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Hampson, Matthew Richard. "Structure and dynamics in framework materials." Thesis, Durham University, 2007. http://etheses.dur.ac.uk/1999/.
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This thesis details a study of framework materials of the AM2O8 and AM2O7 families, which are of interest due to their unusual thermal expansion properties, phase transitions and often complex structures. The combination of results from NMR and diffraction techniques has enabled several new insights into the structure and dynamics to be made. Chapter 1 reviews the literature on negative thermal expansion materials that are of relevance to this project. Chapter 2 outlines the background to the key experimental techniques employed in this work. Chapter 3 outlines 17O isotopic enrichment techniques and qualitative results for several AM2O8 phases. 17O NMR results for cubic ZrW2O8 including variable temperature spectra and 2DExchange Spectroscopy (EXSY) are presented. The a / ß phase transition and low temperature oxygen mobility in ZrW2O8 are investigated. NMR results enabled the determination of a mechanism of oxygen exchange different to the previously suggested mechanism, which is disproved. The results of in situ diffraction experiments to investigate phase transitions inZrMo2O8 are also presented. 17O enriched samples of cubic-, trigonal- and LT- ZrMo2O8 samples were prepared, and their 17O NMR spectra recorded. Chapter 4 describes quantitative 17O NMR studies used to characterise oxygen dynamics inZrW2O8. The results of a range of NMR experiments, including a combination of 1D EXSY and saturation recovery experiments, are interpreted to give a measure of the rate and the activation energy for oxygen exchange. The experiments and derivation of the required theoretical background are detailed. Chapter 5 outlines a range of structural studies on AM2O7 materials. The room temperature superstructure of HfP2O7 is determined using a combination of X-Ray and neutron diffraction.31P NMR is reported for the high temperature phases of HfP2O7 and ZrP2O7 for the first time. The symmetry of the high temperature phase of HfP2O7 is investigated by Rietveld refinement of neutron diffraction data. Unusual effects in the 51V NMR spectra of HfV2O7 and ZrV2O7 are also reported. Chapter 6 outlines preliminary work on computational methods to investigate the structural dependence of the 31P NMR chemical shift of pyrophosphate materials. DFT calculations of NMR parameters were carried out, and a methodology developed for the derivation of suitable theoretical model structures.
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Roeder, H. "Defects and dynamics of modulated structure materials." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375323.
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Dong, Jingwei. "Electron dynamics in layered materials." Thesis, Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAX019.
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Actuellement,les matériaux lamellaires suscitent un grand intérêt en raison de leurs propriétés électriques et optiques.On peut dire que le domaine de recherche des matériaux à basse dimensionnalité a été initié par la découverte du graphène et c’est rapidement élargi à d'autres matériaux comme les dichalcogénures de métaux de transition,le phosphore noir et le séléniure d'indium.Nos travaux portent sur la dynamique des états excités dans ces composés,ainsi que sur l'évolution de la structure des bandes lors d’un fort dopage de surface.Le manuscrit est organisé comme suit :Lechapitre1 est une introduction générale sur les matériaux lamellaires.En particulier,nous discutons des propriétés structurelles et électroniques des composés plus connus.Lechapitre2 décrit les principes de fonctionnement de la spectroscopique ultra-rapides et montre nombreuses applications sur des matériaux lamellaires.Nous attirons principalement l’attention sur la dynamique des électrons dans les cristaux semi-conducteurs ou avec onde de densité de charge.Lechapitre3 illustre la technique expérimentale que nous avons employée et l’enceinte dans lequel nous avons effectuées les mesures.La dynamique des électrons des matériaux lamellaires a été étudiée au moyen de la spectroscopie photoélectronique résolue en temps et en angle,qui est un outil puissant pour cartographier la structure des bandes électronique et pour suivre la dynamique des électrons photo-injectés via une source laser ultra-rapide. La discussion des données originales de notre travail débute dans lechapitre4.Les mesures TrARPES sur le phosphore noir suivent la distribution électronique dans la bande de conduction en fonction du délai temporale par rapport à l’instant de la photoexcitation.Nos données montrent qu'après thermalisation,les électrons photo-injectés ne produisent pas une diminution de bande d’énergie interdite,ni génèrent-ils une multiplication appréciable du nombre des porteurs.D'autre part,un élargissement Stark de la bande de valence est due à l’écrantage inhomogène d'un potentiel local autour de défauts chargés.Lechapitre5 présente les données ARPES résolues en temps sur une surface de phosphore noir dopée in situ par évaporation des métaux alcalins.Nous mesurons l'effondrement de la bande interdite dans la couche d'accumulation électronique avec une précision inédite et nous observons des états enterrés qui sont détectable à cause de la faible énergie de photons dans notre sonde.Ces états acquièrent une vitesse de bande étonnamment élevée quand la concentration de dopants augmente.Lechapitre6 montre la modification de la dynamique des porteurs chauds lors de la variation du dopage de surface de BP.Dans ce cas, l'analyse proposé est encore préliminaire et doit être complémenté par des calculs ab-initio.Lechapitre7 contient notre travail sur le composé ɛ-InSe.Comme dans le cas de phosphore noir, nous générons une couche d'accumulation de densité électronique variable à la surface du semi-conducteur.En variant le niveau de dopage à partir du limite semi-conducteur jusqu’au limite métallique,nous observons que l’écrantage quantique des phonons optiques longitudinaux n'est pas aussi efficace qu'il le serait dans un système strictement bidimensionnel.Ce résultat indique la présence d’un couplage à distance entre les états confinés à la surface et les phonons polaires du volume.Dans lechapitre8,nous étudions le 1T-TaS2.Ce matériau appartient aux systèmes d'ondes de CDW et a été largement étudié par plusieurs équipes de chercheurs.Dans le 1T-TaS2,la combinaison d'une distorsion structurelle avec des fortes corrélations électroniques conduit à un diagramme de phase complexe et fascinant.Nous reproduisons des données controversées qui ont été récemment publiées dans la littérature et qui identifient une nouvelle instabilité en proximité de la transition métal-isolant.Enfin,lechapitre9 résume les conclusions de nos résultats et aborde brièvement les orientations de recherche à venirCurrently,layered materials attract great interest due to their electrical and optical properties. Such crystals display an electronic band structure that strongly depends on the sample thickness.The large tunability of the electronic screening and gap size can be very attracting for the creation of heterostructures whose properties can be designed on demand. We can say that the research field of low dimensional materials has been boosted by the discovery of graphene and quickly has been enlarged to other materials as transition metal dichalcogenides,black phosphorous and Indium selenide.Our work will focus on the excited state dynamics in these compounds,as well as on the evolution of the band structure upon surface doping.The manuscript is organized as follow:Chapter1 provides a general introduction of layered materials.In particular,we discuss the structural and electronic properties of some relevant compounds.Chapter2 describes the principles of ultrafast spectroscopic methods and shows many applications to the case of the layered materials.We mainly focus our attention on the electron dynamics in semiconducting crystals and charge density waves systems. The electron dynamics of layered materials have been investigated by means of time-and angle-resolved photoelectron spectroscopy (TrARPES),which is a powerful tool to directly map the electronic band structure and to follow the dynamics of the electrons photoinjected via an ultrafast laser source.Chapter3 discusses the experimental technique of choice and the setup where we have been performed in the reported measurements.we begin the discussion of our original data in Chapter4.The TrARPES measurements of layered black phosphorus(BP) monitor the electronic distribution in the conduction and valence band as a function of delay time from photoexcitation.The data show that,after thermalization,the photo-injected electrons do not lead to sizable band gap renormalization,neither do they generate an appreciable amount of carrier multiplication.On the other hand,a Stark broadening of the valence band is ascribed to the inhomogeneous screening of a local potential around charge defects.Chapter5 shows time resolved ARPES data on a BP surface that is doped in-situ by means of alkali metals evaporation. We monitor the collapse of the band-gap in the accumulation layer with unmatched accuracy and we observe that the buried states detected by the low energy photons of our probing pulse acquire a surprisingly high band velocity at large dopants concentration.Chapter6 deals with the modification of hot carrier dynamics upon increasing the surface doping of BP.In this case the reported analysis is still preliminary and needs to be backed by ab-initio calculations.Chapter7 contains our work on layered ɛ-InSe.As in the case of BP,we generate an accumulation layer of varying electronic density on the surface of such semiconductor.By spanning the doping level from the semiconducting to the metallic limit,we observe that quantum screening of Longitudinal Optical phonons is not as efficient as it would be in a strictly bidimensional system,indicating a remote coupling of confined states to polar phonons of the bulk.Furthermore,we show that a 3D Fröhlich interaction with Thomas-Fermi screening can be used to mimic the effects of such a remote coupling at the ɛ-InSe surface.In Chapter8,we study the layered 1T-TaS2.This material belongs to the Charge density waves (CDW) systems and has been extensively investigated by several research groups.In 1T-TaS2,the combination of structural distortion with high electronic correlations leads to a complex and fascinating phase diagram.We could reproduce controversial data that have been recently published in the literature and that identify a new instability in proximity of the metal to-insulator transition.Finally,chapter9 summarizes the conclusions of our work and briefly discusses the perspectives of some future directions of research
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Sridhar, Yerusu R. "Molecular Dynamics Simulations of Organic Photovoltaic Materials: Structure and Dynamics of Oligothiophene/Fullerene Blends." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342545038.
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Sun, Liang. "Structure and Dynamics of Swollen Polymer Brushes." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499675793233755.
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Nicholson, Christopher W. [Verfasser]. "Electronic Structure and Dynamics of Quasi-One Dimensional Materials / Christopher W. Nicholson." Berlin : Freie Universität Berlin, 2018. http://d-nb.info/117122284X/34.
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Chen, Ying. "NMR Applications in Soft Materials Science: Correlation of Structure, Dynamics, and Transport." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/75177.
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This dissertation aims to investigate and correlate structure, dynamics and transport properties of several novel soft materials systems using multiple Nuclear Magnetic Resonance (NMR) methodologies, including solid-state NMR (SSNMR), diffusometry, and imaging, and with the help of X-ray scattering.
First, we report the investigation of structure and dynamics of three polymeric membranes: hydroxyalkyl-containing imidazolium homopolymers, poly(arylene ether sulfone) segmented copolymers, and disulfonated poly(arylene ether sulfone) random copolymers using a wide array of SSNMR techniques, including: 1) ¹³C cross-polarization magic angle spinning (CPMAS) with varying cross-polarization (CP) contact time, 2) ¹³C single-pulse magic angle spinning (MAS) with varying delay time, 3) ²³Na single-pulse MAS, 4) two dimensional phaseadjusted spinning sideband (2D PASS), 5) proton spin−lattice relaxation (T₁), 6) rotating frame spin−lattice relaxation (T₁ρ), and 7) center-band-only detection of exchange (CODEX). These various types of SSNMR spectroscopic methods provide a wealth of structural and dynamic information over a wide range of time scales from a few nanoseconds to seconds.
We further present a picture of rich structural and transport behaviors in supramolecular assemblies formed by amphiphilic wedge molecules using a combination of ²³Na solid-state NMR, ¹H/²H PFG NMR diffusion, relaxation and grazing-incidence small-angle X-ray scattering. Our results show that the liquid crystalline domains in these materials undergo a transition from columnar to bicontinuous cubic phases with a simple increase in humidity, while the amorphous domain boundaries consist of individual wedge molecules with a significant fraction (~ 10%) of total wedge molecules. Multiple-component diffusion of both wedges and water further confirms the structural and dynamic heterogeneity, with the bicontinous cubic phase being able to facilitate much faster water and ion transport than the columnar phase.
We then develop a quantitative approach to probe the migration of two novel “theranostic” polymeric agents (combining “therapeutic” and “diagnostic” functions) into bulk hydrogels using two distinct time-resolved magnetic resonance imaging (MRI) methods. To the best of our knowledge, this is the first work that combines time-resolved MRI experiments to reliably quantify diffusivity of paramagnetic and superparamagnetic nanoparticles in bulk biological media. Our results agree closely with those obtained from fluorescence techniques, yet the capability of our approach allows the analysis of actual nanoparticles diffusion through biogels on mm to cm scales during a range of time periods.
Finally, we employ a combination of NMR techniques to obtain a comprehensive understanding of ion clustering and transport behaviors of ionic liquids inside the benchmark ionic polymer Nafion. Spin relaxation shows that anion relaxation is more influenced by the fixed sulfonate groups than cation relaxation. 2D ¹H-¹⁹F heteronuclear Overhauser effect spectroscopy (HOESY) and 1D ¹⁹F¹⁹F selective nuclear Overhauser effect (NOE) spectroscopy confirm our assumption of the formation of ion clusters at low water content in the ionomer. While we observe non-restricted diffusion behavior for cations, anion diffusion is strongly restricted both between domain boundaries and within domains in the absence of water. The restricted anion diffusion can serve as a reliable probe for detailed multiscale structures of the ionomer.Ph. D.
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Wiper, Paul Vincent. "Novel sol-gel materials for advanced glass products : structure, dynamics and stability." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/7993/.
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Flame retardants are composite materials or chemicals used in thermoplastics, thermosets, textiles, coatings and glasses that inhibit or resist the spread of fire. In 2014 the global market for flame retardants is expected to reach $6.10 billion with a drive in research for designing and developing new fire resistant materials. A commercially available product based on a hydrogel/glass composite is an effective fire and heat resistant glazing that is employed in the commercial and domestic sector. The macroscopic effects of these materials have been investigated; however no information exists on the molecular level properties. Therefore, the aim of this research is to fully characterise a series of hydrogels with the ultimate goal of understanding structure-property relationships. The hydrogels discussed herein are made by drying commercially available sodium-silicate solutions onto traditional float glass to create a sandwich glazing. The materials present a unique challenge to characterise at the molecular level because of their amorphous and metastable nature. NMR spectroscopy has been extensively used in this research because it is shown to be an ideal technique for the elucidation of structures and dynamics in disordered systems. The complete “life-cycle” of the product is investigated; firstly, using solid-state NMR, a thorough and detailed analysis of the hydrogels are presented. The thermal stability of the hydrogels are then investigated by means of short and long term ageing effects, which shows that the product crystallises into the layered silicate makatite. The ability to improve the longevity of the product by inhibiting makatite formation follows with a final section dedicated to understanding different composites of the materials.
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Vachhani, Neal Arvind 1981. "Using narrowband pulse-shaping to characterize polymer structure and dynamics : Deathstar GHz spectroscopy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/27876.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaves 117-122).
(cont.) The validation of this technique for probing amorphous polymer structure and dynamics lays the ground for further study of heterogeneous materials, such as nanocomposites and block copolymers.
A narrowband pulse-shaper called the Deathstar has been used along with a picosecond acoustic technique to study amorphous polymers. The temperature dependence of the longitudinal acoustic velocity and the frequency dependence of the acoustic attenuation have been measured. The frequency range of longitudinal phonons studied is not directly accessible by other spectroscopies. Probing material response in this intermediate regime is valuable because it helps characterize secondary transitions and energy dissipation mechanisms in polymers. Broadband experiments have been done to study the temperature dependence of the acoustic velocity for polystyrene and poly(methyl methacrylate) from 10 K to 300 K. The results are in line with literature values and the predictions of a model based on acoustic impedance mismatch theory. Narrowband studies with the technique used were previously limited to amorphous silica. They are extended for the first time to amorphous polymers. The Deathstar GHz spectroscopy is used to determine the absolute acoustic attenuation coefficient as a function of frequency for PMMA. The values obtained are similar to those found in literature. However, the method used to measured attenuation here is more reliable. The frequency at which attenuation has been measured ranges from 55 GHz to 160 GHz. To explore additional dynamics, attenuation is also measured at temperatures above and below the polymer glass transition. The details of the experimental technique are discussed, and the results are presented.
by Neal Arvind Vachhani.
S.M.
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Dean, Nicky. "Electronic and structural dynamics of complex materials." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543469.
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Maraytta, Nour Abdalmajeed Verfasser], Thomas [Akademischer Betreuer] [Brückel, and Georg [Akademischer Betreuer] Roth. "Structure and dynamics of magnetocaloric materials / Nour Abdalmajeed Maraytta ; Thomas Brückel, Georg Roth." Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/123814957X/34.
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Aeberhard, Philippe C. "Computational modelling of structure and dynamics in lightweight hydrides." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:bfaf28b1-da03-4ce9-8577-5e8c18eb05ae.
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Hydrogen storage in lightweight hydrides continues to attract significant interest as the lack of a safe and efficient storage of hydrogen remains the major technological barrier to the widespread use of hydrogen as a fuel. The metal borohydrides Ca(BH₄)₂ and LiBH₄ form the subject of this thesis; three aspects of considerable academic interest were investigated by density functional theory (DFT) and molecular dynamics (MD) modelling. (i) High-pressure crystal structures of Ca(BH₄)₂ were predicted from a structural analogy between metal borohydrides and isoelectronic metal oxides. The structural stability of hydrogen storage materials under high pressure is an important aspect, as high-pressure polymorphs may provide structures with better hydrogen desorption properties. The isoelectronic analogue of Ca(BH₄)₂ is TiO₂, and structural equivalents of Ca(BH₄)₂ in the baddeleyite, columbite and cotunnite structures of TiO₂ were found to be stable at elevated pressure. Thermodynamic stability was evaluated by computing the Gibbs energy with respect to pressure and temperature. The pressure-dependence of the Helmholtz energy was determined to described a third-order Birch-Murnaghan equation of state, and the harmonic approximation was used to compute the vibrational energy levels and the Helmholtz energy as a function of temperature. The proposed structures are consistent with reports of two hitherto unidentified high-pressure phases observed experimentally. (ii) The disordered structure of the high-temperature phase of LiBH4 was studied by ab initio molecular dynamics (MD) at temperatures ranging from 200-535 K. It was found that the model emerging from analysis of the MD simulations properly accounts for dynamical disorder and fundamentally differs from the published experimental and theoretical structures. The validity of the MD model was corroborated by comparison of calculated pair distribution functions, vibrational spectra and a crystallographic model with neutron diffraction data; good agreement was found. A reassignment of the space group from P63mc to P63/mmc is proposed based on evidence for additional symmetry from MD simulations. (iii) Finally, a new MD-based method was developed to simulate fast ionic diffusion in LiBH₄. The colour diffusion algorithm - a nonequilibrium molecular dynamics method originally developed for the study of model fluids - was adapted and applied to self-diffusion of atoms in a solid for the first time. Calculated diffusion coefficients agreed very well with published measurements, and diffusion pathways that include collective particle effects were determined directly from the simulation results, thereby opening up a promising and efficient new method for the study of phenomena such as superionic conduction.
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Yimer, Yeneneh Yalew. "Molecular Ordering, Structure and Dynamics of Conjugated Polymers at Interfaces: Multiscale Molecular Dynamics Simulations." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1416796729.
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HASHMI, QUAZI SARWAR EHSAN. "NONASSOCIATIVE PLASTICITY MODEL FOR COHESIONLESS MATERIALS AND ITS IMPLEMENTATION IN SOIL-STRUCTURE INTERACTION." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184024.
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A constitutive model based on rate-independent elastoplasticity concepts is developed and used to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths. The model accounts for various factors such as friction, stress path and stress history that influence the behavior of geologic materials. A hierarchical approach is adopted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. Nonassociativeness is introduced as correction or perturbation to the basic model. Deviation of normality of the plastic strain increments to the yield surface F is captured through nonassociativeness. The plastic potential Q is obtained by applying a correction to F. This simplified approach restricts the number of extra parameters required to define the plastic potential Q. The material constants associated with the model are identified, and they are evaluated for three different sands (Leighton Buzzard, Munich and McCormick Ranch). The model is then verified by comparing predictions with laboratory tests from which the constants were found, and typical tests not used for finding the constants. The effect of varying initial density of a material on the stress-strain and volumetric response is investigated. An empirical relation is proposed, whereby one parameter is modified based on the initial density, such that improved predictions can be obtained without increasing the total number of parameters. Implementation of the nonassociative model in a finite element program to solve boundary value problems leads to a nonsymmetric stiffness matrix. Besides, using a nonsymmetric solver, three numerical schemes are investigated. The idea of the schemes is to modify the stiffness matrix such that a symmetric equation solver can be used. Prediction of stress-strain, volumetric response and CPU time for different schemes are compared with the predictions obtained using the nonsymmetric solver. The nonsymmetric equation solver used less CPU time and the solutions were more accurate. Based on the above findings, a soil-footing system is analyzed using the finite element techniques. The associative and nonassociative models are used to predict the behavior. For the nonassociative model, solution is obtained by using a nonsymmetric solver. Results obtained from both models are compared with a model footing test performed in the laboratory.
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Gong, Chuncheng. "Atomic structure and dynamics study of defects in graphene by aberration-corrected transmission electron microscope." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:53bd9a04-71ad-4da8-b982-cb45a005e791.
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Graphene has grabbed enormous research attention due to its multiple unique properties. These properties, however, can be strongly influenced by lattice imperfections. Aberration corrected transmission electron microscopy (AC-TEM) is one of the leading methods to image two-dimensional materials at the atomic level. This thesis addresses the issue of structure and dynamics characterization of dislocations and grain boundaries (GBs) in graphene with single atom sensitivity using the state-of-the-art AC-TEM in Department of Materials, University of Oxford. My first goal is to understand the interaction between dislocation and the edge of graphene. When a dislocation is located near an edge, a decrease in the rippling and increase of the in-plane rotation occurs relative to the dislocations in the bulk. The increased in-plane rotation near the edge causes bond rotations at the edge of graphene to reduce the overall strain in the system. Dislocations are highly stable and remain fixed in their position even when located within a few lattice spacings from the graphene edge. With the aid of an in situ heating holder, the high temperature behavior of dislocations is then investigated. Control of temperature enables the differentiation of electron beam induced effects and thermally driven processes. An analysis of the dislocation movement shows both climb and glide processes, including new complex pathways for migration and large nanoscale rapid jumps between fixed positions in the lattice. The improved understanding of the high temperature dislocation movement provides insights into annealing processes in graphene and the behavior of defects with increased heat. The in situ heterogeneous nucleation and growth of graphene are also studied within the AC-TEM. The growth mechanism consists of alternating carbon cluster attachment and indentation filling to maintain a uniform growth front of lowest energy. The highly polycrystalline graphene seed is found to evolve with time into a higher order crystalline structure. The motion of GBs is discontinuous and mediated by both bond rotation and atom evaporation. These results provide insights into the formation of crystalline seed domains that are generated during bottom-up graphene synthesis. Finally, the formation, reconfiguration and annihilation of GB loops are demonstrated. It is shown that the GB loop cannot fully relaxed under electron beam irradiation with its terminal state being isolated dislocations far apart from each other. Line defects composed of several adjacent excess-atom defects can be found during the reconfiguration process. This work gives detailed information about the stability and behavior of large GB loops in two dimensional materials.
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Gardner, Adam R. "Molecular dynamics of aot/water/isooctane reverse micelles dynamic and structural analysis and effect of zirconium ions on the micelles structure for ZrO2 nanoparticle production /." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1442844.
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Carsí, Rosique Marta. "Molecular mobility. Structure-property relationship of polymeric materials." Doctoral thesis, Universitat Politècnica de València, 2016. http://hdl.handle.net/10251/59460.
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[EN] The present work examines the influence of the chemical structure of polymers on thermal, mechanical and dielectric behavior. The experimental techniques used for the purpose are differential scanning calorimetry, dynamo-mechanical analysis and dielectric spectroscopy. Additionally, in order to confirm the results obtained using the above methods, other techniques such as ray diffraction have also been employed.
Chapters 1 and 2 contain the introduction and the objectives, respectively. Chapter 3 briefly describes the experimental techniques used.
Chapter 4 contains the findings of the comparative analysis of the response to electrical noise fields for three poly(benzyl methacrylates) with different structures. The analysis was carried out under a wide range of frequencies and temperatures on three poly(benzyl methacrylates) containing two dimethoxy groups in positions 2,5-, 2,3- and 3,4-. The results show that the position of the dimethoxy groups on the aromatic ring has a significant effect on the molecular dynamics of poly(benzyl methacrylate). The spectra obtained were of high complexity and therefore, in order to perform a better analysis, numerical methods for time-frequency transformation including the use of parametric regularization techniques were used. We studied the effect of this structural change on the secondary relaxation processes and relaxation process , relating to the glass transition. We also analyzed the effect of the dimethoxy group position on the formation of nanodomains, in which the side chains are predominant, and on the conduction processes of the materials tested.
In Chapter 5, the conductivity of rubbery liquids was studied by analyzing poly(2,3-dimethoxybenzyl methacrylate), which exhibits its own particular behavior. The chapter analyzes the principle of time-temperature superposition, employing different interrelated variables.
Chapter 6 focuses on how the presence of crosslinking affects the molecular mobility of polymethacrylates containing aliphatic alcohol ether residues. In this case, the effect of crosslinking on the secondary and primary relaxation processes was analyzed. The creation of nanodomains in the side chains as a result of the presence of crosslinking was also studied.[ES] En este trabajo se presenta un estudio de la influencia de la estructura química de los polímeros en su comportamiento térmico, mecánico y dieléctrico. Las técnicas experimentales empleadas para ello han sido la calorimetría diferencial de barrido, el análisis dinamo-mecánico y la espectroscopia dieléctrica. Adicionalmente, se han empleado otras técnicas como la difracción de rayos, con objeto de corroborar los resultados obtenidos por las primeras. En los Capítulos 1 y 2 se recoge la introducción y los objetivos, respectivamente. El Capítulo 3 presenta una breve descripción de las técnicas experimentales empleadas. En el Capítulo 4 se recogen los resultados obtenidos en el análisis comparativo de la respuesta a campos de perturbación eléctrica en un amplio rango de frecuencias y temperaturas para tres polimetacrilatos de bencilo con dos grupos dimetoxi en posiciones 2,5-, 2,3- y 3,4-. Los resultados obtenidos señalan el importante efecto de la posición de los grupos dimetoxi en el anillo aromático, sobre la dinámica molecular del polimetacrilato de bencilo. Los espectros obtenidos fueron muy complejos, por ello en orden a llevar a cabo un mejor análisis se emplearon métodos numéricos para la transformación tiempo-frecuencia que incluyeron el uso de técnicas de regularización paramétrica. Se ha estudiado el efecto que dicho cambio estructural ejerce tanto sobre los procesos de relajación secundaria como sobre el proceso de relajación α, relacionado con la transición vítrea. Así mismo, se ha analizado el efecto de la posición de los grupos dimetoxi en la formación de iii nanodominios en los que predominan las cadenas laterales, y su efecto en los procesos de conducción de los materiales analizados. En el Capítulo 5 se recoge el estudio de la conductividad de líquidos gomosos tomando como modelo el poli (metacrilato de 2,3-dimetoxibencilo), por su peculiar comportamiento. En este capítulo se ha realizado un análisis del principio de superposición tiempo-temperatura, empleando para ello diferentes variables relacionadas entre sí. En el Capítulo 6 se recoge el efecto de la presencia de entrecruzante en la movilidad molecular de polimetacrilatos que contienen residuos de éteres de alcoholes alifáticos. En este caso, se ha analizado el efecto de la presencia de entrecruzante tanto en los procesos de relajación secundarios, como en el proceso de relajación principal. También se llevó a cabo un análisis del efecto que la presencia de entrecruzante tiene sobre la creación de nanodominios gobernados por las cadenas laterales.
[CAT] En aquest treball es presenta un estudi de la influència de l'estructura química dels polímers en el seu comportament tèrmic, mecànic i dielèctric. Les tècniques experimentals utilitzades han sigut la calorimetria diferencial de rastreig, l'anàlisi dinamo-mecànic i l'espectroscòpia dielèctrica. Addicionalment, s'han empleat altres tècniques com la difracció de rajos X a fi de corroborar els resultats obtinguts per les primeres. En els Capítols 1 i 2 s'arreplega la introducció i els objectius, respectivament. Al Capítol 3 es presenta una breu descripció de les tècniques experimentals emprades. En el Capítol 4 es recull els resultats obtinguts en l'anàlisi comparativa de la resposta a camps de pertorbació elèctrica en un ampli rang de freqüències i temperatures de tres polimetacrilats de benzil amb dos grups metoxi en posicions 2,5-, 2,3- i 3,4-. Els resultats obtinguts assenyalen l'important efecte de la posició dels grups metoxi en l'anell aromàtic, sobre la dinàmica molecular del polimetacrilat de benzil. Els espectres obtinguts van ser molt complexos, per aquesta raó per a dur a terme un millor anàlisi es van emprar mètodes numèrics per a la transformació temps-freqüència que van incloure l'ús de tècniques de regularització paramètrica. S'ha estudiat l'efecte que el dit canvi estructural exerceix tant sobre els processos de relaxació secundària com sobre el procés de relaxació , relacionat amb la transició vítria. Així mateix, s'ha analitzat l'efecte de la posició dels grups metoxi en la formació de nanodominis en els que predominen les cadenes laterals, i el seu efecte en els processos de conducció dels materials analitzats. En el Capítol 5 s'arreplega l'estudi de la conductivitat de líquids gomosos prenent com a model el poli-(metacrilat de 2,3-dimetoxibencilo), pel seu peculiar comportament. En aquest capítol s'ha realitzat un anàlisi del principi de superposició temps-temperatura, emprant per a això diferents variables relacionades entre sí. En el Capítol 6 s'arreplega l'efecte de la presència d'entrecreuat en la mobilitat molecular de polimetacrilats que contenen residus d'èters d'alcohols alifàtics. En aquest cas, s'ha analitzat l'efecte de la presència d'entrecreuat tant en els processos de relaxació secundaris, com en el procés de relaxació principal. També es va dur a terme un anàlisi de l'efecte que la presència d'entrecreuat químic té sobre la creació de nanodominis governats per les cadenes laterals.
Carsí Rosique, M. (2015). Molecular mobility. Structure-property relationship of polymeric materials [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59460
TESIS
Premiado
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Ali, Fatmah Abdullah Haider. "Examination of atomic scale structure and dynamics of amorphous materials by solid state NMR." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.481489.
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Dewan, Leslie. "Molecular dynamics simulation and topological analysis of the network structure of actinide-bearing materials." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/86266.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references.
Actinide waste production and storage is a complex problem, and a whole-cycle approach to actinide management is necessary to minimize the total volume of waste. In this dissertation, I examine three actinide-bearing materials relevant to both the front end and back end of the nuclear fuel cycle: light water reactor (LWR) spent fuel stored in a crystalline ceramic medium (zircon), LWR spent fuel stored in a glassy medium (alkali borosilicate glass), and three molten salt systems (LiF-BeF2, LiF-ThF4 , and LiF-UF4). I model these materials using molecular dynamics (MD) simulations, and then perform a range of material-dependent analyses - including structural evaluation, species segregation, solubility limits, and assessment of transport properties - to examine their suitability as actinide-bearing materials. The initial portion of this work focuses on actinide waste storage media, examining the microstructural changes induced in zircon and alkali borosilicate glass doped with uranium. Alpha-decay of the uranium changes the structure of the host material, inducing amorphousness, recrystallization, and microcracking, among other structural changes. My work on actinide waste storage shows the utility of topological methods for quantifying the intermediate-range structure of amorphous systems. In many cases, the intermediate-range structure correlates with larger-scale properties, such as density and viscosity. I then identify three molten salt systems of interest - LiF-BeF2 , LiF-ThF4, and LiUF4 - as a focus for analysis. LiF-BeF2 is a coolant salt, and LiF-ThF4 and LiF-UF4 are fuel salts used on the front end of the nuclear fuel cycle in molten salt reactors (MSRs). MSRs can, in some configurations, achieve extremely high actinide bum-ups. Some molten salt reactors can also be fueled by the actinides in spent fuel produced by LWRs. While MSRs have many advantages, research into new designs often proceeds slowly because of gaps in available experimental data for the molten fuel and coolant salts. I use MD simulations to evaluate the transport properties and structure of these salts, and show that these simulations can be used reliably to augment the existing body of experimental data describing the salts' material properties. Furthermore, I examine how the structure of the salt correlates with its material properties, in particular its viscosity. I use network topology-based algorithms to describe the amorphous structure quantitatively. Network-based topological methods have never before been applied to molten salts, and many new insights can be gained from the analysis.
by Leslie Dewan.
Ph. D.
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Graça, Araújo Carlos Moysés. "Hydrogen Storage Materials : Design, Catalysis, Thermodynamics, Structure and Optics." Doctoral thesis, Uppsala universitet, Institutionen för fysik och materialvetenskap, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8574.
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Hydrogen is abundant, uniformly distributed throughout the Earth's surface and its oxidation product (water) is environmentally benign. Owing to these features, it is considered as an ideal synthetic fuel for a new world energetic matrix (renewable, secure and environmentally friendly) that could allow a sustainable future development. However, for this prospect to become a reality, efficient ways to produce, transport and store hydrogen still need to be developed. In the present thesis, theoretical studies of a number of potential hydrogen storage materials have been performed using density functional theory. In NaAlH4 doped with 3d transition metals (TM), the hypothesis of the formation of Ti-Al intermetallic alloy as the main catalytic mechanism for the hydrogen sorption reaction is supported. The gateway hypothesis for the catalysis mechanism in TM-doped MgH2 is confirmed through the investigation of MgH2 nano-clusters. Thermodynamics of Li-Mg-N-H systems are analyzed with good agreement between theory and experiments. Besides chemical hydrides, the metal-organic frameworks (MOFs) have also been investigated. Li-decorated MOF-5 is demonstrated to possess enhanced hydrogen gas uptake properties with a theoretically predicted storage capacity of 2 wt% at 300 K and low pressure. The metal-hydrogen systems undergo many structural and electronic phase transitions induced by changes in pressure and/or temperature and/or H-concentration. It is important both from a fundamental and applied viewpoint to understand the underlying physics of these phenomena. Here, the pressure-induced structural phase transformations of NaBH4 and ErH3 were investigated. In the latter, an electronic transition is shown to accompany the structural modification. The electronic and optical properties of the low and high-pressure phases of crystalline MgH2 were calculated. The temperature-induced order-disorder transition in Li2NH is demonstrated to be triggered by Li sub-lattice melting. This result may contribute to a better understanding of the important solid-solid hydrogen storage reactions that involve this compound.
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Hubartt, Bradley C. "Nucleation and Growth, Defect Structure, and Dynamical Behavior of Nanostructured Materials." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1416828345.
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Petri, Ingrid. "An investigation of the structure of disordered materials by using neutron diffraction." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299847.
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Hussain, Tanveer. "Computational Insights on Functional Materials for Clean Energy Storage : Modeling, Structure and Thermodynamics." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-206938.
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The exponential increase in the demands of world’s energy and the devastating effects of current fossil fuels based sources has forced us to reduce our dependence on the current sources as well as finding cleaner, cheaper and renewable alternates. Being abundant, efficient and renewable, hydrogen can be opted as the best possible replacement of the diminishing and harmful fossil fuels. But the transformation towards the hydrogen-based economy is hindered by the unavailability of suitable storage medium for hydrogen. First principles calculations based on density functional theory has been employed in this thesis to investigate the structures modelling and thermodynamics of various efficient materials capable of storing hydrogen under chemisorption and physisorption mechanisms. Thanks to their high storage capacity, abundance and low cost, metal hydride (MgH2) has been considered as promising choice for hydrogen storage. However, the biggest drawback is their strong binding with the absorbed hydrogen under chemisorption, which make them inappropriate for operation at ambient conditions. Different strategies have been applied to improve the thermodynamics including doping with light and transitions metals in different phases of MgH2 in bulk form. Application of mechanical strain along with Al, Si and Ti doping on MgH2 (001) and (100) surfaces has also been found very useful in lowering the dehydrogenation energies that ultimately improve adsorption/desorption temperatures. Secondly, in this thesis, two-dimensional materials with high surface area have been studied for the adsorption of hydrogen in molecular form (H2) under physisorption. The main disadvantage of this kind of storage is that the adsorption of H2 with these nanostructures likes graphane, silicene, silicane, BN-sheets, BC3 sheets are low and demand operation at cryogenic conditions. To enhance the H2 binding and attain high storage capacity the above-mentioned nanostructures have been functionalized with light metals (alkali, alkaline) and polylithiated species (OLi2, CLi3, CLi4). The stabilities of the designed functional materials for H2 storage have been verified by means of molecular dynamics simulations.
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李德利 and Deli Li. "Thermodynamic formulation for damaging materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31233764.
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Li, Deli. "Thermodynamic formulation for damaging materials /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1367173X.
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Lee, Min-I. "Atomic structure, electronic states and relaxation dynamics in photovoltaic materials and interfaces from photoemission-related spectroscopies." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS220/document.
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L'efficacité du processus photovoltaïque dépend du matériau actif à travers la structure de bande et la dynamique des porteurs de charge. Dans cette thèse, nous avons relié les propriétés électroniques et la dynamique de relaxation à la structure atomique des matériaux utilisés pour deux technologies différentes de cellules solaires, celle à base d’hétérostructures de silicium, et celle à base de pérovskites hybrides organiques-inorganiques. Dans les cellules solaires de silicium, nous avons analysé l'influence des défauts sur les propriétés électroniques des hétérostructures de silicium amorphe (a-Si:H/a-SIC:H/c-Si) par spectroscopies des niveaux de coeur et de la bande de valence. En particulier, nous avons quantifié le nombre de liaisons pendantes induites dans la couche a-Si:H par irradiation, et nous avons identifié les états électroniques qui leur sont associés. Enfin nous avons expliqué les transitions précédemment observées par photoluminescence. Dans les cellules solaires à pérovskite hybride, nous avons corrélé la structure atomique, la structure électronique et la dynamique électronique pour des pérovskites bi- et tridimensionnelles. Dans ce but nous avons utilisé tout un panel de techniques complémentaires: diffraction des rayons X, spectroscopie de photoémission résolue en angle, spectroscopie de photoémission inverse et photoémission à deux photons résolue en temps. Pour la pérovskite bidimensionnelle (C₆H₅C₂H₄NH₃)₂PbI₄, nous avons déterminé expérimentalement les bandes de valence et de conduction et nous les avons comparées aux simulations de la fonction spectrale. Pour la pérovskite tridimensionnelle CH₃NH₃PbI₃, nous avons aussi déterminé les structures de bande expérimentale et simulée. Des signatures spectrales très larges ont été observées expérimentalement, ce qui relaxe les conditions de transition optique avec un impact éventuel sur l'efficacité des cellules solaires. Tant dans les expériences que dans les calculs, nous observons que le poids spectral suit une périodicité cubique alors que le système est structurellement dans une phase tétragonale. Cette contradiction apparente s'explique par la largeur spectrale des bandes, qui cache le repliement dû à la distorsion tétragonale. En ce qui concerne la dynamique de relaxation, nous avons observé que les porteurs photoexcités se thermalisent dans une échelle de temps subpicoseconde par couplage aux vibrations des cations organiques. À des échelles de temps plus longues (10~100 picosecondes), la diffusion électronique contrôle la dynamique. Cette dynamique est affectée par les défauts induits par recuit, qui localisent les électrons photoexcités pendant plus de 300 picosecondesThe efficiency of the photovoltaic process depends on the electronic band structure of the active material and the charge carrier dynamics. In this thesis, we have studied how these issues are related to the atomic structure in materials for two different technologies of solar cells, namely silicon heterostructure solar cells, and hybrid organic-inorganic perovskite solar cells. In silicon heterostructure solar cells, we have analyzed the impact of defects on the electronic properties of amorphous silicon heterostructures (a-Si:H/a-SIC:H/c-Si) by core level and valence band spectroscopies. In particular, we have quantified the number of dangling bonds inside a-Si:H layer upon irradiation, we have identified the electronic states associated to them, and we have understood the transitions previously observed by photoluminescence. In perovskite solar cells, we have correlated the atomic structure, the electronic structure and the electronic dynamics for two- and three-dimensional hybrid organic-inorganic perovskites. We have used with this goal a whole panel of complementary techniques: X-ray diffraction, angle-resolved photoemission spectroscopy, inverse photoemission spectroscopy, and time-resolved two-photon photoemission. In the two-dimensional perovskite (C₆H₅C₂H₄NH₃)₂PbI₄, the valence and conduction bands have been determined experimentally and compared to spectral function simulations. In the three-dimensional perovskite CH₃NH₃PbI₃, we have again determined the band structure and simulated it. Very broad spectral features have been experimentally observed, which relax the optical transition conditions impacting in the solarcell efficiencies. In both experiments and calculations, we observe that the spectral weight follows a cubic periodicity while the system is structurally in the tetragonal phase. This apparent contradiction is explained by the band broadness, which hides the band folding of the tetragonal distortion. As for the relaxation dynamics, we have observed that the photoexcited carriers thermalize in a subpicosecond time scale through the coupling to organic cation vibrations. At longer timescales (10~100 picoseconds), the electron diffusion controls the dynamics. This dynamics is affected by the annealing-induced defects, which localize the photoexcited electrons for more than 300 picoseconds
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Cadien, Adam. "The Structure and Dynamics of Monatomic Liquid Polymorphs; Case Studies in Cerium and Germanium." Thesis, George Mason University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3706976.
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The study of liquid polymorphism is at the frontier of fundamental thermodynamics and materials science. Liquid polymorphism occurs when a single material has multiple structurally unique liquid phases. Water was the first substance suggested to exhibit multiple liquid phases, a number of monatomic semiconductors and metals have been found to exhibit similar characteristics since then. A better understanding of the liquid-liquid phase transition is needed to tackle problems in glass sciences, it is also relevant to geophysical studies of the Earth's core and mantle and has applications in nanotechnology.
Computational methods are critical to developing a better understanding of liquids. Through simulation thermodynamic obstacles that hamper experiments can be artificially bypassed, metastable regions outside the equilibrium phase diagram can be accessed and all of the properties of the system are directly recorded. Computationally it is much simpler to iterate over a range of environmental variables such as temperature, pressure and composition, and measure a system's response. In this thesis ab-initio and semi-empirical approximations are used to accurately describe the complex many body interactions that take place in liquids.
Two independent case studies of liquid polymorphism are presented here. The first is a stable liquid-liquid phase transition was found to occur in Cerium which was initially discovered through X-Ray diffraction experiments and later confirmed through simulation. This phase transition is predicted to end at a critical point.
The second is a comprehensive study of the structure and dynamics of Germanium's many metastable amorphous and liquid phases. This is currently the largest ab-initio based study of the dynamics of Germanium's metastable liquid phases. Methods ranging from the mean square displacement to the van Hove function and intermediate scattering function are introduced and analyzed. The micro-structural characteristics are quantified and correlated with the mobility in the material revealing dynamical heterogeneity.
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Riegner, David C. "Molecular Dynamics Simulations of Metallic Glass Formation and Structure." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471860872.
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Zhang, Hanyu. "ANALYZING THE SHORT-RANGE ORDER OF METALLIC GLASS THROUGH X-RAY ABSORPTION FINE STRUCTURE (XAFS) SPECTROSCOPY." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554911796709215.
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Li, Lan. "Molecular dynamics simulations of the deformation of nano-structured materials." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1324388961&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Schnadt, Joachim. "Studies of Model Nanostructured Materials : Geometric and Electronic Structure, and sub-10 fs Charge Transfer Dynamics." Doctoral thesis, Uppsala University, Department of Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2636.
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A number of nanostructured systems has been investigated by means of Photoemission and X-ray absorption spectroscopies and by Scanning tunneling microscopy with emphasis on the geometric and electronic structure and the excited-state charge transfer dynamics. These systems comprise aromatic molecules on semiconductor surfaces (titanium dioxide), metal clusters, and an alkali-C60 compound.
Electronic and geometric structure are complementary to each other, and changes in the geometric structure are accompanied by changes in the electronic structure. Therefore, a detailed investigation of the latter makes it possible to draw conclusions on the former. In particular, this close relationship has been used to characterise the adsorbate geometry of the pyridine-carboxylic acid monomers on rutile TiO2(110), which is determined by the strong substrate bond as well as interadsorbate interactions. Similarly, it has been found that bi-isonicotinic acid adsorbs on a nanostructured anatase TiO2 film by forming strong bonds between both carboxylic groups and the substrate titanium atoms. For deposited metal clusters, the core binding energies are found to mirror the cluster size.
Resonant core electron spectroscopies have been employed to elucidate the excited-state charge transfer dynamics with respect to the transfer of an excited electron from the bi-isonicotinic acid and isonicotinic acid adsorbates to a titanium dioxide semiconductor surface. An important aspect has been the development of new variations of the method in order to be able to unravel the spectra of these relatively complex systems. While a strong excitonic effect localises the excited electron on the adsorbate for the lowest excited state, excitation to the higher excited states leads to an ultrarapid charge transfer on a low- to sub-femtosecond timescale.
In LiC60 the character of the alkali-C60 bond has been investigated. The balance between the different energy contributions points to an ionic bond with an important element of covalency.
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Maalouf, Manale W. "Structure and Dynamics Influencing Proton Transport in Materials for High Temperature (120 °C) PEM Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1311010188.
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Gowers, Richard. "Developing dual-scale models for structured liquids and polymeric materials." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/developing-dualscale-models-for-structured-liquids-and-polymeric-materials(edfe6991-79de-45a9-84e4-9e9dfb68faa4).html.
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Computer simulation techniques for exploring the microscopic world are quickly gaining popularity as a tool to complement theoretical and experimental approaches. Molecular dynamics (MD) simulations allow the motion of an N–body soft matter system to be solved using a classical mechanics description. The scope of these simulations are however limited by the available computational power, requiring the development of multiscale methods to make better use of available resources. Dual scale models are a novel form of molecular model which simultaneously feature particles at two levels of resolution. This allows a combination of atomistic and coarse-grained (CG) force fields to be used to describe the interactions between particles. By using this approach, targeted details in a molecule can be described at high resolution while other areas are treated with fewer degrees of freedom. This approach aims to allow for simulating the key features of a system at a reduced computational cost. In this thesis, two generations of a methodology for constructing dual scale models are presented and applied to various materials including polyamide, polyethene, polystyrene and octanol. Alongside a variety of well known atomistic force fields, these models all use iterative Boltzmann inversion (IBI) force fields to describe the CG interactions. In addition the algorithms and data structures for implementing dual scale MD are detailed, and expanded to include a multiple time step (MTS) scheme for optimising its peformance. Overall the IBI and atomistic force fields were compatible with each other and able to correctly reproduce the expected structural results. The first generation methodology featured bonds directly between atoms and beads, however these did not produce the correct structures. The second generation used only atomistic resolution bonds and this improved the intramolecular structures greatly for a relatively minor cost. In both the polyamide and octanol systems studied, the models were also able to properly describe the hydrogen bonding. For the CG half of the force field, it was possible to either use preexisting force field parameters or develop new parameters in situ. The resulting dynamical behaviour of the models was unpredictable and remains an open question both for CG and dual scale models. The theoretical performance of these models is faster than the atomistic counterpart because of the reduced number of pairwise interactions that must be calculated and this scaling was seen with the proposed reference implementation. The MTS scheme was successful in improving the performance with no effects on the quality of results. In summary this work has shown that dual scale models are able to correctly reproduce the structural behaviour of atomistic models at a reduced computational cost. With further steps towards making these models more accessible, they will become an exciting new option for many types of simulation.
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Hamilton, Myles. "The structure and dynamics of liquid semiconductors and superionic conductors by neutron scattering." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311368.
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Delandar, Arash Hosseinzadeh. "Modeling defect structure evolution in spent nuclear fuel container materials." Doctoral thesis, KTH, Materialteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-206175.
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Materials intended for disposal of spent nuclear fuel require a particular combination of physical and chemical properties. The driving forces and mechanisms underlying the material’s behavior must be scientifically understood in order to enable modeling at the relevant time- and length-scales. The processes that determine the mechanical behavior of copper canisters and iron inserts, as well as the evolution of their mechanical properties, are strongly dependent on the properties of various defects in the bulk copper and iron alloys. The first part of the present thesis deals with precipitation in the cast iron insert. A nodular cast iron insert will be used as the inner container of the spent nuclear fuel. Precipitation is investigated by computing effective interaction energies for point defect pairs (solute–solute and vacancy–solute) in bcc iron using first-principles calculations. The main considered impurities in the iron matrix include 3sp (Si, P, S) and 3d (Cr, Mn, Ni, Cu) solute elements. By computing interaction energies possibility of formation of different second phase particles such as late blooming phases (LBPs) in the cast iron insert is evaluated. The second part is devoted to the fundamentals of dislocations and their role in plastic deformation of metals. Deformation of single-crystal copper under high strain rates is simulated by employing dislocation dynamics (DD) method to examine the effect of strain rate on mechanical properties as well as dislocation microstructure development. Creep deformation of copper canister at low temperatures is studied. The copper canister will be used in the long-term storage of spent nuclear fuel as the outer shell of the waste package to provide corrosion protection. A glide rate is derived based on the assumption that at low temperatures it is controlled by the climb rate of jogs on the dislocations. Using DD simulation creep deformation of copper at low temperatures is modeled by taking glide but not climb into account. Moreover, effective stresses acting on dislocations are computed using the data extracted from DD simulations.QC 20170428
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Xu, Tao. "The structure-property relation in nanocrystalline materials: a computational study on nanocrystalline copper by Monte Carlo and molecular dynamics simulations." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/37108.
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Nanocrystalline materials have been under extensive study in the past two decades. The reduction in grain size induces many abnormal behaviors in the properties of nanocrystalline materials, that have been investigated systematically and quantitatively. As one of the most fundamental relations in materials science, the structure-property relation should still apply on materials of nano-scale grain sizes. The characterization of grain boundaries (GBs) and related entities remains a big obstacle to understanding the structure-property relation in nanocrystalline materials. It is challenging experimentally to determine the topological properties of polycrystalline materials due to the complex and disordered grain boundary network presented in the nanocrystalline materials. The constantly improving computing power enables us to study the structure-property relation in nanocrystalline materials via Monte Carlo and molecular dynamic simulations.
In this study, we will first propose a geometrical construction method based on inverse Monte Carlo simulation to generate digital microstructures with desired topological properties such as grain size, interface area, triple junction length as well as their statistical distributions. The influences on the grain shapes by different topological properties are studied. Two empirical geometrical laws are examined including the Lewis rule and Aboav-Weaire law. Secondly, defect free nanocrystalline Copper (nc-Cu) samples are generated by filling atoms into the Voronoi structure and then relaxed by molecular dynamics simulations. Atoms in the relaxed nc-Cu samples are then characterized into grain atoms, GB interface atoms, GB triple junction atoms and vertex atoms using a newly proposed method. Atoms in each GB entity can also be identified. Next, the topological properties of nc-Cu samples before and after relaxation are calculated and compared, indicating that there exists a physical limit in the number of atoms to form a stable grain boundary interface and triple junction in nanocrystalline materials. In addition, we are able to obtain the statistical averages of geometrical and thermal properties of atoms across each GB interfaces, the so-called GB profiles, and study the grain size, misorientation and temperature effects on the microstructures in nanocrystalline materials. Finally, nc-Cu samples with different topological properties are deformed under simple shear using MD simulation in an attempt to study the structure-property relation in nanocrystalline materials.
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Locht, Inka L. M. "Theoretical methods for the electronic structure and magnetism of strongly correlated materials." Doctoral thesis, Uppsala universitet, Materialteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-308699.
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In this work we study the interesting physics of the rare earths, and the microscopic state after ultrafast magnetization dynamics in iron. Moreover, this work covers the development, examination and application of several methods used in solid state physics. The first and the last part are related to strongly correlated electrons. The second part is related to the field of ultrafast magnetization dynamics. In the first part we apply density functional theory plus dynamical mean field theory within the Hubbard I approximation to describe the interesting physics of the rare-earth metals. These elements are characterized by the localized nature of the 4f electrons and the itinerant character of the other valence electrons. We calculate a wide range of properties of the rare-earth metals and find a good correspondence with experimental data. We argue that this theory can be the basis of future investigations addressing rare-earth based materials in general. In the second part of this thesis we develop a model, based on statistical arguments, to predict the microscopic state after ultrafast magnetization dynamics in iron. We predict that the microscopic state after ultrafast demagnetization is qualitatively different from the state after ultrafast increase of magnetization. This prediction is supported by previously published spectra obtained in magneto-optical experiments. Our model makes it possible to compare the measured data to results that are calculated from microscopic properties. We also investigate the relation between the magnetic asymmetry and the magnetization. In the last part of this work we examine several methods of analytic continuation that are used in many-body physics to obtain physical quantities on real energies from either imaginary time or Matsubara frequency data. In particular, we improve the Padé approximant method of analytic continuation. We compare the reliability and performance of this and other methods for both one and two-particle Green's functions. We also investigate the advantages of implementing a method of analytic continuation based on stochastic sampling on a graphics processing unit (GPU).
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Ding, Ding-Kuo. "Structures and dynamics of disclinations and inversion walls in nematic polymers." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/33510.
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Shakhov, Alexander. "Structure-Dynamics Relationships in Complex Fluids and Disordered Porous Solids Assessed using NMR." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-153105.
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A NMR study of the structure-dynamics relationships in heterogeneous materials is presented. In the first part, transport in soft-matter systems is studied using the pulsed field gradient NMR technique (PFG NMR). The molecular crowding effect in biological matter has been addressed using polymer solutions as model systems. By performing ensemble-based diffusion studies, the earlier obtained data on anomalous diffusion have been complemented. The transition to normal diffusion on a larger time scale has been shown. Taking advantages of the NMR approach, transport properties of microemulsions consisting of micellar colloids dissolved in liquid crystals have been investigated. The self-diffusivities measured under equilibrium conditions have shown weak correlations with microscopic ordering and macroscopic phase transitions occurring in the systems under study. The formation of micelles is shown to be decisive for macroscopic separation at the isotropic-nematic transition.
The second part of the thesis covers heterogeneous effects in diffusion for fluids in porous solids, as probed using a combination of NMR diffusometry and structure characterization methods. Ionic liquids have been investigated, revealing a complex behavior under confinement. The attempts to correlate the observed characteristics of the ionic liquids with their internal chemical structure were undertaken. Finally, the series of nanoporous glasses with tunable pore structure characteristics were studied. Strong correlations between their structure and the preparation conditions as well as between the resulting transport properties have been shown.
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Lencer, Alexander Dominic André [Verfasser]. "Design rules, local structure and lattice-dynamics of phase-change materials for data storage applications / Alexander Dominic Andre Lencer." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2010. http://d-nb.info/101515025X/34.
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Selli, Daniele. "Structure Property and Prediction of Novel Materials using Advanced Molecular Dynamics Techniques: Novel Carbons, Germaniums and High-Performance Thermoelectrics." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-150244.
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By means of advanced molecular dynamic techniques, we predict the stability of novel materials based on carbon, germanium and PbSe. This topological solutions have been studied and characterised at a DFT/DFTB level of theory and interesting optical, mechanical, electronic and heat transport properties have been pointed out.
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O'Sullivan, Eoin. "Electronic states and dynamics in semiconductor structures." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325987.
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Blomqvist, Andreas. "Insights into Materials Properties from Ab Initio Theory : Diffusion, Adsorption, Catalysis & Structure." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-131331.
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In this thesis, density functional theory (DFT) calculations and DFT based ab initio molecular dynamics simulations have been employed in order to gain insights into materials properties like diffusion, adsorption, catalysis, and structure. In transition metals, absorbed hydrogen atoms self-trap due to localization of metal d-electrons. The self-trapping state is shown to highly influence hydrogen diffusion in the classical over-barrier jump temperature region. Li diffusion in Li-N-H systems is investigated. The diffusion in Li3N is shown to be controlled by the concentration of vacancies. Exchanging one Li for H (Li2NH), gives a system where the diffusion no longer is dependent on the concentrations of vacancies, but instead on N-H rotations. Furthermore, exchanging another Li for H (LiNH2), results in a blockade of Li diffusion. For high-surface area hydrogen storage materials, metal organic frameworks and covalent organic frameworks, the hydrogen adsorption is studied. In metal organic frameworks, a Li-decoration is also suggested as a way to increase the hydrogen adsorption energy. In NaAlH4 doped with transition metals (TM), the hypothesis of TM-Al intermetallic alloys as the main catalytic species is supported. The source of the catalytic effect of carbon nanostructures on hydrogen desorption from NaAlH4 is shown to be the high electronegativity of the carbon nanostructures. A space-group optimized ab initio random structure search method is used to find a new ground state structure for BeC2 and MgC2. The fast change between the amorphous and the crystalline phase of GeSbTe phase-change materials is suggested to be due to the close resemblance between the local amorphous structure and the crystalline structure. Finally, we show that more than 80% of the voltage in the lead acid battery is due to relativistic effects.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 702
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Zhang, Xiaowei. "Conceptual study of adaptive energy absorbers /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20ZHANG.
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Lam, Stephen Tsz Tang. "Accelerated atomistic prediction of structure, dynamics and material properties in molten salts." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129108.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, September, 2020Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 122-142).
Various advanced nuclear reactors including fluoride high-temperature salt-cooled reactors (FHRs), molten salt reactors (MSRs) and fusion devices have proposed to use molten salt coolants. However, there remain many uncertainties in the chemistry, dynamics and physicochemical properties of many salts, especially over the course of reactor operation, where impurities are introduced, and compositional and thermodynamic changes occur. Density functional theory (DFT) and ab initio molecular dynamics (AIMD) were used for property, structure and chemistry predictions for a variety of salts including LiF, KF, NaF, BeF2, LiCl, KCl, NaCl, prototypical Flibe (66.6%LiF-33.3%BeF2), and Flinak (46.5%LiF-11.5NaF-42%KF). Predictions include thermophysical and transport properties such as bulk density, thermal expansion coefficient, bulk modulus, and diffusivity, which were compared to available experimental data.
DFT consistently overpredicted bulk density by about 7%, while all other properties generally agreed with experiments within experimental and numerical uncertainties. Local structure was found to be well predicted where pair distribution functions showed similar first peak distances (+ 0.1 A) and first shell coordination numbers (+ 0.4 on average), indicating accurate simulation of chemical structures and atomic distances. Diffusivity was also generally well predicted within experimental uncertainty (+20%). Validated DFT and AIMD methods were applied to study tritium in prototypical salts since it is an important corrosive and diffusive impurity found in salt reactors. It was found that tritium species diffusivity depended on its speciation (TF vs. T2), which was related to chemical structures formed in Flibe and Flinak salts. Further, predictions allowed comparison with and interpretation of past contradictory experimental results found in the literature.
Lastly, robust neural network interatomic potentials (NNIPs) were developed for LiF and Flibe. The LiF NNIP accurately reproduced DFT calculations for pair interactions, solid LiF and liquid molten salt. The Flibe NNIP was developed for molten salt at the reactor operating temperature of 973K and was found to reproduce local structures calculated from DFT and showed good stability and accuracy during extended MD simulation. Ab initio methods and NNIPs can play a major role in advanced reactor development. Combined with experiments, these methods can greatly improve fundamental understanding and accelerate materials discovery, design and selection.
by Stephen Tsz Tang Lam.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
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Gonçalves, Marques Mário Rui [Verfasser], Miguel [Gutachter] Marques, Wolfgang [Gutachter] Paul, and Patrick [Gutachter] Rinke. "The structure and dynamics of materials using machine learning / Mário Rui Gonçalves Marques ; Gutachter: Miguel Marques, Wolfgang Paul, Patrick Rinke." Halle (Saale) : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2020. http://d-nb.info/1212434870/34.
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Curtarolo, Stefano 1969. "Coarse-graining and data mining approaches to the prediction of structures and their dynamics." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17034.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.Includes bibliographical references (p. 245-263).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Predicting macroscopic properties of materials starting from an atomistic or electronic level description can be a formidable task due to the many orders of magnitude in length and time scales that need to be spanned. A characteristic of successful approaches to this problem is the systematic coarse-graining of less relevant degrees of freedom in order to obtain Hamiltonians that span larger length and time scale. Attempts to do this in the static regime (i.e. zero temperature) have already been developed, as well as thermodynamical models where all the internal degrees of freedom are removed. In this thesis, we present an approach that leads to a dynamics for thermodynamic-coarse-grained models. This allows us to obtain temperature-dependent and transport properties. The renormalization group theory is used to create new local potential models between nodes, within the approximation of local thermodynamical equilibrium. Assuming that these potentials give an averaged description of node dynamics, we calculate thermal and mechanical properties. If this method can be sufficiently generalized it may form the basis of a Multiscale Molecular Dynamics method with time and spatial coarse-graining. In the second part of the thesis, we analyze the problem of crystal structure prediction, by using quantum calculations.
(cont.) This is a fundamental problem in materials research and development, and it is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this thesis, we transfer the concept of heuristic rule extraction to a large library of ab-initio calculated information, and demonstrate that this can be developed into a tool for crystal structure prediction. In addition, we analyze the ab-initio results and prediction for a large number of transition-metal binary alloys.
by Stefano Curtarolo.
Ph.D.
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Kwak, Seung-Keon. "New modeling and control design techniques for aircraft structural dynamics using smart materials /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488188894442033.
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Ramzan, Muhammad. "Structural, Electronic and Mechanical Properties of Advanced Functional Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205243.
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The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage. Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials. Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies. MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method. Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature. In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.
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Salahshoor, Pirsoltan Hossein. "Nanoscale structure and mechanical properties of a Soft Material." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-theses/924.
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"Recently, hydrogel have found to be promising biomaterials since their porous structure and hydrophilicity enables them to absorb a large amount of water. In this study the role of water on the mechanical properties of hydrogel are studied using ab-initio molecular dynamics (MD) and coarse-grained simulations. Condensed-Phased Optimized Molecular Potential (COMPASS) and MARTINI force fields are used in the all-atom atomistic models and coarse-grained simulations, respectively. The crosslinking process is modeled using a novel approach by cyclic NPT and NVT simulations starting from a high temperature, cooling down to a lower temperature to model the curing process. Radial distribution functions for different water contents (20%, 40%, 60% and 80%) have shown the crosslinks atoms are more hydrophilic than the other atoms. Diffusion coefficients are quantified in different water contents and the effect of crosslinking density on the water diffusion is studied. Elasticity parameters are computed by constant strain energy minimization in mechanical deformation simulations. It is shown that an increase in the water content results in a decrease in the elastic. Finally, continuum hyper elastic model of contact lens is studied for three different loading scenarios using Finite Element Model. "