This graduate work deals with the study and preparation of gel polymer electrolytes with flame retardants for lithium-ion batteries. The theoretical part describes the types of electrolytes, their features, benefits, how they differ and where they are used in detail. The basis of this section is gel electrolytes with flame retardants, to measure their electrical and electrochemical properties. The experimental part deals with the preparation of samples of gel electrolytes with different percentages of flame retardant, where varied species of flame retardants and measuring their electrical conductivity and potential windows. Impedance spectroscopy, cyclic voltammetry and dynamic-analytical thermal analysis were selected as measuring methods.

This diploma thesis is focused on study of electric and optoelectric properties of conjugated polymers. The theoretical part describes the relationship between molecular structure of conjugated materials and their chosen macroscopic physical properties like absorption of visible and ultraviolet radiation, electrical conductivity and photoconductivity. This part also describes photochromism and its utilization for construction of light driven current switch. The experimental part studies this switch based on change of photochromic species dipole moment dispersed in conjugated conducting polymer. The active switching unit is represented by photochromic spiropyran 1’,3’-dihydro-1’,3’,3’-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2’-(2H)-indol] which is dispersed in conjugated conducting polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylen]. The influence of the photochromic conversion on the polymer matrix was studied by absorption spectroscopy, current-voltage measurements and spectrally resolved steady state photoconductivity and transient photoconductivity.

Dielektrická relaxační spektroskopie je jednou z užitečných metod pro studium molekulární dynamiky materiálů. Díky nedávnému pokroku v přístrojové a měřicí technice je dnes možné získat dielektrické spektrum v širokém frekvenčním intervalu a pro velice rozdílné materiály. Cílem mé práce bylo studium dielektrických relaxačních spekter a vodivosti oxidů titanu, niobu, tantalu, lanthanu a hafnia pro katody pracující na principu studené emise. Cílem výzkumu bylo analyzovat frekvenční a teplotní chování těchto oxidů, včetně jejich vodivosti, v širokém frekvenčním a teplotním rozsahu, a pokusit se stanovit původ relaxačního mechanismu. Vzhledem k tomu, že původně zadaný rozsah oxidů byl dosti široký, soustředila se pozornost pouze na oxidy tantalu a niobu, rovněž s ohledem na jejich aplikace v elektrolytických kondenzátorech. Elektrické, tepelné a mechanické (při zpracování) vlastnosti oxidů tantalu a niobu jsou dnes již dobře prozkoumány. K dispozici je však jen málo poznatků o jejich dielektrických relaxačních mechanismech. Výsledky získané pro Ta2O5 ukazují existence relaxačního maxima, nacházejícího se v experimentálně dostupném teplotním a frekvenčním intervalu 187 K – 385 K a 1 Hz – 10 MHz. Frekvence ztrátového maxima se řídí Arrheniovým zákonem s aktivační energií 0.048 eV. Ve vodivostních spektrech vykazují tenké vrstvy Ta2O5 na nízkých frekvencích ustálenou hodnotu a při vysokých frekvencích monotónní nárůst, který závisí na teplotě. Pozorovanou vodivost lze popsat mocninnou funkcí s exponentem nepatrně větším než jedna (tzv. superlineární závislost). Výsledky získané pro Nb2O5 v podobné teplotní a frekvenční oblasti, 218 K – 373 K, 1 Hz – 1 MHz rovněž ukazují jedno relaxační maximum. Frekvence ztrátového maxima se opět řídí Arrheniovým zákonem s poněkud vyšší aktivační energií 0.055 eV. Niobové kondenzátory vykazují vodivostní mechanismus shodný s kondenzátory tantalovými.

π-Conjugated two-dimensional covalent organic frameworks (2D COFs) are emerging as a novel class of electro-active materials for (opto-)electronic and chemiresistive sensing applications. However, understanding the intricate interplay between chemistry, structure and conductivity in π-conjugated 2D COFs remains elusive. Here, we report a detailed charac-terization for the electronic properties of two novel samples consisting of Zn- and Cu-phthalocyanine-based pyrazine-linked 2D COFs. These 2D COFs are synthesized by condensation of metal-phthalocyanine (M=Zn and Cu) and pyrene derivatives. The obtained polycrystalline-layered COFs are p-type semiconductors both with a band gap of ~1.2 eV. Mobilities up to ~5 cm²/Vs are resolved in the dc limit, which represent a lower threshold induced by charge carrier localization at crystalline grain boundaries. Hall Effect measurements (dc limit) and terahertz (THz) spectroscopy (ac limit) in combination with den-sity functional theory (DFT) calculations demonstrate that varying metal center from Cu to Zn in the phthalocyanine moiety has a negligible effect in the conductivity (~5×10⁻⁷ S/cm), charge carrier density (~10¹² cm⁻³), charge carrier scattering rate (~3×10¹³ s⁻¹), and effective mass (~2.3m₀) of majority carriers (holes). Notably, charge carrier transport is found to be aniso-tropic, with hole mobilities being practically null in-plane and finite out-of-plane for these 2D COFs.

Transition metal oxide coupling with carbon is an effective method for improving electrical conductivity of battery electrodes and avoiding the degradation of their lithium storage capability due to large volume expansion/contraction and severe particle aggregation during the lithium insertion and desertion process. In our present work, we develop an effective approach to fabricate the nanocomposites of porous rod-shaped Fe₃O₄ anchored on reduced graphene oxide (Fe₃O₄/rGO) by controlling the in situ nucleation and growth of β-FeOOH onto the graphene oxide (β-FeOOH/GO) and followed by dielectric barrier discharge (DBD) hydrogen plasma treatment. Such well-designed hierarchical nanostructures are beneficial for maximum utilization of electrochemically active matter in lithium ion batteries and display superior Li uptake with high reversible capacity, good rate capability, and excellent stability, maintaining 890 mA h g⁻¹ capacity over 100 cycles at a current density of 500 mA g⁻¹.

In this work, the effects of epitaxial strain and film thickness on the lattice structure, microstructure, magnetization and electrical conduction of La1-xSrxCoO3 (LSCO) (x = 0.18 and 0.30) thin films have been studied using thickness-dependent film series on several types of single-crystalline substrates. Alternatively, the direct effect of strain has been probed using a piezoelectric substrate. La0.7Sr0.3CoO3 is a ferromagnetic metal, whereas La0.82Sr0.18CoO3 is at the phase boundary between the ferromagnetic metal and an insulating spin glass phase. Epitaxial biaxial strain in La1-xSrxCoO3 (x = 0.18-0.3) films is known to reduce the ferromagnetic double exchange interactions. It has further been suggested for the control of the crystal field splitting of the Co ions which may be utilized to manipulate the spin state. The LSCO (x = 0.18 and 0.30) films have been grown by pulsed laser deposition (PLD) on substrates of LaAlO3, SrTiO3, (PbMg1/3Nb2/3O3)0.72(PbTiO3)0.28 (PMN-PT) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT), which provide different strain states and, in the case of PMN-PT, a reversibly controllable strain. Thickness-dependent series of La0.82Sr0.18CoO3 on SrTiO3 and LaAlO3 as well as of La0.7Sr0.3CoO3 on LSAT have been studied. The lattice parameters of the epitaxially grown films were determined from X-ray diffraction measurements (Bragg-Brentano method and reciprocal space mapping). Large tensile strains of 2% can be achieved in thicker films of up to 100 nm. On the other hand, the films under larger tensile strain have cracks and reveal ordered superstructures in HRTEM images which are tentatively attributed to ordered oxygen vacancies. The Curie temperature and the magnetic moment of the x = 0.18 films increases towards larger film thickness in qualitative agreement with the joined effects of strain relaxation and finite thickness on magnetic ordering. In order to separate the direct strain effect from the thickness effect, the Curie temperature, the magnetic moment and the (rather large) coercivity of the films have been investigated in two electrically controlled strain states for a film on PMN-PT. Non-cracked, sufficiently thick x = 0.18 films show metallic behaviour with large magnetoresistance. The crack-free x = 0.3 films on LSAT undergo an insulator-to-metal transition with increasing thickness and also show large magnetoresistance, both consistent with a percolative transport behaviour. The spin state of the Co ions appears to remain unchanged in the investigated doping range.

No description available.

Die zuverlässige Berechnung der elektrischen Leitfähigkeit vieler Materialien aus ersten Prinzipien erfordert die Berücksichtigung der anharmonischen Gitterdynamik. Der ab initio Kubo-Greenwood (KG)-Ansatz, der die KG-Leitfähigkeitsformel und die ab initio-Molekulardynamik kombiniert, scheint vielversprechend zu sein, da er die Anharmonizität des Gitters auf natürliche Weise berücksichtigt. Seine Anwendung auf kristalline Materialien hat jedoch bisher nur wenig Beachtung gefunden. Diese Arbeit beschreibt den KG-Ansatz und stellt eine numerische Implementierung dieses Ansatzes für den harmonischen Kristall Si und den anharmonischen Kristall SnSe vor. Die Fallstudie für Si zeigt erhebliche numerische Schwierigkeiten bei den KG-Berechnungen auf. Insbesondere behindert die erforderliche dichte k-Punkt-Abtastung die Konvergenz in Superzellengröße und macht die Berechnungen nur innerhalb der (semi-)lokalen Dichtefunktionaltheorie (DFT) durchführbar. Außerdem führt die notwendige Einführung eines Verbreiterungsparameters (η) zu einer erheblichen Unsicherheit bei der Bestimmung der Leitfähigkeit. Um diese Probleme zu lösen, werden rechnerisch effiziente Strategien diskutiert, darunter: (i) der "Scherenoperator"-Ansatz zur Korrektur des DFT-Bandlückenproblems; (ii) das "Optimal-η-Schema" zur Wahl eines geeigneten Wertes von η; und (iii) die Finite-Size-Scaling-Methode zur Ableitung der Leitfähigkeit in der thermodynamischen Grenze. Es wird festgestellt, dass die KG-Berechnungen mit diesen Strategien Leitfähigkeiten in angemessener Übereinstimmung mit den Experimenten ergeben. Der Vergleich mit früheren ab initio Boltzmann-Transportberechnungen zeigt jedoch, dass das η-Problem und die Frage der Konvergenz in Superzellengröße weiter verbesserte Konzepte erfordern. Die Fallstudie für SnSe zeigt sehr ähnliche numerische Schwierigkeiten wie im Fall von Si. Es werden Einblicke in die Auswirkung der Anharmonizität auf die Konvergenz der Superzellengröße gegeben. / Reliable first-principles calculation of the electrical conductivity in many materials requires accounting for the anharmonic lattice dynamics. The ab initio Kubo-Greenwood (KG) approach, which combines the KG conductivity formula and ab initio molecular dynamics, appears to be promising because it naturally includes lattice anharmonicity. However, its application to crystalline materials has so far received very little attention. This thesis describes the KG approach and presents a numerical implementation of this approach for the harmonic crystal Si and the anharmonic crystal SnSe. The case study for Si identifies considerable numerical difficulties in the KG calculations. In particular, the dense k-point sampling required hinders supercell-size convergence and makes the calculations only feasible within (semi)local density-functional theory (DFT). Besides, the necessary introduction of a broadening parameter (η) introduces a significant uncertainty in determining the conductivity. To address these issues, computationally efficient strategies are discussed, including: (i) the "scissor operator" approach to correct the DFT band-gap problem; (ii) the "optimal-η scheme" to choose an appropriate value of η; and (iii) the finite-size scaling method to deduce the conductivity in the thermodynamic limit. It is found that with these strategies, the KG calculations yield conductivities in reasonable agreement with experiment. Yet, comparison with previous ab initio Boltzmann transport calculations shows that the η problem and the issue of supercell-size convergence still require improved concepts. The case study for SnSe shows very similar numerical difficulties as in the case of Si. Insights into the effect of anharmonicity on the supercell-size convergence are provided.

Ce travail de thèse porte sur le développement et l’optimisation de capteurs dans le cadre du contrôle non destructif (CND) par courants de Foucault (CF). Le manuscrit présente plusieurs réalisations de capteurs CF souples gravés sur film Kapton. Un premier volet décrit l’évaluation des paramètres électromagnétiques (conductivité électrique σ et perméabilité magnétique µ) des matériaux typiquement rencontrés en CND par CF. Des méthodes conventionnelles pour estimer σ et µ ont été investiguées et mises en œuvre : il s’agit de la méthode à quatre pointes et du perméamètre. Néanmoins, ces méthodes présentent des difficultés pratiques au regard de l’état de surface (peinture, corrosion,…) et de la géométrie de l’échantillon. Deux capteurs ont donc été conçus : le premier composé d’une bobine d’émission et d’une bobine de réception afin d’évaluer la conductivité des matériaux purement conducteurs, puis le second composé d’un bobinage émetteur et d’une GMR pour évaluer la perméabilité magnétique. La conception des motifs et des résultats expérimentaux sont présentés dans le manuscrit. Le second volet décrit le développement d’un imageur CF flexible statique. L’imageur est un capteur multiélément composé de 576 récepteurs disposés en matrice permettant d’inspecter la surface d’une pièce sans déplacement du capteur par rapport à cette dernière. Le contrôle par l’imageur statique permet d’obtenir une image pixélisée de la surface sous le capteur. L’imageur a été optimisé de manière à détecter un défaut surfacique d’au moins 1 mm de long et d’orientation donnée quel que soit son emplacement vis-à-vis des bobines réceptrices. La conception du capteur et son évaluation expérimentale sont donnés dans le manuscrit. / The work of this thesis focuses on the development and the optimization of probes for non-destructive testing (NDT) by Eddy Currents (EC). The manuscript presents several achievements of flexible EC probes engraved on Kapton film. The first part describes the evaluation of the electromagnetic parameters (electrical conductivity σ and magnetic permeability µ) of materials typically encountered in NDT by EC. Conventional methods to estimate σ and μ have been investigated and implemented: it is the four-point probe and the permeameter. However, these methods present practical difficulties relating to the surface condition (paint, corrosion,…) and the sample geometry. Two probes have therefore been designed: the first is composed of a transmitting and a receiving coil in order to evaluate the conductivity of purely conductive materials, and the second is composed of a transmitter coil and a GMR for evaluate the magnetic permeability. Design patterns and experimental results are presented in the manuscript. The second part describes the development of a flexible static EC imager. The imager is a multielement probe composed of 576 receivers arranged in a matrix allowing to inspect the surface of a structure under test without moving the probe relative to the sample surface. The inspection by the static imager provides a pixelated image of the surface under the probe. The imager has been optimized to detect a surface defect of at least 1 mm long of given orientation regardless of its location relative to the receiver coils. The design of the probe and its experimental evaluation are given in the manuscript.

The essence of this graduate thesis is to summarize knowledge about the aprotic gel electrolytes. In the graduate thesis, there are explained methods for mensuration electrochemical properties of the aprotic gel electrolytes. In the theoretical part, I focus on the knowledge related to gel polymeric electrolytes, their history, properties, mechanisms and application. In the experimental part, I describe the preparation of the samples of the gel polymeric electrolytes, in which I evaluate their properties, electrical conductivity and potencial window.