Summary Serpentinites from the northern Vermont were examined for the distribution and abundance of As. XRD and electron microprobe showed the samples are composed of antigorite, chromite, magnetite, and carbonate minerals (magnesite, dolomite, calcite). The concentration in As when the samples were dissolved in H3PO4 was 10% of the concentration in As when the samples were dissolved in concentrated HF/HNO3, suggesting that As is mainly incorporated in the structure of antigorite. X-ray absorption near-edge structure spectra showed that the As is As(III) in the samples. Extended X-ray absorption fine structure spectra suggested that the As has a tetrahedral coordination and is located in the Si-site in serpentine.

In this thesis, we have performed systematical study of anomalous electric and magnetic behaviors of the 3d transition metal oxides; colossal magnetoresistance (La1−xRxMnO3 where R is a divalent alkaline earth ion) and Multiferroic (Ho1-xLaxMn2O5) systems by X-ray and Neutron scattering techniques. In our study, the enhancement of the transfer temperature for La0.8Ba0.2MnO3 under strain effect from the SrTiO3 substrate could be possible due to two reasons which one is Sr diffusion from SrTiO3 substructure, and other one is the octahedral MnO6 high symmetry are increasing. We focus the intrinsic strain effect on La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 films, and findings show that due to the different ionic sizes of doped Ca or Ba ions, the strain effect acts differently in the way it deforms. The interfacial strain effect produces opposite influences on the lattice symmetry, the average Mn¡VO bond lengths, the average oxygen disorders, the coupling symmetries inside and in the vicinity of the MnO6 octahedrons, as well as producing an opposing trend in metal-insulator and magnetic transition temperatures of the strained La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 films. The strain effects on the electronic structures of La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 thin films have been studied by O K-edge x-ray absorption near edge structure (XANES) spectroscopy. For La0.67Ca0.33MnO3, the first-principles calculations reveal that the features in the XANES spectra are associated with hybridized states between O 2p and Mn minority-spin 3d t2g and eg, La 5d/Ca 3d, and Mn 4s/Ca 4p states. An analysis of these features shows that the tensile strain decreases substantially La¡VO and Ca¡VO hybridization and TC for La0.67Ca0.33MnO3. For La0.8Ba0.2MnO3, the small compressive strain enhances slightly La¡VO and Ba¡VO hybridization and TC. In this thesis, the influence of the local structure distortion on the magnetic transition in La doped HoMn2O5 Multiferroics has been investigated systematically. The orthorhombic crystal structure of Ho1−xLaxMn2O5 is maintained up to x¡Ø0.2 but decomposed into multiphase for x¡Ù0.25. By doping La ions to a concentration of 0.1¡Øx¡Ø0.2, the formation of the RMnO3 1(13) phase can be suppressed and single-phase Ho1−xLaxMn2O5 (0.1¡Øx¡Ø0.2) compounds can be formed under 1 atm flowing oxygen. For x=0.2, a ferromagnetic FM transition at 150 K is superimposed on the paramagnetic background, which implies that the compound undergoes a ferromagnetic to antiferromagnetic (AFM) transition. This unique FM to AFM transition is observed for the first time. The FM transition is attributed to the formation of magnetic clusters in a host paramagnetic matrix. The anomalous magnetic clusters phenomena observed in Ho0.8La0.2Mn2O5 can be directly attributed to the different properties between Ho and La ions, and the differences of Ho and La ions are not only in the ionic radius but also in the electron negativity. During 90~150K, X-ray scattering diffraction presented the new addition peaks indicates the new electric density distribution, and the Neutron powder scattering diffraction (NPD) refining results show that the local structure of R-O (R: La, Ho) is un-symmetry which is conflict to the La Extended X-ray absorption fine structure (EXAFS) (which shows that the local structure of La-O becomes more symmetry than H-O. Since the refining values of the NPD are an average of entire crystal, such that it cannot tell the local changes. X-ray absorption spectrum (XAS) and EXAFS, in contrarily, can provide the local information. They implies that the temperature evolutions of the coupling strength with O 2p or unoccupied density state are opposite for the Ho and La ions in our Ho0.8La0.2Mn2O5 sample. Therefore, local change of ions position and charge redistribution happens in this specific temperature range.

No description available.

Summary Serpentinites from the northern Vermont were examined for the distribution and abundance of As. XRD and electron microprobe showed the samples are composed of antigorite, chromite, magnetite, and carbonate minerals (magnesite, dolomite, calcite). The concentration in As when the samples were dissolved in H3PO4 was 10% of the concentration in As when the samples were dissolved in concentrated HF/HNO3, suggesting that As is mainly incorporated in the structure of antigorite. X-ray absorption near-edge structure spectra showed that the As is As(III) in the samples. Extended X-ray absorption fine structure spectra suggested that the As has a tetrahedral coordination and is located in the Si-site in serpentine.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (p. [153]-167).

Summary Serpentinites from the northern Vermont were examined for the distribution and abundance of As. XRD and electron microprobe showed the samples are composed of antigorite, chromite, magnetite, and carbonate minerals (magnesite, dolomite, calcite). The concentration in As when the samples were dissolved in H3PO4 was 10% of the concentration in As when the samples were dissolved in concentrated HF/HNO3, suggesting that As is mainly incorporated in the structure of antigorite. X-ray absorption near-edge structure spectra showed that the As is As(III) in the samples. Extended X-ray absorption fine structure spectra suggested that the As has a tetrahedral coordination and is located in the Si-site in serpentine.

<p>Water is one of the most common compounds on earth and is essential for all biological activities. Water has, however, been a mystery for many years due to the large number of unusual chemical and physical properties, e.g. decreased volume during melting and maximum density at 4 °C. The origin of the anomalies behavior is the nature of the hydrogen bond. This thesis will presented an x-ray absorption spectroscopy (XAS) study to reveal the hydrogen bond structure in liquid water.</p><p>The x-ray absorption process is faster than a femtosecond and thereby reflects the molecular orbital structure in a frozen geometry locally around the probed water molecules. The results indicate that the electronic structure of liquid water is significantly different from that of the solid and gaseous forms. The molecular arrangement in the first coordination shell of liquid water is actually very similar as the two-hydrogen-bonded configurations at the surface of ice. This discovery suggests that most molecules in liquid water have two-hydrogen-bonded configurations with one donor and one acceptor hydrogen bond compared to the four-hydrogen-bonded tetrahedral structure in ice. This result is controversial since the general picture is that the structure of liquid water is very similar to the structure of ice. The results are, however, consistent with x-ray and neutron diffraction data but reveals serious discrepancies with structures based on current molecular dynamics simulations. The two-hydrogen-bond configuration in liquid water is rigid and heating from 25 °C to 90 °C introduce a minor change in the hydrogen-bonded configurations. Furthermore, XAS studies of water in aqueous solutions show that ion hydration does not affect the hydrogen bond configuration of the bulk. Only water molecules in the close vicinity to the ions show changes in the hydrogen bond formation. XAS data obtained with fluorescence yield are sensitive enough to resolved electronic structure of water molecules in the first hydration sphere and to distinguish between different protonated species. Hence, XAS is a useful tool to provide insight into the local electronic structure of a hydrogen-bonded liquid and it is applied for the first time on water revealing unique information of high importance.</p>

Water is one of the most common compounds on earth and is essential for all biological activities. Water has, however, been a mystery for many years due to the large number of unusual chemical and physical properties, e.g. decreased volume during melting and maximum density at 4 °C. The origin of the anomalies behavior is the nature of the hydrogen bond. This thesis will presented an x-ray absorption spectroscopy (XAS) study to reveal the hydrogen bond structure in liquid water. The x-ray absorption process is faster than a femtosecond and thereby reflects the molecular orbital structure in a frozen geometry locally around the probed water molecules. The results indicate that the electronic structure of liquid water is significantly different from that of the solid and gaseous forms. The molecular arrangement in the first coordination shell of liquid water is actually very similar as the two-hydrogen-bonded configurations at the surface of ice. This discovery suggests that most molecules in liquid water have two-hydrogen-bonded configurations with one donor and one acceptor hydrogen bond compared to the four-hydrogen-bonded tetrahedral structure in ice. This result is controversial since the general picture is that the structure of liquid water is very similar to the structure of ice. The results are, however, consistent with x-ray and neutron diffraction data but reveals serious discrepancies with structures based on current molecular dynamics simulations. The two-hydrogen-bond configuration in liquid water is rigid and heating from 25 °C to 90 °C introduce a minor change in the hydrogen-bonded configurations. Furthermore, XAS studies of water in aqueous solutions show that ion hydration does not affect the hydrogen bond configuration of the bulk. Only water molecules in the close vicinity to the ions show changes in the hydrogen bond formation. XAS data obtained with fluorescence yield are sensitive enough to resolved electronic structure of water molecules in the first hydration sphere and to distinguish between different protonated species. Hence, XAS is a useful tool to provide insight into the local electronic structure of a hydrogen-bonded liquid and it is applied for the first time on water revealing unique information of high importance.

Nuclear energy can be used to reliably generate large quantities of electricity while providing minimal lifetime CO2 emissions. Given the extreme importance of safety in the nuclear industry, it is necessary to have a fundamental understanding of the materials used throughout the nuclear fuel cycle. It is of particular to importance to develop an understanding of these materials at an atomic level. In this thesis, X-ray absorption spectroscopy (XAS), along with several other X-ray based techniques, has been used to study materials that are produced or proposed for use in the nuclear fuel cycle. Uranium mining and milling operations generate large quantities of waste, known as mine and mill tailings. At their McClean Facility in Northern Saskatchewan, AREVA Resources Canada disposes of the tailings waste using the JEB Tailings Management Facility (TMF). AREVA monitors the mineralization of elements of concern (i.e., Ni, As, Fe, Mo, Ra, and U) within the TMF as part of its on-going commitment towards managing the facility’s environmental impact. Molybdenum (Mo) is predicted to mineralize as insoluble powellite (CaMoO4) within the TMF. However, no experimental evidence confirmed the presence of powellite in the TMF. In Chapter 2, the presence of powellite, and other Mo-bearing minerals, was determined using powder X-ray diffraction (XRD), X-ray fluorescence imaging, and Mo K-edge XAS. The results of this study confirmed that powellite was present in the TMF and showed that Mo K-edge XAS was the only effective way to detect the Mo minerals within the TMF. New materials for use as nuclear fuels were also investigated in this thesis. Spent nuclear fuel must be securely stored for long periods of time due to the presence transuranic elements (TRU; i.e., Pu, Am, Np, Cm), and the use of inert matrix fuels (IMF), which consist of actinides embedded in a neutron transparent (inert) material, have been proposed for to “burn-up” or transmute these TRU species. Stabilized ZrO2 materials have been proposed for use in IMF applications, and in Chapter 3 the thermal stability of a series of NdxYyZr1-x-yO2-\delta materials made by a ceramic synthetic route have been studied using powder XRD, scanning electron microscopy (SEM), and X-ray absorption spectroscopy. (Nd was used as a surrogate for Am.) The results of this study showed that the fluorite structure of the NdxYyZr1-x-yO2- \delta materials was stabilized when y >= 0.05, and that the local environment around Zr was independent of composition or annealing temperature. The effect of synthetic method on the thermal stability of the NdxYyZr1-x-yO2-\delta materials was also determined, and this is the subject of Chapter 4. In this study a series of NdxY0.25-xZr0.75O1.88 materials were synthesized using a low-temperature co precipitation synthesis, and these then annealed at 1400 °C and 1500 °C. The as-synthesized and annealed materials were characterized by powder XRD, SEM, and XAS. This study confirmed that the thermal stability of the materials was dependent on synthetic method, and that materials made using a solid-state method were superior to those produced by a solution-based approach. Y-stabilized zirconia has a low thermal conductivity, which is not ideal for a nuclear fuel. The thermal conductivity could be increased if a lighter cation, such as Sc, was used to stabilize the fluorite structure. In Chapter 5, the thermal stability of a series of NdxScyZr1-x-yO2-\delta materials was investigated. The as-synthesized and annealed materials were studied by powder XRD, SEM, and XAS. These results showed that the fluorite structure was only stable in the annealed materials when x+y >= 0.15 and y >= 0.10. The results of this study provided insight into the possible use of scandia-stabilized zirconia for use as an inert matrix fuel. This studies presented in this thesis have used X-ray absorption spectroscopy and a number of other techniques to characterize materials important to the nuclear fuel cycle. The studies presented here were only possible because of the unique information that can be obtained using XAS. This thesis serves to highlight the importance of XAS as a technique and how it can be applied to solve problems related to the material science of the nuclear fuel cycle.

Understanding the fundamental electronic properties of materials is a key step to develop innovations in many fields of technology. For example, this has allowed to design molecular based devices like organic field effect transistors, organic solar cells and molecular switches. In this thesis, the properties of advanced functional materials, in particular metal-organic molecules and molecular building blocks of 2D materials, are investigated by means of Density Functional Theory (DFT), the GW approximation (GWA) and the Bethe-Salpeter equation (BSE), also in conjunction with experimental studies. The main focus is on calculations aiming to understand spectroscopic results. In detail, the molecular architectures of lutetium-bis-phthalocyanine (LuPc2) on clean and hydrogenated vicinal Si(100)2×1, and of the biphenylene molecule on Cu(111) were analysed by means of X-ray Photoelectron spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy; DFT calculations were performed to obtain insights into the atomic and electronic structures. Furthermore, detailed information about the electronic states of the gas phase iron phthalocyanine (FePc) and of the gas phase biphenylene molecule were obtained through XPS and NEXAFS spectroscopy. I have studied by means of DFT, multiplet and GWA calculations the electronic correlation effects in these systems. Also the optical, electronic and excitonic properties of a hypothetical 2D material based on the biphenylene molecule were investigated by GWA and BSE calculations. Monolayers of metal-free phthalocyanine (H2Pc) on Au(111) and of FePc on Au(111) and Cu(100)c(2×2)-2N/Cu(111) with and without pyridine modifier were studied by XPS and final state calculations. A multiplet approach to compute L-edges employing the hybridizations function, known from dynamical mean field theory, was proposed and applied to transition metal oxides.