO-Bi 2O 3-V 2O 5 system ( M=M 2+). The crystal structure of Sr 0.5Bi 3V 2O 10 has been determined from single crystal X-ray diffraction data, space group P1¯ and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å 3. Ca 0.5Bi 3V 2O 10 is isostructural with Sr 0.5Bi 3V 2O 10, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å 3 and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi 2O 2) along c-axis formed by linkage of BiO 8 and BiO 6 polyhedra interconnected by MO 8 polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10 -5 and 3.63×10 -5 S cm -1 for Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10, respectively at 725 °C.

  1. Impact of mechanical stress on ferroelectricity in (Hf0.5Zr0.5)O2 thin films

    NASA Astrophysics Data System (ADS)

    Shiraishi, Takahisa; Katayama, Kiliha; Yokouchi, Tatsuhiko; Shimizu, Takao; Oikawa, Takahiro; Sakata, Osami; Uchida, Hiroshi; Imai, Yasuhiko; Kiguchi, Takanori; Konno, Toyohiko J.; Funakubo, Hiroshi

    2016-06-01

    To investigate the impact of mechanical stress on their ferroelectric properties, polycrystalline (Hf0.5Zr0.5)O2 thin films were deposited on (111)Pt-coated SiO2, Si, and CaF2 substrates with thermal expansion coefficients of 0.47, 4.5, and 22 × 10-6/ °C, respectively. In-plane X-ray diffraction measurements revealed that the (Hf0.5Zr0.5)O2 thin films deposited on SiO2 and Si substrates were under in-plane tensile strain and that their volume fraction of monoclinic phase decreased as this strain increased. In contrast, films deposited on CaF2 substrates were under in-plane compressive strain, and their volume fraction of monoclinic phase was the largest among the three kinds of substrates. The maximum remanent polarization of 9.3 μC/cm2 was observed for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2, while ferroelectricity was barely observable for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2/CaF2. This result suggests that the in-plane tensile strain effectively enhanced the ferroelectricity of the (Hf0.5Zr0.5)O2 thin films.

  2. 43 CFR 2920.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Definitions. 2920.0-5 Section 2920.0-5... Easements: General Provisions § 2920.0-5 Definitions. As used in this part, the term: (a) Authorized officer... Land Management to use and manage the lands in a manner consistent with the terms of the easement....

  3. 43 CFR 2091.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

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  4. 43 CFR 2091.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

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  5. 43 CFR 2300.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

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  6. 28 CFR 0.5 - Attorney General.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 28 Judicial Administration 1 2013-07-01 2013-07-01 false Attorney General. 0.5 Section 0.5 Judicial Administration DEPARTMENT OF JUSTICE ORGANIZATION OF THE DEPARTMENT OF JUSTICE Office of the Attorney General § 0.5 Attorney General. The Attorney General shall: (a) Supervise and direct...

  7. 43 CFR 2610.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 2610.0-5 Section 2610.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) CAREY ACT GRANTS Carey Act Grants, General § 2610.0-5 Definitions. As used in the...

  8. 43 CFR 2300.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 2300.0-5 Section 2300.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) LAND WITHDRAWALS Withdrawals, General § 2300.0-5 Definitions. As used in this part, the term:...

  9. 43 CFR 2911.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 2911.0-5 Section 2911.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) LEASES Airport § 2911.0-5 Definitions. As used in this subpart, the term: (a) Act means the...

  10. 43 CFR 8223.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

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  11. 43 CFR 1784.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 1784.0-5 Section 1784.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR GENERAL MANAGEMENT (1000) COOPERATIVE RELATIONS Advisory Committees § 1784.0-5 Definitions. As used in this subpart, the...

  12. 43 CFR 8223.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

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  13. Effect of surface fluorine substitution on high voltage electrochemical performances of layered LiNi0.5Co0.2Mn0.3O2 cathode materials

    NASA Astrophysics Data System (ADS)

    Wang, Ding; Wang, Zhixing; Li, Xinhai; Guo, Huajun; Xu, Yan; Fan, Yulei; Pan, Wei

    2016-05-01

    A strategy of surface fluorine substitution to enhance the high voltage electrochemical performance of LiNi0.5Co0.2Mn0.3O2 material has been proposed. The inter-slab spacing distance is broaden by fluorine doping, which is deduced from the lattice parameters calculated by Rietveld refinement method. Scanning electron microscopy indicates the fluorine substitution stimulates the growth of the primary particles. Though the initial discharge capacities of LiNi0.5Co0.2Mn0.3O2-zFz (z = 0.02, 0.04, 0.06) is somewhat reduced, the capacity retention under high oxidation state were improved compared to that of bare one. For the optimal composition of LiNi0.5Co0.2Mn0.3O1.98F0.02, it exhibits a capacity retention of 81.1% at 1C after 100 cycles and delivers a discharge capacity of 123.5 mAh g-1 at 10C, and that of bare sample are just 70.1% and 109.6 mAh g-1, respectively. Cyclic voltammetry and electron impedance spectroscopy measurements demonstrate that the fluorine doping could significantly lower the cell polarization and retard the impedance rise. Transmission electron microscope analysis of cycled electrodes is also performed and it implies that fluorine substitution can effectively safeguard the electrode from HF erosion to maintain the bulk structural stable permanently.

  14. Grain size engineering for ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films by an insertion of Al{sub 2}O{sub 3} interlayer

    SciTech Connect

    Kim, Han Joon; Park, Min Hyuk; Kim, Yu Jin; Lee, Young Hwan; Jeon, Woojin; Gwon, Taehong; Moon, Taehwan; Kim, Keum Do; Hwang, Cheol Seong

    2014-11-10

    The degradation of ferroelectric (FE) properties of atomic layer deposited Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films with increasing thickness was mitigated by inserting 1 nm-thick Al{sub 2}O{sub 3} interlayer at middle position of the thickness of the FE film. The large P{sub r} of 10 μC/cm{sup 2}, which is 11 times larger than that of single layer Hf{sub 0.5}Zr{sub 0.5}O{sub 2} film with equivalent thickness, was achieved from the films as thick as 40 nm. The Al{sub 2}O{sub 3} interlayer could interrupt the continual growth of Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films, and the resulting decrease of grain size prevented the formation of non-ferroelectric monoclinic phase. The Al{sub 2}O{sub 3} interlayer also largely decreased the leakage current of the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films.

  15. Giant dielectric permittivity and weak ferromagnetic behavior in Bi0.5La0.5Fe0.5Cr0.5O3 ceramic

    NASA Astrophysics Data System (ADS)

    Tirupathi, Patri; Raju, K.; Peetla, Naresh; Pantangi, Ramakrishna; Pastor, Mukul

    2016-05-01

    A pervoskite (Bi0.5La0.5)(Fe0.5Cr0.5)O3 (BLFC) nanoparticles were synthesized by high energy ball milling. Rietveld refined X-ray diffraction studies revealed that this compound shows orthorhombic structure with Pbnm space group. The dielectric studies were investigated in wide frequency (102-106) range indicating giant dielectric permittivity behavior similar to LaFeO3 ceramic. The noted dielectric loss relaxation frequency dependent is as following the Arrhenius law can be ascribed as polaronic conduction. Further, magnetic transition at around 337 K and coexistence of weak ferromagnetic and antiferromagnetic behavior is observed below magnetic transition.

  16. Site symmetry of Er3+ in In0.5Ga0.5P

    NASA Astrophysics Data System (ADS)

    Jeong, B. S.; Hong, Y. K.; An, J. Y.; Choi, J. C.; Chung, C. H.; Park, H. L.

    1995-01-01

    The site and site symmetry of Er3+ in LPE grown In0.5Ga0.5P have been investigated for the first time through Raman and polarized luminescence spectroscopic techniques. The Er3+ site was found to be ErIn in In0.5Ga0.5P. The site symmetry of Er3+ in In0.5Ga0.5P was positively confirmed asC2v.

  17. 43 CFR 2920.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Definitions. 2920.0-5 Section 2920.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) LEASES, PERMITS AND EASEMENTS Leases, Permits and Easements: General Provisions §...

  18. 43 CFR 3142.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Definitions. 3142.0-5 Section 3142.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Paying...

  19. 43 CFR 3142.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 3142.0-5 Section 3142.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Paying...

  20. 43 CFR 3142.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Definitions. 3142.0-5 Section 3142.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Paying...

  1. 43 CFR 3142.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Definitions. 3142.0-5 Section 3142.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Paying...

  2. 43 CFR 9212.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Definitions. 9212.0-5 Section 9212.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR TECHNICAL SERVICES (9000) FIRE MANAGEMENT Wildfire Prevention §...

  3. 43 CFR 9212.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Definitions. 9212.0-5 Section 9212.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR TECHNICAL SERVICES (9000) FIRE MANAGEMENT Wildfire Prevention §...

  4. 43 CFR 9212.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Definitions. 9212.0-5 Section 9212.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR TECHNICAL SERVICES (9000) FIRE MANAGEMENT Wildfire Prevention §...

  5. 43 CFR 9212.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 9212.0-5 Section 9212.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR TECHNICAL SERVICES (9000) FIRE MANAGEMENT Wildfire Prevention §...

  6. 43 CFR 4700.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Definitions. 4700.0-5 Section 4700.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR RANGE MANAGEMENT (4000) PROTECTION, MANAGEMENT, AND CONTROL OF WILD FREE-ROAMING HORSES AND BURROS General §...

  7. 43 CFR 2300.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Definitions. 2300.0-5 Section 2300.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... employee of the Bureau of Land Management to whom has been delegated the authority to perform the...

  8. 43 CFR 2911.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Definitions. 2911.0-5 Section 2911.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT...). (b) Authorized officer means any employee of the Bureau of Land Management who has been delegated...

  9. 43 CFR 8340.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Definitions. 8340.0-5 Section 8340.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... Bureau of Land Management. (c) Bureau means the Bureau of Land Management. (d) Official use means use...

  10. 43 CFR 8340.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Definitions. 8340.0-5 Section 8340.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... Bureau of Land Management. (c) Bureau means the Bureau of Land Management. (d) Official use means use...

  11. 43 CFR 4100.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Definitions. 4100.0-5 Section 4100.0-5 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR RANGE MANAGEMENT (4000) GRAZING ADMINISTRATION-EXCLUSIVE OF ALASKA Grazing Administration-Exclusive of Alaska; General §...

  12. Enhanced electrostricitive properties and thermal endurance of textured (Bi0.5Na0.5)TiO3-BaTiO3-(K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Hao, Jigong; Ye, Chenggen; Shen, Bo; Zhai, Jiwei

    2013-08-01

    Textured 0.92(Bi0.5Na0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3 (BNT-BT-KNN) ceramics have been produced by tape casting with pure-phase (Bi0.5Na0.5)TiO3 templates. Through the approach of texture construction, enhanced electrostrictive response was obtained with an electrostrictive coefficient Q33 (˜0.024 m4/C2 at 60 kV/cm) and good thermostability comparable with that of traditional Pb-based electrostrictors. Even at an electric-field as low as 35 kV/cm or at a temperature as high as 180 °C, samples still possess a large electrostrictive response with Q33 > 0.022 m4/C2, suggesting it is very promising for practical applications as a lead-free electrostrictive material owning to its wide usage range. Moreover, reducing the applied electric-filed or increasing temperature can both induce the predominant to pure electrostriction transition due to the little contributions of electrostriction strain from ferroelectric domain switching. Our work may provide a new recipe for designing high-performance BNT-based lead-free electrostrictive materials by means of texture construction.

  13. Highly Textured Superconducting FeSe0.5Te0.5 Thin Films on Glass Substrates

    NASA Astrophysics Data System (ADS)

    Chen, Li; Tsai, Chen-Fong; Lee, Joon Hwan; Zhang, Xinghang; Wang, Haiyan

    2013-02-01

    Superconducting FeSe0.5Te0.5 thin films are deposited on amorphous substrates, i.e., glass substrates by a pulsed laser deposition (PLD) technique. Microstructural characterizations show that the films are highly textured along (00l) with good crystallinity. The superconducting critical transition temperature (Tc) ranges from ˜8 to ˜10 K. The self-field critical current density (Jcsf) at 4 K is ˜1.2×104 A/cm2. The in-field critical current density (Jcinfield) decreases slowly under high magnetic field confirmed by both transport and magnetization measurements. The growth of high quality superconducting FeSe0.5Te0.5 thin films on amorphous substrates demonstrates a low cost architecture for future Fe-based superconductor coated conductors.

  14. Photocarrier dynamics in transition metal dichalcogenide alloy Mo0.5W0.5S2.

    PubMed

    He, Jiaqi; He, Dawei; Wang, Yongsheng; Zhao, Hui

    2015-12-28

    We report a transient absorption study of photocarrier dynamics in transition metal dichalcogenide alloy, Mo0.5W0.5S2. Photocarriers were injected by a 400-nm pump pulse and detected by a 660-nm probe pulse. We observed a fast energy relaxation process of about 0.7 ps. The photocarrier lifetime is in the range of 50 - 100 ps, which weakly depends on the injected photocarrier density and is a few times shorter than MoS2 and WS2, reflecting the relatively lower crystalline quality of the alloy. Saturable absorption was also observed in Mo0.5W0.5S2, with a saturation energy fluence of 32 μJ cm(-2). These results provide important parameters on photocarrier properties of transition metal dichalcogenide alloys. PMID:26832001

  15. 43 CFR 1815.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ....0-5 Definitions. Major disaster means any hurricane, tornado, storm, flood, high water, winddriven..., which, in the determination of the President, is or threatens to be of sufficient severity and...

  16. 43 CFR 1815.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ....0-5 Definitions. Major disaster means any hurricane, tornado, storm, flood, high water, winddriven..., which, in the determination of the President, is or threatens to be of sufficient severity and...

  17. 43 CFR 1815.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ....0-5 Definitions. Major disaster means any hurricane, tornado, storm, flood, high water, winddriven..., which, in the determination of the President, is or threatens to be of sufficient severity and...

  18. 43 CFR 1815.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ....0-5 Definitions. Major disaster means any hurricane, tornado, storm, flood, high water, winddriven..., which, in the determination of the President, is or threatens to be of sufficient severity and...

  19. 43 CFR 2520.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) DESERT-LAND ENTRIES Desert-Land Entries: General § 2520.0-5 Definitions. (a) As used in the desert-land laws and the regulations of this subpart:...

  20. 43 CFR 2520.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) DESERT-LAND ENTRIES Desert-Land Entries: General § 2520.0-5 Definitions. (a) As used in the desert-land laws and the regulations of this subpart:...

  1. 43 CFR 2520.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) DESERT-LAND ENTRIES Desert-Land Entries: General § 2520.0-5 Definitions. (a) As used in the desert-land laws and the regulations of this subpart:...

  2. 43 CFR 2520.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) DESERT-LAND ENTRIES Desert-Land Entries: General § 2520.0-5 Definitions. (a) As used in the desert-land laws and the regulations of this subpart:...

  3. Proton conduction and chemical stability of (La{sub 0.5}Sr{sub 0.5})(Mg{sub 0.5+y}Nb{sub 0.5-y})O{sub 3-{delta}}

    SciTech Connect

    Kawasaki, Yuya; Okada, Sachio; Ito, Naoki; Matsumoto, Hiroshige Ishihara, Tatsumi

    2009-02-04

    Electrical conduction properties of complex perovskite-type oxides in the (La{sub 0.5}Sr{sub 0.5})(Mg{sub 0.5+y}Nb{sub 0.5-y})O{sub 3-{delta}} (y = 0.02-0.06) series at intermediate-high temperatures were investigated; introduction of protons by hydration of oxide-ion vacancies was expected by increasing the Mg/Nb ratio from unity. The conductivity depended on y and a maximum conductivity was obtained at y = 0.04: {sigma} = 4.9 x 10{sup -6} S cm{sup -1} at 400 deg. C in wet H{sub 2} atmospheres. From electromotive force measurements of hydrogen and water vapor concentration cells, electrical conduction in wet H{sub 2} atmospheres can be attributed to ionic conduction, and proton conduction is dominant below 700 deg. C. Unlike other perovskite-type proton conductors, (La{sub 0.5}Sr{sub 0.5})(Mg{sub 0.54}Nb{sub 0.46})O{sub 3-{delta}} was stable in CO{sub 2} atmospheres even in the low-intermediate temperature region due to dilution of reactive strontium by lanthanum.

  4. Determination of the density of the defect states in Hf{sub 0.5}Zr{sub 0.5}O{sub 2} high-k film Deposited by using rf-magnetron sputtering technique

    SciTech Connect

    Lu, W.; Lu, J. X.; Ou, X.; Liu, X. J.; Cao, Y. Q.; Li, A. D.; Xu, B.; Xia, Y. D.; Yin, J.; Liu, Z. G.

    2014-08-15

    A memory structure Pt/Al{sub 2}O{sub 3}/Hf{sub 0.5}Zr{sub 0.5}O{sub 2}/Al{sub 2}O{sub 3}/p-Si was fabricated by using atomic layer deposition and rf-magnetron sputtering techniques, and its microstructure has been investigated by using the high resolution transmission electron microscopy (HRTEM). By measuring the applied gate voltage dependence of the capacitance for the memory structure, the planar density of the trapped charges in Hf{sub 0.5}Zr{sub 0.5}O{sub 2} high-k film was estimated as 6.63 × 10{sup 12} cm{sup −2}, indicating a body defect density of larger than 2.21 × 10{sup 19} cm{sup −3}. It is observed that the post-annealing in N{sub 2} can reduces the defect density in Hf{sub 0.5}Zr{sub 0.5}O{sub 2} film, which was ascribed to the occupancy of oxygen vacancies by nitrogen atoms.

  5. Radiation hardness of Ga0.5In0.5 P/GaAs tandem solar cells

    NASA Technical Reports Server (NTRS)

    Kurtz, Sarah R.; Olson, J. M.; Bertness, K. A.; Friedman, D. J.; Kibbler, A.; Cavicchi, B. T.; Krut, D. D.

    1991-01-01

    The radiation hardness of a two-junction monolithic Ga sub 0.5 In sub 0.5 P/GaAs cell with tunnel junction interconnect was investigated. Related single junction cells were also studied to identify the origins of the radiation losses. The optimal design of the cell is discussed. The air mass efficiency of an optimized tandem cell after irradiation with 10(exp 15) cm (-2) 1 MeV electrons is estimated to be 20 percent using currently available technology.

  6. Infrared absorption spectra of a Nd0.5Ho0.5Fe3(BO3)4 crystal

    NASA Astrophysics Data System (ADS)

    Gerasimova, Yu. V.; Sofronova, S. N.; Gudim, I. A.; Oreshonkov, A. S.; Vtyurin, A. N.; Ivanenko, A. A.

    2016-01-01

    Infrared absorption spectra of a Nd0.5Ho0.5Fe3(BO3)4 crystal in the spectral range of 30-1700 cm-1 have been measured at temperatures from 6 to 300 K. The experimental spectra have been analyzed based on the semiempirical calculation of the lattice dynamics and the analysis of correlation diagrams of borate complexes. No changes associated with structural phase transitions have been detected in the temperature range of measurements; the effect of magnetic ordering on the infrared absorption spectra has not been observed.

  7. Stress-induced shifting of the morphotropic phase boundary in sol-gel derived Pb(Zr{sub 0.5}Ti{sub 0.5})O{sub 3} thin films

    SciTech Connect

    Zhang, S.Q.; Wang, L.D.; Li, W.L.; Liu, C.Q.; Wang, J.N.; Li, N.; Darvishi, A. Rajabtabar; Fei, W.D.

    2011-08-15

    Highlights: {yields} Differing from Pb(Zr{sub 0.5}Ti{sub 0.5})O{sub 3} bulk ceramic with a tetragonal phase, our results indicate that for PZT thin films with the same composition monoclinic phase coexisting with tetragonal phase can appear. {yields} Tensile stress is suggested to play a role in shifting the morphotropic phase boundary to titanium-rich region in PZT thin films. {yields} The deteriorated ferroelectric properties can be attributed mainly to the presence of thin non-ferroelectric layer and large tensile stress. -- Abstract: The structure evolution of Pb(Zr{sub 0.5}Ti{sub 0.5})O{sub 3} thin films with different thicknesses on the Pt(1 1 1)/Ti/SiO{sub 2}/Si substrates has been investigated using X-ray diffraction and Raman scattering. Differing from Pb(Zr{sub 0.5}Ti{sub 0.5})O{sub 3} bulk ceramic with a tetragonal phase, our results indicate that for PZT thin films with the same composition monoclinic phase with Cm space group coexisting with tetragonal phase can appear. It is suggested that tensile stress plays a role in shifting the morphotropic phase boundary to titanium-rich region in PZT thin films. The deteriorated ferroelectric properties of PZT thin films can be attributed mainly to the presence of thin non-ferroelectric layer and large tensile stress.

  8. 43 CFR 3150.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... placing explosive charges, where permissible, for seismic exploration. (b) Casual use means activities..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) ONSHORE OIL AND GAS GEOPHYSICAL EXPLORATION Onshore Oil and Gas Geophysical Exploration; General § 3150.0-5 Definitions. As used in this part, the term:...

  9. 43 CFR 3141.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Leasing in Special Tar Sand Areas § 3141.0-5 Definitions. As used in this subpart, the term: (a) Combined hydrocarbon lease means a lease issued in a Special Tar Sand Area for the removal of any gas and...

  10. 43 CFR 3141.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Leasing in Special Tar Sand Areas § 3141.0-5 Definitions. As used in this subpart, the term: (a) Combined hydrocarbon lease means a lease issued in a Special Tar Sand Area for the removal of any gas and...

  11. 43 CFR 3141.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Leasing in Special Tar Sand Areas § 3141.0-5 Definitions. As used in this subpart, the term: (a) Combined hydrocarbon lease means a lease issued in a Special Tar Sand Area for the removal of any gas and...

  12. 43 CFR 3141.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING IN SPECIAL TAR SAND AREAS Leasing in Special Tar Sand Areas § 3141.0-5 Definitions. As used in this subpart, the term: (a) Combined hydrocarbon lease means a lease issued in a Special Tar Sand Area for the removal of any gas and...

  13. 43 CFR 8224.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., DEPARTMENT OF THE INTERIOR RECREATION PROGRAMS PROCEDURES Fossil Forest Research Natural Area § 8224.0-5..., bitumen, lignite, asphaltum and tar sands, even though they are of biologic origin: (c) Fossil Forest or Fossil Forest Research Natural Area means those public lands as described in section 103(a) of the...

  14. 43 CFR 2300.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) LAND WITHDRAWALS Withdrawals, General § 2300.0-5... employee of the Bureau of Land Management to whom has been delegated the authority to perform the...

  15. 43 CFR 3180.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) ONSHORE OIL AND GAS UNIT AGREEMENTS: UNPROVEN AREAS Onshore Oil and Gas Unit Agreements: General § 3180.0-5 Definitions. The following terms, as used in this... or plan. Unitized substances. Deposits of oil and gas contained in the unitized land which...

  16. 43 CFR 3130.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL AND GAS LEASING: NATIONAL PETROLEUM RESERVE, ALASKA Oil and Gas Leasing, National Petroleum Reserve, Alaska: General § 3130.0-5 Definitions. As used in... exploring, testing, surveying or otherwise investigating the potential of a lease for oil and gas or...

  17. 43 CFR 3130.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL AND GAS LEASING: NATIONAL PETROLEUM RESERVE, ALASKA Oil and Gas Leasing, National Petroleum Reserve, Alaska: General § 3130.0-5 Definitions. As used in... exploring, testing, surveying or otherwise investigating the potential of a lease for oil and gas or...

  18. 43 CFR 3180.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) ONSHORE OIL AND GAS UNIT AGREEMENTS: UNPROVEN AREAS Onshore Oil and Gas Unit Agreements: General § 3180.0-5 Definitions. The following terms, as used in this... or plan. Unitized substances. Deposits of oil and gas contained in the unitized land which...

  19. 43 CFR 3180.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) ONSHORE OIL AND GAS UNIT AGREEMENTS: UNPROVEN AREAS Onshore Oil and Gas Unit Agreements: General § 3180.0-5 Definitions. The following terms, as used in this... or plan. Unitized substances. Deposits of oil and gas contained in the unitized land which...

  20. 43 CFR 3180.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) ONSHORE OIL AND GAS UNIT AGREEMENTS: UNPROVEN AREAS Onshore Oil and Gas Unit Agreements: General § 3180.0-5 Definitions. The following terms, as used in this... or plan. Unitized substances. Deposits of oil and gas contained in the unitized land which...

  1. 43 CFR 3130.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL AND GAS LEASING: NATIONAL PETROLEUM RESERVE, ALASKA Oil and Gas Leasing, National Petroleum Reserve, Alaska: General § 3130.0-5 Definitions. As used in... exploring, testing, surveying or otherwise investigating the potential of a lease for oil and gas or...

  2. 43 CFR 3130.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL AND GAS LEASING: NATIONAL PETROLEUM RESERVE, ALASKA Oil and Gas Leasing, National Petroleum Reserve, Alaska: General § 3130.0-5 Definitions. As used in... exploring, testing, surveying or otherwise investigating the potential of a lease for oil and gas or...

  3. 43 CFR 8224.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., DEPARTMENT OF THE INTERIOR RECREATION PROGRAMS PROCEDURES Fossil Forest Research Natural Area § 8224.0-5... Land Management designated to perform the duties described in this subpart: (b) Fossil means the..., bitumen, lignite, asphaltum and tar sands, even though they are of biologic origin: (c) Fossil Forest...

  4. 43 CFR 8224.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., DEPARTMENT OF THE INTERIOR RECREATION PROGRAMS PROCEDURES Fossil Forest Research Natural Area § 8224.0-5... Land Management designated to perform the duties described in this subpart: (b) Fossil means the..., bitumen, lignite, asphaltum and tar sands, even though they are of biologic origin: (c) Fossil Forest...

  5. 43 CFR 8224.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., DEPARTMENT OF THE INTERIOR RECREATION PROGRAMS PROCEDURES Fossil Forest Research Natural Area § 8224.0-5... Land Management designated to perform the duties described in this subpart: (b) Fossil means the..., bitumen, lignite, asphaltum and tar sands, even though they are of biologic origin: (c) Fossil Forest...

  6. 43 CFR 3400.0-5 - Definitions.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...-5 Definitions. As used in this group: (a) Alluvial valley floor has the meaning set forth in 30 CFR... consistent with 40 CFR 1508.9. (k) Exploration has the meaning set forth in § 3480.0-5(a)(17) of this title... approved mining or exploration plan. This is the same as the Federal lease bond referred to in 30 CFR...

  7. 43 CFR 3400.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...-5 Definitions. As used in this group: (a) Alluvial valley floor has the meaning set forth in 30 CFR... consistent with 40 CFR 1508.9. (k) Exploration has the meaning set forth in § 3480.0-5(a)(17) of this title... approved mining or exploration plan. This is the same as the Federal lease bond referred to in 30 CFR...

  8. 43 CFR 3400.0-5 - Definitions.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...-5 Definitions. As used in this group: (a) Alluvial valley floor has the meaning set forth in 30 CFR... consistent with 40 CFR 1508.9. (k) Exploration has the meaning set forth in § 3480.0-5(a)(17) of this title... approved mining or exploration plan. This is the same as the Federal lease bond referred to in 30 CFR...

  9. 43 CFR 3400.0-5 - Definitions.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...-5 Definitions. As used in this group: (a) Alluvial valley floor has the meaning set forth in 30 CFR... consistent with 40 CFR 1508.9. (k) Exploration has the meaning set forth in § 3480.0-5(a)(17) of this title... approved mining or exploration plan. This is the same as the Federal lease bond referred to in 30 CFR...

  10. 43 CFR 4700.0-5 - Definitions.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... HORSES AND BURROS General § 4700.0-5 Definitions. As used in this part, the term: (a) Act means the Act... Horse and Burro Act. (b) Authorized officer means any employee of the Bureau of Land Management to whom... means using a wild horse or burro because of its characteristics of wildness for direct or...

  11. Dielectric and electrical characteristics of La0.5Na0.5Ga0.5V0.5O3

    NASA Astrophysics Data System (ADS)

    Acharya, Truptimayee; Choudhary, R. N. P.

    2016-07-01

    La0.5Na0.5Ga0.5V0.5O3 (LNGVO) ceramic was prepared using a high-temperature solid-state reaction method. The structural phase, microstructure, dielectric, ferroelectric and optical properties of the material were systematically investigated. The preliminary structural analysis using x-ray diffraction (XRD) data shows the formation of the material in an orthorhombic crystal structure at room temperature. Detailed studies of dielectric and electrical properties have been carried out over a wide range of frequency (1 kHz-1 MHz) and temperature (25-450 °C) in order to elucidate the basic mechanism of the conduction and relaxation process. The dielectric characteristics show that the ceramic is a relaxor with strong diffuse phase transition and frequency dispersion. The nature of the variation of ac conductivity as a function of frequency obeys the universal power law, and confirms the existence of a hopping conduction mechanism in the material. The material also exhibits ferroelectricity at room temperature with a very low value of remnant polarization. The ionic conductivity and transport number of the ferroelectric ionic conductor were obtained with the standard experiment and calculation respectively. The material shows NTCR behavior similar to that of a semi-conductor. Similar behavior has also been observed in the study of I-V characteristics of the material.

  12. Comparative Dielectric and Ferroelectric Characteristics of Bi0.5Na0.5TiO3, CaCu3Ti4O12, and 0.5Bi0.5Na0.5TiO3-0.5CaCu3Ti4O12 Electroceramics

    NASA Astrophysics Data System (ADS)

    Singh, Laxman; Yadava, Shiva Sundar; Sin, Byung Cheol; Rai, Uma Shanker; Mandal, K. D.; Lee, Youngil

    2016-06-01

    The dielectric and ferroelectric characteristics of Bi0.5Na0.5TiO3 (BNT), CaCu3Ti4O12 (CCTO), and 0.5Bi0.5Na0.5TiO3-0.5CaCu3Ti4O12 (BNT/CCTO) ceramics are compared. X-ray diffraction patterns confirmed the formation of single phase of all the ceramics after sintering at 950°C for 15 h. Scanning electron microscopy images of the sintered ceramics reveal average grain sizes in the range from 200 nm to 2.5 μm. Energy-dispersive x-ray mapping and x-ray photoelectron spectroscopy show the presence of the elements Bi, Na, Ca, Cu, Ti, and O with uniform distribution in the ceramics. BNT/CCTO exhibits high dielectric constant ( ɛ r ˜ 6.9 × 104) compared with BNT ( ɛ r ˜ 0.13 × 104) and CCTO ( ɛ r ˜ 1.68 × 104) ceramics at 1 kHz and 503 K. The high dielectric constant of BNT/CCTO compared with BNT and CCTO is associated with a major contribution from grain boundaries, as confirmed by impedance and modulus analyses. The P- E hysteresis loop of all the ceramics measured at room temperature and 50°C exhibited typical ferroelectric nature. The remanent polarization ( P r) of BNT (1.58 μC/cm2) and CCTO (0.654 μC/cm2) ceramics are higher than that of BNT/CCTO (0.267 μC/cm2) ceramic.

  13. Lead-free Mn-doped (K0.5,Na0.5)NbO3 piezoelectric thin films for MEMS-based vibrational energy harvester applications

    NASA Astrophysics Data System (ADS)

    Won, Sung Sik; Lee, Joonhee; Venugopal, Vineeth; Kim, Dong-Joo; Lee, Jinkee; Kim, Ill Won; Kingon, Angus I.; Kim, Seung-Hyun

    2016-06-01

    Lead-free Mn-doped (K0.5, Na0.5)NbO3 (KNN) thin films were fabricated by the chemical solution deposition method. The addition of small concentration of Mn dopant effectively reduced the leakage current density and enhanced the piezoelectric properties of the films. The leakage current density of 0.5 mol. % Mn-doped KNN film showed the lowest value of ˜10-7 A/cm2 at 10 V compared to the films with other doping concentrations and the piezoelectric d33 and e31 coefficients of this film were ˜90 pm/V and -8.5 C/m2, respectively. The maximum power and power density of the lead-free thin film-based vibrational energy harvesting device were 3.62 μW and 1800 μW/cm3 at the resonance frequency of 132 Hz and the acceleration of 1.0 G. The results prove that the 0.5 mol. % Mn-doped KNN film is an attractive candidate transducer layer for the piezoelectric MEMS energy harvesting device applications with a small volume and a long-lasting power source.

  14. Atomic Layer Deposition of Al2O3-Ga2O3 Alloy Coatings for Li[Ni0.5Mn0.3Co0.2]O2 Cathode to Improve Rate Performance in Li-Ion Battery.

    PubMed

    Laskar, Masihhur R; Jackson, David H K; Guan, Yingxin; Xu, Shenzhen; Fang, Shuyu; Dreibelbis, Mark; Mahanthappa, Mahesh K; Morgan, Dane; Hamers, Robert J; Kuech, Thomas F

    2016-04-27

    Metal oxide coatings can improve the electrochemical stability of cathodes and hence, their cycle-life in rechargeable batteries. However, such coatings often impose an additional electrical and ionic transport resistance to cathode surfaces leading to poor charge-discharge capacity at high C-rates. Here, a mixed oxide (Al2O3)1-x(Ga2O3)x alloy coating, prepared via atomic layer deposition (ALD), on Li[Ni0.5Mn0.3Co0.2]O2 (NMC) cathodes is developed that has increased electron conductivity and demonstrated an improved rate performance in comparison to uncoated NMC. A "co-pulsing" ALD technique was used which allows intimate and controlled ternary mixing of deposited film to obtain nanometer-thick mixed oxide coatings. Co-pulsing allows for independent control over film composition and thickness in contrast to separate sequential pulsing of the metal sources. (Al2O3)1-x(Ga2O3)x alloy coatings were demonstrated to improve the cycle life of the battery. Cycle tests show that increasing Al-content in alloy coatings increases capacity retention; whereas a mixture of compositions near (Al2O3)0.5(Ga2O3)0.5 was found to produce the optimal rate performance. PMID:27035035

  15. In0.5Ga0.5As self-assembled quantum dots on GaP/Si

    NASA Astrophysics Data System (ADS)

    Song, Yuncheng

    This thesis focuses on demonstrating monolithic integration of III-V optoelectronic devices with Si by means of GaP on Si templates. Though high-quality epitaxial GaP on Si has been developed, GaP itself is not useful for most photonic applications due to its indirect bandgap. Historically, deep level impurities have allowed the realization of GaP light emitting diodes (LEDs), but these devices had low efficiency and the gain was insufficient for laser action. The lattice matched dilute nitride material Ga(NAsP) is an option for direct bandgap material on GaP, but N-related point defects make the material challenging to grow. InxGa1--xAs self-assembled quantum dots (SAQDs) grown on GaP offer another path to integration of direct-bandgap III-V material onto Si. The use of InxGa 1--xAs allows access to a wide range of bulk bandgaps (1.42-0.36 eV for x=0-1) and the potential for great flexibility in emission wavelength from visible to near-infrared. While chip-to-chip optical communication remains a goal, a range of sensing applications could also benefit from the direction integration of Si electronics with light sources. Sample growth was carried out by solid-source molecular beam epitaxy (MBE) using conditions similar to those used for the well-known case of InAs/GaAs SAQDs. SAQD formation was through Stranski--Krastanov (S-K) growth mode, as evidenced by reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). Cross-sectional transmission microscopy (XTEM) with several two-beam conditions confirmed that both the SAQDs and the GaP cap layer were free of dislocations. Intense photoluminescence was visible from the quantum dots at both 80 K and room temperature to the unaided eye in ambient lighting. The photoluminescence results also showed that emission energy can be controlled by varying the In0.5Ga0.5As deposition thickness. The commercial availability of high-quality GaP/Si templates enabled research on In0.5Ga0.5As

  16. An In0.5Ga0.5N nanowire photoanode for harvesting deep visible light photons

    NASA Astrophysics Data System (ADS)

    Fan, S.; Woo, S. Y.; Vanka, S.; Botton, G. A.; Mi, Z.

    2016-07-01

    III-nitride semiconductors hold tremendous promise for realizing high efficiency photoelectrodes. However, previously reported InGaN photoelectrodes generally exhibit very low photocurrent densities, due to the presence of extensive defects, dislocations, and indium phase separation. Here, we show that In0.5Ga0.5N nanowires with nearly homogeneous indium distribution can be achieved by plasma-assisted molecular beam epitaxy. Under AM1.5G one sun illumination, the InGaN nanowire photoanode exhibits a photocurrent density of 7.3 mA/cm2 at 1.2 V (vs. NHE) in 1M HBr. The incident-photon-to-current efficiency is above 10% at 650 nm, which is significantly higher than previously reported values of metal oxide photoelectrodes.

  17. Performance improvement of Li-rich layer-structured Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 by integration with spinel LiNi 0.5 Mn 1.5 O 4

    SciTech Connect

    Feng, Xin; Yang, Zhenzhong; Tang, Daichun; Kong, Qingyu; Gu, Lin; Wang, Zhaoxiang; Chen, Liquan

    2015-01-01

    Li-rich layered Li1+xMnyM1-x-yO2 (or denoted xLi2MnO3center dot1-xLiMO2, M = Ni, Co, Mn, etc.) are promising cathode materials for high energy-density Li-ion batteries. However, their commercial applications suffer from problems such as a drop in the capacity and discharge voltage during cycling. In this work, the cycling performance of a layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 is improved by integration with spinel LiNi0.5Mn1.5O4 to obtain a layered-spinel composite. Characterization by powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) as well as cyclic voltammetry (CV) indicates that delayed degradation of layered Li2MnO3 and the suppressed growth of LiMn2O4-like spinel are responsible for the performance improvement.

  18. Layed Perovskite PRBA0.5SR0.5CO205 as High Performance Cathode for Solid Oxide Fuels Using Photon Conducting Electrolyte

    SciTech Connect

    Brinkman, K.

    2010-05-05

    The layered perovskite PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+{delta}} (PBSC) was investigated as a cathode material for a solid oxide fuel cell using a proton-conducting electrolyte based on BaCe{sub 0.7}Y{sub 0.2}Zr{sub 0.1}O{sub 3-{delta}} (BCYZ). The sintering conditions for the PBSC-BCYZ composite cathode were optimized resulting in the lowest area-specific resistance and apparent activation energy obtained with the cathode sintered at 1200 C for 2h. The maximum power densities of the PBSC-BCYZ/BZCY/NiO-BCYZ cell were 0.179, 0.274, 0.395, and 0.522 Wcm{sup -2} at 550, 600, 650, and 700 C, respectively with a 15{micro}m thick electrolyte. A relatively low cell interfacial polarization resistance of 0.132 {Omega}cm{sup 2} at 700 C indicated that the PBSC-BCYZ could be a good cathode candidate for intermediate temperature SOFCs with proton-conducting electrolyte.

  19. Structural and magnetic properties of epitaxial Heusler alloy Fe{sub 2}Cr{sub 0.5}Co{sub 0.5}Si

    SciTech Connect

    Wang, Yu-Pu; Han, Gu-Chang; Qiu, Jinjun; Yap, Qi-Jia; Lu, Hui; Teo, Kie-Leong

    2014-05-07

    This paper reports the study of structural and magnetic properties of Heusler alloy Fe{sub 2}Cr{sub 0.5}Co{sub 0.5}Si (FCCS) thin film and its tunnel magnetoresistance (TMR) effect. The smooth quaternary Heusler alloy FCCS film with surface roughness of rms value of 0.25 nm measured by atomic force microscopy and partial L2{sub 1} phase was obtained by magnetron sputtering at room temperature followed by in-situ annealing at 400 °C. The saturation magnetization and coercivity of FCCS are 410 emu/cm{sup 3} and 20 Oe, respectively. The magnetic tunnel junctions (MTJs) using FCCS as free layer were studied in detail as a function of post-annealing temperature. A TMR ratio of 15.6% has been achieved with 300 °C post-annealing. This is about twice the highest TMR ratio obtained in MTJs using Fe{sub 2}CrSi. The enhancement of TMR ratio can be attributed to the successful tuning of the Fermi level of Fe{sub 2}CrSi close to the center of the minority band gap by Co-doping.

  20. Chernobyl fallout in the uppermost (0-3 cm) humus layer of forest soil in Finland, North East Russia and the Baltic countries in 2000--2003.

    PubMed

    Ylipieti, J; Rissanen, K; Kostiainen, E; Salminen, R; Tomilina, O; Täht, K; Gilucis, A; Gregorauskiene, V

    2008-12-15

    The situation resulting from the Chernobyl fallout in 1987 was compared to that in 2000--2001 in Finland and NW Russia and that in 2003 in the Baltic countries. 786 humus (0-3 cm layer) samples were collected during 2000--2001 in the Barents Ecogeochemistry Project, and 177 samples in the Baltic countries in 2003. Nuclides emitting gamma-radiation in the 0-3 cm humus layer were measured by the Radiation and Nuclear Safety Authority-STUK in Finland. In 1987 the project area was classified by the European Commission into four different fallout classes. 137Cs inventory Bg/m2 levels measured in 2000--2003 were compared to the EU's class ranges. Fitting over the whole project area was implemented by generalizing the results for samples from the Baltic countries, for which Bq/m2 inventories could be calculated. A rough estimation was made by comparing the mass of organic matter and humus with 137Cs concentrations in these two areas. Changes in 137Cs concentration levels are illustrated in both thematic maps and tables. Radionuclide 137Cs concentrations (Bq/kg d.w.) were detected in the humus layer at all the 988 sampling sites. 134Cs was still present in 198 sites 15 years after the nuclear accident in Chernobyl. No other anthropogenic nuclides emitting gamma-radiation were detected, but low levels of 60Co, 125Sb and 154Eu isotopes were found in 14 sites. Fifteen years after the Chernobyl accident, the radioactive nuclide 137Cs was and still is the most significant fallout radionuclide in the environment and in food chains. The results show that the fallout can still be detected in the uppermost humus layer in North East Europe. PMID:18845315

  1. Synthesis and crystal structure of Bi6(Bi0.5Cu0.5)V2O15+y

    NASA Astrophysics Data System (ADS)

    Gupta, Akanksha; Uma, S.

    2015-10-01

    The structure of the oxide with composition Bi6(Bi0.5Cu0.5)V2O15+y has been solved based on single crystal X-ray diffraction and is found to be monoclinic (S. G. I2), a=11.276(1) Å, b=5.4513(2) Å, c=11.055(3) Å, β=96.70°(1). The crystal was twinned by 180° rotoinversion about [ 1 bar 0 1] in the direct lattice as found in the the phosphates, Bi6TiP2O16 and Bi6+xM1-xP2O15+y (M=Mn, Fe and Ni), wherein chains of edge sharing (OBi4) tetrahedral units are connected by layers of VO4 tetrahedra and (Bi/Cu)O6-x (x=oxygen vacancies) octahedra.

  2. Magnetic properties of nanocrystalline Fe0.5Ni0.5 permalloy

    NASA Astrophysics Data System (ADS)

    De, D.; Majumdar, S.; Giri, S.

    2012-06-01

    We investigate magnetic properties of nanocrystalline Fe0.5Ni0.5 alloy embedded in the amorphous SiO2 host with volume fractions φ ≈ 10%. The static and dynamic aspects of the magnetic properties are investigated by investigating thermal and time dependence of low-field dc magnetization. Signature of strong interparticle interaction is noted in the magnetization results. The relaxation process at low temperature is fitted with stretched exponential function, displaying coexistence of ferromagnetic and glassy magnetic components.

  3. Structural and electrical properties of 1 − x(Na{sub 0.5}K{sub 0.5})NbO{sub 3}–x(Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} ceramics

    SciTech Connect

    Lee, Tae-Ho; Lee, Sung-Gap Yeo, Jin-Ho; Jung, Hye-Rin

    2014-10-15

    Highlights: • We fabricated lead-free (Na{sub 0.5}K{sub 0.5})NbO{sub 3} ceramics. • We studied the structural and electrical properties of 1 − x(Na{sub 0.5}K{sub 0.5})NbO{sub 3}–x(Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} ceramics. • The structural and electrical properties improved with increasing amount of (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3}. - Abstract: In this study, 1 − x(Na{sub 0.5}K{sub 0.5})NbO{sub 3}–x(Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} ceramics were fabricated using the conventional mixed oxide method. The effects of the addition of (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} on the structural and electrical properties of the specimens were investigated for their application in piezoelectric devices. As the results of X-ray diffraction analysis show, all specimens display the typical polycrystalline perovskite structure without the presence of the second phase. Sintered densities increased with an increase in the amount of (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} added and the specimen with 0.08 mol% of (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} added showed the maximum value of 4.54 g/cm{sup 3}. Both average grain size and densification increased with an increase in the amount of (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3}. The electromechanical coupling factor, dielectric constant ϵ{sub r}, dielectric loss tan δ, d{sub 33} and Curie temperature of the 0.92(Na{sub 0.5}K{sub 0.5})NbO{sub 3}–0.08(Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} specimens doped with 0.08 mol% of (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} were 0.31, 1338, 0.021, 138 and 445 °C, respectively.

  4. Magnetization reversal in the orthochromite Y0 . 5 Gd0.5 CrO3

    NASA Astrophysics Data System (ADS)

    Duran, Alejandro; Escudero, Roberto; Escamilla, Raul; Morales, Fransisco; Verdin, Eduardo

    Complex oxide of transition metal with perovskite structure represent fascinating playground for basic solid state research: new electronics and exotic ground states emerge via the competing interplay like spin, orbital, charge as well as lattice degree of freedom. Accordingly, orthochromites are not exception to the rule. In these compounds have been found ferroelectric polarization, spin reorientation transition along with the characteristic behavior known as; magnetization reversal (MR) consisting that a characteristic temperature, T*, the system becomes diamagnetic. In this work, the magnetic behavior of the equimolar Y0.5Gd0.5CrO3 composition was studied. Negative magnetization was observed at T*~70 K in FC mode, and applied field of 100 Oe. The characteristic hysteresis loop in the M-H graph of the pristine sample disappears for a wide range of temperature below of TN, and the characteristic spin reorientation is shifted from 14 K in GdCrO3 to 5 K for Y0.5Gd0.5CrO3. The negative magnetization is explained according the model that take into account the anisotropic and antisymmetric exchange interaction between Gd +3 - Cr +3 sublattice. A.D. and R.E. thanks to grants by DGAPA-PAPIIT, IN103213 and IN 106014 respectively.

  5. Magnetoresistance of La0.5Sr0.5MnO3 nanoparticle compact

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Hong; Ji, Tian-Hao; Wang, Yi-Qian; Chen, Xin; Li, Run-Wei; Cai, Jian-Wang; Sun, Ji-Rong; Shen, Bao-Gen; Yan, Chun-Hua

    2000-05-01

    Magnetization, resistance, and current-voltage (I-V) measurements have been performed in La0.5Sr0.5MnO3 compact prepared by pressing sol-gel nanoparticles (46 nm) at 723 K with a high pressure (4 GPa). The pressed compound orders ferromagnetically at 340 K (TC) and has a substantial drop in the thermomagnetic curve below 158 K (TDP). After undergoing a metal-to-semiconductor transition at 140 K (TMS), the compound reenters into a strong semiconducting state below 60 K, demonstrating a charge localized behavior induced by the small grain rather than the magnetic disorder which is related with the frozen spin clusters below TDP. Instead of showing a feature near TMS, the magnetoresistance (MR) ratio increases almost linearly with decreasing temperature. The large low field MR corresponding to the sharp rise of magnetization is obtained at 5 K and, evidenced as the spin polarized intergrain tunneling (SPIT) effect by the nolinear I-V curve. Although La0.5Sr0.5MnO3 has a relatively high TC, the SPIT MR decays rapidly from 17.6% (5 K, 0.3 T) to 7.6% (150 K, 0.3 T), indicating that if trying to put the low field sensitivity of SPIT MR into application at room temperature, the selected compound having a higher TC seems to be a prerequisite.

  6. Copper uranyl phosphate and arsenate incorporating an organic ligand with a pillared layer structure: [Cu(4,4 Prime -bpy)(UO{sub 2}){sub 0.5}(HPO{sub 4})(H{sub 2}PO{sub 4})]{center_dot}H{sub 2}O and [Cu(4,4 Prime -bpy)(UO{sub 2}){sub 0.5}(HAsO{sub 4})(H{sub 2}AsO{sub 4})]{center_dot}1.5H{sub 2}O

    SciTech Connect

    Wang, Chih-Min; Lii, Kwang-Hwa

    2013-01-15

    Two mixed-metal uranium compounds, [Cu(4,4 Prime -bpy)(UO{sub 2}){sub 0.5}(HPO{sub 4})(H{sub 2}PO{sub 4})]{center_dot}H{sub 2}O (1) and [Cu(4,4 Prime -bpy)(UO{sub 2}){sub 0.5}(HAsO{sub 4})(H{sub 2}AsO{sub 4})]{center_dot}1.5H{sub 2}O (2) have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction, fluorescence spectroscopy, and magnetic susceptibility. They are the first examples of mixed-metal uranium phosphate and arsenate incorporating an organic ligand. Their structures contain copper uranyl phosphate/arsenate layers which are covalently linked by 4,4 Prime -bpy pillars to form a 3-D framework structure. The fluorescence spectrum of 1 shows the characteristic vibronic structure of the UO{sub 2}{sup 2+} moiety despite the presence of copper(II) ions in its structure. The two compounds are isostructural and crystallize in the monoclinic space group C2/c with a=20.184(4) A, b=8.921(2) A, c=19.095(3) A, {beta}=115.15(1) Degree-Sign , and R{sub 1}=0.0244 for 1, and a=20.184(1) A, b=9.0210(5) A, c=19.714(1) A, {beta}=114.879(1) Degree-Sign , and R{sub 1}=0.0399 for 2. - Graphical abstract.: A new copper uranyl phosphate and the arsenate analog have been presented. The compounds contain copper uranyl phosphate/arsenate layers covalently linked by 4,4 Prime -bipyridine pillars into an open-framework structure.

  7. Enhancing the High-Voltage Cycling Performance of LiNi(0.5)Mn(0.3)Co(0.2)O2 by Retarding Its Interfacial Reaction with an Electrolyte by Atomic-Layer-Deposited Al2O3.

    PubMed

    Su, Yantao; Cui, Suihan; Zhuo, Zengqing; Yang, Wanli; Wang, Xinwei; Pan, Feng

    2015-11-18

    High-voltage (>4.3 V) operation of LiNi(x)Mn(y)Co(z)O2 (NMC; 0 ≤ x, y, z < 1) for high capacity has become a new challenge for next-generation lithium-ion batteries because of the rapid capacity degradation over cycling. In this work, we investigate the performance of LiNi(0.5)Mn(0.3)Co(0.2)O2 (NMC532) electrodes with and without an atomic-layer-deposited (ALD) Al2O3 layer for charging/discharging in the range from 3.0 to 4.5 V (high voltage). The results of the electrochemical measurements show that the cells with ALD Al2O3-coated NMC532 electrodes have much enhanced cycling stability. The mechanism was investigated by using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and electrochemical methods. We find that the ultrathin ALD Al2O3 film can reduce the interface resistance of lithium-ion diffusion and enhance the surface stability of NMC532 by retarding the reactions at NMC532/electrolyte interfaces for preventing the formation of a new microstructure rock-salt phase NiO around the NMC532 surfaces. PMID:26501963

  8. (Y0.5In0.5)Ba(Co,Zn)4O7 cathodes with superior high-temperature phase stability for solid oxide fuel cells

    SciTech Connect

    Young Nam, Kim; Kim, Jung-Hyun; Paranthaman, Mariappan Parans; Manthiram, Arumugam; Huq, Ashfia

    2012-01-01

    (Y0.5In0.5)BaCo4-xZnxO7 (1.0 x 2.0) oxides crystallizing in a trigonal P31c structure have been synthesized and explored as cathode materials for solid oxide fuel cells (SOFC). At a given Zn content, the (Y0.5In0.5)BaCo4-xZnxO7 sample with 50 % Y and 50 % In exhibits much improved phase stability at intermediate temperatures (600 - 800 oC) compared to the samples with 100 % Y or In. However, the substitution of Zn for Co in (Y0.5In0.5)Ba(Co4-xZnx)O7 (1.0 x 2.0) decreases the amount of oxygen loss on heating, total electrical conductivity, and cathode performance in SOFC while providing good long-term phase stability at high temperatures. Among the various chemical compositions investigated in the (Y0.5In0.5)Ba(Co4-xZnx)O7 system, the (Y0.5In0.5)BaCo3ZnO7 sample offers a combination of good electrochemical performance and low thermal expansion coefficient (TEC) while maintaining superior phase stability at 600 800 oC for 100 h. Fuel cell performances of the (Y0.5In0.5)Ba(Co3Zn)O7 + Ce0.8Gd0.2O1.9 (GDC) (50 : 50 wt. %) composite cathodes collected with anode-supported single cell reveal a maximum power density value of 521 mW cm-2 at 700 oC.

  9. Isosbestic Point and Magnetoresistance Components in Ho_{0.5} Lu_{0.5} B_{12}

    NASA Astrophysics Data System (ADS)

    Khoroshilov, A. L.; Azarevich, A. N.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Krasnorussky, V. N.; Voronov, V. V.; Shitsevalova, N. Yu; Filippov, V. B.; Gabani, S.; Flachbart, K.; Sluchanko, N. E.

    2016-01-01

    We present the results of precise magnetoresistance (MR) measurements of an antiferromagnetic cage-glass solid solution Ho_{0.5} Lu_{0.5} B_{12} in magnetic fields up to 80 kOe and at temperatures between 1.9 and 100 K. The analysis of results allows to separate the positive and negative contributions to MR. The dominant MR-term was found to be the high field positive contribution Δ ρ /ρ _{(m+)} =μ _D^2 H^2 which is caused by the drift mobility μ _D of charge carriers. It was also shown that the negative MR observed at temperatures T ≤ 10 K may be described by the well-known relation between MR and local magnetization Δ ρ /ρ _{(-)} =M_{loc}^2 obtained by Yosida in the framework of s-d exchange model. We discuss as well the scattering of charge carriers on antiferromagnetic nanosize domains of Ho^{3+} ions with effective magnetic moments 3.5-5.5 μ _B as the mechanism responsible for the appearance of the negative MR component.

  10. Magnetisation configuration at the interface of Fe_0.5Mn_0.5/Co(111)

    NASA Astrophysics Data System (ADS)

    Ujfalussy, Balazs; Schultess, T. C.; Stocks, G. M.; Canning, A.

    2002-03-01

    The microscopic understanding of the interface of a ferromagnet and an antiferromagnet is of fundamental importance in the problem of exchange bias. Of particular interest is the interface between Fe_0.5Mn_0.5/Co(111) however, it is rather difficult to study it experimentally. We performed an ab-initio spin-dynamics calculation to determine the magnetization configuration of this interface. We find that the magnetization changes from a 3Q-like state to a 1Q-like state which is perpendicular to the magnetization of the Co at the interface. We comment on the range of the interaction and possible mechanism of exchange bias. This work was supported by the Division of Materials Sciences and Engineering, and by the Director, Office of Advanced Scientific Computing Research, Division of Mathematical Information and Computational Sciences Division, of the U.S. Department of Energy, under contract number DE-AC03-76SF00098 and subcontract DE-AC05-00OR22725 with UT-Battelle LLC.

  11. Influence of electron beam irradiation on the structural, electrical and thermal properties of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Nagaraja, B. S.; Rao, Ashok; Babu, P. D.; Sanjeev, Ganesh; Okram, G. S.

    2016-01-01

    We present systematic studies on the effect of electron beam irradiation on structural, electrical and thermal properties of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 manganites. The XRD patterns and Rietveld analysis show that the samples remain single phased even after they undergo electron beam irradiation. Both the series of the samples Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 show insulating trends in their temperature dependent electrical resistivity, ρ(T) behavior. The resistivity data for both the series of samples (pristine as well as irradiated) indicate that the small polaron hopping model is valid in high temperature region; on contrary, variable range hopping model governs the low temperature regime. Magnetic studies demonstrate that the Neel temperatures of pristine and irradiated samples of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 do not change appreciably when they are subjected to irradiation. Thermo-electrical power is observed to increase with irradiation in Gd0.5Sr0.5MnO3 samples, whereas for Dy0.5Sr0.5MnO3 samples a decrease in thermo-electric power is seen when the samples are irradiated.

  12. Electrostatic versus Electrochemical Doping and Control of Ferromagnetism in Ion-Gel-Gated Ultrathin La0.5Sr0.5CoO3-δ.

    PubMed

    Walter, Jeff; Wang, Helin; Luo, Bing; Frisbie, C Daniel; Leighton, Chris

    2016-08-23

    Recently, electrolyte gating techniques employing ionic liquids/gels in electric double layer transistors have proven remarkably effective in tuning charge carrier density in a variety of materials. The ability to control surface carrier densities at levels above 10(14) cm(-2) has led to widespread use in the study of superconductivity, insulator-metal transitions, etc. In many cases, controversy remains over the doping mechanism, however (i.e., electrostatic vs electrochemical (e.g., redox-based)), and the technique has been less applied to magnetic materials. Here, we discuss ion gel gating of nanoscale 8-unit-cell-thick hole-doped La0.5Sr0.5CoO3-δ (LSCO) films, probing in detail the critical bias windows and doping mechanisms. The LSCO films, which are under compressive stress on LaAlO3(001) substrates, are metallic and ferromagnetic (Curie temperature, TC ∼ 170 K), with strong anomalous Hall effect and perpendicular magnetic anisotropy. Transport measurements reveal that negative gate biases lead to reversible hole accumulation (i.e., predominantly electrostatic operation) up to some threshold, whereas positive bias immediately induces irreversibility. Experiments in inert/O2 atmospheres directly implicate oxygen vacancies in this irreversibility, supported by atomic force microscopy and X-ray photoelectron spectroscopy. The results are thus of general importance, suggesting that hole- and electron-doped oxides may respond very differently to electrolyte gating. Reversible voltage control of electronic/magnetic properties is then demonstrated under hole accumulation, including resistivity, magnetoresistance, and TC. The sizable anomalous Hall coefficient and perpendicular anisotropy in LSCO provide a particularly powerful probe of magnetism, enabling direct extraction of the voltage-dependent order parameter and TC shift. The latter amounts to ∼7%, with potential for much stronger modulation at lower Sr doping. PMID:27479878

  13. BaZr0.5Ti0.5O3 : Lead-free relaxor ferroelectric or dipolar glass

    NASA Astrophysics Data System (ADS)

    Filipič, C.; Kutnjak, Z.; Pirc, R.; Canu, G.; Petzelt, J.

    2016-06-01

    Glassy freezing dynamics was investigated in BaZr0.5Ti0.5O3 (BZT50) ceramic samples by means of dielectric spectroscopy in the frequency range 0.001 Hz-1 MHz at temperatures 10 cm it has been found that a ferroelectric state cannot be induced, in contrast to the case of typical relaxors. This suggests that—at least for the above field amplitudes—BZT50 effectively behaves as a dipolar glass, which can be characterized by a negative value of the static third order nonlinear permittivity. The relaxation spectrum has been analyzed by means of the frequency-temperature plot, which shows that the longest relaxation time obeys the Vogel-Fulcher relation τ =τ0exp [E0/(T -T0) ] with the freezing temperature of 48.1 K, whereas the corresponding value for the shortest relaxation time is ˜0 K, implying an Arrhenius type behavior. By applying a standard expression for the static linear permittivity of dipolar glasses and/or relaxors the value of the Edwards-Anderson order parameter q (T ) has been evaluated. It is further shown that q (T ) can be described by the spherical random bond-random field model of relaxors.

  14. Structural and dielectric properties of lead free Bi0.5Na0.5TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Pattipaka, Srinivas; Mahesh, P.; Pamu, D.

    2016-05-01

    The lead free Bi0.5Na0.5TiO3 (BNT) ceramics were synthesized by using a solid state reaction method. The effect of sintering temperature on structure and dielectric properties of BNT ceramics studied systematically. It was observed that the samples calcined at 800 °C and sintered at 1100 °C shown the maximum density (5.67 g/cm3), with larger crystallite size (52 nm), high dielectric constant (ɛr = 694 at 1 kHz), and low dielectric loss (tanδ = 0.103). The XRD pattern reveals that rhombohedral phase with R3c space group at room temperature. The temperature dependent ɛr and tanδ displayed the two phase transitions including ferroelectric to anti-ferroelectric low phase transition (198 °C) and anti-ferroelectric to para electric phase transition (330 °C). The high frequency dielectric analysis revealed that weak relaxor behaviour presented in the system.

  15. Synthesis and electrochemical assessment of Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} ceramics and derived composite electrolytes

    SciTech Connect

    Martins, Natércia C.T.; Rajesh, Surendran; Marques, Fernando M.B.

    2015-10-15

    Highlights: • Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} prepared for the first time through solid state reaction. • High energy milling needed to assist the ceramic route. • Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} is oxide-ion conductor in air and n-type conductor at low pO{sub 2}. • Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} decomposes slightly when exposed to alkaline carbonates. • Composites based on Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} show standard electrical performance. - Abstract: Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} was prepared for the first time through high temperature (1600 °C for 5 h) solid state reaction, after high energy milling to enhance the mechano-chemical interaction of precursor oxides (CeO{sub 2} and Yb{sub 2}O{sub 3}). Single phase formation was confirmed by powder X-ray diffraction. Impedance spectroscopy data obtained under wide temperature (300–800 °C) and oxygen partial pressure (0.21 to about 10{sup −25} atm) ranges indicates that this material exhibits predominant oxide-ion conductivity under oxidizing conditions while n-type electronic conductivity prevails at low oxygen partial pressure. The mixed oxide shows modest ionic conductivity (1.1 × 10{sup −3} S cm{sup −1} at 800 °C) with activation energy of 1.3 eV in the 600–800 °C temperature range. When combined with molten carbonates (Li{sub 2}CO{sub 3} + Na{sub 2}CO{sub 3}, 1:1 molar ratio) to produce composite electrolytes, Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} slightly decomposed. However, the composite electrical performance is still acceptable and closely matches the conductivity of similar materials (>0.1 S cm{sup −1} immediately above 500 °C)

  16. Fabrication and evaluation of a single-element Bi0.5Na0.5TiO3-based ultrasonic transducer.

    PubMed

    Hejazi, M Mehdi; Jadidian, Bahram; Safari, Ahmad

    2012-08-01

    This paper discusses the fabrication and characterization of a single-element ultrasonic transducer with a lead-free piezoelectric active element. A piezoelectric ceramic with composition of 0.88Bi(0.5)Na(0.5)TiO(3)-0.08Bi(0.5)K(0.5)TiO(3)- 0.04Bi(0.5)Li(0.5)TiO(3) was chosen as the active element of the transducer. This composition exhibited a thickness coupling coefficient (kt) of 0.45, a dielectric constant of 440 (at 1 kHz), and a longitudinal piezoelectric coefficient (d(33)) of 84 pC·N(-1). To make the transducer, the ceramic was sandwiched between an epoxy-tungsten backing layer and a silver epoxy matching layer. An epoxy lens was also incorporated into the transducer's design to focus the ultrasound beam. The focused transducer with a center frequency of about 23 MHz demonstrated a -6-dB bandwidth of 55% and an insertion loss of -32 dB; the -20-dB pulsed length was measured to be 150 ns. A phantom made of copper wires (30 μm in diameter) was utilized to investigate the imaging capability of the transducer. The results indicated that the fabricated transducer, with a lateral resolution of 260 μm and a relatively high depolarization temperature, could be considered as a candidate for replacement of lead-based ultrasonic transducers. PMID:22899131

  17. 16 CFR 0.5 - Laws authorizing monetary claims.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Laws authorizing monetary claims. 0.5 Section 0.5 Commercial Practices FEDERAL TRADE COMMISSION ORGANIZATION, PROCEDURES AND RULES OF PRACTICE ORGANIZATION § 0.5 Laws authorizing monetary claims. The Commission is authorized to entertain monetary...

  18. Structure and electrical properties of 0.80 Na0.5 Bi0.5 TiO3-0.16 K0.5 Bi0.5 TiO3-0.04 BaTiO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Aravinth, K.; Muneeswaran, M.; Babu, G. Anandha; Giridharan, N. V.; Ramasamy, P.

    2016-05-01

    Lead free pervoskite 0.80 Na0.5 Bi0.5 TiO3-0.16 K0.5 Bi0.5 TiO3-0.04 BaTiO3 (NKBBT) ceramics were fabricated via conventional solid state processing technique sintered at 1200 °C and their crystal structures and electrical properties were systematically studied. Structure of the prepared NKBBT ceramics was confirmed by Powder X-ray diffraction analysis. The dependence of dielectric constant on temperature for various frequencies (100 Hz-100 KHz) has been determined. The diffuse transition is observed in the variation of dielectric constant and it provides evidence for the relaxor characteristics. The ferroelectric response of the NKBBT ceramics with different frequency was studied. Polarisation electric field hysteresis loops revealed that the remnant polarization is 6.88 µC/cm2 and coercive electric field is 66.42 kV/cm.

  19. Electric polarization of Sr0.5Ba0.5MnO3: a multiferroic Mott insulator

    NASA Astrophysics Data System (ADS)

    Nourafkan, Reza

    2015-03-01

    Multiferroics, materials which display simultaneous magnetic and ferroelectric orders, are interesting both for their rich physics and for their promising practical applications. The search for multiferroic materials with strong-magnetoelectric coupling is challenging and requires an understanding of how the magnetic order, or more specifically the correlations, influence the electric polarization and vice versa. A calculations of the electric polarization in the paramagnetic (PM) insulating phase of multiferroics is essential to address this mutual influence. Ab inito calculations of the electric polarization are based on the modern theory of polarization, which is a single-electron theory. Thus, a correlation driven insulating state is beyond the scope of this approach. Here we show that combining correlated band structure calculations (DFT+DMFT) with a formula for the electric polarization of interacting insulators, expressed in terms of the full Green and vertex functions, allows for the first time to reliably calculate the polarization in the PM phase. We focus on the Mott insulator Sr0.5Ba0.5MnO3, in which both magnetic and ferroelectric instabilities are related to the Mn ions. We predict a ferroelectric polarization of ~= 16 . 5 μC / cm2 in the high temperature paramagnetic phase and recover the measured value of ~= 13 . 3 μC / cm2 in the low temperature antiferromagnetic phase. Our calculations reveal that the the driving force behind the ferroelectric distortion comes from the tendency of Mn eg states to establish a stronger covalency with the surrounding oxygens. This covalency is reduced by correlations, in particular by Hund coupling. On the other hand, the half-filled Mn t2 g orbitals give rise to the magnetic ordering which decreases the ionic displacement, hence its contribution to the polarization. For fixed ionic displacement, the magnetic order also slightly decreases the electronic contribution to the electric polarization by partially

  20. Li0.5Al0.5Mg2(MoO4)3

    PubMed Central

    Ennajeh, Ines; Zid, Mohamed Faouzi; Driss, Ahmed

    2013-01-01

    The title compound, lithium/aluminium dimagnesium tetra­kis­[orthomolybdate(VI)], was prepared by a solid-state reaction route. The crystal structure is built up from MgO6 octa­hedra and MoO4 tetra­hedra sharing corners and edges, forming two types of chains running along [100]. These chains are linked into layers parallel to (010) and finally linked by MoO4 tetra­hedra into a three-dimensional framework structure with channels parallel to [001] in which lithium and aluminium cations equally occupy the same position within a distorted trigonal–bipyramidal coordination environment. The title structure is isotypic with LiMgIn(MoO4)3, with the In site becoming an Mg site and the fully occupied Li site a statistically occupied Li/Al site in the title structure. PMID:24426975

  1. Ni-doped La0.5Sr0.5TiO3 nanofibers: Fabrication and intrinsic ferromagnetism

    NASA Astrophysics Data System (ADS)

    Ponhan, Wichaid; Amornkitbamrung, Vittaya; Maensiri, Santi

    2016-06-01

    We report room-temperature ferromagnetism in ∼104–133 nm nanofibers of La0.5Sr0.5Ti1‑ x Ni x O3 (0.02 ≤ x ≤ 0.05). As-spun nanofibers of La0.5Sr0.5Ti1‑ x Ni x O3 are fabricated by an electrospinning technique. Nanofibers of the as spun and calcined La0.5Sr0.5Ti1‑ x Ni x O3 samples are characterized using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), X-ray absorption near edge structure (XANES) determination, and vibrating sample magnetometry (VSM). The results of XRD analysis and TEM together with selected electron diffraction (SEAD) analysis indicate that La0.5Sr0.5Ti1‑ x Ni x O3 nanofibers have a cubic perovskite structure with no secondary phase. The as-spun samples are paramagnetic, whereas the La0.5Sr0.5Ti1‑ x Ni x O3 samples are ferromagnetic having specific magnetizations of 0.098–0.484 emu/g at 10 kOe. The XPS spectra show that there are some oxygen vacancies in the nanofibers, which its may play an important role in inducing room-temperature ferromagnetism in La0.5Sr0.5Ti1‑ x Ni x O3 nanofibers. XANES spectra show that most of the Ni ions in La0.5Sr0.5Ti1‑ x Ni x O3 nanofibers are in the Ni2+ state mixed with some Ni metal. The finding of room temperature ferromagnetism in this nanofibrous structure of the La0.5Sr0.5Ti1‑ x Ni x O3 system is of interest in research on diluted magnetic oxides.

  2. Near-infrared emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: synthesis and bright luminescence

    PubMed Central

    2012-01-01

    We present how CdTe0.5Se0.5 cores can be coated with Cd0.5Zn0.5S shells at relatively low temperature (around 200°C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd0.5Zn0.5S shell on the CdTe0.5Se0.5 core, even though the PL efficiency of the cores is low (≤1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe0.5Se0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging. PMID:23130948

  3. Fabrication of highly spin-polarized Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} thin-films

    SciTech Connect

    Vahidi, M.; Zhang, S. K.; Yu, L.; Huang, M.; Newman, N.; Gifford, J. A.; Chen, T. Y.; Krishnamurthy, S.; Yu, Z. G.; Youngbull, C.

    2014-04-01

    Ferromagnetic Heusler Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} epitaxial thin-films have been fabricated in the L2{sub 1} structure with saturation magnetizations over 1200 emu/cm{sup 3}. Andreev reflection measurements show that the spin polarization is as high as 80% in samples sputtered on unheated MgO (100) substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.

  4. Flowerlike CeO2 microspheres coated with Sr2Fe1.5Mo0.5Ox nanoparticles for an advanced fuel cell

    NASA Astrophysics Data System (ADS)

    Liu, Yanyan; Tang, Yongfu; Ma, Zhaohui; Singh, Manish; He, Yunjuan; Dong, Wenjing; Sun, Chunwen; Zhu, Bin

    2015-07-01

    Flowerlike CeO2 coated with Sr2Fe1.5Mo0.5Ox (Sr-Fe-Mo-oxide) nanoparticles exhibits enhanced conductivity at low temperatures (300-600 oC), e.g. 0.12 S cm-1 at 600 oC, this is comparable to pure ceria (0.1 S cm-1 at 800 oC). Advanced single layer fuel cell was constructed using the flowerlike CeO2/Sr-Fe-Mo-oxide layer attached to a Ni-foam layer coated with the conducting transition metal oxide. Such fuel cell has yielded a peak power density of 802 mWcm-2 at 550 oC. The mechanism of enhanced conductivity and cell performance were analyzed. These results provide a promising strategy for developing advanced low-temperature SOFCs.

  5. Non-random cation distribution in hexagonal Al 0.5Ga 0.5PO 4

    NASA Astrophysics Data System (ADS)

    Kulshreshtha, S. K.; Jayakumar, O. D.; Sudarsan, V.

    2010-05-01

    Based on powder X-ray diffraction and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) investigations of mixed phosphate Al 0.5Ga 0.5PO 4, prepared by co-precipitation method followed by annealing at 900 °C for 24 h, it is shown that Al 0.5Ga 0.5PO 4 phase crystallizes in hexagonal form with lattice parameter a=0.491(2) and c=1.106(4) nm. This hexagonal phase of Al 0.5Ga 0.5PO 4 is similar to that of pure GaPO 4. The 31P MAS NMR spectrum of the mixed phosphate sample consists of five peaks with systematic variation of their chemical shift values and is arising due to existence of P structural units having varying number of the Al 3+/Ga 3+ cations as the next nearest neighbors in the solid solution. Based on the intensity analysis of the component NMR spectra of Al 0.5Ga 0.5PO 4, it is inferred that the distribution of Al 3+ and Ga 3+ cations is non-random for the hexagonal Al 0.5Ga 0.5PO 4 sample although XRD patterns showed a well-defined solid solution formation.

  6. Synthesis and luminescence characterization of Sr(0.5)Ca(0.5)TiO3:Sm(3+) phosphor.

    PubMed

    Vidyadharan, Viji; Remya, Mohan P; Gopi, Subhash; Thomas, Sunil; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2015-11-01

    The spectroscopic properties of trivalent samarium doped Sr0.5Ca0.5TiO3 perovskite phosphor material (Sr0.5Ca0.5TiO3:xSm(3+), x=0.05, 0.1, 0.5, 1, 1.5) synthesized by the solid state method have been studied. The X-Ray Diffraction profile confirms the orthorhombic perovskite Sr0.5Ca0.5TiO3 structure of the prepared samples. The SEM study reveals the surface morphology. The Judd-Ofelt intensity parameters were calculated for 0.5 wt% Sm(3+) doped Sr0.5Ca0.5TiO3. Transition probabilities, branching ratios and radiative lifetime were evaluated by using Judd-Ofelt analysis. The emission spectra under 405 nm excitation shows five emission peaks at 564 nm, 599 nm, 645 nm, 707 nm and 776 nm corresponding to the transitions (4)G5/2→(6)Hj (j=5/2, 7/2, 9/2, 11/2 and 13/2) respectively. The higher values of branching ratio and stimulated emission cross-section for (4)G5/2→(6)H7/2 transition of Sr0.5Ca0.5TiO3:0.5 wt% Sm(3+) shows its suitability in the field of visible lasers and optical fiber amplifiers. The experimental lifetimes of Sm(3+) doped samples were estimated using the decay curves corresponding to (4)G5/2→(6)H7/2 transition upon 405 nm excitation. Concentration dependence on emission intensity and experimental lifetime were also studied. From the CIE diagram we can see that as the concentration of Sm(3+) ions increases from 0.05 wt% to 1.5 wt% the CIE color co-ordinates changes from greenish yellow to yellowish orange. PMID:26057096

  7. 129I AMS at 0.5 MV tandem accelerator

    NASA Astrophysics Data System (ADS)

    Alfimov, Vasily; Synal, Hans-Arno

    2010-04-01

    The 129I measurement program has been established at the 0.5 MV 'Tandy' accelerator of the PSI/ETH Zürich AMS facility. This development was made possible by using a SiN window instead of Mylar one in a gas ionization detector. The setting up of the 129I measurement at Tandy is simple, the acquired performance is stable and reliable, and the quality of results is equal to or better than at our larger EN-tandem. With this setup, high sample throughput, which is required in many 129I studies, can be easily achieved. The measurements are performed in the +3 charge state. At this charge state the major difficulty in the 129I +3 identification is caused by a highly abundant 43 +1 ( m = 43, q = +1) molecule interference. This is a positive molecular ion, because its intensity reduces exponentially with an increase in gas stripper pressure. We conclude that this molecule is 27Al 16O + ( m/ q = 43/1 = 129/3) and comes from the break-up of (Al 2O 3 + Al) - ( m = 129) precursor at the terminal: (Al 2O 3 + Al) - → 27Al 16O +. The expected isobaric interferences 43Ca +1 and 86Sr +2, which also originate from the break-up of molecules in the stripper, were found to be low and do not disturb the 129I +3 measurements. The best repeatable performance with our standard sample material was achieved at 0.14 μg/cm 2 Ar gas stripper pressure with machine blanks showing ˜6 × 10 -14 normalized 129I/I ratio and 9% transmission through the accelerator. However, high 27Al 16O + molecular rates were observed from the user samples, and in order to destroy these molecules we had to increase the stripper pressure to ˜0.22 μg/cm 2. This increase in the stripper pressure degraded the machine blank values to ˜9 × 10 -14 and reduced transmission to 8%. Nevertheless, the achieved measurement conditions are sufficient for measurement of nearly all 129I samples that have been submitted to PSI/ETH over the last few years.

  8. Growth of ˜5 cm2V-1s-1 mobility, p-type Copper(I) oxide (Cu2O) films by fast atmospheric atomic layer deposition (AALD) at 225°C and below

    NASA Astrophysics Data System (ADS)

    Muñoz-Rojas, D.; Jordan, M.; Yeoh, C.; Marin, A. T.; Kursumovic, A.; Dunlop, L. A.; Iza, D. C.; Chen, A.; Wang, H.; MacManus Driscoll, J. L.

    2012-12-01

    Phase pure, dense Cu2O thin films were grown on glass and polymer substrates at 225°C by rapid atmospheric atomic layer deposition (AALD). Carrier mobilities of 5 cm2V-1s-1 and carrier concentrations of ˜1016 cm-3 were achieved in films of thickness 50 - 120 nm, over a >10 cm2 area. Growth rates were ˜1 nm.min-1 which is two orders of magnitude faster than conventional ALD.. The high mobilities achieved using the atmospheric, low temperature method represent a significant advance for flextronics and flexible solar cells which require growth on plastic substrates.

  9. Structure, phase evolution, and microwave dielectric properties of (Ag0.5Bi0.5)(Mo0.5W0.5)O4 ceramic with ultralow sintering temperature.

    PubMed

    Zhou, Di; Li, Wen-Bo; Guo, Jing; Pang, Li-Xia; Qi, Ze-Ming; Shao, Tao; Xie, Hui-Dong; Yue, Zhen-Xing; Yao, Xi

    2014-06-01

    In the present work, the microwave dielectric ceramic (Ag0.5Bi0.5)(Mo0.5W0.5)O4 was prepared by using the solid-state reaction method. (Ag0.5Bi0.5)(Mo0.5W0.5)O4 was found to crystallize in the scheelite structure, in which Ag(+) and Bi(3+) occupy the A site randomly with 8-coordination while Mo(6+) and W(6+) occupy the B site with 4-coordination, at a sintering temperature above 500 °C, with lattice parameters a = b = 5.29469(2) Å and c = 11.62114(0) Å, space group I4(1)/a (No. 88), and acceptable Rp = 9.38, Rwp = 11.2, and Rexp = 5.86. High-performance microwave dielectric properties, with permittivity ∼26.3, Qf value ∼10,000 GHz, and temperature coefficient ∼+20 ppm/°C, were obtained in the sample sintered at 580 °C. Its chemical compatibility with aluminum at its sintering temperature was revealed and confirmed by both X-ray and energy dispersive spectrometer analysis. This ceramic could be a good candidate for ultralow-temperature cofired ceramics. PMID:24848200

  10. 16 CFR 0.5 - Laws authorizing monetary claims.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Laws authorizing monetary claims. 0.5... ORGANIZATION § 0.5 Laws authorizing monetary claims. The Commission is authorized to entertain monetary claims..., unless the adjudicative officer finds that the party has committed a willful violation of law...

  11. Thermochromic effect at room temperature of Sm0.5Ca0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Boileau, A.; Capon, F.; Barrat, S.; Laffez, P.; Pierson, J. F.

    2012-06-01

    Sm0.5Ca0.5MnO3 thermochromic thin films were synthesized using dc reactive magnetron co-sputtering and subsequent annealing in air. The film structure was studied by x-ray diffraction analysis. To validate the thermochromic potentiality of Sm0.5Ca0.5MnO3, electrical resistivity and infrared transmittance spectra were recorded for temperatures ranging from 77 K to 420 K. The temperature dependence of the optical band gap was estimated in the near infrared range. Upon heating, the optical transmission decreases in the infrared domain showing a thermochromic effect over a wide wavelength range at room temperature.

  12. Epitaxial La0.5Sr0.5CoO3 thin films: Structure, magnetism, and transport

    NASA Astrophysics Data System (ADS)

    Torija, M. A.; Sharma, M.; Fitzsimmons, M. R.; Varela, M.; Leighton, C.

    2008-07-01

    La1-xSrxCoO3 has received considerable attention in bulk form. This is due to interest in the fundamental magnetic properties (spin-state transitions and magnetic phase separation) as well as potential applications in ferroelectric memory and solid-oxide fuel cells. The structure and properties in thin film form are not well understood, and the influence of dimensional confinement on effects such as magnetic phase separation is unknown. Here, we report a comprehensive investigation of structure, magnetism, and transport in strained epitaxial La0.5Sr0.5CoO3 (001) films deposited on SrTiO3 (001) substrates by reactive dc magnetron sputtering. The crystalline quality, phase purity, strain state, oxygen stoichiometry, morphology, and magnetic and electronic properties of the epilayers are all probed and are found to be particularly sensitive to the total sputtering gas pressure and the ratio of reactive to inert gas (PO2/PAr). The various structure-property relationships are discussed in detail, particularly with respect to the degree of oxygenation and oxygen-induced resputtering. The films are strained and tetragonally distorted due to the 1.9% lattice mismatch with SrTiO3. Significant strain relaxation occurs at thicknesses around 200 Å, resulting in a crossover from two-dimensional-like to three-dimensional growth. Polarized neutron reflectometry was combined with x-ray reflectometry to obtain chemical and magnetic depth profiles, which are compared with cross-sectional scanning transmission electron microscopy. The results indicate a thin (˜10 Å) layer at the film/substrate interface with significantly different structural properties to the bulk of the film, as well as a strongly graded magnetic and chemical profile at the film surface due to the significant roughness. The Curie temperature was found to decrease very slowly as the thickness is reduced down to ˜50 Å, at which point a rapid decrease occurs, almost coincident with a sharp decrease in saturation

  13. Fully gapped superconductivity in In-doped topological crystalline insulator Pb0.5Sn0.5Te

    NASA Astrophysics Data System (ADS)

    Du, Guan; Du, Zengyi; Fang, Delong; Yang, Huan; Zhong, R. D.; Schneeloch, J.; Gu, G. D.; Wen, Hai-Hu

    2015-07-01

    Superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb0.5Sn0.5Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb0.5Sn0.5 )0.7In0.3Te is produced by In doping in Pb0.5Sn0.5Te , and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb0.5Sn0.5 )0.7In0.3Te on a (001)-oriented surface. The spectrum can be well fitted by an anisotropic s -wave gap function of Δ (θ )=0.72 +0.18 cos4 θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.

  14. Fabrication and properties of Mn 0.5Zn 0.5Fe 2O 4 nanofibers

    NASA Astrophysics Data System (ADS)

    Li, Qiailing; Wang, Wenting

    2010-08-01

    Zn-doped α-FeOOH nanofiber was synthesized by coprecipitation method. Then the α-FeOOH was enwraped by the complex of the Mn 2+ and citric acid. The morphology of α-FeOOH did not transform after the calcination process and Mn 0.5Zn 0.5Fe 2O 4 nanofiber was successfully prepared. The phase, morphology, particle diameter and the magnetic properties of samples were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicated that Mn 0.5Zn 0.5Fe 2O 4 nanofibers with an aspect ratio over 40 and a diameter of 20 nm were prepared. Compared with the amorphous Mn 0.5Zn 0.5Fe 2O 4, the anisotropy of the Mn 0.5Zn 0.5Fe 2O 4 nanofiber increased, resulting in the higher coercivity and magnetization of the obtained sample. With an increase in the calcination temperature, the diameter and the saturation magnetization of the sample increased, while the aspect ratio and coercivity decreased. The coercivity of the sample obtained at 700 °C was maximal (up to 185.4 Oe). The saturation magnetization of the sample obtained at 900 °C was maximal (up to 65.3 emu/g). The use of citric acid method prevented the presence of Mn(OH) 2, resulting in the decrease of the calcination temperature.

  15. Preparation and Thermoelectric Properties of the Skutterudite-Related Phase Ru(0.5)Pd(0.5)Sb3

    NASA Technical Reports Server (NTRS)

    Caillat, T.; Kulleck, J.; Borshchevsky, A.; Fleurial, J.-P.

    1996-01-01

    A new skutterudite phase Ru(0.5)Pd(0.5)Sb3 was prepared. This new phase adds to a large number of already known materials with the skutterudite structure which have shown good potential for thermoelectric applications. Single phase, polycrystalline samples were prepared and characterized by x-ray analysis, electron probe microanalysis, density, sound velocity, thermal-expansion coefficient, and differential thermal analysis measurements. Ru(0.5)Pd(0.5)Sb3 has a cubic lattice, space group Im3 (T(sup 5, sub h)), with a = 9.298 A and decomposes at about 920 K. The Seebeck coefficient, the electrical resistivity, the Hall effect, and the thermal conductivity were measured on hot-pressed samples over a wide range of temperatures. Preliminary results show that Ru(0.5)Pd(0.5)Sb3 behaves as a heavily doped semiconductor with an estimated band gap of about 0.6 eV. The lattice thermal conductivity of Ru(0.5)Pd(0.5)Sb3 is substantially lower than that of the binary isostructural compounds CoSb3 and IrSb3. The unusually low thermal conductivity might be explained by additional hole and charge transfer phonon scattering in this material. The potential of this material for thermoelectric applications is discussed.

  16. Fully gapped superconductivity in In-doped topological crystalline insulator Pb0.5Sn0.5Te

    DOE PAGESBeta

    Du, Guan; Gu, G. D.; Du, Zengyi; Fang, Delong; Yang, Huan; Zhong, R. D.; Schneeloch, J.; Wen, Hai -Hu

    2015-07-27

    In this study, superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb0.5Sn0.5Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb0.5Sn0.5)0.7In0.3Te is produced by In doping in Pb0.5Sn0.5Te, and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb0.5Sn0.5)0.7In0.3Te on a (001)-oriented surface. The spectrum can be well fitted by an anisotropic s-wave gap function of Δ =more » 0.72 + 0.18cos4θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.« less

  17. Magnetic interactions in BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices

    PubMed Central

    Xu, Qingyu; Sheng, Yan; Khalid, M.; Cao, Yanqiang; Wang, Yutian; Qiu, Xiangbiao; Zhang, Wen; He, Maocheng; Wang, Shuangbao; Zhou, Shengqiang; Li, Qi; Wu, Di; Zhai, Ya; Liu, Wenqing; Wang, Peng; Xu, Y. B.; Du, Jun

    2015-01-01

    The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces. PMID:25766744

  18. Liquid phase sintering of 20Bi(Zn0.5Ti0.5)O 3-80BaTiO3 dielectrics with bismuth-zinc-borate and bismuth borosilicate glasses

    NASA Astrophysics Data System (ADS)

    Shahin, David I.

    Dielectrics in the Bi(Zn0.5Ti0.5)O3-BaTiO 3 system (specifically 20BZT-80BT, in mol%) are promising candidates for high energy density capacitor applications due to broad temperature-dependent dielectric constant maxima and a relatively field-independent permittivity. Bulk samples require sintering temperatures of greater than 1180°C to reach useful densities. Due to incompatibility of Bi with low-pO2 processing, BZT-BT-based multilayer capacitors must utilize noble metal electrodes that resist oxidation during sintering. Sintering temperatures must be reduced to allow use of less expensive electrode materials (Cu, etc.). This work studies the reduced temperature sintering behavior and dielectric properties of BZT-BT sintered with 30Bi2O3-30ZnO-40B 2O3 and 50Bi2O3-25B2O 3-25SiO2 (mol%) liquid phase formers. Dielectrics sintered with 1v% borate additions and 5v% additions of either the borate or borosilicate achieved relative densities greater than 95% after sintering at 1000°C for four hours. All compositions retained the relaxor behavior exhibited by pure 20BZT-80BT. Increased borate additions led to greater dielectric constant reductions, while increased borosilicate additions yielded no clear trend in the dielectric constant reduction. Energy densities were estimated between 0.3-0.5 J/cm3; smaller glass additions typically led to larger energy densities. Dielectrics sintered with 1v% borate additions are of interest due to their high relative densities (approx. 96%) and energy densities of approximately 0.5 J/cm3 under 100kV/cm electric fields. Studies of BZT-BT/glass interfaces revealed the formation of crystalline interfacial layers less than 10 microns thick. The borate formed a bismuth titanate phase (likely Bi4Ti3O12) during heating to 700°C, whereas the borosilicate formed a barium silicate phase (likely BaSiO3) during processing to 800°C. Similar phases are expected to be present in the liquid phase sintered dielectrics and likely affect the BZT

  19. Structure and dielectric dispersion in cubic-like 0.5K0.5Na0.5NbO3-0.5Na1/2Bi1/2TiO3 ceramic

    NASA Astrophysics Data System (ADS)

    Liu, Laijun; Knapp, Michael; Schmitt, Ljubomira Ana; Ehrenberg, Helmut; Fang, Liang; Fuess, Hartmut; Hoelzel, Markus; Hinterstein, Manuel

    2016-05-01

    The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K0.5Na0.5NbO3-0.5Na1/2Bi1/2TiO3 (KNN-50BNT) has been examined in detail by synchrotron x-ray diffraction (SD), selected-area electron diffraction (SAED), neutron diffraction (ND), and temperature-dependent dielectric characterization. The SD pattern of KNN-50BNT presents a pure perovskite structure with pseudocubic symmetry. However, superlattice reflections were observed by SAED and completely indexed by tetragonal symmetry with P4bm space group in ND pattern. The relaxor behavior of KNN-50BNT is compared with Pb-based and Ba-based relaxors and discussed in the framework of the Vogel-Fulcher law and the new glass model. The KNN-50BNT ceramic exhibits the strongest dielectric dispersion among them.

  20. Phase formation, structure and dielectric properties of ceramics (Na0.5Bi0.5)TiO3-(K0.5Na0.5)NbO3-BiFeO3

    NASA Astrophysics Data System (ADS)

    Kaleva, G. M.; Mosunov, A. V.; Sadovskaya, N. V.; Politova, E. D.; Stefanovich, S. Yu.

    2016-04-01

    Influence of BiFeO3 (BF) on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of solid solutions close to the morphotropic phase boundary in the (Na0.5Bi0.5)TiO3-(K0.5Na0.5)NbO3 system additionally modified by the low-melting KCl additives has been studied. The formation of pure perovskite structure samples decrease in the unit cell parameters and increase in the TC value stimulated by the BF addition have been revealed. It was proved that modification of compositions by small amounts of the BF and KCl additives leads to improvement of dielectric parameters.

  1. First-principles studies on Ti 3Si 0.5Ge 0.5C 2 under pressure

    NASA Astrophysics Data System (ADS)

    Feng, Wenxia; Hu, Haiquan; Cui, Shouxin; Zhang, Guiqing; Lv, Zengtao; Wu, Cheng

    2011-11-01

    The structural, electronic and elastic properties of Ti 3Si 0.5Ge 0.5C 2 have been investigated by using the pseudopotential plane-wave method within the density-functional theory. Our calculated equation of state (EOS) is consistent with the experimental results. The density of states (DOS) indicates that Ti 3Si xGe 1- xC 2 ( x=0, 0.5, 1.0) are metallic, and these compounds have nearly the same electrical conductivity. The elastic constants for Ti 3Si 0.5Ge 0.5C 2 are obtained at zero pressure, which is compared to Ti 3SiC 2 and Ti 3GeC 2. We can conclude that Ti 3Si 0.5Ge 0.5C 2 is brittle in nature by analyzing the ratio between bulk and shear moduli. There appears to be little effect on the electronic and elastic properties with the Ge substitution to Si atoms in Ti 3SiC 2.

  2. Experimental investigation of the excess charge and time constant of minority carriers in the thin diffused layer of 0.1 ohm-cm silicon solar cells

    NASA Technical Reports Server (NTRS)

    Godlewski, M. P.; Brandhorst, H. W., Jr.; Lindholm, F. A.; Sah, C. T.

    1976-01-01

    An experimental method is presented that can be used to interpret the relative roles of bandgap narrowing and recombination processes in the diffused layer. This method involves measuring the device time constant by open-circuit voltage decay and the base region diffusion length by X-ray excitation. A unique illuminated diode method is used to obtain the diode saturation current. These data are interpreted using a simple model to determine individually the minority carrier lifetime and the excess charge. These parameters are then used to infer the relative importance of bandgap narrowing and recombination processes in the diffused layer.

  3. Electrical Characteristics and Preparation of (Ba0.5Sr0.5)TiO3 Films by Spray Pyrolysis and Rapid Thermal Annealing

    NASA Astrophysics Data System (ADS)

    Koo, Horng-Show; Chen, Mi; Ku, Hong-Kou; Kawai, Tomoji

    2007-04-01

    Functional films of (Ba0.5Sr0.5)TiO3 on Pt (1000 Å)/Ti (100 Å)/SiO2 (2000 Å)/Si substrates are prepared by spray pyrolysis and subsequently rapid thermal annealing. Barium nitrate, strontium nitrate and titanium isopropoxide are used as starting materials with ethylene glycol as solvent. For (Ba0.5Sr0.5)TiO3 functional thin film, thermal characteristics of the precursor powder scratched from as-sprayed films show a remarkable peak around 300-400 °C and 57.7% weight loss up to 1000 °C. The as-sprayed precursor film with coffee-like color and amorphous-like phase is transformed into the resultant film with white, crystalline perovskite phase and characteristic peaks (110) and (100). The resultant films show correspondent increases of dielectric constant, leakage current and dissipation factor with increasing annealing temperatures. The dielectric constant is 264 and tangent loss is 0.21 in the resultant films annealed at 750 °C for 5 min while leakage current density is 1.5× 10-6 A/cm2 in the film annealed at 550 °C for 5 min.

  4. Dual Extraction of Photogenerated Electrons and Holes from a Ferroelectric Sr0.5Ba0.5Nb2O6 Semiconductor.

    PubMed

    Fan, Dayong; Zhu, Jian; Wang, Xiuli; Wang, Shengyang; Liu, Yong; Chen, Ruotian; Feng, Zhaochi; Fan, Fengtao; Li, Can

    2016-06-01

    The separation of photogenerated charges is a critical factor in photocatalysis. Recently, anomalous photovoltaic (APV) field effects (Voc ∼ 10(3) V/cm) in ferroelectrics, with their strong driving force for charge separation, have attracted much attention in photocatalysis and photoelectrocatalysis. However, it is still unknown whether photogenerated electrons and holes can be simultaneously extracted by the strong driving force toward the surface of ferroelectrics and can become available for surface reactions. This issue becomes critically important in photocatalysis because the surface reaction utilizes both the electrons and holes that reach the surface. In this work, a model lateral symmetric structure, metal/Sr0.5Ba0.5Nb2O6/metal (metal = Ag or Pt), as an electrode was fabricated. The dual extractions of photogenerated electrons and holes on the two opposite metal electrodes were achieved, as revealed by photovoltaic and ferroelectrical hysteresis measurements and photoassisted Kelvin probe force microscopy (KPFM). It was found that the high Schottky barriers of the two opposite Sr0.5Ba0.5Nb2O6-Pt electrodes are key factors that alter the two space charge regions (SCRs) by a poling effect. The resulting built-in electrical fields with parallel directions near both electrodes significantly enhance the charge separation ability. Our model unravels the driving force of charge separation in ferroelectric semiconductors, thus demonstrating the potential for highly efficient charge separation in photocatalysis. PMID:27183145

  5. Optical properties of small GaN-Al0.5Ga0.5N quantum dots grown on (11-22) GaN templates

    NASA Astrophysics Data System (ADS)

    Sellés, Julien; Rosales, Daniel; Gil, Bernard; Cassabois, Guillaume; Guillet, Thierry; Brault, Julien; Damilano, Benjamin; Vennéguès, Philippe; de Mierry, Philippe; Massies, Jean

    2015-03-01

    GaN/Al0.5Ga0.5N quantum dots deposited on the (11-22) plane have been grown by combining Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE). The (11-22) GaN oriented template was realized by MOVPE starting from a M-plane oriented sapphire substrate. The average dot sizes are the following: between 15 and 20 nm in the <-1-123> and <1-100> directions and a height ranging between 0.8 and 1.4 nm. Their density is ranging between 2 and 8x1010cm-2. The crystal field splitting is measured in Al0.5Ga0.5N via polarized microphotoluminescence. We study the photoluminescence properties of small quantum dots which present innovative optical properties among which are the evolution of the polarization of the emitted photons at different temperatures. We also analyze the distortion of the photoluminescence at different time delays after the excitation pulse. A redshift is found that is attributed to the complex thermally-induced delocalization of the carriers through the assembly of dots from the smaller ones to the bigger ones.

  6. Large electrostrain and high optical temperature sensitivity in BaTiO3-(Na0.5Ho0.5)TiO3 multifunctional ferroelectric ceramics.

    PubMed

    Li, Jun; Chai, Xiaona; Wang, Xusheng; Xu, Chao-Nan; Gu, Yihao; Zhao, Haifeng; Yao, Xi

    2016-08-01

    Ferroelectric (1 -x)BaTiO3-x(Na0.5Ho0.5)TiO3 ceramics with ferroelectric and up-conversion luminescent multifunctions were designed and fabricated by a solid state reaction process. Their structure, ferroelectric, piezoelectric, up-conversion photoluminescence and relative optical temperature sensing properties were investigated systematically. Crystal structure analysis and Rietveld refinements based on the powder X-ray diffraction data show that the ceramics crystallized in the tetragonal perovskite space group P4mm at room temperature. Enhanced electrical properties and strong green up-conversion luminescence with thermally coupled green emission bands centered at 523 and 553 nm were observed. For a typical sample x equals 0.05, a large electrostrain of 0.279% was obtained under a 70 kV cm(-1) electric field that is comparable to that of the PZT4. Meanwhile, the excellent optical temperature sensitivity (0.0063 K(-1) at 480 K) is higher than that of Er-doped BaTiO3 nanocrystal materials. The results suggest that the BaTiO3-(Na0.5Ho0.5)TiO3 material should be an attractive material for piezoelectric actuator and temperature sensing device applications. PMID:27244098

  7. Enhanced susceptibility in LNiO3 perovskites ( L = La,Pr,Nd,Nd0.5Sm0. 5)

    PubMed

    Zhou; Goodenough; Dabrowski; Klamut; Bukowski

    2000-01-17

    The temperature dependence of the resistivity rho(T) and of the dc magnetic susceptibility chi(T) were measured on high-quality LNiO3 (L = La,Pr,Nd,Nd0.5Sm0.5) samples synthesized under high oxygen pressure. Subtraction of the rare-earth contribution to chi(T) allows the presentation of the evolution of the susceptibility of the NiO3 array from Pauli to Curie-Weiss paramagnetism with decreasing bandwidth. A metal-insulator transition occurring at a temperature T(t) = T(N) is first order for L = Pr and Nd; it becomes second order and produces no anomaly in chi(-1)(T) at a T(t)>T(N) for L = Nd0.5Sm0.5. In the antiferromagnetic domain T

  8. Superconductivity induced by In substitution into the topological crystalline insulator Pb0.5Sn0.5Te

    NASA Astrophysics Data System (ADS)

    Zhong, R. D.; Schneeloch, J. A.; Liu, T. S.; Camino, F. E.; Tranquada, J. M.; Gu, G. D.

    2014-07-01

    Indium substitution turns the topological crystalline insulator (TCI) Pb0.5Sn0.5Te into a possible topological superconductor. To investigate the effect of the indium concentration on the crystal structure and superconducting properties of (Pb0.5Sn0.5)1-xInxTe, we have grown high-quality single crystals using a modified floating-zone method and have performed systematic studies for indium content in the range 0≤x≤0.35. We find that the single crystals retain the rocksalt structure up to the solubility limit of indium (x ˜0.30). Experimental dependencies of the superconducting transition temperature (Tc) and the upper critical magnetic field (Hc2) on the indium content x have been measured. The maximum Tc is determined to be 4.7 K at x =0.30, with μ0Hc2(T =0)≈5 T.

  9. Strong red emission in Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics

    NASA Astrophysics Data System (ADS)

    Sun, Haiqin; Peng, Dengfeng; Wang, Xusheng; Tang, Mianmian; Zhang, Qiwei; Yao, Xi

    2011-07-01

    The photoluminescence of Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics prepared by conventional solid-state reaction were investigated. A bright red emission is observed at room temperature, which ascribed to 1D2→3H4 transition. The excitation bands are mainly located at 440 ˜ 505 nm, which is adaptable to the emission band of commercial blue light-emitting diodes (LEDs) chips. The optimal emission intensity was also obtained when Pr doping level was 0.003 mol. Meanwhile, the enhanced ferroelectric properties were obtained by Pr doping. The results show that Pr doped (Bi0.5Na0.5)TiO3 ceramics as a multifunctional material may be useful for white LEDs, sensor, and optical-electro integration.

  10. Structural and Dielectric Studies on Pb(Mg0.5Mo0.5)O3 Compound

    NASA Astrophysics Data System (ADS)

    Barbur, I.; Ardelean, I.; Borodi, G.; Ciomos, D.

    Structural and dielectric measurements were performed on Pb(Mg0.5Mo0.5)O3 (PMM). Polycrystalline samples of PMM were synthesized by solid-state reaction technique at normal pressure. The X-ray measurements indicate formation of single-phase perovskite structure with absence of Mg and Mo ions ordering. The temperature dependence of the relative dielectric constant suggests that PMM undergoes a phase transition (FE or AFE) at 63°C.

  11. Interrelation between Structure Magnetic Properties in La0.5Sr0.5CoO3

    SciTech Connect

    Biegalski, Michael D; Takamura, Y; Mehta, A; Gai, Zheng; Kalinin, Sergei; Ambaye, Hailemariam; Lauter, Valeria; He, Jun; Kim, Young Min; Borisevich, Albina Y; Siemons, Wolter; Christen, Hans M

    2014-01-01

    Differing anisotropic strain induced from the underlying substrates not only control the long-range structural symmetries in La0.5Sr0.5CoO3 but also impact the magnetic properties of these epitaxial thin films. The two dominant structural distortions: oxygen octahedral tilts and epitaxial strain, however, have complex and non-intuitive effects on the splitting of the t2g states and consequently on magnetization.

  12. Solid state synthesis and characterization of bulk FeTe0.5Se0.5 superconductors

    NASA Astrophysics Data System (ADS)

    Onar, K.; Yakinci, M. E.

    2016-01-01

    FeTe0.5Se0.5 polycrystalline superconductor samples were synthesized by solid- state reaction method at different heating temperatures. The morphological and structural characterization of FeTe0 5Se0.5 samples were carried out by X-rays Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy. The electrical, magnetic and thermal transport properties were investigated up to 8 T by using physical property measurement system. The results reveal that the sensitivity of electrical and magnetic properties strongly depends on the heat treatment cycles. The upper critical field, Hc2(0), was determined with the magnetic field parallel to the sample surface. It gives a maximum value of 36.3 T. The lower critical field, Hc1(T), was obtained as 210, 140 and 70 Oe at 5, 8 and 12 K, respectively. The coherence length, ξ, at the zero field, was calculated to be 1.94 nm and suggested a transparent intergrain boundaries peculiarity. The μ0Hc2(0)/kBTc rate shows higher value (3.36 T/K) than the Pauli limit (1.84 T/K) which suggests unconventional nature of superconductivity for the polycrystalline FeTe0.5Se0.5 superconducting samples.

  13. Fabrication and Characterization of Mn0.5Zn0.5Fe2O4 Magnetic Nanofibers

    NASA Astrophysics Data System (ADS)

    Xiang, Jun; Shen, Xiang-Qian; Song, Fu-Zhan; Meng, Xian-Feng

    2010-01-01

    Mn0.5Zn0.5Fe2O4 Magnetic nanofibers were fabricated by calcining electrospun polymer/inorganic composite nanofibers and characterized by thermogravimetric and differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and a vibrating sample magnetometer. The experimental results show that the pure spinel structure is basically formed when the composite nanofibers are calcined at 450°C for 2h. With the increasing calcination temperature, both the saturation magnetization and coercivity of nanofiber samples increase initially along with the growth of Mn0.5Zn0.5Fe2O4 nanocrystals contained in the nanofibers. However, when the calcination temperature reaches 550°C, the saturation magnetization of nanofibers starts to dramatically decrease owing to the formation of the α-Fe2O3 phase at this temperature. The prepared Mn0.5Zn0.5Fe2O4 nanofibers calcined at 500°C for 2h have diameters ranging from 100 to 200nm. Their saturation magnetization and coercivity are 12.37 emu/g and 4.81 kA/m at room temperature, respectively.

  14. Synthesis and characterization of Sm0.5Ba0.5MnO3-δ as anode materials for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Abdalla, A. M.; Radenahmad, N.; Abu Bakar, M. S.; . I. Petra, Pg M.; Azad, A. K.

    2016-03-01

    The material performance is a crucial issue in the current fuel cell technology, and for this reason we present this new series of Samarium family which can be used as electrode giving a high performance in a particular application. Sm0.5Ba0.5MnO3-δ was prepared by solid state reaction method and characterized by using X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Rietveld analysis of XRD data shows that the material has an Orthorhombic crystal structure with cell parameter a = 3.883(1) Å b = 3.8742(5) Å c = 7. 762(4) Å, in the Pmmm space group. TGA analyses shows that the materials is going to decrease by 0.32%. The density of the materials was calculated from structural refinement and found to be 8.372 gm/cm3.

  15. Magneto-optical spectra and electron structure of Nd0.5Gd0.5Fe3(BO3)4 single crystal

    NASA Astrophysics Data System (ADS)

    Malakhovskii, A. V.; Gnatchenko, S. L.; Kachur, I. S.; Piryatinskaya, V. G.; Sukhachev, A. L.; Temerov, V. L.

    2016-03-01

    Polarized absorption spectra and magnetic circular dichroism (MCD) spectra of Nd0.5Gd0.5Fe3(BO3)4 single crystal were measured in the range of 10000-21000 cm-1 and at temperatures 2-300 K. On the basis of these data, in the paramagnetic state of the crystal, the 4f states of the Nd3+ ion were identified in terms of the irreducible representations and in terms of | J , ± MJ > wave functions of the free atom. The changes of the Landé factor during f-f transitions were found theoretically in the | J , ± MJ > wave functions approximation and were determined experimentally with the help of the measured MCD spectra. In the majority of cases the experimentally found values are close to the theoretically predicted ones.

  16. The dielectric properties of La(Mg0.5Ti0.5)O3 ceramics studied by Raman-scattering, infrared reflectivity spectroscopy, and first-principles calculations.

    PubMed

    Liu, Hsiang-Lin; Hsueh, Hung-Chung; Lin, I-Nan; Yang, Ming-Ti; Lee, Wei-Chung; Chen, Yi-Chun; Chia, Chia-Ta; Cheng, Hsiu-Fung

    2011-06-01

    La(Mg(0.5)Ti(0.5))O(3) (LMT) ceramics were prepared by either the solid-state reaction (LMT)(SS) or the citric-acid chemical method (LMT)(CA). A combination of Raman scattering, infrared reflectivity, and first-principles calculations was carried out to elucidate the correlation between lattice dynamics and the dielectric properties of these materials. Twelve Raman-active phonons are observed in both samples, displaying similar frequency positions. Interestingly, the A(g) phonon (g(11) mode) of (LMT)(SS) at about 717 cm(-1) involving the oxygen octahedron breathing vibrations demonstrates a narrower linewidth, suggesting its better crystallinity. Furthermore, an infrared-active u(2) phonon band due to the vibrations of O(I) and O(II) layers, which possesses the largest oscillator strength, exhibits stronger intensity for (LMT)(SS), as compared with those for (LMT)(CA). Additionally, the Q × f values (the product of dielectric Q values and measurement frequency) of (LMT)(SS) estimated from either microwave cavity or infrared spectroscopic measurements are larger than those of (LMT)(CA). These results indicate that the better coherence of lattice vibrations in (LMT)(SS) leads to its higher Q × f value, providing evidence for a strong connection between optical spectroscopic behavior and microwave dielectric characteristics in these materials. PMID:21576769

  17. Electrostatic doping limits and control of magnetism in electrolyte gated LaAlO3(001)/La0.5Sr0.5CoO3-δ thin films

    NASA Astrophysics Data System (ADS)

    Walter, Jeff; Wang, Helin; Leighton, Chris

    Recently developed ionic liquid/gel gating techniques have proven remarkably expedient in the study of charge density effects in a variety of conductors, ranging from organics to complex oxides. Here we present electrolyte gate control of magnetism in ultrathin (8 u.c.) La0.5Sr0.5CoO3-δ (LSCO) films, using ion gels in electric double layer transistors. The LSCO films are initially metallic and ferromagnetic (Tc ~ 170 K), with anomalous Hall conductivity up to 40 S/cm, and strong perpendicular magnetic anisotropy. Based on extensive temperature and gate voltage dependences we first determined the limits for electrostatic vs. electrochemical operation, concluding that negative bias enables reversible hole accumulation, whereas positive bias irreversibly induces oxygen vacancies. Following this we demonstrated clear voltage-control of resistivity, magnetoresistance, andTc. Utilizing the anomalous Hall conductivity as an exceptional probe of the magnetic order parameter in the gated surface region, a 12 K shift in Tc is obtained. This compares favorably to the state-of-the-art and exhibits potential for much larger modulation in films of lower Sr content. Work supported by NSF MRSEC.

  18. Low-Temperature Sintering of Ba0.5Sr0.5TiO3-SrMoO4 Dielectric Tunable Composite Ceramics for LTCC Applications

    NASA Astrophysics Data System (ADS)

    Tang, Linjiang; Wang, Jinwen; Zhai, Jiwei

    2013-08-01

    A sintering-aid system using melting of B-Li glass for barium strontium titanate (BST)-based compositions to be used in low-temperature cofired ceramic (LTCC) layers is introduced. The effects of the sintering aid on the microstructure, dielectric properties, and application in LTCC were investigated. The composition Ba0.5Sr0.5TiO3-SrMoO4 with 3 wt.% B-Li glass sintered at 950°C exhibits optimized dielectric properties, including low dielectric constant (368), low dielectric loss (0.007), and moderate tunability (13%, 60 kV/cm) at 10 kHz. At 1.44 GHz, it possesses a dielectric constant of 218 and Q value of 230. LTCC multilayer ceramic capacitors fabricated by the tape-casting process have steady relative tunability of 12% at 300 V, suggesting that BST50-SrMoO4-B-Li glass composite ceramic is a promising candidate for electrically tunable LTCC microwave device applications.

  19. A study on the wake-up effect of ferroelectric Hf0.5Zr0.5O2 films by pulse-switching measurement

    NASA Astrophysics Data System (ADS)

    Kim, Han Joon; Park, Min Hyuk; Kim, Yu Jin; Lee, Young Hwan; Moon, Taehwan; Kim, Keum Do; Hyun, Seung Dam; Hwang, Cheol Seong

    2016-01-01

    The appearance of ferroelectric (FE) and anti-ferroelectric (AFE) properties in HfO2-based thin films is highly intriguing in terms of both the scientific context and practical application in various electronic and energy-related devices. Interestingly, these materials showed a ``wake-up effect'', which refers to the increase in remanent polarization with increasing electric field cycling number before the occurrence of the fatigue effect. In this work, the wake-up effect from Hf0.5Zr0.5O2 was carefully examined by the pulse-switching experiment. In the pristine state, the Hf0.5Zr0.5O2 film mostly showed FE-like behavior with a small contribution from AFE-like distortion, which could be ascribed to the involvement of the AFE phase. The field cycling of only 100 cycles almost completely transformed the AFE phase into the FE phase by depinning the pinned domains. The influence of field cycling on the interfacial layer was also examined through the pulse-switching experiments.

  20. Aurivillius-Popper mixed superconductors in BiO--CuO--(Sr/sub 0. 5/, Ca/sub 0. 5/)O system

    SciTech Connect

    Fukuhara, M.; Bhalla, A.S.; Mulay, L.N.; Newnham, R.E.

    1989-03-01

    We report the effect of inhomogeneities on the electric resistivity and ac magnetic susceptibility in Aurivillius-like bismuth mixed phase oxides of the BiO--Cuo--(Sr/sub 0.5/, Ca/sub 0.5/)O system and propose a crystal structure of the major phase having highest T/sub c/. Nominal Aurivillius compositions with molar ratios of BiO/(Sr/sub 0.5/, Ca/sub 0.5/)O = 1/2 are superconductors with T/sub c/ ranging from 83 to 107 K, and are accompanied by a large expansion during sintering due to the formation of Kirkendall voids. T/sub c/ increases with decreasing of the c lattice parameter. An oxide BiSrCaCu/sub 2/O/sub x/ (n = 2) shows a maximum T/sub c/ value of 107 K and an onset of superconductivity at a much higher temperature. It seems that the structure of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ consists of an Aurivillius-like phase having two perovskite layers and a Popper mixed phase. The ac magnetic susceptibility showed an overall decrease in susceptibility with time up to 220 days. This appears to be related to the relief of intralattice strain.

  1. A study on the wake-up effect of ferroelectric Hf0.5Zr0.5O2 films by pulse-switching measurement.

    PubMed

    Kim, Han Joon; Park, Min Hyuk; Kim, Yu Jin; Lee, Young Hwan; Moon, Taehwan; Kim, Keum Do; Hyun, Seung Dam; Hwang, Cheol Seong

    2016-01-21

    The appearance of ferroelectric (FE) and anti-ferroelectric (AFE) properties in HfO2-based thin films is highly intriguing in terms of both the scientific context and practical application in various electronic and energy-related devices. Interestingly, these materials showed a "wake-up effect", which refers to the increase in remanent polarization with increasing electric field cycling number before the occurrence of the fatigue effect. In this work, the wake-up effect from Hf0.5Zr0.5O2 was carefully examined by the pulse-switching experiment. In the pristine state, the Hf0.5Zr0.5O2 film mostly showed FE-like behavior with a small contribution from AFE-like distortion, which could be ascribed to the involvement of the AFE phase. The field cycling of only 100 cycles almost completely transformed the AFE phase into the FE phase by depinning the pinned domains. The influence of field cycling on the interfacial layer was also examined through the pulse-switching experiments. PMID:26511062

  2. Improved bipolar resistive switching memory characteristics in Ge0.5Se0.5 solid electrolyte by using dispersed silver nanocrystals on bottom electrode.

    PubMed

    Kim, Jang-Han; Nam, Ki-Hyun; Hwang, Inchan; Cho, Won-Ju; Park, Byoungchoo; Chung, Hong-Bay

    2014-12-01

    Resistive switching random-access memory (ReRAM) devices based on chalcogenide solid electrolytes have recently become a promising candidate for future low-power nanoscale nonvolatile memory application. The resistive switching mechanism of ReRAM is based on the formation and rupture of conductive filament (CF) in the chalcogenide solid electrolyte layers. However, the random diffusion of metal ions makes it hard to control the CF formation, which is one of the major obstacles to improving device performance of ReRAM devices. We demonstrate the spin-coated metal nanocrystals (NCs) enhance the bipolar resistive switching (BRS) memory characteristics. Compared to the Ag/Ge0.5Se0.5/Pt structure, excellent resistive switching memory characteristics were obtained from the Ag/Ge0.5Se0.5/Ag NCs/Pt structure. Ag NCs improve the uniformity of resistance values and reduce the reset voltage and current. A stable DC endurance (> 100 cycles) and a high data retention (> 10(4) sec) were achieved by spin coating the Ag NCs on the Pt bottom electrode for ReRAMs. PMID:25971090

  3. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures.

    PubMed

    Renshaw Wang, X; Sun, L; Huang, Z; Lü, W M; Motapothula, M; Annadi, A; Liu, Z Q; Zeng, S W; Venkatesan, T; Ariando

    2015-01-01

    We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context. PMID:26669575

  4. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures

    PubMed Central

    Renshaw Wang, X.; Sun, L.; Huang, Z.; Lü, W. M.; Motapothula, M.; Annadi, A.; Liu, Z. Q.; Zeng, S. W.; Venkatesan, T.; Ariando

    2015-01-01

    We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context. PMID:26669575

  5. Dielectric relaxation and magnetodielectric response in DyMn0.5Cr0.5O3

    NASA Astrophysics Data System (ADS)

    Yuan, B.; Yang, J.; Zuo, X. Z.; Kan, X. C.; Zu, L.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Sun, Y. P.

    2015-09-01

    We investigate the structural, magnetic, and magnetodielectric properties of DyMn0.5Cr0.5O3. The sample can be indexed with an orthorhombic phase with B site disordered space group Pbnm. The valence state of both Mn and Cr ions are suggested to be +3 based on the results of x-ray photoelectron spectroscopy. Two thermally excited dielectric relaxation at temperatures TN2 < T< 300 K and large magnetodielectric effect (MDC = 20%-30%) due to the disordered arrangement of Mn3+/Cr3+ ions associated with electron hopping between them are observed. The absence of any noticeable magnetoresistance effect (MR < 0.5%) demonstrates that the observed magnetodielectric effect is an intrinsic behavior. These results suggest that DyMn0.5Cr0.5O3 is a magnetodielectric compound, whose dielectric properties are dependence of the applied magnetic field, which exhibits such effects near room temperature and holds great promise for future device applications.

  6. Charge-ordered ferromagnetic phase in La(0.5)Ca(0.5)MnO3.

    PubMed

    Loudon, James C; Mathur, Neil D; Midgley, Paul A

    Mixed-valent manganites are noted for their unusual magnetic, electronic and structural phase transitions. For example, the La(1-x)Ca(x)MnO(3) phase diagram shows that below transition temperatures in the range 100-260 K, compounds with 0.2 < x < 0.5 are ferromagnetic and metallic, whereas those with 0.5 < x < 0.9 are antiferromagnetic and charge ordered. In a narrow region around x = 0.5, these totally dissimilar ground states are thought to coexist. It has been shown that charge order and charge disorder can coexist in the related compound, La(0.25)Pr(0.375)Ca(0.375)MnO(3). Here we present electron microscopy data for La(0.5)Ca(0.5)MnO(3) that shed light on the distribution of these coexisting phases, and uncover an additional, unexpected phase. Using electron holography and Fresnel imaging, we find micrometre-sized ferromagnetic regions spanning several grains coexisting with similar-sized regions with no local magnetization. Holography shows that the ferromagnetic regions have a local magnetization of 3.4 +/- 0.2 Bohr magnetons per Mn atom (the spin-aligned value is 3.5 micro (B) per Mn). We use electron diffraction and dark-field imaging to show that charge order exists in regions with no net magnetization and, surprisingly, can also occur in ferromagnetic regions. PMID:12490944

  7. Charge-ordered ferromagnetic phase in La0.5Ca0.5MnO3

    NASA Astrophysics Data System (ADS)

    Loudon, James C.; Mathur, Neil D.; Midgley, Paul A.

    2002-12-01

    Mixed-valent manganites are noted for their unusual magnetic, electronic and structural phase transitions. For example, the La1-xCaxMnO3 phase diagram shows that below transition temperatures in the range 100-260K, compounds with 0.2 < x < 0.5 are ferromagnetic and metallic, whereas those with 0.5 < x < 0.9 are antiferromagnetic and charge ordered. In a narrow region around x = 0.5, these totally dissimilar ground states are thought to coexist. It has been shown that charge order and charge disorder can coexist in the related compound, La0.25Pr0.375Ca0.375MnO3. Here we present electron microscopy data for La0.5Ca0.5MnO3 that shed light on the distribution of these coexisting phases, and uncover an additional, unexpected phase. Using electron holography and Fresnel imaging, we find micrometre-sized ferromagnetic regions spanning several grains coexisting with similar-sized regions with no local magnetization. Holography shows that the ferromagnetic regions have a local magnetization of 3.4 +/- 0.2Bohr magnetons per Mn atom (the spin-aligned value is 3.5µB per Mn). We use electron diffraction and dark-field imaging to show that charge order exists in regions with no net magnetization and, surprisingly, can also occur in ferromagnetic regions.

  8. Magnetocaloric and phase coexistence in La0.5Ca0.5-xSrxMnO3 manganites

    NASA Astrophysics Data System (ADS)

    Khondabi, M.; Ahmadvand, H.; Kameli, P.; Amirzadeh, P.; Salamati, H.; Dasgupta, P.; Poddar, A.

    2015-12-01

    Structural, magnetic, and magnetocaloric properties of the phase separated La0.5Ca0.5-xSrxMnO3 (x = 0, 0.2, 0.3, 0.4, and 0.5) manganites have been studied. The results show that the phase coexistence state can be investigated by magnetocaloric studies (especially the field dependence of magnetic entropy change at constant temperature). Magnetic entropy change (△SM) shows positive (negative) peak at the vicinity of TN (TC). However, in the intermediate temperatures between TN and TC, both the sign and magnitude of △SM are strongly dependent on temperature and magnetic field, manifesting the competition of ferromagnetic (FM) (negative △SM) and non-FM (positive △SM) phases. This behavior is more pronounced in the parent compound, La0.5Ca0.5MnO3, in which the intermediate phase separation ranges between 160 and 225 K. The substitution of Ca by Sr enhances the ferromagnetic state, weakens the phase separation, and thus narrows the temperature range in which the field related effects (such as the sign change of △SM) are observed.

  9. Structure and dielectric properties of solid solutions Bi7Ti4 + x W x Ta1-2 x O21 ( x = 0-0.5)

    NASA Astrophysics Data System (ADS)

    Zubkov, S. V.; Vlasenko, V. G.; Shuvaeva, V. A.; Shevtsova, S. I.

    2016-01-01

    A number of solid solutions Bi7Ti4 + x W x Ta1-2 x O21 ( x = 0-0.5) have been synthesized from oxides by solid-phase reaction. The crystal structure, the electrophysical characteristics, and the microstructure of the prepared ceramic samples have been studied. According to X-ray powder diffraction, all the compounds are single-phase with the structure of mixed-layer Aurivillius phases ( m = 2.5) with the orthorhombic crystal lattice (space group I2 cm, Z = 2). Temperature dependences of the relative permittivity ɛ( T) of the compound have been measured, from which it has been found that the Curie temperature T C of perovskite-like oxides Bi7Ti4 + x W x Ta1-2 x O21 ( x = 0-0.5) decreases linearly as substitution parameter x decreases. The activation energies of charge carriers have been found in different temperature ranges.

  10. Structural And Electrical Properties oF (La0.5-xPrxBa0.5)(Mn0.5Ti0.5)O3 Perovskite

    NASA Astrophysics Data System (ADS)

    Alias, Nor Hayati; Shaari, Abdul Halim; Wan Yusoff, Wan Mohd Daud; Mahmood, Che Seman

    2010-01-01

    A single phase monoclinic new perovskite based titano-manganite (La0.5-xPrxBa0.5)(Mn0.5Ti0.5)O3 has been successfully prepared by ceramic solid-state technique at sintering temperature of 1300° C. The concentration of Pr (Praseodymium), x, in molar proportion in A site has been varied as x = 0, 0.02 and 0.2. Analysis has been carried out to determine the electrical properties of the synthesized material at frequency ranging from 5 Hz to 1 MHz; and at temperature range between 25° C to 200° C. It is found that Pr addition promoted liquid phase sintering diffusion, porosity and agglomeration formation at 1300° C. Dual relaxation is observed in unsubstituted Pr sample x = 0 and high Pr substituted sample x = 0.2. This phenomenon was a combinational contribution from a quasi dc (QDC) or low frequency dispersion (LFD), two cole-cole relaxational responses and a resistor. While low concentrated Pr substituted sampled x = 0.02 shows a combinational contribution from a quasi dc (QDC) or low frequency dispersion (LFD), single cole-cole relaxational response and a resistor at room temperature. Pr substitution at x = 0 (max 12000) and x = 0.2 (max 16000) showed high dielectric values compared to low substituted sample x = 0.02. Variation of dielectric loss tangent (tan δ) are observed for all samples at temperature ranged studied.

  11. Synthesis and characterization of (Bi{sub 0.5}Ba{sub 0.5}) (Fe{sub 0.5}Ti{sub 0.5}) O{sub 3} ceramic

    SciTech Connect

    Parida, B.N.; Das, Piyush R.; Padhee, R.; Suara, D.; Mishra, A.; Rout, J.; Choudhary, R.N.P.

    2015-01-15

    Graphical abstract: Temperature variation of (a) dielectric constant (b) dielectric loss of the sample. - Highlights: • The high values of dielectric permittivity and low value of tangent loss. • It used for microwave applications. • The impedance and dielectric relaxation in the material is non exponential and non Debye-type. • Its ac conductivity obeys Jonscher universal power law. - Abstract: The polycrystalline sample of (Bi{sub 0.5}Ba{sub 0.5}) (Fe{sub 0.5}Ti{sub 0.5}) O{sub 3} (BF–BT) was prepared by a standard mixed oxide method. Analysis of room temperature XRD pattern and Raman/FTIR spectra of the compound does not exhibit any change in its crystal structure of BaTiO{sub 3} on addition of BiFeO{sub 3} in equal ratio. The surface morphology of the gold-plated sintered pellet sample recorded by SEM (scanning electron microscope) exhibits a uniform distribution of grains with less porosity. Detailed studies of nature and quantity of variation of dielectric constant, tangent loss, and polarization with temperature and frequency indicate the existence of ferroelectric phase transition at high-temperature. There is a low-temperature anti-ferromagnetic phase transition below 375 °C in the material. Detailed studies of electrical properties (impedance, modulus, etc.) of the material confirmed a strong correlation between micro-structure and properties.

  12. Phase diagram and electrostrictive properties of Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Shan-Tao; Yan, Feng; Yang, Bin; Cao, Wenwu

    2010-09-01

    Phase diagram of Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 ternary system has been analyzed and (0.94-x)BNT-0.06BT-xKNN (0.15≤x≤0.30) ceramics have been prepared and investigated. Pseudocubic structures were confirmed by x-ray diffractions and its preliminary Rietveld refinements. P-E, S-E, and S-P2 profiles (where P, E, and S denote polarization, electric field, and strain, respectively) indicate electrostrictive behavior of all ceramics. The compositions with x =0.20 and 0.25 show pure electrostrictive characteristics. The dissipation energy, electrostrictive strain, and electrostrictive coefficient have been determined and compared with other lead-free and lead-containing electrostrictors. The electrostrictive coefficient can reach as high as 0.026 m4/C2, about 1.5 times of the value of traditional Pb-based electrostrictors.

  13. High-field electromechanical response of Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 across its morphotropic phase boundary

    NASA Astrophysics Data System (ADS)

    Moosavi, A.; Bahrevar, M. A.; Aghaei, A. R.; Ramos, P.; Algueró, M.; Amorín, H.

    2014-02-01

    Lead-free (1 - x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3 [(BNKTx); x = 0.18, 0.20, 0.22, 0.24] piezoelectric ceramics were prepared via conventional solid-state reactions. Phase characterization using x-ray diffraction showed coexistence of perovskite rhombohedral and tetragonal polymorphs as anticipated for compositions across the morphotropic phase boundary (MPB). Electrical and electromechanical properties were studied as a function of x. Permittivity and polarization figures were comparable to the best values previously reported. Largest piezoelectric and high field electromechanical responses were obtained for BNKT0.20 samples, considered to have optimum MPB phases. This material exhibited giant field-induced strains of 0.13% and 0.38% under electric fields of 1 and 2.4 kV mm-1 at room temperature by a phase-change mechanism. Figures are comparable to those reported for other BNT-based systems, but under significantly lower driving fields, which is a clear advantage for actuation.

  14. Formation of self-organized In 0.5Ga 0.5As quantum dots on GaAs by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chyi, Jen-Inn; Nee, Tzer-En; Lee, Ching-Ting; Shieh, Jia-Lin; Pan, Jen-Wei

    1997-05-01

    Self-organized In 0.5Ga 0.5As quantum dots have been successfully grown on vicinal GaAs substrates by molecular beam epitaxy. The density of the quantum dots can be changed by nucleating the dots under different As overpressure. Substrate tilt angle of 15° results in much larger dot size and density than that of 4° due to the closely spaced step edges on the surface. Through investigations of the dots grown on In 0.1Ga 0.9As buffer, the strain energy of the buffer layer is also found to be an important factor that affects the size and density of the quantum dots.

  15. Polarized neutron reflection study of the unidirectional magnetic anisotropy of Permalloy on Ni 0.5Co 0.5O

    NASA Astrophysics Data System (ADS)

    Felcher, G. P.; Huang, Y. Y.; Carey, M.; Berkowitz, A.

    1993-03-01

    Couples of ferromagnetic Permalloy/antiferromagnetic metal oxide exhibit unidirectional magnetic anisotropy along a magnetic field applied during cooling. Polarized neutron reflection has been used to check if the effect is due to a bias of the antiferromagnetic configuration in the oxide, where the layer immediately adjacent to the Permalloy is polarized parallel to the easy direction of magnetization. The measurements were made on a sample consisting of 300ÅPermalloy/500ÅNi 0.5Co 0.5O. Polarized neutron reflectivities were taken at the four corners of the magnetic hysteresis loop at 20 K. A faint magnetic signal consistent with the unidirectional bias of the F / AF structure was observed. This behavior is discussed in the light of the current theories.

  16. Observation of indium ion migration-induced resistive switching in Al/Mg0.5Ca0.5TiO3/ITO

    NASA Astrophysics Data System (ADS)

    Lin, Zong-Han; Wang, Yeong-Her

    2016-08-01

    Understanding switching mechanisms is very important for resistive random access memory (RRAM) applications. This letter reports an investigation of Al/Mg0.5Ca0.5TiO3 (MCTO)/ITO RRAM, which exhibits bipolar resistive switching behavior. The filaments that connect Al electrodes with indium tin oxide electrodes across the MCTO layer at a low-resistance state are identified. The filaments composed of In2O3 crystals are observed through energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, nanobeam diffraction, and comparisons of Joint Committee on Powder Diffraction Standards (JCPDS) cards. Finally, a switching mechanism resulting from an electrical field induced by In3+ ion migration is proposed. In3+ ion migration forms/ruptures the conductive filaments and sets/resets the RRAM device.

  17. Direct band gap optical emission from Ge islands grown on relaxed Si{sub 0.5}Ge{sub 0.5}/Si (100) substrate

    SciTech Connect

    Aluguri, R.; Manna, S.; Ray, S. K.

    2014-01-07

    Strained Ge islands have been grown on fully relaxed Si{sub 0.5}Ge{sub 0.5} substrate by pulsed laser ablation technique. The formation of strained Ge islands has been found for film with higher thickness following Stranski–Krastanov growth mechanism. The variation of strain with changing Ge layer thickness has been analyzed using Raman spectroscopy and high-resolution X-ray diffraction techniques. X-ray photoelectron spectra have shown the absence of any Si-Ge intermixing and oxidation of Ge films. A strong no-phonon photoluminescence emission from Ge islands has been observed, showing the superior optical characteristics of the islands grown on relaxed substrate.

  18. Structure, electrical properties and temperature characteristics of Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-Bi0.5Li0.5TiO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Lin, Dunmin; Zheng, Qiaoji; Xu, Chenggang; Kwok, K. W.

    2008-11-01

    (1- x- y)Bi0.5Na0.5TiO3- xBi0.5K0.5TiO3- yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique, and their structure, electrical properties, and temperature characteristics have been studied systematically. The ceramics can be well-sintered at 1050-1150 °C. The increase in K+ concentration decreases the grain-growth rate and promotes the formation of grains with a cubic shape, while the addition of Li+ decreases greatly the sintering temperature and assists in the densification of BNT-based ceramics. The results of XRD diffraction show that K+ and Li+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a pure perovskite structure. As x increases from 0.05 to 0.50, the ceramics transform gradually from rhombohedral phase to tetragonal phase and consequently a morphotropic phase boundary (MPB) is formed at 0.15≤ x≤0.25. The concentration y of Li+ has no obvious influence on the crystal structure of the ceramics. Compared with pure Bi0.5Na0.5TiO3, the partial substitution of K+ and Li+ for Na+ lowers greatly the coercive field E c and increases the remanent polarization P r of the ceramics. Because of the MPB, lower E c and large P r, the piezoelectricity of the ceramics is improved significantly. For the ceramics with the compositions near the MPB ( x=0.15-0.25 and y=0.05-0.10), the piezoelectric properties become optimum: piezoelectric coefficient d 33=147-231 pC/N and planar electromechanical coupling factor k P=20.2-41.0%. In addition, the ceramics exhibit relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The depolarization temperature T d shows a strong dependence on the concentration x of K+ and reaches the lowest values at the MPB. The temperature dependences of the ferroelectric and dielectric properties at high temperatures may imply that the ceramics may contain both the polar and non-polar regions at temperatures above T d.

  19. Microwave properties of Ba0.5Sr0.5TiO3 thin film coplanar phase shifters

    NASA Astrophysics Data System (ADS)

    Suherman, P. M.; Jackson, T. J.; Tse, Y. Y.; Jones, I. P.; Chakalova, R. I.; Lancaster, M. J.; Porch, A.

    2006-05-01

    Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45 MHz-50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications.

  20. Strain enhanced charge order melting in Pr0.5Ca0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Baisnab, Dipak Kumar; Kumary, T. Geetha; Satya, A. T.; Mani, Awadhesh; Janaki, J.; Nithya, R.; Vaidhyanathan, L. S.; Janawadkar, M. P.; Bharathi, A.

    2011-06-01

    The effect of strain on charge order melting in half doped manganite Pr0.5Ca0.5MnO3 thin films of different thicknesses has been investigated. The films were deposited on (100) oriented MgO substrates by pulsed laser deposition technique and were characterized by x-ray diffraction, electrical resistivity and magnetoresistance measurements. A field induced charge order melting is observed for films with very small thickness. The charge order transition temperature and the magnetic field induced charge order melting appears to be governed by the nature of strain that is experienced by the film.

  1. Exact size control of KTa0.5Nb0.5O3 nanoparticles using flexible hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Lin, Jiaqi; Chen, Gaoru; Yang, Wenlong; Jiang, Zhichao; Li, Haidong; Wang, Li; Yan, Zhehua; Wang, Xuan; Lei, Qingquan

    2016-04-01

    KTa0.5Nb0.5O3 (KTN) nanoparticles with a perovskite structure were synthesized in orthogonal experiments under different hydrothermal conditions. Controlled sizes were generated by analyzing four variables using an orthogonal array experimental design (OA16 matrix): reaction temperature, KOH concentration, reaction time and solution volume. The effects of the four factors on the KTN nanoparticle size were systematically examined using range analysis and analysis of variance. The KOH concentration had the largest effect on the average size of the KTN nanoparticles. The KTN particles with a designed grain size can be obtained by controlling the four effect factors.

  2. Impedance and modulus spectroscopy analysis of Mn0.5Zn0.5Fe2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Aireddy, H.; Bidayat, U.; Das, A. K.

    2013-02-01

    Nanocrystalline spinel ferrite of Mn0.5Zn0.5Fe2O4 was prepared by sol-gel method. Structural analysis using high resolution X-ray diffraction, scanning electron microscope, and high resolution transmission electron microscope, reveals the formation of single phase compound in cubic symmetry of spinel structure. The variation of impedance spectra with temperature indicates retention of typical negative temperature coefficient of resistivity, and the presence of temperature dependent electrical relaxation phenomena. Complex modulus spectra confirmed the presence of non-Debye type single relaxation process. The relaxation observed at low temperatures and low frequencies corresponds to grain boundary polarization.

  3. Ethylene production by ODHE in catalytically modified Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) membrane reactors.

    PubMed

    Lobera, M Pilar; Escolástico, Sonia; Garcia-Fayos, Julio; Serra, José M

    2012-08-01

    Process intensification by the integration of membranes and high-temperature reactors offers several advantages with regard to conventional process schemes, that is, energy saving, safe operation, reduced plant/unit size, and higher process performance, for example, higher productivity, catalytic activity, selectivity, or stability. We present the study of oxidative dehydrogenation of ethane at 850 °C on a catalytic membrane reactor based on a mixed ionic-electronic conducting membrane. The surface of the membrane made of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) has been activated by using different porous catalytic layers based on perovskites. The layer was deposited by screen printing, and the porosity and thickness was studied for the catalyst composition. The different catalyst formulations are based on partial substitution of A- and B-site atoms of doped strontium ferrite/cobaltites (A(0.6)Sr(0.4)Co(0.5)Fe(0.5)O(3-δ) and Ba(0.6)Sr(0.4)BO(3-δ)) and were synthesized by an ethylenediaminetetraacetic acid-citrate complexation route. The use of a disk-shaped membrane in the reactor enabled the direct contact of gaseous oxygen and hydrocarbons to be avoided, and thus, the ethylene content increased. High ethylene yields (up to ≈81 %) were obtained by using a catalytic coating based on Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ), which included macropores produced by the addition of graphite platelets into the screen-printing ink. The promising catalytic results obtained with this catalytically modified membrane reactor are attributed to the combination of 1) the high activity, as a result of the high temperature and oxygen species diffusing through the membrane; 2) the control of oxygen dosing and the low concentration of molecules in the gas phase; and 3) suitable fluid dynamics, which enables appropriate feed contact with the membrane and the rapid removal of products. PMID:22791570

  4. Nonlinear optical responses in two-dimensional transition metal dichalcogenide multilayer: WS2, WSe2, MoS2 and Mo 0.5 W0.5 S2.

    PubMed

    Bikorimana, S; Lama, P; Walser, A; Dorsinville, R; Anghel, S; Mitioglu, A; Micu, A; Kulyuk, L

    2016-09-01

    Synthetic two-dimensional transition metal dichalcogenides such as, tungsten disulphide (WS2), tungsten diselenide (WSe2), molybdenum disulphide (MoS2) as well as mixed molybdenum tungsten disulphide (Mo0.5W0.5S2) single crystals were grown by the chemical vapor transport method using halogens (bromine or chlorine) as transport agents. Multi- layer samples were cleaved from the single crystals, and their nonlinear optical (NLO) properties were obtained from both open aperture and closed aperture Z-scan measurements using a picosecond mode-locked Nd: YAG laser operating at a wavelength of 1064 nm, with pulse duration of 25 ps, and 20 Hz repetition rate. Both WS2 and MoS2 exhibited nonlinear saturable absorption (SA), whereas WSe2 and Mo0.5W0.5S2 showed nonlinear two-photon absorption (2PA). A large 2PA coefficient β as high as + 1.91x10-8 cm/W was obtained for the Mo0.5W0.5S2, and an index of refraction coefficient γ = -2.47x10-9 cm2/W was obtained for the WSe2 sample. PMID:27607672

  5. Li(V0.5Ti0.5)S2 as a 1 V lithium intercalation electrode

    NASA Astrophysics Data System (ADS)

    Clark, Steve J.; Wang, Da; Armstrong, A. Robert; Bruce, Peter G.

    2016-03-01

    Graphite, the dominant anode in rechargeable lithium batteries, operates at ~0.1 V versus Li+/Li and can result in lithium plating on the graphite surface, raising safety concerns. Titanates, for example, Li4Ti5O12, intercalate lithium at~1.6 V versus Li+/Li, avoiding problematic lithium plating at the expense of reduced cell voltage. There is interest in 1 V anodes, as this voltage is sufficiently high to avoid lithium plating while not significantly reducing cell potential. The sulfides, LiVS2 and LiTiS2, have been investigated as possible 1 V intercalation electrodes but suffer from capacity fading, large 1st cycle irreversible capacity or polarization. Here we report that the 50/50 solid solution, Li1+x(V0.5Ti0.5)S2, delivers a reversible capacity to store charge of 220 mAhg-1 (at 0.9 V), 99% of theoretical, at a rate of C/2, retaining 205 mAhg-1 at C-rate (92% of theoretical). Rate capability is excellent with 200 mAhg-1 at 3C. C-rate is discharge in 1 h. Polarization is low, 100 mV at C/2. To the best of our knowledge, the properties/performances of Li(V0.5Ti0.5)S2 exceed all previous 1 V electrodes.

  6. Superconductivity and abnormal pressure effect in Sr{}_{0.5}La{}_{0.5}FBiSe2 superconductor

    NASA Astrophysics Data System (ADS)

    Li, Lin; Xiang, Yongliang; Chen, Yihong; Jiao, Wenhe; Zhang, Chuhang; Zhang, Li; Dai, Jianhui; Li, Yuke

    2016-04-01

    Through the solid state reaction method, we synthesized a new BiSe2-based superconductor Sr{}0.5La{}0.5FBiSe2 with superconducting transition temperature T {}c ≈ \\quad 3.8 K. A strong diamagnetic signal below T c in susceptibility χ (T) is observed indicating the bulk nature of superconductivity. Different to most BiS2-based compounds where superconductivity develops from a semiconducting-like normal state, the present compound exhibits a metallic behavior down to T c . Under weak magnetic field or pressure, however, a remarkable crossover from metallic to insulating behaviors takes place around T min where the resistivity picks up a local minimum. With increasing pressure, T {}c decreases monotonously and T min shifts to high temperatures, while the absolute value of the normal state resistivity at low temperatures first decreases and then increases with pressure up to 2.5 GPa. These results imply that the electronic structure of Sr{}0.5La{}0.5FBiSe2 may be different to those in the other BiS2-based systems.

  7. Charge ordered ferromagnetic phase in La_0.5Ca_0.5MnO_3

    NASA Astrophysics Data System (ADS)

    Mathur, Neil

    2003-03-01

    Charge order and ferromagnetism should be mutually exclusive in the manganites, because ferromagnetism in these materials is normally promoted by delocalised electrons. Surprisingly, a phase that is both strongly charge ordered and fully ferromagnetic is observed [1] at 90 K in La_0.5Ca_0.5MnO_3, using Fresnel imaging, dark-field TEM and electron holography. This new phase coexists with the two low temperature phases that were already known to coexist in La_0.5Ca_0.5MnO_3. (One of these expected phases is ferromagnetic but not charge-ordered, the other is charge-ordered but not ferromagnetic.) Strain fields could be responsible for the novel microscopic texture presented here - perhaps creating conditions in which nearest neighbour hopping is sufficient to promote ferromagnetism. Similarly, strain fields are believed to cause sub-micron phase separation in the manganites. It therefore seems that the manganites can adapt to their environments over a wide range of length scales [2]. [1] http://xxx.lanl.gov/abs/cond-mat/0209436 [2] Neil Mathur and Peter Littlewood, Physics Today, early 2003.

  8. Octahedral distortion induced magnetic anomalies in LaMn0.5Co0.5O3 single crystals

    NASA Astrophysics Data System (ADS)

    Manna, Kaustuv; Bhadram, Venkata Srinu; Elizabeth, Suja; Narayana, Chandrabhas; Anil Kumar, P. S.

    2014-07-01

    Single crystals of LaMn0.5Co0.5O3 belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)-oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn0.5Co0.5O3 crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal.

  9. 0.5 gigapixel microscopy using a flatbed scanner.

    PubMed

    Zheng, Guoan; Ou, Xiaoze; Yang, Changhuei

    2013-12-01

    The capability to perform high-resolution, wide field-of-view (FOV) microscopy imaging is highly sought after in biomedical applications. In this paper, we report a wide FOV microscopy system that uses a closed-circuit-television (CCTV) lens for image relay and a flatbed scanner for data acquisition. We show that such an imaging system is capable of capturing a 10 mm × 7.5 mm FOV image with 0.78 µm resolution, resulting in more than 0.5 billion pixels across the entire image. The resolution and field curve of the proposed system were characterized by imaging a USAF resolution target and a hole-array target. To demonstrate its application, 0.5 gigapixel images of histology slides were acquired using this system. PMID:24466471

  10. 0.5% levobupivacaine versus 0.5% ropivacaine: Are they different in ultrasound-guided sciatic block?

    PubMed Central

    Pham Dang, Charles; Langlois, Cécile; Lambert, Chantal; Nguyen, Jean-Michel; Asehnoune, Karim; Lejus, Corinne

    2015-01-01

    Context and Aims: Little is known about onset and duration of sciatic block after 0.5% levobupivacaine (Levo) versus 0.5% ropivacaine (Ropi) for ultrasound-guided technique. We assessed these parameters in the ultrasound-guided block, to know for the practice. Setting and Design: A comparative randomized double-blind study was conducted in the University Hospital. Materials and Methods: Were included 35 adults of ASA I-II, scheduled for foot surgery, presenting clear imaging of their sciatic nerve at mid-thigh. A volume of 20 mL of either 0.5% Levo or 0.5% Ropi were injected around the sciatic nerve at mid-thigh using ultrasound guidance (out of the plane) followed by placement of a catheter to use, if necessary, for perioperative analgesia. A femoral single shot block was systematically performed to block the saphenous nerve. The onset times until complete foot block (primary outcome) and the sensory and motor block duration (secondary outcome) were assessed using Wilcoxon test. Values were expressed as medians (1st-3rd quartile). Results: Except for two delayed sciatic blocks in each group, the onset time otherwise was 35 min (20-60) in Ropi versus 40 min (30-60) in Levo, P = 0.5. Sensory block lasted longer in Levo, 17 h (14-27) compared with 15 h (10-17) in Ropi, P = 0.04. No significant between-group difference was found with motor block durations, 15 h (12-18) in Levo and 15 h (12-16) in Ropi, P = 0.3. Conclusion: No difference of onset times was found in ultrasound-guided sciatic block whether using Levo or Ropi. Levo induced a longer-lasting sensory block. PMID:25558190

  11. Enhanced tunable characteristics of the Na0.5Bi0.5TiO3-NaTaO3 relaxor-type system.

    PubMed

    Spreitzer, Matjaz; König, Jakob; Jancar, Bostjan; Suvorov, Danilo

    2007-12-01

    We have investigated the voltage-tunable characteristics of the Na(0.5)Bi(0.5)TiO(3)-NaTaO(3) homogeneity region, for which samples were prepared using a conventional solid-state reaction. The highest value of the relative tunability (n(r)) was obtained for the sample with 5 mol% of NaTaO(3), i.e., 47% at 1 MHz and a 70 kV/cm dc bias field. This sample also showed the highest value of the dielectric losses (tan delta) and temperature coefficient of the dielectric constant (tau(epsilon)), i.e., 0.05 and 4478 ppm/K, respectively. As the concentration of NaTaO(3) increased up to 90 mol% n(r), tan delta, and tau(epsilon) gradually decreased toward 22%, 0.0002 and -899 ppm/K, respectively. The dielectric constant of the samples varied in a similar manner between 662 and 130. At microwave frequencies, the dielectric losses of the samples substantially increased due to their relaxor-type nature. The lowest value was obtained for the samples with 90 mol% of NaTaO(3), i.e., 0.002. The tunable characteristics of the samples are related to the ferroelectric and dielectric properties, and it appears that the dielectric tunability of the Na(0.5)Bi(0.5)TiO(3)-NaTaO(3) system originates from its relaxor-type behavior. PMID:18276566

  12. Monoclinic crystal structure of polycrystalline Na0.5Bi0.5TiO3

    NASA Astrophysics Data System (ADS)

    Aksel, Elena; Forrester, Jennifer S.; Jones, Jacob L.; Thomas, Pam A.; Page, Katharine; Suchomel, Matthew R.

    2011-04-01

    Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. Na0.5Bi0.5TiO3 (NBT), one of the widely studied compositions, has been assumed thus far to exhibit the rhombohedral space group R3c at room temperature. High-resolution powder x-ray diffraction patterns, however, reveal peak splitting in the room temperature phase that evidence the true structure as monoclinic with space group Cc. This peak splitting and Cc space group is only revealed in sintered powders; calcined powders are equally fit to an R3c model because microstructural contributions to peak broadening obscure the peak splitting.

  13. Ferroelectricity and ferroelectric resistive switching in sputtered Hf0.5Zr0.5O2 thin films

    NASA Astrophysics Data System (ADS)

    Fan, Zhen; Xiao, Juanxiu; Wang, Jingxian; Zhang, Lei; Deng, Jinyu; Liu, Ziyan; Dong, Zhili; Wang, John; Chen, Jingsheng

    2016-06-01

    Ferroelectric properties and ferroelectric resistive switching (FE-RS) of sputtered Hf0.5Zr0.5O2 (HZO) thin films were investigated. The HZO films with the orthorhombic phase were obtained without capping or post-deposition annealing. Ferroelectricity was demonstrated by polarization-voltage (P-V) hysteresis loops measured in a positive-up negative-down manner and piezoresponse force microscopy. However, defects such as oxygen vacancies caused the films to become leaky. The observed ferroelectricity and semiconducting characteristics led to the FE-RS effect. The FE-RS effect may be explained by a polarization modulated trap-assisted tunneling model. Our study not only provides a facile route to develop ferroelectric HfO2-based thin films but also explores their potential applications in FE-RS memories.

  14. Phase separation and direct magnetocaloric effect in La0.5Ca0.5MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Amirzadeh, P.; Ahmadvand, H.; Kameli, P.; Aslibeiki, B.; Salamati, H.; Gamzatov, A. G.; Aliev, A. M.; Kamilov, I. K.

    2013-03-01

    A series of phase separated La0.5Ca0.5MnO3 manganite samples with different grain sizes were studied by ac susceptibility, direct magnetocaloric effect (ΔT), and heat capacity measurements. The ac susceptibility shows that fractions of ferromagnetic and antiferromagnetic phases and consequently the phase separated state can be controlled by means of sintering temperature. Lower sintering temperature leads to a ferromagnetic state, while higher sintering temperature increases antiferromagnetic phase fraction, resulting in a phase separated state. In the phase separated samples, ΔT shows a conventional positive peak near TC and an anomalous positive peak at lower temperature near TN. The anomalous positive peak appears at higher magnetic field and is accompanied with thermal hysteresis. It is suggested that the anomalous magnetocaloric behaviors result from phase separation and first order magnetostructural phase transition. This study shows that direct magnetocaloric effect is a useful technique for the study of manganites.

  15. Diode pumped Nd:Lu0.5Y0.5VO4-LBO red laser at 671 nm

    NASA Astrophysics Data System (ADS)

    Li, Y. L.; Liu, J. Y.; Zhang, Y. C.

    2012-03-01

    We report a efficient compact red laser at 671 nm generation by intracavity frequency doubling of a continuous wave laser operation of a diode pumped Nd:Lu0.5Y0.5VO4 laser on the 4 F 3/2-4 I 13/2 transition at 1342 nm. An LBO crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an absorbed pump power of 17.8 W, as high as 2.25 W of continuous wave output power at 671 nm is achieved with 10-mm-long LBO. The optical-to-optical conversion efficiency is up to 12.6%, and the fluctuation of the red output power was better than 3.6% in the given 30 min.

  16. Complex domain structure in polycrystalline Pb(Sc0.5Nb0.5)O3

    NASA Astrophysics Data System (ADS)

    Ursic, Hana; Drnovsek, Silvo; Malic, Barbara

    2016-03-01

    This letter provides evidence of ferroelectric domains existing in polycrystalline B-site cation disordered Pb(Sc0.5Nb0.5)O3. A complex domain structure with variations in characteristic length and morphology is observed below the relaxor-ferroelectric phase transition at ~98 °C. At room temperature the micrometer-sized wedge-like, lamellar-like and irregularly shaped domains are found. By approaching the relaxor-ferroelectric phase transition temperature, the domain structure changes; the fraction of micrometer-sized domains is progressively decreasing. Approximately 100 nm large domains, which form mottled patterns, are observed, and associated with polar nano domains as described in other relaxor materials.

  17. Unraveling the magnetic properties of BiFe0.5Cr0.5O3 thin films

    NASA Astrophysics Data System (ADS)

    Vinai, G.; Khare, A.; Rana, D. S.; Di Gennaro, E.; Gobaut, B.; Moroni, R.; Petrov, A. Yu.; Scotti di Uccio, U.; Rossi, G.; Miletto Granozio, F.; Panaccione, G.; Torelli, P.

    2015-11-01

    We investigate the structural, chemical, and magnetic properties on BiFe0.5Cr0.5O3 (BFCO) thin films grown on (001) (110) and (111) oriented SrTiO3 (STO) substrates by x-ray magnetic circular dichroism and x-ray diffraction. We show how highly pure BFCO films, differently from the theoretically expected ferrimagnetic behavior, present a very weak dichroic signal at Cr and Fe edges, with both moments aligned with the external field. Chemically sensitive hysteresis loops show no hysteretic behavior and no saturation up to 6.8 T. The linear responses are induced by the tilting of the Cr and Fe moments along the applied magnetic field.

  18. Synthesis of functionalized Co0.5Zn0.5Fe2O4 nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Bohara, R. A.; Yadav, H. M.; Thorat, N. D.; Mali, S. S.; Hong, C. K.; Nanaware, S. G.; Pawar, S. H.

    2015-03-01

    In this paper, we report a simple one step method for the synthesis of uniform, water dispersible amine functionalized Co0.5Zn0.5Fe2O4 nanoparticles (AF-CZF) of size about 6 nm. The synthesis process was accomplished by refluxing Fe(acac)3, Co(acac)2 and Zn(acac)2 in diethylene glycol and ethanolamine. The magnetic nanoparticles were characterized by XRD, TGDTA, FTIR, SEM and TEM techniques. Their magnetic properties were also studied by using SQUID. The synthesized particles show superparamagnetism at room temperature. AF-CZF nanoparticles exhibit good cell viability, which is above 95% at a concentration of 80 μg mL-1 on MCF7 cell line. The AF-CZF can be a new versatile platform for many interesting biomedical applications.

  19. Zr and Sn substituted (Na0.5Bi0.5)TiO3 -based solid solutions

    NASA Astrophysics Data System (ADS)

    Ishchuk, V. M.; Gusakova, L. G.; Kisel, N. G.; Kuzenko, D. V.; Spiridonov, N. A.; Sobolev, V. L.

    2016-02-01

    The paper attempts to investigate the phase formation of a Zr- and Sn-substituted [(Na0.5Bi0.5)0.80Ba0.20](Ti1-yBy)O3 system during its solid state synthesis. The synthesis was found to be a multi-step process associated with the formation of a number of intermediate phases which however depended on the compositions and sintering temperatures. Single phase solid solutions were obtained when the sintering temperature was increased to 1000 °C-1100 °C. Increase in the concentration of substituting ions, on the one hand, tends to linearly increase the crystal cell size whereas the tolerance factor, on the other hand, gets reduced bolstering the stability of anti-ferroelectric phase as compared to that of ferroelectric phase’.

  20. Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3

    NASA Astrophysics Data System (ADS)

    Sharma, Mohit K.; Singh, Karan; Mukherjee, K.

    2016-09-01

    We report a detailed investigation of magnetization, magnetocaloric effect and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to perovskite family. Our results reveal that the compound is in canted magnetic state (CMS) where ferromagnetic correlations are present in an antiferromagnetic state. Magnetic entropy change of this compound follows a power law (∆SM∼Hm) dependence of magnetic field. In this compound, inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional magnetocaloric effect (CMCE) above it. The exponent 'm' is found to be independent of temperature and field only in the IMCE region. Investigation of temperature and magnetic field dependence studies of exchange bias, reveal a competition between effective Zeeman energy of the ferromagnetic regions and anisotropic exchange energy at the interface between ferromagnetic and antiferromagnetic regions. Variation of exchange bias due to temperature and field cycling is also investigated.

  1. Magnetocaloric and magnetic properties of SmFe0.5Mn0.5O3 complex perovskite

    NASA Astrophysics Data System (ADS)

    Silva-Santana, M. C.; daSilva, C. A.; Barrozo, P.; Plaza, E. J. R.; de los Santos Valladares, L.; Moreno, N. O.

    2016-03-01

    In this paper, we have investigated the physical properties of SmFe0.5Mn0.5O3 complex perovskite samples, synthesized by means of combustion reaction method. X-ray powder diffraction indicates the formation of single phase perovskite with orthorhombic structure. Low magnetic field measurements show remarkable transition at 234 K related to spin reorientation. The magnetocaloric effect shows two peaks related to magnetic behavior changes, at 18 K and at 234 K. The transition about 234 K presents inverse magnetocaloric effect. The entropy variation from magnetocaloric effect shows power law as function of applied magnetic field with maximum entropy change 5.6 J/kg K with field variation of 70 kOe. Critical exponents extracted from ΔS vs. H presents a remarkable sharp peak near antiferromagnetic to weak ferromagnetic transition temperature.

  2. Ternary monodispersed Mn0.5Zn0.5Fe2O4 ferrite nanoparticles: preparation and magnetic characterization

    NASA Astrophysics Data System (ADS)

    Parekh, Kinnari; Upadhyay, Ramesh V.; Belova, Lyubov; Rao, K. V.

    2006-12-01

    A ternary system of Mn0.5Zn0.5Fe2O4 has been synthesized for the first time using thermal decomposition of metal acetylacetonate in the presence of a high temperature boiling point solvent and fatty acids. Unlike the results of synthesis of this material by other techniques, we obtain nearly monodispersed nanoparticles, rendering them ideal for applications like in hyperthermia. The crystal structure and morphology of the particles obtained using x-ray diffraction (XRD) and transmission electron microscopy (TEM) are those of a single phase spinel structure with no other impurity phases. The particles are of 7 nm average diameter, with a very narrow (<10%) size distribution. The oleic acid surfactant on the particles shows a 28% weight loss in thermo-gravimetric analyses (TGAs), which corresponds to a monolayer thickness of the coating. Magnetic measurements show the particles to be superparamagnetic with a characteristic blocking temperature of around 50 K.

  3. Improvement of cycling performance in Ti substituted 0.5Li2MnO3-0.5LiNi0.5Mn0.5O2 through suppressing metal dissolution

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shinji; Noguchi, Hideyuki; Zhao, Wenwen

    2015-03-01

    Ti substituted 0.5Li2MnO3-0.5LiNi0.5Mn0.5O2 cathode material with the composition of Li1.5Ni0.25Mn0.75-xTixO2.5 has been synthesized by spray pyrolysis method. A great variety of characterization methods have been applied to study the influence of Ti substitution for Mn on the structural, morphological and electrochemical performances of Li1.5Ni0.25Mn0.75-xTixO2.5. X-ray diffraction (XRD) results of Li1.5Ni0.25Mn0.75-xTixO2.5 show that they exhibit similar XRD patterns as those of lithium-excess manganese metal oxide based cathode materials. It is confirmed from energy dispersive x-ray spectroscopy (EDX) data that Ti was homogenously substituted for Mn and well distributed in the host structure. X-ray absorption near edge structure (XANES) spectra analysis reveals that oxidation state of Mn in Li1.5Ni0.25Mn0.75-xTixO2.5 remains +4 while that of Ni changes from +2 to +4 during the initial activation process. Further investigation of the local structure of transition metal (TM) ions indicates that Ti has same coordination environment as that of Mn. Drastic capacity fade occurred in full cells with Li1.5Ni0.25Mn0.75O2.5 cathode and graphite anode, while full cell with Ti substituted cathode shows high capacity retention after 100 cycles. Further examination of the amount of dissolved transition metal (TM) ions after long cycling test enable us to demonstrate that substitution of Mn with Ti in Li1.5Ni0.25Mn0.75O2.5 has a significant impact on suppressing the TM ions dissolution and its deposition on both separator and anode thus leads to improved cycleability.

  4. Investigation of Al y Ga1‑ y N/Al0.5Ga0.5N quantum dot properties for the design of ultraviolet emitters

    NASA Astrophysics Data System (ADS)

    Brault, Julien; Matta, Samuel; Ngo, Thi-Huong; Korytov, Maxim; Rosales, Daniel; Damilano, Benjamin; Leroux, Mathieu; Vennéguès, Philippe; Khalfioui, Mohamed Al; Courville, Aimeric; Tottereau, Olivier; Massies, Jean; Gil, Bernard

    2016-05-01

    Self-assembled Al y Ga1‑ y N quantum dots (QDs), with y = 0 and 0.1, have been grown by molecular beam epitaxy on Al0.5Ga0.5N(0001) oriented layers using sapphire substrates. The QD formation has been followed in situ by reflection high energy electron diffraction (RHEED). A two- to three-dimensional (2D–3D) transition of the layer morphology is observed, characterized by a change of the RHEED pattern from streaky lines to Bragg spots. High QD densities, from 1010 up to near 1012 cm‑2, have been obtained. By decreasing the GaN QD size and incorporating Al inside the QDs, a strong variation in the photoluminescence (PL) emission has been observed, enabling to cover a large spectral range from near UV (3 eV) to UV-B (3.95 eV). By combining temperature-dependent and time-resolved PL measurements, the internal quantum efficiency of the QDs has been determined at both low and high temperatures as a function of the PL energy.

  5. Ag Doping Effects on Y0.5Gd0.5Ba2Cu3O7-δ multilayers derived by low-fluorine metalorganic solution deposition

    NASA Astrophysics Data System (ADS)

    Sun, M. J.; Yang, W. T.; Liu, Z. Y.; Bai, C. Y.; Guo, Y. Q.; Lu, Y. M.; Lu, Q.; Cai, C. B.

    2015-09-01

    Various artificial multilayers consisting of Y0.5Gd0.5Ba2Cu3O7-δ (YGdBCO) superconducting films were built up on an oxide buffered Hastelloy substrate using the low-fluorine metallorganic deposition method (MOD). Microscopic and superconducting performances are studied on composite YGdBCO multilayer films with and without alternate ultrathin layers of Ag, which comparatively demonstrates the Ag doping effects in such architectures. X-ray diffraction and scanning electron microscopy imply that the growth thermodynamic parameters of the YGdBCO are modified, resulting in a better c-axis orientation and a higher in-plane texture, as well as a superior surface, and finally give rise to great improvement of superconducting performance. To understand the above Ag doping effects further, the critical Gibbs free energy ΔG*(r) on nucleation of MOD-YGdBCO films on the biaxially textured buffer layers is analyzed with respect to the additions of Ag, which shows the competition between a-axis and c-axis growths subject to supersaturation. As a consequence, Ag additions may reduce the supersaturation at the growth interfaces, and hence give rise to a wider window of c-axis nucleation.

  6. Switching of morphotropic phase boundary and large strain response in lead-free ternary (Bi0.5Na0.5)TiO3-(K0.5Bi0.5)TiO3-(K0.5Na0.5)NbO3 system

    NASA Astrophysics Data System (ADS)

    Hao, Jigong; Shen, Bo; Zhai, Jiwei; Liu, Chunze; Li, Xiaolong; Gao, Xingyu

    2013-03-01

    In this work, we report the phase diagram of lead-free ternary (1 - y)[(1 - x)(Bi0.5Na0.5)TiO3-x(Bi0.5K0.5)TiO3]-y(K0.5Na0.5)NbO3 (BNT-BKT-KNN) system and study the switching characteristics of the morphotropic phase boundary (MPB). The addition of KNN intrinsically changes the structural nature of the system with the shift of MPB from MPB(I) between ferroelectric rhombohedral and ferroelectric tetragonal phases to MPB(II) between ferroelectric rhombohedral and relaxor pseudocubic phases. As the MPB(I) switches to MPB(II), large piezoelectric response with d33 ˜ 150pC/N that obtained for BNT-0.20BKT near MPB(I) almost disappears. Instead, a significant jump of electric-filed-induced strain S up to 0.32%-0.46% (Smax/Emax = 400-575 pm/V) is achieved near MPB(II) due to the shift of the ferroelectric-relaxor transition temperature TF-R down to room temperature. In this study, giant strain ˜0.46% occurs in a very narrow region in the BNT-BKT-KNN system with x = 0.20, y = 0.01, which lies on an underlying tricritical triple point of a rhombohedral (R), tetragonal (T), and pseudocubic (Pc) phases. In-situ high-energy X-ray scattering experiments with external electric field reveal an initial electric-field-induced distortion from the Pc structure for the MPB(II) compositions, while those with single R phase shows no such distortion, which suggests that the large strain achieved near the MPB(II) is likely to be induced by the electric-field-induced structure distortion due to its relative instability structure. We believe that the discovery of a compositional line in the pseudo-ternary system, where the strain response is consistently derivable, should be useful for designing high-performance piezoelectric materials in other BNT-based systems by searching MPBs.

  7. Influence of electric field on local phase transformations in relaxor ferroelectrics PbSc0.5Ta0.5O3 and Pb0.78Ba0.22Sc0.5Ta0.5O3

    NASA Astrophysics Data System (ADS)

    Maier, B. J.; Steilmann, T.; Gospodinov, M.; Bismayer, U.; Mihailova, B.

    2012-12-01

    In situ temperature-dependent Raman-scattering experiments under an external dc electric field E have been performed on PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PST-Ba) in order to give further insights into the atomistic mechanism of polar coupling in perovskite-type (ABO3) relaxor ferroelectrics near the intermediate characteristic temperature T⋆. The polarized Raman spectra collected under an electric field E applied along the cubic [100], [110], or [111] crystallographic direction were analyzed in terms of hard-mode spectroscopy. The T⋆(E) dependence was derived from the behavior of the phonon mode near 230 cm-1 localized in off-centered B-site cations. In the case of stoichiometric PST, the increase of T⋆ with E is much stronger when the field is applied along [111] than when E is along [100] or [110]. This indicates that the actual polar B-cation shifts are along the cubic body diagonals, implying a rhombohedral structure of the polar nanoregions. The T⋆(E)-dependence reveals that the local structural distortions associated with locally coupled polar displacements of B-site cations reach saturation near 0.5 kV/cm. When Pb2+ is partially replaced by Ba2+, the strong increase of T⋆ with E occurs if the electric field is applied along the [110] direction. This indicates that the substitution disorder on the A-site lowers the symmetry of the polar nanoregions to orthorhombic or monoclinic. The T⋆(E) dependence determined from the B-cation localized mode shows saturation near 2.0 kV/cm, indicating that the zero-field structural state of PST-Ba exhibits less coupled polar shifts of B-site cations as compared to that of PST. According to the E-dependence of the Raman scattering near 55 cm-1, for both compounds the overall response of the Pb system to the external electric field in the vicinity of T⋆(E) resembles antiferroelectric behavior, which along with the fact that the coupling between the B-site cations is ferroelectric, suggests that

  8. Properties of (Bi0.5Na0.5)TiO3-BaTiO3-(Bi0.5Na0.5)(Mn1/3Nb2/3)O3 Lead-Free Piezoelectric Ceramics and Its Application to Ultrasonic Cleaner

    NASA Astrophysics Data System (ADS)

    Tou, Tonshaku; Hamaguti, Yuki; Maida, Yuichi; Yamamori, Haruo; Takahashi, Kazutoshi; Terashima, Yoshimitsu

    2009-07-01

    The lead-free piezoelectric ceramics 0.82(Bi0.5Na0.5)TiO3-0.15BaTiO3-0.03(Bi0.5Na0.5)(Mn1/3Nb2/3)O3 (abbreviated as BNT-BT-BNMN) was prepared by a conventional process of ceramic engineering. The X-ray diffractometer (XRD) analysis showed that all compositions could form a single perovskite phase. The ceramics showed excellent piezoelectric properties with a coupling factor kt=41%, a mechanical quality factor Qm=500, a piezoelectric constant d33=110 pC/N, a relative permittivity ɛ33T/ɛ0=520, a dissipation factor tan δ=0.66%, a Curie point Tc=260 °C, and a density ρ=5.5 g/cm3. The physical properties of the ceramics were superior to those of hard Pb(Zr,Ti)O3 (PZT). The high-power characteristics of the ceramics were superior to those of hard PZT. A cylinder sample of lead-free ceramics was used to fabricate a bolt-clamped Langevin transducer (BLT) for application in the ultrasonic cleaner. The vibration velocity of BLT using the ceramics was higher than that of hard PZT under the same input power. The cleaning effect of an ultrasonic cleaner using the BLTs was very high and sufficiently good for commercial application.

  9. Luminous Red Galaxies at Z=0.4-0.5

    NASA Technical Reports Server (NTRS)

    Heap, Sally; Lindler, Don

    2009-01-01

    We report on a study of approx.20,000 luminous red galaxies (LRG's) at z=0.4-0.5 observed by the Sloan Digital Sky Survey. In order to differentiate among them, we measured restframe magnitudes, u (3000-3500 A), b (4200-4800 A), and y (5700-6300 A) from the spectra themselves. The galaxies show a significant range in restframe colors and absolute magnitudes. We binned the spectra according to the restframe u-b color and y-band absolute magnitude in order to increase the S/N. We used 3 approaches to estimate the ages and metal content of these binned spectra: via their spectral energy distributions, from spectral-line indices, and by full spectral fitting. The three methods usually produce discordant results

  10. Possible radio emission from Uranus at 0.5 MHz

    NASA Technical Reports Server (NTRS)

    Brown, L. W.

    1975-01-01

    Radio emission from the direction of Uranus was detected in data from the radio astronomy experiment on the IMP-6 spacecraft. Previously, emission from the direction of Jupiter and Saturn was observed by the IMP-6 at a number of frequencies near 1 MHz during the period April 1971 to October 1972. These radio bursts were identified in the IMP-6 data through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. This technique was applied to the direction of the planet Uranus with possible positive results. Over the approximately 500 days of data, three to six bursts with unique spectral characteristics were found. Identification with Uranus is confused by the likely presence of low level terrestrial and solar emission. The observed events persisted less than three minutes and are strongest in intensity near 0.5 MHz.

  11. The role of Pt underlayer on the magnetization dynamics of perpendicular magnetic anisotropy Pt/Co2FeAl0.5Si0.5/MgO

    NASA Astrophysics Data System (ADS)

    Besbas, Jean; Loong, Li Ming; Wu, Yang; Yang, Hyunsoo

    2016-06-01

    We investigate the role of Pt on the magnetization dynamics of Pt/Co2FeAl0.5Si0.5/MgO with perpendicular magnetic anisotropy using the time resolved magneto-optic Kerr effect. Pt/Co2FeAl0.5Si0.5/MgO shows ultrafast magnetization dynamics comparable to 3d ferromagnets and can be fully demagnetized. The demagnetization time τd ˜ 0.27 ps and magnetic heat capacity are independent of the Pt underlayer, whereas the value of the electron-phonon coupling time τe ˜ 0.77 ps depends on the presence of the Pt layer. We further measure the effective damping αeff ˜ 1 that does not scale as the inverse demagnetization time (1/τd), but is strongly affected by the Pt layer.

  12. Colossal elastoresistance, electroresistance and magnetoresistance in Pr0.5Sr0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Guo, Xuexiang; Gao, J.

    2016-05-01

    Pr0.5Sr0.5MnO3 thin films on substrates of (001)-oriented LaAlO3 were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of ~1.3% brings a great resistivity change of ~98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I1 μA)-ρ(I1000 μA)]/ρ(I1 μA) reaches ~70% at T=25 K, much higher than ER~7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence.

  13. Dielectric dynamics of the polycrystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Pečnik, Tanja; Eršte, Andreja; Matavž, Aleksander; Bobnar, Vid; Ivanov, Maksim; Banys, Juras; Xiang, Feng; Wang, Hong; Malič, Barbara; Glinšek, Sebastjan

    2016-05-01

    Polycrystalline Ba0.5Sr0.5TiO3 films, with thicknesses between 90 and 600 nm, were prepared on alumina substrates at 900 °C by chemical solution deposition (CSD) and a dielectric spectroscopy investigation of the in-plane properties was performed. The 5-kHz permittivity ε‧ shows a non-monotonic thickness dependence, reaching 1230 at room temperature for the 310-nm-thick film, whose grain size is ∼75 nm. Its 15-GHz-value and losses are 1105 and 0.05, respectively. The temperature of the permittivity maximum T max at 5 kHz decreases with increasing thickness from 277 to 250 K for the 170- and 600-nm-thick films, respectively, which has been linked to the residual biaxial stress. A hysteresis is observed in the permittivity ε‧-electric field E DC characteristics in all the films up to ∼50 K above T max . Frequency dispersion in which permittivity decreases with increasing frequency is present below T max in films thicker than 90 nm. The high permittivity values of the thinnest films, which are among the highest reported in the (Ba,Sr)TiO3 films with grain sizes below 75 nm, are a direct proof of the optimized CSD processing conditions.

  14. Structural characteristics of thermally evaporated Cu0.5Ag0.5InSe2 thin films

    NASA Astrophysics Data System (ADS)

    Gullu, H. H.; Parlak, M.

    2016-05-01

    In this work, Cu0.5Ag0.5InSe2 (CAIS) thin film samples were prepared by thermal evaporation of Cu, Ag, InSe and Se evaporants sequentially on glass substrates. Following the deposition, annealing processes were applied at different temperatures. The as-grown and annealed CAIS samples were nearly stoichiometric in the detection limit of the compositional measurement. The x-ray diffraction (XRD) measurements revealed that they were in polycrystalline structure with a preferred orientation along the (112) direction. Moreoever, the crystallinity of the films improved with increasing annealing temperature. According to the results of Raman measurements, the highest Raman intensity was found in the A1 mode which is directly proportional to the crystallinity of the samples. The surface properties of the thin films were analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). These results showed that there was a Se agglomeration on the deposited film surfaces and with annealing processes segregation effects were observed on the surface of the annealed samples. X-ray photoelectron spectroscopy (XPS) measurements were carried out to get information about surface and near-surface properties of the films. The results from the surface and depth surface analyses of the films were found to be in agreement with the energy dispersive spectroscopy (EDS) analysis.

  15. Hydrothermal synthesis, evolution, and electrochemical performance of LiMn0.5Fe0.5PO4 nanostructures.

    PubMed

    Xiang, Wei; Zhong, Yan-Jun; Ji, Jun-Yi; Tang, Yan; Shen, HuiHui; Guo, Xiao-Dong; Zhong, Ben-He; Dou, Shi Xue; Zhang, Zhi-Ye

    2015-07-28

    LiMn0.5Fe0.5PO4 (LMFP) materials are synthesized by the hydrothermal approach in an organic-free and surfactant-free aqueous solution. The phase and morphological evolution of the material intermediates at different reaction temperatures and times are characterized by XRD, SEM and TEM, respectively. The results show that during temperature increase, the solubility product (Ksp) of the precursors (Li3PO4, Fe3(PO4)2 and (Mn,Fe)3(PO4)2) is the decisive parameter for the precipitation processes. Once the temperature locates at the range of 100-110 °C, the unstable precursors dissolve quickly and then LMFP nuclei are formed, followed by a dissolution-reprecipitation process. As the reaction progresses, the primary particles self-aggregate to form rod or plate particles to reduce the overall surface energy through oriented attachment (OA) and the Ostwald ripening (OR) mechanism. Moreover, the resultant concentration of the precursor significantly affects the crystal size of LMFP by altering the supersaturation degree of solution at the nucleation stage. The carbon coated LMFP nanostructure synthesized at 0.6 mol L(-1) (resultant concentration of PO4(3-)) delivers discharge capacities of 155, 100 and 81 mA h g(-1) at 0.1, 5 and 20 C rate, respectively. The understanding of nanostructural evolution and its influence on the electrochemical performance will pave a way for a high-performance LMFP cathode. PMID:26119980

  16. Compositional inhomogeneityand segregation in (K0.5Na0.5)NbO3 ceramics

    DOE PAGESBeta

    Chen, Kepi; Tang, Jing; Chen, Yan

    2016-03-11

    The effects of the calcination temperature of (K0.5Na0.5)NbO3 (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated in this report. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700 °C and 750 °C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900 °C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on the densification, the abnormalmore » grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800 °C, with piezoelectric constant d33=128.3 pC/N, planar electromechanical coupling coefficient kp=32.2%, mechanical quality factor Qm=88, and dielectric loss tan δ=2.1%.« less

  17. Improved magnetic properties of microwave processed Mn0.5Zn0.5Fe2O4 particles

    NASA Astrophysics Data System (ADS)

    Suneetha, T.; Kashyap, Subhash C.; Gupta, Hem C.

    2013-02-01

    Mn0.5Zn0.5Fe2O4 nanoparticles, first prepared by citrate precursor route, have been processed by two different methods to obtain polycrystalline samples. In one case the pressed pellets are processed in microwave H-field at 500 °C for different duration: 1, 3 and 5 min, and in another case the pellets are conventionally sintered at 500 °C for 180 min. The powder x-ray diffraction patterns confirmed the single cubic phase in the all samples. The scanning electron micrographs revealed the grain growth during microwave processing, with the particle size increasing to 1μm for the sample heated at 500 °C for 5 min, whereas the sintered samples had a particle size of ˜20 nm. A maximum saturation magnetization of 56 emu/g at room temperature was estimated by vibration sample magnetometer for this sample; where as conventional sintered sample has 24 emu/g. With microwave processing we can obtain microcrystalline samples with improved magnetization in a short span of 5 min.

  18. Low temperature dielectric and impedance studies on magnetoelectric Pb(Fe0.5Nb0.5)O3 ceramic

    NASA Astrophysics Data System (ADS)

    Matteppanavar, Shidaling; Shivaraja, I.; Rayaprol, Sudhindra; Angadi, Basavaraj

    2016-05-01

    The structural, microstructural, low temperature dielectric and impedance properties of Pb(Fe0.5Nb0.5)O3 (PFN) ceramic prepared by single step solid-state reaction method have been investigated. Processing parameters such as calcination, sintering temperature and sintering durations were optimized to get better dielectric properties. It was found that the above ceramics sintered at 1050 °C for 4 hr exhibited single phase, maximum density and uniform microstructure. X-ray diffraction (XRD) and neutron diffraction (ND) reveals that the system exhibit single phase without any kind of secondary phases at room temperature (RT) with monoclinic crystal structure (Cm). Surface morphology of the compounds was studied by Scanning electron microscope (SEM). Impedance spectroscopy is used to study the electrical behaviour of PFN in the frequency range from 100Hz to 1MHz and in the temperature range from 120 to 293 K. The frequency-dependent electrical data are analyzed by impedance formalisms. The complex impedance shows the relaxation (conduction) mechanism in the sample.

  19. Conduction mechanism in Eu0.5Sr0.5Mn0.9Cr0.1O3 perovskite

    NASA Astrophysics Data System (ADS)

    Modi, Anchit; Bhat, Masroor Ahmad; Pandey, Devendra K.; Gaur, N. K.

    2016-05-01

    A systematic study of polycrystalline sample with composition Eu0.5Sr0.5Mn0.9Cr0.1O3 has been undertaken and synthesized by conventional solid state reaction techniques. The room temperature XRD study reveals the single phase formation of the reported compound with orthorhombic structure having Pbnm space group. The temperature dependent resistivity study indicates the highly resistive nature of the compound especially in the low temperature region exhibits a semiconductor behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the temperature scale T* ˜ 9.05×106 K and finally the density of state at Fermi level N(EF) is calculated to be ˜ 61.63 × 1018 eV-1 cm-3.

  20. Single phase synthesis and room temperature neutron diffraction studies on multiferroic PbFe{sub 0.5}Nb{sub 0.5}O{sub 3}

    SciTech Connect

    Matteppanavar, Shidaling; Angadi, Basavaraj; Rayaprol, Sudhindra

    2013-02-05

    The lead-iron-niobate, (PbFe{sub 0.5}Nb{sub 0.5}O{sub 3} or PFN) was synthesized by low temperature sintering Single Step / Solid State Reaction Method. The 700 Degree-Sign C/2 hrs. calcined powder was sintered at 1050 Degree-Sign C/1 hr. The sintered pellets were characterized through X-Ray Diffraction and Neutron Diffraction at room temperature. It is found from the XRD pattern that the materials is in single phase with no traces of pyrochlore phase. It was also confirmed from the neutron diffraction pattern, the structure of PFN to be monoclinic, space group Cm. Structural studies has been carried out by refining the obtained neutron diffraction data by Rietveld refinement method using Fullprof program. The neutron diffraction pattern at 300 K (room temperature) was selected to refine the structure. The lattice parameters obtained are; a = 5.6709 A, b = 5.6732 A, c = 4.0136 A, and {alpha}= 90, {beta}= 89.881, {gamma}= 90. The P-E measurements showed hysteretic behavior with high remnant polarization.

  1. A high stability Ni-La0.5Ce0.5O2-δ asymmetrical metal-ceramic membrane for hydrogen separation and generation

    NASA Astrophysics Data System (ADS)

    Zhu, Zhiwen; Sun, Wenping; Wang, Zhongtao; Cao, Jiafeng; Dong, Yingchao; Liu, Wei

    2015-05-01

    In this work, hydrogen permeation properties of Ni-La0.5Ce0.5O2-δ (LDC) asymmetrical cermet membrane are investigated, including hydrogen fluxes (JH2) under different hydrogen partial pressures, the influence of water vapor on JH2 and the long-term stability of the membrane operating under the containing-CO2 atmosphere. Ni-LDC asymmetrical membrane shows the best hydrogen permeability among LDC-based hydrogen separation membranes, inferior to Ni-BaZr0.1Ce0.7Y0.2O3-δ asymmetrical membrane. The water vapor in feed gas is beneficial to hydrogen transport process, which promote an increase of JH2 from 5.64 × 10-8 to 6.83 × 10-8 mol cm-2 s-1 at 900 °C. Stability testing of hydrogen permeation suggests that Ni-LDC membrane remains stable against CO2. A dual function of combining hydrogen separation and generation can be realized by humidifying the sweep gas and enhance the hydrogen output by 1.0-1.5 times. Ni-LDC membrane exhibits desirable performance and durability in dual-function mode. Morphologies and phase structures of the membrane after tests are also characterized by SEM and XRD.

  2. Effect of sintering temperature on composition, microstructure and electrical properties of K0.5Na0.5NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Singh, Rajan; Kulkarni, A. R.; Harendranath, C. S.

    2014-02-01

    Lead free potassium sodium niobate (K0.5Na0.5NbO3) ceramic powders were synthesized by colloidal coating method. The calcined powders (800 °C) were sintered conventionally at three different temperatures (1050 °C, 1100 °C and 1150 °C) and the effect of sintering temperature on density, microstructure, composition and electrical properties was investigated. All the samples showed a single phase perovskite structure with orthorhombic symmetry similar to KNbO3 ceramics. Microstructure examined under FEG-SEM revealed an optimum microstructure, in terms of grain size, porosity and uniformity, at the sintering temperature of 1100 °C, which also showed density of 92% of ρTh. As the sintering temperature increased the X-ray diffraction peaks shifted to lower 2θ values indicating excess volatilization of Na at higher temperature as compared to K. This was further confirmed through elemental Probe X-ray microanalysis and ICP-AES studies. Dielectric constant (εr), dielectric loss (tanδ), ferroelectric (P-E loop) and piezoelectric (d33) properties showed considerable improvement and leakage current decreased with increasing sintering temperature. The sample sintered at 1100 °C showed marked improvement in maximum dielectric constant (573) at RT at 1 kHz, minimum tangent loss (0.04) at RT at 1 kHz, maximum remnant polarization (13.5 μC/cm2), lower leakage current (7.6×10-7 A/cm2) and maximum d33 value (100 pC/N).

  3. Compositional variations in In0.5Ga0.5N nanorods grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cherns, D.; Webster, R. F.; Novikov, S. V.; Foxon, C. T.; Fischer, A. M.; Ponce, F. A.; Haigh, S. J.

    2014-05-01

    The composition of InxGa1 - xN nanorods grown by molecular beam epitaxy with nominal x = 0.5 has been mapped by electron microscopy using Z-contrast imaging and x-ray microanalysis. This shows a coherent and highly strained core-shell structure with a near-atomically sharp boundary between a Ga-rich shell (x ˜ 0.3) and an In-rich core (x ˜ 0.7), which itself has In- and Ga-rich platelets alternating along the growth axis. It is proposed that the shell and core regions are lateral and vertical growth sectors, with the core structure determined by spinodal decomposition.

  4. Design of Si0.5Ge0.5 based tunnel field effect transistor and its performance evaluation

    NASA Astrophysics Data System (ADS)

    Singh, Gurmeet; Amin, S. Intekhab; Anand, Sunny; Sarin, R. K.

    2016-04-01

    In this work, the performance comparison of two heterojunction PIN TFETs having Si channel and Si0.5Ge0.5 source with high-k (SiGe DGTFET HK) and hetero-gate dielectric (SiGe DGTFET HG) respectively with those of two homojunction Si based PIN (DGTFET HK and DGTFET HG) TFETs is performed. Similarly, by employing the technique of pocketing at source junction in above four PIN TFETs, the performances of resultant four PNPN TFETs (SiGe PNPN DGTFET HK, SiGe PNPN DGTFET HG, PNPN DGTFET HK and PNPN DGTFET HG) are also compared with each other. Due to lower tunnel resistance of SiGe based heterojunction PIN and PNPN TFETs, the DC parameters such as ON current, ON-OFF current ratio, average subthreshold slope are improved significantly as compared to Si based PIN and PNPN TFETs respectively. The output characteristics of HG architectures in Si based homojunction PIN and PNPN TFETs is observed to be identical to with respective Si based HK PIN and PNPN TFET architectures. However, the output characteristics of HG architectures in SiGe based heterojunction PIN and PNPN TFETs degrade as compared to their respective SiGe based HK PIN and PNPN TFET architectures. In ON state, SiGe based HK and HG PIN and PNPN TFETs have lower gate capacitance (Cgg) as compared to their respective Si based HK and HG PIN and PNPN TFETs. Moreover, HG architecture suppresses gate to drain capacitance (Cgd) and ambipolar conduction. Transconductance (gm) and cut off frequency (fT) is also observed to be higher for SiGe based PIN and PNPN TFETs.

  5. Possible radio emission from Uranus at 0.5 MHz

    NASA Technical Reports Server (NTRS)

    Brown, L. W.

    1976-01-01

    Radio emission from the direction of Uranus has been detected in data from the Goddard radio astronomy experiment on the IMP-6 spacecraft. Previously, emission from the direction of Jupiter and Saturn had been observed by IMP-6 at a number of frequencies near 1 MHz and were identified through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. This technique was applied to the direction of Uranus with possible positive results. Over the approximately 500 days of data, three to six bursts with unique spectral characteristics have been found. The events persisted less than 3 minutes and are strongest in intensity near 0.5 MHz. Identification with Uranus is confused by the likely presence of low-level terrestrial and solar emission. Because of the unfavorable angular separation of earth and Uranus, there is a possibility that the bursts are atypical terrestrial magnetospheric phenomena, although the uniqueness of the set of events indicates the probable detection of radiation from Uranus.

  6. Large magnetic response in (Bi4Nd)Ti3(Fe0.5Co0.5)O15 ceramic at room-temperature

    NASA Astrophysics Data System (ADS)

    Yang, F. J.; Su, P.; Wei, C.; Chen, X. Q.; Yang, C. P.; Cao, W. Q.

    2011-12-01

    Ceramics of Nd/Co co-substituted Bi5Ti3FeO15, i.e., (Bi4Nd)Ti3(Fe0.5Co0.5)O15 were prepared by the conventional solid-state reaction method. The X-ray diffraction pattern demonstrates that the sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi2Ti2O7 also existed. The ferroelectric and magnetic Curie temperatures were determined to be 1077 K and 497 K, respectively. The multiferroic property of the sample at room temperature was demonstrated by ferroelectric and magnetic measurements. Remarkably, by Nd/Co co-substituting, the sample exhibited large magnetic response with 2Mr = 330 memu/g and 2Hc = 562 Oe at applied magnetic field of 8 kOe at room temperature. The present work suggests the possibility of doped Bi5Ti3FeO15 as a potential multiferroic.

  7. Tuning the metal-insulator transition temperature of Sm0.5Nd0.5NiO3 thin films via strain

    NASA Astrophysics Data System (ADS)

    Gardner, H. Jeffrey; Singh, Vijay; Zhang, Le; Hong, Xia

    2014-03-01

    We have investigated the effect of substrate induced strain and film thickness on the metal-insulator transition of the correlated oxide Sm0.5Nd0.5NiO3 (SNNO). We have fabricated epitaxial 3 - 40 nm thick SNNO films on (001) LaAlO3 (LAO), (001) SrTiO3 (STO), and (110) NdGaO3 (NGO) via off-axis RF magnetron sputtering. The SNNO films are atomically smooth with (001) orientation as determined by atomic force microscopy and x-ray diffraction. SNNO films grown on LAO, subject to compressive strain, exhibit a sharp metal-insulator transition at lower temperatures. Conversely, films grown on STO and NGO, subject to tensile strain, exhibit a smeared albeit above room temperature metal-insulator transition. For all substrates, we have observed that the metal-insulator transition temperature (TMI) increases monotonically with decreasing film thickness until the electrically dead layer is reached (below 4 nm). We discuss the effect of strain and oxygen deficiencies on the TMI of SNNO thin films.

  8. Initial oxidation kinetics and energetics of Cu 0.5Au 0.5 (0 0 1) film investigated by in situ ultrahigh vacuum transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Zhou, Guang-Wen; Eastman, Jeffrey A.; Yang, Judith C.

    2006-06-01

    The initial oxidation behavior of Cu 0.5Au 0.5 (0 0 1) thin film was investigated by in situ ultrahigh vacuum transmission electron microscopy to model nano-oxidation of alloys with one active component and one noble component. The formation of irregular-shaped octahedron Cu 2O islands with cube-on-cube crystallographic orientation to the substrate film was observed at all temperature studied. The energetics of Cu 2O nucleation for Cu and Cu 0.5Au 0.5 oxidation was compared. Cu 0.5Au 0.5 oxidation has lower nucleation activation energy due to the reduced mismatch strain between Cu 2O and Cu 0.5Au 0.5 films. On the other hand, the reaction kinetics for Cu 0.5Au 0.5 alloy oxidation is slower due to the higher diffusion activation energy of Cu.

  9. Brillouin light scattering investigation of the thickness dependence of Dzyaloshinskii-Moriya interaction in C o0.5F e0.5 ultrathin films

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Gabor, M. S.; Roussigné, Y.; Stashkevich, A.; Chérif, S. M.; Zighem, F.; Tiusan, C.

    2016-05-01

    C o0.5F e0.5 (CoFe) ultrathin films of various thicknesses (0.8 nm ≤tCoFe≤1.6 nm ) have been grown by sputtering on (001) MgO single crystal or Si/SiO2 substrates, using Pt as capping or buffer layers, respectively. The x-ray diffraction revealed an in-plane epitaxial (isotropic) growth of Pt on MgO (Si). Their magnetic properties have been studied by vibrating sample magnetometry and Brillouin light scattering (BLS) in the Damon-Eshbach geometry. Vibrating sample magnetometry characterizations show that films grown on MgO are in-plane magnetized, while films deposited on Si are perpendicularly magnetized for CoFe thickness below 1.4 nm. The BLS measurements reveal a pronounced nonreciprocal spin waves propagation, which increases with decreasing CoFe thickness. This nonreciprocity was attributed to an interfacial Dzyaloshinskii-Moriya interaction (DMI) induced by Pt interface with CoFe. Moreover, the DMI sign has been found to depend on the stacks order: it is positive (negative) for CoFe/Pt (Pt/CoFe). The effective thickness dependence of the DMI effective constant shows two regimes due to the degradation of the interfaces as the CoFe thickness decreases. We thus show that the magnetic dead layer should be taken into account to precisely determine the surface DMI constant Ds. Therefore, for the thickest samples, the surface DMI constants are nearly opposite: -1.27 and 1.32 pJ m-1 for Pt/CoFe and its reversed system, respectively.

  10. Structure, morphology, optical and magnetic response of ZnO, Mn3O4 and doped Zn0.5Mn0.5O nanoparticles as-synthesized using a chemical co-precipitation method

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Dwivedi, Sonam

    2016-03-01

    Nano-polycrystalline samples of pristine and Mn-doped ZnO were synthesized using the feasible chemical co-precipitation method to investigate structural, vibrational and magnetic properties. From the x-ray diffraction pattern, ZnO was indexed and fitted in a single-phase wurtzite structure (hexagonal phase, P63mc). The simulation of Mn3O4 was performed according to the initial parameter of tetragonal symmetry (I41/amd space group). For the Zn0.5Mn0.5O sample, fitting was undertaken with both P63mc and I41/amd structural models, and showed that the diffraction profile is a result of the superposition of both spectral contributions. The average grain size obtained for different compositions of ZnO, Mn3O4, and Zn0.5Mn0.5O are 84.79, 72.26 and 68.24 nm, respectively. The optical band gap was obtained as 3.41 and 4.17 eV for the ZnO and Zn0.5Mn0.5O samples, respectively. The Raman spectrum of Zn0.5Mn0.5O also verified a mixed behaviour of ZnO and Mn3O4 lattice vibration and presents two broad bands around 657 and 537 cm-1. Room temperature magnetization-magnetic (M-H) field measurements showed the diamagnetic nature of ZnO, and the paramagnetic behaviour of Mn3O4, and Zn0.5Mn0.5O nanocrystalline samples.

  11. Improved Dielectric Properties of Heterostructured Ba2.5Sr0.5TiO3 Thin Film Composites for Microwave Dielectric Devices

    NASA Technical Reports Server (NTRS)

    Jain, M.; Majumder, S. B.; Katiyar, R. S.; Bhalla, A. S.; Agrawal, D. C.; Kulkarni, V. N.; VanKeuls, F. W.; Miranda, F. A.; Romanofsky, R. R.; Mueller, C. H.; Fernandez, F.

    2002-01-01

    In the present work we have deposited MgO and Ba(sub 0.5)Sr(sub 0.5)TiO(sub 3)(BST50) thin layers in different sequences to make MgO:BST50 hetero-structured thin films. These films were characterized by X-ray diffraction and Rutherford backscattering technique and found to be highly (100) textured. The figure of merit {(C(sub0)-C(sub v)/(C(sub0-tandelta)} of the hetero-structured films was found to be higher as compared to pure BST50 films measured at 1 MHz frequency with electric field of 25.3 kV/cm. These films were used to make eight element coupled micro-strip phase shifter and characterized in a frequency range of 13-15 GHz. The high frequency figure of merit (kappa factor, defined as the ratio of degree of phase shift per dB loss) measured at around 14 GHz with electric field of 333 kV/cm has been markedly improved (around 64.28 deg/dB for hetero-structured film as compared to 24.65 deg /dB for pure film). Improvement in dielectric properties in a wide frequency range in the MgO:BST are believed to be due to the higher densification of the hetero-structured films.

  12. Upper critical fields in a FeSe0.5Te0.5 superconducting single crystal

    NASA Astrophysics Data System (ADS)

    Velasco-Soto, D.; Rivera-Gómez, F. J.; Santillán-Rodríguez, C. R.; Sáenz-Hernández, R. J.; Botello-Zubiate, M. E.; Matutes Aquino, J. A.

    2013-05-01

    A single crystal with a nominal composition FeSe0.5Te0.5 was obtained by the Bridgman method. A quartz ampulla with the sample inside was vacuum-sealed and maintained at 1050 °C for 37 h to homogenize the sample. Subsequently, the quartz ampulla with the sample was moved with a speed of 2.2 mm/h to a furnace which was at 450 °C. X-ray diffraction confirmed the tetragonal structure of the grown single crystal with the cleavage plane corresponding to the ab plane. Resistance measurements were carried out with magnetic fields from 0 to 9 T, applied parallel to the c axis and ab plane, respectively. A zero-field critical temperature Tc = 14 K was determined. The upper critical field vs. temperature phase diagram was built for temperatures where the resistance drops to 90%, 50%, and 10% of the normal state resistance. The linear extrapolation to T = 0 K gave upper critical fields of 57.2, 51.8, and 46.0 T for Hǁc axis and 109.6, 95.5, and 80.9 T for Hǁab. Applying the Werthamer-Helfand-Hohenberg (WHH) theory, upper critical fields of 39.6, 35.9, and 31.8 T and coherence lengths of 28.8, 30.3, and 32.1 Å were obtained for Hǁc; while for Hǁab, upper critical fields of 51.3, 40.7, and 37.5 T and coherence lengths of 22.3, 26.7, and 31.5 Å were obtained. The value of μ0Hc2/kBTc calculated by the WHH theory exceeds the Pauli limit (1.84 T/K) indicating the unconventional nature of superconductivity. The activation energy U0 has two different rates of change with the applied magnetic field probably due to two different thermal activation mechanisms; the origin of which requires further investigation. A similar behavior is observed in the irreversibility lines.

  13. Crystal structure, oxidation state and magnetism of SrxLa2-xCu0.5Ru0.5O4 (x=1, 1.5)

    NASA Astrophysics Data System (ADS)

    Lü, Minfeng; Deng, Xiaolong; Waerenborgh, João C.; Wu, Xiaojie; Meng, Jian

    2014-03-01

    SrxLa2-xCu0.5Ru0.5O4 (x=1, 1.5) oxides with K2NiF4-type structure were prepared by solid state reaction and characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, magnetic and electrical resistivity measurements. The SrLaCu0.5Ru0.5O4 phase was obtained for the first time with a negligible amount of impurities. The octahedral Cu/RuO6 units are more elongated in SrLaCu0.5Ru0.5O4 than in Sr1.5La0.5Cu0.5Ru0.5O4 indicating a greater extent of static Jahn-Teller distortion. XPS suggests that mixed ion pairs Ru5+/Ru4+↔Cu+/Cu2+ are present in SrLaCu0.5Ru0.5O4, while Ru remains as Ru5+ and Cu as Cu2+ in Sr1.5La0.5Cu0.5Ru0.5O4. Both samples show spin-glass behavior, which can be explained by competition between ferromagnetic and antiferromagnetic superexchange interactions. The negative Weiss temperature estimated for SrLaCu0.5Ru0.5O4, -318 K, is significantly lower than -11.5 K deduced for Sr1.5La0.5Cu0.5Ru0.5O4 which may be related to the higher static Jahn-Teller distortion in the former oxide.

  14. Giant Dielectric Behavior of BaFe0.5Nb0.5O3 Perovskite Ceramic

    NASA Astrophysics Data System (ADS)

    Intatha, Uraiwan; Eitssayeam, Sukum; Tunkasiri, Tawee

    2009-12-01

    Single-phase cubic Ba(Fe,Nb)0.5O3 (BFN) powder was synthesized by solid-state reaction at 1443 K for 4 hour in air. X-ray diffraction indicated that the BFN oxide mixture calcined at 1200°C crystallizes to the pure cubic perovskite phase. BFN ceramics were produced from this powder by sintering at 1623-1673 K for 4 hrs in air. Samples prepared under these conditions achieved up to 94.7% of the theoretical density. The temperature dependence of their dielectric constant and loss tangent, measured at difference frequencies, shows an increase in the dielectric constant with temperature which is probably due to disorder on the B site ion of the perovskite. Non-Debye type of relaxation phenomena has been observed in the BFN ceramics as confirmed by Cole-Cole plots. The higher value of ɛ' at the lower frequency is explained on the basis of the Maxwell-Wagner (MW) polarization model.

  15. Giant Dielectric Behavior of BaFe0.5Nb0.5O3 Perovskite Ceramic

    NASA Astrophysics Data System (ADS)

    Intatha, Uraiwan; Eitssayeam, Sukum; Tunkasiri, Tawee

    Single-phase cubic Ba(Fe,Nb)0.5O3 (BFN) powder was synthesized by solid-state reaction at 1443 K for 4 hour in air. X-ray diffraction indicated that the BFN oxide mixture calcined at 1200°C crystallizes to the pure cubic perovskite phase. BFN ceramics were produced from this powder by sintering at 1623-1673 K for 4 hrs in air. Samples prepared under these conditions achieved up to 94.7% of the theoretical density. The temperature dependence of their dielectric constant and loss tangent, measured at difference frequencies, shows an increase in the dielectric constant with temperature which is probably due to disorder on the B site ion of the perovskite. Non-Debye type of relaxation phenomena has been observed in the BFN ceramics as confirmed by Cole-Cole plots. The higher value of ɛ‧ at the lower frequency is explained on the basis of the Maxwell-Wagner (MW) polarization model.

  16. Discontinuity in heat capacity of Fe0.5Co0.5(110) alloy thin films

    NASA Astrophysics Data System (ADS)

    Ramírez-Dámaso, G.; Castillo-Alvarado, F.-L.; Cruz-Torres, A.; Rójas-Hernández, E.

    2016-07-01

    In this work we calculate heat capacity of alloy thin films of FeCo on the surface of the plane (110), using three parameters, the concentration x(i), the lattice long range order parameter t(i) and the magnetic order parameter σ(i), being i the number of layers of the thin film. The formulations reported by Hill [1] in the context of small particles and Valenta's model [2] can be applied to the film structure when we treat a thin film as a system divided into subsystems equivalent to two-dimensional parallel layers. The FeCo bulk alloy is completely homogeneous while a thin film have spatial discontinuities in their surfaces. We consider three ferromagnetic thin films formed by 11, 15 and 19 layers in the Helmholtz's free energy, which is minimized applying their first partial derivatives with respect to chemical composition, long range order parameter and magnetic order parameter. We calculate internal energy and heat capacity as a function of temperature and we verify that have two jumps as are reported in literature for the bulk; there are many results of bulk or surface effects of FeCo, but no enough results about ferromagnetic FeCo thin films and this fact does this work interesting.

  17. Electrical properties of (110) epitaxial lead-free ferroelectric Na0.5Bi0.5TiO3 thin films grown by pulsed laser deposition: Macroscopic and nanoscale data

    NASA Astrophysics Data System (ADS)

    Bousquet, M.; Duclère, J.-R.; Gautier, B.; Boulle, A.; Wu, A.; Députier, S.; Fasquelle, D.; Rémondière, F.; Albertini, D.; Champeaux, C.; Marchet, P.; Guilloux-Viry, M.; Vilarinho, P.

    2012-05-01

    We report the electrical properties, measured both at the macroscopic and nanometric scales, of epitaxial (110)-Na0.5Bi0.5TiO3 (NBT) thin films grown on (110)Pt/(110)SrTiO3 by pulsed laser deposition (PLD). The influence of the A-site composition (Na and/or Bi excess) on both the structural/microstructural characteristics and the electrical properties is discussed. Whatever the composition of the NBT target, the final layers are systematically epitaxially grown, with NBT crystallites mainly (110)-oriented, and as well (100)-oriented for some minor proportion. Atomic force microscopy (AFM) images reveal the coexistence of two kinds of grains presenting different shapes: namely flat and elongated grains, corresponding to (100)- and (110)-oriented NBT crystallites, respectively. The macroscopic ferroelectric properties were measured at room temperature. A rather well-defined shape of the hysteresis loops was obtained: the incorporation of a Bi excess in the target clearly improves the saturation of the loops. The ferroelectric performances are a remanent polarization (Pr) value, ranging from 7 to 14 μC/cm2, associated with a coercive field (Ec) in the range 68-85 kV/cm. In addition, at 105 Hz, the relative permittivity was about ɛr ˜ 255-410 and the dielectric losses (tan δ) were ˜6%-7%. Finally, the electrical properties at the local scale were investigated by coupling piezoresponse force microscopy (PFM) and tunneling AFM (TUNA) measurements. The collected data reveal that the two types of grains behave differently. The PFM amplitude signal of (110)-oriented grains is very contrasted and such grains are often divided in ferroelectric bi-domains of nanometric sizes, whereas the response of (100)-oriented grains is less contrasted and more homogeneous. The interpretation of the PFM signal is provided. The piezoloop recorded on a (110)NBT grain is strongly distorted and shifted along the vertical axis, in agreement with the vertical drift observed for macroscopic

  18. Structure and dielectric properties of solid solutions Bi7Ti4 + x W x Nb1 - 2 x O21 ( x = 0-0.5)

    NASA Astrophysics Data System (ADS)

    Vlasenko, V. G.; Zubkov, S. V.; Shuvaeva, V. A.

    2015-05-01

    The structural and electrophysical characteristics of a series of solid solutions of layered perovskite-type oxides Bi7Ti4 + x W x Nb1 - 2 x O21 ( x = 0-0.5) have been investigated. According to X-ray powder dif- fraction data, all the studied compounds are single-phase and have the structure of Aurivillius phases ( m = 2.5) with an orthorhombic crystal lattice (space group I2 cm, Z = 2). The changes in the tetragonal and orthorhombic distortions of perovskite-like layers in the compounds have been considered depending on their chemical composition. The temperature dependences of the relative permittivity ɛ( T) have been measured. It has been shown that the Curie temperature T C of the perovskite-type oxides Bi7Ti4 + x W x Nb1 - 2 x O21 ( x = 0-0.5) decreases linearly with an increase in the parameter x. The activation energies of charge carriers have been obtained in different temperature ranges. It has been found that there are three temperature regions with very different activation energies due to different natures of charge carriers in the studied compounds.

  19. First-principles investigations on thermodynamic properties of the ordered and disordered Si0.5Ge0.5 alloys

    NASA Astrophysics Data System (ADS)

    Zhu, Yan; Zhang, Xinyu; Zhang, Suhong; Sun, Xiaowei; Wang, Limin; Ma, Mingzhen; Liu, Riping

    2014-05-01

    The structure, formation energy, and thermodynamic properties of Si0.5Ge0.5 alloys are investigated through first-principles method. The ordered and disordered structures of Si0.5Ge0.5 compounds are considered. Our results show that thermodynamic instabilities of Si0.5Ge0.5 alloys at 0 K can be judged from the calculated formation energy. However, the alloy might be prepared at specified environment owing to the entropy effects considered. Moreover, the temperature dependence of the heat capacity, Debye temperature and thermal expansion coefficient of ordered and disordered structures are discussed.

  20. Hidden but important parameters in Ga{sub 0.5}In{sub 0.5}P cell growth

    SciTech Connect

    Kurtz, S.R.; Olson, J.M.; Bertness, K.A.

    1996-05-01

    Despite their best intentions, authors often omit from publications many important technical details. These omissions can lead to contradictions in the literature and inhibit {open_quotes}researchers{close_quotes} abilities to duplicate published results. Here, the authors explore {open_quote}hidden{close_quote} parameters that are usually not reported, either because they are unknown (e.g., impurity levels) or because they are considered to be of little importance. Specifically the authors focus on the effects - and how to reduce the effects - of growth parameters in nearby layers (diffusion), impurities (oxygen), and the cooldown atmosphere (hydrogen passivation).

  1. X-ray photoelectron spectroscopic study of direct reforming catalysts Ln0.5Sr0.5Ti0.5Mn0.5O3±d (Ln = La, Nd, and Sm) for high temperature-operating solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Keunsoo; Jeong, Jihoon; Azad, Abul K.; Jin, Sang Beom; Kim, Jung Hyun

    2016-03-01

    Chemical states of lanthanide doped perovskite for direct reforming anode catalysts, Ln0.5Sr0.5Ti0.5Mn0.5O3±d (Ln = La, Nd, and Sm) have been studied by X-ray Photoelectron Spectroscopy (XPS) in order to determine the effects of various lanthanide substitution in complex perovskites for high temperature-operating solid oxide fuel cells (HT-SOFC). The charge state of lanthanide ions remained at 3+ and the binding energies of the lanthanide ions in Ln0.5Sr0.5Ti0.5Mn0.5O3±d were located in a relatively lower range compared to those of conventional lanthanide oxides. Mn and Ti were regarded as charge compensation components in Ln0.5Sr0.5Ti0.5Mn0.5O3±d; Mn was more influential than Ti. In the cases of substituting Nd and Sm into Ln0.5Sr0.5Ti0.5Mn0.5O3±d, some portion of Ti showed metallic behavior; the specific Mn satellite peak indicating an electro-catalytic effect had occurred. Three types of oxygen species comprised of lattice oxygen, carbonate species, and adsorbed oxygen species were observed in Ln0.5Sr0.5Ti0.5Mn0.5O3±d from the O 1s spectra; a high portion of lattice oxygen was observed in both Nd0.5Sr0.5Ti0.5Mn0.5O3±d (NSTM) and Sm0.5Sr0.5Ti0.5Mn0.5O3±d (SSTM). In various respects, NSTM and SSTM will be desirable reforming catalysts and anode candidates for high temperature solid oxide fuel cell.

  2. Ce-Substituted Co0.5Ni0.5Fe2O4: Structural, morphological, electrical, and dielectric properties

    NASA Astrophysics Data System (ADS)

    Abbas, Syed Samar; Gul, Iftikhar Hussain; Ameer, Shahid; Anees, Muhammad

    2015-01-01

    Functional nano ceramics, especially rare earth substituted ferrites, have numerous applications in microelectronics. They have certain novel characteristics associated with various rare earth substitutions associated with electronics. A series of cerium-substituted cobalt nickel ferrite nanoparticles with nominal composition CexCo0.5Ni0.5Fe2-xO4 (where x = 0.00, 0.05, 0.10, 0.15, and 0.20) was prepared in powder form by chemical co-precipitation and sol-gel auto combustion methods. Samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), dielectric properties, and DC electrical resistivity. XRD analysis of all the samples confirms the formation of the spinel structure of Fd-3m space group. Crystallite size " t" was found to decrease, whereas both x-ray density " D x " and lattice constant " a" were found to increase by increasing Ce concentration from 8.35 Å to 8.36 Å and 8.37 Å for sol-gel and coprecipitation, respectively. SEM results show the presence of uniformly distributed and almost spherical-shaped particles for both techniques. FTIR measurements were used to further confirm the composition, i.e., cation substitution. The DC electrical resistivity of the x = 0.00 sample is higher than Ce-substituted ferrite samples and in the range of 108 O-cm at 373 K. Dielectric spectroscopy is also studied from 100 Hz to 5 MHz as a function of frequency. To our knowledge, this is the first reported research of this particular composition.

  3. Formation of solar cells based on Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) ferroelectric thick film

    SciTech Connect

    Irzaman, Syafutra, H. Arif, A. Alatas, H.; Hilaluddin, M. N.; Kurniawan, A.; Iskandar, J.; Dahrul, M.; Ismangil, A.; Yosman, D.; Aminullah; Prasetyo, L. B.; Yusuf, A.; Kadri, T. M.

    2014-02-24

    Growth of Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) 1 M thick films are conducted with variation of annealing hold time of 8 hours, 15 hours, 22 hours, and 29 hours at a constant temperature of 850 °C on p-type Si (100) substrate using sol-gel method then followed by spin coating process at 3000 rpm for 30 seconds. The BST thick film electrical conductivity is obtained to be 10{sup −5} to 10{sup −4} S/cm indicate that the BST thick film is classified as semiconductor material. The semiconductor energy band gap value of BST thick film based on annealing hold time of 8 hours, 15 hours, 22 hours, and 29 hours are 2.58 eV, 3.15 eV, 3.2 eV and 2.62 eV, respectively. The I-V photovoltaic characterization shows that the BST thick film is potentially solar cell device, and in accordance to annealing hold time of 8 hours, 15 hours, 22 hours and 29 hours have respective solar cell energy conversion efficiencies of 0.343%, 0.399%, 0.469% and 0.374%, respectively. Optical spectroscopy shows that BST thick film solar cells with annealing hold time of 8 hours, 15 hours, and 22 hours absorb effectively light energy at wavelength of ≥ 700 nm. BST film samples with annealing hold time of 29 hours absorb effectively light energy at wavelength of ≤ 700 nm. The BST thick film refraction index is between 1.1 to 1.8 at light wavelength between ±370 to 870 nm.

  4. Ubiquitous CM and DM

    NASA Technical Reports Server (NTRS)

    Crowley, Sandra L.

    2000-01-01

    Ubiquitous is a real word. I thank a former Total Quality Coach for my first exposure some years ago to its existence. My version of Webster's dictionary defines ubiquitous as "present, or seeming to be present, everywhere at the same time; omnipresent." While I believe that God is omnipresent, I have come to discover that CM and DM are present everywhere. Oh, yes; I define CM as Configuration Management and DM as either Data or Document Management. Ten years ago, I had my first introduction to the CM world. I had an opportunity to do CM for the Space Station effort at the NASA Lewis Research Center. I learned that CM was a discipline that had four areas of focus: identification, control, status accounting, and verification. I was certified as a CMIl graduate and was indoctrinated about clear, concise, and valid. Off I went into a world of entirely new experiences. I was exposed to change requests and change boards first hand. I also learned about implementation of changes, and then of technical and CM requirements.

  5. Cobalt-free Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3-δ as a bi-functional electrode material for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Yang, Guangming; Shen, Jian; Chen, Yubo; Tadé, Moses O.; Shao, Zongping

    2015-12-01

    In this study, we investigate a cobalt-free titanium-doped perovskite oxide with the nominal composition of Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3-δ (BSFCuTi) as a potential electrode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). In comparison to Ba0.5Sr0.5Fe0.9Cu0.1O3-δ, BSFCuTi exhibits improved phase stability and a reduced thermal expansion coefficient even though the electrical conductivity decreases. A low area specific resistance of 0.088 Ω cm2 is achieved at 600 °C based on a symmetrical cell test, which is comparable to the result for the benchmark Ba0.5Sr0.5Co0.8Fe0.2O3-δ cobalt-based perovskite electrocatalyst. Stable operation for a period of 200 h is also demonstrated. The I-V test shows a very high power output of 1.16 W cm-2 for a single cell using a BSFCuTi cathode at 600 °C. In addition, the BSFCuTi can be partially reduced under a reducing atmosphere to prepare a suitable anode material. A cell with BSFCuTi as the material for both electrodes and a thick Gd0.2Ce0.8O1.9 electrolyte (300 μm) delivers an attractive power density of 480 mW cm-2 at 800 °C. The high activity, favorable stability and bi-functionality make BSFCuTi a promising electrode material for IT-SOFCs.

  6. Structure and dielectric properties of Na0.5Bi0.5TiO3-CaTiO3 solid solutions

    NASA Astrophysics Data System (ADS)

    Birks, E.; Dunce, M.; Ignatans, R.; Kuzmin, A.; Plaude, A.; Antonova, M.; Kundzins, K.; Sternberg, A.

    2016-02-01

    Despite wide studies of Na0.5Bi0.5TiO3, structure of this material and its connection with the observed physical properties still raise numerous questions due to mutually contradicting results obtained. Here, structure and dielectric properties of poled and unpoled Na0.5Bi0.5TiO3-CaTiO3 solid solutions are studied, projecting the obtained concentration dependence of structure and dielectric properties on pure Na0.5Bi0.5TiO3 as the end member of this material group. X-ray diffraction patterns for Na0.5Bi0.5TiO3-CaTiO3 solid solutions reveal dominating of an orthorhombic Pnma phase, even for the compositions approaching the end composition (Na0.5Bi0.5TiO3), whereas structure of pure Na0.5Bi0.5TiO3 can be considered, assuming coexistence of rhombohedral and orthorhombic phases. This allows one to avoid appearance of a large difference of rhombohedral distortions between the unpoled and poled Na0.5Bi0.5TiO3, if the rhombohedral distortion is calculated as for single R3c phase. Features of dielectric permittivity, corresponding to the observed structural phase transition, are identified. It is discussed that the rhombohedral R3c phase is responsible for appearance of the frequency-dependent shoulder of dielectric permittivity temperature dependence, characteristic for unpoled Na0.5Bi0.5TiO3.

  7. Preparation Process and Dielectric Properties of Ba(0.5)Sr(0.5)TiO3-P(VDF-CTFE) Nanocomposites

    NASA Technical Reports Server (NTRS)

    Zhang, Lin; Wu, Peixuang; Li, Yongtang; Cheng, Z. -Y.; Brewer, Jeffrey C.

    2014-01-01

    Ceramic-polymer 0-3 nanocomposites, in which nanosized Ba(0.5)Sr(0.5)TiO3 (BST) powders were used as ceramic filler and P(VDF-CTFE) 88/12 mol% [poly(vinylidene fluoridechlorotrifluoroethylene)] copolymer was used as matrix, were studied over a concentration range from 0 to 50 vol.% of BST powders. It is found that the solution cast composites are porous and a hot-press process can eliminate the porosity, which results in a dense composite film. Two different configurations used in the hot-press process are studied. Although there is no clear difference in the uniformity and microstructure of the composites prepared using these two configurations, the composite prepared using one configuration exhibit a higher dielectric constant with a lower loss. For the composite with 40 vol. BST, a dielectric constant of 70 with a loss of 0.07 at 1 kHz is obtained at room temperature. The composites exhibit a lower dielectric loss than the polymer matrix at high frequency. However, at low frequency, the composites exhibit a higher loss than the polymer matrix due to a low frequency relaxation process that appears in the composites. It is believed that this relaxation process is related to the interfacial layer formed between BST particle and the polymer matrix. The temperature dependence of the dielectric property of the composites was studied. It is found that the dielectric constant of these composites is almost independent of the temperature over a temperature range from 20 to 120 C. Key words: A. Polymer-matrix composites (PMCs); B. Electrical Properties; E. Casting; E. Heat treatment; Dielectric properties.

  8. 21-cm Intensity Mapping

    NASA Astrophysics Data System (ADS)

    Chang, Tzu-Ching; GBT-HIM Team

    2016-01-01

    The redshifted 21-cm emission from neutral hydrogen has emerged as a powerful probe for large-scale structure; a significant fraction of the observable universe can be mapped in the Intensity Mapping regime out to high redshifts. At redshifts around unity, the 21-cm emission traces the matter distribution and can be used to measure the Baryon Acoustic Oscillation (BAO) signature and constrain dark energy properties. I will describe our HI Intensity Mapping program at the Green Bank Telescope (GBT), aiming at measuring the 21cm power spectrum at z=0.8. A 800-MHz multi-beam focal-plane array for the GBT is currently under construction in order to facilitate a large-scale survey for BAO and the redshift-space distortion measurements for cosmological constraints.

  9. One-dimensional SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers and enhancement magnetic property.

    PubMed

    Song, Fuzhan; Shen, Xiangqian; Liu, Mingquan; Xiang, Jun

    2011-08-01

    SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers of diameters about 100 nm with mass ratio 1:1 have been prepared by the electrospinning and calcination process. The SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrites are formed after calcined at 700 degrees C for 2 hours. The composite ferrite nanofibers are fabricated from nanosized Ni(0.5)Zn(0.5)Fe2O4 and SrFe12O19 ferrite grains with a uniform phase distribution. The ferrite grain size increases from about 11 to 36 nm for Ni(0.5)Zn(0.5)Fe12O4 and 24 to 56 nm for SrFe12O19 with the calcination temperature increasing from 700 to 1100 degrees C. With the ferrite grain size increasing, the coercivity (Hc) and remanence (Mr) for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers initially increase, reaching a maximum value of 118.4 kA/m and 31.5 Am2/kg at the grain size about 40 nm (SrFe12O19) and 24 nm (Ni(0.5)Zn(0.5)Fe2O4) respectively, and then show a reduction tendency with a further increase of the ferrite grain size. The specific saturation magnetization (Msh) of 63.2 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers obtained at 900 degrees C for 2 hours locates between that for the single SrFe12O19 ferrite (48.5 Am2/kg) and the single Ni(0.5)Zn(0.5)Fe2O4 ferrite (69.3 Am2/kg). In particular, the Mr value 31.5 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers is much higher than that for the individual SrFe12O19 (25.9 Am2/kg) and Ni(0.5)Zn(0.5)Fe2O4 ferrite (11.2 Am2/kg). These enhanced magnetic properties for the composite ferrite nanofibers can be attributed to the exchange-coupling interaction in the composite. PMID:22103109

  10. Superconductivity phase diagram of Se-substituted CeO0.5F0.5Bi(S1-xSex)2

    NASA Astrophysics Data System (ADS)

    Mizuguchi, Yoshikazu; Hiroi, Takafumi; Miura, Osuke

    2016-02-01

    We investigated the effects of Se substitution on the lattice constants and superconducting properties of CeO0.5F0.5Bi(S1-xSex)2. With increasing Se concentration, the a lattice constant increased, while the c lattice constant did not show any significant increase between x = 0.1 and x = 0.5. Bulk superconductivity was observed in samples with x = 0.2-0.4, and the superconducting transition temperature was the highest at x = 0.3. The obtained superconductivity phase diagram was compared to those of LaO0.5F0.5Bi(S1-xSex)2 and NdO0.5F0.5Bi(S1-xSex)2.

  11. Terahertz radiation from InAs/Al xGa 1- xSb ( x=0.5) heterostructures

    NASA Astrophysics Data System (ADS)

    Suzuki, Masato; Kiwa, Toshihiko; Tonouchi, Masayoshi; Nakajima, Yoji; Sasa, Shigehiko; Inoue, Masataka

    2004-04-01

    We observed terahertz radiation from InAs/Al 0.5Ga 0.5Sb heterostructures excited by femtosecond pulses of mode-locked Ti:sapphire laser in the temperature range of 20- 300 K. The radiation pseudo-reflected is monitored in time domain by a low temperature grown GaAs photoswitch. Although the waveforms are almost identical irrespective of temperatures, their maximum amplitude is strongly temperature dependent and peaks at around 100 K. Laser power dependence of the amplitude indicates that the excitation at power densities above 57 W/ cm2 induce saturation presumably due to screening effect.

  12. Halogens in CM Chondrites

    NASA Astrophysics Data System (ADS)

    Menard, J. M.; Caron, B.; Jambon, A.; Michel, A.; Villemant, B.

    2013-09-01

    We set up an extraction line of halogens (fluorine, chlorine) by pyrohydrolysis with 50 mg of rock. We analyzed 7 CM2 chondrites found in Antarctica and found that the Cl content of meteorites with an intact fusion crust is higher than those without.

  13. Enhanced electrical and ferroelectric properties in a multiferroic (BiFeO3/Bi0.5Na0.5TiO3)3/LaNiO3 superlattices structure

    NASA Astrophysics Data System (ADS)

    Cheng, X. Q.; Miao, J.; Wu, S. Z.; Shao, F.; Guo, L. Q.; Xu, X. G.; Jiang, Y.

    2014-02-01

    Artificial multiferroic superlattices (SL), consisting of BiFeO3 (16 nm)/Bi0.5Na0.5TiO3 (5 nm) (BFO/BNT SL), were grown on (001) SrTiO3 single crystal by pulsed laser deposition method. The cross-sectional, surface morphology, and crystallographic structure of BFO/BNT SL and BFO single layer were investigated. It was found that the electrical, ferroelectric, and magnetic properties of BFO/BNT SL exhibit a remarkably enhancement compared with BFO single layer. The influence of BNT buffering layer, lattice strain, and interfaces interplay of the SL structure are supposed to benefit their ferroelectric and ferromagnetic properties. Our works suggested the BFO/BNT SL with an improved multiferroic characteristics have a promising application for the future informational storage devices.

  14. A cobalt-free Sm0.5Sr0.5Fe0.8Cu0.2O3-δ-Ce0.8Sm0.2O2-δ composite cathode for proton-conducting solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Ling, Yihan; Yu, Jia; lin, Bin; Zhang, Xiaozhen; Zhao, Ling; Liu, Xingqin

    2011-03-01

    A cobalt-free composite Sm0.5Sr0.5Fe0.8Cu0.2O3-δ-Ce0.8Sm0.2O2-δ (SSFCu-SDC) is investigated as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs) in intermediate temperature range, with BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) as the electrolyte. The XRD results show that SSFCu is chemically compatible with SDC at temperatures up to 1100 °C. The quad-layer single cells of NiO-BZCYYb/NiO-BZCYYb/BZCYYb/SSFCu-SDC are operated from 500 to 700 °C with humidified hydrogen (∼3% H2O) as fuel and the static air as oxidant. It shows an excellent power density of 505 mW cm-2 at 700 °C. Moreover, a low electrode polarization resistance of 0.138 Ω cm2 is achieved at 700 °C. Preliminary results demonstrate that the cobalt-free SSFCu-SDC composite is a promising cathode material for H-SOFCs.

  15. NuSTAR Observations of Heavily Obscured Quasars at z Is Approximately 0.5

    NASA Technical Reports Server (NTRS)

    Lansbury, G. B.; Alexander, D. M.; Del Moro, A.; Gandhi, P.; Assef, R. J.; Stern, D.; Aird, J.; Ballantyne, D. R.; Balokovic, M.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Christensen, F. E.; Craig, W. W.; Elvis, M.; Grefenstette, B. W.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Koss, M.; LaMassa, S. M.; Luo, B.; Mullaney, J. R.; Teng, S. H.; Urry, C. M.; Zhang, W. W.

    2014-01-01

    We present NuSTAR hard X-ray observations of three Type 2 quasars at z approx. = 0.4-0.5, optically selected from the Sloan Digital Sky Survey. Although the quasars show evidence for being heavily obscured, Compton-thick systems on the basis of the 2-10 keV to [O(sub III)] luminosity ratio and multiwavelength diagnostics, their X-ray absorbing column densities (N(sub H)) are poorly known. In this analysis, (1) we study X-ray emission at greater than 10 keV, where X-rays from the central black hole are relatively unabsorbed, in order to better constrain N(sub H). (2) We further characterize the physical properties of the sources through broad-band near-UV to mid-IR spectral energy distribution analyses. One of the quasars is detected with NuSTAR at greater than 8 keV with a no-source probability of less than 0.1%, and its X-ray band ratio suggests near Compton-thick absorption with N(sub H) is approximately greater than 5 × 10(exp 23) cm(exp -2). The other two quasars are undetected, and have low X-ray to mid-IR luminosity ratios in both the low-energy (2-10 keV) and high-energy (10-40 keV) X-ray regimes that are consistent with extreme, Compton-thick absorption (N(sub H) is approximately greater than 10(exp 24) cm(exp -2)). We find that for quasars at z is approximately 0.5, NuSTAR provides a significant improvement compared to lower energy (less than 10 keV) Chandra and XMM-Newton observations alone, as higher column densities can now be directly constrained.

  16. NuSTAR observations of heavily obscured quasars at z ∼ 0.5

    SciTech Connect

    Lansbury, G. B.; Alexander, D. M.; Moro, A. Del; Gandhi, P.; Aird, J.; Assef, R. J.; Stern, D.; Ballantyne, D. R.; Baloković, M.; Grefenstette, B. W.; Harrison, F. A.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Christensen, F. E.; Craig, W. W.; Elvis, M.; Hailey, C. J.; Hickox, R. C.; Koss, M.; and others

    2014-04-10

    We present NuSTAR hard X-ray observations of three Type 2 quasars at z ≈ 0.4-0.5, optically selected from the Sloan Digital Sky Survey. Although the quasars show evidence for being heavily obscured, Compton-thick systems on the basis of the 2-10 keV to [O III] luminosity ratio and multiwavelength diagnostics, their X-ray absorbing column densities (N {sub H}) are poorly known. In this analysis, (1) we study X-ray emission at >10 keV, where X-rays from the central black hole are relatively unabsorbed, in order to better constrain N {sub H}. (2) We further characterize the physical properties of the sources through broad-band near-UV to mid-IR spectral energy distribution analyses. One of the quasars is detected with NuSTAR at >8 keV with a no-source probability of <0.1%, and its X-ray band ratio suggests near Compton-thick absorption with N {sub H} ≳ 5 × 10{sup 23} cm{sup –2}. The other two quasars are undetected, and have low X-ray to mid-IR luminosity ratios in both the low-energy (2-10 keV) and high-energy (10-40 keV) X-ray regimes that are consistent with extreme, Compton-thick absorption (N {sub H} ≳ 10{sup 24} cm{sup –2}). We find that for quasars at z ∼ 0.5, NuSTAR provides a significant improvement compared to lower energy (<10 keV) Chandra and XMM-Newton observations alone, as higher column densities can now be directly constrained.

  17. Atomic disorder of Li0.5Ni0.5O thin films caused by Li doping: estimation from X-ray Debye–Waller factors

    PubMed Central

    Yang, Anli; Sakata, Osami; Yamauchi, Ryosuke; Kumara, L. S. R.; Song, Chulho; Katsuya, Yoshio; Matsuda, Akifumi; Yoshimoto, Mamoru

    2015-01-01

    Cubic type room-temperature (RT) epitaxial Li0.5Ni0.5O and NiO thin films with [111] orientation grown on ultra-smooth sapphire (0001) substrates were examined using synchrotron-based thin-film X-ray diffraction. The 11 and 22 rocking curves including six respective equivalent reflections of the Li0.5Ni0.5O and NiO thin films were recorded. The RT B 1 factor, which appears in the Debye–Waller factor, of a cubic Li0.5Ni0.5O thin film was estimated to be 1.8 (4) Å2 from its 11 and 22 reflections, even though the Debye model was originally derived on the basis of one cubic element. The corresponding Debye temperature is 281 (39) K. Furthermore, the B 2 factor in the pseudo-Debye–Waller factor is proposed. This parameter, which is evaluated using one reflection, was also determined for the Li0.5Ni0.5O thin film by treating Li0.5Ni0.5O and NiO as ideal NaCl crystal structures. A structural parameter for the atomic disorder is introduced and evaluated. This parameter includes the combined effects of thermal vibration, interstitial atoms and defects caused by Li doping using the two Debye–Waller factors. PMID:26664345

  18. Boundary Layers of Air Adjacent to Cylinders

    PubMed Central

    Nobel, Park S.

    1974-01-01

    Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for νwindd between 200 and 30,000 cm2/second (where νwind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855

  19. Electron-phonon superconductivity in LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}

    SciTech Connect

    Feng, Yanqing; Du, Yongping; Wan, Xiangang Wang, Bogen; Ding, Hang-Chen; Savrasov, Sergey Y.; Duan, Chun-Gang

    2014-06-21

    We report density functional calculations of the electronic structure, Fermi surface, phonon spectrum and electron–phonon coupling for the newly discovered superconductor LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}. It is confirmed that there is a strong Fermi surface nesting at (π,π,0), which results in unstable phonon branches. Combining the frozen phonon total energy calculations and an anharmonic oscillator model, we find that the quantum fluctuation prevents the appearance of static long–range order. The calculation shows that LaO{sub 0.5}F{sub 0.5}BiSe{sub 2} is highly anisotropic, and same as its cousin LaO{sub 0.5}F{sub 0.5}BiS{sub 2}, this compound is also a conventional electron-phonon coupling induced superconductor.

  20. Effect of annealing temperature on photoelectrochemical properties of nanocrystalline MoBi2(Se0.5Te0.5)5 thin films

    NASA Astrophysics Data System (ADS)

    Salunkhe, Manauti; Pawar, Nita; Patil, P. S.; Bhosale, P. N.

    2014-10-01

    Nanocrystalline MoBi2(Se0.5Te0.5)5 thermoelectric thin films have been deposited on ultrasonically cleaned glass and FTO-coated glass substrates by Arrested Precipitation Technique. The change in properties of MoBi2(Se0.5Te0.5)5 thin films were examined after annealing at the temperature 473 K for 3 h. The structural, morphological, compositional and electrical properties of thin films were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, etc. Thermoelectric properties of the thin films have been evaluated by measurements of electrical conductivity and Seebeck coefficient in the temperature range 300-500 K. Our aim is to investigate the effect of annealing on behaviour of MoBi2(Se0.5Te0.5)5 thin films along with photoelectrochemical properties.

  1. Influence of Co doping on structural and electrical properties of La0.5Ce0.5Mn1-xCoxO3 manganites

    NASA Astrophysics Data System (ADS)

    Mansuri, Irfan; Shaikh, M. W.; Kuo, Y. K.; Varshney, Dinesh

    2013-02-01

    The effect of Co doping on structural, electrical and magnetic properties of half doped La0.5Ce0.5Mn1-xCoxO3 (x = 0, 0.05) is investigated. The structure of the compounds crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La0.5Ce0.5MnO3 exhibits metal-semiconductor transition (TMS ˜ 225 K). However, La0.5Ce0.5Mn1-xCo0.05O3 manganites show semiconducting behavior throughout temperature range. The magnetic susceptibility measurement confirms that both the samples undergo a transition from paramagnetic to ferromagnetic phase. The metallic resistivity (T < TMS) is analyzed by considering the electron-electron, electron-phonon and spin fluctuation mechanism while semiconducting resistivity is fitted with small polaron conduction model.

  2. Degenerate rhombohedral and orthorhombic states in Ca-substituted Na0.5Bi0.5TiO3

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajeev; Kothai, V.; Garg, Rohini; Agrawal, Anupriya; Senyshyn, Anatoliy; Boysen, Hans

    2009-07-01

    Neutron powder diffraction and temperature dependent dielectric studies were carried out on Ca-substituted Na0.5Bi0.5TiO3, i.e., (Na0.5Bi0.5)1-xCaxTiO3. Stabilization of an orthorhombic phase even at a low Ca concentration (0.050.5Bi0.5TiO3 (NBT) is susceptible to orthorhombic distortion. The orthorhombic and rhombohedral phases coexist for x =0.10, suggesting these phases to be nearly degenerate. The orthorhombic distortion favoring tendency of Ca assists in promoting the inherent instability with regard to this structure in pure NBT, which was reported recently.

  3. Transport and photoresponse properties in Pr0.5Ca0.5CoO3/Nb-SrTiO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, S. G.; Gu, A.; Yan, X. L.; Hao, L. M.; Xie, Y.; Zhang, T.; Jin, K. X.

    2015-01-01

    Transport and photoresponse properties of the heterostructure consisting of a Pr0.5Ca0.5CoO3 film and a Nb-SrTiO3 substrate were investigated. The Pr0.5Ca0.5CoO3 film exhibits semiconducting behavior and the resistances are decreased when irradiated by a 532 nm laser. The rectifying behaviors are observed in the heterostructure. The ideality factors and the diffusion voltages monotonically decrease with increasing the temperature. The photovoltatges of the heterostructure under the irradiation approach the saturation at about 8.5 \\text{mW/mm}2 . The minority carrier lifetime of τp=0.281 \\text{s} is estimated from the time response properties in the falling process of photovoltages. These results reveal that the Pr0.5Ca0.5CoO3 heterostructures have great potentials in photoresponse and photoelectric conversion applications.

  4. Quantification of multiple sclerosis lesion volumes in 1.5 and 0.5 T anisotropically filtered and unfiltered MR exams.

    PubMed

    Mitchell, J R; Karlik, S J; Lee, D H; Eliasziw, M; Rice, G P; Fenster, A

    1996-01-01

    Recently, guidelines for the use of MRI in the monitoring of MS have recommended the use of imaging systems with mid-field (0.5-1.0 T) or high-field (greater than 1.0 T) strengths. Higher field strengths provide many advantages, including increased signal-to-noise ratios (SNR). SNR also may be increased by post-processing algorithms that reduce noise. In this paper we evaluate the impact on operator variability of (a) lesion quantification in high-field (1.5 T) versus mid-field (0.5 T) exams; and (b) an anisotropic diffusion filter algorithm that reduces image noise without blurring or moving object boundaries. Inter- and intra-operator reliability and variability were studied using repeated quantification of lesions in 1.5 and 0.5 T filtered and unfiltered MR exams of a MS patient. Results indicate that inter-operator variability in 1.5 T unfiltered exams was 0.34 cm3 and was significantly larger than that in 1.5 T filtered (0.27 cm3), 0.5 T unfiltered (0.26 cm3), and 0.5 T filtered (0.24 cm3) exams. Similarly, intra-operator variability in 1.5 T unfiltered exams was 0.23 cm3 and was significantly larger than that in 1.5 T filtered (0.19 cm3), 0.5 T unfiltered (0.19 cm3), and 0.5 T filtered (0.18 cm3) exams. In addition, the minimum significant change between two successive measurements of lesion volume by the same operator, was 0.64 cm3 in 1.5 T unfiltered exams, but 0.53 cm3 or less in other exams. For two different operators making successive measurements, the minimum significant change was 0.94 cm3 in 1.5 T unfiltered exams, but only 0.75 cm3 or less in other exams. Finally, the number of lesions to be monitored for an average change in volume at a given power and significance level was greater by 30%-60% for quantification in 1.5 T unfiltered exams. These results suggest that inter- and intra-operator variability are reduced by anisotropic filtering, and by quantification in 0.5 T exams. Reduced operator variabilities may result from higher detail signal

  5. Distortional phase transitions accompanying spin reorientation in the intermetallide Tb/sub 0. 5/Nd/sub 0. 5/Fe/sub 2/

    SciTech Connect

    Ilyushin, A.S.; Kakhadze, S.O.; Makhmud, I.A.

    1988-01-01

    The thermal expansion and spin reorientation in the intermetallide Tb/sub 0.5/Nd/sub 0.5/Fe/sub 2/ at temperatures ranging from 4.2 to 300/sup 0/K were studied by the method of low-temperature x-ray diffractometry. It was established that with spin reorientation in Tb/sub 0.5/Nd/sub 0.5/Fe/sub 2/ the orientation of the magnetic moment vector changes from <111> to <110> with the formation of corner magnetic phases.

  6. Synthesis and characterization of FeSe1-xTex (x=0, 0.5, 1) superconductors

    NASA Astrophysics Data System (ADS)

    Zargar, Rayees A.; Hafiz, A. K.; Awana, V. P. S.

    2015-08-01

    In this study, FeTe1-xSex (x=0,0.5,1) samples were prepared by conventional solid state reaction method and investigated by powder XRD, SEM, Raman and resistivity measurement techniques to reveal the effect of tellurium (Te) substitution in FeSe matrix. Rietveld analysis was performed on room temperature recorded, X-ray diffraction (XRD) patterns of pure FeSe, FeTe and FeSe0.5Te0.5 which shows that all the compounds are crystallized in a tetragonal structure. SEM images show the dense surface morphology. Raman spectra recorded in the range from 100 to 700 cm-1 at ambient temperature has been interpreted by P4/nmm space group of the lattice. The variation in intensity and shift in peak positions of some phonon modes has been discussed on the basis of variation in crystalline field effect by substituting Te in FeSe lattice. The resistivity versus temperature curves reveals that FeSe becomes superconductor at 7 K and FeSe0.5Te0.5 shows superconductivity below 14 K while FeTe is non-superconducting compound.

  7. Fully gapped superconductivity in In-doped topological crystalline insulator Pb0.5Sn0.5Te

    SciTech Connect

    Du, Guan; Gu, G. D.; Du, Zengyi; Fang, Delong; Yang, Huan; Zhong, R. D.; Schneeloch, J.; Wen, Hai -Hu

    2015-07-27

    In this study, superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb0.5Sn0.5Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb0.5Sn0.5)0.7In0.3Te is produced by In doping in Pb0.5Sn0.5Te, and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb0.5Sn0.5)0.7In0.3Te on a (001)-oriented surface. The spectrum can be well fitted by an anisotropic s-wave gap function of Δ = 0.72 + 0.18cos4θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.

  8. Transition metal redox and Mn disproportional reaction in LiMn0.5Fe0.5PO4 electrodes cycled with aqueous electrolyte

    NASA Astrophysics Data System (ADS)

    Zhuo, Zengqing; Hu, Jiangtao; Duan, Yandong; Yang, Wanli; Pan, Feng

    2016-07-01

    We performed soft x-ray absorption spectroscopy (sXAS) and a quantitative analysis of the transition metal redox in the LiMn0.5Fe0.5PO4 electrodes upon electrochemical cycling. In order to circumvent the complication of the surface reactions with organic electrolyte at high potential, the LiMn0.5Fe0.5PO4 electrodes are cycled with aqueous electrolyte. The analysis of the transitional metal L-edge spectra allows a quantitative determination of the redox evolution of Mn and Fe during the electrochemical cycling. The sXAS analysis reveals the evolving Mn oxidation states in LiMn0.5Fe0.5PO4. We found that electrochemically inactive Mn2+ is formed on the electrode surface during cycling. Additionally, the signal indicates about 20% concentration of Mn4+ at the charged state, providing a strong experimental evidence of the disproportional reaction of Mn3+ to Mn2+ and Mn4+ on the surface of the charged LiMn0.5Fe0.5PO4 electrodes.

  9. Effect of rare-earth (Er and Gd) substitution on the magnetic and multiferroic properties of DyFe0.5Cr0.5O3.

    PubMed

    Sharma, Mohit K; Basu, Tathamay; Mukherjee, K; Sampathkumaran, E V

    2016-10-26

    We report the results of our investigations on the influence of partial substitution of Er and Gd for Dy on the magnetic and magnetoelectric properties of DyFe0.5Cr0.5O3, which is known to be a multiferroic system. Magnetic susceptibility and heat capacity data, apart from confirming the occurrence of magnetic transitions at ~121 and 13 K in DyFe0.5Cr0.5O3, bring out that the lower transition temperature only is suppressed by rare-earth substitution. Multiferroic behavior is found to persist in Dy0.4Ln0.6Fe0.5Cr0.5O3 (Ln  =  Er and Gd). There is an evidence for magnetoelectric coupling in all these materials with qualitative differences in its behavior as the temperature is changed across these two transitions. Remnant electric polarization is observed for all the compounds. The most notable observation is that electric polarization is seen to get enhanced as a result of rare-earth substitution with respect to that in DyFe0.5Cr0.5O3. Interestingly, a similar trend is seen in the magnetocaloric effect, consistent with the existence of magnetoelectric coupling. The results thus provide evidence for the tuning of magnetoelectric coupling by rare-earth substitution in this family of oxides. PMID:27588356

  10. Research on Cs activation mechanism for Ga0.5Al0.5As(0 0 1) and GaN(0 0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Shen, Yang; Chen, Liang; Qian, Yunsheng; Dong, Yanyan; Zhang, Shuqin; Wang, Meishan

    2015-01-01

    Based on first-principle density functional theory (DFT), plane wave with ultrasoft pseudopotential method was used to calculate and compare the Cs activation mechanism for Ga0.5Al0.5As(0 0 1) surface and GaN(0 0 0 1) surface. In this work, eight possible Cs adsorption sites are chosen for the Ga0.5Al0.5As(0 0 1) surface while five high-symmetry sites are considered in the calculation model of GaN(0 0 0 1) surface. Results show that Cs adsorption lowers the surface work function and benefits to get the most stable adsorption sites. Then dipole moment with different Cs coverage on two surfaces is investigated. The dipole moment decreases with the increase of Cs coverage and GaN(0 0 0 1) surface changes more obviously than Ga0.5Al0.5As(0 0 1) surface. The repulsion between Cs atomic dipole-dipole is enhanced and it causes depolarization and work function rising again. Finally, an activation experiment is performed to verify the result of our calculations, GaN photocathodes gets the minimum work function earlier than Ga0.5Al0.5As photocathodes.

  11. Thermal Conductivities and Thermal Expansion Coefficients of (Sm0.5Gd0.5)2(Ce1- x Zr x )2O7 Ceramics

    NASA Astrophysics Data System (ADS)

    Hongsong, Zhang; Lei, Shi; Yongde, Zhao; Gang, Li; Zhenjun, Li

    2015-09-01

    The (Sm0.5Gd0.5)2(Ce1- x Zr x )2O7 oxides were prepared by solid-state reaction, and their phase compositions, microstructures, and thermophysical properties were investigated. Results of x-ray diffraction reveal that pure (Sm0.5Gd0.5)2(Ce1- x Zr x )2O7 oxides with fluorite structure are successfully synthesized in the current study. The thermal expansion coefficient decreases with increasing content of ZrO2, which is higher than that of 7 wt.% yttria-stabilized zirconia (YSZ). The substitution of Zr4+ for Ce4+ reduces the thermal conductivity of Sm2Ce2O7 oxide. The thermal conductivity decreases from 1.69 W/m K ( x = 0) to 1.22 W/m K ( x = 0.3) at 1000 °C. The composition with x = 0.3 exhibits the lowest thermal conductivity at all temperatures, and the thermal conductivity of (Sm0.5Gd0.5)2 (Ce1- x Zr x )2O7 ceramics was obviously lower than those of fully dense 7 wt.% YSZ. These results suggested promising potential applications of the (Sm0.5Gd0.5)2 (Ce1- x Zr x )2O7 ceramics for high-temperature thermal barrier coatings.

  12. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex. PMID:26032295

  13. Structural, thermal and electrical conductivity characteristics of Ln{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} (Ln: La, Nd and Sm) complex perovskites as anode materials for solid oxide fuel cell

    SciTech Connect

    Jeong, Jihoon; Azad, Abul K.; Schlegl, Harald; Kim, Byungjun; Baek, Seung-Wook; Kim, Keunsoo; Kang, Hyunil; Kim, Jung Hyun

    2015-03-15

    The Ti and Mn replaced complex perovskites, Ln{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} (Ln: La, Nd and Sm), were reported as potential anode materials for high temperature-operating solid oxide fuel cells (HT-SOFCs). For the present research study, synthesis, crystallographic, thermal and electrical conductivity properties of Ln{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} complex perovskites were investigated using X-ray diffraction (XRD), Rietveld method, thermogravimetric analysis (TGA) and electrical conductivity to apply these oxide materials for the HT-SOFC anode materials. XRD results showed that Ln{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} oxide systems synthesized as single phases did not react with 8 mol% yttria stabilized zirconia (8YSZ) and 10 mol% Gd-doped cerium oxide (CGO91) up to 1500 °C and did not decompose under dry 3.9% hydrogen at 850 °C. The crystal structures of La{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} (LSTM), Nd{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} (NSTM) and Sm{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d} (SSTM) showed orthorhombic symmetry with the space group Pbnm and SSTM showed a more distorted structure. Thermogravimetric analysis (TGA) proved weight gains in these three sample occurred under oxidizing conditions and weight loss under reducing conditions. Electrical conductivity values of NSTM were higher than those of LSTM and SSTM under oxidizing and reducing conditions. - Graphical abstract: The B-site cations (Ti/Mn) are surrounded by regular octahedra of oxygen in Nd{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Mn{sub 0.5}O{sub 3±d}(NSTM). These octahedra are linked together in a corner sharing three dimensional framework, while Nd/Sr ion occupies 12-coordinated A-site between these octahedra. The Ti/Mn–O{sub 6} octahedra are elongated along the c-axis. The crystal structure distortion was due to the smaller ionic radius of the A-site cations, which force the (Ti

  14. Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics

    NASA Astrophysics Data System (ADS)

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

  15. Fabrication of (111)-oriented Ca{sub 0.5}Sr{sub 0.5}IrO{sub 3}/SrTiO{sub 3} superlattices—A designed playground for honeycomb physics

    SciTech Connect

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca{sub 0.5}Sr{sub 0.5}IrO{sub 3} perovskite and two layers of SrTiO{sub 3} perovskite on SrTiO{sub 3}(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

  16. Effect of impurity substitution on band structure and mass renormalization of the correlated FeTe0.5Se0.5 superconductor

    NASA Astrophysics Data System (ADS)

    Thirupathaiah, S.; Fink, J.; Maheshwari, P. K.; Kishore, V. V. Ravi; Liu, Z.-H.; Rienks, E. D. L.; Büchner, B.; Awana, V. P. S.; Sarma, D. D.

    2016-05-01

    Using angle-resolved photoemission spectroscopy (ARPES), we studied the effect of the impurity potential on the electronic structure of FeTe0.5Se0.5 superconductor by substituting 10% of Ni for Fe, which leads to an electron doping of the system. We could resolve three hole pockets near the zone center and an electron pocket near the zone corner in the case of FeTe0.5Se0.5 , whereas only two hole pockets near the zone center and an electron pocket near the zone corner are resolved in the case of Fe0.9Ni0.1Te0.5Se0.5 , suggesting that the hole pocket having predominantly the x y orbital character is very sensitive to the impurity scattering. Upon electron doping, the size of the hole pockets decreases and the size of the electron pockets increases as compared to the host compound. However, the observed changes in the size of the electron and hole pockets are not consistent with the rigid-band model. Moreover, the effective mass of the hole pockets is reduced near the zone center and of the electron pockets is increased near the zone corner in the doped Fe0.9Ni0.1Te0.5Se0.5 as compared to FeTe0.5Se0.5 . We refer these observations to the changes of the spectral function due to the effect of the impurity potential of the dopants.

  17. Structural and Mössbauer spectroscopy characterization of bulk and nanostructured TiFe0.5 Ni0.5/graphite compounds and their hydrides

    NASA Astrophysics Data System (ADS)

    Martínez, M. A. R.; André-Filho, J.; Félix, L. L.; Coaquira, J. A. H.; Garg, V. K.; Oliveira, A. C.; Mestnik-Filho, J.

    2015-06-01

    The structural and hyperfine properties of bulk TiFe0.5Ni0.5 intermetallic and ball-milled TiFe0.5Ni0.5/graphite compounds and their hydrides have been studied. The bulk and nanostructured TiFe0.5Ni0.5 compounds crystallize in the cubic crystal structure of CsCl (B2). After hydrogenation, the formation of hydrogen-poor phase (∝-phase) and hydride phase ( β-phase) have been determined for the bulk compound. However, the formation of the ∝-phase and the hydrogen-richest phase ( γ-phase) and other secondary phases have been determined for the ball-milled TiFe0.5Ni0.5/graphite sample. It has been determined that the ball-milled TiFe0.5Ni0.5/graphite sample presents a large amount of the γ-phase which indicates that the presence of graphite nearby nanostructured intermetallic grains enhances the absorption of hydrogen. Mossbauer results are consistent with the structural results. Meanwhile, no significant changes in the isomer shift (IS) value has been determined for the α-phase with respect to the intermetallic compound, a strong increase in the IS value has been determined for the β- and γ-phases with respect to the ∝-phase. That increase indicates a decrease of the s-electron density at the Fe nuclei due to the charge transfer from the metal to the nearby hydrogen atoms.

  18. Effects of A-site nonstoichiometry on oxide ion conduction in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Prasertpalichat, Sasiporn; Schmidt, Whitney; Cann, David P.

    2016-06-01

    Lead free 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by ˜3-4 orders of magnitude and an associated activation energy of 1.57eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities (ρ˜103Ω-cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi0.5Na0.5)TiO3. Long term annealing studies were also conducted at 800∘C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 ceramics are very sensitive to Bi/Na stoichiometry.

  19. A Gel-Polymer Sn-C/LiMn0.5Fe0.5PO4 Battery Using a Fluorine-Free Salt.

    PubMed

    Di Lecce, Daniele; Fasciani, Chiara; Scrosati, Bruno; Hassoun, Jusef

    2015-09-30

    Safety and environmental issues, because of the contemporary use of common liquid electrolytes, fluorinated salts, and LiCoO2-based cathodes in commercial Li-ion batteries, might be efficiently mitigated by employing alternative gel-polymer battery configurations and new electrode materials. Herein we study a lithium-ion polymer cell formed by combining a LiMn0.5Fe0.5PO4 olivine cathode, prepared by simple solvothermal pathway, a nanostructured Sn-C anode, and a LiBOB-containing PVdF-based gel electrolyte. The polymer electrolyte, here analyzed in terms of electrochemical stability by impedance spectroscopy (EIS) and voltammetry, reveals full compatibility for cell application. The LiBOB electrolyte salt and the electrochemically delithiaded Mn0.5Fe0.5PO4 have a higher thermal stability compared to conventional LiPF6 and Li0.5CoO2, as confirmed by thermogravimetric analysis (TGA) and by galvanostatic cycling at high temperature. LiMn0.5Fe0.5PO4 and Sn-C, showing in lithium half-cell a capacity of about 120 and 350 mAh g(-1), respectively, within the gelled electrolyte configuration are combined in a full Li-ion polymer battery delivering a stable capacity of about 110 mAh g(-1), with working voltage ranging from 2.8 to 3.6 V. PMID:26348604

  20. Characterization of Cu3P phase in Sn3.0Ag0.5Cu0.5P/Cu solder joints

    NASA Astrophysics Data System (ADS)

    Chen, Jian-xun; Zhao, Xing-ke; Zou, Xu-chen; Huang, Ji-hua; Hu, Hai-chun; Luo, Hai-lian

    2014-01-01

    This article reports the effects of phosphorus addition on the melting behavior, microstructure, and mechanical properties of Sn3.0Ag0.5Cu solder. The melting behavior of the solder alloys was determined by differential scanning calorimetry. The interfacial microstructure and phase composition of solder/Cu joints were studied by scanning electron microscopy and energy dispersive spectrometry. Thermodynamics of Cu-P phase formation at the interface between Sn3.0Ag0.5Cu0.5P solder and the Cu substrate was characterized. The results indicate that P addition into Sn3.0Ag0.5Cu solder can change the microstructure and cause the appearance of rod-like Cu3P phase which is distributed randomly in the solder bulk. The Sn3.0Ag0.5Cu0.5P joint shows a mixture of ductile and brittle fracture after shear testing. Meanwhile, the solidus temperature of Sn3.0Ag0.5Cu solder is slightly enhanced with P addition.

  1. Effect of Zn2+ Substitution on the Structure and Magnetic Properties of Co0.5Cu0.5Fe2O4 Synthesized by Solvothermal Method

    NASA Astrophysics Data System (ADS)

    Huang, Xusheng; Zhou, Yuan; Wu, Wenwei; Xu, Jiawei; Liu, Shangqian; Liu, Dongsheng; Wu, Juan

    2016-06-01

    A series of Zn2+ doped Co-Cu ferrites with the formula Co0.5Cu0.5- x Zn x Fe2O4 (0.0 ≤ x ≤ 0.3) have been successfully synthesized using the solvothermal method. X-ray diffraction and scanning electron microscopy results indicate that a high-crystallized cubic Co0.5Cu0.5- x Zn x Fe2O4 with rod-like structure is obtained when the precursor is calcined at 800°C in air for 3 h. The lattice parameters increase with the increase of Zn2+ additional amount, attributed to the larger ionic radius of the substituted ion Zn2+ than Cu2+ ionic radius. Zn2+ substitution can improve the magnetic properties of Co0.5Cu0.5- x Zn x Fe2O4. Co0.5Cu0.4Zn0.1Fe2O4 obtained at 800°C has the highest specific saturation magnetization (73.7 ± 0.9 emu/g) and magnetic moment (3.13 ± 0.04 B.M.).

  2. Temperature dependent structures and properties of Bi0.5Na0.5TiO3-based lead free piezoelectric composite.

    PubMed

    Zhang, Ji; Sun, Lei; Geng, Xiao-Yu; Zhang, Bin-Bin; Yuan, Guo-Liang; Zhang, Shan-Tao

    2016-07-01

    The thermal depolarization around 100 °C of the Bi0.5Na0.5TiO3-based piezoelectric solid solutions leads to the disappearance of macroscopic ferroelectric/piezoelectric properties and remains a long-standing obstacle for their actual applications. In this communication, we report lead-free piezoelectric composites of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3:0.5ZnO (BNT-6BT:0.5ZnO, where 0.5 is the mole ratio of ZnO to BNT-6BT) with deferred thermal depolarization, which is experimentally confirmed by systematic temperature dependent dielectric, ferroelectric, piezoelectric measurements. Especially, based on temperature dependent X-ray diffraction measurements on unpoled and poled samples, thermal depolarization is confirmed to have no relationship with the structural phase transition, the possible mechanism for the deferred thermal depolarization is correlated with the ZnO-induced local electric field which can suppress the depolarization field. We believe our results may be helpful for understanding the origin of thermal depolarization in BNT-based piezoelectric materials, and thus provide an effective way to overcoming this obstacle. PMID:27334673

  3. La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowders prepared by the hydrothermal method

    SciTech Connect

    Putjuso, Thanin; Maensiri, Santi; Hunpratub, Sitchai; Swatsitang, Ekaphan

    2012-09-15

    Graphical abstract: LRTEM image of the single-phase La{sub 0.5}Sr{sub 0.5}TiO{sub 3} particles. It is seen from the figure that the product has a plate-like morphology with average particles sizes in the range of 100–300 nm. In addition, the SAED data taken from an individual particle (lower inset) shows the presence of sharp diffraction rings, which are indicative of polycrystalline La{sub 0.5}Sr{sub 0.5}TiO{sub 3} formation. The high-resolution TEM image (upper inset) shows for further confirmation of a crystalline structure of La{sub 0.5}Sr{sub 0.5}TiO{sub 3} powder. This image shows a clearly resolved crystalline domain with uniform interplanar spacing of 0.276 nm. Highlights: ► La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowder is prepared in 2 M KOH solution by hydrothermal method. ► The solution is heat treated at 220 °C for 24 h in air. ► LRTEM reveals a plate-like morphology of particle with average size of 100–300 nm. ► HRTEM image shows a crystalline domain with interplanar spacing of 0.276 nm. -- Abstract: La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowders were prepared by the hydrothermal method. The influence of processing parameters, including KOH concentration, reaction temperature and reaction time on the obtained products were studied. The structure and morphology of the obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that pure phase La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowders can be successfully synthesized with 2 M KOH concentration at a low temperature of 220 °C for 24 h. In addition, the product has a plate-like shape with particle sizes in the range of 25–100 nm as estimated by TEM.

  4. Enhanced nanoscale resistive switching memory characteristics and switching mechanism using high-Ge-content Ge0.5Se0.5 solid electrolyte

    PubMed Central

    2012-01-01

    We demonstrate enhanced repeatable nanoscale bipolar resistive switching memory characteristics in Al/Cu/Ge0.5Se0.5/W, as compared with Al/Cu/Ge0.2Se0.8/W structures, including stable AC endurance (>105 cycles), larger average SET voltage (approximately 0.6 V), excellent data retention (>105 s) at 85°C, and a high resistance ratio (>104) with a current compliance of 8 μA and a small operation voltage of ±1.5 V. A small device size of 150 × 150 nm2 and a Cu nanofilament with a small diameter of 30 nm are both observed by high-resolution transmission electron microscope in the SET state. The GexSe1 − x solid electrolyte compositions are confirmed by both energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The switching mechanism relies on the smaller barrier heights for holes rather than for electrons; the positively charged Cuz+ ions (i.e., holes) migrate through the defects in the GexSe1 − x solid electrolytes during SET/RESET operations. Hence, the Cu nanofilament starts to grow at the Ge0.5Se0.5/W interface, and starts to dissolve at the Cu/Ge0.5Se0.5 interface, as illustrated in the energy band diagrams. Owing to both the higher barrier for hole injection at the Cu/Ge0.5Se0.5 interface than at the Cu/Ge0.2Se0.8 interface and greater thermal stability, the resistive switching memory characteristics of the Al/Cu/Ge0.5Se0.5/W are improved relative to the Al/Cu/Ge0.2Se0.8/W devices. The Al/Cu/Ge0.5Se0.5/W memory device can also be operated with a low current compliance of 1 nA, and hence, a low SET/RESET power of 0.61 nW/6.4 pW is achieved. In addition, a large memory size of 1,300 Pbit/in2 is achieved with a small nanofilament diameter of 0.25 Å for a small current compliance of 1 nA. PMID:23130908

  5. Microwave characterization of Pb1-xCaxFe0.5Nb0.5O3 multiferroics at X-band

    NASA Astrophysics Data System (ADS)

    Dhiman, Tanvi; Singh, Charanjeet; Puri, Maalti; Kaur, Harpreet; Kaur, Randeep; Bindra Narang, S.

    2015-10-01

    The microwave characteristics of Pb1- x Ca x Fe0.5Nb0.5O3 multiferroics ( x = 0.0, 0.4, 0.45, 0.5, 0.55, 0.6), have been investigated as a function of frequency and substitution. The results depict -13.99 dB reflection loss at 11.65 GHz in composition x = 0.6. Microwave absorption is enhanced with substitution of Ca2+ ions and undoped composition 0.0 behaves as electromagnetic shield. The model governing microwave absorption is discussed and different compositions for electromagnetic applications have been suggested.

  6. A mixed iron-manganese based pyrophosphate cathode, Na2Fe0.5Mn0.5P2O7, for rechargeable sodium ion batteries.

    PubMed

    Shakoor, Rana A; Park, Chan Sun; Raja, Arsalan A; Shin, Jaeho; Kahraman, Ramazan

    2016-02-01

    The development of secondary batteries based on abundant and cheap elements is vital. Among various alternatives to conventional lithium-ion batteries, sodium-ion batteries (SIBs) are promising due to the abundant resources and low cost of sodium. While there are many challenges associated with the SIB system, cathode is an important factor in determining the electrochemical performance of this battery system. Accordingly, ongoing research in the field of SIBs is inclined towards the development of safe, cost effective cathode materials having improved performance. In particular, pyrophosphate cathodes have recently demonstrated decent electrochemical performance and thermal stability. Herein, we report the synthesis, electrochemical properties, and thermal behavior of a novel Na2Fe0.5Mn0.5P2O7 cathode for SIBs. The material was synthesized through a solid state process. The structural analysis reveals that the mixed substitution of manganese and iron has resulted in a triclinic crystal structure (P1[combining macron] space group). Galvanostatic charge/discharge measurements indicate that Na2Fe0.5Mn0.5P2O7 is electrochemically active with a reversible capacity of ∼80 mA h g(-1) at a C/20 rate with an average redox potential of 3.2 V. (vs. Na/Na(+)). It is noticed that 84% of initial capacity is preserved over 90 cycles showing promising cyclability. It is also noticed that the rate capability of Na2Fe0.5Mn0.5P2O7 is better than Na2MnP2O7. Ex situ and CV analyses indicate that Na2Fe0.5Mn0.5P2O7 undergoes a single phase reaction rather than a biphasic reaction due to different Na coordination environment and different Na site occupancy when compared to other pyrophosphate materials (Na2FeP2O7 and Na2MnP2O7). Thermogravimetric analysis (25-550 °C) confirms good thermal stability of Na2Fe0.5Mn0.5P2O7 with only 2% weight loss. Owing to promising electrochemical properties and decent thermal stability, Na2Fe0.5Mn0.5P2O7, can be an attractive cathode for SIBs. PMID

  7. Investigations of sol gel-derived highly (100)-oriented Ba0.5Sr0.5TiO3 : MgO composite thin films for phase-shifter applications

    NASA Astrophysics Data System (ADS)

    Jain, M.; Majumder, S. B.; Katiyar, R. S.; Bhalla, A. S.; Miranda, F. A.; van Keuls, F. W.

    2005-02-01

    Sol gel deposition of highly oriented Ba0.5Sr0.5TiO3 : MgO composite thin films has shown desirable dielectric constant reduction and higher figure of merit for phase-shifter applications. In this multilayer configuration, MgO distributed homogeneously through the Ba0.5Sr0.5TiO3 (BST50) matrix, and it helped in tailoring the dielectric constant and reducing the loss tangent significantly. In the present study, the high-frequency dielectric behavior of the films has been evaluated by fabricating an eight-element coupled microstrip phase shifter and measuring the degree of phase shift and insertion loss as a function of applied voltage at room temperature. An increase in phase-shifter figure of merit (degree of phase shift per dB insertion loss) from 28°/dB for pure BST50 to 71°/dB for a BST50 : MgO film (at 14 GHz and 333 kV/cm) has been observed.

  8. Magnetic penetration-depth measurements of a suppressed superfluid density of superconducting Ca0.5Na0.5Fe2As2 single crystals by proton irradiation

    NASA Astrophysics Data System (ADS)

    Kim, Jeehoon; Haberkorn, N.; Graf, M. J.; Usov, I.; Ronning, F.; Civale, L.; Nazaretski, E.; Chen, G. F.; Yu, W.; Thompson, J. D.; Movshovich, R.

    2012-10-01

    We report on the dramatic effect of random point defects, produced by proton irradiation, on the superfluid density ρs in superconducting Ca0.5Na0.5Fe2As2 single crystals. The magnitude of the suppression is inferred from measurements of the temperature-dependent magnetic penetration depth λ(T) using magnetic force microscopy. Our findings indicate that a radiation dose of 2×1016 cm-2 produced by 3 MeV protons results in a reduction of the superconducting critical temperature Tc by approximately 10%. In contrast, ρs(0) is suppressed by approximately 60%. This breakdown of the Abrikosov-Gorkov theory may be explained by the so-called “Swiss cheese model,” which accounts for the spatial suppression of the order parameter near point defects similar to holes in Swiss cheese. Both the slope of the upper critical field and the penetration depth λ(T/Tc)/λ(0) exhibit similar temperature dependences before and after irradiation. This may be due to a combination of the highly disordered nature of Ca0.5Na0.5Fe2As2 with large intraband and simultaneous interband scattering as well as the s±-wave nature of short coherence length superconductivity.

  9. Upper Critical Field, Critical Current Density and Activation Energy of the New La1-xSmxO0.5F0.5BiS2 (x = 0.2, 0.8) Superconductors

    NASA Astrophysics Data System (ADS)

    Kalai Selvan, Ganesan; Singh Thakur, Gohil; Manikandan, Krishnan; Uwatoko, Yoshia; Haque, Zeba; Gupta, Laxmi Chand; Ganguli, Ashok Kumar; Arumugam, Sonachalam

    2015-12-01

    Critical current density (Jc), thermal activation energy (U0), and upper critical field (Hc2) of La1-xSmxO0.5F0.5BiS2 (x = 0.2, 0.8) superconductors are investigated from magnetic field dependent ρ(T) studies. The estimated upper critical field (Hc2) has low values of 1.04 T for x = 0.2 and 1.41 T for x = 0.8. These values are lower than Sm free LaO0.5F0.5BiS2 superconductor (1.9 T). The critical current density (Jc) is estimated to be 1.35 × 105 and 5.07 × 105 A/cm2 (2 K) for x = 0.2 and 0.8 respectively, using the Bean's model. The thermal activation energy (U0/kB) is 61 K for x = 0.2 and 140 K for x = 0.8 as calculated from Arrhenius plots at low magnetic field (1 T) and indicates a strong flux pinning potential which might be co-existing with applied magnetic field.

  10. Terahertz conductivity of topological surface states in Bi1.5Sb0.5Te1.8Se1.2

    PubMed Central

    Tang, Chi Sin; Xia, Bin; Zou, Xingquan; Chen, Shi; Ou, Hong-Wei; Wang, Lan; Rusydi, A.; Zhu, Jian-Xin; Chia, Elbert E. M.

    2013-01-01

    Topological insulators are electronic materials with an insulating bulk and conducting surface. However, due to free carriers in the bulk, the properties of the metallic surface are difficult to detect and characterize in most topological insulator materials. Recently, a new topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was found, showing high bulk resistivities of 1–10 Ω.cm and greater contrast between the bulk and surface resistivities compared to other Bi-based topological insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity of BSTS single crystals, disentangling the surface and bulk contributions. We find that the Drude spectral weight is 1–2 orders of magnitude smaller than in other Bi-based topological insulators, and similar to that of Bi2Se3 thin films, suggesting a significant contribution of the topological surface states to the conductivity of the BSTS sample. Moreover, an impurity band is present about 30 meV below the Fermi level, and the surface and bulk carrier densities agree with those obtained from transport data. Furthermore, from the surface Drude contribution, we obtain a ~98% transmission through one surface layer — this is consistent with the transmission through single-layer or bilayer graphene, which shares a common Dirac-cone feature in the band structure. PMID:24343202

  11. 47 CFR 0.5 - General description of Commission organization and operations.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false General description of Commission organization and operations. 0.5 Section 0.5 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL COMMISSION ORGANIZATION Organization General § 0.5 General description of Commission organization and operations. (a) Principal staff units. The Commission...

  12. 30 CFR 57.22233 - Actions at 0.5 percent methane (I-C mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 0.5 percent methane (I-C mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22233 Actions at 0.5 percent methane (I-C mines). If methane reaches 0.5 percent in the mine atmosphere, ventilation...

  13. 17 CFR 270.0-5 - Procedure with respect to applications and other matters.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Procedure with respect to applications and other matters. 270.0-5 Section 270.0-5 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) RULES AND REGULATIONS, INVESTMENT COMPANY ACT OF 1940 § 270.0-5...

  14. Effects of capping on GaN quantum dots deposited on Al{sub 0.5}Ga{sub 0.5}N by molecular beam epitaxy

    SciTech Connect

    Korytov, M.; Benaissa, M.; Huault, T.; Neisius, T.

    2009-04-06

    The impact of the capping process on the structural and morphological properties of GaN quantum dots (QDs) grown on fully relaxed Al{sub 0.5}Ga{sub 0.5}N templates was studied by transmission electron microscopy. A morphological transition between the surface QDs, which have a pyramidal shape, and the buried ones, which have a truncated pyramid shape, is evidenced. This shape evolution is accompanied by a volume change: buried QDs are bigger than surface ones. Furthermore a phase separation into Al{sub 0.5}Ga{sub 0.5}N barriers was observed in the close vicinity of buried QDs. As a result, the buried QDs were found to be connected with the nearest neighbors by thin Ga-rich zones, whereas Al-rich zones are situated above the QDs.

  15. Thermoelectric properties of PbSe0.5Te0.5: x (PbI2) with endotaxial nanostructures: a promising n-type thermoelectric material

    NASA Astrophysics Data System (ADS)

    Rawat, P. K.; Paul, B.; Banerji, P.

    2013-05-01

    In the present investigation, we report on the thermoelectric properties of PbSe0.5Te0.5: x (PbI2) from room temperature to 625 K. High-resolution transmission electron micrographs of the samples reveal endotaxial nanostructures embedded in a PbSe0.5Te0.5 matrix. The combined effect of mass fluctuation and nanostructures reduces the thermal conductivity to a great extent compared to PbTe and PbSe, without affecting the carrier mobility. As a result, a thermoelectric figure of merit with a value of 1.5 is achieved at 625 K. This value is significantly higher than that of the available state-of-the-art n-type materials.

  16. Static and dynamic magnetic characteristics of BaCo 0.5Mn 0.5Ti 1.0Fe 10O 19

    NASA Astrophysics Data System (ADS)

    Choopani, Saeed; Keyhan, Neda; Ghasemi, Ali; Sharbathi, Ali; Maghsoudi, Iman; Eghbali, Mohammad

    2009-07-01

    The effect of Mn 2+Co 2+Ti 4+ substitution on microwave absorption has been studied for BaCo 0.5Mn 0.5Ti 1.0Fe 10O 19 ferrite-acrylic resin composites in frequency range from 12 to 20 GHz. X-ray diffraction (XRD), scanning electron microscope (SEM), vibrating sample magnetometer, AC susceptometer and vector network analyzer were used to analyze the structural, magnetic and microwave absorption properties. The results showed that the magnetoplumbite structures for all samples have been formed. Based on microwave measurement on reflectivity, BaCo 0.5Mn 0.5Ti 1.0Fe 10O 19 may be a good candidate for electromagnetic compatibility and other practical applications at high frequency.

  17. Electric field-induced tuning of magnetism in PbFe{sub 0.5}Nb{sub 0.5}O{sub 3} at room temperature

    SciTech Connect

    Rayaprol, S. E-mail: brangadi@gmail.com; Mukherjee, S.; Kaushik, S. D.; Matteppanavar, S.; Angadi, B. E-mail: brangadi@gmail.com

    2015-08-07

    We study the influence of electrical poling, carried out at room temperature, on the structure and magnetism of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} by analyzing the differences observed in structural and magnetic properties before and after the electrical poling. The changes observed in magnetization of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} before and after electrical poling exhibit considerably strong converse magnetoelectric effect at room temperature. In addition, the strengthening of Fe/Nb-O bond due to electrical poling is discussed on the basis of Raman spectral studies and analysis of neutron diffraction patterns. The potential tunability of magnetization with electrical poling can be an ideal tool for realization of application potential of this multiferroic material.

  18. Ultrahigh strain response with fatigue-free behavior in (Bi0.5Na0.5)TiO3-based lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Hao, Jigong; Xu, Zhijun; Chu, Ruiqing; Li, Wei; Du, Juan; Li, Guorong

    2015-12-01

    In this letter, we report a lead-free piezoelectric ceramic system (Bi0.5Na0.5)1-x Ba x Ti0.98 (Fe0.5Sb0.5)0.02O3 which shows a surprisingly high field-induced nonlinear strain of 0.57% comparable to those obtained in Pb-based antiferroelectrics. The ultrahigh strain response of the composition stems from the composition proximity to the ferroelectric-nonpolar phase boundary, which leads to reversible transformation between a nonpolar phase and a polar ferroelectric phase under cyclic fields. In particular, this material is very attractive for its exceptionally good fatigue resistance (up to 106 cycles) and high temperature stability (25-100 °C) due to its stable nonpolar phase and lower defect density. These findings render the current material a great opportunity for novel applications in ultra-large stroke and nonlinear actuators demanding improved cycling and thermal reliabilities.

  19. High electrostrictive strain induced by defect dipoles in acceptor-doped (K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Dai, Ye-Jing; Zhao, Yong-Jie; Zhao, Zhe; Zhao, Zhi-Hao; Zhou, Qi-Wu; Zhang, Xiao-Wen

    2016-07-01

    Acceptor doping is an efficient method to improve ferroelectric material performance through the formation of defect dipoles. Here, a high electrostrictive strain of 0.16–0.19%, and large d33\\ast of  >300 pm V‑1 are obtained in CuO-doped (K0.5Na0.5)NbO3 ceramics. We analyzed the orientation relationship and the interaction between defect dipole polarization (P d) along <0 0 1> orientation and spontaneous polarization (P s) parallel to <1 1 0> in orthorhombic (K0.5Na0.5)NbO3. Thus, a ‘coupling effect’ mechanism was suggested to explain how the P d and P s can work together to contribute to the electrostrictive strains in this lead-free piezoelectric ceramic.

  20. Global and local structural variations near the antiferroelectric regime in Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}

    SciTech Connect

    Thangavelu, Karthik; Rayaprol, S.; Siruguri, V.; Sastry, P. U.; Asthana, Saket

    2015-06-24

    Rietveld refinement of neutron and x-ray diffraction data of Na{sub 0.5}Bi{sub 0.5}TiO{sub 3} shows R3c phase stabilization at room temperature. The intermediate antiferroelectric region between 180°C to 280°C exhibits phase coexistence i.e R3c + Pnma, along with decrease in octahedral tilt angle and increase in unit cell volume. The local structural changes observed from Raman scattering in the A-O, Ti-O and TiO{sub 6} phonon modes favor the global structural variation. A possible antiparallel cation displacement due to Pnma phase formation leads to the origin of antiferroelectric ordering in Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}.

  1. Crystal structure of the ordered perovskite: BaBi{sub 0.5}Sb{sub 0.5}O{sub 3}

    SciTech Connect

    Fu, W.T.; Graaff, R.A.G. de; Gelder, R. de

    1997-06-01

    The structure of BaBi{sub 0.5}Sb{sub 0.5}O{sub 3} is determined by single crystal X-ray diffraction. It is an ordered perovskite, having rhombohedral symmetry, space group R {bar 3}m (No. 166), with lattice parameters a = 6.043(1) {angstrom} and {alpha} = 60.05(2)(degree). The final agreement factor R based on F{sup 2} for 6420 reflections was 0.052. An important structural feature of BaBi{sub 0.5}Sb{sub 0.5}O{sub 3} is the displacements of oxygen atoms from their ideal positions within the pseudo-cubic [110]{sub p} planes, creating an alternative arrangement of (larger) BiO{sub 6} and (smaller) SbO{sub 6} octahedra. Therefore, the valence states of bismuth and antimony can be readily assigned as Bi(III) and Sb(V).

  2. Ferrimagnetic and spin-glass transition in the Aurivillius compound SrBi5Ti4Cr0.5Co0.5O18

    NASA Astrophysics Data System (ADS)

    Yuan, B.; Yang, J.; Zuo, X. Z.; Song, D. P.; Tang, X. W.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Sun, Y. P.

    2015-06-01

    Single-phase polycrystalline SrBi5Ti4CrO18 and SrBi5Ti4Cr0.5Co0.5O18 were synthesized by a modified Pechini method. Both samples have an orthorhombic structure with the space group B2cb. The valence state of Cr is suggested to be +3 and the Co ions exist in the form of Co2+ and Co3+ based on the results of x-ray photoelectron spectroscopy. The sample SrBi5Ti4CrO18 exhibits the paramagnetic state, whereas SrBi5Ti4Cr0.5Co0.5O18 undergoes a ferrimagnetic transition at 89 K originating from the antiferromagnetic coupling of Cr-based and Co-based sublattices. In addition, SrBi5Ti4Cr0.5Co0.5O18 shows a typical spin-glass behavior below 89 K with zν = 6.02 and τ0 = (1.75 ± 0.33) × 10-14 s as evidenced by the results of the frequency dependence of ac susceptibility and magnetic relaxation measurements. In particular, both the dielectric constant and dielectric loss of SrBi5Ti4Cr0.5Co0.5O18 exhibit the characteristics of dielectric relaxation around 89 K with the activation energy of (0.14 ± 0.02) eV, which can be ascribed to the electron hopping of Co2+-VO-Co3+ through the bridging oxygen vacancies.

  3. Co-doping of (Bi0.5Na0.5)TiO3: secondary phase formation and lattice site preference of Co

    NASA Astrophysics Data System (ADS)

    Schmitt, V.; Staab, T. E. M.

    2012-11-01

    Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) is considered to be one of the most promising lead-free alternatives to piezoelectric lead zirconate titanate (PZT). However, the effect of dopants on the material has so far received little attention from an atomic point of view. In this study we investigated the effects of cobalt-doping on the formation of additional phases and determined the preferred lattice site of cobalt in BNT. The latter was achieved by comparing the measured x-ray absorption near-edge structure (XANES) spectra to numerically calculated spectra of cobalt on various lattice sites in BNT. (Bi0.5Na0.5)TiO3 + x mol% Co (x = 0.0, 0.5, 1.0, 2.6) was synthesized via solid state reaction. As revealed by SEM backscattering images, a secondary phase formed in all doped specimens. Using both XRD and SEM-EDX, it was identified as Co2TiO4 for dopant levels >0.5 mol%. In addition, a certain amount of cobalt was incorporated into BNT, as shown by electron probe microanalysis. This amount increased with increasing dopant levels, suggesting that an equilibrium forms together with the secondary phase. The XANES experiments revealed that cobalt occupies the octahedral B-site in the BNT perovskite lattice, substituting Ti and promoting the formation of oxygen vacancies in the material.

  4. Ordered structure and thermal expansion in tungsten bronze Pb₂K(0.5)Li(0.5)Nb₅O₁₅.

    PubMed

    Lin, Kun; Rong, Yangchun; Wu, Hui; Huang, Qingzhen; You, Li; Ren, Yang; Fan, Longlong; Chen, Jun; Xing, Xianran

    2014-09-01

    The crystal structure and thermal expansion behaviors of a new tetragonal tungsten bronze (TTB) ferroelectric, Pb2K(0.5)Li(0.5)Nb5O15, were systematically investigated by selected-area electron diffraction (SAED), neutron powder diffraction, synchrotron X-ray diffraction (XRD), and high-temperature XRD. SAED and Rietveld refinement reveal that Pb2K(0.5)Li(0.5)Nb5O15 displays a commensurate superstructure of simple orthorhombic TTB structure at room temperature. The structure can be described with space group Bb2₁m. The transition to a paraelectric phase (P4/mbm) occurs at 500 °C. Compared with Pb2KNb5O15 (PKN), the substitution of 0.5K(+) with small 0.5Li(+) into PKN causes the tilting of NbO6 octahedra away from the c axis with Δθ ≈ 10° and raises the Curie temperature by 40 °C, and the negative thermal expansion coefficient along the polar b axis increases more than 50% in the temperature range 25-500 °C. We present that, by introduction of Li(+), the enhanced spontaneous polarization is responsible for the enhanced negative thermal expansion along the b axis, which may be caused by more Pb(2+) in the pentagonal caves. PMID:25116333

  5. Nuclear magnetic resonance study of thin Co2FeAl0.5Si0.5 Heusler films with varying thickness

    NASA Astrophysics Data System (ADS)

    Alfonsov, A.; Peters, B.; Yang, F. Y.; Büchner, B.; Wurmehl, S.

    2015-02-01

    Type, degree, and evolution of structural order are important aspects for understanding and controlling the properties of highly spin-polarized Heusler compounds, in particular, with respect to the optimal film growth procedure. In this work, we compare the structural order and the local magnetic properties revealed by nuclear magnetic resonance (NMR) spectroscopy with the macroscopic properties of thin Co2FeAl 0.5Si 0.5 Heusler films with varying thickness. A detailed analysis of the measured NMR spectra presented in this paper enables us to find a very high degree of L 21 -type ordering up to 81% concomitantly with excess Fe of 8%-13% at the expense of Al and Si. We show that the formation of certain types of order depends not only on the thermodynamic phase diagrams as in bulk samples, but also that the kinetic control may contribute to the phase formation in thin films. It is an exciting finding that Co2FeAl 0.5Si 0.5 can form an almost ideal L 21 structure in films, though with a considerable amount of Fe-Al/Si off stoichiometry. Moreover, the very good quality of the films as demonstrated by our NMR study suggests that the technique of off-axis sputtering used to grow the films sets the stage for the optimized performance of Co2FeAl 0.5Si 0.5 in spintronic devices.

  6. Valence states and metamagnetic phase transition in partially B -site-disordered perovskite EuMn0.5Co0.5O3

    NASA Astrophysics Data System (ADS)

    Vasiliev, A. N.; Volkova, O. S.; Lobanovskii, L. S.; Troyanchuk, I. O.; Hu, Z.; Tjeng, L. H.; Khomskii, D. I.; Lin, H.-J.; Chen, C. T.; Tristan, N.; Kretzschmar, F.; Klingeler, R.; Büchner, B.

    2008-03-01

    The valence states of transition metals were studied by measuring the x-ray absorption spectra at both MnL2,3 and CoL2,3 edges of partially B -site-disordered perovskite EuMn0.5Co0.5O3 . By comparison with analogous spectra in various Co- and Mn-based compounds, the divalent state of the Co ions and the tetravalent state of the Mn ions were established analogous to Mn4+/Co2+ charge ordering found by Dass and Goodenough [Phys. Rev. B 67, 014401 (2003)] in LaMn0.5Co0.5O3 . The specific heat and magnetic susceptibility data indicate the formation of the magnetically ordered state at TC˜120K . The first-order metamagnetic transitions seen in EuMn0.5Co0.5O3 at T

  7. Effect of Pr Addition on Properties of Sn-0.5Ag-0.7Cu-0.5Ga Lead-Free Solder

    NASA Astrophysics Data System (ADS)

    Xujing, Nan; Songbai, Xue; Peizhuo, Zhai; Dongxue, Luo

    2016-07-01

    In this paper, the effect of Pr addition on the microstructure and properties of Sn-0.5Ag-0.7Cu-0.5Ga lead-free solder was investigated. It was found that the properties of Sn-0.5Ag-0.7Cu-0.5Ga-xPr solder, such as wettability and mechanical properties, could be obviously improved, and the optimal content of Pr was about 0.06 wt.%. The microstructure of Sn-0.5Ag-0.7Cu-0.5Ga-0.06Pr solder showed that the β-Sn matrix and intermetallic compound (IMC) grains were significantly refined, and refinement and homogenization of the microstructure achieved maximum efficiency, which played the role of fine grain strengthening and second phase strengthening. However, as the content of Pr exceeded 0.06 wt.%, some uneven distributed black phases of PrSn3 were found in the β-Sn matrix, which seriously worsened the microstructure and properties of the solders. As a surface-active element, the segregation of Pr at the molten solder interface could give rise to decreasing the interface tension. Consequently, adding a suitable amount of Pr could play a positive role in improving the properties of the solders.

  8. Band gap modification and ferroelectric properties of Bi{sub 0.5}(Na,K){sub 0.5}TiO{sub 3}-based by Li substitution

    SciTech Connect

    Quan, Ngo Duc; Hung, Vu Ngoc; Quyet, Nguyen Van; Chung, Hoang Vu; Dung, Dang Duc

    2014-01-15

    We report on the reduction of band gap in Bi{sub 0.5}(Na{sub 0.82-x}Li{sub x}K{sub 0.18}){sub 0.5}(Ti{sub 0.95}Sn{sub 0.05})O{sub 3} from 2.99 eV to 2.84 eV due to the substitutions of Li{sup +} ions to Na{sup +} sites. In addition, the lithium substitution samples exhibit an increasing of the maximal polarizations from 21.8 to 25.7 μC/cm{sup 2}. The polarization enhancement of ferroelectric and reduction of the band gaps are strongly related to the Li substitution concentration as evaluated via the electronegative between A-site and oxygen and tolerance factor. The results are promising for photovoltaic and photocatalytic applications.

  9. Influence of 2mol% Na/Bi excess on multiferroic properties of (Na0.5Bi0.5) 0.99La0.01Ti0.988 Fe0.012O3 lead free system

    NASA Astrophysics Data System (ADS)

    Parmar, Kusum; Sharma, Hakikat; Kotnala, R. K.; Negi, N. S.

    2016-05-01

    Lead free (Na0.5Bi0.5) 0.99La0.01Ti0.988 Fe0.012O3 (NBLTF) system has been synthesized by sol gel method without and with 2 mol% excess of Na and Bi. X-ray diffraction patterns of NBLTF samples confirm perovskite structure having rhombohedral R3c phase symmetry. Metal oxide band observed at ~ 629 cm-1 wavnumber in FTIR spectra also confirm formation of perovskite phase in samples. Microstructural analysis exhibits dense crystal growth having better grains connectivity for NBLTF sample with 2 mol% excess Na/Bi which is supported by room temperature DC resistivity measurements. Dense crystal growth and low leakage current with 2 mol% excess Na/Bi is reported to improve multiferroic properties of NBLTF sample and provides new insight to explore single phase lead free multiferroic system.

  10. Enhanced ferroelectric and piezoelectric response in Mn-doped Bi0.5Na0.5TiO3-BaTiO3 lead-free film by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Jin, Chengchao; Wang, Feifei; Leung, Chung Ming; Yao, Qirong; Tang, Yanxue; Wang, Tao; Shi, Wangzhou

    2013-10-01

    Mn-doped Bi0.5Na0.5TiO3-BaTiO3 thin film with the composition around the morphotropic phase boundary was grown on Pt-electrodized Si substrate by pulsed laser deposition. Highly (1 0 0)-oriented film with pure perovskite structure was obtained through carefully controlling the growth conditions. Well-defined ferroelectric P-E loop was obtained with the average remnant polarization Pr and coercive field Ec of ∼11.3 μC/cm2 and ∼6.5 kV/mm, respectively. Polycrystalline structures and multidomain states were revealed by piezoresponse force microscopy and large local strain response was obtained with the normalized strain Smax/Emax up to 92 pm/V. The excellent global electrical properties make it quite promising in environmental-friendly ferroelectric and piezoelectric devices.

  11. Growth and electric properties of (100)-oriented Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 thin film by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Jin, Chengchao; Wang, Feifei; Leung, Chung Ming; Tang, Yanxue; Wang, Tao; Yao, Qirong; Shi, Wangzhou

    2014-06-01

    Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 (BNBMT) thin film with the composition near the morphotropic phase boundary was grown on (La0.6Sr0.4)CoO3-electroded SrTiO3 single-crystal substrate by using pulsed laser deposition method. Ascribed to the crystal structure and lattice similarity, (100)-oriented BNBMT film with pure single-phase perovskite structure was obtained through carefully controlling the growth conditions. Enhanced ferroelectric and dielectric properties were obtained with large remanent polarization P r of ˜21 μC/cm2, coercive field E c of ˜7.4 kV/mm and dielectric constant of ˜750 at 1 kHz. The excellent global electrical properties of the BNBMT film are promising for environmentally friendly ferroelectric devices.

  12. Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2-xFexO5+δ

    NASA Astrophysics Data System (ADS)

    Choi, Sihyuk; Yoo, Seonyoung; Kim, Jiyoun; Park, Seonhye; Jun, Areum; Sengodan, Sivaprakash; Kim, Junyoung; Shin, Jeeyoung; Jeong, Hu Young; Choi, Yongman; Kim, Guntae; Liu, Meilin

    2013-08-01

    Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co2-xFexO5+δ, which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm-2 at 600°C, representing an important step toward commercially viable SOFC technologies.

  13. Study of ZrxZn0.5-xNi0.5Fe2O4 0≤x≤0.25: Synthesis, structural, magnetic and electrical properties

    NASA Astrophysics Data System (ADS)

    Saini, Jasmeen; Kumar, Rupesh; Rajput, Jaspreet Kaur; Kumar, Arvind

    2016-03-01

    Zirconium substituted zinc-nickel ferrite nanoparticles with chemical composition of ZrxZn0.5-xNi0.5Fe2O4 (0≤x≤0.25) have been synthesized successfully by solution combustion method using high purity nitrates and fueling agent urea. Powder XRD study confirms the single phase formation of composite ferrite which belongs to cubic spinel structure. TEM further reveals the morphology of well dispersed Zn-Ni ferrite nanoparticles to be spherical. Effect of change of doping concentration of Zirconium is observed using FTIR. The saturation magnetization gradually decreases with the increase in Zr substitution and reaches minimum when x=0.25 whereas the coercivity value reaches minimum when x=0.15. DC electrical resistivity has been found to vary with increasing Zr content. The good electrical resistivity (>107 Ωcm) qualify the ceramic for high frequency transformer applications.

  14. Design considerations and parameter study for a 0.5TeV PWFA afterburner

    NASA Astrophysics Data System (ADS)

    Huang, Chengkun; Lu, W.; Tzoufras, M.; Zhou, M.; Decyk, V. K.; Joshi, C.; Mori, W. B.

    2007-11-01

    A recent plasma wakefield acceleration (PWFA) experiment using short (˜100fs), high peak current (>10KA) electron beam as driver has demonstrated sustained acceleration gradients of ˜50GeV/m over 85 cm distance [1]. The rapid progress of PWFA experiments has attracted interest regarding the possibility of making an afterburner for a linear collider. In the afterburner concept, an electron beam is placed into the wakefield to extract energy deposited in the wake. We investigate the afterburner concept based on the present understanding of the key physics. Possible design scenarios such as single stage acceleration or integrated design with plasma lens final focusing are studied. The final energy, charges, emittance, energy spread and energy stability of the accelerated electron beam are taken as intrinsic design considerations. Parameters are suggested for a 0.5 TeV afterburner. We also present full scale 3D particle-in-cell simulations of the possible design using a highly efficient and accurate quasi-static code QuickPIC. [1] Blumenfeld et. al., Nature 445, 741 (2007).

  15. Seeded FEL Amplifier-Buncher in the 0.5-9 THz for Advanced Accelerators

    SciTech Connect

    Tochitsky, S. Ya.; Reiche, S.; Sung, C.; Rosenzweig, J. B.; Joshi, C.; Gottschalk, S. C.; Kelly, R.

    2009-01-22

    Longitudinal modulation of a relativistic electron beam in the THz range is important for advanced laser- or beam-driven plasma accelerators operating in the 10{sup 16}-10{sup 18} cm{sup -3} plasma density range. We describe a single-pass FEL amplifier-buncher which is under construction at the UCLA Neptune laboratory. Microbunching on the 0.5-3 THz frequency scale is achieved during the process of a resonant FEL interaction between an electron beam and a THz seed pulse. A narrow-band, low-power THz seed source based on the frequency mixing of CO{sub 2} laser lines in a GaAs nonlinear crystal is built and fully characterized. The THz radiation pulse generated by this source will be guided through a hollow waveguide inside the planar FEL undulator driven by a regular photoinjector. By using a time-dependent FEL code GENESIS 1.3, we optimized the undulator parameters and analyzed the dynamics of the modulated electron beam. At present, the THz FEL microbuncher is being built and we update the status of the project.

  16. Optimization Study of the Ames 0.5 Two-Stage Light Gas Gun

    NASA Technical Reports Server (NTRS)

    Bogdanoff, D. W.

    1996-01-01

    There is a need for more faithful simulation of space debris impacts on various space vehicles. Space debris impact velocities can range up to 14 km/sec and conventional two-stage light gas guns with moderately heavy saboted projectiles are limited to launch velocities of 7-8 km/sec. Any increases obtained in the launch velocities will result in more faithful simulations of debris impacts. It would also be valuable to reduce the maximum gun and projectile base pressures and the gun barrel erosion rate. In this paper, the results of a computational fluid dynamics (CFD) study designed to optimize the performance of the NASA Ames 0.5' gun by systematically varying seven gun operating parameters are reported. Particularly beneficial effects were predicted to occur if (1) the piston mass was decreased together with the powder mass and the hydrogen fill pressure and (2) the pump tube length was decreased. The optimum set of changes in gun operating conditions were predicted to produce an increase in muzzle velocity of 0.7-1.0 km/sec, simultaneously with a substantial decrease in gun erosion. Preliminary experimental data have validated the code predictions. Velocities of up to 8.2 km/sec with a 0.475 cm diameter saboted aluminum sphere have been obtained, along with large reductions in gun erosion rates.

  17. Ferroelectric dielectric properties of Ba{sub 0.5}Sr{sub 0.5}(Ti{sub 0.80}Sn{sub 0.20})O{sub 3} thin films grown by the soft chemical method

    SciTech Connect

    Souza, I.A.; Cavalcante, L.S.; Cilense, M.

    2006-10-15

    Polycrystalline Ba{sub 0.5}Sr{sub 0.5}(Ti{sub 0.80}Sn{sub 0.20})O{sub 3} (BST:Sn) thin films with a perovskite structure were prepared by the soft chemical method on a platinum-coated silicon substrate from spin-coating technique. The resulting thin films showed a dense structure with uniforain size distribution. The dielectric constant of the films estimated from C-V curve is around 1134 and can be ascribed to a reduction in the oxygen vacancy concentration. The ferroelectric nature of the film indicated by butterfly-shaped C-V curves and confirmed by the hysteresis curve, showed remnant polarization of 14{mu}C/cm{sup 2} and coercive field of 74kV/cm at frequency of 1MHz. At the same frequency, the leakage current density at 1.0V is equal to 1.5x10{sup -7}A/cm{sup 2}. This work clearly reveals the highly promising potential of BST:Sn for application in memory devices.

  18. Defect dipole induced large recoverable strain and high energy-storage density in lead-free Na0.5Bi0.5TiO3-based systems

    NASA Astrophysics Data System (ADS)

    Cao, Wenping; Li, Weili; Feng, Yu; Bai, Terigele; Qiao, Yulong; Hou, Yafei; Zhang, Tiandong; Yu, Yang; Fei, Weidong

    2016-05-01

    In this letter, we propose an effective route to obtain large recoverable strain, purely electrostrictive effects and high energy-storage density by inducing defect dipoles into Na0.5Bi0.5TiO3 (NBT)-based relaxor ferroelectrics. It has been found that pinched and double polarization hysteresis loops with high maximum polarization (Pmax) and negligible remanent polarization (Pr) can be observed due to the presence of acceptor-induced defect dipoles. A large recoverable strain of 0.24% with very little hysteresis and high electrostriction coefficient of 0.022 m4 C2 with purely electrostrictive characteristics were acquired when 11 mol. ‰ Mn-doped. Meanwhile, a high recoverable energy density of 1.06 J/cm3 with excellent temperature stability was obtained at the same composition owing to the enlarged value of Pmax-Pr (36.8 μC/cm2) and relatively high electric field (95 kV/cm). Our achievement can open up the exciting opportunities for ferroelectric materials in high-precision positioning devices and high electric power pulse energy storage applications.

  19. Investigation of Sm 0.5Sr 0.5CoO 3- δ/Co 3O 4 composite cathode for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Haizhou; Liu, Huanying; Cong, You; Yang, Weishen

    The electrochemical properties of an Sm 0.5Sr 0.5CoO 3- δ/Co 3O 4 (SSC/Co 3O 4) composite cathode were investigated as a function of the cathode-firing temperature, SSC/Co 3O 4 composition, oxygen partial pressure and CO 2 treatment. The results showed that the composite cathodes had an optimal microstructure at a firing temperature of about 1100 °C, while the optimum Co 3O 4 content in the composite cathode was about 40 wt.%. A single cell with this optimized C 40-1100 cathode exhibited a very low polarization resistance of 0.058 Ω cm 2, and yielded a maximum power density of 1092 mW cm -2 with humidified hydrogen fuel and air oxidant at 600 °C. The maximum power density reached 1452 mW cm -2 when pure oxygen was used as the oxidant for a cell with a C 30-1100 cathode operating at 600 °C due to the enhanced open-circuit voltage and accelerated oxygen surface-exchange rate. X-ray diffraction and thermogravimetric analyses, as well as the electrochemical properties of a CO 2-treated cathode, also implied promising applications of such highly efficient SSC/Co 3O 4 composite cathodes in single-chamber fuel cells with direct hydrocarbon fuels operating at temperatures below 500 °C.

  20. Co-electrolysis of steam and CO2 in a solid oxide electrolysis cell with La0.75Sr0.25Cr0.5Mn0.5O3-δ -Cu ceramic composite electrode

    NASA Astrophysics Data System (ADS)

    Xing, Ruimin; Wang, Yarong; Zhu, Yongqiang; Liu, Shanhu; Jin, Chao

    2015-01-01

    Cu impregnation has been performed to improve electronic conductivity of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) material in reducing atmosphere, and solid oxide electrolysis cells (SOECs) with the configuration of LSCF|LSGM|LSCM-Cu are prepared and evaluated for high temperature steam and carbon dioxide co-electrolysis. Electrochemical impedance spectra (EIS) and voltage-current curves are carried out to characterize the cell performances. Compared with LSCF|LSGM|LSCM cell without Cu impregnation for steam electrolysis under the same conditions, EIS results show that LSCF|LSGM|LSCM-Cu cell not only displays lower ohmic resistance and better electrochemical performances, but also their resistance increases with the percentage of the fed CO2 under open circuit voltage, in which the polarization resistance dominates. With the applied electrolysis voltage of 1.65 V and the operating temperature of 750 °C, the maximum consumed current density increases from 1.31 A cm-2 without CO2 to 1.82 A cm-2 with 37.5% CO2. Although there is an increase of 2.0% in the applied electrolysis voltage, the cell has exhibited an excellent durability test for more than 50 h with the electrolysis current density of 0.33 A cm-2 and the gas mixture of 50% AH-25% H2-25% CO2 at 750 °C.

  1. Structure and Magnetic Order in the Series BixRE1-xFe0.5Mn0.5O3 (RE = La, Nd)

    SciTech Connect

    Bridges, Craig A; Safa-Sefat, Athena; Payzant, E Andrew; Cranswick, Lachlan; Paranthaman, Mariappan Parans

    2011-01-01

    The influence of Bi3+ on the structure and magnetic properties of the rare-earth containing perovskites REFe0.5Mn0.5O3 (RE= La,Nd) was studied, and the limit of bismuth substitution was determined to be x 0.5 in BixRE1-xFe0.5Mn0.5O3+ (RE= La,Nd) at ambient pressure. Both X-ray and Neutron powder diffraction data were used to determine the crystal structures. Crystal structures in both La and Nd series were determined to be GdFeO3-type Pnma with the exception of the Bi0.3La0.7Fe0.5Mn0.5O3+ sample, which is monoclinic I2/a in the a-b-b- tilt scheme. Bond valence results suggest that the oxidation states are most consistent with Fe3+ and Mn3+, with some oxidation to form Mn4+ suggested by Rietveld refinement of oxygen excess and bismuth deficiency from neutron powder diffraction data. The samples undergo a transition to G-type antiferromagnetic order along with a weak ferromagnetic component, mixed with cluster-glass type behavior. Long range ordering temperatures TN in the range of 240-255K were also observed, with a significantly lower ordered magnetic moment in the case of lanthanum (M ~ 1.7-1.9 B) than in the case of neodymium (M ~ 2.1 B). The substitution of bismuth into the lattice results with a drop in T N relative to the lanthanide end-members, but exhibits no clear correlation with the magnitude of the ordered moment on the B-site.

  2. Synergistic effects of intrinsic cation disorder and electron-deficient substitution on ion and electron conductivity in La1-xSrxCo0.5Mn0.5O3-δ (x = 0, 0.5, and 0.75).

    PubMed

    Meng, Junling; Yuan, Na; Liu, Xiaojuan; Yao, Chuangang; Liang, Qingshuang; Zhou, Defeng; Meng, Fanzhi; Meng, Jian

    2015-03-16

    The effects of intrinsic cation disorder and electron-deficient substitution for La1-xSrxCo0.5Mn0.5O3-δ (LSCM, x = 0, 0.5, and 0.75) on oxygen vacancy formation, and their influence on the electrochemical properties, were revealed through a combination of computer simulation and experimental study. First-principles calculations were first performed and found that the tendency of the oxygen vacancy formation energy was Mn(3+)-O*-Mn(4+) < Co(2+)-O*-Co(3+) < Co(2+)-O*-Mn(4+), meaning that antisite defects not only facilitate the formation of oxygen vacancy but introduce the mixed-valent transition-metal pairs for high electrical conductivity. Detailed partial density of states (PDOS) analysis for Mn on Co sites (MnCo) and Co on Mn sites (CoMn) indicate that Co(2+) is prone to being Co(3+) while Mn(4+) is prone to being Mn(3+) when they are on antisites, respectively. Also it was found that the holes introduced by Sr tend to enter the Co sublattice for x = 0.5 and then the O sublattice when x = 0.75, which further promotes oxygen vacancy formation, and these results are confirmed by both the calculated PDOS results and charge-density difference. On the basis of microscopic predictions, we intentionally synthesized a series of pure LSCM compounds and carried out comprehensive characterization. The crystal structures and their stability were characterized via powder X-ray Rietveld refinements and in situ high-temperature X-ray diffraction. X-ray photoelectron spectroscopy testified to the mixed oxidation states of Co(2+)/Co(3+) and Mn(3+)/Mn(4+). The thermal expansion coefficients were found to match the Ce0.8Sm0.2O2-δ electrolyte well. The electrical conductivities were about 41.4, 140.5, and 204.2 S cm(-1) at doping levels of x = 0, 0.5, and 0.75, and the corresponding impedances were 0.041, 0.027, and 0.022 Ω cm(2) at 850 °C, respectively. All of the measured results testify that Sr-doped LaCo0.5Mn0.5O3 compounds are promising cathode materials for intermediate

  3. Dielectric relaxation and magnetodielectric response in DyMn{sub 0.5}Cr{sub 0.5}O{sub 3}

    SciTech Connect

    Yuan, B.; Yang, J. Zuo, X. Z.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Kan, X. C.; Zu, L.; Sun, Y. P.

    2015-09-28

    We investigate the structural, magnetic, and magnetodielectric properties of DyMn{sub 0.5}Cr{sub 0.5}O{sub 3}. The sample can be indexed with an orthorhombic phase with B site disordered space group Pbnm. The valence state of both Mn and Cr ions are suggested to be +3 based on the results of x-ray photoelectron spectroscopy. Two thermally excited dielectric relaxation at temperatures T{sub N2} < T< 300 K and large magnetodielectric effect (MDC = 20%–30%) due to the disordered arrangement of Mn{sup 3+}/Cr{sup 3+} ions associated with electron hopping between them are observed. The absence of any noticeable magnetoresistance effect (MR < 0.5%) demonstrates that the observed magnetodielectric effect is an intrinsic behavior. These results suggest that DyMn{sub 0.5}Cr{sub 0.5}O{sub 3} is a magnetodielectric compound, whose dielectric properties are dependence of the applied magnetic field, which exhibits such effects near room temperature and holds great promise for future device applications.

  4. Development Status of Adjustable X-Ray Optics with 0.5 Arcsecond Resolution

    NASA Technical Reports Server (NTRS)

    Reid, P. B.; ODell, Stephen; Elsner, Ron; Ramsey, Brian; Gubarev, Misha; Aldcroft, T.; Allured, R.; Cotroneo, V.; Johnson-Wilke, R. L.; McMuldroch, S.; Swartz, D. A.; Trolier-McKinstry, S.; Vikhlinin, A.; Wilke, R.

    2014-01-01

    We report on the continuing development of adjustable, grazing incidence X-ray optics for 0.5 arcsec telescopes. Adjustable X-ray optics offer the potential for achieving sub-arcsecond imaging resolution while sufficiently thin and light-weight to constitute a mirror assembly with several square meters collecting area. The adjustable mirror concept employs a continuous thin film of piezoelectric material deposited on the back of the paraboloid and hyperboloid mirror segments. Individually addressable electrodes on the piezoelectric layer allow the introduction of deformations in localized "cells" which are used to correct mirror figure errors resulting from fabrication, mounting and aligning the thin mirrors, residual gravity release and temperature changes. We describe recent results of this development. These include improving cell yield to approx. 100 per cent, measurements of hysteresis and stability, comparisons of modeled and measured behavior, simulations of mirror performance, and the development and testing of conical Wolter- I mirror segments. We also present our plans going forward toward the eventual goal of achieving TRL 6 prior to the 2020 Decadal Review.

  5. Nickel-zinc ferrite/permalloy (Ni0.5Zn0.5Fe2O4/Ni-Fe) soft magnetic nanocomposites fabricated by electro-infiltration

    NASA Astrophysics Data System (ADS)

    Wen, Xiao; Kelly, Stefan J.; Andrew, Jennifer S.; Arnold, David P.

    2016-05-01

    Magnetically soft NiZn ferrite (Ni0.5Zn0.5Fe2O4) nanoparticles are embedded within a permalloy (Ni-Fe) matrix via an electro-infiltration process as thin films intended for use as on-chip inductor cores in the MHz frequency regime. A layer of NiZn ferrite nanoparticles is first deposited, and then permalloy is electroplated through the voids to encapsulate the particles and form three-dimensional ferrite/alloy nanocomposites. The composites are estimated to contain 37% ferrite by volume and exhibit a relative permeability of ˜320, a saturation of ˜1.15 T, and an operational bandwidth of 93 MHz. Compared to a permalloy thin film of similar thickness, the nanocomposite exhibits 39% higher electrical resistivity and 50% higher bandwidth.

  6. Optical Properties of Ferroelectric Epitaxial K0.5Na0.5NbO3 Films in Visible to Ultraviolet Range.

    PubMed

    Chernova, E; Pacherova, O; Kocourek, T; Jelinek, M; Dejneka, A; Tyunina, M

    2016-01-01

    The complex index of refraction in the spectral range of 0.74 to 4.5 eV is studied by variable-angle spectroscopic ellipsometry in ferroelectric K0.5Na0.5NbO3 films. The 20-nm-thick cube-on-cube-type epitaxial films are grown on SrTiO3(001) and DyScO3(011) single-crystal substrates. The films are transparent and exhibit a significant difference between refractive indices Δn = 0.5 at photon energies below 3 eV. The energies of optical transitions are in the range of 3.15-4.30 eV and differ by 0.2-0.3 eV in these films. The observed behavior is discussed in terms of lattice strain and strain-induced ferroelectric polarization in epitaxial perovskite oxide films. PMID:27074042

  7. Optical Properties of Ferroelectric Epitaxial K0.5Na0.5NbO3 Films in Visible to Ultraviolet Range

    PubMed Central

    Pacherova, O.; Kocourek, T.; Jelinek, M.; Dejneka, A.; Tyunina, M.

    2016-01-01

    The complex index of refraction in the spectral range of 0.74 to 4.5 eV is studied by variable-angle spectroscopic ellipsometry in ferroelectric K0.5Na0.5NbO3 films. The 20-nm-thick cube-on-cube-type epitaxial films are grown on SrTiO3(001) and DyScO3(011) single-crystal substrates. The films are transparent and exhibit a significant difference between refractive indices Δn = 0.5 at photon energies below 3 eV. The energies of optical transitions are in the range of 3.15–4.30 eV and differ by 0.2–0.3 eV in these films. The observed behavior is discussed in terms of lattice strain and strain-induced ferroelectric polarization in epitaxial perovskite oxide films. PMID:27074042

  8. Influences of phase transition and microstructure on dielectric properties of Bi0.5Na0.5Zr1-xTixO3 ceramics

    PubMed Central

    2012-01-01

    Bismuth sodium zirconate titanate ceramics with the formula Bi0.5Na0.5Zr1-xTixO3 [BNZT], where x = 0.3, 0.4, 0.5, and 0.6, were prepared by a conventional solid-state sintering method. Phase identification was investigated using an X-ray diffraction technique. All compositions exhibited complete solubility of Ti4+ at the Zr4+ site. Both a decrease of unit cell size and phase transition from an orthorhombic Zr-rich composition to a rhombohedral crystal structure in a Ti-rich composition were observed as a result of Ti4+ substitution. These changes caused dielectric properties of BNZT ceramics to enhance. Microstructural observation carried out employing SEM showed that average grain size decreased when addition of Ti increased. Grain size difference of BNZT above 0.4 mole fraction of Ti4+ displayed a significant increase of dielectric constant at room temperature. PMID:22221960

  9. Scandium induced structural transformation and B′:B″ cationic ordering in Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} multiferroic ceramics

    SciTech Connect

    Mallesham, B.; Ranjith, R.; Manivelraja, M.

    2014-07-21

    The current study explores non-magnetic Sc{sup 3+} induced structural transformation, evolution of local B-site cation ordering and associated effect on ferroelectric phase transition temperature T{sub max} (temperature corresponding to dielectric maxima) on increasing the atom percent of Sc substitution in [Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} (PFN)] ceramics. In this regard, the phase pure Pb[(Fe{sub 0.5−x}Sc{sub x})Nb{sub 0.5}]O{sub 3} ceramics with x varying from 0 to 0.5 were synthesized through solid state reaction route. The detailed structural analysis through Rietveld refinement confirms the room temperature transformation from a monoclinic Cm to rhombohedral R3m structure at x = 0.3 mol. % of Sc. Absorption spectra studies show that there is a considerable increment in the bandgap at higher scandium content. Most interestingly, the T{sub max} exhibited an increment for lower scandium contents (x = 0.1 to 0.25) followed by a drop in T{sub max} (x = 0.3 to 0.5). Such anomalous behavior in T{sub max} is expected to arise due to the onset of B′, B″ local cation ordering beyond Sc content x = 0.25. The B-site cation ordering at and beyond x = 0.3 was also confirmed by the evolution of cation order induced Pb-O coupled vibrational mode in Raman scattering studies. In addition, the Mössbauer spectra of PFN (x = 0) and Pb(Fe{sub 0.4}Sc{sub 0.1}Nb{sub 0.5})O{sub 3} (x = 0.1) are reported to verify the spin state and oxidation state of iron. The lattice distortion due to the radius ratio difference between a Sc{sup 3+} cation and Fe{sup 3+} cation in low spin state is responsible for the structural transformation, which in turn facilitates a B′:B″ cation ordering.

  10. TsuSpeedv0.5: Inversion of flow depth and flow speed along a cross section

    NASA Astrophysics Data System (ADS)

    Tang, H.; Weiss, R.

    2013-12-01

    Modern tsunami deposits are employed to estimate the overland flow characteristics of the tsunami. With the help of the overland-flow characteristics, the characteristics of the causative tsunami wave can be estimated. The understanding of tsunami deposits has tremendously improved over the last decades, and the importance of tsunami sediment studies for hazard assessments was highlight after the 2004 Sumatra tsunami. Tsunami deposits are studied in forward and inversion models. There are three prominent inversion models: (a) Moore's advection model (Moore et al., 2007), (b) Soulsby Inundation model (Soulsby et al. 2007), and (c) TsuSedMod (Jaffe et al., 2007). TsuSpeedv0.5 incorporates all three models and adds new modules to better estimate the characteristics of individual sediment layers. TsuSpeedv0.5 takes a grain-size distribution of a sampled tsunami deposits and initial estimates for the flow depths at the shore and the location of the sampled tsunami deposits as input. TsuSpeedv0.5 then computes sediment concentration, grain-size distribution of sediment source and flow speed to match the tsunami sediment thickness and grain size distribution from field observation, on which the final estimate of the grain-size distribution, flow speed, and froude number for each layer is based. Furthermore, the characteristics of the tsunami deposit matched (as good as it gets) at the sample location are then also extrapolated along a cross section. Keywords: Tsunami; Tsunami sediment; Sediment transport; Flow depth;Flow Speed

  11. Spin reorientation in multiferroic spinel Co0.5Fe0.5Cr2O4 with Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Myoung, Bo Ra; Kim, Chul Sung

    2015-05-01

    We studied the magnetic properties of multiferroic spinel Co0.5Fe0.5Cr2O4, especially focusing on the spin-ordering, spin-reorientation, and charge re-distribution effects. From the Rietveld refinement analysis, the crystal structure was identified to be a normal cubic spinel of Fd-3m. Based on the temperature-dependent measurements of the magnetization and magnetic hyperfine field (Hhf), Curie temperature (TC) of Co0.5Fe0.5Cr2O4 was determined to be around 86 K where Hhf ≅ 0. From the change of slope in the M-T curve, the conical-spiral magnetic ordering temperature was determined to be 20 K, which coincides with Hhf measurement. Also, we have observed the decrease in the slope of the electric quadrupole splitting (ΔEQ) curve above 20 K, suggesting that the change in ΔEQ around TS is originated from charge redistribution due to the spin-relocation associated with the distortion of each tetrahedral site around Fe2+ ion above TS. This indicates that Co0.5Fe0.5Cr2O4 has the noncollinear conical-spiral spin ordering with incommensurate spin structure below TS, while above TS, it has ferrimagnetic spin ordering with commensuration in the collinear state. In addition, the Jahn-teller distortion temperature is measured to be around 155 K, since both ΔEQ and Δ1 of 5T2g band decrease rapidly with increasing temperature and disappear around 155 K.

  12. Significantly enhanced ferroelectricity and magnetic properties in (Sr0.5Ca0.5)TiO3-modified BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Liu, Xiao Qiang; Chen, Xiang Ming

    2015-05-01

    BiFeO3 multiferroic ceramics were modified by introducing (Sr0.5Ca0.5)TiO3 to form solid solutions. The single phase structure was easy to be obtained in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with Mr = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe3+ by Ti4+, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

  13. Synthesis of manganite perovskite Ca{sub 0.5}Sr{sub 0.5}MnO{sub 3} nanoparticles in w/o-microemulsion

    SciTech Connect

    Lopez-Trosell, Alejandra . E-mail: Lopez.Alejandra@chem.tu-berlin.de; Schomaecker, Reinhard . E-mail: schomaecker@tu-berlin.de

    2006-02-02

    In this paper, w/o-microemulsions were employed to produce nanoparticles of the perovskite Ca{sub 0.5}Sr{sub 0.5}MnO{sub 3}, which have a size of approximately 20-50 nm. The procedure was carried out using sodium hydroxide or ammonia as co-precipitation agent. The precursor was transformed to perovskite by calcinations at 580 deg. C. Nanosized particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N{sub 2} adsorption (BET)

  14. Chemical potential fluctuations in topological insulator (Bi0.5Sb0.5)2Te3-films visualized by photocurrent spectroscopy

    NASA Astrophysics Data System (ADS)

    Kastl, Christoph; Seifert, Paul; He, Xiaoyue; Wu, Kehui; Li, Yongqing; Holleitner, Alexander

    2015-06-01

    We investigate the photocurrent properties of the topological insulator (Bi0.5Sb0.5)2Te3 on SrTiO3-substrates. We find reproducible, submicron photocurrent patterns generated by long-range chemical potential fluctuations, occurring predominantly at the topological insulator/substrate interface. We fabricate nano-plowed constrictions which comprise single potential fluctuations. Hereby, we can quantify the magnitude of the disorder potential to be in the meV range. The results further suggest a dominating photo-thermoelectric current generated in the surface states in such nanoscale constrictions.

  15. Direct band-gap measurement on epitaxial Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} Heusler-alloy films

    SciTech Connect

    Alhuwaymel, Tariq F.; Carpenter, Robert; Yu, Chris Nga Tung; Kuerbanjiang, Balati; Lazarov, Vlado K.; Abdullah, Ranjdar M.; El-Gomati, Mohamed; Hirohata, Atsufumi

    2015-05-07

    In this study, a newly developed band-gap measurement technique has been used to characterise epitaxial Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS) films. The CFAS films were deposited on MgO(001) substrate by ultra high vacuum molecular beam epitaxy. The band-gap for the as deposited films was found to be ∼110 meV when measured at room temperature. This simple technique provides a macroscopic analysis of the half-metallic properties of a thin film. This allows for simple optimisation of growth and annealing conditions.

  16. Strain control of superlattice implies weak charge-lattice coupling in La{sub 0.5}Ca{sub 0.5}MnO{sub 3}

    SciTech Connect

    Cox, S.; Chapman, J. C.; Midgley, P. A.; Mathur, N. D.; Rosten, E.; Kos, S.; Littlewood, P. B.; Calderon, M. J.; Kang, D.-J.

    2006-04-01

    We have recently argued that manganites do not possess stripes of charge order, implying that the electron-lattice coupling is weak [Loudon et al., Phys. Rev. Lett. 94, 097202 (2005)]. Here we independently argue the same conclusion based on transmission electron microscopy measurements of a nanopatterned epitaxial film of La{sub 0.5}Ca{sub 0.5}MnO{sub 3}. In strain relaxed regions, the superlattice period is modified by 2% to 3% with respect to the parent lattice, suggesting that the two are not strongly tied.

  17. Collective dipole behavior and unusual morphotropic phase boundary in ferroelectric Pb(Zr(0.5)Ti(0.5))O3 nanowires.

    PubMed

    Fu, Xiujun; Naumov, Ivan I; Fu, Huaxiang

    2013-02-13

    Dipole collective behavior and phase transition in ferroelectric (FE) Pb(Zr(0.5)Ti(0.5))O(3) nanowires, caused by modulated electric fields, are reported. Our result also leads to the finding of a rather outstanding electromechanical d(31) response in a 8.4 nm diameter PZT wire, which may potentially outperform bulk PMN-PT and PZN-PT. Moreover, we further demonstrate the existence of a new type of morphotropic phase boundary (MPB) that bridges two dissimilar structure phases of different order parameters. Microscopic insights for understanding the collective behavior and the structural phase within the new MPB are provided. PMID:23256599

  18. Quantitative study of atomic ordering in Ga0.5In0.5P thin films by 31P nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Tycko, Robert; Dabbagh, Gary; Kurtz, Sarah R.; Goral, John P.

    1992-06-01

    We use 31P nuclear-magnetic-resonance (NMR) spectra to measure the degree of cation ordering in thin films of the semiconductor alloy Ga0.5In0.5P grown by organometallic vapor-phase epitaxy. We show that the five possible GanIn4-nP clusters in GaxIn1-xP give rise to resolved NMR lines under magic-angle spinning, allowing a determination of the degree of cation ordering from the relative areas of the five lines. The ordering is shown to be weak (order parameter <=0.6) even in films that appear highly ordered in transmission electron microscopy.

  19. A 0.5 cm(3) four-channel 1.1 mW wireless biosignal interface with 20 m range.

    PubMed

    Morrison, Tim; Nagaraju, Manohar; Winslow, Brent; Bernard, Amy; Otis, Brian P

    2014-02-01

    This paper presents a self-contained, single-chip biosignal monitoring system with wireless programmability and telemetry interface suitable for mainstream healthcare applications. The system consists of low-noise front end amplifiers, ADC, MICS/ISM transmitter and infrared programming capability to configure the state of the chip. An on-chip packetizer ensures easy pairing with standard off-the-shelf receivers. The chip is realized in the IBM 130 nm CMOS process with an area of 2×2 mm(2). The entire system consumes 1.07 mW from a 1.2 V supply. It weighs 0.6 g including a zinc-air battery. The system has been extensively tested in in vivo biological experiments and requires minimal human interaction or calibration. PMID:24681927

  20. Anti-P2 structured Na0.5NbO2 and its negative strain effect

    SciTech Connect

    Wang, Xuefeng; Gao, Yurui; Shen, Xi; Li, Yejing; Kong, Qingyu; Lee, Sungsik; Wang, Zhaoxiang; Yu, Richeng; Hu, Yong-Sheng; Chen, Liquan

    2015-01-01

    Layer-structured oxides are studied for their essential roles in various applications (e.g. high-energy batteries and superconductors) due to their distinctive physical structures and chemical properties. Most of the layered AxMO2 (A = alkali ions, M = transition metals) are composed of MO6 octahedra and various A coordination polyhedra such as octahedra (O), tetrahedra (T) or trigonal prisms (P). Herein, we report a new layered oxide material, anti-P2 Na0.5NbO2, which is composed of NbO6 trigonal prisms and NaO6 octahedra. Its lattice shrinks as sodium (Na) ions are intercalated in it and expands when the ions are deintercalated (a negative volume or strain effect). Analysis by X-ray absorption spectroscopy and density functional theory (DFT) calculations indicates that the negative volume effect is mainly a result of the enhanced interlayer (Na–O) interaction and the weakened Nb– Nb and Nb–O bonding in the O–Nb–O slab upon Na intercalation. Moreover, Na0.5NbO2 exhibits high structural stability, a long cycle life and prominent rate performance for Na-ion batteries. These distinctive features make Na0.5NbO2 an ideal ‘‘volume buffer’’ to compensate for positive-strain electrode materials. These findings will arouse great interest in anti-P2 layered oxides for materials science and applications, and enrich the understanding of novel negative-strain materials for energy storage either as excellent independent active electrode materials or as volume buffers for constructing long-life composite electrodes made of positive-strain materials.

  1. Electrical Characterization Induced by Structural Modulation in (Ca0.28Ba0.72)2.5-0.5 x (Na0.5K0.5) x Nb5O15 Ceramics

    NASA Astrophysics Data System (ADS)

    Yang, Bian; Wei, Lingling; Wang, Zhongming; Kang, Shoucheng; Chao, Xiaolian; Yang, Zupei

    2016-01-01

    (Ca0.28Ba0.72)2.5-0.5 x (Na0.5K0.5) x Nb5O15 ceramics (CBNKN, 0.0 ≤ x ≤ 0.4) with `unfilled' tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of alkalis-introducing concentration in A-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. Pure tungsten bronze structure could be obtained in all compositions according to the x-ray diffraction patterns. Raman spectroscopy results showed that co-introducing Na+ and K+ in A sites to decrease the structural vacancy could enhance the dielectric and ferroelectric properties, which was attributed to the stronger interaction inside NbO6 octahedron and large distortion degree of NbO6 polar unit. Traditional temperature dependence of dielectric characteristics and well-saturated ferroelectric hysteresis loops were observed for all CBNKN ceramics. The better comprehensive dielectric and ferroelectric properties were obtained at x = 0.2 due to the bigger distortion degree of NbO6 polar unit and the highest densification. Whereas higher alkalis-introducing concentration would deteriorate the physical and electrical properties due to the poor sintering behavior. In addition, the frequency dependence of ɛ around transition temperature ( T c) and the temperature dependence of ferroelectric properties were discussed to further clarify the relationship between composition and performance.

  2. Active diagenetic formation of metal-rich layers in N. E. Atlantic sediments

    NASA Astrophysics Data System (ADS)

    Wallace, H. E.; Thomson, J.; Wilson, T. R. S.; Weaver, P. P. E.; Higgs, N. C.; Hydes, D. J.

    1988-06-01

    Sediment cores from the Porcupine Abyssal Plain exhibit an indurated layer 0.5-3 cm thick at depths of approximately 50 cm. This is some 15-20 cm below the glacial/Holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of RUDDIMAN and MCINTYRE (1981). The layer is forming currently at the oxic/post-oxic boundary in the sediments, as revealed by pore water data: O 2 and NO -3 are present in solution above the layer, while Fe 2+, Mn 2+, PO 3-4 and NH +4 are present in solution below, and all these species show concentration gradients indicating fluxes into the layer. These data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by WILSONet al. (1986a,b). The elements Mn, Ni, Co, Fe, P, V, Cu, Zn and U are all enriched to varying degrees in the vicinity of the layer. Some differential stratification of these elements in the vertical, consistent with a redox control, is observed at one site with a 0.5 cm layer, with Mn, Ni and Co above, Fe, P, V and Cu in the layer, and U below. At another site the metal-rich layer has higher Fe and P concentrations and is more indurated. Here all enrichments except Co are contained within a single layer sample, 3 cm thick.

  3. Large magnetoresistance in current-perpendicular-to-plane pseudo spin-valves using Co2Fe(Ga0.5Ge0.5) Heusler alloy and AgZn spacer

    NASA Astrophysics Data System (ADS)

    Du, Ye; Furubayashi, T.; Sasaki, T. T.; Sakuraba, Y.; Takahashi, Y. K.; Hono, K.

    2015-09-01

    Fully epitaxial pseudo spin-valves (PSVs) using 10-nm-thick Co2Fe(Ga0.5Ge0.5) (CFGG) ferromagnetic layers and a 5-nm-thick AgZn space layer annealed at 630 °C show a large current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) output with resistance-change area product, ΔRA, of 21.5 mΩ μm2 and MR ratio of 59.6% at room temperature. These values are substantially enhanced to ΔRA of 59.8 mΩ μm2 and MR ratio of 200.0% at 10 K. The large MR is attributed to the high spin polarization of the CFGG electrodes with the enhanced L21 ordering induced by the atomic diffusion of Zn through the CFGG layers. The CPP-PSV shows relatively large ΔRA of 10.9 mΩ μm2 with the MR ratio of 25.6% for the low annealing temperature of 350 °C, which is a practically useful feature for read sensor applications.

  4. Large magnetoresistance in current-perpendicular-to-plane pseudo spin-valves using Co{sub 2}Fe(Ga{sub 0.5}Ge{sub 0.5}) Heusler alloy and AgZn spacer

    SciTech Connect

    Du, Ye; Hono, K.; Furubayashi, T.; Sasaki, T. T.; Sakuraba, Y.; Takahashi, Y. K.

    2015-09-14

    Fully epitaxial pseudo spin-valves (PSVs) using 10-nm-thick Co{sub 2}Fe(Ga{sub 0.5}Ge{sub 0.5}) (CFGG) ferromagnetic layers and a 5-nm-thick AgZn space layer annealed at 630 °C show a large current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) output with resistance-change area product, ΔRA, of 21.5 mΩ μm{sup 2} and MR ratio of 59.6% at room temperature. These values are substantially enhanced to ΔRA of 59.8 mΩ μm{sup 2} and MR ratio of 200.0% at 10 K. The large MR is attributed to the high spin polarization of the CFGG electrodes with the enhanced L2{sub 1} ordering induced by the atomic diffusion of Zn through the CFGG layers. The CPP-PSV shows relatively large ΔRA of 10.9 mΩ μm{sup 2} with the MR ratio of 25.6% for the low annealing temperature of 350 °C, which is a practically useful feature for read sensor applications.

  5. Synthesis, Characterization and Electrochemical Analysis of Composite Cathode Material 0.5Li2MnO3-0.25LiMn2O4-0.25LiNi0.5Mn0.5O2 for LIB applications

    NASA Astrophysics Data System (ADS)

    Lopez de Victoria, Monica; Shojan, Jifi; Torres, Loraine; Katiyar, Rajesh; Dorvilien, Valerio; Katiyar, Ram

    Structural stability, environment friendliness, low cost as well as good electrochemical performances are the major requirements for cathode materials. Li2MnO3 based composite cathode materials are one of the widely investigated positive cathode materials due to their ability to provide high discharge capacity and good rate capability. We have synthesized layered- spinel composite cathode material 0.5Li2MnO3-0.25LiMn2O4 -0.25LiNi0.5Mn0.5O2 by sol-gel synthesis technique and surface characterized using XRD, Raman, SEM and EDX. Peaks corresponding to layered and spinel structures are identified by XRD and Raman studies. SEM images depict the nano-sized particles and EDX data confirms the presence of constituent transition metals and oxygen. Electrochemical studies were performed on coin cells, which were assembled in the Ar- filled glove box using Li as anode and spread material as cathode. LiPF6 with EC:DMC::1:2 ratio was used as the electrolyte. CV, EIS and charge discharge studies shows that the developed cathode material is a promising electrode for next generation Li ion batteries. Nasa Epscore Grant.

  6. Pressure-induced phase transition in La1–xSmxO0.5F0.5BiS2

    DOE PAGESBeta

    Fang, Y.; Yazici, D.; White, B. D.; Maple, M. B.

    2015-09-15

    Electrical resistivity measurements on La1–xSmxO0.5F0.5BiS2 (x = 0.1, 0.3, 0.6, 0.8) have been performed under applied pressures up to 2.6 GPa from 2 K to room temperature. The superconducting transition temperature Tc of each sample significantly increases at a Sm-concentration dependent pressure Pt, indicating a pressure-induced phase transition from a low-Tc to a high-Tc phase. At ambient pressure, Tc increases dramatically from 2.8 K at x = 0.1 to 5.4 K at x = 0.8; however, the Tc values at P > Pt decrease slightly with x and Pt shifts to higher pressures with Sm substitution. In the normal state,more » semiconducting-like behavior is suppressed and metallic conduction is induced with increasing pressure in all of the samples. Furthermore, these results suggest that the pressure dependence of Tc for the BiS2-based superconductors is related to the lattice parameters at ambient pressure and enable us to estimate the evolution of Tc for SmO0.5F0.5BiS2 under pressure.« less

  7. Twofold spin reorientation and field-induced incomplete phase transition in single-crystal Dy0.5Pr0.5FeO3

    NASA Astrophysics Data System (ADS)

    Wu, Hailong; Cao, Shixun; Liu, Ming; Cao, Yiming; Kang, Baojuan; Zhang, Jincang; Ren, Wei

    2014-10-01

    We report an intriguing twofold spin reorientation transition of type Γ4(Gx,Ay,Fz)→Γ1(Ax,Gy,Cz)→Γ2(Fx,Cy,Gz) for the Fe3+ magnetic sublattice near spin reorientation temperatures TSR1˜77 K and TSR2˜45 K in a rare-earth orthoferrite Dy0.5Pr0.5FeO3 single crystal. Magnetic-field-induced incomplete spin-configuration transitions (Γ4→Γ41→Γ42 for H =20kOe and Γ4→Γ42 for H =40kOe) were observed by measurement of magnetization as a function of temperature. The spin reorientation temperature of a Dy0.5Pr0.5FeO3 single crystal can be controlled by changing the magnitude of the applied magnetic field. We also show that spin reorientation of the Γ1→Γ4 type between TSR2 and TSR1 can be induced by an applied magnetic field along the c axis. The origin of the intriguing magnetic behavior is ascribed to the anisotropic effective field whose strength is determined by the interactions with R3+(R =Dy,Pr) spins and can be modified by the external applied magnetic field. It provides deeper insight into the Fe3+-R3+ magnetic interaction which dominates the sophisticated magnetic phase transitions in the rare-earth orthoferrites.

  8. Structural, dielectric and magnetic properties of (Pb1-xCax)(Fe0.5Nb0.5)O3 solid solution ceramics

    NASA Astrophysics Data System (ADS)

    Puri, Maalti; Bahel, Shalini; Raevski, I. P.; Narang, Sukhleen Bindra

    2016-06-01

    Ceramic samples of (Pb1-xCax)(Fe0.5Nb0.5)O3 with x=0.0, 0.20, 0.40, 0.45, 0.50, 0.55, 0.60 and 1.0 were fabricated by columbite precursor method. All the synthesized samples have a perovskite structure and unit cell volume decreases with increasing Ca content. The substitution of Ca for Pb has been found to have a pronounced effect on structural, dielectric and magnetic properties. Saturated magnetic loops were observed at room temperature for compositions with x≥0.40. The observed maximal magnetization at room temperature is rather small and varies non-monotonically with increasing Ca contents. It is supposed that room-temperature magnetic properties of (Pb1-xCax)(Fe0.5Nb0.5)O3 ceramics might be due to the presence of ferromagnetic impurity, presumably PbFe12O19 and/or CaFe12O19.

  9. Evidence of spin glass like ordering and electronic phase arrest in Pr3+ doped Sm0.5Sr0.5MnO3 bulk manganites

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Panda, J.; Nath, T. K.

    2012-06-01

    The effect of doping of rare earth Pr3+ ion replacing Sm3+ in Sm0.5Sr0.5MnO3 is investigated in details. Measurements of linear and non linear ac magnetic susceptibility, resistivity, magnetoresistance on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 shows various interesting features with doping level x=0.15. Here we observe the frequency independent FM-PM transition at higher temperature followed by a frequency dependent re-entered magnetic transition at lower temperature through complex ac susceptibility measurements. We have ascribed our observation to the formation of finite size ferromagnetic clusters which are formed as a consequence of intrinsic phase separation and undergo Spin glass-like freezing below certain temperature in this manganite. The magnetoresistance of the samples also show strong irreversibility with respect to sweeping of the field between highest positive and negative values. All these experimental results have been attributed to phase separation effect and kinetic arrest of electronically phase separated system.

  10. 59Co nuclear magnetic resonance study of the local distribution of atoms in the Heusler compound Co2FeAl0.5Si0.5

    NASA Astrophysics Data System (ADS)

    Wurmehl, Sabine; Kohlhepp, Jürgen T.; Swagten, Henk J. M.; Koopmans, Bert

    2012-02-01

    In this work, the spin-echo nuclear magnetic resonance (NMR) technique is used to probe the local structure of Co2FeAl0.5Si0.5 bulk samples. The 59Co NMR spectrum of the Heusler compound Co2FeAl0.5Si0.5 consists of four main resonance lines with an underlying sub-structure. The splitting into the main resonance lines is explained by contributions of the B2 type structure. The sub-lines are attributed to a random distribution of Al and Si. By comparing the experimental results with an appropriate multinomial distribution, the fraction of the Al/Si intermixing and the ratio between the contributing structure types is assigned. The main structural contribution of as-cast bulk samples is of B2 type with 38% of L21 contributions. The L21 contribution can be enhanced to 59% by an appropriate annealing process. However, B2 contributions are still present after annealing. Additional foreign phases such as fcc-Co and Co-Al, with relative contributions of less than one percent, are also found in both as-cast and annealed samples. Resonance lines related to slight amounts of the ternary, parental Heusler compounds Co2FeAl and Co2FeSi are also observed.

  11. Pressure-induced phase transition in La1 -xSmxO0.5F0.5BiS2

    NASA Astrophysics Data System (ADS)

    Fang, Y.; Yazici, D.; White, B. D.; Maple, M. B.

    2015-09-01

    Electrical resistivity measurements on La1 -xSmxO0.5F0.5BiS2 (x =0.1 ,0.3 ,0.6 ,0.8 ) have been performed under applied pressures up to 2.6 GPa from 2 K to room temperature. The superconducting transition temperature Tc of each sample significantly increases at a Sm-concentration-dependent pressure Pt, indicating a pressure-induced phase transition from a low-Tc to a high-Tc phase. At ambient pressure, Tc increases dramatically from 2.8 K at x =0.1 to 5.4 K at x =0.8 ; however, the Tc values at P >Pt decrease slightly with x , and Pt shifts to higher pressures with Sm substitution. In the normal state, semiconducting-like behavior is suppressed, and metallic conduction is induced with increasing pressure in all of the samples. These results suggest that the pressure dependence of Tc for the BiS2-based superconductors is related to the lattice parameters at ambient pressure and enable us to estimate the evolution of Tc for SmO0.5F0.5BiS2 under pressure.

  12. Location of trivalent lanthanide dopant energy levels in (Lu{sub 0.5}Gd{sub 0.5}){sub 2}O{sub 3}

    SciTech Connect

    Retot, H.; Viana, B.; Bessiere, A.; Galtayries, A.

    2011-06-15

    The location of Ln{sup 3+} dopant energy levels relative to bands in (Lu{sub 0.5}Gd{sub 0.5}){sub 2}O{sub 3} was studied. A several-steps analysis of XPS measurements on heavy lanthanides sesquioxides Ln{sub 2}O{sub 3} (Ln = Gd, Tb, Dy, Er, Tm, Yb, Lu) and on Sc{sub 2}O{sub 3} and Y{sub 2}O{sub 3} reference materials were used to locate Ln{sup 3+} dopant ground state relative to the top of the valence band in (Lu{sub 0.5}Gd{sub 0.5}){sub 2}O{sub 3} within an error bar of {+-}0.4 eV. The agreement between XPS data and model was found improved relative to previous studies. When compared to XPS analysis, prediction based on optical absorption shows a slight underestimation attributed to the lack of precision in Ce{sup 4+} charge transfer band measurement.

  13. Synthesis, Structure, and Electrochemical Performance of High Capacity Li2Cu0.5Ni0.5O2 Cathodes

    DOE PAGESBeta

    Ruther, Rose E; Zhou, Hui; Dhital, Chetan; Saravanan, Kuppan; Kercher, Andrew K.; Chen, Guoying; Huq, Ashfia; Delnick, Frank M.; Nanda, Jagjit

    2015-09-08

    Orthorhombic Li2NiO2, Li2CuO2, and solid solutions thereof have been studied as potential cathode materials for lithium-ion batteries due to their high theoretical capacity and relatively low cost. While neither endmember shows good cycling stability, the intermediate composition, Li2Cu0.5Ni0.5O2, yields reasonably high reversible capacities. A new synthetic approach and detailed characterization of this phase and the parent Li2CuO2 are presented. The cycle life of Li2Cu0.5Ni0.5O2 is shown to depend critically on the voltage window. The formation of Cu1+ at low voltage and oxygen evolution at high voltage limit the electrochemical reversibility. In situ X-ray absorption spectroscopy (XAS), in situ Raman spectroscopy,more » and gas evolution measurements are used to follow the chemical and structural changes that occur as a function of cell voltage.« less

  14. Synthesis of FeNi3/(Ni0.5Zn0.5)Fe2O4 nanocomposite and its high frequency complex permeability

    NASA Astrophysics Data System (ADS)

    Lu, Xuegang; Liang, Gongying; Zhang, Yumei; Zhang, Wei

    2007-01-01

    FeNi3/(Ni0.5Zn0.5)Fe2O4 nanocomposite particles were successfully synthesized using the hydrazine reduction combined with ammonia co-precipitation ferrite coating method. The x-ray and transmission electron microscopy analysis showed that face-centred cubic-structured FeNi3 nanoparticles were coated with spinel Ni-Zn ferrite. The composite particles were nearly spherical with diameters of about 80-200 nm and exhibited typical soft magnetic properties. The saturation magnetization (Ms) of the composite was greatly improved, compared with that of traditional ferrite. With increasing ferrite content, the eddy-current loss was effectively suppressed and a notable high frequency characteristic, in which the real part μ' of the permeability was almost independent of the frequency, was observed. The imaginary part μ'' remained at an extremely low value below the frequency of 300 MHz. The cut-off frequency fr was estimated to be above 1 GHz. The highest value of μ' reached 13 when the ratio of FeNi3 to Ni0.5Zn0.5Fe2O4 was 1:1. Two peaks were observed in the permeability spectra, which may be ascribed to the ferromagnetic resonances of FeNi3 and Ni-Zn ferrite respectively.

  15. Poling-Written Ferroelectricity in Bulk Multiferroic Double-Perovskite BiFe0.5Mn0.5O3.

    PubMed

    Delmonte, Davide; Mezzadri, Francesco; Gilioli, Edmondo; Solzi, Massimo; Calestani, Gianluca; Bolzoni, Fulvio; Cabassi, Riccardo

    2016-06-20

    We present a comprehensive study of the electrical properties of bulk polycrystalline BiFe0.5Mn0.5O3, a double perovskite synthesized in high-pressure and high-temperature conditions. BiFe0.5Mn0.5O3 shows an antiferromagnetic character with TN = 288 K overlapped with an intrinsic antiferroelectricity due to the Bi(3+) stereochemical effect. Beyond this, the observation of a semiconductor-insulator transition at TP ≈ 140 K allows one to define three distinct temperature ranges with completely different electrical properties. For T > TN, electric transport follows an ordinary thermally activated Arrhenius behavior; the system behaves as a paramagnetic semiconductor. At intermediate temperatures (TP < T < TN), electric transport is best described by Mott's variable range hopping model with lowered dimensionality D = 1, stabilized by the magnetic ordering process and driven by the inhomogeneity of the sample on the B site of the perovskite. Finally, for T < TP, the material becomes a dielectric insulator, showing very unusual poling-induced soft ferroelectricity with high saturation polarization, similar to the parent compound BiFeO3. Under external electric poling, the system irreversibly evolves from antiferroelectric to polar arrangement. PMID:27247990

  16. Enhanced photocatalytic activity over Cd0.5Zn0.5S with stacking fault structure combined with Cu2+ modified carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Gong, Beini; Lu, Yonghong; Wu, Pingxiao; Huang, Zhujian; Zhu, Yajie; Dang, Zhi; Zhu, Nengwu; Lu, Guining; Huang, Junyi

    2016-03-01

    For enhanced photocatalytic performance of visible light responsive CdZnS, a series of Cd0.5Zn0.5S solid solutions were fabricated by different methods. It was found that the semiconductor obtained through the precipitation-hydrothermal method (CZS-PH) exhibited the highest photocatalytic hydrogen production rate of 2154 μmol h-1 g-1. The enhanced photocatalytic hydrogen production of CZS-PH was probably due to stacking fault formation as well as narrow bandgap, a large surface area and a small crystallite size. Based on this, carbon nanotubes modified with Cu2+ (CNTs (Cu)) were used as a cocatalyst for CZS-PH. The addition of CNTs (Cu) enhanced notably the absorption of the composites for visible light. The highest photocatalytic hydrogen production rate of the Cd0.5Zn0.5S-CNTs (Cu) composite was 2995 μmol h-1 g-1 with 1.0 wt.% of CNTs (Cu). The improvement of the photocatalytic activity by loading of CNTs (Cu) was not due to alteration of bandgap energy or surface area, and was probably attributed to suppression of the electron-hole recombination by the CNTs, with Cu2+ anchored in the interface optimizing the photogenerated electron transfer pathway between the semiconductor and CNTs. We report here the successful combination of homojunction and heterojunction in CdZnS semiconductor, which resulted in promotion of charge separation and enhanced photocatalytic activity.

  17. Superparamagnetic state by linear and non-linear AC magnetic susceptibility in Mn0.5Zn0.5Fe2O4 ferrites nanoparticles.

    PubMed

    Suneetha, T; Kundu, S; Kashyap, Subhash C; Gupta, H C; Nath, T K

    2013-01-01

    The Mn0.5Zn0.5Fe2O4 nanoparticles has been synthesized using citrate-gel-precursor method. The direct mixing of nitrates and acetates yields homogeneous nanoparticles. Phase formation and crystal structure of the synthesized powder were examined through the X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectra of the sample confirm the spinel structure. The average particle size was determined by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The average particle size is found to be about 13 nm. Superparamagnetic-like nature of the nanoparticles of Mn0.5Zn0.5Fe2O4 has been revealed through various dc and linear and non-linear ac magnetization measurements. However, the nanoparticles do not behave like ideal non-interacting superparamagnets. The magnetic particle size is found to be about 8 nm with saturation magnetization about 18.1 emu/g. The blocking temperature (T(B)) of the nanoparticle assembly is found to be about 150 K as observed from dc and ac magnetization measurements. The frequency dependence of the blocking temperature (T(B)) is found to follow Vogel-Fulcher law. The associated characteristic time tau0 is found to be 10(-5) s. This value is different from that generally found for non-interacting superparamagnetic (SPM) systems (tau0 = 10(-9)-10(-10) s). PMID:23646726

  18. Sintering behavior and dielectric properties of Bi3+-substituted Nd(Zn0.5Ti0.5)O3 microwave ceramics

    NASA Astrophysics Data System (ADS)

    Hu, Mingzhe; Ding, Zhao; Xiong, Gang; Ji, Denghui; Zhang, Kesheng

    2015-12-01

    The sintering behavior and dielectric properties of Bi3+-substituted Nd(Zn0.5Ti0.5)O3 (abbreviated as NZT) microwave ceramics (Nd1-xBix)(Zn0.5Ti0.5)O3 (0 ≤ x ≤ 0.15) (abbreviated as NBZT) are investigated. XRD results reveal the formation of single perovskite solid solutions for x ≤ 0.05 samples. For x > 0.05 samples, pyrochlore phase begins to segregate from the perovskite phase and its volume fraction increases with x. B-site Zn2+/Ti4+ 1:1 long range order (LRO) is detected by Raman Spectroscopy. The degree of LRO varies as a function of sintering conditions and chemical composition. The microwave dielectric properties of the composition are measured. By substituting Bi3+ for Nd3+, the temperature coefficient of resonant frequency (τf) tunes toward zero, however, the microwave quality factor, (Qf) deteriorates. For x = 0.03, τf reaches a minimum value of -18.9ppm/∘C with relative permittivity of ɛr = 48.2 and Qf = 1430GHz, respectively. The effect of Bi-doping on the Qf value is discussed.

  19. The role of chemical structure on the magnetic and electronic properties of Co2FeAl0.5Si0.5/Si(111) interface

    NASA Astrophysics Data System (ADS)

    Kuerbanjiang, Balati; Nedelkoski, Zlatko; Kepaptsoglou, Demie; Ghasemi, Arsham; Glover, Stephanie E.; Yamada, Shinya; Saerbeck, Thomas; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas P. A.; Bell, Gavin R.; Hamaya, Kohei; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-04-01

    We show that Co2FeAl0.5Si0.5 film deposited on Si(111) has a single crystal structure and twin related epitaxial relationship with the substrate. Sub-nanometer electron energy loss spectroscopy shows that in a narrow interface region there is a mutual inter-diffusion dominated by Si and Co. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that the film has B2 ordering. The film lattice structure is unaltered even at the interface due to the substitutional nature of the intermixing. First-principles calculations performed using structural models based on the aberration corrected electron microscopy show that the increased Si incorporation in the film leads to a gradual decrease of the magnetic moment as well as significant spin-polarization reduction. These effects can have significant detrimental role on the spin injection from the Co2FeAl0.5Si0.5 film into the Si substrate, besides the structural integrity of this junction.

  20. Oxygen-Vacancy-Induced Antiferromagnetism to Ferromagnetism Transformation in Eu0.5Ba0.5TiO3−δ Multiferroic Thin Films

    PubMed Central

    Li, Weiwei; Zhao, Run; Wang, Le; Tang, Rujun; Zhu, Yuanyuan; Lee, Joo Hwan; Cao, Haixia; Cai, Tianyi; Guo, Haizhong; Wang, Can; Ling, Langsheng; Pi, Li; Jin, Kuijuan; Zhang, Yuheng; Wang, Haiyan; Wang, Yongqiang; Ju, Sheng; Yang, Hao

    2013-01-01

    Oxygen vacancies (VO) effects on magnetic ordering in Eu0.5Ba0.5TiO3−δ (EBTO3−δ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO3−δ thin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the VO. Eu0.5Ba0.5TiO3 ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperature of 1.85 K has been found in the EBTO3−δ thin films. Spin-polarized Ti3+ ions, which originated from the VO, has been proven to mediate a FM coupling between the local Eu 4f spins and were believed to be responsible for the great change of the magnetic ordering. Considering the easy formation of VO, our work opens up a new avenue for achieving co-existence of FM and FE orders in oxide materials. PMID:24018399

  1. Superparamagnetic behavior of heat treated Mg0.5Zn0.5Fe2O4 ferrite nanoparticles studied by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Srinivas, Ch.; Singh, S. B.; Tirupanyam, B. V.; Meena, S. S.; Yusuf, S. M.; Prasad, S. A. V.; Krishna, K. S. Rama; Sastry, D. L.

    2016-05-01

    Nanoparticles of Mg0.5Zn0.5Fe2O4 ferrite have been synthesized by co-precipitation method. XRD and Mössbauer spectroscopic results of Mg0.5Zn0.5Fe2O4 annealed at 200 °C, 500 °C and 800 °C are reported. It was observed that the crystallite size increases and the lattice parameter decreases with increase in annealing temperature. The observed decrease in lattice strain supports the increase in crystallite size. The Mössbauer spectra of the samples annealed at 200 °C and 500 °C exhibits superparamagnetic doublets whereas the Mössbauer spectrum of the sample annealed at 800 °C exhibits paramagnetic doublet along with weak sextet of hyperfine interaction. The values of isomer shift resemble the presence of high spin iron ions. The studied ferrite nanoparticles are suitable for biomedical applications. The results are incorporated employing core-shell model and cation redistribution.

  2. Enhancement of transition temperature in Fe{sub x}Se{sub 0.5}Te{sub 0.5} film via iron vacancies

    SciTech Connect

    Zhuang, J. C.; Yeoh, W. K. E-mail: zxshi@seu.edu.cn; Cui, X. Y.; Ringer, S. P.; Kim, J. H.; Shi, D. Q.; Wang, X. L.; Dou, S. X.; Shi, Z. X. E-mail: zxshi@seu.edu.cn

    2014-06-30

    The effects of iron deficiency in Fe{sub x}Se{sub 0.5}Te{sub 0.5} thin films (0.8 ≤ x ≤ 1) on superconductivity and electronic properties have been studied. A significant enhancement of the superconducting transition temperature (T{sub C}) up to 21 K was observed in the most Fe deficient film (x = 0.8). Based on the observed and simulated structural variation results, there is a high possibility that Fe vacancies can be formed in the Fe{sub x}Se{sub 0.5}Te{sub 0.5} films. The enhancement of T{sub C} shows a strong relationship with the lattice strain effect induced by Fe vacancies. Importantly, the presence of Fe vacancies alters the charge carrier population by introducing electron charge carriers, with the Fe deficient film showing more metallic behavior than the defect-free film. Our study provides a means to enhance the superconductivity and tune the charge carriers via Fe vacancy, with no reliance on chemical doping.

  3. Structure and magnetic properties of the perovskite YCo{sub 0.5}Fe{sub 0.5}O{sub 3}

    SciTech Connect

    Wei, Yingfen; Gui, Hong; Zhao, Zhenjie; Xie, Wenhui; Li, Junrui; Li, Xiaohong; Liu, Yong; Xin, Shengwei

    2014-12-15

    Y Co{sub 0.5}Fe{sub 0.5}O{sub 3}, in a structure of perovskite, has been successfully prepared with citrate precursors at 950-1100 °C in air by the sol-gel method. The X-ray diffraction patterns show that the samples are orthorhombic within the space group Pnma, where the Co and Fe ions are disordered at the 4b crystallographic sites. The crystal structure refinement undertaken by the Rietveld method has shown that the distortion of Co(Fe)O{sub 6} octahedra are large, where the ratio of Co/Fe-O bonding length along a axis to that in the bc plane is about 1.07. Such a large crystal lattice distortion implies a strong lattice-magnetism coupling, which may be utilized in the magnetoelectric devices. Magnetic measurement indicates that the Y Co{sub 0.5}Fe{sub 0.5}O{sub 3} is antiferromagnetic but showing weak ferromagnetism. We find that Fe{sup 3+} ions are in high-spin states, while Co{sup 3+} ions are in low-spin states which do not contribute to the magnetism. Both Fe{sup 3+} and Co{sup 3+} ions are not Jahn-Teller activated although the lattice distortion is large.

  4. Epitaxial Ferroelectric Ba(0.5)Sr(0.5)TiO3 Thin Films for Room-Temperature High-Frequency Tunable Element Applications

    NASA Technical Reports Server (NTRS)

    Chen, C. L.; Feng, H. H.; Zhang, Z.; Brazdeikis, A.; Miranda, F. A.; VanKeuls, F. W.; Romanofsky, R. R.; Huang, Z. J.; Liou, Y.; Chu, W. K.; Chu, C. W.

    1999-01-01

    Perovskite Ba(0.5)SR(0.5)TiO3 thin films have been synthesized on (001) LaAl03 substrates by pulsed laser ablation. Extensive X-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of <100>(sub BSTO)//<100>(sub LAO). Rutherford Backscattering Spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield chi(sub min) Of only 2.6 %. The dielectric property measurements by the interdigital technique at 1 MHz show room temperature values of the relative dielectric constant, epsilon(sub r), and loss tangent, tan(sub delta), of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba(0.5)SR(0.5)TiO3 films can be used for development of room-temperature high-frequency tunable elements.

  5. Structural, Dielectric, and Electrical Properties of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3

    NASA Astrophysics Data System (ADS)

    Panda, Niranjan; Pattanayak, Samita; Choudhary, R. N. P.

    2015-12-01

    Polycrystalline samples of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3 (BPFZTO) with x = 0.0, 0.2, 0.3, and 0.4 were prepared by high-temperature solid-state reaction. Preliminary structural analysis of calcined powders of the materials by use of x-ray powder diffraction confirmed formation of single-phase systems with the tetragonal structure. Room-temperature scanning electron micrographs of the samples revealed uniform distribution of grains of low porosity and different dimensions on the surface of the samples. The frequency-temperature dependence of dielectric and electric properties was studied by use of dielectric and complex impedance spectroscopy over a wide range of frequency (1 kHz to 1 MHz) at different temperatures (25-500°C). The dielectric constant of BiFeO3 (BFO) was enhanced by substitution with Pb(Zr0.5Ti0.5)O3 (PZT) whereas the dielectric loss of the BPFZTO compounds decreased with increasing PZT content. A significant contribution of both grains and grain boundaries to the electrical response of the materials was observed. The frequency-dependence of the ac conductivity of BPFZTO followed Jonscher's power law. Negative temperature coefficient of resistance behavior was observed for all the BPFZTO samples. Conductivity by thermally excited charge carriers and oxygen vacancies in the materials was believed to be of the Arrhenius-type.

  6. Temperature dependence of magneto-transport properties in Co2Fe(Ga0.5Ge0.5)/Cu lateral spin valves

    NASA Astrophysics Data System (ADS)

    Ikhtiar, Kasai, S.; Takahashi, Y. K.; Furubayashi, T.; Mitani, S.; Hono, K.

    2016-02-01

    The non-local spin signals of Co2Fe(Ga0.5Ge0.5)/Cu lateral spin valves with sub-micron size dimensions were measured with varying temperatures. The non-local spin signal reaches 54 mΩ at 4 K, while it degrades down to 13 mΩ at room temperature. Analysis based on the one-dimensional spin diffusion model clarifies the dominant source for degrading of the spin signal is suppression of the spin diffusion length in Cu, not the spin polarization, indicating Co2Fe(Ga0.5Ge0.5) keeps half-metallic nature even at room temperature. The temperature dependence of non-local spin signal was found to exhibit a downturn at 36 K. The presence of magnetic impurities, detrimental effect of which becomes more pronounced for diffusive transport in long Cu wires, is suggested to cause the observed downturn in non-local spin signals.

  7. [Synthesis and spectra characterization of nano-sized Ce(1-x)(Fe(0.5)La(0.5))xO(2-delta) solid solutions].

    PubMed

    Zhang, Guo-fang; Zhang, Yang-huan; Ge, Qi-lu; Zhang, Yin; Liu, Ling-sheng; Zhang, Lian-lian

    2011-12-01

    Ce(1-x)(Fe(0.5)La(0.5))xO(2-delta) solid solutions were obtained via hydrothermal method. The structure of the solid solutions and the cell parameters were characterized by XRD analysis technique, the electron transition properties and doping effectswere measured by UV-Vis diffraction spectrum and Raman spectrum technique. XRD results showed that Ce(1-x)(Fe(0.5)La(0.5))xO(2-delta) id solutions exhibited cubic fluorite structure till the doping content increased to 0.30. Tiny Fe2O3 phase was observed when x = 0.30. The particle size was kept nanoscaled, and location of different kind of doping ions in CeO2 lattice was discussed. By increasing the doping content, the cell parameter was kept increasing gradually till x = 0.18, then it remained almost constant. The UV-Vis diffraction spectrum analysis showed that the absorption threshold edge redshifted, the band gap energy decreased with increasing the doping content. The valence of Fe ions in the lattice of CeO2 was +3. The F2g Raman mode also showed a downshift, and the peak gradually became broader, which further proved the influence of the dopant. PMID:22295785

  8. Octahedral distortion induced magnetic anomalies in LaMn{sub 0.5}Co{sub 0.5}O{sub 3} single crystals

    SciTech Connect

    Manna, Kaustuv Elizabeth, Suja; Anil Kumar, P. S.; Bhadram, Venkata Srinu; Narayana, Chandrabhas

    2014-07-28

    Single crystals of LaMn{sub 0.5}Co{sub 0.5}O{sub 3} belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)–oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn{sub 0.5}Co{sub 0.5}O{sub 3} crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal.

  9. Influence of epitaxial growth on phase competition in Pr 0.5Sr 0.5MnO 3 films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Chen, Yuansha; Ma, Yubin; Lian, Guijun; Zhang, Yan; Xiong, Guangcheng

    2012-03-01

    A series of Pr0.5Sr0.5MnO3 (PSMO) films with various thickness were epitaxially grown on substrates of (0 0 1)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT), LaAlO3 (LAO) and SrTiO3 (STO), and (0 1 1)-oriented STO using pulse laser deposition. Influence of epitaxial growth on phase competition was investigated. A ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition upon cooling is present in both largely compressed situations deposited on LAO (0 0 1) and tensile cases deposited on STO (0 0 1) but absent in little strained films grown on LSAT (0 0 1), indicating that the antiferromagnetic insulating state is favored by strains. On the other hand, the 400 nm films deposited on (0 1 1)-oriented STO as well as LAO substrates show FMM-AFI transition. These results reveal that both the orientation of epitaxial growth and substrate-induced strain affect the FMM-AFI transition.

  10. Multiferroicity and magnetoelectric coupling enhanced large magnetocaloric effect in DyFe{sub 0.5}Cr{sub 0.5}O{sub 3}

    SciTech Connect

    Yin, L. H.; Yang, J.; Dai, J. M.; Song, W. H.; Zhang, R. R.; Sun, Y. P.

    2014-01-20

    DyFe{sub 0.5}Cr{sub 0.5}O{sub 3} has been synthesized using a sol-gel method. It exhibits ferroelectricity at the antiferromagnetic ordering temperature T{sub N1}∼261 K. Large magnetocaloric effect (MCE) (11.3 J/kg K at 4.5 T) enhanced by magnetoelectric coupling due to magnetic field and temperature induced magnetic transition was observed. Temperature-dependent Raman study shows an anomalous behavior near T{sub N1} in the phonon modes related to the vibration of Dy atoms and stretching of CrO{sub 6}/FeO{sub 6} octahedra, suggesting the ferroelectricity in DyFe{sub 0.5}Cr{sub 0.5}O{sub 3} is associated with the spin-phonon coupling with respect to both Dy and Cr/Fe ions. These results suggest routes to obtain high-temperature multiferroicity and large MCE for practical applications.

  11. CdTe(1-x)Se(x)/Cd0.5Zn0.5S core/shell quantum dots: core composition and property.

    PubMed

    Yang, Ping; Cao, Yongqiang; Li, Xiaoyu; Zhang, Ruili; Liu, Ning; Zhang, Yulan

    2014-08-01

    Alloy CdTe(1-x)Se(x) quantum dots (QDs) have been fabricated by an organic route using Cd, Te and Se precursors in a mixture of trioctylamine and octadecylphosphonic acid at 280 °C. The variation of photoluminescence (PL) peak wavelength of the CdTe(1-x)Se(x) QDs compared with CdTe QDs confirmed the formation of an alloy structure. The Se component drastically affected the stability of CdTe(1-x)Se(x) QDs. A Cd0.5Zn0.5S shell coating on CdTe(1-x)Se(x) cores was carried out using oleic acid as a capping agent. CdTe(1-x)Se(x)/Cd0.5Zn0.5S core/shell QDs revealed dark red PL while a yellow PL peak was observed for the CdTe(1-x)Se(x) cores. The PL efficiency of the core/shell QDs was drastically increased (less than 1% for the cores and up to 65% for the core/shell QDs). The stability of QDs in various buffer solutions was investigated. Core/shell QDs can be used for biological applications because of their high stability, tunable PL and high PL efficiency. PMID:23946281

  12. Localization Effect on Pt-Loaded Ce0.5Zr0.5O2 Nanoparticles Inserted Into Mesoporous SBA-16 by Hydrothermal Processing.

    PubMed

    Yotou, Hiroaki; Okamoto, Takumi; Ito, Miho; Sekino, Tohru; Tanaka, Shun-Ichiro

    2015-09-01

    We succeeded to use hydrothermal treatment to insert prefabricated Pt-loaded Ce0.5Zr0.5O2 (PtCZ) nanoparticles into the mesopores of the SBA-16 mesoporous silica without disordering of the mesoporous structure. Samples prepared by the hydrothermal treatment exhibited superior oxygen storage capacity compared to that of simple dry mixed sample. The oxygen storage capacity of the hydrothermally treated PtCZ is attributed to the localized PtCZ nanoparticles inside the mesopores of the SBA-16. FTIR analysis suggested that the PtCZ nanoparticles inside the mesopores possess the Si-O-Zr linkages that are bonded to the inner walls of the SBA-16 host. This linkage is the key reason for the superior oxygen storage capacity of PtCZ localized in the mesopores by hydrothermal treatment. It is considered that the formation of the Si-O-Zr linkage in the hydrothermally treated samples resulted in crystalline distortions of Ce0.5Zr0.5O2 nanoparticles inside the mesopores, and which contribute to enhance the oxygen storage capacity of PtCZ. PMID:26716294

  13. Theoretical study of magnetic properties and x-ray magnetic circular dichroism of the ordered Fe{sub 0.5}Pd{sub 0.5} alloy

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-01-01

    A detailed theoretical study of magnetic and structural properties of Fe{sub 0.5}Pd{sub 0.5} ordered face-centered tetragonal (fct) alloy, using both the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), is presented. The total energy surface as a function of the lattice parameters a and c shows a long valley where stable structures may exist. Our calculation using the GGA predicts a magnetic phase transition from perpendicular to parallel magnetization as a function of the lattice parameter, whereas LSDA favors always the [001] magnetization axis for all values of the lattice parameters. The spin and orbital magnetic moments and x-ray magnetic circular dichroism spectra are calculated for the easy [001] and the hard [100] magnetization axis and for three sets of experimental lattice parameters, and are compared to the available experimental results on these films. A supercell calculation for a 4 monolayer Fe{sub 0.5}Pd{sub 0.5} thin film produced similar results. While the spin magnetic moments are in fair agreement with experiment, the orbital magnetic moments are considerably underestimated. To improve the agreement with experiment we included an atomic orbital polarization term; however, the computed orbital moments scarcely changed. (c) 2000 The American Physical Society.

  14. Chemically stable perovskites as cathode materials for solid oxide fuel cells: La-doped Ba0.5Sr0.5Co0.8Fe0.2O(3-δ).

    PubMed

    Kim, Junyoung; Choi, Sihyuk; Jun, Areum; Jeong, Hu Young; Shin, Jeeyoung; Kim, Guntae

    2014-06-01

    Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) (BSCF) has won tremendous attention as a cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFC) on the basis of its fast oxygen-ion transport properties. Nevertheless, wide application of BSCF is impeded by its phase instabilities at intermediate temperature. Here we report on a chemically stable SOFC cathode material, La0.5Ba0.25Sr0.25Co0.8Fe0.2O(3-δ) (LBSCF), prepared by strategic approaches using the Goldschmidt tolerance factor. The tolerance factors of LBSCF and BSCF indicate that the structure of the former has a smaller deformation of cubic symmetry than that of the latter. The electrical property and electrochemical performance of LBSCF are improved compared with those of BSCF. LBSCF also shows excellent chemical stability under air, a CO2-containg atmosphere, and low oxygen partial pressure while BSCF decomposed under the same conditions. Together with this excellent stability, LBSCF shows a power density of 0.81 W cm(-2) after 100 h, whereas 25 % degradation for BSCF is observed after 100 h. PMID:24737665

  15. Treatment of trichostasis spinulosa with 0.5-millisecond pulsed 755-nm alexandrite laser.

    PubMed

    Badawi, Ashraf; Kashmar, Mouhamad

    2011-11-01

    Trichostasis spinulosa (TS) is a follicular disorder in which multiple hairs in a keratinous sheath project above the skin surface. Current treatments provide temporary relief and side effects are common. We report the successful treatment of TS in 20 patients using a short-pulsed 755-nm alexandrite laser. The 20 patients (skin types II-V) presented with TS lesions on the tip of their nose. All patients received a single treatment (one to three passes) with the laser with cold air cooling but without anaesthesia or analgesia. Treatment parameters were as follows: pulse duration 0.5 ms, fluence 15-17 J/cm(2), and spot size 5 mm. The entire procedure required less than 5 min to perform. The patients were followed up for 3 months for any adverse effects or recurrence. In all patients the lesions disappeared immediately after treatment with minimal or no pain. Erythema was minimal and lasted 5-20 min in all patients. Patients were very satisfied. The treated areas were still clear 4 to 5 weeks later, and a second treatment was not considered necessary. There were adverse effects other than the erythema and there was no recurrence within the follow-up period of 3 months. A single treatment with a short-pulsed 755-nm alexandrite laser appears to be a rapid, minimally painful, and effective treatment for TS in patients of skin types II to V. PMID:21842223

  16. Elaboration of Ti{sub 0.5}Pb{sub 0.5}Sr{sub 2}CaCu{sub 2}O{sub x} superconducting phases by an ultrasonic spray-pyrolysis process

    SciTech Connect

    Abraham, R.; Guenard, F.; Lebbou, K.; Trosset, S.; Cohen-Adad, M.T.; Jorda, J.L.; Couach, M.

    1998-02-01

    An ultrasonic spray-pyrolysis process has been used to prepare a homogeneous T{sub 10.5}Pb{sub 0.5}Sr{sub 2}CaCu{sub 2}O{sub x} high-temperature superconductor. Depending on experimental conditions, the grain morphology changes from platelet to cauliflower-like, contrary to the three copper layers series. The (Tl/Pb)-Sr-1212 phase has remarkable stability and does not decompose before melting. The critical temperature onset, about 80 K, is similar to that for samples prepared by the usual sintering methods.

  17. Dielectric constant tunability at microwave frequencies and pyroelectric behavior of lead-free submicrometer-structured (Bi0.5Na0.5)1-xBaxTiO3 ferroelectric ceramics.

    PubMed

    Martínez, Félix L; Hinojosa, Juan; Doménech, Ginés; Fernández-Luque, Francisco J; Zapata, Juan; Ruiz, Ramon; Pardo, Lorena

    2013-08-01

    In this article, we show that the dielectric constant of lead-free ferroelectric ceramics based on the solid solution (1-x)(Bi(0.5)Na(0.5))TiO(3)-xBaTiO(3), with compositions at or near the morphotropic phase boundary (MPB), can be tuned by a local applied electric field. Two compositions have been studied, one at the MPB, with x = 0.06 (BNBT6), and another one nearer the BNT side of the phase diagram, with x = 0.04 (BNBT4). The tunability of the dielectric constant is measured at microwave frequencies between 100 MHz and 3 GHz by a nonresonant method and simultaneously applying a dc electric field. As expected, the tunability is higher for the composition at the MPB (BNBT6), reaching a maximum value of 60% for an electric field of 900 V/cm, compared with the composition below this boundary (BNBT4), which saturates at 40% for an electric field of 640 V/cm. The high tunability in both cases is attributed to the fine grain and high density of the samples, which have a submicrometer homogeneous grain structure with grain size of the order of a few hundred nanometers. Such properties make these ceramics attractive for microwave tunable devices. Finally, we have tested these ceramics for their application as infrared pyroelectric detectors and we have found that the pyroelectric figure of merit is comparable to traditional lead-containing pyroelectrics. PMID:25004530

  18. Structure and properties of Bi(Zn0.5Ti0.5)O3- Pb(Zr(1-x)Ti(x))O3 ferroelectric single crystals grown by a top-seeded solution growth technique.

    PubMed

    Wang, Bixia; Wu, Xiaoqing; Ren, Wei; Ye, Zuo-Guang

    2015-06-01

    Bi(Zn0.5Ti0.5)O3 (BZT)-modified Pb(Zr(1-x)Ti(x))O3 (PZT) single crystals have been grown using a top-seeded solution growth technique and characterized by various methods. The crystal structure is found to be rhombohedral by means of X-ray powder diffraction. The composition and homogeneity of the as-grown single crystals are studied by laser ablation inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. The domain structure of a (001)(cub) platelet is investigated by polarized light microscopy (PLM), which confirms the rhombohedral symmetry. The paraelectric-to-ferroelectric phase transition temperature T(C) is found to be 313°C with the absence of rhombohedral-tetragonal phase transition. The ferroelectric properties of the ternary crystals are enhanced by the BZT substitution with a remanent polarization of 28 μC/cm(2) and a coercive field E(C) of 22.1 kV/cm. PMID:26067036

  19. Magnetoelectric coupling study in multiferroic Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} ceramics through small and large electric signal standard measurements

    SciTech Connect

    Raymond, Oscar; Siqueiros, Jesus M.; Font, Reynaldo; Portelles, Jorge

    2011-05-01

    Multifunctional multiferroic materials such as the single phase compound Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} (PFN), where ferroelectric and antiferromagnetic order coexist, are very promising and have great interest from the academic and technological points of view. In this work, coupling of the ferroelectric and magnetic moments is reported. For this study, a combination of the small signal response using the impedance spectroscopy technique and the electromechanical resonance method with the large signal response through standard ferroelectric hysteresis measurement, has been used with and without an applied magnetic field. The measurements to determine the electrical properties of the ceramic were performed as functions of the bias and poling electric fields. A simultaneous analysis of the complex dielectric constant {epsilon}-tilde, impedance Z-tilde, electric modulus M-tilde, admittance Y-tilde, and the electromechanical parameters and coupling factors is presented. The results are correlated with a previous study of structural, morphological, small signal dielectric frequency-temperature response, and the ferroelectric hysteretic, magnetic and magnetodielectric behaviors. The observed shifts of the resonance and antiresonance frequency values can be associated with change of the ferroelectric domain size favored by the readjustment of the oxygen octahedron when the magnetic field is applied. From P-E hysteresis loops obtained without and with an external applied magnetic field, a dc magnetoelectric coupling effect with maximum value of 4 kV/cm T (400 mV/cm Oe) was obtained.

  20. Dielectric, ferroelectric, and piezoelectric properties of the lead-free (1-x)(Na0.5Bi0.5)TiO3-xBiAlO3 solid solution

    NASA Astrophysics Data System (ADS)

    Yu, Huichun; Ye, Zuo-Guang

    2008-09-01

    Lead-free piezoelectric ceramics derived from the solid solution of (1-x)(Na0.5Bi0.5)TiO3-xBiAlO3 (NBT-BA) (x =0-0.10) have been synthesized by solid state reactions. A pure perovskite phase was formed for x ≤0.08. The temperature dependence of dielectric constant indicates an increased broadness of the dielectric peak as the amount of BA increases. The large dielectric loss of NBT ceramics at low frequency and high temperature has been significantly reduced by the substitution of BA. The high coercive field is decreased and ferroelectric hysteresis loops were displayed at room temperature. The NBT-BA ceramics exhibit improved ferroelectric and piezoelectric properties compared to pure NBT ceramics, with Pr=52 μC/cm2, Ec=44 kV/cm, d33=130 pC/N, and kp=0.23 for 0.92NBT-0.08BA.

  1. Nonlinear optical properties of pulsed laser deposited Gd2O3 and Dy2O3 doped K0.5Na0.5NbO3 thin films

    NASA Astrophysics Data System (ADS)

    Peddigari, Mahesh; Pattipaka, Srinivas; Bharti, Gyan Prakash; Khare, Alika; Dobbidi, Pamu

    2016-08-01

    We report the structural and nonlinear optical properties of Gd2O3 and Dy2O3 doped (K0.5Na0.5)NbO3 (KNN) lead-free thin films fabricated by pulsed laser deposition technique. The crystal structure of the films was analyzed by using Rietveld method. The higher tetragonality and improved surface morphology was observed for the rare-earth oxide doped films. The change in crystal structure and tetragonality with these dopants was explained in terms of change in the internal vibration modes of NbO6 octahedra. The nonlinear optical properties of the films were measured by using single beam Z-scan technique with a continuous wave He-Ne laser (λ = 632.8 nm). All the films have shown a large third-order nonlinear susceptibility and observed to be enhanced for rare-earth doped KNN thin films (|χ(3)| = 2.69 × 10-3 esu). The maximum nonlinear refractive index, n2 = 2.02 × 10-5 cm2/W, and nonlinear absorption coefficient, β = 3.48 cm/W, were obtained for Gd2O3, and Dy2O3 doped films respectively. These results indicate that rare-earth doped KNN thin films are potential candidates for nonlinear photonic applications.

  2. Preparation and characterization of La0.75Sr0.25Cr0.5Mn0.5O3-δ-yttria stabilized zirconia cathode supported solid oxide electrolysis cells for hydrogen generation

    NASA Astrophysics Data System (ADS)

    Xing, Ruimin; Wang, Yarong; Liu, Shanhu; Jin, Chao

    2012-06-01

    La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM)-YSZ cathode supported solid oxide electrolysis cells (SOECs), with the LSM-YSZ|YSZ|LSCM-YSZ configuration, have been prepared and evaluated for high temperature hydrogen generation. Electrochemical impedance spectra (EIS) and voltage-current curves were recorded out to characterize the cell performance. EIS results showed that the cell resistance increased as the proportion of steam in the feed supply increased, at open circuit voltage. The hydrogen generation rate calculated from Faraday's law is 561 ml cm-2 h-1 at 850 °C with 80 vol.% absolute humidity (AH) at a 1.6 V electrolysis voltage. Although there is a 8.2% increase of the applied electrolysis voltage, the cell has endured a test lasting more than 103 h with 45 vol.% AH and 0.33 A cm-2 electrolysis current density at 850 °C. Energy-dispersive X-ray (EDX) spectroscopy analysis showed that there is no elemental diffusion between the electrode and electrolyte interface after the durability test. Scanning electron microscopy (SEM) images indicate that the slight split between the LSCM-YSZ cathode and the YSZ electrolyte is responsible for the increase of ohmic resistance of the cell; this resistance rise led to the degradation of the cell performance.

  3. Microstructure and ferroelectric properties of epitaxial cation ordered PbSc0.5Ta0.5O3 thin films grown on electroded and buffered Si(100)

    NASA Astrophysics Data System (ADS)

    Chopra, Anuj; Pantel, Daniel; Kim, Yunseok; Alexe, Marin; Hesse, Dietrich

    2013-08-01

    Epitaxial PbSc0.5Ta0.5O3 (001) films with an epitaxial LaNiO3 bottom electrode were deposited on CeO2/yttria-stabilized zirconia-buffered Si (100) substrates. Crystal orientation, in-plane and out-of-plane lattice parameters, surface morphology, and microstructure were analyzed by X-ray diffraction, X-ray reciprocal lattice mapping measurements, atomic force microscopy, and transmission electron microscopy, respectively. XRD superstructure reflections indicate that the films are cation ordered. Polarization-field and switching current-voltage hysteresis curves were measured at room temperature. The measured spontaneous polarization Ps, remnant polarization Pr, and coercive voltage Vc were found to be 14 μC/cm2, 4 μC/cm2, and 1.1 V, respectively, at room temperature. Furthermore, field as well as frequency dependence of the dielectric constant were measured at room temperature. Piezoelectric measurements performed on these PST films showed a sharp non-linearity, which is attributed to the possibility of field induced phase transition and/or percolation of polar nano regions.

  4. Intrinsic magnetic, structural and resistivity properties of ferromagnetic Mn{sub 0.5}Zn{sub 0.5}Al{sub x}Fe{sub 2−x}O{sub 4} nanoparticles

    SciTech Connect

    Haralkar, S.J.; Kadam, R.H.; More, S.S.; Shirsath, Sagar E.; Mane, M.L.; Patil, Swati; Mane, D.R.

    2013-03-15

    Highlights: ► Al{sup 3+} ion substituted Mn–Zn ferrite nanoparticles. ► Single phase cubic spinel structure changes with Al{sup 3+} substitution. ► Magnetization and coercivity decreased with increasing Al{sup 3+}. ► Resistivity increased with Al{sup 3+} substitution. - Abstract: In this work the nano-structural, magnetic and resistivity properties of Al{sup 3+} substituted Mn–Zn ferrites powders were investigated. Mn{sub 0.5}Zn{sub 0.5}Al{sub x}Fe{sub 2−x}O{sub 4} powders, where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 were obtained by the sol–gel auto-combustion method. X-ray diffraction data indicate that, after substitution, all the samples consisted of the main spinel phase in combination with a small amount of a foreign Al{sub 2}O{sub 3} phase. The addition of Al{sup 3+} resulted in a reduction of particle size and density of the prepared samples. Cation distribution in the present study was estimated by using X-ray diffraction data. The tetrahedral site radii initially increased with Al{sup 3+} content while the octahedral site radii decreased with the Al{sup 3+} substitution. FTIR spectra show two strong absorption bands at 529–548 cm{sup −1} and 445–452 cm{sup −1} which are the typical bands for the cubic spinel crystal structure. The magnetic properties were measured by employing a vibrating sample magnetometer. It was observed that the saturation magnetization, coercivity and anisotropy field decreased with the increase of Al{sup 3+} substitution. Introduction of Al{sup 3+} ions into the Mn–Zn ferrite increased the values of the resistivity, especially in the lower temperature range.

  5. Self-assembled monolayers and chemical derivatization of Ba 0.5Sr 0.5TiO 3 thin films: Applications in phase shifter devices

    NASA Astrophysics Data System (ADS)

    Morales-Cruz, Angel L.; Keuls, Fred W. Van; Miranda, Félix A.; Cabrera, Carlos R.

    2005-11-01

    Thin films of barium strontium titanate (Ba 1- xSr x TiO 3 (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible S sbnd O interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm -1, which is characteristic of an O

  6. High Piezoelectric Response in (Li0.5Sm0.5)2+-Modified 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 Near the Nonergodic-Ergodic Relaxor Transition

    NASA Astrophysics Data System (ADS)

    Xu, Jiwen; Li, Qinglin; Zhou, Changrong; Zeng, Weidong; Xiao, Jianrong; Ma, Jiafeng; Yuan, Changlai; Chen, Guohua; Rao, Guanghui; Li, Xuqiong

    2016-06-01

    The (Bi0.5Na0.5)TiO3-BaTiO3 system is a promising Pb-free piezoelectric material to substitute for environmentally undesirable Pb-based ferroelectrics. However, understanding the origin of its high piezoelectric response is a fundamental issue that has remained unclear for decades. Here, complex ions (Li0.5Sm0.5)2+ were introduced to dictate the stability of the electrically-induced ferroelectric state in 0.93(Bi0.5Na0.5)1- x (Li0.5Sm0.5) x TiO3-0.07BaTiO3 relaxor ceramics. The applied electric field induces a phase transition from a non-ergodic state to a ferroelectric state as well as the realignment of ferroelectric domains. The non-ergodic relaxor state with x = 0-0.02 is accompanied by relatively high piezoelectric activity and the strongest piezoelectricity is observed near the crossover from the nonergodic to the ergodic state. The stable␣ferroelectric state cannot survive after the removal of the application electric field for the high doping level due to the enhancement of the random field, which is responsible for the rapid decrease of piezoelectric properties for x > 0.02 compositions.

  7. Phase structure and piezoelectric properties of (1-x)K0.48Na0.52Nb0.95Sb0.05O3-x(Bi0.5Na0.5)0.9(Li0.5Ce0.5)0.1ZrO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Xing, Jie; Tan, Zhi; Jiang, Laiming; Chen, Qiang; Wu, Jiagang; Zhang, Wen; Xiao, Dingquan; Zhu, Jianguo

    2016-01-01

    (1-x)K0.48Na0.52Nb0.95Sb0.05O3-x(Bi0.5Na0.5)0.9(Li0.5Ce0.5)0.1ZrO3 [(1-x)KNNS-xBNLCZ] lead-free piezoceramics were prepared by the conventional solid state sintering method. The effects of BNLCZ contents on their phase structure, microstructure, and piezoelectric properties were investigated. All the samples show a pure perovskite structure, and no secondary phases were formed in the detected range. The rhombohedral and tetragonal phases of (1-x)KNNS-xBNLCZ coexist in the composition range of 0.0325 ≤ x ≤ 0.0425 at room temperature. A remarkably strong piezoelectricity was obtained by the addition of appropriate BNLCZ contents. The excellent piezoelectric properties of the ceramics with x = 0.04 were obtained: d33 ˜ 485 pC/N, kp ˜ 48%, and TC ˜ 227 °C. All the results show that the introduction of (Bi0.5Na0.5)0.9(Li0.5Ce0.5)0.1ZrO3 is a very effective way to form the rhombohedral and tetragonal phase coexistence of potassium-sodium niobate-based ceramics, which can improve its piezoelectric properties.

  8. 77 FR 53892 - Determination That ALOXI (Palonosetron Hydrochloride) Capsules, 0.5 Milligram (Base), Were Not...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-04

    ...The Food and Drug Administration (FDA) has determined that ALOXI (palonosetron hydrochloride (HCl)) Capsules, 0.5 milligram (mg) (base), were not withdrawn from sale for reasons of safety or effectiveness. This determination will allow FDA to approve abbreviated new drug applications (ANDAs) for palonosetron HCl capsules, 0.5 mg (base), if all other legal and regulatory requirements are...

  9. Dielectric and piezoelectric properties of CeO2-added nonstoichiometric (Na0.5K0.5)0.97(Nb0.96Sb0.04)O3 ceramics for piezoelectric energy harvesting device applications.

    PubMed

    Oh, Youngkwang; Noh, Jungrae; Yoo, Juhyun; Kang, Jinhee; Hwang, Larkhoon; Hong, Jaeil

    2011-09-01

    In this study, nonstoichiometric (Na(0.5)K(0.5))(0.97)(Nb(0.96)Sb(0.04))O(3) ceramics were fabricated and their dielectric and piezoelectric properties were investigated according to the CeO(2) addition. In this ceramic composition, CeO(2) addition improved sinterability, electromechanical coupling factor k(p), mechanical quality factor Q(m), piezoelectric constant d(33), and g(33). At the sintering temperature of 1100°C, for the 0.2wt% CeO(2) added specimen, the optimum values of density = 4.359 g/cm(3), k(p) = 0.443, Q(m) = 588, ε(r) = 444, d(33) = 159 pC/N, and g(33) = 35 × 10(-3) V·m/N, were obtained. A piezoelectric energy harvesting device using 0.2 wt% CeO(2)- added lead-free (K(0.5)Na(0.5))(0.97)(Nb(0.96)Sb(0.04))O(3) ceramics and a rectifying circuit for energy harvesting were fabricated and their electrical characteristics were investigated. Under an external vibration acceleration of 0.7 g, when the mass, the frequency of vibration generator, and matching load resistance were 2.4 g, 70 Hz, and 721 Ω, respectively, output voltage and power of piezoelectric harvesting device indicated the optimum values of 24.6 mV(rms) and 0.839 μW, respectively-suitable for application as the electric power source of a ubiquitous sensor network (USN) sensor node. PMID:21937318

  10. Polyhedral Serpentine Grains in CM Chondrites

    NASA Technical Reports Server (NTRS)

    Zega, Thomas J.; Garvie, Laurence A. J.; Dodony, Istvan; Stroud, Rhonda M.; Buseck, Peter R.

    2005-01-01

    CM chondrites are primitive rocks that experienced aqueous alteration in the early solar system. Their matrices and fine-grained rims (FGRs) sustained the effects of alteration, and the minerals within them hold clues to the aqueous reactions. Sheet silicates are an important product of alteration, and those of the serpentine group are abundant in the CM2 chondrites. Here we expand on our previous efforts to characterize the structure and chemistry of serpentines in CM chondrites and report results on a polyhedral form that is structurally similar to polygonal serpentine. Polygonal serpentine consists of tetrahedral (T) sheets joined to M(2+)-centered octahedral (O) sheets (where (M2+) is primarily Mg(2+) and Fe(2+)), which give rise to a 1:1 (TO) layered structure with a 0.7-nm layer periodicity. The structure is similar to chrysotile in that it consists of concentric lizardite layers wrapped around the fiber axis. However, unlike the rolled-up chrysotile, the tetrahedral sheets of the lizardite layers are periodically inverted and kinked, producing sectors. The relative angles between sectors result in 15- and 30-sided polygons in terrestrial samples.

  11. Redox centers evolution in phospho-olivine type (LiFe0.5Mn0.5 PO4) nanoplatelets with uniform cation distribution.

    PubMed

    Paolella, Andrea; Bertoni, Giovanni; Dilena, Enrico; Marras, Sergio; Ansaldo, Alberto; Manna, Liberato; George, Chandramohan

    2014-03-12

    In phospho-olivine type structures with mixed cations (LiM1M2PO4), the octahedral M1 and M2 sites that dictate the degree of intersites order/disorder play a key role in determining their electrochemical redox potentials. In the case of LiFexMn1-xPO4, for example, in micrometer-sized particles synthesized via hydrothermal route, two separate redox centers corresponding to Fe(2+)/Fe(3+) (3.5 V vs Li/Li(+)) and Mn(2+)/Mn(3+) (4.1 V vs Li/Li(+)), due to the collective Mn-O-Fe interactions in the olivine lattice, are commonly observed in the electrochemical measurements. These two redox processes are directly reflected as two distinct peak potentials in cyclic voltammetry (CV) and equivalently as two voltage plateaus in their standard charge/discharge characteristics (in Li ion batteries). On the contrary, we observed a single broad peak in CV from LiFe0.5Mn0.5PO4 platelet-shaped (∼10 nm thick) nanocrystals that we are reporting in this work. Structural and compositional analysis showed that in these nanoplatelets the cations (Fe, Mn) are rather homogeneously distributed in the lattice, which is apparently the reason for a synergetic effect on the redox potentials, in contrast to LiFe0.5Mn0.5PO4 samples obtained via hydrothermal routes. After a typical carbon-coating process in a reducing atmosphere (Ar/H2), these LiFe0.5Mn0.5PO4 nanoplatelets undergo a rearrangement of their cations into Mn-rich and Fe-rich domains. Only after such cation rearrangement (via segregation) in the nanocrystals, the redox processes evolved at two distinct potentials, corresponding to the standard Fe(2+)/Fe(3+) and Mn(2+)/Mn(3+) redox centers. Our experimental findings provide new insight into mixed-cation olivine structures in which the degree of cations mixing in the olivine lattice directly influences the redox potentials, which in turn determine their charge/discharge characteristics. PMID:24564785

  12. Topotactic lithium exchange in the precursor catalyst VOHPO[sub 4][center dot]0. 5H[sub 2]O: The crystal structure of LiVOPO[sub 4][center dot]0. 5 H[sub 2]O

    SciTech Connect

    Lozano-Calero, D.; Bruque, S.; Aranda, M.A.G.; Martinez-Lara, M.; Moreno, L. )

    1993-04-01

    The synthesis and properties of a new lithium vanadyl(IV) phosphate, LiVOPO[sub 4][center dot]0.5H[sub 2]O, are reported. The synthesis was carried out by a lithium exchange reaction in VO(HPO[sub 4])[center dot]0.5H[sub 2]O with LiOH at low temperature in a nonaqueous medium. The crystal structure of LiVOPO[sub 4][center dot]0.5H[sub 2]O (space group P[sub 2[sub 1]2[sub 1]2], a = 7.4651(6) [Angstrom], b = 9.4167(8) [Angstrom], c = 6.0762(6) [Angstrom], Z = 4) was refined by the Rietveld method from laboratory X-ray powder diffraction data, giving R[sub wp] = 8.0% and R[sub F] = 6.5%. The structure is made up of layers made of VO[sub 6] dimers which are linked by phosphate groups. The framework of the starting material is maintained but the vanadium coordination sphere is more distorted and the lithium position is deduced from a difference Fourier map. The structural, thermal, and spectroscopic features are compared to those of the closely related H-derivative. 27 refs., 8 figs., 3 tabs.

  13. Sub-0.5 nm equivalent oxide thickness scaling for Si-doped Zr1-xHfxO2 thin film without using noble metal electrode.

    PubMed

    Ahn, Ji-Hoon; Kwon, Se-Hun

    2015-07-22

    The dielectric properties of the Si-doped Zr1-xHfxO2 thin films were investigated over a broad compositional range with the goal of improving their properties for use as DRAM capacitor materials. The Si-doped Zr1-xHfxO2 thin films were deposited on TiN bottom electrodes by atomic layer deposition using a TEMA-Zr/TEMA-Hf mixture precursor for deposition of Zr1-xHfxO2 film and Tris-EMASiH as a Si precursor. The Si stabilizer increased the tetragonality and the dielectric constant; however, at high fractions of Si, the crystal structure degraded to amorphous and the dielectric constant decreased. Doping with Si exhibited a larger influence on the dielectric constant at higher Hf content. A Si-doped Hf-rich Zr1-xHfxO2 thin film, with tetragonal structure, exhibited a dielectric constant of about 50. This is the highest value among all reported results for Zr and Hf oxide systems, and equivalent oxide thickness (EOT) value of under 0.5 nm could be obtained with a leakage current of under 10(-7) A·cm(-2), which is the lowest EOT value ever reported for a DRAM storage capacitor system without using a noble-metal-based electrode. PMID:26125098

  14. Structural and magnetic study of RFe{<_0.5}V{<_0.5}O{<_3} (R = Y, Eu, Nd, La) perovskite compounds.

    SciTech Connect

    Gateshki, M.; Suescun, L.; Kolesnik, S.; Mais, J.; Dabrowski, B.

    2011-06-01

    B-site disordered RFe{sub 0.5}V{sub 0.5}O{sub 3} compounds, with R=La, Nd, Eu and Y, have been prepared by solid-state reaction technique and their structures and magnetic properties have been investigated through X-ray powder diffraction, time-of-flight neutron powder diffraction and magnetization measurements at temperatures ranging from 5 to 700 K. The four compounds can be described as distorted perovskites with space group symmetry Pbnm and a{sup +}b{sup -}b{sup -} tilt system. The studied compounds also show antiferromagnetic ordering with Neel temperatures of 299, 304, 304, and 335 K respectively. The magnetic structures of R=La, Nd and Y compounds were determined from the neutron powder diffraction as Gz with observed magnetic moments of 2.55, 2.54 and 2.69 {mu}{sub B} at 30, 40 and 40 K, respectively.

  15. Flux Pinning by Cr Nanoparticles in Cu_{0.5} Tl_{0.5} Ba2 Ca2 Cu3 O_{10-δ } Superconductor

    NASA Astrophysics Data System (ADS)

    Waqee-ur-Rehman, M.; Mumtaz, M.; Qasim, Irfan; Nadeem, K.

    2016-04-01

    Increase in flux pinning strength of Cu_{0.5} Tl_{0.5} Ba2 Ca2 Cu3 O_{10-δ } (CuTl-1223) superconductor has been observed after addition of Cr nanoparticles. We have thoroughly investigated the infield response of Cr nanoparticles-added CuTl-1223 superconductor in an external applied magnetic field in the range of 0-7 T. Solid-state reaction technique has been employed to synthesize (Cr)x -CuTl-1223; x = 0-1.00 wt% nanoparticle-superconductor composites. The flux pinning mechanism has been analyzed on the basis of thermally activated flux flow model in the presence of a small current (10 μ A). The increase in activation energy and decrease in transition width of CuTl-1223 superconducting phase show the enhancement in its flux pinning strength upon the addition of Cr nanoparticles.

  16. Electronic structure of random Al sub 0. 5 Ga sub 0. 5 As alloys: Test of the special-quasirandom-structures'' description

    SciTech Connect

    Hass, K.C.; Davis, L.C. ); Zunger, A. )

    1990-08-15

    The spectral properties of an {ital sp}{sup 3}{ital s*} tight-binding Hamiltonian for a random, unrelaxed Al{sub 0.5}Ga{sub 0.5}As alloy are calculated using three different techniques: the coherent-potential approximation, the recursion method (as applied to a {gt}2000 atom supercell), and the recently introduced special-quasirandom-structures'' (SQS) approach. Over a broad range of scattering strengths, the dominant spectral features predicted by the first two techniques are well reproduced by calculations for an SQS with 16 atoms/unit-cell ( SQS-8''). This suggests that the SQS approach might also be useful in cases where the other methods are difficult to apply, e.g., in first-principles calculations for structurally relaxed alloys.

  17. Effect of Quenching on Magnetoresistance Properties in the Pr 0.5Sr 0.5MnO 3 Perovskite Manganite

    NASA Astrophysics Data System (ADS)

    Boujelben, W.; Ellouze, M.; Cheikh-Rouhou, A.; Pierre, J.; Joubert, J. C.

    2002-05-01

    We report on the magnetization, resistivity and magnetoresistance (MR) measurements on polycrystalline Pr0.5Sr0.5MnO3. Quenching samples from 1400°C to room temperature in water (sample I) or in air (sample II) leads to different behaviors. Powder X-ray diffraction patterns for samples I and II could be indexed, respectively, in rhombohedral perovskite structure with R3c space group and in the orthorhombic one with Imma space group. Magnetization measurements show that both samples exhibit a paramagnetic-ferromagnetic transition at 280 K (sample I) and 265 K (sample II). At low temperature, sampleI presents a ferromagnetic spin-canted state, while sample II behaves as an antiferromagnet below 160 K. Resistivity and magnetoresistance studies show a net difference as a function of the quenching conditions.

  18. Dielectric Properties of SrMnO3-doped K0.5Na0.5NbO3 Lead-Free Ceramics

    NASA Astrophysics Data System (ADS)

    Deng, Jianming; Sun, Xiaojun; Liu, Laijun; Liu, Saisai; Huang, Yanmin; Fang, Liang; Elouadi, Brahim

    2016-05-01

    (1-x)K0.5Na0.5NbO3-xSrMnO3 (0.02 ≤ x ≤ 0.08) (KNN-xSM) ceramics were fabricated by a conventional solid-state technique. X-ray diffraction of the samples revealed that the crystal structure changes from orthorhombic to tetragonal, and finally to pseudocubic symmetry with increasing x. Temperature dependence of dielectric properties showed that the temperature (T m) corresponding to the maximum of dielectric permittivity decreased with increasing x. Two dielectric relaxation processes occurred at high temperatures, which were attributed to grain and grain boundary responses, respectively. Polarization hysteresis loops (P-E) at different electrical fields were displayed. P rmax degenerated with the increase of SM due to the thermally activated leakage current increases. The relationship between electrical properties and defect compensation mechanism is discussed.

  19. Ordering of the heavy anions in mixed BaFBr{sub 0.5}I{sub 0.5} crystals: Experimental results

    SciTech Connect

    Rey, J.M.; Bill, H.; Hagemann, H.; Kubel, F.

    2005-11-01

    Mixed matlokite hosts of composition BaFBr{sub x}I{sub 1-x}(0{<=}x{<=}1) (pure and doped with Sm{sup 2+}, Eu{sup 2+}) were studied with x-ray crystallography, luminescence, Raman, and electron paramagnetic resonance (EPR) spectroscopy. Results are presented for BaFBr{sub 0.5}I{sub 0.5} which demonstrate that a ferrielectric domain structure is formed due to the fact that the heavy halogen ions form separate sublattices with randomly distributed domain walls. The space group of a domain is P4 mm (No. 99). The EPR data from Eu{sup 2+} allowed to determine the volume fraction of domains.

  20. Temperature dependence of optical properties (3HgSe)0.5(In2Se3)0.5, doped with Mn or Fe

    NASA Astrophysics Data System (ADS)

    Koziarskyi, I. P.; Marianchuk, P. D.; Maistruk, E. V.; Koziarskyi, D. P.

    2012-01-01

    The values of refraction index, the main reflection index and reflection coefficient for the investigated crystals were determined on the basis of the study of reflection and transmission coefficients of (3HgSe)0.5(In2Se3)0.5 crystals doped with Mn or Fe. The investigation was carried out on the wavelengths interval of 0.9<=λ<=26.6 μm. Basing on the dependencies α2 on the energy of incident electromagnetic radiation it was determined that in crystals the direct allowed interband optical transitions occur, and the value of the band gap was obtained. The influence of temperature on the optical transmittance has been studied in the interval of 120-300 K.

  1. Temperature dependence of optical properties (3HgSe)0.5(In2Se3)0.5, doped with Mn or Fe

    NASA Astrophysics Data System (ADS)

    Koziarskyi, I. P.; Marianchuk, P. D.; Maistruk, E. V.; Koziarskyi, D. P.

    2011-09-01

    The values of refraction index, the main reflection index and reflection coefficient for the investigated crystals were determined on the basis of the study of reflection and transmission coefficients of (3HgSe)0.5(In2Se3)0.5 crystals doped with Mn or Fe. The investigation was carried out on the wavelengths interval of 0.9<=λ<=26.6 μm. Basing on the dependencies α2 on the energy of incident electromagnetic radiation it was determined that in crystals the direct allowed interband optical transitions occur, and the value of the band gap was obtained. The influence of temperature on the optical transmittance has been studied in the interval of 120-300 K.

  2. Diffuse phase transition and high-temperature dielectric relaxation study on (Bi0.5Na0.5)1-xBaxTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Chen, Feng; Liu, Qiu-Xiang; Tang, Xin-Gui; Jiang, Yan-Ping; Yue, Jing-Long; Li, Jin-Kai

    2016-09-01

    Lead free (Bi0.5Na0.5)1-xBaxTiO3 (x=0.6, 0.7, 0.8, 0.9) ferroelectric ceramics were synthesized by the traditional solid state reaction method. Sintering was carried out at 1200 °C for 2 h in air atmosphere. The structural, microstructure and Ferroelectric of ceramics were investigated. In dielectric studies, a diffuse phase transition was exhibited and a dielectric relaxation behavious was observed at high temperature range. Impedance analysis characterized grain and grain boundaries resistivities of the ceramics and calculated activation energy and the activation energy for conduction. Polaron theory indicates that the relaxation of the samples at high temperatures was associated with the hopping ions caused by oxygen vacancies.

  3. Anisotropic magnetoresistance of epitaxial Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} film

    SciTech Connect

    Chen, X. G.; Yang, Y. B.; Wang, C. S.; Liu, S. Q.; Zhang, Y.; Han, J. Z.; Yang, Y. C.; Yang, J. B.

    2014-01-28

    The magnetic field and temperature dependent anisotropic magnetoresistance (AMR) of the epitaxial grown Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} thin films was investigated. It was found that the magnetoresistance exhibited the characteristics of magnetic polaron hopping. A two-fold symmetric AMR occurred in the ferromagnetic region (∼220 K < T < ∼150 K), while a four-fold symmetric AMR appeared under a high magnetic field in the antiferromagnetic orbital ordered region (T < ∼150 K). The angular dependence of the resistance showed a hysteresis effect under magnetic field at low temperature. It is believed that these phenomena are attributed to the spin canting effect, which originates from the melting of orbital ordering under the external magnetic field in the antiferromagnetic region.

  4. Growth and diode-pumped laser operation of Pr3+:β-(Y0.5,Gd0.5)F3 at various transitions.

    PubMed

    Werner Metz, Philip; Marzahl, Daniel-Timo; Guguschev, Christo; Bertram, Rainer; Kränkel, Christian; Huber, Günter

    2015-06-15

    We report on the crystal growth of the orthorhombic low-temperature β-phase of (Y0.5,Gd0.5)F3 (YGF) single crystals. The crystals were activated with trivalent praseodymium (Pr3+) and characterized with respect to their ground state absorption and stimulated emission properties. Under InGaN-laser-diode pumping, laser oscillation was obtained at more than ten wavelengths in the green, orange, red, and dark red spectral regions. In these initial experiments, output powers exceeding 100 mW and slope efficiencies between 10% and 30% were obtained. To the best of our knowledge, these results represent the first application of YGF crystals as laser host material for any active ion. PMID:26076240

  5. Effect of pressure-driven local structural rearrangement on the superconducting properties of FeSe0.5Te0.5

    NASA Astrophysics Data System (ADS)

    Bendele, M.; Guguchia, Z.; von Rohr, F.; Irifune, T.; Shinmei, T.; Kantor, I.; Pascarelli, S.; Joseph, B.; Marini, C.

    2014-11-01

    The pressure dependence of the superconducting transition temperature Tc, the local structure, and the electronic properties of the iron chalcogenide superconductor FeSe0.5Te0.5 was investigated by means of SQUID magnetometry and site-selective polarized x-ray absorption spectroscopy at the iron and selenium K -edges. The measurements reveal a discontinuous decrease of the local bond distances by crossing a tetragonal to monoclinic structural phase transition at pS˜2.7 GPa. The electronic structure, however, evolves evenly, but the superconducting properties are highly affected by changes in the local structure. These results underline the close connection of the lattice and the superconductivity in the iron-based superconductors.

  6. Effect of sintering treatment on structural and magnetic properties of Ni0.5Co0.5Fe2O4 ferrites

    NASA Astrophysics Data System (ADS)

    Nandan, Brajesh; Bhatnagar, M. C.

    2016-05-01

    Two sets of Ni0.5Co0.5Fe2O4 ferrites were synthesized using sol-gel method. Both the samples were heat treated at different temperatures. The effect of sintering treatment analyzed on structural and magnetic properties. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used for structural analysis. Alternating gradient magnetometer (AGM) is used for magnetic measurements. In structural analysis, grains size is calculated using Debye - Scherrer's formula and Williamson-Hall (W-H) plot. From both the techniques, grain size is found nearly same and increased in size with increase sintering temperature. Increased particle size is confirmed from SEM micrographs. Strain value is calculated from intercept of W-H plot. In both the samples, compressive strain in nature is found. Magnetic properties were also varying under different heat treatment. The change in magnetic properties with change in structural change at different sintering treatment is discussed in this report.

  7. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1−yCryO3 thin films

    PubMed Central

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-01-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1−yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm2. The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides. PMID:27001006

  8. Effect of Oxygen-deficiencies on Resistance Switching in Amorphous YFe0.5Cr0.5O3−d films

    PubMed Central

    Wang, Xianjie; Hu, Chang; Song, Yongli; Zhao, Xiaofeng; Zhang, Lingli; Lv, Zhe; Wang, Yang; Liu, Zhiguo; Wang, Yi; Zhang, Yu; Sui, Yu; Song, Bo

    2016-01-01

    Herein, we demonstrate the contribution of the oxygen-deficiencies on the bipolar resistance switching (RS) properties of amorphous-YFe0.5Cr0.5O3−d (a-YFCO) films. The a-YFCO films were prepared under various oxygen pressures to tune the concentration of oxygen-deficiencies in the films. The XPS data verify that the oxygen-deficiencies increase with decreasing oxygen pressure. The RS property becomes more pronounced with more oxygen-deficiencies in a-YFCO films. Based on the Ohmic conduction measurements in the low resistance state, we confirm that the RS mechanism is related to the migration of oxygen-deficiencies. The enhanced RS and long retention in a-YFCO suggest a great potential for applications in nonvolatile memory devices. PMID:27452114

  9. Fundamental limitation to the magnitude of piezoelectric response of (001)pc textured K0.5Na0.5NbO3 ceramic

    SciTech Connect

    Gupta, Shashaank; Belianinov, Alex; Okatan, Mahmut B; Jesse, Stephen; Kalinin, Sergei V; Priya, Shashaank

    2014-01-01

    (001)pc textured K0.5Na0.5NbO3 (KNN) ceramic was found to exhibit a 65% improvement in the longitudinal piezoelectric response as compared to its random counterpart. Piezoresponse force microscopy study revealed the existence of larger 180 and non-180 domains for textured ceramic as compared to that of the random ceramic. Improvement in piezoresponse by the development of (001)pc texture is discussed in terms of the crystallographic nature of KNN and domain morphology. A comparative analysis performed with a rhombohedral composition suggested that the improvement in longitudinal piezoresponse of polycrystalline ceramics by the development of (001)pc texture is limited by the crystal structure.

  10. Synthesis and characterization of Mn0.5Zn0.5Fe2O4 and Fe3O4 nanoparticle ferrofluids for thermo-electric conversion

    NASA Astrophysics Data System (ADS)

    Sansom, C. L.; Jones, P.; Dorey, R. A.; Beck, C.; Stanhope-Bosumpim, A.; Peterson, J.

    2013-06-01

    Ferrofluids containing nanoparticles of Mn0.5Zn0.5Fe2O4 (MZ5) and Fe3O4 (magnetite) have been examined as potential thermal transport media and energy harvesting materials. The ferrofluids were synthesized by chemical co-precipitation and characterized by EDX to determine composition and by TEM to determine particle size and agglomeration. A range of particle coatings and carrier fluids were used to complete the fluid preparation. Commercially available ferrofluids were tested in custom built rigs to demonstrate both thermal pumping (for waste heat removal applications) and power induction (for power conversion and energy harvesting applications). The results indicate that simple ferrofluids possess the necessary properties to remove waste heat, either into thermal storage or for conversion to electrical power.

  11. Correlation between electrical and magnetic properties of polycrystalline La0.5Ca0.5Mn0.98Bi0.02O3

    NASA Astrophysics Data System (ADS)

    Krichene, A.; Bourouina, M.; Venkateshwarlu, D.; Solanki, P. S.; Rayaprol, S.; Ganesan, V.; Boujelben, W.; Kuberkar, D. G.

    2016-06-01

    We have reported in this work the study of correlation between electrical transport and magnetic properties of La0.5Ca0.5Mn0.98Bi0.02O3 polycrystalline sample prepared by solid state method. Structural analysis reveals that presently studied compound crystallizes in the orthorhombic structure with Pnma space group. Temperature dependence of magnetization indicates that our studied compound undergoes a paramagnetic-ferromagnetic transition at Curie temperature TC=237 K. Magnetotransport analysis was successfully carried out using percolation model in the temperature range 40-300 K for magnetic field values up to 14 T. Strong correlation between electrical and magnetic properties was observed along with the absence of charge ordering inside the structure of our sample.

  12. Magnetoresistance reversal in antiperovskite compound Mn{sub 3}Cu{sub 0.5}Zn{sub 0.5}N

    SciTech Connect

    Zhang, X. H.; Yin, Y.; Yuan, Q.; Han, J. C.; Zhang, Z. H.; Jian, J. K.; Zhao, J. G. E-mail: songbo@hit.edu.cn; Song, B. E-mail: songbo@hit.edu.cn

    2014-03-28

    We report detailed investigations of the structure, magnetic properties, electronic transport, and specific heat in Mn-based antiperovskite compounds Mn{sub 3}Cu{sub 0.5}Zn{sub 0.5}N. Most strikingly, there are several fascinating features: (i) The magnetoresistance at 30 kOe (40 kOe) exceeds ∼1% (∼2%) over a temperature span of ∼70 K (∼25 K) from 5 to 140 K; (ii) magnetoresistance fluctuates at temperatures of 100–200 K, including an obvious sign reversal from negative to positive at ∼140 K. Analysis of the specific heat reveals that the magnetoresistance reversal may originate from the reconstruction of the Fermi surface accompanying an antiferromagnetic-ferromagnetic transition.

  13. Unexpected ferromagnetic ordering enhancement with crystallite size growth observed in La{sub 0.5}Ca{sub 0.5}MnO₃ nanoparticles

    SciTech Connect

    Iniama, G.; Ita, B. I.; Presa, P. de la Hernando, A.; Alonso, J. M.; Multigner, M.; Cortés-Gil, R.; Ruiz-González, M. L.; Gonzalez-Calbet, J. M.

    2014-09-21

    In this paper, the physical properties of half-doped manganite La{sub 0.5}Ca{sub 0.5}MnO₃ with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense of antiferromagnetic one as crystallite size is reduced to 15 nm. However, contrary to previously reported works, an enhancement of saturation magnetization is observed as crystallite size increases from 15 to 22 nm. This unexpected behavior is accompanied by an unusual cell volume variation that seems to induce ferromagnetic-like behavior at expense of antiferromagnetic one. Besides, field cooled hysteresis loops show exchange bias field and coercivity enhancement for increasing cooling fields, which suggest a kind of core-shell structure with AFM-FM coupling for crystallite sizes as small as 15 nm. It is expected that inner core orders antiferromagnetically, whereas uncompensated surface spins behave as spin glass with ferromagnetic-like ordering.

  14. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1-yCryO3 thin films.

    PubMed

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-01-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1-yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm(2). The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides. PMID:27001006

  15. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1‑yCryO3 thin films

    NASA Astrophysics Data System (ADS)

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-03-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1‑yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm2. The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides.

  16. Unraveling the magnetic properties of BiFe{sub 0.5}Cr{sub 0.5}O{sub 3} thin films

    SciTech Connect

    Vinai, G.; Petrov, A. Yu.; Panaccione, G.; Torelli, P.; Khare, A.; Rana, D. S.; Di Gennaro, E.; Scotti di Uccio, U.; Miletto Granozio, F.; Gobaut, B.; Moroni, R.; Rossi, G.

    2015-11-01

    We investigate the structural, chemical, and magnetic properties on BiFe{sub 0.5}Cr{sub 0.5}O{sub 3} (BFCO) thin films grown on (001) (110) and (111) oriented SrTiO{sub 3} (STO) substrates by x-ray magnetic circular dichroism and x-ray diffraction. We show how highly pure BFCO films, differently from the theoretically expected ferrimagnetic behavior, present a very weak dichroic signal at Cr and Fe edges, with both moments aligned with the external field. Chemically sensitive hysteresis loops show no hysteretic behavior and no saturation up to 6.8 T. The linear responses are induced by the tilting of the Cr and Fe moments along the applied magnetic field.

  17. Infrared reflectivity investigation of the phase transition sequence in Pr0.5Ca0.5MnO3

    NASA Astrophysics Data System (ADS)

    Ribeiro, J. L.; Vieira, L. G.; Gomes, I. T.; Araújo, J. P.; Tavares, P.; Almeida, B. G.

    2016-06-01

    This work reports an infrared reflectivity study of the phase transition sequence observed in Pr0.5Ca0.5MnO3. The need to measure over an extended spectral range in order to properly take into account the effects of the high frequency polaronic absorption is circumvented by adopting a simple approximate method, based on the asymmetry present in the Kramers Kronig inversion of the phonon spectrum. The temperature dependence of the phonon optical conductivity is then investigated by monitoring the behavior of three relevant spectral moments of the optical conductivity. This combined methodology allows us to disclose subtle effects of the orbital, charge and magnetic orders on the lattice dynamics of the compound. The characteristic transition temperatures inferred from the spectroscopic measurements are compared and correlated with those obtained from the temperature dependence of the induced magnetization and electrical resistivity.

  18. Direct band gap optical emission from compressively strained Ge films grown on relaxed Si{sub 0.5}Ge{sub 0.5} substrate

    SciTech Connect

    Aluguri, R.; Manna, S.; Ray, S. K.

    2013-10-14

    Compressively strained Ge films have been grown on relaxed Si{sub 0.5}Ge{sub 0.5} virtual substrate in ultra high vacuum using molecular beam epitaxy. Structural characterization has shown that the Ge films are compressively strained with partial strain relaxation in a film thicker than 3.0 nm, due to onset of island nucleation. Photoluminescence spectra exhibit the splitting of degenerate Ge valence band into heavy hole and light hole bands with a broad direct band gap emission peak around 0.81 eV. Temperature and excitation power dependent emission characteristics have been studied to investigate the mechanism of luminescence quenching at high temperatures and the role of non-radiative recombination centers.

  19. Dielectric Properties of SrMnO3-doped K0.5Na0.5NbO3 Lead-Free Ceramics

    NASA Astrophysics Data System (ADS)

    Deng, Jianming; Sun, Xiaojun; Liu, Laijun; Liu, Saisai; Huang, Yanmin; Fang, Liang; Elouadi, Brahim

    2016-08-01

    (1- x)K0.5Na0.5NbO3- xSrMnO3 (0.02 ≤ x ≤ 0.08) (KNN- xSM) ceramics were fabricated by a conventional solid-state technique. X-ray diffraction of the samples revealed that the crystal structure changes from orthorhombic to tetragonal, and finally to pseudocubic symmetry with increasing x. Temperature dependence of dielectric properties showed that the temperature ( T m) corresponding to the maximum of dielectric permittivity decreased with increasing x. Two dielectric relaxation processes occurred at high temperatures, which were attributed to grain and grain boundary responses, respectively. Polarization hysteresis loops ( P- E) at different electrical fields were displayed. P rmax degenerated with the increase of SM due to the thermally activated leakage current increases. The relationship between electrical properties and defect compensation mechanism is discussed.

  20. Possible surface antiferromagnetism and no evidence for intergranular tunneling magnetoresistance in La0.5Sr0.5CoO3-δ cobaltites

    NASA Astrophysics Data System (ADS)

    Troyanchuk, I. O.; Bushinsky, M. V.; Lobanovsky, L. S.

    2013-12-01

    The magnetization and magnetoresistance (MR) of La0.5Sr0.5CoO3-δ have been studied as function of surface/volume ratio and oxygen deficit. All the samples have positive and negative components of MR at low temperature. The small positive component is predominated in low field regime below and well above the coercive field. The positive MR under magnetic moment reorientation is in contradiction with scenario of negative intergranular tunneling magnetoresistance being the hallmark of half-metallic polycrystalline oxides. The oxygen deficit leads to a gradual stabilization of antiferromagnetic phase in bulk and concomitant enhancement of the MR. The decrease in value of magnetization and enhancement of the negative MR component in compacted at high pressure/room temperature powder with a large surface/volume ratio can be ascribed to antiferromagnetism at the surface.

  1. Good Quality Factor in GdMnO3-Doped (K0.5Na0.5)NbO3 Piezoelectric Ceramics

    NASA Astrophysics Data System (ADS)

    Bucur, Raul Alin; Badea, Iuliana; Bucur, Alexandra Ioana; Novaconi, Stefan

    2016-06-01

    (1 - x)(K0.5Na0.5)NbO3 - xGdMnO3 (KNN- xGM) ferroelectric ceramics (0 ≤ x ≤ 5 mol.%) were obtained through a solid state technique. For all the studied compositions, orthorhombic perovskite crystalline structures were obtained at room temperature. GdMnO3 suppresses the grain growth and gives rather homogenous microstructures as the concentration increases. The doped ceramics exhibita good dielectric response, a "hard" ferroelectric behavior and good piezoelectric properties. An improved mechanical quality factor of 1180 and a high Curie temperature T C = 400°C, coupled with k p = 0.426, makes the composition x = 1 mol.% GdMnO3 suitable for lead-free piezoelectric materials for high-power and high-temperature applications.

  2. Effect of Natural Aging and Cold Working on Microstructures and Mechanical Properties of Al-4.6Cu-0.5Mg-0.5Ag alloy

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Te; Lee, Sheng-Long; Bor, Hui-Yun; Lin, Jing-Chie

    2013-06-01

    This research investigates the effects of natural aging and cold working prior to artificial aging on microstructures and mechanical properties of Al-4.6Cu-0.5Mg-0.5Ag alloy. Mechanical properties relative to microstructure variations were elucidated by the observations of the optical microscope (OM), differential scanning calorimeter (DSC), electrical conductivity meter (pct IACS), and transmission electron microscopy (TEM). The results showed that natural aging treatment has little noticeable benefit on the quantity of precipitation strengthening phases and mechanical properties, but it increases the precipitation strengthening rate at the initial stage of artificial aging. Cold working brings more lattice defects which suppress Al-Cu (GP zone) and Mg-Ag clustering, and therefore the precipitation of Ω phase decreases. Furthermore, more dislocations are formed, leading to precipitate the more heterogeneous nucleation of θ' phase. The above-mentioned precipitation phenomena and strain hardening effect are more obvious with higher degrees of cold working.

  3. Single crystalline La0.5Sr0.5MnO3 microcubes as cathode of solid oxide fuel cell

    SciTech Connect

    Mingjia Zhi; Guangwen Zhou; Zhanglian Hong; Jin Wang; Randall Gemmen; Kirk Gerdes; Ayyakkannu Manivannan; Dongling Mae; Nianqiang Wu

    2010-09-13

    The efficiency of solid oxide fuel cells (SOFCs) is heavily dependent on the electrocatalytic activity of the cathode toward the oxygen reduction reaction (ORR). In order to achieve better cathode performance, single crystalline La0.5Sr0.5MnO3 (LSM) microcubes with the {200} facets have been synthesized by the hydrothermal method. It is found that the LSM microcubes exhibit lower polarization resistance than the conventional polycrystalline La0.8Sr0.2MnO3 powder in air from 700 #2;C to 900 #2;C. The ORR activation energy of the LSM microcubes is lower than that of the conventional powder. The ORR kinetics for the microcubes is limited by the charge transfer step while that for the conventional powder is dominated by the oxygen adsorption and dissociation on the cathode surface.

  4. Flux Pinning by Cr Nanoparticles in Cu_{0.5}Tl_{0.5}Ba2Ca2Cu3O_{10-δ } Superconductor

    NASA Astrophysics Data System (ADS)

    Waqee-ur-Rehman, M.; Mumtaz, M.; Qasim, Irfan; Nadeem, K.

    2016-09-01

    Increase in flux pinning strength of Cu_{0.5}Tl_{0.5}Ba2Ca2Cu3O_{10-δ }(CuTl-1223) superconductor has been observed after addition of Cr nanoparticles. We have thoroughly investigated the infield response of Cr nanoparticles-added CuTl-1223 superconductor in an external applied magnetic field in the range of 0-7 T. Solid-state reaction technique has been employed to synthesize (Cr)x-CuTl-1223; x = 0-1.00 wt% nanoparticle-superconductor composites. The flux pinning mechanism has been analyzed on the basis of thermally activated flux flow model in the presence of a small current (10 μ A). The increase in activation energy and decrease in transition width of CuTl-1223 superconducting phase show the enhancement in its flux pinning strength upon the addition of Cr nanoparticles.

  5. Hydrogen-induced phase separation in amorphous Cu0.5Ti0.5 alloys. I. Room-temperature experiments

    NASA Astrophysics Data System (ADS)

    Rodmacq, B.; Maret, M.; Laugier, J.; Billard, L.; Chamberod, A.

    1988-07-01

    The influence of hydrogen on the structure of an amorphous Cu0.5Ti0.5 alloy has been studied by means of x-ray and neutron scattering. These experiments include large-angle x-ray and neutron scattering and small-angle neutron scattering with hydrogen-deuterium substitution. The results indicate that large hydrogen contents (hydrogen-to-metal ratio of 0.84) induce a phase separation into Cu and TiHx regions on a scale of about 10-15 Å. Experiments on samples loaded with hydrogen by electrolysis or from the gas phase show that such a phase separation does not depend on the method of hydrogen loading. The results of a computer simulation with nearest-neighbor Cu-Ti permutations reproduce the main features of the diffraction data and confirm the large change of chemical ordering between Cu and Ti atoms upon hydrogen absorption.

  6. Strong room temperature magnetism in highly resistive strained thin films of BiFe0.5Mn0.5O3

    NASA Astrophysics Data System (ADS)

    Choi, E.-M.; Patnaik, S.; Weal, E.; Sahonta, S.-L.; Wang, H.; Bi, Z.; Xiong, J.; Blamire, M. G.; Jia, Q. X.; MacManus-Driscoll, J. L.

    2011-01-01

    We report highly resistive strongly ferromagnetic strained thin (˜30 nm) films of BiFe0.5Mn0.5O3 (BFMO) grown on (001) SrTiO3 substrates using pulsed laser deposition. The films are tetragonal with high epitaxial quality and phase-purity. The magnetic moment and coercivity values at room temperature are 90 emu/cc (0.58μB/B-site ion) at H =3 kOe and 274 Oe, respectively. The magnetic transition temperature is strongly enhanced up to ˜600 K, which is ˜500 K higher than for pure bulk BiMnO3. Strained BFMO is a potential room temperature spin filter material for magnetic tunnel devices.

  7. Optical spectra of LaMn0.5Ga0.5O3: A contribution to the assignment of the electronic transitions in manganites

    NASA Astrophysics Data System (ADS)

    Nucara, A.; Miletto Granozio, F.; Mohamed, W. S.; Vecchione, A.; Fittipaldi, R.; Perna, P. P.; Radovic, M.; Vitucci, F. M.; Calvani, P.

    2014-01-01

    We have prepared a LaMn0.5Ga0.5O3 thin film deposited by Pulsed Laser Deposition on a LSAT substrate and we have measured its transmittance in the visible and near UV range, from 300 to 10 K. The aim was to shed light on the origin of the electronic bands in the LMO family through a comparison with the corresponding spectra collected previously on the parent compound. Two out of the four bands detected have been assigned to the intersite d-d transitions between Mn+3 ions. The other ones were ascribed to the p-d Mn-O charge-transfer transitions. We are thus led to a “mixed” interpretation where both a Mott-Hubbard and a charge-transfer approach concur to interpret the electronic spectrum of those manganites.

  8. Room-Temperature Magnetocapacitance in Fe-Doped K0.5Na0.5Nb0.95Ta0.05O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Huan; Yang, Wenlong; Li, Yu; Meng, Qingxin; Zhou, Zhongxiang

    2012-10-01

    Ferroelectric and magnetic properties of Fe-doped potassium-sodium tantalate niobate (K0.5Na0.5(Nb0.95Ta0.05)1-xFexO3-x; x = 0 and 0.01) ceramics prepared by the conventional sintering method were investigated. In comparison with pure ceramics, the 0.01 Fe-doped ceramics show magnetic and ferroelectric properties simultaneously at room temperature. The relative dielectric constant significantly decreases after applying a magnetic field for the Fe-doped ceramics, indicating the coupling between ferroelectric and ferromagnetic orders. Magnetocapacitance of -0.77% was observed at room temperature and 50 kHz by the application of a magnetic field of 5000 Oe.

  9. Scintillation properties of Li6Y0.5Gd0.5(BO3)3: Ce3+ single crystal

    NASA Astrophysics Data System (ADS)

    Fawad, U.; Rooh, Gul; Kim, H. J.; Park, H.; Kim, Sunghwan; Khan, Sajid

    2015-01-01

    The Ce3+ doped mixed crystals of Li6Y(BO3)3 and Li6Gd(BO3)3 are grown by Czochralski technique with equal mole ratios of both Yttrium and Gadolinium i.e. Li6Y0.5Gd0.5(BO3)3. The grown crystals have the dimensions of ∅10×30 mm2. Powder X-ray diffraction (XRD) analysis confirmed single phase of the grown crystals. X-ray and laser induced luminescence spectra are presented. Scintillation properties such as energy resolution, light yield, decay time and α/β ratio under the excitation of 137Cs γ-ray photons and 241Am α-particles are also reported in this article.

  10. Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries

    PubMed Central

    Zhao, Yunlong; Xu, Lin; Mai, Liqiang; Han, Chunhua; An, Qinyou; Xu, Xu; Liu, Xue; Zhang, Qingjie

    2012-01-01

    Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g –1, one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire. PMID:23150570

  11. Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries.

    PubMed

    Zhao, Yunlong; Xu, Lin; Mai, Liqiang; Han, Chunhua; An, Qinyou; Xu, Xu; Liu, Xue; Zhang, Qingjie

    2012-11-27

    Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La(0.5)Sr(0.5)CoO(2.91) (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g(-1), one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire. PMID:23150570

  12. Anomalous field-induced magnetoresistance behavior in Pr0.5Sr0.5MnO3 at low temperatures

    NASA Astrophysics Data System (ADS)

    Kumar, Dhirendra; Shahee, Aga; Rawat, Rajeev; Lalla, N. P.

    2012-06-01

    Low-temperature (LT) XRD and magnetoresistance (MR) have been studied in the single phase polycrystalline Pr0.5Sr0.5MnO3 with space-group I4/mcm. The resistance-vs-temperature (R-T) variation at zero-field show a broad paramagnetic to ferromagnetic metallic (FMM) transition at Tc ˜ 240K and it further undergoes FMM to antiferromagnetic insulating (AFMI) transition at TN ˜ 90K with a broad hysteresis indicates a disorder broadened first order phase transition (FOPT). The zero-field cooled (ZFC) MR at 5K shows an open loop with virgin curve lying outside the envelope curve. This anomalous behavior vanishes with increasing temperature. This has been attributed to field-induced transformation of AFMI to FMM phase, which remains arrested down to zero magnetic field at 5K.

  13. Effect of vanadium doping on structural, magnetic and magnetocaloric properties of La0.5Ca0.5MnO3

    NASA Astrophysics Data System (ADS)

    Mansouri, M.; Omrani, H.; Cheikhrouhou-Koubaa, W.; Koubaa, M.; Madouri, A.; Cheikhrouhou, A.

    2016-03-01

    We report the effect of vanadium doping on structural, magnetic and magnetocaloric properties of La0.5Ca0.5Mn1-xVxO3 (x=0.05; 0.1). Our samples were elaborated using the conventional solid state reaction method at high temperatures. X-Ray powder diffraction at room temperature indicates that our samples crystallize in the orthorhombic structure with Pbnm space group. Magnetic measurements reveal a paramagnetic-ferromagnetic transition with decreasing temperature. Magnetocaloric studies show that the maximum of the magnetic entropy change and the relative cooling power (RCP) are found to be 2.42 J Kg-1 K-1 and 162.75 J Kg-1 for x=0.05 and 3.12 J Kg-1 K-1 and 221.31 J Kg-1 for x=0.1 under a field change of 5 T.

  14. Thickness-dependent cation order and disorder in PbSc0.5Ta0.5O3 thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Chopra, Anuj; Birajdar, Balaji I.; Berger, Andreas; Alexe, Marin; Hesse, Dietrich

    2014-01-01

    We report on thickness-dependent cation ordering and ferroelectric properties of (001)-oriented epitaxial PbSc0.5Ta0.5O3 (PST) thin films grown by pulsed laser deposition on SrTiO3 (001) and Si (001) substrates. The PST film thickness was varied from 30 to 200 nm. Only films thicker than 40 nm reveal (partial) cation ordering, which increases with thickness as confirmed by the appearance and intensity of superstructure reflections in x-ray diffraction and transmission electron microscopy. In accordance with the two-state thermodynamic model, temperature-dependent dielectric constant investigations showed the presence of two kinds of phase transitions belonging to the normal ferroelectric and the relaxor state, respectively, both being present in the PST films. The influence of cation ordering on the phase transition and ferroelectric properties is discussed in detail.

  15. Antiferromagnetic resonance in charge ordering state of Pr 0.5Ca 0.5MnO 3- δ single crystal

    NASA Astrophysics Data System (ADS)

    Kawamata, S.; Noguchi, S.; Okuda, K.; Nojiri, H.; Motokawa, M.

    2001-05-01

    An antiferromagnetic resonance (AFMR) is observed in the charge ordered antiferromagnetic phase of Pr 0.5Ca 0.5MnO 3- δ single crystal for the first time. Above the Néel temperature, TN=173 K, a paramagnetic resonance with g=2.0 is observed. There is no significant change of the resonance spectra at the charge ordering transition temperature, TCO=242 K. Below TN, a branch of AFMR is found. Since the resonance field of this mode increases linearly as the frequency is decreased, this branch is assigned as the spin-flop mode. Below 60 K, the critical fields, BC, evaluated as the extrapolation of this mode to zero frequency agree well with the insulator-metal transition fields, BCO, at which the melting of the charge-ordering phase occurs. Present results indicate that the temperature dependence of BCO is affected by the temperature dependence of BC.

  16. Microstructures and superconducting properties of single domain (Sm 0.5,Eu 0.5)Ba 2Cu 3O 7- δ superconductors fabricated in air

    NASA Astrophysics Data System (ADS)

    Hu, A.; Sakai, N.; Ogasawara, K.; Murakami, M.

    2002-01-01

    Single-domain (Sm 0.5,Eu 0.5)Ba 2Cu 3O 7- δ grains were obtained via modified melt processing in air using NdBa 2Cu 3O 7- δ seeds. The facet growth front was observed in the a/b growth direction and the stepwise growth front in the c growth direction. A series of crystal defects: dislocations, twin boundaries and local chemical variations between rare earth and Ba were revealed by transmission electron microscopy and energy dispersive spectrum analysis. In addition, a slightly higher concentration of Sm than Eu was revealed in the matrix. A high Tc value up to 94.5 K and enhanced Jc values over a wide field range at 77 K were obtained after Ar post-annealing. A pellet of diameter 16 mm trapped 0.45 T field at 77 K.

  17. Microwave dielectric and optical properties of amorphous and crystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Goud, J. Pundareekam; Joseph, Andrews; Ramakanth, S.; Naidu, Kuna Lakshun; Raju, K. C. James

    2016-05-01

    The thin films of composition Ba0.5Sr0.5TiO3 (BST5) were deposited by Pulsed Laser Deposition technique on amorphous fused silica substrates at room temperature (RT) and at 700°C. The film deposited at RT is amorphous while the other crystallized in cubic structure. The refractive index (n) and optical band gap (Eg) extracted from transmission spectra in the 190 -2500 nm range. Microwave dielectric properties were investigated using the Split Post Dielectric Resonators (SPDR) technique at spot frequencies of 10GHz and 20GHz. The experimental results show that thin films deposited at high temperature (700°C) shows very high dielectric constant for both 10GHz and 20 GHz. These high dielectric constant films can be used in a wide range of applications such as capacitors, non-volatile high speed random access memories, and electro-optic devices.

  18. Spin-reorientation and weak ferromagnetism in antiferromagnetic TbMn{sub 0.5}Fe{sub 0.5}O{sub 3}

    SciTech Connect

    Nhalil, Hariharan E-mail: hariharan.nhalil@gmail.com; Sanathkumar, R.; Elizabeth, Suja; Nair, Harikrishnan S.; Strydom, André M.

    2015-05-07

    Orthorhombic single crystals of TbMn{sub 0.5}Fe{sub 0.5}O{sub 3} are found to exhibit spin-reorientation, magnetization reversal, and weak ferromagnetism. Strong anisotropy effects are evident in the temperature dependent magnetization measurements along the three crystallographic axes a, b, and c. A broad magnetic transition is visible at T{sub N}{sup Fe/Mn}=286 K due to paramagnetic to A{sub x}G{sub y}C{sub z} ordering. A sharp transition is observed at T{sub SR}{sup Fe/Mn}=28 K, which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to G{sub x}A{sub y}F{sub z} configuration. The negative magnetization observed below T{sub SR}{sup Fe/Mn} along c axis is explained in terms of domain wall pinning. A component of weak ferromagnetism is observed in field-scans along c-axis but below 28 K. Field-induced steps-like transitions are observed in hysteresis measurement along b axis below 28 K. It is noted that no sign of Tb-order is discernible down to 2 K. TbMn{sub 0.5}Fe{sub 0.5}O{sub 3} could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions.

  19. Analysis of conductivity and dielectric spectra of Mn0.5Zn0.5Fe2O4 with coupled Cole-Cole type anomalous relaxations

    NASA Astrophysics Data System (ADS)

    Kumar, N. S. K.; Shahid, T. S.; Govindaraj, G.

    2016-05-01

    Most of the crystalline materials seldom show a well-defined dielectric loss peak due to domination of dc conductivity contribution, but effects of loss peaks are seen at high frequencies. Ac electrical data of nano-crystalline Mn0.5Zn0.5Fe2O4 synthesised by chemical co-precipitation method show such behaviour. Properly combined and formulated conduction and dielectric relaxation functions are required for such materials. Cole-Cole type relaxation function in the combined conduction and dielectric process is formulated for complex resistivity ρ*(ω), complex permittivity ε*(ω), complex conductivity σ*(ω) and complex electric modulus M*(ω). Conduction and dielectric relaxation are linked to Jonscher's idea of 'pinned dipole' and 'free dipole' to understand the relaxation dynamics. The physical parameters of 'pinned dipole' and 'free dipole' formalism are unique for all representations like ρ*(ω), ε*(ω), σ*(ω) and M*(ω). 'Pinned dipole' relaxation time τc related to conduction process and 'free dipole' relaxation time τd related to dielectric process show Arrhenius behaviour with the same activation energy. Correlation of dc conductivity σc with τc and τd indicates the coupled dynamics of 'pinned dipole' and 'free dipole'. Time-temperature scaling of conduction and dielectric relaxation reveals that the mechanism of coupled dynamics of 'pinned dipole' and 'free dipole' is temperature independent. Hopping of charge carriers with dynamics of disordered cation distribution of host matrix generates a coupled conduction and dielectric relaxation in Mn0.5Zn0.5Fe2O4.

  20. Ultrasonic transducers based on undoped lead-free (K0.5Na0.5)NbO3 ceramics.

    PubMed

    Bah, Micka; Giovannelli, Fabien; Schoenstein, Frederic; Brosseau, Christophe; Deschamps, Jean-Robert; Dorvaux, Frédéric; Haumesser, Lionel; Le Clezio, Emmanuel; Monot-Laffez, Isabelle

    2015-12-01

    Lead zirconate titanate (PZT) ceramics are the dominant piezoelectric elements for non-destructive evaluation (NDE) and ultrasonic transducers devices. However, the presence of lead content may impose the scientific community to develop lead-free ceramics, concerning human health and environmental safety. During the past ten years, many contributions have highlighted the potential properties of complex compositions like LiNbO3, LiTaO3 and LiSbO3 in the lead-free (K0.5Na0.5)NbO3 KNN system. In this context, for the first time, the practical applications and the effectiveness of simply undoped (K0.5Na0.5)NbO3 (KNN) ceramics are investigated. KNN powder is prepared by conventional solid state mixed oxide route. Ceramics of this material are prepared using conventional sintering (CS) and spark plasma sintering (SPS). Thickness coupling factor kt of 44-46%, planar coupling factor kp of 29-45%, relative permittivity at constant strain ε33,r(S) of 125-243 and acoustic impedance Z of 23-30 MRay are obtained for these two kinds of undoped KNN ceramics. Both ceramics are used to build single-element ultrasonic transducers. Relative bandwidth of 49-78% and insertion loss of -27 and -51dB are obtained for SPS and CS transducers, respectively. These results are suitable for use in non-destructive evaluation. The effectiveness of undoped KNN is evaluated using the KLM model, and compared to standard PZT based probe. Finally, chemical aging test of undoped KNN has demonstrated its stability in water. PMID:26117145

  1. Li(V0.5Ti0.5)S2 as a 1 V lithium intercalation electrode

    PubMed Central

    Clark, Steve J.; Wang, Da; Armstrong, A. Robert; Bruce, Peter G.

    2016-01-01

    Graphite, the dominant anode in rechargeable lithium batteries, operates at ∼0.1 V versus Li+/Li and can result in lithium plating on the graphite surface, raising safety concerns. Titanates, for example, Li4Ti5O12, intercalate lithium at∼1.6 V versus Li+/Li, avoiding problematic lithium plating at the expense of reduced cell voltage. There is interest in 1 V anodes, as this voltage is sufficiently high to avoid lithium plating while not significantly reducing cell potential. The sulfides, LiVS2 and LiTiS2, have been investigated as possible 1 V intercalation electrodes but suffer from capacity fading, large 1st cycle irreversible capacity or polarization. Here we report that the 50/50 solid solution, Li1+x(V0.5Ti0.5)S2, delivers a reversible capacity to store charge of 220 mAhg−1 (at 0.9 V), 99% of theoretical, at a rate of C/2, retaining 205 mAhg−1 at C-rate (92% of theoretical). Rate capability is excellent with 200 mAhg−1 at 3C. C-rate is discharge in 1 h. Polarization is low, 100 mV at C/2. To the best of our knowledge, the properties/performances of Li(V0.5Ti0.5)S2 exceed all previous 1 V electrodes. PMID:26996753

  2. Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La0.5Ca0.5MnO3)

    NASA Astrophysics Data System (ADS)

    Joy, Lija K.; Shanmukharao Samatham, S.; Thomas, Senoy; Ganesan, V.; Al-Harthi, Salim; Liebig, A.; Albrecht, M.; Anantharaman, M. R.

    2014-12-01

    Lanthanum calcium manganites (La0.5Ca0.5MnO3) with a composition close to charge ordering, synthesized by high energy ball milling, was found to exhibit colossal thermoelectric power. Thermoelectric power (TEP) data was systematically analyzed by dividing the entire temperature range (5 K-300 K) into three different regimes to explore different scattering mechanisms involved. Mandal's model has been applied to explain TEP data in the region below the Curie temperature (TC). It has been found that the variation of thermoelectric power with temperature is pronounced when the system enters the charge ordered region at T < 200 K. For temperatures lower than 120 K, due to the co-existence of charge ordered state with a spin-glass state, the variation of thermoelectric power is maximum and exhibited a peak value of -80 mV/K at 58 K. This has been explained by incorporating Kondo properties of the spin-glass along with magnon scattering. FC-ZFC magnetization measurements indicate the existence of a glassy state in the region corresponding to a maximum value of thermoelectric power. Phonon drag contribution instead of spin-glass contribution is taken into account to explain TEP in the region 120 K < T < TC. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > TC). The optimal Mn4+-Mn3+ concentration in charge ordered La0.5Ca0.5MnO3 was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound.

  3. Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La{sub 0.5}Ca{sub 0.5}MnO{sub 3})

    SciTech Connect

    Joy, Lija K.; Anantharaman, M. R.; Shanmukharao Samatham, S.; Ganesan, V.; Thomas, Senoy; Al-Harthi, Salim; Liebig, A.; Albrecht, M.

    2014-12-07

    Lanthanum calcium manganites (La{sub 0.5}Ca{sub 0.5}MnO{sub 3}) with a composition close to charge ordering, synthesized by high energy ball milling, was found to exhibit colossal thermoelectric power. Thermoelectric power (TEP) data was systematically analyzed by dividing the entire temperature range (5 K–300 K) into three different regimes to explore different scattering mechanisms involved. Mandal's model has been applied to explain TEP data in the region below the Curie temperature (T{sub C}). It has been found that the variation of thermoelectric power with temperature is pronounced when the system enters the charge ordered region at T < 200 K. For temperatures lower than 120 K, due to the co-existence of charge ordered state with a spin-glass state, the variation of thermoelectric power is maximum and exhibited a peak value of −80 mV/K at 58 K. This has been explained by incorporating Kondo properties of the spin-glass along with magnon scattering. FC-ZFC magnetization measurements indicate the existence of a glassy state in the region corresponding to a maximum value of thermoelectric power. Phonon drag contribution instead of spin-glass contribution is taken into account to explain TEP in the region 120 K < T < T{sub C}. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > T{sub C}). The optimal Mn{sup 4+}-Mn{sup 3+} concentration in charge ordered La{sub 0.5}Ca{sub 0.5}MnO{sub 3} was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound.

  4. Structural evolution of Na{sub 0.5}K{sub 0.5}NbO{sub 3} at high temperatures

    SciTech Connect

    Ishizawa, Nobuo; Wang, Jun; Sakakura, Terutoshi; Inagaki, Yumi; Kakimoto, Ken-ichi

    2010-11-15

    Changes in structure and dielectric properties at elevated temperatures have been investigated on single-crystals of sodium potassium niobate, Na{sub 0.5}K{sub 0.5}NbO{sub 3}, grown by the flux method. Single-crystal X-ray diffraction studies revealed that the crystals underwent orthorhombic-tetragonal and tetragonal-cubic phase transitions at 465 and 671 K during heating and 446 and 666 K during cooling, respectively. Both transitions were accompanied by volumetric discontinuities of collapse upon heating and expansion upon cooling, suggesting that the transitions were of the first order. The coordination numbers of an Nb showed a decreasing tendency with decreasing temperature, i.e., 6 in cubic, 5+1 in tetragonal and 4+2 in orthorhombic. An Na atom occupied a slightly different position from the K atom in 12-fold coordination, resulting in fewer coordination numbers of 8+4 in cubic and tetragonal and 7+5 in orthorhombic. The spontaneous polarisation (P{sub s}) estimated from the atom positions and formal charges were approximately 0.29 C m{sup -2} in orthorhombic and 0.18 C m{sup -2} in tetragonal. The contribution of the alkaline oxide components to P{sub s} was estimated to be approximately 15% in both ferroelectric forms. The temperature-induced transitions were also confirmed through the dielectric constant and dielectric loss at various frequencies and the differential scanning calorimetry. -- Graphical abstract: Changes in pseudocubic cell volume of an Na{sub 0.5}K{sub 0.5}NbO{sub 3} as a function of temperature; the inset is an enlargement near the transition between the orthorhombic and tetragonal forms. Display Omitted

  5. Topology and temperature dependence of the diffuse X-ray scattering in Na0.5Bi0.5TiO3 ferroelectric single crystals

    PubMed Central

    Gorfman, Semën; Keeble, Dean S.; Bombardi, Alessandro; Thomas, Pam A.

    2015-01-01

    The results of high-resolution measurements of the diffuse X-ray scattering produced by a perovskite-based Na0.5Bi0.5TiO3 ferroelectric single crystal between 40 and 620 K are reported. The study was designed as an attempt to resolve numerous controversies regarding the average structure of Na0.5Bi0.5TiO3, such as the mechanism of the phase transitions between the tetragonal, P4bm, and rhombohedral | monoclinic, R3c | Cc, space groups and the correlation between structural changes and macroscopic physical properties. The starting point was to search for any transformations of structural disorder in the temperature range of thermal depoling (420–480 K), where the average structure is known to remain unchanged. The intensity distribution around the {032} pseudocubic reflection was collected using a PILATUS 100K detector at the I16 beamline of the Diamond Light Source (UK). The data revealed previously unknown features of the diffuse scattering, including a system of dual asymmetric L-shaped diffuse scattering streaks. The topology, temperature dependence, and relationship between Bragg and diffuse intensities suggest the presence of complex microstructure in the low-temperature R3c | Cc phase. This microstructure may be formed by the persistence of the higher-temperature P4bm phase, built into a lower-temperature R3c | Cc matrix, accompanied by the related long-range strain fields. Finally, it is shown that a correlation between the temperature dependence of the X-ray scattering features and the temperature regime of thermal depoling is present. PMID:26877721

  6. Reactive sintering of (K0.5Bi0.5)TiO3-BiFeO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Fisher, John G.; Kim, Min-Gu; Kim, Daeung; Cha, Su-Jeong; Vu, Hung Van; Nguyen, Dieu; Kim, Young-Hun; Moon, Su-Hyun; Lee, Jong-Sook; Hussain, Ali; Kim, Myong-Ho

    2015-05-01

    Ceramics based on BiFeO3 are potential lead-free replacements for Pb(Zr,Ti)O3 in a variety of applications such as sensors, transducers and actuators. Recently, ceramics in the (K0.5Bi0.5)TiO3-BiFeO3 system were developed which have excellent piezoelectric properties. However, these ceramics are difficult to sinter to high density. The present work studies the use of reactive sintering to prepare 0.4(K0.5Bi0.5)TiO3-0.6BiFeO3 ceramics. Undoped and MnO-doped powders were prepared by ball milling K2CO3, (BiO)2CO3, TiO2, α-FeO(OH) and MnCO3 in ethanol with zirconia milling media. The decomposition and calcination reactions of the starting materials were studied using differential scanning calorimetry/thermogravimetric analysis, X-ray diffraction and Fourier transform infra-red analysis. Samples were sintered in the temperature range from 1000 to 1075°C and their structures and microstructures examined using X-ray diffraction, micro-Raman scattering and scanning electron microscopy. MnO doping reduced the rhombohedral distortion of the unit cell. The dielectric, ferroelectric and piezoelectric properties of selected undoped and MnO-doped samples were measured. Both undoped and MnO-doped samples displayed relaxor-type behavior. MnO doping reduced the conductivity of the samples, which exhibit a well-defined activation energy of 1.21 eV. Undoped samples have strain vs. electric field properties comparable to those reported in the literature.

  7. Li(V0.5Ti0.5)S2 as a 1 V lithium intercalation electrode.

    PubMed

    Clark, Steve J; Wang, Da; Armstrong, A Robert; Bruce, Peter G

    2016-01-01

    Graphite, the dominant anode in rechargeable lithium batteries, operates at ∼0.1 V versus Li(+)/Li and can result in lithium plating on the graphite surface, raising safety concerns. Titanates, for example, Li4Ti5O12, intercalate lithium at∼1.6 V versus Li(+)/Li, avoiding problematic lithium plating at the expense of reduced cell voltage. There is interest in 1 V anodes, as this voltage is sufficiently high to avoid lithium plating while not significantly reducing cell potential. The sulfides, LiVS2 and LiTiS2, have been investigated as possible 1 V intercalation electrodes but suffer from capacity fading, large 1st cycle irreversible capacity or polarization. Here we report that the 50/50 solid solution, Li1+x(V0.5Ti0.5)S2, delivers a reversible capacity to store charge of 220 mAhg(-1) (at 0.9 V), 99% of theoretical, at a rate of C/2, retaining 205 mAhg(-1) at C-rate (92% of theoretical). Rate capability is excellent with 200 mAhg(-1) at 3C. C-rate is discharge in 1 h. Polarization is low, 100 mV at C/2. To the best of our knowledge, the properties/performances of Li(V0.5Ti0.5)S2 exceed all previous 1 V electrodes. PMID:26996753

  8. Donor-doping and reduced leakage current in Nb-doped Na0.5Bi0.5TiO3

    NASA Astrophysics Data System (ADS)

    Li, Ming; Li, Linhao; Zang, Jiadong; Sinclair, Derek C.

    2015-03-01

    Low levels of so-called "donor-doping" in titanate-based perovskite oxides such as La for Ba, Sr, and Nb for Ti in (Ba, Sr)TiO3 can significantly reduce the resistivity of these typical (d0) dielectric materials and expand application areas to positive temperature coefficient resistors, thermoelectrics, conductive wafers as thin film substrates, and solid oxide fuel cell anode materials. Here, we show low levels of Nb-doping (≤1 at. %) on the Ti-site in the well-known lead-free piezoelectric perovskite oxide Na0.5Bi0.5TiO3 (NBT) produces completely different behaviours whereby much higher resistivity is obtained, therefore indicating a different donor-doping (substitution) mechanism. There is a switch in conduction mechanism from oxygen-ions in undoped NBT with an activation energy (Ea) of <0.9 eV to electronic (band gap) conduction in 0.5-1 at. % Nb-doped NBT with Ea ˜ 1.5-1.8 eV. This demonstrates the necessity of further systematic doping studies to elucidate the defect chemistry of NBT which is clearly different to that of (Ba,Sr)TiO3. This defect chemistry needs to be understood if NBT-based materials are going to be manufactured on a large scale for commercial applications. This study also illustrates different donor-doping mechanisms to exist within the family of d0 titanate-based perovskites.

  9. The cross-plane thermoelectric properties of p-Ge/Si{sub 0.5}Ge{sub 0.5} superlattices

    SciTech Connect

    Ferre Llin, L.; Samarelli, A.; Weaver, J. M. R.; Dobson, P. S.; Paul, D. J.; Cecchi, S.; Chrastina, D.; Isella, G.; Etzelstorfer, T.; Stangl, J.; Müller Gubler, E.

    2013-09-30

    The electrical conductivity, Seebeck coefficients, and thermal conductivities of a range of p-type Ge/Si{sub 0.5}Ge{sub 0.5} superlattices designed for thermoelectric generation and grown by low energy plasma enhanced chemical vapor deposition have been measured using a range of microfabricated test structures. For samples with barriers around 0.5 nm in thickness, the measured Seebeck coefficients were comparable to bulk p-SiGe at similar doping levels suggesting the holes see the material as a random bulk alloy rather than a superlattice. The Seebeck coefficients for Ge quantum wells of 2.85 ± 0.85 nm increased up to 533 ± 25 μV/K as the doping was reduced. The thermal conductivities are between 4.5 to 6.0 Wm{sup −1}K{sup −1} which are lower than comparably doped bulk Si{sub 0.3}Ge{sub 0.7} but higher than undoped Si/Ge superlattices. The highest measured figure of merit ZT was 0.080 ± 0.011 obtained for the widest quantum well studied. Analysis suggests that interface roughness is presently limiting the performance and a reduction in the strain between the quantum wells and barriers has the potential to improve the thermoelectric performance.

  10. Structure and properties of La-modified Na0.5Bi0.5TiO3 at ambient and elevated temperatures

    NASA Astrophysics Data System (ADS)

    Aksel, Elena; Forrester, Jennifer S.; Foronda, Humberto M.; Dittmer, Robert; Damjanovic, Dragan; Jones, Jacob L.

    2012-09-01

    The crystal structure and property changes of sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) piezoelectric ceramics are reported as a function of La modification (0.5-2.0 at. %) and increasing temperature using high resolution x-ray diffraction, permittivity, depolarization, and polarization and strain hysteresis measurements. La substitution is found to decrease the depolarization temperature of NBT (e.g., 1.5 at. % La substitution lowers the depolarization temperature by 60 °C relative to the unmodified composition) with little impact on the room temperature polarization and strain hysteresis. The room temperature structures of the various NBT compositions were modeled using a mixture of the monoclinic Cc space group and the cubic Pm3¯m phase, where the Pm3¯m phase is used to model local regions in the material which do not obey the long range Cc space group. With increasing La substitution, the lattice parameter distortions associated with the Cc phase approached that of the prototypical cubic unit cell and the fraction of the Pm3¯m phase increased. The relationship between these crystallographic changes and the depolarization behavior of La-modified NBT is discussed.

  11. Structural properties and application in lithium cells of Li(Ni0.5Co0.5)1-yFeyO2 (0 ≤ y ≤ 0.25) prepared by sol-gel route: Doping optimization

    NASA Astrophysics Data System (ADS)

    Abdel-Ghany, A. E.; Hashem, A. M.; Elzahany, E. A.; Abuzeid, H. A.; Indris, S.; Nikolowski, K.; Ehrenberg, H.; Zaghib, K.; Mauger, A.; Julien, C. M.

    2016-07-01

    Layered Li(Co0.5Ni0.5)1-yFeyO2 (0.0 ≤ y ≤ 0.25) oxides were prepared by citric-acid assisted sol-gel method. Elemental and structural properties were investigated by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman scattering (RS) and Mössbauer spectroscopy, and magnetometry. EDX images show a homogeneous distribution of Fe ions. XRD and RS spectroscopy reveal that the materials crystallize as a LiNiO2sbnd LiCoO2sbnd LiFeO2 solid solution with the typical rhombohedral α-NaFeO2 structure (R 3 bar m S.G.) up to y = 0.2 at which composition a secondary phase was observed. For y > 0.2 the XRD results show the appearance of the α-LiFeO2 phase with the cubic structure (Fm3m S.G.). The degree of cation mixing investigated by XRD analysis and magnetic measurements is z < 0.04, for y < 0.2. Electrochemical tests of Li(Co0.5Ni0.5)1-yFeyO2 (0.0 ≤ y ≤ 0.1) oxides in lithium cells show the influence of iron substitution. The best results have been obtained for the composition y(Fe) = 0.05, where the electrical conductivity is maximum. A specific capacity 32 mAh g-1 is maintained at 8C rate.

  12. HEXIT-SAT: a mission concept for x-ray grazing incidence telescopes from 0.5 to 70 keV

    NASA Astrophysics Data System (ADS)

    Fiore, Fabrizio; Perola, Giuseppe C.; Pareschi, Giovanni; Citterio, Oberto; Anselmi, Alberto; Comastri, Andrea

    2004-10-01

    While the energy density of the Cosmic X-ray Background (CXB) provides a statistical estimate of the super massive black hole (SMBH) growth and mass density in the Universe, the lack, so far, of focusing instrument in the 20-60 keV (where the CXB energy density peaks), frustrates our effort to obtain a comprehensive picture of the SMBH evolutionary properties. HEXIT-SAT (High Energy X-ray Imaging Telescope SATellite) is a mission concept capable of exploring the hard X-ray sky with focusing/imaging instrumentation, to obtain an unbiased census of accreting SMBH up to the redshifts where galaxy formation peaks, and on extremely wide luminosity ranges. This will represent a leap forward comparable to that achieved in the soft X-rays by the Einstein Observatory in the late 70'. In addition to accreting SMBH, and very much like the Einstein Observatory, this mission would also have the capabilities of investigating almost any type of the celestial X-ray sources. HEXIT-SAT is based on high throughput (>400 cm2 @ 30 keV; >1200 cm2 @ 1 keV), high quality (15 arcsec Half Power Diameter) multi-layer optics, coupled with focal plane detectors with high efficiency in the full 0.5-70keV range. Building on the BeppoSAX experience, a low-Earth, equatorial orbit, will assure a low and stable particle background, and thus an extremely good sensitivity for faint hard X-ray sources. At the flux limits of 1/10 microCrab (10-30 keV) and 1/3 microCrab (20-40 keV) (reachable in one Msec observation) we should detect ~100 and ~40 sources in the 15 arcmin FWHM Field of View respectively, thus resolving >80% and ~65% of the CXB where its energy density peaks.

  13. Synthesis and thermoelectric properties of the novel A-site deficient Zn{sub 0.5}Rh{sub 2}O{sub 4} compound

    SciTech Connect

    Nakamura, Yuta; Kakemoto, Hirofumi; Nishiyama, Shin; Irie, Hiroshi

    2012-08-15

    A novel thermoelectric material, A-site-deficient spinel Zn{sub 0.5}Rh{sub 2}O{sub 4}, was prepared by subtracting Li ions from Li{sub 0.5}Zn{sub 0.5}Rh{sub 2}O{sub 4} immersed in a K{sub 2}S{sub 2}O{sub 8} aqueous solution. The electric conductivity ({sigma}) increased 6-fold after extracting Li ({sigma}=8.8 S/cm (Li{sub 0.5}Zn{sub 0.5}Rh{sub 2}O{sub 4}), 50 S/cm (Zn{sub 0.5}Rh{sub 2}O{sub 4}) at 600 Degree-Sign C), whereas the Seebeck coefficient (S) only slightly increased (S=203 {mu}V/K (Li{sub 0.5}Zn{sub 0.5}Rh{sub 2}O{sub 4}), 216 {mu}V/K (Zn{sub 0.5}Rh{sub 2}O{sub 4}) at 600 Degree-Sign C). In Zn{sub 0.5}Rh{sub 2}O{sub 4}, a mixed-valence configuration of Rh{sup 3+} and Rh{sup 4+} at a ratio of 1 to 1 and a half-deficient A-site were realized, resulting in high {sigma} and even slightly increased S, which were likely attributed to the rather high power factor of 2.3 Multiplication-Sign 10{sup -4} W/m K{sup 2} at 600 Degree-Sign C. Our findings demonstrate that controlling the Rh{sup 4+}/Rh{sup 3+} ratio is a promising method for enhancing the thermoelectric properties. - Graphical abstract: Temperature dependence of power factor (PF) of Li{sub 0.5}Zn{sub 0.5}Rh{sub 2}O{sub 4}, Li{sub 0.25}Zn{sub 0.5}Rh{sub 2}O{sub 4}, and Zn{sub 0.5}Rh{sub 2}O{sub 4} thin films. Highlights: Black-Right-Pointing-Pointer A-site-deficient Zn{sub 0.5}Rh{sub 2}O{sub 4} was prepared by subtracting Li from Li{sub 0.5}Zn{sub 0.5}Rh{sub 2}O{sub 4}. Black-Right-Pointing-Pointer A mixed-valence configuration with a Rh{sup 4+}/Rh{sup 3+} ratio of 1 was likely realized. Black-Right-Pointing-Pointer Such a configuration lead to an enhanced {sigma} of 50S/cm and S of 216 {mu}V/K at 600 Degree-Sign C. Black-Right-Pointing-Pointer Controlling the Rh{sup 4+}/Rh{sup 3+} ratio is a candidate for enhancing the thermoelectricity.

  14. Raman Scattering in Tl_0.5Pb_0.5Sr_1.25Ba_0.75 Ca_1Cu_2Ox Thin-Films

    NASA Astrophysics Data System (ADS)

    Subramanyam, G.; Boolchand, P.; Chandrasekhar, M.

    1997-03-01

    RF sputtered c-axis oriented thin-films of the titiled 1212 superconductor have been deposited on LaAlO3 substrates. Films possess a tetragonal structure and a T_c=85K. Raman modes due to A_1g and B_1g vibrations are observed, of which the Cu mode at 124 cm-1, the 0(1) out of phase mode at 294 cm-1 and the 0(2) mode at 543 cm-1 are upshifted in frequency relative to pure T11212.footnote K.F.McCarty, et al. Physica C156, 119 (1988) Two new modes are observed: one at 341 cm-1 corresponding to the 0(1) in-phase vibration calculated( A.D.Kulkarni et al. Phys. Rev. B41, 6409 (1990)) to be at 358 cm-1; and a second at 627 cm-1, which may be due to disallowed 0(3) vibration, observed due to symmetry breaking in the alloyed compound. * Supported by Roy J. Carver Foundation ** Supported by NSF grant DMR-9424556. ***Supported by DOE grant DEFG02-9OER45427 through Midwest Superconductivity Consortium.

  15. Effect of A-site La and Ba doping on threshold field and characteristic temperatures of PbSc0.5Ta0.5O3 relaxor studied by acoustic emission

    NASA Astrophysics Data System (ADS)

    Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.

    2012-09-01

    The structural transitions in Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PLST) relaxor crystals were studied by means of acoustic emission (AE) under an external electric field (E) and compared with those observed in pure PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) [E. Dul'kin et al., EPL 94, 57002 (2011)]. Similar to both the PST and PBST compounds, in zero field PLST exhibits AE corresponding to a para-to-antiferroelectric incommensurate phase transition at Tn = 276 K, lying in the vicinity of dielectric temperature maximum (Tm). This AE signal exhibits a nontrivial behavior when applying E resembling the electric-field-dependence of Tn previously observed for both the PST and PBST, namely, Tn initially decreases with the increase of E, attains a minimum at a threshold field Eth = 0.5 kV/cm, accompanied by a pronounced maximum of the AE count rate Ṅ = 12 s-1, and then starts increasing as E enhances. The similarities and difference between PST, PLST, and PBST with respect to Tn, Eth, and Ṅ are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric field due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of substituting ion, and (iii) change in the tolerance factor and elastic field to the larger ionic radius of the substituting A-site ion due to the different radius of the substituting ion. The first two mechanisms influence the actual values of Tn and Eth, whereas the latter is shown to affect the normalized Ṅ, indicating the fractions undergoing a field-induced crossover from a modulated antiferroelectric to a ferroelectric state. Creation of secondary random electric field, caused by doping-induced A-site-O ionic chemical bonding, is discussed.

  16. NuSTAR Reveals Extreme Absorption in z < 0.5 Type 2 Quasars

    NASA Astrophysics Data System (ADS)

    Lansbury, G. B.; Gandhi, P.; Alexander, D. M.; Assef, R. J.; Aird, J.; Annuar, A.; Ballantyne, D. R.; Baloković, M.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Civano, F.; Comastri, A.; Craig, W. W.; Del Moro, A.; Grefenstette, B. W.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Koss, M.; LaMassa, S. M.; Luo, B.; Puccetti, S.; Stern, D.; Treister, E.; Vignali, C.; Zappacosta, L.; Zhang, W. W.

    2015-08-01

    The intrinsic column density (NH) distribution of quasars is poorly known. At the high obscuration end of the quasar population and for redshifts z < 1, the X-ray spectra can only be reliably characterized using broad-band measurements that extend to energies above 10 keV. Using the hard X-ray observatory NuSTAR, along with archival Chandra and XMM-Newton data, we study the broad-band X-ray spectra of nine optically selected (from the SDSS), candidate Compton-thick (NH > 1.5 × 1024 cm-2) type 2 quasars (CTQSO2s); five new NuSTAR observations are reported herein, and four have been previously published. The candidate CTQSO2s lie at z < 0.5, have observed [O iii] luminosities in the range 8.4\\lt {log}({L}[{{O} {{III}}]}/{L}⊙ )\\lt 9.6, and show evidence for extreme, Compton-thick absorption when indirect absorption diagnostics are considered. Among the nine candidate CTQSO2s, five are detected by NuSTAR in the high-energy (8-24 keV) band: two are weakly detected at the ≈3σ confidence level and three are strongly detected with sufficient counts for spectral modeling (≳90 net source counts at 8-24 keV). For these NuSTAR-detected sources direct (i.e., X-ray spectral) constraints on the intrinsic active galactic nucleus properties are feasible, and we measure column densities ≈2.5-1600 times higher and intrinsic (unabsorbed) X-ray luminosities ≈10-70 times higher than pre-NuSTAR constraints from Chandra and XMM-Newton. Assuming the NuSTAR-detected type 2 quasars are representative of other Compton-thick candidates, we make a correction to the NH distribution for optically selected type 2 quasars as measured by Chandra and XMM-Newton for 39 objects. With this approach, we predict a Compton-thick fraction of {f}{CT}={36}-12+14 %, although higher fractions (up to 76%) are possible if indirect absorption diagnostics are assumed to be reliable.

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

    PubMed Central

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

    2015-01-01

    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. PMID:25716551

  18. 17 CFR 275.0-5 - Procedure with respect to applications and other matters.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... EXCHANGE COMMISSION (CONTINUED) RULES AND REGULATIONS, INVESTMENT ADVISERS ACT OF 1940 § 275.0-5 Procedure... the Commission under the Act other than an application for registration as an investment adviser....

  19. Crystal structure, phase transitions, and magnetic properties of titanium doped La0.5Sr0.5MnO3 perovskites

    NASA Astrophysics Data System (ADS)

    Hazzez, M.; Ihzaz, N.; Boudard, M.; Oumezzine, M.

    2016-04-01

    The current paper investigates the effect of titanium substitution on the structure as well as the magnetic properties of La0.5Sr0.5Mn1-xTixO3 (0≤x≤0.5) polycrystalline powder. The samples studied crystallize in a distorted perovskite structures of tetragonal (space group I4/mcm) symmetry with octahedral tilting scheme (a0a0c-), leading to the absence of octahedral tilting all along two perovskite main directions and to an out-of-phase along the third direction, or rhombohedral (space group R 3 bar c) symmetry with octahedral tilting scheme (a-a-a-) yielding to out-of-phase along the three perovskite main directions. As the Ti content increases, a better matching of the (Mn/Ti)-O distances and (Mn/Ti)-O-(Mn/Ti) bond angle occurs. This phenomenon is created by an elongation of the (Mn/Ti)-O distance, as Mn4+ is substituted by the larger ion Ti4+. In the whole compositional range, the symmetry-adapted to atomic displacements, responsible for the out-of-phase tilting of the (Mn/Ti)O6 octahedra, stays active, anticipating tetragonal-to-rhombohedral phase transition. Taking in to account what has been explained above, measurements of magnetic properties show a decrease of magnetic ordering temperature when Ti content increases, which in turn leads to the diminution of the exchange interaction caused by reducing the FM coupling and the replacement of neighboring manganese Mn3+-O-Mn4+ by Mn3+-O-Ti4+ bonds. This phenomenon results in broadening of the paramagnetic to ferromagnetic phase transition range. Further changes in magnetic properties with the increase in Ti concentration are studied.

  20. Optimising apodized grating couplers in a pure SOI platform to -0.5 dB coupling efficiency.

    PubMed

    Bozzola, Angelo; Carroll, Lee; Gerace, Dario; Cristiani, Ilaria; Andreani, Lucio Claudio

    2015-06-15

    We present a theoretical optimisation of 1D apodized grating couplers in a "pure" Silicon-On-Insulator (SOI) architecture, i.e. without any bottom reflector element, by means of a general mutative method. We perform a comprehensive 2D Finite Difference Time Domain study of chirped and apodized grating couplers in 220 nm SOI, and demonstrate that the global maximum coupling efficiency in that platform is capped to 65% (-1.9 dB). Moving to designs with thicker Si-layers, we identify a new record design in 340 nm SOI, with a simulated coupling efficiency of 89% (-0.5 dB). Going to thicker Si layers does not further improve the efficiency, implying that -0.5 dB may be a global maximum for a grating coupler in SOI without a bottom-reflector. Even after allowing for 193 nm UV-lithographic fabrication constraints, the 340 nm design still offers -0.7 dB efficiency. These new apodized designs are the first pure SOI couplers compatible with deep-UV lithography to offer better than -1 dB insertion losses. With only very minor changes to existing deposition and lithography recipes, they are compatible with the multi-project wafer runs already offered by Si-Photonics foundries. PMID:26193602

  1. Crystal and magnetic study of the disordered perovskites Ca(Mn{sub 0.5}Sb{sub 0.5})O{sub 3} and Ca(Fe{sub 0.5}Sb{sub 0.5})O{sub 3}

    SciTech Connect

    Retuerto, M.; Martinez-Lope, M.J.; Garcia-Hernandez, M.; Munoz, A.; Fernandez-Diaz, M.T.; Alonso, J.A.

    2010-10-15

    We have investigated the double perovskites Ca{sub 2}MSbO{sub 6} (M = Mn, Fe) that have been prepared by solid-state reaction (M = Fe) and wet chemistry procedures (M = Mn). The crystal and magnetic structures have been studied from X-ray (XRD) and neutron powder diffraction (NPD) data. Rietveld refinements show that the crystal structures are orthorhombic (space group Pbnm) with complete disorder of M and Sb cations, so the formula should be rewritten as Ca(M{sub 0.5}Sb{sub 0.5})O{sub 3}. Due to this disorder no evidences of Jahn-Teller distortion can be observed in the MnO{sub 6} octahedra of Ca(Mn{sub 0.5}Sb{sub 0.5})O{sub 3}, in contrast with the ordered double perovskite Sr{sub 2}MnSbO{sub 6}. Ca(Fe{sub 0.5}Sb{sub 0.5})O{sub 3} behaves as an antiferromagnet with an ordered magnetic moment for Fe{sup 3+} of 1.53(4){mu}{sub B} and a propagation vector k = 0, as investigated by low-temperature NPD. The antiferromagnetic ordering is a result of the high degree of Fe/Sb anti-site disorder of the sample, which originates the spontaneous formation of Fe-rich islands, characterized by the presence of strong Fe-O-Fe antiferromagnetic couplings with enough long-range coherence to produce a magnetic contribution perceptible by NPD. By contrast, the magnetic structure of Ca(Mn{sub 0.5}Sb{sub 0.5})O{sub 3} cannot be observed by low-temperature NPD because the magnitude of the ordered magnetic moments is below the detection threshold for neutrons.

  2. MODIFIED EQUIPARTITION CALCULATION FOR SUPERNOVA REMNANTS. CASES α = 0.5 AND α = 1

    SciTech Connect

    Arbutina, B.; Urošević, D.; Vučetić, M. M.; Pavlović, M. Z.; Vukotić, B.

    2013-11-01

    The equipartition or minimum energy calculation is a well-known procedure for estimating the magnetic field strength and the total energy in the magnetic field and cosmic ray particles by using only the radio synchrotron emission. In one of our previous papers, we have offered a modified equipartition calculation for supernova remnants (SNRs) with spectral indices 0.5 < α < 1. Here we extend the analysis to SNRs with α = 0.5 and α = 1.

  3. Improved electrochemical properties of BiOF-coated 5 V spinel Li[Ni 0.5Mn 1.5]O 4 for rechargeable lithium batteries

    NASA Astrophysics Data System (ADS)

    Kang, Han-Byeol; Myung, Seung-Taek; Amine, Khalil; Lee, Sung-Man; Sun, Yang-Kook

    The electrochemical properties of BiOF-coated 5 V spinel Li[Ni 0.5Mn 1.5]O 4 were investigated at elevated temperatures (55 °C). As observed by scanning and transmission electron microscopy, BiOF nanolayers with ∼10 nm thickness were coated on the surface of Li[Ni 0.5Mn 1.5]O 4. The BiOF coating layer protected the surface of the active materials from HF generated by the decomposition of LiPF 6 in the electrolyte during electrochemical cycling. The dissolution of transition metal elements was also suppressed upon cycling. Therefore, the capacity retention of the BiOF-coated Li[Ni 0.5Mn 1.5]O 4 was obviously improved compared to the pristine Li[Ni 0.5Mn 1.5]O 4 at 55 °C.

  4. High-Resolution Chandra Spectroscopy of γ Cassiopeiae (B0.5e)

    NASA Astrophysics Data System (ADS)

    Smith, Myron A.; Cohen, David H.; Gu, Ming Feng; Robinson, Richard D.; Evans, Nancy Remage; Schran, Prudence G.

    2004-01-01

    γ Cas is the prototypical classical B0.5e star and is now known to be the primary in a wide binary system. It has long been famous for its unique hard X-ray characteristics, among which are variations that correlate with changes in a number of optical light and UV line and continuum properties. These peculiarities have led to a picture in which processes on or near the Be star produce the observed X-ray emission. In this paper we report on a 53 ks Chandra High Energy Transmission Grating Spectrometer observation of this target. An inspection of our spectrum shows that it is quite atypical for a massive star. The emission lines appear weak because of a strong short-wavelength continuum that arises from a hot plasma with kT=11-12 keV. The spectrum exhibits many lines, the strongest of which are Lyα features of H-like species from Fe through the even-Z intermediate elements (S, Si, Mg, and Ne), down to O and N. Line ratios of the ``rif triplet'' for a variety of He-like ions and of Fe XVII are consistent with the dominance of collisional atomic processes. However, the presence of Fe and Si fluorescence K features indicates that photoionization also occurs in nearby cold gas. The line profiles indicate a mean velocity at rest with an rms line broadening of 500 km s-1 and little or no asymmetry. An empirical global-fitting analysis of the line and continuum spectrum suggests that there are actually three or four plasma emission components. The first is the dominant hot (12 keV) component, of which some fraction (10%-30%) is heavily absorbed, while the remainder is affected by a much lower column density of only 3×1021 cm-2. The hot component has a Fe abundance of only 0.22+/-0.05 solar. The other two or three major emission components are ``warm'' and are responsible for most other emission lines. These components are dominated by plasma having temperatures near 0.1, 0.4, and 3 keV. Altogether, the warm components have an emission measure of about 14% of the hot

  5. Detecting the 21 cm forest in the 21 cm power spectrum

    NASA Astrophysics Data System (ADS)

    Ewall-Wice, Aaron; Dillon, Joshua S.; Mesinger, Andrei; Hewitt, Jacqueline

    2014-07-01

    We describe a new technique for constraining the radio-loud population of active galactic nuclei at high redshift by measuring the imprint of 21 cm spectral absorption features (the 21 cm forest) on the 21 cm power spectrum. Using semi-numerical simulations of the intergalactic medium and a semi-empirical source population, we show that the 21 cm forest dominates a distinctive region of k-space, k ≳ 0.5 Mpc- 1. By simulating foregrounds and noise for current and potential radio arrays, we find that a next-generation instrument with a collecting area of the order of ˜ 0.1 km2 (such as the Hydrogen Epoch of Reionization Array) may separately constrain the X-ray heating history at large spatial scales and radio-loud active galactic nuclei of the model we study at small ones. We extrapolate our detectability predictions for a single radio-loud active galactic nuclei population to arbitrary source scenarios by analytically relating the 21 cm forest power spectrum to the optical depth power spectrum and an integral over the radio luminosity function.

  6. Structural, optical and electrical properties of ZnSe{sub 0.5}CdS{sub 0.5} alloy films

    SciTech Connect

    Venugopal, R.; Vijayalakshmi, R.P.; Reddy, D.R.; Reddy, B.K.

    1995-11-01

    Thin films of ZnSe{sub 0.5}CdS{sub 0.5} (t {approximately} 0.60 mm) were deposited at two substrate temperatures (350 and 470 K) by vacuum evaporation. The X-ray diffractograms (XRDs) indicated that the films were polycrystalline in nature with wurtzite structure irrespective of substrate temperature (T{sub s}). The increase in lattice parameter with T{sub s} could be due to better stoichiometry observed in the films formed at higher T{sub s}. The refractive index of the films formed at higher T{sub s} was generally higher. The refractive index and extinction coefficient were high at lower wavelength and this might be due to the free carrier absorption. The electrical conductivity and Hall measurements were carried out by dc Van der Pauw technique. The temperature dependence of Hall mobilities shows that grain boundary scattering mechanism dominates and the grain boundary potential was found to be 0.055 eV in these films.

  7. Low-frequency transient dynamic clusters in simulated amorphous Ni0.5Zr0.5 around the glass temperature

    NASA Astrophysics Data System (ADS)

    Ladadwa, I.; Teichler, H.

    2008-10-01

    Molecular dynamics results are reported concerning cooperatively rearranging regions in simulated Ni0.5Zr0.5 melts down to 700K . Emphasis is laid on discriminating between clusters of mobile atoms (CMA) from low-frequency dynamics and the all-frequency case, where the former characterize fluctuations and relaxations on the scale of the late β regime and α decay, while the latter include, in addition, reversible high-frequency vibrations. Separation of the low-frequency part of the dynamics is carried out by low-pass filtering, exploiting the separation of time scales below the critical temperature Tc of the mode-coupling theory. With increasing temperature, the low-frequency and all-frequency dynamics merge in the range of Tc when the separation of time scales disappears. In the low-frequency CMA, the average size of correlated clusters of connected atoms turns out to be nearly one order of magnitude larger than in the all-frequency CMA. The low-frequency CMA appear as local clusters propagating extremely slowly in space with characteristic time scale of μs at 700K , the scale of the onset of α decay.

  8. Raman, dielectric and AC-conductivity behavior of Dy2O3 contained K0.5Na0.5NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Mahesh, P.; Pamu, D.

    2016-05-01

    Lead-free piezoelectric (K0.5Na0.5)NbO3+ x wt% Dy2O3 (x = 0 - 1.5) (KNND) ceramics have been prepared by solid state reaction method. The effect of Dy2O3 on the dielectric and electrical conductivity responses of KNN ceramics were investigated in a broad temperature (from 133 K to 673 K) and frequency (106 Hz to 108 Hz) range. Temperature dependent dielectric analysis revealed that the polymorphic phase transition orthorhombic to tetragonal transition temperature (TO-T) shifted from 199°C to room temperature with enhanced dielectric permittivity (ɛ' = 994) with the addition of Dy2O3. The effect of Dy2O3 on structural properties of KNND ceramics are analyzed interms of changes in the internal modes of NbO6 octahedra by using Raman spectroscopy. Temperature dependent (133 K - 306 K) AC-conductivity follows the variable range hopping mechanism in different temperature regimes.

  9. Coherent A1g Phonon in thin Film Superconductor FeSe0.5Te0.5: π/2 Phase Difference over Superconducting Phase Transition

    NASA Astrophysics Data System (ADS)

    Zhao, Jimin; Wu, Yanling; Hu, Minhui; Tian, Yichao; Cao, Lixin; Wang, Rui

    2014-03-01

    Coherent A1 g phonon mode in a thin film superconductor FeSe0.5Te0.5 was generated and detected using ultrafast laser pulses. At below and above the transition temperature Tc, the coherent lattice oscillation we observed exhibited a π/2 phase difference, manifesting a ``displacive limit ~ impulsive limit'' transition upon crossing a phase transition within the same sample. We ascribe this π/2 phase difference to the different lifetimes (τc) of excited charge density components that couples to the fully symmetric A1 g phonon mode, i.e. the different strength of electron-phonon couplings. In the superconducting and paramagnetic metallic states the lifetimes of such carrier excitations are largely different. Our investigation reveals possible correlation of superconducting electrons with zone-center optical phonons. Our 170nm thin film sample contains tension stress, which leads to enhanced Tc and thus facilitated our measurements. Financially supported by the National Basic Research Program of China (2012CB821402), the NSFC (11274372, 10974246) and the External Cooperation Program of Chinese Academy of Sciences (GJHZ1403).

  10. Unravelling the complex nanostructure of La0.5-xLi0.5-xSr2xTiO3 Li ionic conductors.

    PubMed

    García-González, Ester; Urones-Garrote, Esteban; Várez, Alejandro; Sanz, Jesús

    2016-04-19

    The origin of the intricate nanostructure of La0.5-xLi0.5-xSr2xTiO3 (0.0625 ≤ x ≤ 0.25) perovskite-type Li ion conductors has been investigated. Reciprocal space electron diffraction analysis and aberration-corrected STEM by combining annular bright field (ABF) and high angle annular dark field (HAADF) imaging methods have been used to elucidate the complex local atomic arrangements which cannot be adequately described by average crystal structure models. Two different local crystal structures endotaxially-related at the nanoscale without compositional phase separation associated, constituting the crystals. Self-organization of the two different ordered regions arises as a consequence of the competition between two distortive forces in the crystal lattice: octahedral tilting and second-order Jahn-Teller distortion of TiO6 octahedra. Changes in the distribution of A species suggest different Li ion conduction pathways for the two structures and this scenario has difficult long-range Li mobility. The detailed study performed may be helpful in understanding the local structural changes affecting Li and their relation to the conductivity in LLTO-derived ionic conductors. PMID:27009477

  11. Morphology of the Tin Whiskers on the Surface of a Sn-3Ag-0.5Cu-0.5Nd Alloy

    NASA Astrophysics Data System (ADS)

    Chuang, Tung-Han; Jain, Chao-Chi

    2011-03-01

    Rapid growth of tin whiskers has been observed on the surface of rosette-shaped NdSn3 intermetallic phase in a Sn-3Ag-0.5Cu-0.5Nd alloy after air storage. It is shown that various cross sections of NdSn3 rosettes in the solder matrix reveal different morphologies of tin whiskers, which can be classified as four types: long fibers, short fibers, tiny sprouts, and hillocks. The fibrous whiskers and tiny sprouts are found on the surfaces of specimens exposed to air at room temperature and 423 K (150 °C), while hillocks appear only after storage at 423 K (150 °C). In addition, it is observed that, in most cases, each oxidized NdSn3 intermetallic phase contains only a single whisker at its center. Through metallographic observations and chemical analyses on the cross sections of the oxidized NdSn3 intermetallics, a "successive compressive stress model" has been proposed to interpret the tin whisker growth on the surface of a rare earth (RE)-containing solder.

  12. Chemical durability and leaching mechanism of Ce0.5Eu0.5PO4 ceramics: Effects of temperature and pH values

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaofeng; Teng, Yuancheng; Wu, Lang; Huang, Yi; Ma, Jiyan; Wang, Guolong

    2015-11-01

    Ce0.5Eu0.5PO4 ceramics with high relative density were prepared by hot-press (HPS) and pressureless (PLS) sintering. The effects of temperature and pH values on the chemical durability of the ceramics were investigated. The results show that an increase of acidity significantly accelerated the corrosion of the samples. In alkaline leachates, further release elements were prevented by the newborn surface precipitation. The leach rate (Rn) of HPS sample was similar to that of PLS specimen in deionized water, but higher Rn for PLS sample was found in pH = 11 solution. Moreover, apparent activation energy of the dissolution of Eu (40 ± 4 kJ mol-1) is much higher than that of Ce (20 ± 1 kJ mol-1), leading to the higher normalized elemental leach rate of Eu. Both the Eu and Ce elements have low leach rates (10-12-10-9 m d-1) after 42 days in all the leachates studied in this work.

  13. Synthesis and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 ceramic by molten salt method

    NASA Astrophysics Data System (ADS)

    Su, Yanli; Wang, Ying

    2016-03-01

    Na0.5Bi0.5Cu3Ti4O12 (NBCTO) powder was prepared by molten salt method at 700, 750, 800, and 850 °C in NaCl-KCl flux salts, respectively. X-ray diffraction data revealed that the main NBCTO phase of powder was synthesized at a low temperature of 700 °C for 2 h in NaCl-KCl flux, which was reduced by about 250 °C compared with the conventional solid-state reaction method. The evolution of the microstructure was observed by scanning electron microscopy, and the dielectric properties of NBCTO ceramics affected by sintering temperature and sintering time were studied in detail in this paper. The complex impedance plots were also employed to analyze the dielectric properties of NBCTO ceramics. The average grain size of the sintered ceramic increased with the increase in sintering temperature, which lead to the increased dielectric constant of the NBCTO ceramic, whereas the sintering time has affected the dielectric constant slightly. A high dielectric constant of more than 104 and a low loss tangent (tan δ) of 0.06 (at 10 kHz) were obtained for the NBCTO ceramic sintered at 1040 °C for 12 h.

  14. Growth of Cu 0.5Tl 0.5Ba 2Ca 3Cu 4-yZn yO 12-δ superconductor with optimum carriers

    NASA Astrophysics Data System (ADS)

    Mumtaz, M.; Khan, Nawazish A.; Khan, E. U.

    2010-05-01

    We have tried to vary the carriers concentration in Cu 0.5Tl 0.5Ba 2Ca 3Cu 4-yZn yO 12-δ ( y = 0, 1, 1.5, 2, 2.5) superconductor with the help of post-annealing experiments carried out in nitrogen, oxygen and air and to investigate its effects on the superconductivity parameters. The zero resistivity critical temperature [ T c( R = 0)], the magnitude of diamagnetism and critical current [ I c( H = 0)] are found to increase in Zn free samples after post-annealing in oxygen and air, while these superconducting properties have been suppressed after post-annealing in nitrogen at 550 °C for 6 h. The post-annealing of Zn-doped samples in air has marginally increased the superconducting properties, while these properties have been suppressed after post-annealing in nitrogen and oxygen. These studies have led us to the definite conclusion that the Zn-doped material has grown with optimum carriers concentration.

  15. Pulse and quasi-static remagnetization peculiarities and relaxation properties of Nd0.5Sr0.5MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Dovgii, V. T.; Linnik, A. I.; Kamenev, V. I.; Tarenkov, V. Yu.; Sidorov, S. L.; Todris, B. M.; Mikhailov, V. I.; Davideiko, N. V.; Linnik, T. A.; Popov, Ju. F.; Balbashov, A. M.

    2016-06-01

    Hysteresis features of magnetization and resistance of Nd0.5Sr0.5MnO3 single crystal in quasi-static (up to 9 T) and pulse (up to 14 T) magnetic fields are studied. The relaxation processes of magnetization and resistance after the action of a magnetic field of 9 T are also studied. It is shown that relaxation curves are approximated by two exponents with different time constants. These two constants relate to relaxation of the metastable ferromagnetic phase towards two different crystal structures (Imma and p21/m). Mechanism of phase transitions: antiferromagnetic insulator↔ferromagnetic metal (AFM/I↔FM/M) and existence of a high-conductive state of a sample after removal of magnetizing field in the temperature range below 150 K is proposed. The mechanism is connected with structural transition induced by magnetic field (due to magnetostriction) and slow relaxation of the FM-phase (larger volume) to the equilibrium AFM-phase (smaller volume) after field removal. It is shown that during pulse magnetization at the temperature 18 K time required for the AFM/I→FM/M phase transition is by six-seven orders of magnitude less than for realization of the FM/M→AFM/I phase transition.

  16. Thermoelectric and electrical properties of Ba0.5Sr0.5Co x Ru x Fe(12-2 x)O19 ferrite*

    NASA Astrophysics Data System (ADS)

    Singh, Charanjeet; Jaroszewski, Maciej; Bindra Narang, Sukhleen; Ravinder, D.

    2016-04-01

    Thermoelectric and electrical characteristics investigation of M-type hexagonal ferrite, Ba0.5Sr0.5CoxRuxFe(12-2x)O19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2), have been carried out from 303 K to 473 K. The static current density-electric field characteristics have been measured at room temperature. The Seebeck coefficient indicates n-type behavior at lower substitution and p-type conduction at higher substitution. The different electrical parameters are affected by change in grain size with substitution of Co2+ and Ru4+ ions. The existence of polarons is confirmed from increase in conductivity with frequency. The static conduction due to applied electric field is discussed qualitatively in terms of space charge limited current, ionic hopping, Poole-Frenkel and Schottky-Richardson mechanisms. The large current density has been observed at higher substitution. Contribution to the Topical Issue "Materials for Dielectric Applications", edited by Maciej Jaroszewski and Sabu Thomas.

  17. Effect of A Site and Oxygen Vacancies on the Structural and Electronic Properties of Lead-Free KTa0.5Nb0.5O3 Crystal

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Lin, Jiaqi; Li, Xiaokang; Xiu, Hanjiang; Shen, Yanqing

    2016-04-01

    The structural and electronic properties of lead-free potassium tantalite niobate KTa0.5Nb0.5O3 (KTN) with A site vacancies V_{{K}}0 , V_{{K}}^{1 - } and oxygen vacancies V_{{O}}0 , V_{{O}}^{2 + } , were investigated by first-principles calculations, which indicated that A site vacancies V_{{K}}0 are likely to form in the KTN compared with V_{{K}}^{1 - } , and oxygen vacancies V_{{O}}^{2 + } are likely to form compared with V_{{O}}0 in the KTN according to the investigation of formation energy. The results show that K and O vacancies have significant influence on the atomic interactions of the atoms and the electronic performance of the materials. And Ta atoms are more easily influenced by the K and O vacancies than the Nb atoms from the atomic displacements in KTN with K and O vacancies. The investigation of density of state indicates that the compensation of electrons in KTN with vacancies make the hybridization become stronger among Ta d, Nb d and O p orbitals. Besides, Mulliken population of all the Ta and Nb atoms in KTN with charged vacancies are influenced by complement electrons. The strength of the Nb-O bond is stronger than Ta-O based on the changes of bond lengths and Mulliken population.

  18. Aging, rejuvenation, and memory effects in short-range Ising spin glass: Cu_0.5Co_0.5Cl_2-FeCl3 GBIC

    NASA Astrophysics Data System (ADS)

    Suzuki, M.; Suzuki, I. S.

    2004-03-01

    Cu_0.5Co_0.5Cl_2-FeCl3 GBIC undergoes a spin glass (SG) transition at Tg (= 3.92 ± 0.11 K). The system shows a dynamic behavior that has some similarities and some significant differences compared to a 3D Ising SG.^1 Here we report on non-equilibrium aging dynamics which has been studied using zero-field cooled (ZFC) magnetization and low frequency AC magnetic susceptibility.^2 The time dependence of the relaxation rate S(t) = (1/H)dM_ZFC/dln t for the ZFC magnetization after the ZFC aging protocol, shows a peak at a characteristic time t_cr near a wait time t_w, corresponding to a crossover from quasi equilibrium dynamics to non-equilibrium. The time t_cr strongly depends on t_w, temperature, magnetic field, and the temperature shift. The rejuvenation effect is observed in both i^' and i^'' under the T-shift and H-shift procedures. The memory of the specific spin configurations imprinted during the ZFC aging protocol can be recalled when the system is re-heated at a constant heating rate. The aging, rejuvenation, and memory effects are discussed in terms of the scaling concepts derived from numerical studies on 3D Edwards-Anderson spin glass model. 1. I.S. Suzuki and M. Suzuki, Phys. Rev. B 68, 094424 (2003) 2. M. Suzuki and I.S. Suzuki, cond-mat/0308285

  19. Al3+ doping effects and high-field phase diagram of La0.5Sr0.5Mn1-x Al x O3

    NASA Astrophysics Data System (ADS)

    Shang, C.; Xia, Z. C.; Wei, M.; Jin, Z.; Chen, B. R.; Shi, L. R.; Ouyang, Z. W.; Huang, S.; Xiao, G. L.

    2016-01-01

    Magnetization measurements of La0.5Sr0.5Mn1-x Al x O3 (0  ⩽  x  ⩽  0.25) under pulsed high magnetic fields up to 50 T have been carried out, in which the Al3+ ions doping and magnetic field effects on the charge-ordering/antiferromagnetic to ferromagnetic phase transitions have been discussed. A triple-phase diagram with the critical field, doping level and temperature has been determined, in which the antiferromagntic and ferromagnetic phase boundaries were clearly defined. The change from long-range charge-ordered/antiferromagnetic phases to the robust short-range ones upon the Al3+-doping was observed. According to the experimental results, we assume that Al3+ ion doping at the Mn sites dilutes the Mn3+-O-Mn4+ network, weakens the double-exchange interaction and further suppresses the FM phase (metallic conduction), which leads to the critical magnetic fields destroying the antiferromagnetic order increase with the increase of the doping level.

  20. Effects of strain on the electronic structure and magnetic properties in SrMn0.5Fe0.5O3.

    PubMed

    Mi, Chun-Wei; Chin, Yi-Ying; Hsiao, Yen-Fu; Fang, Hau-Wei; Luo, Chih-Wei; Wu, Kaung-Hsiung; Uen, Tzeng-Ming; Lin, Jiunn-Yuan; Lin, Hong-Ji; Juang, Jenh-Yih

    2016-09-01

    The electronic structure and magnetic properties of SrMn0.5Fe0.5O3 powder and films grown on (1 0 0)-SrTiO3 (STO) and (1 0 0)-LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) were investigated by temperature dependent magnetization and soft x-ray absorption. The results exhibit characteristics of 3d (5) Fe(3+), [Formula: see text], and 3d (3)  +  3d (4) [Formula: see text] Mn(4+) at room temperature in all samples. However, the features of 3d (5) Fe(3+) and 3d (3) Mn(4+) increased significantly for SMFO/LAO at 35 K, which also displayed substantial competition between antiferromagnetic and ferromagnetic order well-above the Néel temperature of SrFeO3 (T N ~ 134 K). We attributed this to being caused by charge disproportionation resulting from ligand-hole localization, which is more favorable to take place when the sample is under compressive strain. PMID:27355241