Browsing by Author "Li, WH"

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    The cold-neutron triple-axis spectrometer SIKA at OPAL
    (Australian Institute of Physics, 2018-01-31) Deng, G; Yano, SI; Wu, CM; Peng, JC; Gardner, JS; Imamovic, E; Vorderwisch, P; Li, WH; McIntyre, GJ
    SIKA is a high-flux cold-neutron triple-axis spectrometer funded by Ministry of Science and Technology of Taiwan and currently being operated by National Synchrotron Radiation Research Center. It is located on the OPAL reactor face at the Australian Nuclear Science and Technology Organization (ANSTO). Its incident energy ranges from 2.6meV to 30meV with the highest flux at ~8meV. SIKA is equipped with a multiplexing analyzer consisting of an array of 13 PG crystal blades, a multi-wire detector, a single detector and a diffraction detector. The most frequently-used single-detector mode and the multi-Q constant-Ef mode are demonstrated by using the standard samples, namely, MnF2 and Pb single crystals, respectively. The spin-wave excitation of MnF2, the phonon dispersion of thermoelectric material SeSn, the spin dynamics of the spin-glass system (Ni0.40Mn0.60)TiO3, and other experimental data from SIKA are demonstrated as examples of SIKA’s capabilities and performance. The spin-wave excitation was observed in the quasi-one-dimensional spinladder compound SrCa13Cu24O41, indicating the low background of SIKA. These results indicate that SIKA is a highly-flexible cold triple-axis spectrometer with reasonably low background.
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    The cold-neutron triple-axis spectrometer SIKA at OPAL
    (International Conference on Neutron Scattering, 2017-07-12) Deng, G; Yano, S; Wu, CM; Peng, JC; Imamovic, E; Vorderwisch, P; Li, WH; Gardner, JS
    SIKA is a high-flux cold-neutron triple-axis spectrometer built on the cold source CG4 of the 20MW Open Pool Australian Light-water (OPAL) reactor at Australian Nuclear Science and Technology Organization (ANSTO) by Taiwan.[1] As a state-of-the-art triple-axis spectrometer, SIKA is equipped with a large double-focusing pyrolytic graphite (PG) monochromator, a multiblade PG analyser and a multi-detector system. The design, functions, and capabilities of SIKA are presented. The spin wave excitation of MnF2, the phonon dispersion of thermoelectric material SeSn,[2] the spin dynamics of spin glass system (Ni0.40Mn0.60)TiO3[3] and other experimental data from SIKA are demonstrated as examples of SIKA’s capabilities and performance.
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    Complex magnetic incommensurability in multiferroic Co3TeO6
    (International Conference on Neutron Scattering, 2017-07-12) Lee, CH; Wang, CW; Zhao, Y; Li, WH; Lynn, JW; Harris, AB; Rule, KC; Yang, HD; Berger, H
    Monoclinic cobalt tellurate Co3TeO6 has been characterized1-3 as a type-II multiferroic, where the order parameters of electrical polarization and spontaneous magnetization are closely coupled.4,5 In this study, polarized and unpolarized neutron diffractions have been carried out to investigate the nature of the magnetic structures and transitions in monoclinic Co3TeO6. As the temperature is lowered below TM1= 26 K long range order develops, which is fully incommensurate (ICM) in all three crystallographic directions in the crystal. Below TM2 = 19.5 K, additional commensurate magnetic peaks develop, consistent with the ?4 irreducible representation, along with a splitting of the ICM peaks along the h direction which indicates that there are two separate sets of magnetic modulation vectors. Below TM3 = 18 K, this small additional magnetic incommensurability disappears, ferroelectricity develops, a commensurate ?3 irreducible representation appears, and the k component of the ICM wave vector disappears. Below TM4= 15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin.
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    Correlation of thermostability and conformational changes of catechol 2, 3-dioxygenases from two disparate micro-organisms
    (Elsevier Science BV, 2013-10-01) Sokolova, AV; Huang, SL; Duff, AP; Gilbert, EP; Li, WH
    We have investigated the structure of recombinant catechol 2, 3-dioxygenase (C23O) purified from two species in which the enzyme has evolved to function at different temperature. The two species are mesophilic bacterium Pseudomonas putida strain mt-2 and thermophilic archaea Sulfolobus acidocaldarius DSM639. Using the primary sequence analysis, we show that both C23Os have only 30% identity and 48% similarity but contain conserved amino acid residues forming an active site area around the iron ion. The corresponding differences in homology, but structural similarity in active area residues, appear to provide completely different responses to heating the two enzymes. We confirm this by small angle X-ray scattering and demonstrate that the overall structure of C23O from P. putida is slightly different from its crystalline form whereas the solution scattering of C230 from S. acidocaldarius at temperatures between 4 and 85 degrees C ideally fits the calculated scattering from the single crystal structure. The thermostability of C230 from S. acidocaldarius correlates well with conformation in solution during thermal treatment. The similarity of the two enzymes in primary and tertiary structure may be taken as a confirmation that two enzymes have evolved from a common ancestor. © 2013, Elsevier Ltd.
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    Effects of oxygen deficiency on the magnetic ordering of Mn in Tb0.9Na0.1MnO2.9
    (Institute of Physics, 2008-03-12) Yang, CC; Wu, CM; Li, WH; Chan, TS; Liu, RS; Chen, YY; Avdeev, M
    Monovalent Na+ ions have been incorporated into a multiferroic TbMnO3 compound. Structural studies, using high-resolution neutron diffraction patterns, show that monovalent Na+-doping results in a noticeable oxygen deficiency in the compound. The alternations in crystalline and magnetic structures due to oxygen deficiency are investigated by neutron diffraction and magnetic susceptibility measurements. Na-doping turns the modulated incommensurate Mn spin structure, observed for the parent compound, into a simple commensurate one. The observed magnetic diffraction patterns agree very well with that calculated assuming a D-type arrangement for the Mn spins, with the moments pointing along the c-axis direction. No significant alternation in the ordering temperature of the Mn moments is found. © 2008, Institute of Physics
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    Fe-excess ions as electronic charge suppliers for zero thermal expansion in the normal state of Fe1.16Te0.6Se0.4
    (The Physical Society of Japan, 2015-08-27) Karna, SK; Lee, CH; Li, WH; Sankar, R; Chou, FC; Avdeev, M
    We report on the observation of a zero thermal expansion of the crystalline lattice of Fe1.16Te0.6Se0.4 in the normal state, using neutron and x-ray diffraction, ac magnetic susceptibility, magnetization and resistivity measurements. Superconductivity develops below 15 K. Magnetic hysteresis loops are revealed at all temperatures studied, with the loop opening at 5 K being noticeably larger than that at 300 K. An extremely large thermal expansion of the lattice is observed in the superconducting state. Thermal expansion coefficients of the lattice are quenched upon loss of superconductivity. Zero thermal expansion is retained over a very broad temperature range from 20 to 200 K. These behaviors are understood as being due to the electronic charge redistribution, in which the excess Fe ions on the interstitial sites act as electronic charge suppliers that strengthen the electronic connections between the Te/Se and Fe ions on the lattice sites once the temperature is raised. ©2015 The Physical Society of Japan
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    In operando detection of lithium diffusion behaviors at low temperature in 18650 Li-ion battery anode
    (Elsevier, 2018-12-15) Wu, CM; Chang, CC; Avdeev, M; Pan, PI; Li, WH
    Lithium diffusion process in an 18650 cell was investigated in-operando using neutron diffraction. The graphite anode delithiation rate and the amount of discharge capacity during the discharging process were correlated with the temperature and current rate. At room temperature, the lithium diffusion rate in LiC6 phase at the high rate capability (C/5) is same as at low rate capability (C/20), which means that lithium diffusion in LiC6 crystal phase is independent of the current rate in this range during the discharge process. Lowering temperature to −20 °C decreases both the lithium diffusion and capacity, although the latter can be partially recovered by using lower C-rate. © 2018 Elsevier B.V.
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    Large magnetoresistance and charge transfer between the conduction and magnetic electrons in layered oxyselenide BiOCu0.96Se
    (Royal Society of Chemistry, 2013-8-27) Karna, SK; Hung, CH; Wu, CM; Wang, CW; Li, WH; Sankar, R; Chou, FC; Avdeev, M
    The electrical and magnetic properties of slightly Cu-deficient BiOCu0.96Se have been investigated using neutron and X-ray diffraction, ac magnetic susceptibility, magnetization and electric resistivity measurements. The layered BiOCu0.96Se crystallizes into a tetragonal lattice with a P4/nmm symmetry. Thermal profiles of the electrical resistivity reveal a semiconductor type behavior, but depart from its course at low temperatures when antiferromagnetic coupling becomes thermally loosened at 140 K. Positive magnetoresistances are obtained at all temperatures studied. With an applied magnetic field of 0.5 kOe, the magnetoresistance reaches 235% at 2 K. It decreases with increasing temperature, but stabilizes to 70% above 60 K. Both ferromagnetic and antiferromagnetic coupling are detected between the Cu spins in the SeCu4 pyramidal blocks, which results in a non-collinear spin arrangement at low temperatures. The antiferromagnetic component becomes disordered above TN = 140 K, whereas the ferromagnetic moment persists up to TC = 300 K. Interlayer charge transfer between the conduction and magnetic electrons gives rise to an anomaly in the magnetic order parameter. © 2013, Royal Society of Chemistry.
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    SIKA - a new triple-axis-spectrometer for cold neutrons
    (Australian Institute of Physics, 2006-12-05) Li, WH; Yang, CC; Vorderwisch, P
    The new OPAL reactor at ANSTO will be among the world-top research reactors equipped with a cold neutron source. A cold-neutron triple-axis-spectrometer named SIKA, designed and to be operated by a research team from Taiwan, will extend the day-one instrumentation at OPAL especially for measurements of low-energy excitations in single crystals (phonon or magnon dispersion relations) or, in an elastic mode, of weak superstructure reflections. Modern applications of such a spectrometer are magnetic-field driven quantum-phase transitions and magnetic-field induced ordering phenomena in high TC superconductors. Whereas a high resolution of such a spectrometer is inherently given by the use of cold neutrons, a high intensity of measured signals will be obtained using focusing methods. An option to work with polarised neutrons will also be available. We describe the conceptual design of SIKA and its expected performance, both based on MonteCarlo simulations using the codes McStas and MCNP. Finally we compare SIKA with other state-of-the-art cold-neutron triple-axis-spectrometers.
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    SIKA - the cold-neutron triple-axis spectrometer with multiplexing analyzer at Bragg Institute
    (Asia - Oceania Neutron Scattering Association, 2015-07-19) Deng, GC; McIntyre, GJ; Wu, CM; Gardner, JS; Vorderwisch, P; Li, WH
    SIKA is a high-flux cold-neutron triple-axis spectrometer funded by Ministry of Science and Technology of Taiwan and currently being operated by National Synchrotron Radiation Research Center. It locates at the OPAL reactor face at the Australian Nuclear Science and Technology Organisation (ANSTO). Its incident energy ranges from 2.5meV to 30meV with the highest flux at ~8meV. With an advanced design, SIKA is equipped with an analyzer array of 13 PG(002) blades (Fig. 1), a multi-wire detector, and a separate diffraction detector. Such a design allows SIKA to run in a traditional step-by-step mode or in various mapping (or dispersive) modes by changing the configuration of analyzers and detectors. Several typical mapping modes are analyzed and simulated using Monte Carlo ray-tracing package SIMRES of RESTRAX. [1] The performance of different mapping modes are demonstrated and evaluated, providing the dispersion relations of these operation modes as references for experimental studies. In hotcommissioning, a multiplexing mode with constant Ef was used to measure the phonon dispersion in a Pb single crystal. The simulation and experiment results demonstrate the flexibility and fast data-collecting potential of SIKA as a next generation cold neutron triple-axis spectrometer.
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    Simulation of energy dispersive mode for RITA-type cold neutron triple axis spectrometer SIKA
    (Australian Institute of Physics, 2012-02-02) Deng, GC; Vorderwisch, P; Wu, CM; McIntyre, GJ; Li, WH
    SIKA, a high flux cold triple axis spectrometer at OPAL reactor, is equipped with a 13-blade analyser and position sensitive detector. This multiplexing design endows SIKA with high flexibility to run in either traditional or dispersive modes. In this study, the energy dispersive mode for two different energy transfers is simulated using the Monte Carlo ray-trace package SIMRES. The results show that SIKA could work effectively in this mode at low and intermediate energy transfers with reasonable energy and Q resolution. The simulated energy resolution is about 0.23 meV for an energy transfer of ħω = 5 meV and increases to 1.8 meV for ħω = 15 meV. This work provides a valuable reference for future inelastic neutron scattering experiments on SIKA.
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    Simulation of multiple operation modes for the cold neutron triple axis spectrometer SIKA at Bragg Institute
    (Australian Institute of Physics, 2012-02-02) Deng, GC; Vorderwisch, P; Wu, CM; McIntyre, GJ; Li, WH
    The coming high flux cold-neutron triple axis spectrometer, SIKA at Bragg Institute, is built with an unconventional design, equipped with a multi-strip analyzer array of 13 PG(002) blades (see Fig. 1), a linear position-sensitive detector and a separate diffraction detector. Such a design allows SIKA to run in a traditional step-by-step mode or various mapping (or dispersive) modes by changing the configuration of analyzers and detectors. In this study, several typical mapping modes are analyzed and simulated using Monte Carlo ray-trace package SIMRES of RESTRAX. [1] The performance of different mapping modes are demonstrated and evaluated, providing the dispersion relations of these operation modes as references for experimental studies. The simulation shows the flexibility and fast data collecting potential of SIKA as a new generation of triple axis spectrometer. The simulated data could be compared with the experimental data in the future and as a reference to the selection of effective operation modes.