Th. 3e cycle--Sci. des matér.--Paris 7, 1983.

In dieser Arbeit werden drei Lanthanmanganat-Systeme mittels SQUID-(Superconducting Quantum Interference Device) Magnetometrie und XMCD-(X-ray Magnetic Circular Dich-roism) Messungen an den jeweiligen Absorptionskanten (XANES: X-ray Absorption Near Edge Structure) sowie im kantenfernen Bereich (MEXAFS: Magnetic Extended X-ray Ab-sorption Fine Structure) im Hinblick auf die Klärung ihrer magnetischen (Unter-)Struktur untersucht. Bei Lanthanmanganaten wird sowohl im Verlauf des spingemittelten als auch spinabhängigen Absorptionskoeffizienten an der Mn K Kante immer eine energetisch über 40eV ausgedehnte Doppelstruktur beobachtet. Durch Vergleich mit theoretischen Bandstrukturrechnungen und Messungen an Referenzsystemen lassen sich diese Strukturen auf zwei energetisch getrennte, resonante Übergänge in leere Mn 4p Zustände zurückführen. Die Ursachen liegen in der Kristallstruktur der Lanthanmanganate und damit ihrer Bandstruktur begründet. XMCD-Messungen an den La L2,3 Kanten zeigen, dass dieses Element zur Gesamtmagnetisierung dieser Verbindungen nur ein unerhebliches Moment beiträgt und daher in einer Xenon-ähnlichen Elektronenkonfiguration vorliegt. Durch die interatomare Coulombwechselwirkung der nahezu unbesetzten La 5d Zustände mit den magnetisch aktiven Ionen im Kristall dienen XMCD-Messungen an den La L2,3 Kanten als Sonde für die magnetische Lanthanumgebung. Ähnliches gilt für die entsprechenden MEXAFS. Der proportionale Zusammenhang der Größe der MEXAFS mit dem Spinmoment der Nachbarionen besitzt auch bei den Lanthanmanganat-Systemen mit den stark hybridisierten Elektronen der Mn 3d Schale Gültigkeit. Der Spinmoment-Korrelationskoeffizient aSpin gilt auch hier, was eine weitere Bestätigung des MEXAFS-Modells auch für oxidische Systeme ist. Im dotierten System La1.2Nd0.2Sr1.6Mn2O7 koppelt das Neodymmoment innerhalb einer Doppellage antiferromagnetisch zum Mn-Untergitter. Durch die Neodym-Dotierung am La/Sr-Platz im Kristall ist die ferromagnetische Kopplung der Doppellagen untereinander abge-schwächt und die Rückkehr in die antiferromagnetische Phase nach dem Abschalten des äußeren Magnetfeldes damit erleichtert. Das Mn-Bahnmoment ist von nahezu verschwindender Größe („gequencht“). Das System La1.2Sr1.8Mn2-xRuxO7 zeigt mit zunehmendem Rutheniumgehalt eine Erhöhung der Curie-Temperatur, was bei Ruddlesden-Popper Phasen zum ersten Mal beobachtet wurde. Das Ru-Untergitter und das Mn-Gitter sind zueinander antiparallel gekoppelt. Durch Bestimmung der Valenzen von Mn und Ru wird ein dem Superaustausch ähnliches Kopplungsmodell entworfen, womit der Anstieg in der Curie-Temperatur erklärbar ist. Das neu entwickelte XMCD-Experiment auf Basis eines Phasenschiebers und digitaler Sig-nalaufbereitung durch eine Lock-In Software besitzt ein Signal-Rausch Verhältnis in der Nähe der Photonenstatistik und liefert einen großen Zeit- und Qualitätsgewinn gegenüber Messmethoden mit Magnetfeldwechsel. Auf teure analoge Lock-In Messverstärker kann verzichtet werden. Zukünftig erweitert sich mit diesem Aufbau die für XMCD-Experimente zugängliche Anzahl an Synchrotronstrahlplätzen. Diese Experimente sind jetzt auch mit linear polarisierter Röntgenstrahlung an Wiggler/Undulator Strahlplätzen und zukünftigen XFELs (X-ray Free Electron Laser) durchführbar. / In this work three Lanthanum Manganate systems are investigated in terms of their magnetic (sub) structures. These investigations are done with SQUID- (Superconducting Quantum Interference Device) magnetometry and XMCD- (X-ray Magnetic Circular Dichroism) measurements at the respective absorption edges (XANES: X-ray Absorption Near Edge Structure) as well as in the MEXAFS (Magnetic Extended X-ray Absorption Fine Structure) range. For Lanthanum Manganates at the Mn K edge there is always seen a double peak structure in the shape of the spin dependent and spin averaged absorption coefficient, which is energetically expanded over more than 40eV. These structures are ascribed to two energetic separated, resonant transitions into empty Mn 4p states by comparing with theoretical band structure calculations and measurements of reference systems and are caused in the crystal structure of the Lanthanum Manganates and with it their band structure. XMCD-measurements at the La L2,3 edges show that this element adds only a negligible magnetic moment to the total magnetisation and La is therefore in a Xenon-like electronic configuration. These measurements probe the magnetic neighbourhood of the Lanthanum in the crystal due to the interatomic Coulomb interaction of the almost empty La 5d states with the magnetic active ions like the MEXAFS. The proportionality of the MEXAFS amplitude with the spin-moment of the neighboring ions is even valid here for Lanthanum Manganate systems with their strongly hybridized Mn 3d shell electrons. The validity of the correlation coefficient of the spin-moment aSpin confirms the MEXAFS-model also for oxide systems. In the doped system La1.2Nd0.2Sr1.6Mn2O7 the Neodymium moment couples antiferromagnetically with the Mn-sublattice within a double layer. The ferromagnetic coupling of the double layers is weak among each other due to the Nd doping at the La/Sr crystal position. Therefore the reversion into the antiferromagnetic phase is relieved after switching off the external magnetic field. The orbital moment of Mn is almost vanishing (“quenched”). The system La1.2Sr1.8Mn2-xRuxO7 shows an increasing of the Curie-temperature with an increase of the Ruthenium doping level, observed for the first time for Ruddlesden-Popper phases. The Ru-sublattice is antiparallel coupled to the Mn-sublattice. A superexchange like coupling model is composed through determination of the valences of Mn and Ru, also explaining the increase of the Curie-temperature. A new XMCD-experiment is developed with phase retarder and digital signal processing through Lock-In software with signal to noise ratio nearby photon statistics. This experiment provides a huge benefit in time and quality compared to XMCD-measurement with changing the external magnetic field. Also there is no need of expensive Lock-In analog amplifiers. Now the number of synchrotron beamlines for XMCD-measurements are increased and XMCD-experiments are realizable also at Wiggler/Undulator beamlines with linear polarized radiation and in future at XFEL (X-ray Free Electron Laser).

The strain effect on La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 thin films on SrTiO3 (001) substrate with different thicknesses has been studied by X-ray absorption near edge spectroscopy (XANES), which can reveal the details of the coupling between cations and anions. The strain may suppress the TC of LCMO films while enhancing that of LBMO films. The theoretical calculation results suggest the unoccupied states of the third structure of XANES are formed by much more complex hybridization of O 2p to Mn 4sp, La 6s and (Ca 4sp or Ba 6sp) orbitals. The change of the absorption intensity of the second and third structures is compatible to the TC change of both films due to the strain effect. This strongly suggests that the strain effect on LCMO and LBMO thin films is mainly associated with the bonding situation between O and La(Ca or Ba) ions.

Terra mine is an abandoned copper and silver mine in the Northwest Territories, Canada, from which mine tailings were deposited into Ho-Hum Lake, adjacent to the mine’s processing plant. The tailings contain elevated levels of arsenic (As), resulting in As levels exceeding Canadian sediment and water quality guidelines in the lake, and in downstream wetland water and sediment. This field and laboratory study focuses on the microbial ecology, and the reduction and oxidation of As, iron (Fe) and sulphur (S), in the wetland downstream from Ho-Hum Lake. This wetland is proposed as a passive remediation system for removal and storage of As. Using microcosm experiments, the stability of As-bearing sediments was compared in the upper, middle and lowestmost areas of the wetland over a 42-day period. Fresh sediments and sediments amended with a 10 mM acetate solution, both mixed with water, were compared. While no significant geochemical differences were found between acetate-amended and unamended microcosms, formation of inorganic As-S species was higher in amended microcosms, suggesting that micro-organisms were more active in the system because they were not carbon-limited. Formation of methylated-As species increased over time in all samples, including abiotic controls. Bacterial sulphate reduction occurred during the first 10 days of the experiment, perhaps resulting in precipitation of sulphide minerals. X-ray adsorption near edge spectroscopy was used to assess solid-state speciation of As in the sediments and indicated that pre-microcosm sediments from all sites showed high proportions of As(III)-S and As(III)-O speciation. Post-microcosm sediments revealed a 13% increase in the proportion of As(V)-O species, whereas abiotic controls showed only an 8% increase. DNA sequencing in post-microcosm sediments identified As, Fe and S reducing bacteria, and the geochemical patterns of As, Fe and S in the microcosms indicate the bacteria are likely active in the system. Microbial diversity and solid-state speciation of As in the sediments were assessed at varying depths at the microcosm sites, but correlation analysis revealed no significant relationship between As speciation and microbial diversity. A positive correlation between diversity and depth, and a negative relationship between As concentration and diversity, were found, perhaps indicating decreasing contamination with depth in the wetland. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2011-07-03 23:27:44.373

Metal oxide materials are a broad class of materials found in many current technologies due to their interesting properties such as magnetism and ferroelectricity. Material properties can be tuned and heavily influenced by disorder at the atomic level, as has been shown in the ferrimagnetic and ferroelectric Al2-x-yGaxFeyO3 materials, which adopt the non-centrosymmetric, orthorhombic GaFeO3 crystal structure-type (Pna21). The significant cation disorder and non centrosymmetric nature of the crystal structure underlie the multiferroic properties in these materials and make them one of the few chemical systems to possess multiferroic ordering near room temperature. Unfortunately, while cation site disorder is responsible for the multiferroic properties observed in these compounds, their complex crystal structure has led to inconsistent reports in the ternary Al2-xFexO3 and Ga2-xFexO3 compounds. X-ray absorption near-edge spectroscopy (XANES) is an element specific technique, which can be used to examine cation site disorder as a function of changes in the average coordination environment around the metal, providing a means of studying these complex materials. In this thesis, XANES was used to investigate factors affecting cation site disorder in a series of Al1-xGaxFeO3 materials (0 ≤ x ≤ 1) adopting the GaFeO3 crystal structure-type. The GaFeO3 crystal structure has four cation sites, of which, the distorted octahedral Fe1 and Fe2 sites are primarily occupied by Fe3+, and the less distorted tetrahedral A1 and octahedral A2 sites are primarily occupied by Al3+ or Ga3+. These materials were initially synthesized using a high temperature ceramic method, and it was found that with increasing Ga3+ content (x) these materials show a decrease in the amount of cation site disorder between the tetrahedral site and the three octahedral sites. This decrease is attributed to the tetrahedral site preference of Ga3+, which inhibits cation site disorder at the A1 site, as opposed to the octahedral site preference observed for Al3+. Additionally, Fe3+ was found to predominantly occupy the three octahedral sites over the tetrahedral site in these materials, likely because of its large ionic size and the strong magnetic coupling between those three sites. The quaternary Al1-xGaxFeO3 materials (0 ≤ x ≤ 1) were synthesized again via two other techniques: a citrate sol-gel method and a co-precipitation method. The oxide network binding the binary metal oxide precursors limits ion mobility in the high temperature ceramic method. The citrate sol-gel and co-precipitation methods were used to generate mixed-metal precursors with a more homogeneous distribution of the metal cations than the binary metal oxide precursors commonly used by the high temperature ceramic method. Mixed-metal precursors reduce the distance the ions have to diffuse, while the nature of the amorphous matrix was found to affect disorder in the resulting material. From analysis of the XANES spectra, the ceramic method showed the least amount of cation site disorder, followed by the citrate sol-gel method and co-precipitation method, respectively. Greater annealing temperatures resulted in an increase in cation site disorder, with the average coordination number of Al3+ and Ga3+ increasing while the average coordination number of Fe3+ decreased. Al1-xGaxFeO3 materials synthesized via the co-precipitation method showed the greatest amount of cation disorder, followed by the citrate sol-gel and high temperature ceramic techniques, respectively. The research presented in this thesis is among the first to examine a large number of materials from the relatively unexplored Al1-xGaxFeO3 system, and has contributed to the growing body of knowledge on the factors affecting cation site disorder in these materials and potentially other systems. Further, despite a simple rationale for understanding the features present in Al L2,3- and Ga K-edge spectra, these studies have shown how effectively XANES can be used to understand subtle changes in the atomic structure of solid-state materials.

This thesis was devised as a fundamental study of the Li-S system by the use of 7Li Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), X-ray Absorption Near- Edge Structure (XANES), and Non-Resonant Inelastic X-ray Scattering (NRIXS). The first part of this thesis reports the first evidence of a stable solid-phase intermediate between elemental sulfur (α-S8) and Li2S, Li2S6, which can be used to understand deeper Li-S battery. The second part of this thesis is based on operando XANES measurements made in the Argonne Photon Source (APS).Linear combination fit (LCF) analyses are performed to interpret the data; and, noticeably, the distinction between short-chain and long-chain polysulfides can be made due to the use of proper reference materials. The results reveal the first detailed observation of typical sulfur redox chemistry upon cycling, showing how sulfur fraction (under-utilization) and sulfide precipitation impact capacity. It also gives new insights into the differences between the charge and discharge mechanisms, resulting in the hysteresis of the cycling profile. Operando XANEs were also performed on het-treated material, which exhibits a particular electrochemical signature, which has never explained. After a preliminary electrochemical study by potentiodynamic cycling with galvanostatic acceleration (PCGA), operando XANES measurements at the sulfur K-edge are performed on heat-treated PCNS. Noticeably, the difference in the XANES signatures of the pristine and the recharged state shows the irreversible process that occurs during the first discharges. At last, electrolytes are investigated by the compilation of quantitative physico-chemical parameters – viscosity, ionic conductivity, and solubility of Li2S and Li2S6 – on novel class of solvents that are glymes with non-polar groups and acetonitrile (ACN) complexed with LiTFSI. 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) is chosen to decrease their viscosities. (ACN)2:LiTFSI attracts particular attention because of the particularly low Li2Sn solubility and. Its good electrochemical performance when mixed with 50 vol% HFE. Operando XANES proves the formation of polysulfides in this electrolyte, although constrains imposed by this novel electrolyte to the XANES experiment complicate the data analysis. The low energy feature evolution shows a more progressive mechanism involved in this electrolyte, which could be linked to the particularly low Li2Sn solubility

No description available.

京都大学 / 0048 / 新制・論文博士 / 博士(工学) / 乙第12929号 / 論工博第4122号 / 新制||工||1626(附属図書館) / 32139 / (主査)教授 田中 庸裕, 教授 田中 勝久, 教授 佐藤 啓文 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Les vitraux du Moyen Âge, dont les pièces de verre contiennent du manganèse, sont fréquemment atteints d'une pathologie communément appelée «brunissement ». Ce phénomène, qui se traduit par la présence de taches brunes riches en manganèse en surface ou subsurface du verre limitant le passage de la lumière et gênant la lisibilité de l'œuvre, est peu documenté et son occurrence parmi les vitraux n'est pas précisément connue. Un des problèmes majeurs pour ce qui concerne la conservation/restauration des œuvres est l'absence de traitements efficaces et durables pour cette pathologie. En France actuellement, l'absence de traitement est donc préconisée, ce qui ne satisfait ni les architectes, ni les conservateurs, ni les restaurateurs. La connaissance approfondie des processus physico-chimiques à l'origine du phénomène de brunissement est donc nécessaire pour proposer des réponses aux questions et aux attentes des conservateurs/restaurateurs. Au cours de cette thèse un panel de 24 échantillons de verres de vitraux historiques et de 3 échantillons archéologiques ont été étudiés par des méthodes microscopiques et spectroscopiques afin i) d'établir des critères d'identification du phénomène de brunissement dû au manganèse et ii) d'obtenir des informations sur la nature des phases brunes et sur le degré d'oxydation du manganèse dans ces phases. Parallèlement à l'étude des échantillons anciens, des verres modèles de composition proche de celle des vitraux médiévaux ont été synthétisés avec deux objectifs : i) la compréhension de la réaction entre le manganèse et le fer et de l'influence des paramètres de fabrication sur la couleur des verres et ii) l'étude de l'influence que peuvent avoir les bactéries dans le développement du phénomène de brunissement / The medieval stained glass windows, which glass composition contain manganese, are often affected by an alteration commonly designated as "browning". This phenomenon results in the presence of Mn-rich brown spots at the surface or subsurface of the glass thus limiting the passage of light and hindering the interpretation of the artwork. Poorly documented, the occurrence of browning among stained glass windows is not precisely described. Currently, one of the major problems in terms of conservation and restoration is that long-term treatments are not available. In these conditions, the recommendations are not to treat the affected glasses, a solution that satisfies neither the architects nor the curators, nor the restorers. In order to answer the questions and expectations of curators and restorers the comprehension of this phenomenon is essential. In this work, a panel of 24 historical and 3 archaeological stained glass samples were studied by microscopic and spectroscopic methods in order to i) establish reliable criteria for identifying the browning phenomenon due to manganese and ii) obtain information on the nature of the dark phases and the oxidation state of manganese in these phases. In parallel with the study of ancient samples, synthetic glasses with medieval-like compositions were synthesized for: i) understanding the reaction between manganese and iron, as well as the influence of the process parameters on the color of glasses and ii) studying the influence of bacteria in the development of the browning phenomenon

Amostras nanoestruturadas do sistema SrTi1-xMnxO3 (STM) com x = 0%, 0.5%, 1%, 2.5%, 5% e 10% na forma de pó foram sintetizadas através do método dos precursores poliméricos. As propriedades térmicas, estruturais e ópticas das amostras STM calcinadas em diferentes temperaturas foram analisadas a temperatura ambiente através de técnicas de análise térmica, difração de raios-x, espectroscopia de absorção de raios-x e fotoluminescência. Os resultados obtidos através das técnicas de analise térmica mostraram que o íon manganês causa um efeito retardante, aumentando a temperatura onde ocorre o início da cristalização. Os resultados de DRX mostraram que no limite de solubilidade estudado, o íon manganês foi incorporado em solução sólida no sítio B na rede do SrTiO3 (ST), assumindo estados de oxidação entre +3,4 e +3,7, indicando que ocorre a criação de defeitos para compensação de cargas, mantendo a neutralidade elétrica do material. A análise dos espectros de fotoluminescência das amostras STM amorfas mostrou que o aumento da quantidade de manganês até 1% leva a um aumento da intensidade fotoluminescência em relação a amostra SrTiO3. Entretanto, a adição de manganês acima desta quantidade leva a uma diminuição pronunciada da intensidade fotoluminescente. Nas amostras amorfas não foi observada uma variação significativa da ordem local ao redor dos átomos de titânio bem como no estado de oxidação dos átomos de manganês à medida que a quantidade de manganês aumenta. Desta forma, a variação da intensidade fotoluminescente não pôde ser atribuída a estes fatores. O aumento da temperatura de calcinação leva a uma diminuição significativa da intensidade fotoluminescente. Uma análise dos espectros XANES medidos na borda K do titânio destas amostras mostrou que ocorre uma maior ordenação dos átomos de Ti nos octaedros de oxigênio [TiO6] a medida que a temperatura de calcinação aumenta, ou seja, à medida que aumenta o grau de cristalinidade das amostras. / Nanostructured SrTi1-xMnxO3 (STM) powder samples with x = 0%, 0.5%, 1%, 2.5%, 5% and 10% were synthesized by the polymeric precursors method. The thermal, structural and optical properties of STM samples heat-treated at different temperatures were analyzed by thermal analysis, X-ray diffraction, X-ray absorption spectroscopy and photoluminescence techniques. The thermal analysis results have shown that manganese ion causes a retarding effect, increasing the onset of the crystallization temperature. The XRD results showed that manganese ion is incorporated in a solid solution in the B site of the SrTiO3 (ST) network for the range of solubility studied, with oxidation states between +3.4 and +3.7, indicating the creation of charge compensation defects, keeping the materials electrical neutrality. The analysis of the photoluminescence (PL) spectra of the STM amorphous samples showed that the PL intensity increases when the amount of manganese is up to 1%. However, higher manganese concentrations leads to a pronounced decrease of the photoluminescence intensity. The amorphous samples showed no significant change of the local order around the titanium atoms, observed as well as in the oxidation state of the manganese atoms as the amount of manganese increases. Thus, the variation of the photoluminescence intensity cannot be explained by these factors. Increasing the calcination temperature leads to a significant decrease of the photoluminescence intensity. An analysis of the XANES spectra measured at the titanium K edge of these samples showed that as the calcination temperature increases, i. e., as it increases the degree of crystallinity, the ordering of the Ti atoms in the oxygen octahedra TiO6 of the samples increases.