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Dissertations / Theses on the topic 'Network Structure - Glasses'
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1
Polidori, Annalisa. "Structure of disordered materials : from geological fluids to network glasses." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715303.
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The method of neutron diffraction with isotopic or isomorphic substitution (NDIS) was employed to investigate the atomic-scale structure of several disordered multi-component materials, thus reducing the complexity of correlations associated with a single diffraction pattern. The solvation of the Cl ion in a 5 molal solution of NaCl in D2O was investigated at temperatures and pressures up to 150 C and 33.8 kbar, respectively, thus extending the state conditions for studying the structure of this geological fluid. Changes to the structure with increasing temperature at 0.1 kbar may be attributed to a reduction in the dielectric permittivity, and the structural variation with increasing pressure at 150 C reflects changes in the structure of water to a more simple-fluid like phase. NDIS with Se-isotopes was used to help untangle the composition-dependent structure of As-Se glasses. The results for As0.30Se0.70 and As0.35Se0.65 favour the formation of a chemically ordered over a chemically disordered network, while the results for As0.40Se0.60 reveal broken chemical order through the appearance of homopolar bonds. The work shows a need to improve previous structural models that were produced by using both the reverse Monte Carlo and first-principles molecular-dynamics methods. Rare-earth clustering in the aluminosilicate glass (R2O3)0.2(Al2O3)0.2(SiO2)0.6 was investigated via NDIS, using Nd and Pr as an isomorphic pair. The results indicate a network structure based on SiO4 tetrahedra along with AlO4 and AlO5 units in the approximate ratio of 4:1. Each rare-earth (R) ion has, on average, 7.3(2) nearest-neighbour oxygen atoms at a distance of rRO = 2.43(2) A, and the R-R nearest neigh-bour distance is 3.9(4) A. The results are discussed by reference to the structure of a rare-earth glass of the same composition, but where Nd/Pr is replaced by a smaller rare-earth ion pair such as Dy or Ho.
2
Stechert, Thorsten Roland. "Glasses for energy applications : atomic scale network structure and properties." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18940.
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Glass is used for the vitrification of high level waste that results from the reprocessing of spent nuclear fuel. A better understanding of the structure of vitrified wastes may lead to insights into the observed compositional flexibility. It is also the starting point for studies of the self-irradiation behaviour of glasses under long-term repository conditions. Appropriate models need to be employed for the study of glasses when using molecular dynamics. The nature of nuclear waste necessitates an accurate structure prediction for a range of compositions and parameters. To this end, the suitability of established potential sets have been compared. The established potential models were used to investigate the structure of zinc containing sodium silicate glass. Once validated, this structure was used to investigate structural changes observed during simulated self-irradiation, where significant changes were observed on the atomic scale. This will provide the basis for further studies of radiation damage, glass-crystal interfaces and damage across glass-crystal interfaces. In order to further enhance the understanding of potential models, a novel glass of composition LiAlF4 has been successfully described, and may become relevant in the future as a thin film coating in Li-ion batteries.
3
Lu, Xiaonan. "Effects of Transition Metal Oxide and Mixed-Network Formers on Structure and Properties of Borosilicate Glasses." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404587/.
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First, the effect of transition metal oxide (e.g., V2O5, Co2O3, etc.) on the physical properties (e.g., density, glass transition temperature (Tg), optical properties and mechanical properties) and chemical durability of a simplified borosilicate nuclear waste glass was investigated. Adding V2O5 in borosilicate nuclear waste glasses decreases the Tg, while increasing the fracture toughness and chemical durability, which benefit the future formulation of nuclear waste glasses. Second, structural study of ZrO2/SiO2 substitution in silicate/borosilicate glasses was systematically conducted by molecular dynamics (MD) simulation and the quantitative structure-property relationships (QSPR) analysis to correlate structural features with measured properties. Third, for bioactive glass formulation, mixed-network former effect of B2O3 and SiO2 on the structure, as well as the physical properties and bioactivity were studied by both experiments and MD simulation. B2O3/SiO2 substitution of 45S5 and 55S5 bioactive glasses increases the glass network connectivity, correlating well with the reduction of bioactivity tested in vitro. Lastly, the effect of optical dopants on the optimum analytical performance on atom probe tomography (APT) analysis of borosilicate glasses was explored. It was found that optical doping could be an effective way to improve data quality for APT analysis with a green laser assisted system, while laser spot size is found to be critical for optimum performance. The combined experimental and simulation approach adopted in this dissertation led to a deeper understanding of complex borosilicate glass structures and structural origins of various properties.
4
Ebrahem, Firaz [Verfasser], Bernd [Akademischer Betreuer] Markert, and Raimund [Akademischer Betreuer] Rolfes. "Molecular structure-property relationships of network glasses under mechanical loading / Firaz Ebrahem ; Bernd Markert, Raimund Rolfes." Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/1230661727/34.
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5
Chen, Ping. "Intermediate phases, boson and floppy modes, and demixing of network structures of binary As-S and As-Se glasses." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250689099.
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Vignarooban, Kandasamy. "Boson Mode, Dimensional Crossover, Medium Range Structure and Intermediate Phase in Lithium- and Sodium-Borate Glasses." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353100044.
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Zaiter, Rayan. "Silver and/or mercury doped thioarsenate and thiogermanate glasses : Transport, structure and ionic sensibility." Thesis, Littoral, 2018. http://www.theses.fr/2018DUNK0485/document.
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Le but de ce travail de thèse consiste à étudier les propriétés physico-chimiques des verres chalcogénures afin de pouvoir les utiliser comme membranes de capteurs chimiques destinés pour le dosage des ions Hg²⁺. Dans un premier temps, les propriétés macroscopiques des systèmes vitreux AgY-As₂S₃ (Y = Br, I), HgS-GeS₂, AgI-HgS-As₂S₃ et AgI-HgS-GeS₂, telles que les densités et les températures caractéristiques (Tg et Tc) ont été mesurées et analysées selon les compositions des verres. Puis, dans un second temps, les propriétés de transport ont été étudiés à l'aide de la spectroscopie d'impédance complexe d'une part, ou d'autre part, par des mesures de la résistivité. Ces dernières montrent que les verres de chalcogénures dopés à l'halogénure d'argent présentent deux différents régimes de transports au-dessus du seuil de percolation xc ≈ 30 ppm : (i) domaine de percolation critique, et (ii) domaine contrôlé par modificateur. Vient ensuite la troisième partie, elle consiste à déchiffrer les relations composition/structure/propriété grâce à plusieurs études structurales. Des mesures par spectroscopie Raman, par diffraction de neutrons et de rayons X haute énergie, par diffusion des neutrons sous petits angles (SANS), ainsi que des modélisations RMC/DFT et AMID ont été réalisées. Enfin, la dernière partie de ce travail était une étude préliminaire des caractéristiques des nouveaux capteurs chimiques. Il a été consacré à l'étude des relations entre la composition et la sensibilité des membranes ainsi qu'aux limites de détection qui les définissentThe aim of the thesis is to study the physicochemical properties of the silver halide doped chalcogenide glasses for the possibility to use them as chemical sensors for quantitative analysis of Hg²⁺ ions. First, the macroscopic properties of AgY-As₂S₃ (Y = Br, I), HgS-GeS₂, AgI-HgS-As₂S₃ and AgI-HgS-GeS₂ glassy systems such as the densities and the characteristic temperatures (Tg and Tc) were measured and analyzed according to the glass compositions. Second, the transport properties were studied using complex impedance and dc conductivity. Measurements show that the silver halide doped chalcogenide glasses exhibit two drastically different ion transport regimes above the percolation threshold at xc ≈ 30 ppm : (i) critical percolation, and (ii) modifier-controlled regimes. Third, to unveil the composition/structure/property relationships, various structural studies were carried out. Raman spectroscopy, high-energy X-ray diffraction, neutron diffraction and small-angle neutron scattering experiments, together with RMC/DFT and AMID modelling were employed. Finally, the last part was a preliminary study of the characteristics of new chemical sensors. It was devoted to study the relationship between the membranes' composition and sensitivity but also detection limits
8
Gunasekera, Kapila J. "Intermediate Phase, Molecular Structure, Aging and Network Topology of Ternary GexSbxSe100-2x Glasses." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1277132558.
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9
Wezka, Kamil. "Pressure induced structural transformations of network forming glasses." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608339.
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The method of in situ high pressure neutron diffraction was employed to measure reliable diffraction patterns to help illuminate the density-driven structural transformations in GeO2, SiO2, B2O3 and GeSe2 glass. The majority of this neutron diffraction work employed the diffractometer D4c at the ILL with a Paris-Edinburgh press which enabled the pressure range from ambient to 8 GPa to be accessed. In the cases of GeO2 and GeSe2 glass, the neutron diffraction with isotopic substitution (NDIS) protocol was developed to provide benchmark experimental results to test the results obtained from various molecular dynamics simulations using different theoretical schemes. For GeO2 glass, from a combination of neutron diffraction and molecular dynamics results, it was found that the increase in density of the glass initially occurs through a reorganisation of corner-shared GeO4 tetrahedra on an intermediate length scale as the pressure is increased from ambient to 5 GPa. At higher pressures, there is a progression from a tetrahedral to an octahedral glass, via the formation of 5-fold coordinated Ge atoms which have a predominantly square pyramidal geometry. In the work on SiO2 and B2O3 glass the pressure range for the in situ high pressure neutron diffraction results was extended to 14.5 GPa and 17.5 GPa, respectively, by using the PEARL diffractometer at ISIS. For both materials the neutron diffraction results provide complementary information to pressure x-ray diffraction studies helping to elucidate the mechanism of network collapse. In the case of SiO2 glass, densification over the measured pressure range occurs predominantly by a reorganisation of corner shared SiO4 tetrahedra on an intermediate length scale. In the case of B2O3 glass, the B-O coordination number changes from 3 to ∼ 3.9 at the pressure is increased from ∼ 8 to 17.5 GPa. For GeSe2 glass, from a combination of neutron diffraction and molecular dynamics results, it was found that the density increase from ambient pressure up ∼ 8 GPa occurs by a reorganisation of both corner and edge-sharing GeSe4 tetrahedra on an intermediate length scale. Above this pressure, 5- and 6-fold coordinated Ge atoms start to form at a similar density and homopolar bonds play an intimate role in the formation of these higher coordinated polyhedra.
10
Dallari, Francesco. "Slow dynamics in colloids and network glasses close to the structural arrest: the Stress-relaxation as a root to equilibrium." Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/367754.
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Microscopically disordered materials are at the core of an increasing number of new material technologies, but crucial limitations in their applications come from the physical aging of their properties and the extreme sensitivity on the system's history, which stem from the their intrinsically out of equilibrium nature. A clear understanding of the aging phenomenon, as well as the effects of the release of internal stresses acting at different length-scales, are still lacking. In this Thesis the slow dynamics of disordered systems is investigated at different length-scales ranging from the micrometre length-scale probed in optical experiments to length-scales of few angstroms probed in wide angle X-ray experiments. The time evolution of the probed out of equilibrium dynamics is thoroughly studied in different glasses exploiting the multi speckle photon correlation technique with different sources. The investigated materials are a set of strong glass-formers (materials that can be found in a wide variety of common glassware) and colloidal suspensions at high volume fractions in an arrested state. The latter class of materials are known as soft glasses and in recent years they are earning great interest and can be found in a lot of industrial products (e.g. wall paint, ink, chocolate) or in production processes (e.g. ceramics). Despite the differences between the probed systems and their production protocols, it is here shown that in all the studied materials the microscopic dynamics displays common trends and that it is strongly connected to the relaxation of the stresses that have remained trapped in these systems after their production.
11
Dallari, Francesco. "Slow dynamics in colloids and network glasses close to the structural arrest: the Stress-relaxation as a root to equilibrium." Doctoral thesis, University of Trento, 2018. http://eprints-phd.biblio.unitn.it/3066/2/Disclaimer_riservatezza_tesi.pdf.
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Microscopically disordered materials are at the core of an increasing number of new material technologies, but crucial limitations in their applications come from the physical aging of their properties and the extreme sensitivity on the system's history, which stem from the their intrinsically out of equilibrium nature. A clear understanding of the aging phenomenon, as well as the effects of the release of internal stresses acting at different length-scales, are still lacking. In this Thesis the slow dynamics of disordered systems is investigated at different length-scales ranging from the micrometre length-scale probed in optical experiments to length-scales of few angstroms probed in wide angle X-ray experiments. The time evolution of the probed out of equilibrium dynamics is thoroughly studied in different glasses exploiting the multi speckle photon correlation technique with different sources. The investigated materials are a set of strong glass-formers (materials that can be found in a wide variety of common glassware) and colloidal suspensions at high volume fractions in an arrested state. The latter class of materials are known as soft glasses and in recent years they are earning great interest and can be found in a lot of industrial products (e.g. wall paint, ink, chocolate) or in production processes (e.g. ceramics). Despite the differences between the probed systems and their production protocols, it is here shown that in all the studied materials the microscopic dynamics displays common trends and that it is strongly connected to the relaxation of the stresses that have remained trapped in these systems after their production.
12
Dash, Shreeram J. "Aging of Selenium glass probed by MDSC and Raman Scattering Experiments: Growth of inter-chain structural correlations leading to network compaction." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1490354472387536.
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13
Burger, Matthew S. "Evidence for the 3-D network of P-centered Pyramidal P(Se1/2)3 and Quasi-tetrahedral Se=P(Se1/2)3 Local Structures and their 3-membered Ring Counterparts Decoupled from the Quasi-1-D Ethylene-like P2Se2+x (x= 2,1,0) Chains in Bulk PxSe100-x Glasses." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627664642854937.
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14
Pumlianmunga. "Influence of local structure and network connectivity on the electrical switching of some Te-based chalcogenide glasses." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5425.
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Chalcogenide glass (ChG) materials have gained wide attention because of their applications in phase change non-volatile memories (PC-RAM), optical rewritable disks (CD-RW and DVD-RW), infrared detection and thermal imaging. One of the significant properties of ChG materials is the change in the resistivity of the material when a metal such as Al, Cu, and Sb are added. Electrical switching is another interesting and important property possessed by several Te based chalcogenides. Switching is the rapid transition between a high resistive OFF state to low resistive ON state driven by an external electric field and characterized by a threshold voltage. The contrast in electrical resistivity between the OFF and ON state is > 103 Ohms. This electrical switching can be of two types: (i) Threshold switching and (ii) memory switching. Upon the removal of the applied field threshold switching device reverts back to the OFF state, whereas the memory device retains the ON state. Memory switching, a non-reversible transition is understood based on the thermal mechanism where the applied electric field drives the system from amorphous/glass (OFF) to crystalline (ON) state. Threshold switching, a reversible transition is understood based on electronic transitions. Electrical switching is mainly influence by the network connectivity, rigidity, local structure, and glass forming ability. Investigations on electrical switching in chalcogenide glasses help in understanding the mechanism of switching which is necessary to select and modify materials for specific switching applications. In this work, we have studied the influence of network connectivity,local structure and glass forming ability on electrical switching in melt quenched bulk Al-Te, Al-Te-Sb, Al-As-Te and GeTe4-As2Se3 chalcogenide glasses. Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Raman Spectroscopy, Magic Angle Nuclear Magnetic Resonance (MAS-NMR), Nano-Indentation methods were used to study the properties of these glasses. From the obtained results the threshold and memory switching exhibited by these glasses were understood uniquely by the thermal mechanism.
15
Lu, Linghong. "Structural principles for dynamics of glass networks." Thesis, 2008. http://hdl.handle.net/1828/900.
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Gene networks can be modeled by piecewise-linear (PL) switching systems of differential equations, called Glass networks after their originator. Networks of interacting genes that regulate each other may have complicated interactions. From a `systems biology' point of view, it would be useful to know what types of dynamical behavior are possible for certain classes of network interaction structure.
A useful way to describe the activity of this network symbolically is to represent it as a directed graph on a hypercube of dimension $n$ where $n$ is the number of elements in the network. Our work here is considering this problem backwards, i.e. we consider different types of cycles on the $n$-cube and show that there exist parameters, consistent with the directed graph on the hypercube, such that a periodic orbit exists.
For any simple cycle on the $n$-cube with a non-branching vertex, we prove by construction that it is possible to have a stable periodic orbit passing through the corresponding orthants for some sets of focal points $F$ in Glass networks. When the simple cycle on the $n$-cube doesn't have a non-branching vertex, a structural principle is given to determine whether it is possible to have a periodic orbit for some focal points. Using a similar construction idea, we prove that for self-intersecting cycles where the vertices revisited on the cycle are not adjacent, there exist Glass networks which have a periodic orbit passing through the corresponding orthants of the cycle. For figure-8 patterns with more than one common vertex, we obtain results on the form of the return map (Poincar{\'e} map) with respect to how the images of the returning cones of the 2 component cycle intersect the returning cone themselves. Some of these allow complex behaviors.