Carlo U Segre
Illinois Institute of Technology, Physics, Faculty Member
... With Integrated Bandwidt (310) 534-3661 FAX (310) 534-3665 email: ird@kaiwan.com Circle No. 129 ... and EA Beliaevskaya, Physica Medica X11(2), 75 (1 996). 4. A. Guinier, G. Fournet, CBWalker, and KL Yudowitch, Small-angle Scattering... more
... With Integrated Bandwidt (310) 534-3661 FAX (310) 534-3665 email: ird@kaiwan.com Circle No. 129 ... and EA Beliaevskaya, Physica Medica X11(2), 75 (1 996). 4. A. Guinier, G. Fournet, CBWalker, and KL Yudowitch, Small-angle Scattering of X-rays (Wiley, New York, 1955). ...
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The phase diagram of the Y-Ba-Cu-O system was determined through structural, superconducting critical temperature and critical current density characterization. The results show that a single-phase compound with a stoichiometry... more
The phase diagram of the Y-Ba-Cu-O system was determined through structural, superconducting critical temperature and critical current density characterization. The results show that a single-phase compound with a stoichiometry YBa2Cu3O(y) is responsible for the high-temperature superconductivity (92.5 K) in this system.
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Films of differently modified PVA (polyvinyl alcohol), TA (phthalocyaninosilicon) and Nafion in different ionic forms (H+, Li+, and Na+) have been prepared by using casting methods. Impedance changes of the films with relative humidity... more
Films of differently modified PVA (polyvinyl alcohol), TA (phthalocyaninosilicon) and Nafion in different ionic forms (H+, Li+, and Na+) have been prepared by using casting methods. Impedance changes of the films with relative humidity are examined. The results demonstrate that the content and hydrophilicity of the hydrophilic group in PVA, ionization of TA, and the cation in Nafion have significant effects on sensing properties of the films.
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A conductivity relaxation experiment has been conducted on an SrFeCo0.5Ox sample by abruptly changing the oxygen partial pressure in the atmosphere and monitoring the change of conductivity as a function of time. The re-equilibrium... more
A conductivity relaxation experiment has been conducted on an SrFeCo0.5Ox sample by abruptly changing the oxygen partial pressure in the atmosphere and monitoring the change of conductivity as a function of time. The re-equilibrium process obeys Fick's second law. By fitting the relaxation data to the solution of the diffusion equation with appropriate boundary conditions, we could determine the oxygen chemical diffusion coefficient and the activation energy. The oxygen diffusion coefficient is 8.9 × 10−7 cm2/s at 900 °C and it increases with increase in temperature. Measured activation energy is 0.92 eV, which is slightly lower than that of other oxides in the system SrFe1 − xCoxOy.
Research Interests: Engineering, Materials Engineering, Condensed Matter Physics, Cyclic Voltammetry, Multidisciplinary, and 18 moreVery Low Frequency Electromagnetics, Electrochemical Impedance Spectroscopy, Diffusion, Relaxation, Physical sciences, Lithium Ion Battery, Activation Energy, Iron, Second Law, CHEMICAL SCIENCES, Temperature measurement, Insertion, Diffusion Coefficient, Spectrum, Ionic Conductivity, Solid State Ionics, Acoustic Diffusion Equation Model, and Boundary Condition(Very Low Frequency Electromagnetics, Electrochemical Impedance Spectroscopy, Diffusion, Relaxation, Physical sciences, Lithium Ion Battery, Activation Energy, Iron, Second Law, CHEMICAL SCIENCES, Temperature measurement, Insertion, Diffusion Coefficient, Spectrum, Ionic Conductivity, Solid State Ionics, Acoustic Diffusion Equation Model, and Boundary Condition)
(Very Low Frequency Electromagnetics, Electrochemical Impedance Spectroscopy, Diffusion, Relaxation, Physical sciences, Lithium Ion Battery, Activation Energy, Iron, Second Law, CHEMICAL SCIENCES, Temperature measurement, Insertion, Diffusion Coefficient, Spectrum, Ionic Conductivity, Solid State Ionics, Acoustic Diffusion Equation Model, and Boundary Condition)
In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction enabled detailed core analysis of phase segregated nanostructured PtRu anode catalysts in an operating direct methanol fuel cell (DMFC). No... more
In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction enabled detailed core analysis of phase segregated nanostructured PtRu anode catalysts in an operating direct methanol fuel cell (DMFC). No change in the core structures of the phase segregated catalyst was observed as the potential traversed the current onset potential of the DMFC. The methodology was exemplified using a Johnson Matthey unsupported PtRu (1:1) anode catalyst incorporated into a DMFC membrane electrode assembly. During DMFC operation the catalyst is essentially metallic with half of the Ru incorporated into a face-centered cubic (FCC) Pt alloy lattice and the remaining half in an amorphous phase. The extended X-ray absorption fine structure (EXAFS) analysis suggests that the FCC lattice is not fully disordered. The EXAFS indicates that the Ru-O bond lengths were significantly shorter than those reported for Ru-O of ruthenium oxides, suggesting that the phases in which the Ru resides in the catalysts are not similar to oxides.
Research Interests: Engineering, Catalysis, X ray absorption spectroscopy, Fourier Analysis, Methanol, and 12 moreAbsorption spectroscopy, Physical sciences, Platinum, The, CHEMICAL SCIENCES, Fine Structure Constant, Spectrum analysis, Direct methanol fuel cell, Electrodes, X ray Fluorescence, X ray powder diffraction, and Ruthenium
Seven bronze bangles from Tell en-Nasbeh, northern Judah, were investigated to understand the phase composition and manufacturing process of the artifacts, and possibly suggest a provenance for their origin. Synchrotron x-ray radiation... more
Seven bronze bangles from Tell en-Nasbeh, northern Judah, were investigated to understand the phase composition and manufacturing process of the artifacts, and possibly suggest a provenance for their origin. Synchrotron x-ray radiation diffraction (XRD) and fluorescence (XRF) were used in the analysis to avoid any destructive sampling and at the same time penetrate through the surface into the core metal. These techniques enabled us to determine that the bangles were not just tin bronze, but leaded tin bronze. Based on excavation reports, it is unlikely that the metal objects were manufactured locally at Tell en-Nasbeh; rather, preliminary XRD and XRF data point towards the neighboring region of Edom as their origin. Despite their political enmity during the Iron Age II, the data suggest that Judahite social demands for bronze may have fostered a strong economic relationship between these two polities.
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An analyzer for detection of fluorescence radiation was developed for fluorescence XAFS of dilute samples at energies above 13 keV. The analyzer is a bent Laue crystal of logarithmic spiral shape. The K fluorescence lines can be collected... more
An analyzer for detection of fluorescence radiation was developed for fluorescence XAFS of dilute samples at energies above 13 keV. The analyzer is a bent Laue crystal of logarithmic spiral shape. The K fluorescence lines can be collected with a large solid angle and ...
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ABSTRACT
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ABSTRACT LIII absorption spectroscopy measurements, using synchrotron radiation on the Ce1-xRxPd3, R=La3+, Y3+, Th4+, and U and the Ce1-xScxAl2 alloy systems are presented. The Ce valence variation from the LIII spectra analysis is... more
ABSTRACT LIII absorption spectroscopy measurements, using synchrotron radiation on the Ce1-xRxPd3, R=La3+, Y3+, Th4+, and U and the Ce1-xScxAl2 alloy systems are presented. The Ce valence variation from the LIII spectra analysis is correlated with the lattice-parameter variations in the alloys. The roles of the volume and valence of the substitutes in determining the Ce valence state are discussed. The results are discussed in terms of hybridization and current electronic theory.
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The Materials Research Collaborative Access Team (MRCAT) beamline 10-ID at the Advanced Photon Source has been in Commissioning since January 1998. This Beamline has been designed as a flexible spectroscopy, scattering, and diffraction... more
The Materials Research Collaborative Access Team (MRCAT) beamline 10-ID at the Advanced Photon Source has been in Commissioning since January 1998. This Beamline has been designed as a flexible spectroscopy, scattering, and diffraction facility for the study of materials in situ. Over 70 users have performed experiments at the beamline during this period. Details about the beamline layout, components, performance and configuration for typical experiments will be presented .
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ABSTRACT Nucleation of crystalline solids, the first stage of crystallization from solution, is not yet fully understood. This is true for both small molecules of low molecular weight and more complicated large molecules. To obtain direct... more
ABSTRACT Nucleation of crystalline solids, the first stage of crystallization from solution, is not yet fully understood. This is true for both small molecules of low molecular weight and more complicated large molecules. To obtain direct structural information about the process of nucleation and crystallization of small molecules, small-angle X-ray scattering (SAXS) has been used to study the crystallization of the amino acid glycine from its supersaturated aqueous solution. The scattering data was analyzed using the unified fit model, which is well-suited for studying complex systems that may contain multiple levels of related structural features. The results suggest that glycine molecules exist as dimers in supersaturated solution. The system obeys power-law behavior that indicates the presence of fractals in the solution. A transformation from mass fractal structure to surface fractal structure is observed during the crystallization process, which could be the signature of a two-step nucleation process.
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We have performed detailed high temperature X-ray diffraction to study the nature of the structural phase of YBa2Cu3O7−δ. The results indicate the existence of a reversible orthorhombic to tetragonal phase transition at a temperature... more
We have performed detailed high temperature X-ray diffraction to study the nature of the structural phase of YBa2Cu3O7−δ. The results indicate the existence of a reversible orthorhombic to tetragonal phase transition at a temperature close to 750°C. If the high temperature tetragonal phase is quenched-in at low temperatures the critical superconducting temperature is considerably reduced from 92.5 K. This suggests that the one dimensional CuO chains present in the orthorhombic structure are necessary for high temperature superconductivity.
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We discuss the influence of oxygen defects and defect ordering on superconductivity in 123 compounds. Because of the complexity of the high-temperature phase diagram, the synthesis history can significantly influence the properties.... more
We discuss the influence of oxygen defects and defect ordering on superconductivity in 123 compounds. Because of the complexity of the high-temperature phase diagram, the synthesis history can significantly influence the properties. Room-temperature annealing experiments show that defect ordering on a short length scale can have a remarkable affect on superconductivity. We propose that structural coherence in the CuO2 planes, which is present only if there is orthorhombic symmetry on at least a short length scale, is a requirement for superconductivity in these compounds.
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The crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y-Ba-Cu-O system was determined using high-resolution neutron powder diffraction. This compound has an orthorhombic structure with space group... more
The crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y-Ba-Cu-O system was determined using high-resolution neutron powder diffraction. This compound has an orthorhombic structure with space group Pmmm and lattice constants a = 3.8231 A, B = 3.8864 A, and c = 11.6807 A. The structure consists of 'dimpled' CuO2 layers in the a-b planes loosely bonded by one-dimensional fencelike square-planar CuO3 chains in the b-c planes.
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The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a search for other structures that display high-temperature superconductivity. The discovery of superconductivity above 70 K in La 3-x Ba 3+ x Cu 6... more
The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a search for other structures that display high-temperature superconductivity. The discovery of superconductivity above 70 K in La 3-x Ba 3+ x Cu 6 O l4+y 3 raises some ...
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... G. Burns, FH Dacol, P. Freitas, TS Plaskett and W. König, Solid State Commun ... Mattausch, W. Bauhofer, A. Simon, F. Garcia-Alvarado, E. Moran, M. Vallet, JM Gonzales-Calbet ... D. Xie, and WB Yelon, in Chemistry of High-Temperature... more
... G. Burns, FH Dacol, P. Freitas, TS Plaskett and W. König, Solid State Commun ... Mattausch, W. Bauhofer, A. Simon, F. Garcia-Alvarado, E. Moran, M. Vallet, JM Gonzales-Calbet ... D. Xie, and WB Yelon, in Chemistry of High-Temperature Superconductivity, edited by David L. Nelson ...
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Samples having the general composition YBa2(Cu1−xFex)3O7−δ have been investigated using x-ray and neutron diffraction, Mossbauer spectroscopy and bulk property measurements. X-ray and neutron data show that samples having x ≥ 0.04 are... more
Samples having the general composition YBa2(Cu1−xFex)3O7−δ have been investigated using x-ray and neutron diffraction, Mossbauer spectroscopy and bulk property measurements. X-ray and neutron data show that samples having x ≥ 0.04 are tetragonal. Neutron diffraction shows that this structure is very similar to that found for undoped YBa2Cu3O7−δ when the oxygen concentration is low, although, in the present case, the total oxygen content is found to be ≥7 for all concentrations. Contrary to the common statement that Fe substitutes onto the Cu sites, it is found from neutron diffraction that the Cu1 site is not occupied, and that Fe appears to have a substantial substitution for Ba. Both Mossbauer spectroscopy and heat capacity measurements show the presence of magnetic transitions at temperatures well below the superconducting transition temperature, with evidence for a large variation in magnetic transition temperatures.
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Materials within the phase diagram Y 2 O 3–BaO–CuO have recently generated great interest because of the observation of superconductivity with a critical temperature (T c) of> 90 K 1, 2; the current... more
Materials within the phase diagram Y 2 O 3–BaO–CuO have recently generated great interest because of the observation of superconductivity with a critical temperature (T c) of> 90 K 1, 2; the current consensus is that YBa 2 Cu 3 O 7-x (x approximately 0.2) is the ...
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Neutron and Mössbauer effect measurements have been made as a function of Fe concentration in orthorhombic (x = 0.01, 0.02) and tetragonal (x ⩾ 0.05), YBa2(Cu1 − xFex)3O7 + δ. A systematic Rietveld analysis of the neutron data for all... more
Neutron and Mössbauer effect measurements have been made as a function of Fe concentration in orthorhombic (x = 0.01, 0.02) and tetragonal (x ⩾ 0.05), YBa2(Cu1 − xFex)3O7 + δ. A systematic Rietveld analysis of the neutron data for all concentrations shows that Fe principally occupies a site slightly displaced (y, y, 0) from the Cul (0, 0, 0) site in order to approach tetrahedral coordination. Neutron data for the x = 0.05 compound at 10 K show no significant difference from those obtained at 297 K. Local ordering of oxygen about an Fe substituent is conducive to placement of a second Fe atom in an adjacent site leading to local aggregation into chains of various lengths. This clustering is reflected in the character of low temperature magnetic Mössbauer spectra and in specific heat measurements. The Mössbauer spectra yield the relative changes in oxygen configurations about Fe atoms as the Fe concentration changes.
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In situ neutron powder diffraction measurements show that the orthorhombic-to-tetragonal phase transition in YBa2Cu3O7-x which occurs near 700 °C in a pure oxygen atmosphere, is an order-disorder transition in which the disordering of... more
In situ neutron powder diffraction measurements show that the orthorhombic-to-tetragonal phase transition in YBa2Cu3O7-x which occurs near 700 °C in a pure oxygen atmosphere, is an order-disorder transition in which the disordering of oxygen atoms into a normally vacant site destroys the one-dimensional Cu-O chains present in the room-temperature orthorhombic structure. For both structures, the oxygen stoichiometry decreases monotonically with increasing temperature. The transition temperature depends on the oxygen partial pressure and occurs when the stoichiometry is near YBa2Cu3O6.5. The tetragonal structure has a partially occupied, nearly octahedral Cu-O arrangement, in contrast to the orthorhombic structure which has one-dimensional Cu-O chains. The observed depression of the superconducting transition temperature in tetragonal YBa2Cu3O7-x, which has been quenched from high temperature, could result either from the disordering of oxygen atoms which destroys the one-dimensional chains or from the absence of Cu3+ ions.