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Dissertations / Theses on the topic 'Transition metal defect model'

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Published: 4 June 2021
Last updated: 16 February 2022

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1

Ackland, G. J. "Non-pairwise potentials and defect modelling for transition metals." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379869.

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2

Andraud, Chantal. "Defauts d'empilement dans le materiau unidimensionnel cscdbr::(3) : etude spectroscopique." Paris 6, 1987. http://www.theses.fr/1987PA066140.

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L'etude des proprietes optiques de cscdbr::(3) a montre l'existence de centres br::(2)**(2-). L'excitation des echantillons par des rayonnements ionisants (rx, faisceau d'electrons) et des experiences d'absorption a deux photons ont permis d'associer les differentes bandes d'emission et d'absorption observees a des transitions appartenant a ces centres. L'existence de ces centres br::(2)**(2-) est attribuee a la presence de defauts d'empilement. L'effet d'une pression hydrostatique, le dopage par des ions pb**(2x) et le recuit des cristaux confirment l'hypothese
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3

Bogaert, Kevin Christopher. "Defect-driven processing of two-dimensional transition metal dichalcogenides." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122072.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 149-161).
Two-dimensional transition metal dichalcogenides (TMDs) are an emerging class of semiconductor materials that offer exciting new properties for future electronic and optoelectronic applications. However, many ongoing challenges related to synthesis and processing must be overcome before this nascent technology can become industrially viable. In this thesis, processing-related phenomena relevant to the fabrication of TMD heterostructures, alloys, and nanoporous membranes are presented. This thesis begins with an investigation of the role of substrate temperature in two-step chemical vapor deposition (CVD) growth of MoS₂/WS₂ heterostructures. We demonstrate diffusion-mediated synthesis of inverted lateral heterostructures following low MoS2 growth temperatures in the second CVD step and homogeneous Mo[subscript x]W[subscript 1-x]S₂ alloyed crystals following higher MoS₂ growth temperatures.
Investigating the nature of this diffusion-mediated process, we identify an energetically favorable atomistic model proposing that transition metal diffusion is driven by a heterogeneous distribution of sulfur vacancies. This model is corroborated by the synthesis of a composition-graded Mo[subscript x]W[subscript 1-x]S₂ alloy crystals in which the final-stage spatial distribution of transition metal atoms correlates with intermediate-stage distribution of point defects. These heterogeneous crystals allow for correlation of the local optical properties with the local composition, demonstrating a variation in photoluminescence intensity spanning two orders of magnitude and reaching the maximum value for equicompositional alloy Mo₀.₅W₀.₅S₂ (x=0.5). Furthermore, the correlation between intermediate-stage distribution of point defects and final-stage spatial distribution of transition metal atoms enables the opportunity for bespoke patterning.
Utilizing a laser annealing technique, we demonstrate the ability to locally induce defects that define the regions of preferential nucleation during subsequent CVD growth. Finally, defect processing is also demonstrated in nanoporous TMD membrane applications. Combining modeling with experimentation, we demonstrate the relationship between vacuum annealing time and temperature with nanopore properties such as average radius and edge structure. Control of these properties is essential for the fabrication of functional nanoporous membrane devices for sensing, filtration, and energy applications. This thesis motivates further work on TMD processing in pursuit of developing a fundamental understanding of the defect-driven diffusion mechanism, a larger library of interesting TMD compositions and structures, as well as industrially viable TMD devices.
by Kevin Christopher Bogaert.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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4

Paul, Marcus. "Synthesis and characterisation of transition metal-doped lithium niobate and lithium tantalate." Thesis, University of Aberdeen, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319341.

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The study of ferroelectric LiNbO3 and LiTaO3 doped with transition metals involves the characterisation of LiNbO3/LiTaO3 solid solutions in the systems Li2O-Nb2O5-MxOy and Li2O-Ta2O5-MxOy (M = Cr, Mn, Fe, Co, Ni, Cu). Compounds were made by solid state reaction at temperatures between 1000 and 1500°C, depending on the system studied. The emphasis of this work is on the characterisation of the defect structure of LiNbO3/LiTaO3 solid solutions using phase diagram determination, X-ray and neutron powder diffraction, EXAFS, ESR and optical spectroscopy. The valence of the incorporated cations was studied by magnetic measurements. The electrical properties of these materials have been investigated using AC impedance spectroscopy. It can be shown that the physical properties of LiNbO3 and LiTaO3 depend strongly on the defects in the structure which can be controlled by purposeful doping with other cations. Structural refinements of the X-ray and neutron powder diffraction data have shown that the defects arising from nonstoichiometry are accommodated by vacancies created on the Li site. This affects the structure when doped with third cations, giving rise to complex substitution mechanisms Spectroscopic studies have shown that the dopants (Cr3+, Mn2+/Mn3+, Co2+, Ni2+, Cu+, Cu2+) are shifted from the central octahedral position towards the adjacent empty octahedron. The electrical properties of LiNbO3 and LiTaO3, measured by AC impedance spectroscopy, depend strongly on the dopant content: the conductivity generally rises, whereas the activation energy for the electrical conductivity drops with increasing dopant concentration. The microstructure of electroceramics can also be probed by AC impedance spectroscopy and it was shown that the texture of all samples was bad due to poor sintering of the pellets. Longer sintering times did not improve the quality of the ceramics which exhibit a large pore size distribution. An important aspect for future work would be the quality improvement of LiNbO3/LiTaO3 based ceramics.
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5

Kummari, Venkata Chandra Sekhar. "A New Approach for Transition Metal Free Magnetic Sic: Defect Induced Magnetism After Self-ion Implantation." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc271849/.

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SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3C-SiC, 4H-SiC and 6H-SiC are the most common polytypes used for research purposes. Among these polytypes 4H-SiC is gaining importance due to its easy commercial availability with a large bandgap of 3.26 eV at room temperature. Controlled creation of defects in materials is an approach to modify the electronic properties in a way that new functionality may result. SiC is a promising candidate for defect-induced magnetism on which spintronic devices could be developed. The defects considered are of room temperature stable vacancy types, eliminating the need for magnetic impurities, which easily diffuse at room temperature. Impurity free vacancy type defects can be created by implanting the host atoms of silicon or carbon. The implantation fluence determines the defect density, which is a critical parameter for defect induced magnetism. Therefore, we have studied the influence of low fluence low energy silicon and carbon implantation on the creation of defects in n-type 4H-SiC. The characterization of the defects in these implanted samples was performed using the techniques, RBS-channeling and Raman spectroscopy. We have also utilized these characterization techniques to analyze defects created in much deeper layers of the SiC due to implantation of high energy nitrogen ions. The experimentally determined depths of the Si damage peaks due to low energy (60 keV) Si and C ions with low fluences (< 1015 cm-2) are consistent with the SRIM-2011 simulations. From RBS-C Si sub-lattice measurements for different fluences (1.1×1014 cm-2 to 3.2×1014 cm-2) of Si implantation in 4H-SiC, the Si vacancy density is estimated to range from 1.29×1022 cm-3 to 4.57×1022 cm-2, corresponding to average vacancy distances of 4.26 Å to 2.79 Å at the damage peak (50±5 nm). Similarly, for C implanted fluences (1.85×1014 cm-2 to 1×1015 cm-2), the Si vacancy density varies from 1.37×1022 cm-3 to 4.22×1022 cm-3 with the average vacancy distances from 4.17 Å to 2.87 Å at the damage peak (110±10 nm). From the Raman spectroscopy, the implantation-induced lattice disorders calculated along the c-axis (LO mode) and perpendicular to c-axis (TO mode) in 4H-SiC are found to be similar. Furthermore, the results obtained from SQUID measurements in C implanted n-type 4H-SiC sample with fluences ranging from 1×1012 to 1.7×1016 ions/cm2 have been discussed. The implanted samples showed diamagnetism similar to the unimplanted sample. To date, to our best of knowledge, no experimental work has been reported on investigating defect induced magnetism for self-ion implantation in n-type 4H-SiC. These first reports of experimental results can provide useful information in future studies for a better understanding of self-ion implantation in SiC-based DMS.
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6

Schmid, John Robert 1952. "A model for estimating allowable transition metal contamination in DRAMs." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/291463.

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Due to new memory-cell architectures, the leakage-current requirements for semiconductor memories will become less stringent with increased levels of integration. The implication of these requirements with regard to allowable metallic contamination levels is investigated with a one-dimensional model based on Shockley-Read-Hall generation-recombination. The model was developed to predict leakage-current in carrier-depleted regions as a function of basic process and metallic contaminant parameters. As device dimensions are reduced, transition metal homogeneous contamination in process chemicals can be an important source of generation-recombination centers that result in the dominant generation-current in the space-charge region. The model allows an estimation of an upper bound for transition metal contamination in advanced processes and is applied for DRAM leakage predictions. Using the model, it is demonstrated that the trend toward lower leakage-current density requirements reverses after the 64-Mbit generation DRAM as a result of memory-cell architecture trends which significantly reduce the space-charge volume.
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7

Petzold, Stefan [Verfasser], Lambert [Akademischer Betreuer] Alff, and Leopoldo [Akademischer Betreuer] Molina-Luna. "Defect Engineering in Transition Metal Oxide-based Resistive Random Access Memory / Stefan Petzold ; Lambert Alff, Leopoldo Molina-Luna." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1204200912/34.

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8

Khalajzadeh, Vahid. "Modeling of shrinkage porosity defect formation during alloy solidification." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6155.

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Among all casting defects, shrinkage porosities could significantly reduce the strength of metal parts. As several critical components in aerospace and automotive industries are manufactured through casting processes, ensuring these parts are free of defects and are structurally sound is an important issue. This study investigates the formation of shrinkage-related defects in alloy solidification. To have a better understanding about the defect formation mechanisms, three sets of experimental studies were performed. In the first experiment, a real-time video radiography technique is used for the observation of pore nucleation and growth in a wedge-shaped A356 aluminum casting. An image-processing technique is developed to quantify the amount of through-thickness porosity observed in the real-time radiographic video. Experimental results reveal that the formation of shrinkage porosity in castings has two stages: 1-surface sink formation and 2- internal porosity evolution. The transition from surface sink to internal porosity is defined by a critical coherency limit of . In the second and third experimental sets, two Manganese-Steel (Mn-Steel) castings with different geometries are selected. Several thermocouples are placed at different locations in the sand molds and castings to capture the cooling of different parts during solidification. At the end of solidification, castings are sectioned to observe the porosity distributions on the cut surfaces. To develop alloys’ thermo-physical properties, MAGMAsoft (a casting simulation software package) is used for the thermal simulations. To assure that the thermal simulations are accurate, the properties are adjusted to get a good agreement between simulated and measured temperatures by thermocouples. Based on the knowledge obtained from the experimental observations, a mathematical model is developed for the prediction of shrinkage porosity in castings. The model, called “advanced feeding model”, includes 3D multi-phase continuity, momentum and pore growth rate equations which inputs the material properties and transient temperature fields, and outputs the feeding velocity, liquid pressure and porosity distributions in castings. To solve the model equations, a computational code with a finite-volume approach is developed for the flow calculations. To validate the model, predicted results are compared with the experimental data. The comparison results show that the advanced feeding model can accurately predict the occurrence of shrinkage porosity defects in metal castings. Finally, the model is optimized by performing several parametric studies on the model variables.
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9

Suntivich, Jin. "Interplay between electronic structure and catalytic activity in transition metal oxide model system." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76134.

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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 109-125).
The efficiency of many energy storage and conversion technologies, such as hydrogen fuel cells, rechargeable metal-air batteries, and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen electrochemical reactions. Transition-metal oxides can exhibit high catalytic activity for oxygen electrochemical reactions, which can be used to improve efficiency and cost of these devices. Identifying a catalyst "design principle" that links material properties to the catalytic activity can accelerate the development of highly active, abundant transition metal oxide catalysts fore more efficient, cost-effective energy storage and conversion system. In this thesis, we demonstrate that the oxygen electrocatalytic activity for perovskite transition metal oxide catalysts primarily correlates to the a* orbital ("eg") occupation. We further find that the extent of B-site transition metal-oxygen covalency can serve as a secondary activity descriptor. We hypothesize that this correlation reflects the critical influences of the a* orbital and transition metal-oxygen covalency on the ability of the surface to displace and stabilize oxygen-species on surface transition metals. We further propose that this ability to stabilize oxygen-species reflect as the rate-limiting steps of the oxygen electrochemical reactions on the perovskite oxide surfaces, and thus highlight the importance of electronic structure in controlling the oxide catalytic activity.
by Jin Suntivich.
Sc.D.
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10

Sawant, Ronit Prasad. "COMSOL Multi-physics model for Transition Metal Dichalcogenides (TMD’s)-Nafion composite Based Electromechanical Actuators." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/1261.

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The ability to convert electrical energy into mechanical motion is of significant interest in many energy conversion technologies. For more than a decade Ionic polymer-metal composite (IPMC) as an electroactive smart polymer material has been extensively studied and has shown great potential as soft robotic actuators, artificial muscles and dynamic sensors in the micro-to-macro size range. IPMC consists of an ion exchange polymer membrane sandwiched between two noble metal electrodes on either side of the membrane. Under applied potential, the IPMC actuator results in bending deformation because of ion migration and redistribution across its surface due to the imposed voltage. Nafion are highly porous polymer materials which have been extensively studied as the ion exchange membrane in IPMC. Nafion has also been mixed with carbon nanotubes, graphene, and metallic nanoparticles to improve actuation and bending characteristics of electro-mechanical actuators. For the first time, liquid phase exfoliated Transition Metal Dichalcogenides (TMDs)-Nafion nanocomposite based electro-mechanical actuators has been studied and demonstrate the improvement in the electromechanical actuation performance. In this thesis, we create a 2D model of the TMD-Nafion based electromechanical actuator in COMSOL Multi-physics software. The behavior of the model is examined at different electric potentials, frequencies, and actuation lengths. The simulation results were compared with the experimental data for validation of the model. The data showed improvement in the actuation for TMD-Nafion actuator when compared with pure Nafion actuator. The improvement in the actuation was due to the increase in diffusivity of the TMD-Nafion actuator in comparison with pure Nafion actuator. This increase in the diffusivity as seen in the model is because of the new proton conducting pathways being established with the addition of TMDs. The model also shows an increase in the stress and strain values with the incorporation of TMDs. With the same length of the actuator we were able to obtain more stress and strain with the addition of TMDs. This helps in improving the performance of the actuator as it would be able to handle more stress cycles which also increases the life of the actuator.
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11

Sheen, Paul David. "Towards a hybrid density functional theory and molecular mechanics model for large transition metal systems." Thesis, University of Bath, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296297.

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12

Bui, Phuong Phuc Nam. "Catalytic Hydrodeoxygenation of Bio-Oil Model Compounds (Ethanol, 2-Methyltetrahydrofuran) over Supported Transition Metal Phosphides." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/52641.

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The objective of this project is to investigate hydrodeoxygenation (HDO), a crucial step in the treatment of bio-oil, on transition metal phosphide catalysts. The study focuses on reactions of simple oxygenated compounds present in bio-oil -- ethanol and 2-methyltetrahydrofuran (2-MTHF). The findings from this project provide fundamental knowledge towards the hydrodeoxygenation of more complex bio-oil compounds. Ultimately, the knowledge contributes to the design of optimum catalysts for upgrading bio-oil. A series of transition metal phosphides was prepared and tested; however, the focus was on Ni2P/SiO2. Characterization techniques such as X-ray diffraction (XRD), temperature-programmed reduction and desorption (TPR and TPD), X-ray photoelectron spectroscopy (XPS), and chemisorption were used. In situ Fourier transform infrared (FTIR) spectroscopy was employed to monitor the surface of Ni2P during various experiments such as: CO and pyridine adsorption and transient state of ethanol and 2-MTHF reactions. The use of these techniques allowed for a better understanding of the role of the catalyst during deoxygenation.
Ph. D.
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13

Mottweiler, Jakob [Verfasser]. "Transition metal-catalyzed oxidative cleavage of lignin and lignin β-O-4 model compounds / Jakob Mottweiler." München : Verlag Dr. Hut, 2016. http://d-nb.info/1100968946/34.

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14

Gade, Lutz Hans. "The systematic build up and modification of high nuclearity osmium and osmium-mercury clusters and their role as model systems for small metal particles." Thesis, University of Cambridge, 1991. https://www.repository.cam.ac.uk/handle/1810/271913.

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15

Nájera, Ocampo Oscar. "Study of the dimer Hubbard Model within Dynamical Mean Field Theory and its application to VO₂." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS462/document.

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J'étudie en détail la solution d'un modèle simplifié d'électrons fortement corrélés, à savoir le modèle de Hubbard dimérisé. Ce modèle est la réalisation la plus simple d'un problème de cluster DMFT. Je fournis une description détaillée des solutions dans une région de coexistence où l'on trouve deux états (méta) stables des équations DMFT, l'un métallique et l'autre isolant. De plus, je décris en détail comment ces états disparaissent à leurs lignes critiques respectives. Je clarifie le rôle clé joué par la corrélation intra-dimère, qui agit ici en complément des corrélations de Coulomb.Je passe en revue la question importante du passage continue entre unisolant Mott et un isolant Peierls où je caractérise une variété de régimes physiques. Dans un subtil changement de la structure électronique, lesbandes de Hubbard évoluent des bandes purement incohérentes (Mott) à desbandes purement cohérentes (Peierls) à travers un état inattendu au caractère mixte. Je trouve une température d'appariement singulet T* en-dessous de laquelle les électrons localisés à chaque site atomique peuvent se lier dans un singulet et minimiser leur entropie. Ceci constitue un nouveau paradigme d'un isolant de Mott paramagnétique.Enfin, je discute la pertinence de mes résultats pour l'interprétation de différentes études expérimentales sur VO₂. Je présente plusieurs arguments qui me permettent d'avancer la conclusion que la phase métallique, à vie longue (métastable) induite dans les expériences pompe-sonde, et l'état métallique métastable M₁, thermiquement activé dans des nano-domaines, sont identiques. De plus, ils peuvent tous être qualitativement décrits, dans le cadre de notre modèle, par un métal corrélé dimérisé
We study in detail the solution of a basic strongly correlated model,namely, the dimer Hubbard model. This model is the simplest realization ofa cluster DMFT problem.We provide a detailed description of the solutions in the ``coexistentregion'' where two (meta)stable states of the DMFT equations are found, onea metal and the other an insulator. Moreover, we describe in detail howthese states break down at their respective critical lines. We clarify thekey role played by the intra-dimer correlation, which here acts in additionto the onsite Coulomb correlations.We review the important issue of the Mott-Peierls insulator crossoverwhere we characterize a variety of physical regimes. In a subtle change inthe electronic structure the Hubbard bands evolve from purely incoherent(Mott) to purely coherent (Peierls) through a state with unexpected mixedcharacter. We find a singlet pairing temperature T* below which thelocalized electrons at each atomic site can bind into a singlet and quenchtheir entropy, this uncovers a new paradigm of a para-magnetic Mottinsulator.Finally, we discuss the relevance of our results for the interpretation ofvarious experimental studies in VO₂. We present a variety of argumentsthat allow us to advance the conclusion that the long-lived (meta-stable)metallic phase, induced in pump-probe experiments, and the thermallyactivated M₁ meta-stable metallic state in nano-domains are the same.In fact, they may all be qualitatively described by the dimerizedcorrelated metal state of our model
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16

Mottweiler, Jakob Verfasser], Carsten [Akademischer Betreuer] [Bolm, and Walter [Akademischer Betreuer] Leitner. "Transition metal-catalyzed oxidative cleavage of lignin and lignin β-O-4 model compounds / Jakob Mottweiler ; Carsten Bolm, Walter Leitner." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1129875717/34.

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17

Mottweiler, Jakob [Verfasser], Carsten [Akademischer Betreuer] Bolm, and Walter [Akademischer Betreuer] Leitner. "Transition metal-catalyzed oxidative cleavage of lignin and lignin β-O-4 model compounds / Jakob Mottweiler ; Carsten Bolm, Walter Leitner." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1129875717/34.

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18

Li, Chunhua. "Gutzwiller Approximation in Strongly Correlated Electron Systems." Thesis, Boston College, 2009. http://hdl.handle.net/2345/917.

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Thesis advisor: Ziqiang Wang
Gutzwiller wave function is an important theoretical technique for treating local electron-electron correlations nonperturbatively in condensed matter and materials physics. It is concerned with calculating variationally the ground state wave function by projecting out multi-occupation configurations that are energetically costly. The projection can be carried out analytically in the Gutzwiller approximation that offers an approximate way of calculating expectation values in the Gutzwiller projected wave function. This approach has proven to be very successful in strongly correlated systems such as the high temperature cuprate superconductors, the sodium cobaltates, and the heavy fermion compounds. In recent years, it has become increasingly evident that strongly correlated systems have a strong propensity towards forming inhomogeneous electronic states with spatially periodic superstrutural modulations. A good example is the commonly observed stripes and checkerboard states in high-$T_\mathrm c$ superconductors under a variety of conditions where superconductivity is weakened. There exists currently a real challenge and demand for new theoretical ideas and approaches that treats strongly correlated inhomogeneous electronic states, which is the subject matter of this thesis. This thesis contains four parts. In the first part of the thesis, the Gutzwiller approach is formulated in the grand canonical ensemble where, for the first time, a spatially (and spin) unrestricted Gutzwiller approximation (SUGA) is developed for studying inhomogeneous (both ordered and disordered) quantum electronic states in strongly correlated electron systems. The second part of the thesis applies the SUGA to the $t$-$J$ model for doped Mott insulators which led to the discovery of checkerboard-like inhomogeneous electronic states competing with $d$-wave superconductivity, consistent with experimental observations made on several families of high-$T_{\mathrm c}$ superconductors. In the third part of the thesis, new concepts and techniques are developed to study the Mott transition in inhomogeneous electronic superstructures. The latter is termed ``SuperMottness'' which is shown to be a general framework that unifies the two paradigms in the physics of strong electronic correlation: Mott transition and Wigner crystallization. A cluster Gutzwiller approximation (CGA) approach is developed that treats the local ($U$) and extended Coulomb interactions ($V$) on equal footing. It is shown with explicit calculations that the Mott-Wigner metal-insulator transition can take place far away from half-filling. The mechanism by which a superlattice potential enhances the correlation effects and the tendency towards local moment formation is investigated and the results reveal a deeper connection among the strongly correlated inhomogeneous electronic states, the Wigner-Mott physics, and the multiorbital Mott physics that can all be united under the notion of SuperMottness. It is proposed that doping into a superMott insulator can lead to coexistence of local moment and itinerant carriers. The last part of the thesis studies the possible Kondo effect that couples the local moment and the itinerant carriers. In connection to the sodium rich phases of the cobaltates, a new Kondo lattice model is proposed where the itinerant carriers form a Stoner ferromagnet. The competition between the Kondo screening and the Stoner ferromagnetism is investigated when the conduction band is both at and away from half-filling
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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19

Hans, Marcus [Verfasser], Jochen M. [Akademischer Betreuer] Schneider, and Christian [Akademischer Betreuer] Mitterer. "Metastable cubic transition metal aluminium nitride and oxynitride coatings: Theoretical phase stability and defect structure predictions and verification by industrial-scale growth experiments / Marcus Hans ; Jochen Michael Schneider, Christian Mitterer." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162451203/34.

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20

Haupricht, Tim Jakobus Thomas [Verfasser], L. H. [Akademischer Betreuer] Tjeng, and T. [Akademischer Betreuer] Michely. "Transition metal impurities in wide bandgap oxides: fundamental model systems for strongly correlated oxides / Tim Jakobus Thomas Haupricht. Gutachter: L. H. Tjeng ; T. Michely." Köln : Universitäts- und Stadtbibliothek Köln, 2011. http://d-nb.info/1038168260/34.

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21

Andrews, Lesley. "Base metal losses to furnace slag during processing of platinum-bearing concentrates." Diss., Pretoria : [s.n.], 2008. http://upetd.up.ac.za/thesis/available/etd-01222009-172643/.

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22

Sobotta, Jessica [Verfasser], Wolfgang [Akademischer Betreuer] Eisenreich, Dieter [Gutachter] Braun, and Wolfgang [Gutachter] Eisenreich. "Investigations of carbon fixation in model organisms and in cell-free prebiotic transition metal-catalyzed reactions / Jessica Sobotta ; Gutachter: Dieter Braun, Wolfgang Eisenreich ; Betreuer: Wolfgang Eisenreich." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1165227533/34.

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23

Ben, Salem Azzedine. "Synthese et caracterisation physique et structurale des conducteurs unidimensionnels de type fe : :(1+x)nb::(3-x)se::(10)." Nantes, 1987. http://www.theses.fr/1987NANT2018.

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Ce compose est le prototype d'une serie de formulation (mm')nb::(2)s::(10)(mm' = fe,v,cr,nb,ta) presentant une chaine trigonale prismatique |nbse::(3)| et une double chaine oelaedrique |(mm')se::(6)|. Ces composes ont une transition metal isolant vers 140 k. L'observation d'une onde de densite de charge aux caracteristiques identiques a celles de nbse::(3) indique que la chaine conductrice est la chaine trigonale prismatique |nbse::(3)|. La variation de la conductivite au voisinage de la transition indique un mecanisme de localisation d'anderson. Les proprietes physiques du compose ou se a ete substitue par s ont ete etudiees. L'etude de l'insertion par li a ete effectuee
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24

Sinjukow, Peter. "A model study for Eu-rich EuO." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97419137X.

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25

Benkaddour, Abdelkhalek. "Proprietes des defauts d'irradiation dans des alliages austenitiques fer-chrome-nickel et des alliages ferritiques fer-chrome : influence de la teneur en chrome." Paris 6, 1987. http://www.theses.fr/1987PA066144.

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Etude par mesure de resistivite electrique, de l'influence de la teneur en chrome sur la production et la migration des defauts ponctuels dans les alliages fe-25%ni-8 a 16%cr(% en poids) et fe-5 a 15%atcr soumis a une irradiation par electrons a 21k. Influence d'un recuit sur ces defauts d'irradiation. Interpretation des resultats par un modele de restauration
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26

Watanabe, T., H. Yokoyama, Y. Tanaka, and J. Inoue. "Predominant magnetic states in the Hubbard model on anisotropic triangular lattices." American Physical Society, 2008. http://hdl.handle.net/2237/11256.

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27

Sarrazin-Baudoux, Christine. "Etude du mixage ionique dans un système à grande limite de solubilité : cas du Cuivre-Nickel, caractérisation de l'adhérence de ces revêtements sur substrat acier." Poitiers, 1987. http://www.theses.fr/1987POIT2305.

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Elaboration de la technique de melange ionique associant l'evaporation de couches minces successives et l'implantation ionique. Etude du melange ionique des multicouches cu-ni. Mise en evidence de deux phenomenes principaux de diffusion en fonction de la temperature. Analyse des phases formees lors du melange ionique. Application de la technique de melange ionique comme procede de depot
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28

Madouri, Ali. "Heterodiffusion du manganese dans la wuestite : fe1-y o::(-)." Paris 7, 1987. http://www.theses.fr/1987PA077285.

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Les coefficients de diffusion de mn dans feo sont mesures en fonction de la temperature (700**(o)c-1100**(o)c) pour quatre valeurs du rapport r=pco::(2)(pco (r=0,7; 1,0; 1,8; 2,5). Les coefficients de diffusion du manganese sont systematiquement plus eleves que les coefficients d'autodiffusion du fer pris dans la litterature (chen et peterson, 1973) a cause de l'energie d'activation de d::(mn) plus faible que celle de d::(fe). Les resultats de diffusion d'interpretent en termes d'interactions attractives entre les lacunes et les atomes de manganese
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29

Duc, Nguyen Manh. "Approche électronique de l'ordre local dans les alliages à base de métaux de transition." Grenoble 1, 1986. http://www.theses.fr/1986GRE10072.

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Modèle de calcul de l'énergie électronique des alliages à base de métaux de transition. Ce modèle est base sur un hamiltonien de liaisons fortes et prend en compte les effets d'hybridation s-d. Calcul de la densité d'états électroniques et des énergies de cohésion. Pour les alliages amorphes de deux métaux de transition, un ordre chimique local est établi. Conséquences sur la densité d'états électronique. Corrélation entre structure électronique et coefficient de hall. Mise en évidence d'une forte hybridation sp-d pour les alliages entre métaux de transition et métaux polyvalents
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30

Maurice, Vincent. "Contribution a l'etude du desordre dans les monocouches chimisorbees." Paris 6, 1987. http://www.theses.fr/1987PA066518.

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Interpretation, a l'aide d'une methode informatisee de type "monte carlo", des diagrammes de diffraction des electrons lents de couches chimisorbees et modelisation des caracteristiques structurales bidimensionnelles liees au desordre. Application au soufre chimisorbe sur des faces de bas indices de metaux de transition
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31

Thum, Lukas [Verfasser], Reinhard [Akademischer Betreuer] Schomäcker, Reinhard [Gutachter] Schomäcker, Robert [Gutachter] Schlögl, and Evgenii [Gutachter] Kondratenko. "Transition metal-doped calcium oxide as model catalyst for the oxygen activation in the oxidative coupling of methane (OCM) reaction / Lukas Thum ; Gutachter: Reinhard Schomäcker, Robert Schlögl, Evgenii Kondratenko ; Betreuer: Reinhard Schomäcker." Berlin : Technische Universität Berlin, 2020. http://d-nb.info/1223981290/34.

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32

Jacquet, Quentin. "Li-rich Li3MO4 model compounds for deciphering capacity and voltage aspects in anionic redox materials." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS332.

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Le réchauffement climatique, provoqué par l’augmentation de la concentration de CO2 dans l’atmosphère, est un problème majeur du 21ème siècle. C’est pourquoi, il est d’une importance capitale de valoriser l’utilisation des énergies renouvelables et des technologies de stockage d’énergie telles que les batteries Li-ion. Suivant ce but, les chercheurs ont mis au point un nouveau matériau d’électrode, le Li-rich NMC, dont l’utilisation permet d’augmenter significativement la capacité des batteries Li-ion grâce à la participation des oxygènes de l’oxyde dans la réaction électrochimique. Cependant, ce nouveau phénomène va de pair avec une hystérésis de potentiel qui empêche la commercialisation du Li-rich NMC. Afin de proposer une solution à l’hystérésis de potentiel tout en continuant à augmenter la capacité des électrodes, des études fondamentales sont nécessaires, notamment: la redox anionique a-t-elle une limite de capacité ? et, quelle est l’origine de l’hystérésis ? Pour répondre à la première question, nous avons conçu des matériaux, de composition chimique A3MO4 (A étant du Li ou Na, et M un mix de Ru, Sb, Nb, Ta ou Ir), ayant une redox anionique exacerbée. Après avoir caractérisé la structure de ces nouveaux matériaux, nous avons étudié leur mécanisme électrochimique et montré que la redox anionique est limitée par la décomposition de l’électrode via formation de O2 ou dissolution. Dans un second temps, par l’étude de deux nouveaux matériaux, Li1.3Ni0.27Ta0.43O2 et Li1.3Mn0.4Ta0.3O2 ayant des hystérésis de potentiel très différentes, nous avons montré le lien entre la redox anionique, la taille de la bande interdite, et l’hystérésis de potentiel
Global warming, due to the increasing CO2 concentration in the atmosphere, is a major issue of the 21th century, hence the need to move towards the use of renewable energies and the development of electrical storage devices, such as Li-ion batteries. Along that line, a new electrode material called Li-rich NMCs have been developed, having higher capacity, 290 mAh/g, than commercial materials, like LiCoO2 (150 mAh/g), thanks to participation of oxygen anions into the redox reaction. This process, called anionic redox, unfortunately comes with voltage hysteresis preventing the commercialization of Li-rich NMC. To alleviate this issue while increasing the capacity, fundamental understanding on anionic redox is needed, specifically concerning two points: is anionic redox limited in terms of capacity? And what is the origin of the voltage hysteresis? In a first part, with the aim to assess the limit of anionic redox capacity, we designed new compounds, having enhanced oxygen oxidation behavior, belonging to the A3MO4 family (A being Li or Na and with M a mix of Ru, Ir, Nb, Sb or Ta). We performed their synthesis, deeply characterized their structure, and, by studying their charge compensation mechanism, we showed that anionic redox is always limited by either O2 release or metal dissolution. In a second part, we designed two new materials, Li1.3Ni0.27Ta0.43O2 and Li1.3Mn0.4Ta0.3O2, having different voltage hysteresis, in order to identify the origin of this phenomenon. Coupling spectroscopic techniques with theoretical calculations, we suggest that the electronic structure, namely the size of the charge transfer band gap, plays a decisive role in voltage hysteresis
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33

Sugimoto, Koudai. "Theoretical Study of Electron Dynamics in Multi-Orbital Antiferromagnetic Metals." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199089.

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34

Schmitt, Miriam. "Microscopic description of magnetic model compounds." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-110282.

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Solid state physics comprises many interesting physical phenomena driven by the complex interplay of the crystal structure, magnetic and orbital degrees of freedom, quantum fluctuations and correlation. The discovery of materials which exhibit exotic phenomena like low dimensional magnetism, superconductivity, thermoelectricity or multiferroic behavior leads to various applications which even directly influence our daily live. For such technical applications and the purposive modification of materials, the understanding of the underlying mechanisms in solids is a precondition. Nowadays DFT based band structure programs become broadly available with the possibility to calculate systems with several hundreds of atoms in reasonable time scales and high accuracy using standard computers due to the rapid technical and conceptional development in the last decades. These improvements allow to study physical properties of solids from their crystal structure and support the search for underlying mechanisms of different phenomena from microscopic grounds. This thesis focuses on the theoretical description of low dimensional magnets and intermetallic compounds. We combine DFT based electronic structure and model calculations to develop the magnetic properties of the compounds from microscopic grounds. The developed, intuitive pictures were challenged by model simulations with various experiments, probing microscopic and macroscopic properties, such as thermodynamic measurements, high field magnetization, nuclear magnetic resonance or electron spin resonance experiments. This combined approach allows to investigate the close interplay of the crystal structure and the magnetic properties of complex materials in close collaboration with experimentalists. In turn, the systematic variation of intrinsic parameters by substitution or of extrinsic factors, like magnetic field, temperature or pressure is an efficient way to probe the derived models. Especially pressure allows a continuous change of the crystal structure on a rather large energy scale without the chemical complexity of substitution, thus being an ideal tool to consistently alter the electronic structure in a controlled way. Our theoretical results not only provide reliable descriptions of real materials, exhibiting disorder, partial site occupation and/or strong correlations, but also predict fascinating phenomena upon extreme conditions. In parts this theoretical predictions were already confirmed by own experiments on large scale facilities. Whereas in the first part of this work the main purpose was to develop reliable magnetic models of low dimensional magnets, in the second part we unraveled the underlying mechanism for different phase transitions upon pressure. In more detail, the first part of this thesis is focused on the magnetic ground states of spin 1/2 transition metal compounds which show fascinating phase diagrams with many unusual ground states, including various types of magnetic order, like helical states exhibiting different pitch angles, driven by the intimate interplay of structural details and quantum fluctuations. The exact arrangement and the connection of the magnetically active building blocks within these materials determine the hybridization, orbital occupation, and orbital orientation, this way altering the exchange paths and strengths of magnetic interaction within the system and consequently being crucial for the formation of the respective ground states. The spin 1/2 transition metal compounds, which have been investigated in this work, illustrate the great variety of exciting phenomena fueling the huge interest in this class of materials. We focused on cuprates with magnetically active CuO4 plaquettes, mainly arranged into edge sharing geometries. The influence of structural peculiarities, as distortion, folding, changed bonding angles, substitution or exchanged ligands has been studied with respect to their relevance for the magnetic ground state. Besides the detailed description of the magnetic ground states of selected compounds, we attempted to unravel the origin for the formation of a particular magnetic ground state by deriving general trends and relations for this class of compounds. The details of the treatment of the correlation and influence of structural peculiarities like distortion or the bond angles are evaluated carefully. In the second part of this work we presented the results of joint theoretical and experimental studies for intermetallic compounds, all exhibiting an isostructural phase transition upon pressure. Many different driving forces for such phase transitions are known like quantum fluctuations, valence instabilities or magnetic ordering. The combination of extensive computational studies and high pressure XRD, XAS and XMCD experiments using synchrotron radiation reveals completely different underlying mechanism for the onset of the phase transitions in YCo5, SrFe2As2 and EuPd3Bx. This thesis demonstrates on a series of complex compounds that the combination of ab-initio electronic structure calculations with numerical simulations and with various experimental techniques is an extremely powerful tool for a successful description of the intriguing quantum phenomena in solids. This approach is able to reduce the complex behavior of real materials to simple but appropriate models, this way providing a deep understanding for the underlying mechanisms and an intuitive picture for many phenomena. In addition, the close interaction of theory and experiment stimulates the improvement and refinement of the methods in both areas, pioneering the grounds for more and more precise descriptions. Further pushing the limits of these mighty techniques will not only be a precondition for the success of fundamental research at the frontier between physics and chemistry, but also enables an advanced material design on computational grounds.
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35

Bessoud, Agnès. "Analyse des interactions dans des alliages à base de métaux de transition." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0091.

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Calcul, a partir d'un hamiltonien de liaisons fortes et de la methode de l'amas-reseau de bethe, de la structure electronique et l'energie de formation d'alliages binaires de structure cubique centree ou cubique a faces centrees. En utilisant l'entropie de configuration traitee par la methode variationnelle des amas, l'energie libre de formation a ete obtenue par minimisation par rapport au parametre d'ordre a courte distance
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36

Darbieu, Marie-Hélène. "Complexes modeles de la methylcobalamine (meb12) : comportement de la liaison co-c en presence de derives de l'etain iv." Toulouse 3, 1987. http://www.theses.fr/1987TOU30148.

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37

Lombardo, Pierre. "Théorie de champ moyen dynamique appliquée à l'étude des propriétés électroniques des oxydes de métaux de transition." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10161.

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Nous avons propose une approche susceptible d'expliquer de nombreuses proprietes electroniques des materiaux dont les porteurs de charge sont soumis a de fortes correlations. Parmi les materiaux consideres, citons en particulier les supraconducteurs a haute temperature critique et les oxydes de metaux de transition de type perovskite. L'approche developpee dans cette these est une extension de la theorie de champ moyen dynamique a des systemes electroniques a plus de un degre de liberte orbital. Elle est basee sur une nouvelle procedure de renormalisation du modele de hubbard a deux bandes pour l'extension aux grandes dimensions spatiales de la structure perovskite. Un traitement selectif des differents processus de sauts entre sites de metal de transition (mt) et d'oxygene (o) plus proche voisins, nous a permis de conserver de nombreux aspects dynamiques non triviaux dans cette limite. Le probleme sur reseau est projete sur un modele d'impurete de type anderson. La solution du probleme local a ete obtenue par la theorie des perturbations iterees et par une extension de l'approximation de non-crossing (nca). La technique de nca nous a permis de decrire correctement d'importantes proprietes spectrales des oxydes de metaux de transition, donnant des informations tres interessantes sur la nature des differentes bandes des densites d'etats du metal de transition et de l'oxygene, et sur leur comportement en fonction du dopage. De plus, le pic coherent de quasiparticule, proche du niveau de fermi, a ete obtenu. Ce pic presente d'interessantes variations en fonction du dopage, mais aussi de la temperature. Ces excitations de basse energie proviennent de resonances de type kondo, entre l'etat vide et un etat hybride mt-o dans le cas du dopage en electrons, et entre cet etat mt-o et un etat singulet de type zhang et rice dans le cas du dopage en trous. L'application de notre approche nca a des familles de materiaux reels comme lamo#3 ou ca#1##xsr#xvo#3 a mis en evidence l'importance fondamentale des excitations a transfert de charge dans ces composes. Une description correcte des proprietes electroniques des oxydes de metaux de transition peut donc etre donnee par une approche de champ moyen dynamique mais necessite la prise en compte a la fois des etats de l'oxygene et de ceux du metal de transition.
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38

Bouillaud, Pascal. "Irradiation aux ions lourds de films minces nanocristallins d'alliages FeCo et FeAl." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37612171v.

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39

Fabregue, Pascal. "Debut de propagation de fissures de fatigue dans un superalliage base nickel de metallurgie des poudres." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0033.

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Etude des proprietes de fatigue des superalliages contenant des inclusions de type ceramique. Determination, a temperature ambiante, des cinetiques de debut de propagation de fissures a partir des defauts presents dans la structure. Mise en evidence, d'un effet de "fissure courte". Il est demontre que deux parametres jouent un role, essentiel dans la differenciation des cinetiques de propagation des fissures courtes et longues : le caractere tridimentionnel des fissures naturelles et le phenomenes de fermeture de fissures
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40

VALADE, FARGES LYDIE. "Conducteurs et supraconducteur moleculaires : complexes de metaux de transition a ligand soufre." Toulouse 3, 1987. http://www.theses.fr/1987TOU30008.

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Etude des proprietes electriques et structurales de deux series de composes a coordinat dmit : composes a etat d'oxydation fractionnaire (m(dmit)::(2))c::(x) et composes donneur-accepteur d(m(dmit)::(2))::(y) (avec m = zn,ni,pt,pd; c = nbu**(+)::(4) et asph**(+)::(4); d = ttf, tmttf, ttmttf, bedt-ttf et tmtsf; n dans (m(dmit)::(2))**(n-) etant egal a 2,1,x,0). Mise en evidence de la nature 2d des composes de la premiere serie et quasi 3d de ceux de la deuxieme; relations structure-conductivite. Mise en evicence de la supraconduction dans le cas du complexe ttf(ni(dmit)::(2))::(2), avec une temperature de transition de 1,62 k sous 7 kbar
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41

Andrieu, Eric. "Influence de l'environnement sur la propagation des fissures dans un superalliage base nickel : l'inconel 718." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376022112.

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42

HAMID-SAMIMI, MOHAMMAD-HASSAN. "Etude et caracterisation des defauts microscopiques du tellure de cadmium." Strasbourg 1, 1989. http://www.theses.fr/1989STR13009.

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Les niveaux des defauts dans la bande interdite du semiconducteur sont etudies ainsi que les phenomenes de transport et les proprietes optiques. On note des effets remarquables de passivation et de modification des defauts par hydrogenation
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43

Li, Zhigang. "Formation et simulation de l'image en microscopie electronique a haute resolution : application a la structure de composes de type "lamellaire"." Toulouse 3, 1987. http://www.theses.fr/1987TOU30282.

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Cette these etudie trois problemes specifiques de la microscopie electronique a haute resolution : le transfert du contraste des images, leur interpretation au moyen de simulations et l'application de cette technique a la determination des structures locales dans les materiaux cristallins, au niveau atomique. Obtention de resultats originaux en ce qui concerne la microstructure de materiaux de type lamelllaire : dans les composes de type re::(6) se::(8) cl::(2), avant et apres insertion d'hydrazine, dans les composes de type mps::(3) et dans taps::(6)se
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44

Belaiche, Mohammed. "Correlations entre structure et proprietes magnetiques des systemes unidimensionnels a empilements exotiques d'ions cu**(2+) et (vo)**(2+)." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13041.

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Correlations entre structure et proprietes magnetiques de systemes unidimensionnels caracterises par des empilements exotiques de metaux de transition tels des phosphates et des sulfates de vanadium et de cuivre. Les chaines ferro ou antiferromagnetiques se sont revelees adaptees a l'etude des correlations magnetostructurales. L'influence de la competition entre diverses interactions est traitee en particulier dans le cas de la frustration 1d. Un traitement quantique est developpe pour l'analyse des proprietes thermodynamiques de composes nouveaux de formule voh(po::(4)), 4h::(2)o; cu::(2)oso::(4), acu::(3)(po::(4))::(4), avec a=ca, sr et cu::(3)(po::(4))::(2)
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45

El-Hage, Jaoudat. "Dynamique des spins electroniques dans deux unidimensionnels : le chac et le chab." Toulouse 3, 1987. http://www.theses.fr/1987TOU30200.

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Variation angulaire de la largeur de raie rpe, de facteur g en bande x pour c::(6)h::(11)nh::(3)cux::(3), pour x = cl, br. Mesure de la vitesse de relaxation longitudinale par la methode de modulation, effet d'un dopage par mn**(2+). Interpretation par les differentes interactions de spins
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46

Berroudji, Sid-Ahmed. "Cinétiques de mise en ordre à courte distance et caractéristiques des lacunes et des autointerstitiels dans des alliages [gamma]-FeNiCr." Grenoble 1, 1988. http://www.theses.fr/1988GRE10095.

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Etude des cinetiques de mise en ordre dans les alliages fe::(59)ni::(25)cr::(16) et fe::(9)ni::(75)cr::(16) par mesure de resistivite electrique. Determination des caracteristiques des lacunes et autointerstitiels par les techniques de trempe a l'helium liquide, de mesure de resistivite lors des cycles alternes de chauffage et de trempe ou lors de cycles continus. Evaluation des enthalpies de formation, de migration et d'autodiffusion. Influence de la composition. Analyse des sursaturations dynamiques de defauts lors de l'irradiation. Determination des frequences de saut des autointerstitiels et de leur enthalpie en fonction de la composition chimique
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47

Fritz, Serge. "Etude des defauts ponctuels dans le mononitrure d'uranium par diffusion, trempe et canalisation apres bombardement ionique." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13184.

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La nature et le comportement des defauts ponctuels thermiques et des defauts d'irradiation dans le mononitrure d'uranium ont ete etudies. Les defauts thermiques ont ete etudies par trempe et une technique de diffusion de traceur a servi a mesurer la diffusivite de l'uranium. L'effet de la pression d'azote sur l'auto-diffusion de l'uranium suggere un mecanisme lacunaire. Une etude de canalisation et de microscopie electronique d'echantillons implantes avec des ions a permis de comprendre le dommage d'irradiation et sa restauration thermique
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48

Guergouri, Kamel. "Etude des defauts cristallins et des proprietes physiques associees dans cdte et ses alliages avec znte, mnte." Paris 6, 1987. http://www.theses.fr/1987PA066412.

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Etude de l'amelioration de cdte dans le cadre de la recherche de semiconducteurs de bonne qualite cristalline. Le premier parametre necessaire a cette amelioration et celui de la substitution de cd par zn (impurete isoelectronique et permet la reduction de la densite de dislocations d'un facteur 10. Proposition d'un modele de durcissement d'alliage pour expliquer ce phenomene. Le 2eme parametre concerne la recherche des conditions de croissance optimales
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49

Chieragatti, Rémy. "Influence de l'orientation cristallographique sur le comportement en fatigue oligocyclique du mar-m200 monocristallin." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0024.

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Etude experimentale sur le superalliage soumis a une charge cyclique uniaxiale suivant la direction de croissance 001 et les orientations 111, 011 et 123 a 650 c et 900c. Analyse des courbes d'ecrouissage cyclique. Caracterisation des systemes de glisement associes aux grandes deformations plastiques. Description par un modele de l'influence quantitative de l'orientation sur les courbes, d'ecrouissage cyclique. Mise en evidence du role preponderant de la periode de propagation des fissures sur l'endommagement. Prevision theorique de la duree de vie en fatigue en utilisant des donnees de fissuration etablies pour une orientation donnee
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50

Mayou, Didier. "Contribution à l'étude de la structure électronique et du transport dans les systèmes métalliques désordonnés." Grenoble 1, 1987. http://www.theses.fr/1987GRE10167.

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Developpement d'un modele pour etudier certains effets du couplage entre bandes differentes sur la structure electronique et le transport. Consequences sur les proprietes physiques. Correlation entre la structure electronique et le signe du coefficient de hall r::(h). Calcul de r::(h) pour cu::(x)(zr,ti,hf)::(1-x). Developpement de nouvelles applications des methodes d'espace direct du type recursion
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