... With Integrated Bandwidt (310) 534-3661 FAX (310) 534-3665 email: [email protected] Circle No. 1... more ... With Integrated Bandwidt (310) 534-3661 FAX (310) 534-3665 email: [email protected] 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). ...
The phase diagram of the Y-Ba-Cu-O system was determined through structural, superconducting crit... 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.
Small angle x-ray scattering is utilized to directly examine the formation of clusters in supersa... more Small angle x-ray scattering is utilized to directly examine the formation of clusters in supersaturated solutions of glycine, in an attempt to understand their role in the nucleation process. The results suggest that the majority of glycine molecules exist as dimers in aqueous solutions, and monomers in 13% (v=v) acetic acid-water mixtures. As the water and acetic acid -water solutions crystallize into and forms, respectively, the findings indicate a direct correlation between molecular self-association in solution and the polymorphic outcome.
Films of differently modified PVA (polyvinyl alcohol), TA (phthalocyaninosilicon) and Nafion in d... 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.
A conductivity relaxation experiment has been conducted on an SrFeCo0.5Ox sample by abruptly chan... 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.
In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction e... 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.
Seven bronze bangles from Tell en-Nasbeh, northern Judah, were investigated to understand the pha... 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.
An analyzer for detection of fluorescence radiation was developed for fluorescence XAFS of dilute... 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 ...
ABSTRACT LIII absorption spectroscopy measurements, using synchrotron radiation on the Ce1-xRxPd3... 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.
The Materials Research Collaborative Access Team (MRCAT) beamline 10-ID at the Advanced Photon So... 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 .
ABSTRACT Nucleation of crystalline solids, the first stage of crystallization from solution, is n... 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.
We have performed detailed high temperature X-ray diffraction to study the nature of the structur... 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.
Physica C-superconductivity and Its Applications, 1991
We discuss the influence of oxygen defects and defect ordering on superconductivity in 123 compou... 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.
The crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y... 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.
The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a searc... 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 ...
... With Integrated Bandwidt (310) 534-3661 FAX (310) 534-3665 email: [email protected] Circle No. 1... more ... With Integrated Bandwidt (310) 534-3661 FAX (310) 534-3665 email: [email protected] 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). ...
The phase diagram of the Y-Ba-Cu-O system was determined through structural, superconducting crit... 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.
Small angle x-ray scattering is utilized to directly examine the formation of clusters in supersa... more Small angle x-ray scattering is utilized to directly examine the formation of clusters in supersaturated solutions of glycine, in an attempt to understand their role in the nucleation process. The results suggest that the majority of glycine molecules exist as dimers in aqueous solutions, and monomers in 13% (v=v) acetic acid-water mixtures. As the water and acetic acid -water solutions crystallize into and forms, respectively, the findings indicate a direct correlation between molecular self-association in solution and the polymorphic outcome.
Films of differently modified PVA (polyvinyl alcohol), TA (phthalocyaninosilicon) and Nafion in d... 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.
A conductivity relaxation experiment has been conducted on an SrFeCo0.5Ox sample by abruptly chan... 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.
In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction e... 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.
Seven bronze bangles from Tell en-Nasbeh, northern Judah, were investigated to understand the pha... 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.
An analyzer for detection of fluorescence radiation was developed for fluorescence XAFS of dilute... 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 ...
ABSTRACT LIII absorption spectroscopy measurements, using synchrotron radiation on the Ce1-xRxPd3... 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.
The Materials Research Collaborative Access Team (MRCAT) beamline 10-ID at the Advanced Photon So... 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 .
ABSTRACT Nucleation of crystalline solids, the first stage of crystallization from solution, is n... 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.
We have performed detailed high temperature X-ray diffraction to study the nature of the structur... 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.
Physica C-superconductivity and Its Applications, 1991
We discuss the influence of oxygen defects and defect ordering on superconductivity in 123 compou... 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.
The crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y... 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.
The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a searc... 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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