Дисертації з теми "Defects Chemistry"
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1
Cromack, Keith Richard. "Photo-induced magnetic defects in conducting polymers." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343059111.
2
Józefowicz, Mikolaj Edward. "Structure and long-lived defects in polyanilines." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343400785.
3
Cliffe, Matthew James. "Disorder and defects in functional molecular frameworks." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:cd827bc8-b3dd-4fda-bdb8-f0dc893d66c2.
Анотація:
This Thesis explores the role of structural defects and disorder and their relationship to experimental data, with a particular emphasis on molecular framework materials. The question of how we can build atomistic models of amorphous materials from experimental data without needing to make system-specific assumptions is addressed. The role of 'structural invariance', i.e. the limited range of distinct local atomic environments within a material, as a restraint within reverse Monte Carlo refinement (RMC) is investigated. The operation of these invariance restraints operate is shown to be system-dependent and the challenges associated with effective refinement, e.g. configurational 'jamming', are also investigated. A generalisation to the 'structural simplicity', i.e. the simplest model, holding all else constant, is most likely to be correct. Three new metrics of structural simplicity are proposed: two intrinsically three-dimensional measures of local geometric invariance and one measure of local symmetry. These metrics are shown to robustly quantify the configurational quality. The ability of these metrics to act as effective restraints for the RMC refinement of amorphous materials is demonstrated by the construction of the first data-driven tetrahedral models of amorphous silicon. The role of defects and disorder within metal–organic frameworks (MOFs) is investigated through the canonical MOF UiO-66(Hf). Through a combination of techniques, including X-ray diffuse scattering, anomalous diffraction, total scattering and electron diffraction measurements, the existence of correlated metal-cluster absences in UiO-66(Hf) is demonstrated. Furthermore the ability to synthetically tune both the interactions and concentration of defects is shown. The thermomechanical properties of defective UiO-66(Hf) are also examined. UiO-66(Hf) is shown to rapidly densify by up to 5% (ΔV/V ) on ligand elimination. The resultant densified phase exhibits colossal (≥100MK-1) volumetric negative thermal expansion (NTE); the largest reported value for any MOF. Finally, the capability to tune the physical properties of MOFs through defect incorporation is demonstrated through the defect-dependence of both the densification and the NTE.
4
Lee, Lawrence Yoon Suk 1972. "Probing and controlling defects in self-assembled monolayers." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102674.
Анотація:
This thesis is focused on the development of a tool for probing defects in self-assembled monolayers (SAMs). Such a tool is necessary for the detailed understanding of fundamental issues in SAM composition and structure. The electrochemical properties of single component and binary ferrocenylalkylthiol SAMs on polycrystalline gold (FcC12S-Au and FcC12S-/CH 3RS-Au) have been investigated in detail. The complex voltammetry obtained for various mixtures of FcC12S-Au SAMs is shown to be linked to local electrostatics caused by the formation of the ferrocenium ion. A procedure involving a Gaussian-Lorentzian fit is used to deconvolute the two peaks consistently observed in the SAMs when the surface mole fraction of the FcC12S-Au ( csurfFc ) ≥ 0.2. The lower potential (Eº' = 250 mV) and higher potential (Eº' = 350 mV) voltammetric peaks are thus assigned to Fc moieties in "isolated" and "clustered" states, respectively. Use of this method to better understand SAM structure is demonstrated by distinguishing the degree of homogeneity in two binary SAMs of similar composition.This characteristic electrochemical property of FcC12S-Au system allows for the quantification of defects in SAMs. This is important because coverage defects, or voids in alkylthiol SAMs, are a critical component of electron transfer mechanisms of soluble redox probes. Short time exposure of a defective SAM to FcC12SH leads to a quantifiable defect-related Fc coverage (GammaFc), with GammaFc < 1% being readily measurable. Using FcC12SH as a label, a number of alkylthiol SAM preparation conditions have been assessed.
FcC12SH is further used to probe the progress of the important alkylthiol-for-alkylthiol exchange reaction in SAMs. It is shown that variation of chain length, reaction temperature, terminal group, applied potential, and the initial defect density determines the extent and the rate of the exchange reaction. Kinetics studies of binary (FcC12S-/CH3RS-Au) SAM formation via co-incubation reveal that although csurfFc is initially close to the solution mole fraction of the FcC12 SH ( csolnFc ), the subsequent exchange reaction leads to a csurfFc which is often quite different from csolnFc .
Finally, the FcC12SH probe is used to further study the reductive voltammetric desorption of alkylthiol SAMs. Defects in a C14S-Au SAM created by excursions to desorptive reduction potentials were quantified by use of the FcC12SH label. A reductive desorption potential followed by re-adsorption, applied to a binary (FcC12S-/C14S-Au) SAM, results in mixing of the phase separated components of the binary SAM.
5
Pressé, Steve 1981. "Role of fluctuations and defects in select condensed matter problems." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43774.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.Page 122 blank. Vita.
Includes bibliographical references.
Defects and fluctuations dominate both static and dynamical properties of systems in the condensed phase. In this work, we focus on three such examples. Firstly, we model the effect of proton fluctuations on the rate of electron transfer in the condensed phase through an electron donor-acceptor assembly linked via an H-bonding bridge. The model suggests that it is possible for the electron transfer rate through a deuterated H-bonding assembly to exceed the rate through a protonated H-bonding bridge at low temperature, consistent with experimental findings. Next, we consider the convergence properties of Jarzynski's non-equilibrium work relation. This relation expresses the free energy change of a system, onto which finite-time work is done, as an ensemble average over all possible trajectories of the system. We quantify the regime of applicability of this equality by considering the role of rare fluctuations which dominate the work average of entropy generating processes. Lastly, we consider fluorophore lifetime variations arising when single molecules are placed near non-planar metallic surfaces. We compute the exact first order self-fields of vertical dipoles located above locally curved perfectly conducting surfaces by invoking a small slope phase perturbation technique. The results suggest that smooth perturbations lead to deviations from the image theory results extensively used to interpret the experimentally observed single molecule lifetime changes.
by Steve Pressé.
Ph.D.
6
Mottishaw, Sinead. "Investigations of the nature, properties and distribution of defects in diamond." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/101511/.
Анотація:
This thesis presents investigations into the nature, properties and distribution of defects in diamond grown by the methods of chemical vapour deposition (CVD) and high pressure, high temperature (HPHT) synthesis. The experimental techniques used include electron paramagnetic resonance, optical absorption, cathodoluminescence, photoluminescence and secondary ion mass spectroscopy (SIMS). The optical spin polarisation of the neutral silicon vacancy defect (SiV0) was shown to be strongly enhanced by resonant excitation at the zero-phonon energy, although there was significant sample to sample variation in the magnitude. The spin polarisation mechanism is different to that observed for the negatively charged nitrogen vacancy defect in diamond and more than one mechanism may be generating spin polarisation. The spin-lattice relaxation time (T1) of the SiV0 ground state was found to change by six orders of magnitude between room temperature and 11 K, where T1 exceeded 25 seconds. At room temperature the achievable optical ground state spin polarisation is limited by the rapid spin-lattice relaxation. Irradiation and annealing studies of silicon doped CVD diamond samples showed that the silicon vacancy concentration can be increased by irradiation and annealing. However, the same processing conditions can also reduce the concentration of grown-in silicon vacancy defects. This work suggests that the relative incorporation efficiency of silicon in different forms in homoepitaxial CVD diamond may depend on the orientation of the substrate, and that the details of post growth silicon vacancy defect production, especially in boron doped diamond, are not yet well understood. HPHT samples in which the13 C isotopic abundance had been increased up to approximately 10% were studied. The variation of the abundance of13 C with distance from the seed was studied using Raman spectroscopy and SIMS, and the nitrogen incorporation by infrared microscopy. Possible explanations of the variations in both are discussed. The incorporation of point and extended defects into diamond grown by heteroepitaxial CVD was studied in a nitrogen doped sample and another grown with efforts to exclude nitrogen. The samples were highly birefringent when observed through cross-polarisers and exhibited strong dislocation related photoluminescence, suggesting significant concentrations of dislocations and dislocation bundles. The nitrogen doped heteroepitaxial CVD sample contained point defects in relative concentrations typically observed in nitrogen doped homoepitaxial CVD diamond; the total nitrogen impurity concentration exceeded 2,000 ppb, whereas in the intrinsic heteroepitaxial CVD sample it was less than a few ppb. Both samples contained a significant concentration of silicon vacancy defects and the photoluminescence spectra indicated that the point defects were subject to significant strain arising from both extended and point defects.
7
Roy, Santanu. "Spectroscopic study of defects in cadmium selenide quantum dots (QDS) and cadmium selenide nanorods (NRS)." Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16118.
Анотація:
Doctor of PhilosophyDepartment of Chemistry
Viktor Chikan
Ever depleting sources of fossil fuel has triggered more research in the field of alternate sources of energy. Over the past few years, CdSe nanoparticles have emerged as a material with a great potential for optoelectronic applications because of its easy exciton generation and charge separation. Electronic properties of CdSe nanoparticles are highly dependent on their size, shape and electronic environment. The main focus of this research is to explore the effect of different electronic environments on various spectroscopic properties of CdSe nanoparticles and link this to solar cell performance. To attain that goal, CdSe quantum dots (QDs) and nanorods (NRs) have been synthesized and either doped with metal dopants or embedded in polymer matrices. Electronic properties of these nanocomposites have been studied using several spectroscopic techniques such as absorption, photoluminescence, time-resolved photoluminescence, confocal microscopy and wide field microscopy. Indium and tin are the two metal dopants that have been used in the past to study the effect of doping on conductivity of CdSe QDs. Based on the photoluminescence quenching experiments, photoluminescence of both indium and tin doped samples suggest that they behave as n-type semiconductors. A comparison between theoretical and experimental data suggests that energy levels of indium doped and tin doped QDs are 280 meV and 100 meV lower than that of the lowest level of conduction band respectively. CdSe nanorods embedded in two different polymer matrices have been investigated using wide field fluorescence microscopy and confocal microscopy. The data reveals significant enhancement in bandedge luminescence of NRs in the vicinity of a conjugated polymer such as P3HT. Photoactive charge transfer from polymers to the surface traps of NRs may account for the observed behavior. Further study shows anti-correlation between bandedge and trap state emission of CdSe NRs. A recombination model has been proposed to explain the results. The origin of traps is also investigated and plausible explanations are drawn from the acquired data.
8
Srinivasan, K. "FDAS : a knowledge-based framework for analysis of defects in woven textile structures." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/8671.
9
Roberts, Sean T. (Sean Thomas). "Hydrogen bond rearrangements and the motion of charge defects in water viewed using multidimensional ultrafast infrared spectroscopy." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57678.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2010."December 2009." Cataloged from PDF version of thesis. Vita.
Includes bibliographical references.
Compared with other molecular liquids, water is highly structured due to its ability to form up to four hydrogen bonds to its nearest neighbors, resulting in a tetrahedral network of molecules. However, this network is highly dynamic, exhibiting fluctuations and rearrangements that take place on femtosecond to picosecond time scales. The transport of excess protons and proton holes in water makes exclusive use of water's hydrogen bonding network. Compared to ions of similar size and charge density, both hydronium and hydroxide ions exhibit anomalously high diffusion rates due to the fact that water molecules that neighbor these ions can undergo a proton transfer reaction with the ion. This allows the structural diffusion of the ion to occur apart from the displacement of individual water molecules. In this thesis we adopt a joint experimental and theoretical approach to characterize the fluctuations of water's hydrogen bonding network and how these fluctuations act to drive the structural diffusion of the aqueous hydroxide ion. The experimental data that we present consists of a series of ultrafast nonlinear infrared spectroscopies, in particular two-dimensional infrared spectroscopy (2D IR), applied to the O-H stretching transition of a dilute solution of HOD in NaOD/D20. The frequency of the O-H stretch, (OH, is highly sensitive to the configuration of its hydrogen bonding partner. 2D IR spectroscopy allows us to measure rapid shifts in OH that reveal time scales for changes in the local environment of the HOD molecule.
(cont.) The calculation of 2D IR spectra from molecular dynamics simulations then allows us to make a direct connection between the results of our experiments and the underlying dynamics of the system that drive both hydrogen bond exchange and the structural diffusion of the hydroxide ion. 2D IR spectra recorded for dilute HOD in D20 show a strong asymmetry, preferentially broadening in the frequency region indicative of strained or broken hydrogen bonds, indicating that these configurations are unstable and quickly return to a hydrogen bond. The time scale over which the 2D spectra broaden, ~60 fs, is similar to the librational period of water and suggests that molecules exchange hydrogen bonding partners though rapid, large amplitude rotations. Molecular dynamics simulations find that the transition state for hydrogen bond exchange resembles a bifurcated hydrogen bond. In roughly half of the examined exchange events, a second solvation shell water molecule inserts across the breaking hydrogen bond. This suggests that hydrogen bond rearrangements are tied to the restructuring of a water molecule's solvation shell. Upon the addition of NaOD to HOD/D20 solution, a large absorption continuum appears to the low frequency side of the O-H stretch due to the formation of strong hydrogen bonds between HOD molecules and OD ions. At early waiting times, 2D IR spectra show large, offdiagonal intensity in this frequency range that rapidly relaxes within ~110 fs.
(cont.) Modeling using an empirical valence bond simulation (MS-EVB) model of aqueous NaOH suggests that as the 0-H stretching potential symmetrizes during proton transfer events, overtone transitions of the shared proton contribute strongly to 2D spectra. The rapid loss of offdiagonal intensity results from the spectral sweeping of these vibrational overtones as the solvent modulates the motion of the shared proton. The collective electric field of the solvent is found to be an appropriate reaction coordinate for the formation and modulation of shared proton states. Over picosecond waiting times, spectral features appear in the 2D IR spectra that are indicative of the exchange of population between OH~ ions and HOD molecules due to proton transfer. The construction of a spectral fitting model gives a lower bound of 3 ps for this exchange. Calculations of structural parameters following proton exchange using the MS-EVB simulation model suggest that the observed exchange process corresponds to the formation and breakage of hydrogen bonds donated by the HOD/OD~ pair formed as a result of the proton transfer. A full description of the structural diffusion of the hydroxide ion requires both a description of the local hydrogen bonding structure of the ion as well as the dielectric fluctuations of the surrounding solvent.
by Sean T. Roberts.
Ph.D.
10
Jensen, Stephen C. "The Role of Interstitials and Surface Defects on Oxidation and Reduction Reactions on Titania." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10768.
Анотація:
This thesis focuses on understanding the influence of defect sites in titanium dioxide that drive many types of thermal and photochemical reactions. Two of the most common defects in vacuum are titanium interstitials and oxygen vacancies. Molecular oxygen fills oxygen vacancies and creates oxygen adatoms. We broadly investigate reduction and oxidation reactions of oxygenates driven by titanium interstitials and oxygen adatoms. First, we focus on the thermal chemistry of oxygen adatoms with butyrophenone and find that it reacts with the adatoms to form a strongly bound complex. The large difference in mobility between complexed and uncomplexed butyrophenone, and the corrugated nature of the \(TiO_2(110)\) surface plane, allows a confined one-dimensional gas to persist, which is characterized by scanning tunneling microscopy (STM). Next, we focus on the reductive coupling of benzaldehyde to stilbene that is driven by titanium interstitials. The diolate intermediate of the reaction is identified by STM and the thermodynamic preference of molecular oxygen to interact with titanium interstitials is exploited to selectively reverse the benzaldehyde diolate intermediates. Additionally, we investigate the photo-oxidative coupling of methanol to methyl formate, the photo-oxidation of butyrophenone and the photo-stability of benzoate. Finally, we identify a water splitting mechanism on reduced titania that creates oxygen adatoms. We demonstrate that the photo-generated oxygen adatoms thermally react with titanium interstitials to make TiOx islands and drive the photo-oxidation of formaldehyde and butyrophenone. Methods used include temperature programmed reaction spectroscopy, STM, and density functional theory.Chemistry and Chemical Biology
11
Werner, Kristin. "On the Role of Oxygen Vacancies in the Surface Chemistry of Ceria (CeO2)." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20496.
Анотація:
Ceroxid (CeO2) wurde in den letzten Jahren als Katalysator für die Hydrierung von Alkinen zu Alkenen entdeckt und hat als solcher großes wissenschaftliches Interesse geweckt. Um weitere Einblicke in die Funktion von CeO2 in der Reaktion zu gewinnen, beschäftigt sich diese Arbeit mit der Adsorption von H2, CO2 und Propin, sowie mit der Interaktion von Hydroxylgruppen und Propin auf CeO2(111)-Oberflächen. Ein besonderer Fokus liegt dabei auf der Rolle von Sauerstoffleerstellen.In recent years, ceria (CeO2) has attracted much scientific interest due to its activity as a catalyst in the selective hydrogenation of alkynes to alkenes. To gain further insights into the role of CeO2 in propyne hydrogenation, this thesis explores the fundamental processes of H2, CO2, and propyne adsorption, as well as the interaction of hydroxyls and propyne on well-defined CeO2(111) surfaces. A special emphasis thereby lies on the role of oxygen (O) vacancies in these processes.
12
Diallo, Ibrahima Castillo. "Theoretical and Experimental Analysis of Optical Properties of Defects in GaN:." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/4989.
Анотація:
Using the Heyd-Scuseria-Ernzherof (HSE06) hybrid functional method along with photoluminescence experimental measurements, we analyze the properties of intrinsic defects such as vacancies, interstitials, antisites, and common complexes. By using configurational coordinate diagrams, we estimate the likelihood of defects to be radiative or non-radiative. Our calculations show that gallium vacancies exhibit a large magnetic moment in the neutral charge state and are most likely non-radiative. We also investigate the correlation between the observed infrared PL bands created in 2.5 MeV electron-irradiated GaN samples and the formation of native defects. It is found that gallium-nitrogen divacancies are possible sources of the broad PL band peaking at 0.95 eV while interstitial gallium is likely to be responsible for the narrow infrared PL band centered around 0.85 eV, with a phonon fine structure at 0.88 eV.
In addition to native defects, we also investigate the blue luminescence band (BL2) peaking at 3.0 eV that is observed in high-resistivity GaN samples. Under extended ultraviolet (UV) light exposure, the BL2 band transforms into the yellow luminescence (YL) band with a maximum at 2.2 eV. Our calculations suggest that the BL2 band is related to a hydrogen-carbon defect complex, either CNON-Hi or CN-Hi. The complex creates defect transition level close to the valence band, which is responsible for the BL2 band. Under UV illumination, the complex dissociates, leaving as byproduct the source of the YL band (CNON or CN) and interstitial hydrogen.
In conclusion, theoretical predictions of thermodynamic and optical transitions of defects in GaN via the HSE06 method, are found to be within less than 0.2 eV when compared to experiment. Hence the HSE formalism is a powerful tool for the identification and characterization of defects responsible for observed PL bands in GaN.
13
KIM, YOUNGKI. "TOPOLOGICAL DEFECTS IN LYOTROPIC AND THERMOTROPIC NEMATICS." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437488066.
14
Kumar, Anusha. "Exploring packing defects, loop interactions and sequence-fitness landscape in a four-helix bundle protein Rop, by combinatorial and high-throughput approaches." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546476128094184.
15
Islam, Md Minhazul. "Study of defects and doping in β-Ga2O3". Bowling Green State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1626237318060463.
16
Suh, Caitlin D. "The Use of High-Throughput Virtual Screening Software in the Proposal of A Novel Treatment for Congenital Heart Defects." Scholarship @ Claremont, 2019. https://scholarship.claremont.edu/cmc_theses/2260.
Анотація:
Conventional screening of potential drug candidates through wet lab affinity experiments using libraries of thousands of modified molecules is time and resource consuming, along with the fact that it contributes to the widening time gap between the discovery of disease-causing mutations and the implementation of resulting novel treatments. It is necessary to explore whether the preliminary use of high-throughput virtual screening (HTVS) software such as PyRx will curb both the time and money spent in discovering novel treatments for diseases such as congenital heart defects (CHDs).
For example, AXIN2, a protein involved in a negative feedback loop inhibiting the Wnt/β-catenin signaling pathway important for cardiogenesis, has recently been associated with CHD. The loss-of-function mutation L10F on the tankyrase-binding domain of AXIN2 has been shown to upregulate the pathway by loss of inhibition ability, leading to the accumulation of intracellular β-catenin. In a different paper, however, AXIN2 has been shown to be stabilized using XAV-939, a small-molecule drug which targets tankyrase. PyRx and VMD will be used to modify the drug in order to increase its binding affinity to AXIN2, stabilizing the protein and reinstating its inhibitory property to treat CHDs. When used in adjunction to wet lab experiments, HTVS software may decrease costs and the time required to bring a potentially life-saving treatment into use.
17
Kamal, Alm Hajer. "Interfacial Adhesion Failure : Impact on print-coating surface defects." Doctoral thesis, KTH, Fiber- och polymerteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-194166.
Анотація:
The aim of this work was to develop a solid knowledge on formulation effects controlling offset ink-paper coating adhesion and to identify key factors of the coating and printing process affecting it. Focus lay on comprehending the impact of pigment dispersant on ink-paper coating adhesion and ultimately on the print quality of offset prints. The work covers laboratory studies, a pilot coating trial designed to produce coated material with a span in surface chemistry and structure, and an industrial offset printing trial. The lab scale studies quantified ink-paper coating adhesion failure during ink setting with a developed laboratory procedure based on the Ink-Surface Interaction Tester (ISIT) and image analysis. Additional polyacrylate dispersant resulted in slower ink setting and reduced ink-paper coating adhesion, with a dependence on its state of salt neutralisation and cation exchange, mainly in the presence of moisture/liquid water. The industrial printing trial on pilot coated papers was designed to study how these laboratory findings affected full scale offset print quality. These trials confirmed the dispersant-sensitive effect on ink-paper coating adhesion, especially at high water feeds. Evaluation of prints from the printing trial resulted in two fundamentally different types of ink adhesion failure being identified. The first type being traditional ink refusal, and the second type being a novel mechanism referred to as ink-lift-off adhesion failure. Ink-lift-off adhesion failure occurs when ink is initially deposited on the paper but then lifted off in a subsequent print unit. In this work, ink adhesion failure by this ink-lift-off mechanism was observed to occur more often than failure due to ink refusal. Print quality evaluation of the industrial prints suggested that water induced mottle was caused by a combination of ink-surface adhesion failure, creating white spots on the print, together with variation in ink layer thickness due to emulsified ink.QC 20161019
18
Jackson, Christine M. "Correlations of Electronic Interface States and Interface Chemistry on Dielectric/III Nitride Heterostructures for Device Applications." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu15257361319909.
19
Kelly, Leah L. "Electronic Structure and Dynamics at Organic Semiconductor / Inorganic Semiconductor Interfaces." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/566997.
Анотація:
In this dissertation, I present the results of my research on a prototypical interface of the metal oxide ZnO and the organic semiconductor C₆₀. I establish that the physics at such oxide / organic interfaces is complex and very different from the extensively investigated case of organic semiconductor / metal interfaces. The studies presented in this dissertation were designed to address and improve the understanding of the fundamental physics at such hybrid organic / inorganic interfaces. Using photoemission spectroscopies, I show that metal oxide defect states play an important role in determining the interfacial electronic properties, such as energy level alignment and charge carrier dynamics. In particular, I show that for hybrid interfaces, electronic phenomena are sensitive to the surface electronic structure of the inorganic semiconductor. I also demonstrate applications of photoemission spectroscopies which are unique in that they allow for a direct comparison of ultrafast charge carrier dynamics at the interface and the electronic structure of defect levels. The research presented here focuses on a achieving a significant understanding of the realistic and device relevant C₆₀ / ZnO hybrid interface. I show how the complex surface structure of ZnO can be modified by simple experimental protocols, with direct and dramatic consequences on the interfacial energy level alignment, carrier dynamics and carrier collection and injection efficiencies. As a result of this careful study of the electronic structure and dynamics at the C₆₀ / ZnO interface, a greater understanding of the role of gap states in interface hybridization and charge carrier localization is obtained. This dissertation constitutes a first step in achieving a fundamental understanding of hybrid interfacial electronic properties.
20
Boivin, Édouard. "Crystal chemistry of vanadium phosphates as positive electrode materials for Li-ion and Na-ion batteries." Thesis, Amiens, 2017. http://www.theses.fr/2017AMIE0032/document.
Анотація:
Ce travail de thèse a pour but d'explorer de nouveaux matériaux de type structural Tavorite et de revisiter certains déjà bien connus. Dans un premier temps, les synthèses de compositions ciblées ont été réalisées selon des procédures variées (voies tout solide, hydrothermale, céramique assistée par sol-gel, broyage mécanique) afin de stabiliser d'éventuelles phases métastables et d'ajuster la microstructure impactant fortement les performances électrochimiques de tels matériaux polyanioniques. Ces matériaux ont ensuite été décrits en profondeur, dans leurs états originaux, depuis leurs structures moyennes, grâce aux techniques de diffraction (diffraction des rayons X sur poudres ou sur monocristaux et diffraction des neutrons) jusqu'aux environnements locaux, en utilisant des techniques de spectroscopie (résonance magnétique nucléaire à l'état solide, absorption des rayons X, infra-rouge et Raman). Par la suite, les diagrammes de phases et les processus d'oxydoréduction impliqués pendant l'activité électrochimique des matériaux ont été étudiés grâce à des techniques operando (diffraction et absorption des rayons X). La compréhension des mécanismes impliqués pendant le cyclage permet de mettre en évidence les raisons de leurs limitations électrochimiques : La synthèse de nouveaux matériaux (composition, structure, microstructure) peut maintenant être développée afin de contrepasser ces limitations et de tendre vers de meilleures performancesThis PhD work aims at exploring new Tavorite-type materials and at revisiting some of the well-known ones. The syntheses of targeted compositions were firstly performed using various ways (all solid state, hydrothermal, sol-gel assisted ceramic, ball milling) in order to stabilize eventual metastable phases and tune the microstructure impacting strongly the electrochemical performances of such polyanionic compounds. The materials were then described in-depth, at the pristine state, from their average long range structures, thanks to diffraction techniques (powder X-rays, single crystal X-rays and neutrons diffraction), to their local environments, using spectroscopy techniques (solid state Nuclear Magnetic Resonance, X-rays Absorption Spectroscopy, Infra-Red and/or Raman). Thereafter, the phase diagrams and the redox processes involved during electrochemical operation of the materials were investigated thanks to operando techniques (SXRPD and XAS). The in-depth understanding of the mechanisms involved during cycling allows to highlight the reasons of their electrochemical limitations: the synthesis of new materials (composition, structure and microstructure) can now be developed to overcome these limitations and tend toward better performance
21
Toorabally, Milad. "Development of negative TiO2-based electrodes by soft chemistry for aqueous proton ions batteries." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS496.
Анотація:
Des batteries vertes qui sont sûres, fabriquées à partir de ressources facilement disponibles et éthiquement sourcées, rentables et faciles à fabriquer sont nécessaires. La technologie lithium-ion, qui utilise des matériaux à base de Li et des solvants inflammables toxiques, ne répond pas actuellement à tous ces critères. Dans cette optique, nous proposons une solution complémentaire aux batteries Li-ion sous la forme d'une batterie proton-ion aqueuse. Les principaux défis posés par les batteries aqueuses proviennent de leur faible densité énergétique, dû à la fenêtre de stabilité électrochimique restreinte de l'eau. Cette limitation réduit le champ des candidats capables d'intercaler des protons sans déclencher des réactions parasites telles que la réaction d'évolution de l'hydrogène (HER). Les matériaux TiO2 présentent une option intéressante pour être utilisés comme électrode négative pour l'insertion de protons. La structure chimique synthétisée en condition solvothermale a été modifiée pour obtenir trois composés distincts : un échantillon titanate de type lépidocrocite amorphe disposé en feuillet, qui a été optimisé par la suite avec des ions zinc chimiquement incorporé dans son interfeuillet, un anatase avec des défauts cationiques et un anatase stœchiométrique. L'analyse électrochimique des échantillons de titanate en feuillet optimisé au zinc et d'anatase défectueux, et leur intégration en tant qu'électrodes négatives dans des conditions de cellule complète, montre des caractéristiques prometteuses avec notamment, une fenêtre de potentiel étendue et une capacité réversible de protons accrue. Ces résultats ont été corrélés à la caractérisation des matériaux et à l'effet sur le transport des protonsGreen batteries that are safe, made of readily available and ethically sourced resources, cost-effective and easy to manufacture are needed. Lithium-ion technology, which uses Li-based materials and toxic flammable solvents, does not currently meet all of these criteria. With this in mind, we propose a complementary solution to Li-ion batteries in the form of an aqueous proton-ion battery. The primary challenges posed by aqueous batteries stem from their low energy density, which is the result of the restricted electrochemical stability window of water. This limitation narrows the field of candidates capable of intercalating protons without triggering parasitic reactions such as the hydrogen evolution reaction (HER). TiO2 materials present an intriguing option for use as a negative electrode for proton insertion. The chemical structure synthesized in solvothermal condition has been modified to achieve three distinct compounds: a layered, amorphous lepidocrocite type titanate sample further optimized with zinc ions chemically incorporated into its interlayer, a cationic defective anatase, and a stoichiometric anatase. The electrochemical analysis of the zinc-optimized layered titanate and defective anatase samples, and their integration as negative electrodes in full-cell conditions, demonstrates promising characteristics with notably, an extended potential window and heightened reversible proton capacity. These results were correlated to the materials characterization and the effect on proton transport
22
Schliesser, Jacob M. "Development and Application of New Solid-State Models for Low-Energy Vibrations, Lattice Defects, Entropies of Mixing, and Magnetic Properties." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5841.
Анотація:
Low-temperature heat capacity data contain information on the physical properties of materials, and new models continue to be developed to aid in the analysis and interpretation of heat capacity data into physically meaningful properties. This work presents the development of two such models and their application to real material systems. Equations describing low-energy vibrational modes with a gap in the density of states (DOS) have been derived and tested on several material systems with known gaps in the DOS, and the origins of such gaps in the DOS are presented. Lattice vacancies have been shown to produce a two-level system that can be modeled with a sum of low-energy Schottky anomalies that produce an overall linear dependence on temperature in the low-temperature heat capacity data. These two models for gaps in the vibrational DOS and the relationship between a linear heat capacity and lattice vacancies and many well-known models have been applied to several systems of materials to test their validity and applicability as well as provide greater information on the systems themselves. A series of bulk and nanoscale Mn-Fe and Co-Fe spinel solid solutions were analyzed using the entropies derived from heat capacity data, and excess entropies of mixing were determined. These entropies show that changes in valence, cation distribution, bonding, and the microstructure between the mixing ions is non-ideal, especially in the nanoparticles. The heat capacity data of ten Al doped TiO2 anatase nanoparticle samples have also been analyzed to show that the Al3+ dopant ions form small regions of short-range order, similar to a glass, within the TiO2 particles, while the overall structure of TiO2 remains unchanged. This has been supported by X-ray diffraction (XRD) and electron energy-loss spectroscopy and provides new insights to the synthesis and characterization of doped materials. The final investigation examines nanocrystalline CuO using heat capacities, magnetization, XRD, and electron microscopy and compares the findings to the known properties of bulk CuO. All of these measurements show transitions between antiferromagnetic and paramagnetic states in the temperature range of about 150-350 K that are greater in number and higher in temperature than the transitions in bulk CuO. These changes are shown to cause an increase in the temperature range of multiferroicity in CuO nanoparticles.
23
Chow, Ernest Ho Hin. "The study of organic crystals by atomic force microscopy." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245569.
Анотація:
Organic crystals are found in everyday goods such as foods, drugs, dyes, and agricultural products. To better understand the solid-state behaviour of organic crystals, the study of their surfaces is crucial, as several reactions occur at the interface between the crystal surface and its immediate environment. While atomic force microscopy (AFM) is a useful tool for studying surfaces, it is not a common technique for studying organic crystals. The rst part of this report aims to address problems of imaging organic crystals by AFM which arise from the nature of the imaging technique and the material property of organic crystals. Methods of detecting and predicting the likelihood of the problems encountered in imaging organic crystals are suggested in order for a more accurate interpretation of the information obtained by this technique. The e ect of humidity on aspirin crystal surfaces is then investigated by AFM. The growth of new features on the surface is believed to be a result of the hydrolysis of aspirin molecules. Mechanisms are suggested based on the observed surface response of aspirin, where surface defects and the mobility of surface molecules are believed to be important factors a ecting reactivity. The last section investigates the solid-state photochemical reaction of anthracene, which is a reaction that should not occur according to the topochemical postulate. The surface response of anthracene crystals to UV light was studied, and the results indicate strong reactivity at sites of surface defects, which is likely due to photodimerisation. A similar mechanism that described the behaviour of aspirin surfaces was suggested for this reaction. In summary, both reactions that were studied provided a better insight towards understanding the solid-state reactivity of organic crystals. The proposed surface mechanisms imply that surface defects and the presence of humidity or solvent vapour are very likely to play a role in determining reactivity. Further studies on the origin of defects are suggested in order to better control the behaviour of organic crystals in the solid-state.
24
Krymowski, Kevin E. "The Effect of Ligand Variation on Two-Dimensional Materials." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1495802952188467.
25
Wei, Tao. "Surface spectroscopic characterization of oxide thin films and bimetallic model catalysts." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1058.
26
Han, Lu. "Synthesis and Characterization of Functionalized Silica Mesoporous Crystals Cationic Surfactant and Co-structure Directing Agent System /." Doctoral thesis, Stockholm : Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38398.
27
Saadatkia, Pooneh. "Optoelectronic Properties of Wide Band Gap Semiconductors." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1562379152593304.
28
Knight, Christopher J. "Hydrogen bond topology order/disorder transitions in ice and the behavior of defects in a disordered ice lattice /." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1236788109.
29
Swaminathan, Narasimhan. "Stress-defect transport interactions in ionic solids." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28273.
Анотація:
Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Qu, Jianmin; Committee Member: Kohl,Paul A.; Committee Member: Liu, Meilin; Committee Member: McDowell, David L.; Committee Member: Zhu, Ting.
30
Vicente, Juvinch R. "Photo-driven Processes in Lead Halide Perovskites Probed by Multimodal Photoluminescence Microscopy." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1585838644331732.
31
Fugate, Elizabeth Anne. "Understanding the Role of Lattice Defects and Metal Composition Ratio on the Photochemistry of CuFeO2 toward Solar Energy Conversion." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu157788103637799.
32
Wilde, Peter Joseph. "The defect chemistry of pyrochlore structured oxides." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309471.
33
Altunata, Serhan. "Generalized quantum defect methods in quantum chemistry." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36257.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.Vita.
Includes bibliographical references (p. 247-254).
The reaction matrix of multichannel quantum defect theory, K, gives a complete picture of the electronic structure and the electron - nuclear dynamics for a molecule. The reaction matrix can be used to examine both bound states and free electron scattering properties of molecular systems, which are characterized by a Rydberg/scattering electron incident on an ionic-core. An ab initio computation of the reaction matrix for fixed molecular geometries is a substantive but important theoretical effort. In this thesis, a generalized quantum defect method is presented for determining the reaction matrix in a form which minimizes its energy dependence. This reaction matrix method is applied to the Rydberg electronic structure of Calcium monofluoride. The spectroscopic quantum defects for the ... states of CaF are computed using an effective one-electron calculation. Good agreement with the experimental values is obtained. The E-symmetry eigenquantum defects obtained from the CaF reaction matrix are found to have an energy dependence characteristic of a resonance. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad shape resonance in the 2E+ Rydberg series.
(cont.) This short-lived resonance is spread over the entire 2E+ Rydberg series and extends well into the ionization continuum. The effect of the shape resonance is manifested as a global "scarring" of the Rydberg spectrum, which is distinct from the more familiar local level-perturbations. This effect has been unnoticed in previous analyses. The quantum chemical foundation of the quantum defect method is established by a many-electron generalization of the reaction matrix calculation. Test results that validate the many-electron theory are presented for the quantum defects of the lsagnpo, E+ Rydberg series of the hydrogen molecule. It is possible that the reaction matrix calculations on CaF and H2 can pave the way for a novel type of quantum chemistry that aims to calculate the electronic structure over the entire bound-state region, as opposed to the current methods that focus on state by state calculations.
by Serhan Altunata.
Ph.D.
34
Gonchar, Anastasia [Verfasser]. "Defect chemistry of single crystalline MgO(001) films / Anastasia Gonchar." Berlin : Freie Universität Berlin, 2011. http://d-nb.info/1025551419/34.
35
Lu, Qiyang. "Controlling properties of functional oxides by tuning oxygen defect chemistry." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115715.
Анотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 164-192).
Oxygen defects are essential building blocks for properties and functionalities of oxides, including electrical conductivity, magnetism, ferroelectricity as well as catalytic and electrocatalytic activity. Therefore, fundamental understanding of how to tune the oxygen defect chemistry is essential for advancing applications based on these defect sensitive properties. This thesis investigated pathways to controlling the concentration and structure of oxygen defects on selected case studies with model oxide systems. Three novel effects were assessed and shown to be operative for obtaining a large impact on the oxygen defect chemistry equilibria. These are heterogeneous chemical doping of the surface for improving surface electrocatalytic activity and stability, electrochemical bias to control phase with drastic changes obtained in electronic and phonon transport properties, as well as strain engineering to alter the oxygen interstitial capacity and oxygen exchange kinetics. Surface chemical modifications were applied to the near-surface regions of Lao.8Sro.2CoO 3 (LSC) by replacing the Co cations locally with less reducible cations, such as Hf and Ti. This strategy was shown to effectively stabilize the LSC surfaces and suppress surface segregation of Sr at elevated temperatures. This introduced surface stability by local chemical doping greatly enhanced the long-term electrochemical performance of LSC electrode, which provides a new route for improving the efficiency of solid oxide fuel and electrolysis cells. Applying electrical bias was investigated as another effective method to tune the oxygen stoichiometry, exemplified by the case studies on SrCoOx (SCO). In situ X-ray diffraction was used to investigate the topotactic phase transition between brownmillerite phase SrCoO2.5 (BM-SCO) and perovskite phase SrCoO 3 6 (P-SCO) triggered electrochemically at elevated temperatures. An electrical bias of merely 30 mV was shown sufficient to trigger the BM-->P phase transition. This is much more feasible than chemically induced phase transition, which requires high pressure (> 1 bar) and specialized pressurized apparatus. Moreover, the evolution of electronic structure during the BM4P phase transition was probed in operando by using ambient-pressure X-ray photoelectron and absorption spectroscopy (AP-XPS/XAS). The similar experimental scheme, which combines in operando surface characterizations and electrochemical controlling of oxygen stoichiometry, was extended to oxide systems beyond perovskites. This allows us to investigate the defect chemistry of oxides in a much broader range of effective oxygen partial pressure than what conventional methods can achieve. Firstly, we showed that the surface defect chemistry equilibrium of fluoritestructured Pro.iCeo.902-6 (PCO) strongly deviated from the bulk counterpart, due to the possibly enhanced defect-defect interactions or lattice strain effect at surfaces. Secondly, we found a novel metal-insulator transition triggered electrochemically in VO, by changing the phase between the metallic dioxide VO2 and the insulating pentoxide V2O5 Lastly, we lowered the operation temperature of this electrochemical control of oxygen stoichiometry down to room temperature by using ionic liquid or ion gels as the electrolyte. We achieved tuning of thermal conductivity in SrCoOx with a range of more than one order of magnitude, by using electrochemically triggered phase transitions at room temperature. We also investigated the effect of lattice strain on oxygen defect formation energy in Ruddlesden-Popper (RP) phase oxide Nd2NiO4+6 (NNO). We found that tensile strain along the c-axis of NNO lattice effectively reduced the formation enthalpy of oxygen interstitials, which can provide a new route for designing the defect chemistry of RP phase oxide for electrocatalytic applications..
by Qiyang Lu.
Ph. D.
36
Williamson, Andrew. "Carrier dynamics, persistent photoconductivity and defect chemistry at zinc oxide photoanodes." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/carrier-dynamics-persistent-photoconductivity-and-defect-chemistry-at-zinc-oxide-photoanodes(ec59e44c-0f17-40e5-ab34-871afbea0ea9).html.
Анотація:
Zinc oxide (ZnO) is a promising photoanode material which has been used in quantum dot-based depleted heterojunction solar cells. The specific influence of the defect chemistry of ZnO on its n-type conductivity remains a focus for research. This thesis presents results from a series of near-ambient pressure (NAP) XPS experiments (at The University of Manchester, UK), used to characterise surface adsorption of O2 and H2O on ZnO(10-10) surfaces in high pressure environments. Water dosing is shown to lead to surface hydroxylation and a change in the surface band bending consistent with an increase in the surface conductivity. Oxygen dosing is also observed to lead to the formation of surface species on the ZnO surface, revealing that ZnO is prone to hydroxylation even in oxygen-rich environments. The role of surface OH on influencing the transient surface photovoltage (SPV) of the ZnO(10-10) surface is probed through a series of time-resolved, pump-probe XPS experiments (at SOLEIL synchrotron, France). It is shown that increasing the degree of surface hydroxylation leads to a decrease in surface band bending, leading to longer-lived transient SPV. Other factors influencing the SPV dynamics are explored, such as the role of the oxygen vacancy concentration. The transient SPV decay lifetime is shown to increase with increasing oxygen vacancy concentration, consistent with the presence of persistent photoconductivity (PPC) in ZnO, mediated by oxygen vacancy-related hole traps. The influence of the concentration of thermally excited carriers in ZnO on the surface band bending is also described, showing that the equilibrium band bending and the surface photovoltage are both reduced at low temperature. It is shown that thermal excitation of carriers from the valence band of ZnO and from neutral oxygen vacancies have negligible influence on the magnitude of equilibrium band bending at the surface. The energy regime consistent with the observed temperature dependence is also consistent with a perturbed-host state 0.2 eV below the conduction band minimum. This meta-stable state is associated with doubly-ionised oxygen vacancies, that mediate the PPC in ZnO. However this does not rule out the contribution from other shallow donor levels such as those associated with hydrogen impurities. The influence of hydrogen on the SPV dynamics in ZnO is explored, through angle-resolved photoemission spectroscopy (ARPES) after implanting hydrogen atoms into the ZnO surface. H implantation is shown to lead to the formation of a 2D electron gas (2DEG) at the surface, consistent with an increase in conductivity at the surface large enough to change the nature of the space-charge region at the ZnO surface from depletion to accumulation.
37
Sokol, Alexey Abramovich. "Defect structures in zeolite crystals." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326272.
38
Gerbig, Oliver [Verfasser], and Joachim [Akademischer Betreuer] Maier. "Defect chemistry in alkali peroxides and superoxides / Oliver Gerbig. Betreuer: Joachim Maier." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1062951441/34.
39
Lupetin, Piero [Verfasser], and Joachim [Akademischer Betreuer] Maier. "Charge carrier defect chemistry of nanoscopic SrTiO3 / Piero Lupetin. Betreuer: Joachim Maier." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/1024490726/34.
40
Parshad, Henrik. "Design of poorly soluble drug salts : pharmaceutical chemical characterization of organic salts /." [Cph.] : Department of Pharmaceutics, The Danish University of Pharmaceutical Sciences, 2003. http://www.dfh.dk/phd/defences/henrikparshad.htm.
41
Ravn, Jacob. "Development of privileged structure based libraries /." Måløv ; Cph. : Medicinal Chemistry Research III, Novo Nordisk A/S og Department of Medicinal Chemistry : The Danish University of Pharmaceutical Sciences, 2004. http://www.dfh.dk/phd/defences/jacobravn.htm.
42
Fritze, Holger [Verfasser]. "Electromechanical properties and defect chemistry of High-Temperature piezoelectric materials / Dr. Holger Fritze." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2008. http://d-nb.info/1010653776/34.
43
Sprague, John Jason 1971. "Mixed conduction and defect chemistry of manganese and molybdenum substituted gadolinium titanate pyrochlore." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85250.
44
Spears, Marlene Ann. "Defect chemistry and electrical properties of ruthenium- and bismuth-substituted gadolinium titanate pyrochlore." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11443.
45
Zhan, Xiaowen. "DEFECT CHEMISTRY AND TRANSPORT PROPERTIES OF SOLID STATE MATERIALS FOR ENERGY STORAGE APPLICATIONS." UKnowledge, 2018. https://uknowledge.uky.edu/cme_etds/88.
Анотація:
Replacing organic liquid electrolytes with nonflammable solid electrolytes can improve safety, offer higher volumetric and gravimetric energy densities, and lower the cost of lithium-ion batteries. However, today’s all-solid-state batteries suffer from low Li-ion conductivity in the electrolyte, slow Li-ion transport across the electrolyte/electrode interface, and slow solid-state Li-ion diffusion within the electrode. Defect chemistry is critical to understanding ionic conductivity and predicting the charge transport through heterogeneous solid interfaces. The goal of this dissertation is to analyze and improve solid state materials for energy storage applications by understanding their defect structure and transport properties.
I have investigated defect chemistry of cubic Li7La3Zr2O12 (c-LLZO), one of the most promising candidate solid electrolytes for all-solid-state lithium batteries. By combining conductivity measurements with defect modeling, I constructed a defect diagram of c-LLZO featuring the intrinsic formation of lithium vacancy-hole pairs. The findings provided insights into tailoring single-phase mixed lithium-ion/electron conducting materials for emerging ionic devices, i.e., composite cathodes requiring both fast electronic and ionic paths in solid-state batteries. I suggested that oxygen vacancies could increase the Li-ion conductivity by reducing the amount of electron holes bound with lithium vacancies.
Using a simpler but also attractive solid electrolyte Li2ZrO3 (LZO) as an example, I significantly improved Li-ion conductivity by creating extra oxygen vacancies via cation doping. In particular, Fe-doped LZO shows the highest Li-ion conductivity reported for the family of LZO compounds, reaching 3.3 mS/cm at 300 °C. This study brought attentions to the long-neglected oxygen vacancy defects in lithium-ion conductors and revealed their critical role in promoting Li-ion transport. More importantly, it established a novel defect engineering strategy for designing Li-oxide based solid electrolytes for all-solid-state batteries.
I surface-modified LiNi0.6Co0.2Mn0.2O2 cathode material with a LZO coating prepared under dry air and oxygen, and systematically investigated the effect of coating atmosphere on their transport properties and electrochemical behaviors. The LZO coating prepared in oxygen is largely amorphous. It not only provided surface protection against the electrolyte corrosion but also enabled faster lithium-ion transport. Additionally, oxygen atmosphere facilitated Zr diffusion from the surface coating to the bulk of LiNi0.6Co0.2Mn0.2O2, which stabilized the crystal structure and enhanced lithium ion diffusion. Consequently, LiNi0.6Co0.2Mn0.2O2 cathodes coated with Li2ZrO3 in oxygen achieved a significant improvement in high-voltage cycling stability and high-rate performance.
46
Sorriaux, Maxime. "Réactivité électrochimique et chimique des matériaux à base d'oxyde de titane avec un liquide ionique chloroaluminé pour batteries à l'aluminium." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS076.
Анотація:
Les changements sociétaux récents rendent nécessaires le développement de nouveaux systèmes de stockage d'énergie. Selon les prévisions, les batteries lithium-ion cesseront de répondre à la demande globale au cours de la prochaine décennie. Dans ce contexte, le développement de nouvelles technologies de batteries est requis. De ce fait, le travail ici proposé explore le système de batterie à l'aluminium. L'étude porte à la fois sur l'électrolyte et sur les matériaux d'électrode. La chimie des défauts est utilisée pour réaliser l'intercalation de l'ion aluminium dans le matériau d'électrode. En effet, les lacunes cationiques, de la structure de l'oxyde de titane choisi, offrent des sites d'insertion privilégiés pour une grande variété d'ions. Cependant, la durée de vie de la batterie est considérablement réduite en raison des interactions entre le matériau d'électrode et le liquide ionique, utilisé comme électrolyteSocietal changes drive the need for new energy storage systems. Forecasts consider that lithium-ion batteries will cease to meet the demand within the next decade. In this regard, the development of new battery technologies is mandatory. That is why, in this work, the aluminium battery system is explored. Investigations are performed on both the electrolyte and the electrode materials. In this study, the aluminium ion intercalation in the electrode material is achieved, using the defect chemistry. Indeed, cationic vacancies within a titanium oxide structure offer favourable insertion sites for a wide variety of ions. However, the battery lifespan is observed to be greatly shortened due to interactions between the electrode material and the ionic liquid used as the electrolyte
47
Holm, Steen Strange. "Studier over referencemetoder til måling af stofskiftehormoner /." Holbæk ; Kbh. : Klinisk biokemisk afdeling, Holbæk Sygehus, Sygehus Vestsjælland : Institut for Analytisk Kemi, Danmarks Farmaceutiske Universitet, 2004. http://www.dfh.dk/phd/defences/SteenStrangeHolm.htm.
48
Dragan, Mirela-Anca. "Defect chemistry, transport properties and thermodynamic stability of acceptor doped and undoped layered La2NiO4." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979096375.
49
Lorger, Simon [Verfasser], and Joachim [Akademischer Betreuer] Maier. "Defect chemistry of bulk and thin film lithium chalcogenides / Simon Lorger ; Betreuer: Joachim Maier." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1189662426/34.
50
Neagu, Dragos. "Materials and microstructures for high temperature electrochemical devices through control of perovskite defect chemistry." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3606.
Анотація:
The development of technologies that enable efficient and reliable energy inter-conversion and storage is of key importance for tempering the intermittent availability of renewable energy sources, and thus for developing an energy economy based on sustainable, clean energy production. Solid oxide electrolysis cells (SOECs) may be used to store excess electrical energy as hydrogen, while solid oxide fuel cells (SOFCs) could convert back hydrogen into electricity, thus balancing energy availability and demand. However, the current state-of-the-art hydrogen electrode used in both SOECs and SOFCs, the Ni-yttria-stabilised zirconia cermet (Ni-YSZ), is unreliable in conjunction with intermittent energy sources, in particular due to its innate redox instability. This thesis explores the fundamental properties of various inherently redox stable A-site deficient titanate perovskite systems (A1-αBO3, B = Ti), seeking to uncover the principles that enhance their properties so that they may be used to replace Ni-YSZ. In particular, this work demonstrates that the versatility of perovskites with respect to the introduction of lattice defects such as vacancies and cation substitutions enables considerable improvements in the extent of reduction, electronic conductivity and overall electrochemical activity. Most importantly, the defect chemistry context set by the presence of A-site vacancies was found to trigger the exsolution of electrocatalytically active nanoparticles from the parent perovskite, upon reduction. This is an entirely new phenomenon which was explored and exploited throughout this study to produce perovskite surfaces decorated with uniformly distributed catalytically active nanoparticles. As demonstrated in this study, the exsolution phenomenon excels in terms of producing nanoparticles with uniform size, distribution, diverse composition and ‘unconventional' surface anchorage. The resulting enhanced properties, and especially the exsolution phenomenon, contributed coherently towards improving the suitability of the perovskites developed here towards their application as hydrogen electrode materials. Consequently, when integrated into SOEC button cells as hydrogen electrodes, they exhibited a step-change increase in performance compared to other perovskites considered to date. Many of the principles and perovskite defect chemistry explored and exemplified in this study on perovskite titanates may be extended to other perovskites as well. In particular the advanced control and understanding achieved in this work over the exsolution phenomenon may inspire the formulation of new and sophisticated oxide materials with advanced functionality.