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Your search keyword '"Sheu, H. -S."' showing total 103 results
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103 results on '"Sheu, H. -S."'

1. Topological defects at octahedral tilting plethora in bi-layered perovskites

Author

Huang, F. -T., Gao, B., Kim, J. -W., Luo, X., Wang, Y., Chu, M. -W., Chang, C. -K., Sheu, H. -S., and Cheong, S. -W.

Subjects
Condensed Matter - Materials Science
Abstract

Oxygen octahedral distortions including tilts/rotations, deformations and off-centering in (layered) perovskites play the key role in their numerous functional properties. At the polar-centrosymmetric phase boundary in bi-layered perovskite Ca3-xSrxTi2O7 with x~1, we found the presence of abundant topological Z8 vortex-antivortex pairs, associated with four oxygen octahedral tilts at domains and another four different oxygen octahedral tilts at domain boundaries. Our discovery opens a new revenue to unveil topological defects associated with various types of oxygen octahedral distortions., Comment: 12 pages, 4 figures

Published
2016
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2. Sodium ion ordering of Na0.77CoO2 under competing multi-vacancy cluster, superlattice and domain formation

Author

Huang, F. -T., Shu, G. J., Chu, M. -W., Kuo, Y. K., Lee, W. L., Sheu, H. S., and Chou, F. C.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

Hexagonal superlattice formed by sodium multi-vacancy cluster ordering in Na$_{0.77}$CoO$_2$ has been proposed based on synchrotron X-ray Laue diffraction study on electrochemically fine-tuned single crystals. The title compound sits closely to the proposed lower end of the miscibility gap of x ~ 0.77-0.82 phase separated range. The average sodium vacancy cluster size is estimated to be 4.5 Na vacancies per layer within a large superlattice size of sqrt{19}a*sqrt{19}a*3c. The exceptionally large Na vacancy cluster size favors large twinned simple hexagonal superlattice of sqrt{19}a, in competition with the smaller di-, tri- and quadri-vacancy clusters formed superlattices of sqrt{12}a and sqrt{13}a. Competing electronic correlations are revealed by the observed spin glass-like magnetic hysteresis below ~ 3K and the twin, triple and mono domain transformations during thermal cycling between 273-373K., Comment: 7 pages, 6 figures

Published
2009
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4. Crystal structure and magnetic properties of iron(II) and cobalt(II) complexes containing tridentate pyridine-tetrazolate ligand: a study by X-ray diffraction and X-ray absorption spectroscopy

Author

Hsu, I.-J., primary, Lai, W.-R., additional, Lin, T.-J., additional, Chen, C.-Y., additional, Yang, C.-W., additional, Chen, Y.-A., additional, Chen, B.-H., additional, Chuang, Y.-C., additional, Sheu, H.-S., additional, Pao, C.-W., additional, Chen, J.-M., additional, and Chiang, M.-H., additional

Published
2023
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5. Sodium vacancy ordering and the co-existence of localized spins and itinerant charges in NaxCoO2

Author

Chou, F. C., Chu, M. -W., Shu, G. J., Huang, F. T., Pai, Woei Wu, Sheu, H. S., Imai, T., Ning, F. L., and Lee, Patrick A.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

The sodium cobaltate family (NaxCoO2) is unique among transition metal oxides because the Co sits on a triangular lattice and its valence can be tuned over a wide range by varying the Na concentration x. Up to now detailed modeling of the rich phenomenology (which ranges from unconventional superconductivity to enhanced thermopower) has been hampered by the difficulty of controlling pure phases. We discovered that certain Na concentrations are specially stable and are associated with superlattice ordering of the Na clusters. This leads naturally to a picture of co-existence of localized spins and itinerant charge carriers. For x = 0.84 we found a remarkably small Fermi energy of 87 K. Our picture brings coherence to a variety of measurements ranging from NMR to optical to thermal transport. Our results also allow us to take the first step towards modeling the mysterious ``Curie-Weiss'' metal state at x = 0.71. We suggest the local moments may form a quantum spin liquid state and we propose experimental test of our hypothesis., Comment: 16 pages, 5 figures

Published
2007
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6. Searching for Stable Na-ordered Phases in Single Crystal Samples of gamma-NaxCoO2

Author

Shu, G. J., Prodi, Andrea, Chu, S. Y., Lee, Y. S., Sheu, H. S., and Chou, F. C.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Abstract

We report on the preparation and characterization of single crystal gamma phase NaxCoO2 with 0.25 < x < 0.84 using a non-aqueous electrochemical chronoamperemetry technique. By carefully mapping the overpotential versus x (for x < 0.84), we find six distinct stable phases with Na levels corresponding to x ~ 0.75, 0.71, 0.50, 0.43, 0.33 and 0.25. The composition with x ~0.55 appears to have a critical Na concentration which separates samples with different magnetic behavior as well as different Na ion diffusion mechanisms. Chemical analysis of an aged crystal reveals different Na ion diffusion mechanisms above and below x_c ~ 0.53, where the diffusion process above x_c has a diffusion coefficient about five times larger than that below x_c. The series of crystals were studied with X-ray diffraction, susceptibility, and transport measurements. The crystal with x = 0.5 shows a weak ferromagnetic transition below T=27 K in addition to the usual transitions at T = 51 K and 88 K. The resistivity of the Curie-Weiss metallic Na0.71CoO2 composition has a very low residual resistivity, which attests to the high homogeneity of the crystals prepared by this improved electrochemical method. Our results on the various stable crystal compositions point to the importance of Na ion ordering across the phase diagram., Comment: 9 pages, 9 figures

Published
2007
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12. Multiscale mechanisms of nutritionally induced property variation in spider silks

Author

Blamires, SJ, Nobbs, M, Martens, PJ, Tso, I-M, Chuang, W-T, Chang, C-K, and Sheu, H-S

Subjects
Species Specificity, General Science & Technology, Tensile Strength, Silk, Animals, Gene Expression, Scattering, Radiation, Spiders, Amino Acids
Abstract

Variability in spider major ampullate (MA) silk properties at different scales has proven difficult to determine and remains an obstacle to the development of synthetic fibers mimicking MA silk performance. A multitude of techniques may be used to measure multiscale aspects of silk properties. Here we fed five species of Araneoid spider solutions that either contained protein or were protein deprived and performed silk tensile tests, small and wide-angle X-ray scattering (SAXS/WAXS), amino acid composition analyses, and silk gene expression analyses, to resolve persistent questions about how nutrient deprivation induces variations in MA silk mechanical properties across scales. Our analyses found that the properties of each spider's silk varied differently in response to variations in their protein intake. We found changes in the crystalline and non-crystalline nanostructures to play specific roles in inducing the property variations we found. Across treatment MaSp expression patterns differed in each of the five species. We found that in most species MaSp expression and amino acid composition variations did not conform with our predictions based on a traditional MaSp expression model. In general, changes to the silk's alanine and proline compositions influenced the alignment of the proteins within the silk's amorphous region, which influenced silk extensibility and toughness. Variations in structural alignment in the crystalline and non-crystalline regions influenced ultimate strength independent of genetic expression. Our study provides the deepest insights thus far into the mechanisms of how MA silk properties vary from gene expression to nanostructure formations to fiber mechanics. Such knowledge is imperative for promoting the production of synthetic silk fibers.

Published
2018

13. Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study.

Author

Chen, J. M., Lee, J. M., Chou, T. L., Chen, S. A., Huang, S. W., Jeng, H. T., Lu, K. T., Chen, T. H., Liang, Y. C., Chen, S. W., Chuang, W. T., Sheu, H.-S., Hiraoka, N., Ishii, H., Tsuei, K. D., Huang, Eugene, Lin, C. M., and Yang, T. J.

Subjects
ELECTRONIC structure, ABSORPTION spectra, X-ray diffraction, JAHN-Teller effect, SYNCHROTRON radiation, HYDROSTATIC pressure, MANGANITE
Abstract

Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO6 octahedra in DyMnO3 on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO3 progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3 shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO6 octahedra in compressed DyMnO3. A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. [ABSTRACT FROM AUTHOR]

Published
2010
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14. Effect of Ca doping on the optical properties of La1.2Sr1.8Mn2O7.

Author

Her, J. L., Liu, H. L., Shen, C. H., Liu, R. S., and Sheu, H. S.

Subjects
SEMICONDUCTOR doping, RAMAN effect, LIGHT scattering, LATTICE dynamics, OPTICAL diffraction, PHONONS, PHYSICS
Abstract

We present x-ray-diffraction, infrared reflectivity, and Raman-scattering measurements of La1.2(Sr1.8-xCax)Mn2O7 as a function of temperature and doping (x=0.0, 0.4, 0.6, and 0.8). At room temperature, x-ray-diffraction data show that the replacement of Sr ions with smaller Ca ions causes a shrinkage of the unit-cell volume. The far-infrared conductivity spectra of all doped samples are typical of an insulator, showing only phonons. When doped with Ca on Sr and a corresponding systematic reduction in Curie temperature (Tc), there is a suppression of the low-frequency optical spectral weight. For the x=0.0 compound, the Raman-active phonon associated with the internal stretching of the oxygen atoms in MnO6 octahedra shows a noticeable hardening below Tc. A polaron transport can be attributed to the observed frequency shifts. Interestingly, this hardening is reduced as the Ca content increases. These observations suggest that Ca doping disrupts the effects of the double-exchange interaction on the lattice degree of freedom, thereby accounting for the characteristic changes in the phase diagram. [ABSTRACT FROM AUTHOR]

Published
2006
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17. New metal chalcogenides found in MnN−1(Gd2−xInx)SN+2 (N = 3, 4, 5): syntheses, structures, and magnetic properties.

Author

Liang, I. C., Weng, C. Y., Huang, C., Chang, C. K., Sheu, H. S., Lin, J. G., and Hsu, K. F.

Subjects
CHALCOGENIDES, MAGNETIC properties, ORTHORHOMBIC crystal system
Abstract

Three new metal chalcogenides have been identified in MnN−1(Gd2−xInx)SN+2 with N = 3, 4, and 5 via a flux-growth synthesis. All compounds crystallize in the same space group of orthorhombic Cmcm with cell constants: Mn2GdInS5 (1), a = 3.789(1) Å, b = 12.411(1) Å, and c = 15.489(1) Å; Mn3Gd2S6 (2), a = 3.778(1) Å, b = 12.505(2) Å, and c = 19.114(2) Å; Mn4Gd2S7 (3), a = 3.769(1) Å, b = 12.466(2) Å, and c = 22.289(3) Å. Compounds 1–3 form a homologous series through the modulation of the MnS unit, whose structures represent a complete system of the corresponding lillianites (N1,N2L) of 3,3L, 4,4L and 5,5L. The gradually wider slabs formed in the series result in a monotonic increase along the c dimensions from 1 to 3. Crystal 3 is the first to achieve a predicted structure of 5,5L. Mn2GdInS5 (1) displays a weak antiferromagnetic (AFM) ordering at 10 K and the Weiss constant (ϑ) of −0.76 K. Mn2Gd1.5In0.5S5 (1a), an isostructure of 1, shifts the AFM transition temperature to 12 K and possesses a slightly larger ϑ constant of −6.06 K. Mn4Gd2S7 (3), featuring the thickest slabs in this series, shows a significant antiferromagnetic behavior beginning at a high temperature of 70 K and has a largest ϑ constant of −40.25 K. A small amount of impurity α-Gd2S3 with an AFM transition temperature around 4 K was characterized in sample 3, which does not interfere with the magnetic ordering of 3 at much higher temperatures. These magnetic chalcogenides display band gaps of 1.66 eV for 1, 1.75 eV for 1a, and 1.44 eV for 3. [ABSTRACT FROM AUTHOR]

Published
2017
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23. Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy andab initioelectronic structure study

Author

Chen, J. M., primary, Lee, J. M., additional, Chou, T. L., additional, Chen, S. A., additional, Huang, S. W., additional, Jeng, H. T., additional, Lu, K. T., additional, Chen, T. H., additional, Liang, Y. C., additional, Chen, S. W., additional, Chuang, W. T., additional, Sheu, H.-S., additional, Hiraoka, N., additional, Ishii, H., additional, Tsuei, K. D., additional, Huang, Eugene, additional, Lin, C. M., additional, and Yang, T. J., additional

Published
2010
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26. Crystal structure and electronic and thermal properties of TbFeAsO0.85

Author

Kaurav, N., primary, Chung, Y. T., additional, Kuo, Y. K., additional, Liu, R. S., additional, Chan, T. S., additional, Chen, J. M., additional, Lee, J.-F., additional, Sheu, H.-S., additional, Wang, X. L., additional, Dou, S. X., additional, Lee, S. I., additional, Shi, Y. G., additional, Belik, A. A., additional, Yamaura, K., additional, and Takayama-Muromachi, E., additional

Published
2009
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27. Pressure-induced structural distortion ofTbMnO3: A combined x-ray diffraction and x-ray absorption spectroscopy study

Author

Chen, J. M., primary, Chou, T. L., additional, Lee, J. M., additional, Chen, S. A., additional, Chan, T. S., additional, Chen, T. H., additional, Lu, K. T., additional, Chuang, W. T., additional, Sheu, H.-S., additional, Chen, S. W., additional, Lin, C. M., additional, Hiraoka, N., additional, Ishii, H., additional, Tsuei, K. D., additional, and Yang, T. J., additional

Published
2009
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36. Performance of X-ray Beam lines at Superconducting Wavelength Shifter

Author

Song, Y. F., primary, Chang, C. H., additional, Liu, C. Y., additional, Chang, S. H., additional, Jeng, U., additional, Lai, Y. H., additional, Liu, D. G., additional, Yin, G. C., additional, Lee, J. F., additional, Sheu, H. S., additional, Chung, S. C., additional, Tsang, K. L., additional, Hwu, Y., additional, and Liang, K. S., additional

Published
2007
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47. Performance of the Taiwan Contract Beamline BL12B2 at SPring-8.

Author

Tang, M. -T., Du, C. -H., Lee, J. -F., Sheu, H. -S., Hsu, C. -H., Jean, Y. -C., Huang, Y. -S., Chen, C. -J., Chao, C. -S., Moriyama, A., Wang, C. -W., Chang, S. -H., Lee, J. -J., Liang, S., Chen, C. -T., and Warwick, T.

Subjects
PARTICLE beams, X-ray diffractometers, PROTEINS, CRYSTALLOGRAPHY, PHOTONS, X-ray scattering
Abstract

The recent status of the SPring-8 Taiwan Contract Beamline BL12B2 is reported. The beamline was designed to provide multiple applications for materials and biological researches. It is equipped with four end stations, including an EXAFS station, a Huber 6-circle diffractometer for X-ray scattering, a curved image plate for the studies of powder diffraction, and a station for the protein crystallography. The beamline construction was completed in 2000 and it has been in full speed operation since September 2001. To enhance the focusing capacity, the beamline optics has been modified in 2002 and a gain of factor of 10 in photon flux was consequently obtained at protein crystallography station. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2004
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