Os supercondutores de alta temperatura crítica apresentam propriedades diferentes dos supercondutores convencionais, uma destas propriedades importantes é a simetria não isotrópica do parâmetro de ordem. Neste trabalho se apresenta um modelo que mostra a presença de simetria d-wave em uma classe de supercondutores de alta Tc, assim como a condição para a existência de ondas de densidade nos estados de equilíbrio. Se analisa primeiro um sistema de três corpos, um bipolaron e dois elétrons, com o objetivo de estudar o efeito da repulsão coulombiana local e não local sobre a simetria do parâmetro de ordem para o caso exato e também o limite de acoplamento forte. Se mostra também a construção de um Hamiltoniano efetivo que desacopla a interação el etron-bipolaron com o fim de abordar o problema coletivo de infinitos corpos e vemos como o modelo proposto prediz a formação de ondas de densidade para uma região especifica dos parâmetros físicos do Hamiltoniano estudado. / High-temperature superconductors have different properties than conventional superconductors, one of these important properties is non-isotropic symmetry of the order parameter. In this work we present a model that shows the presence of symmetry d-wave in a class of superconductors of high Tc , as well as the condition for the existence of density waves in the states of equilibrium. We first analyze a three-body system, a bipolaron and two electrons, in order to study the effect of local and non-local Coulomb repulsion on the symmetry of the order parameter for the exact case and also the strong coupling limit. It is also shown the construction of an effective Hamiltonian that decouples the electron-bipolaron interaction in order to approach the collective problem of infinite bodies and we see how the proposed model predicts the formation of density waves for a specific region of the physical parameters of the studied Hamiltonian.

Os supercondutores de alta temperatura crítica apresentam propriedades diferentes dos supercondutores convencionais, uma destas propriedades importantes é a simetria não isotrópica do parâmetro de ordem. Neste trabalho se apresenta um modelo que mostra a presença de simetria d-wave em uma classe de supercondutores de alta Tc, assim como a condição para a existência de ondas de densidade nos estados de equilíbrio. Se analisa primeiro um sistema de três corpos, um bipolaron e dois elétrons, com o objetivo de estudar o efeito da repulsão coulombiana local e não local sobre a simetria do parâmetro de ordem para o caso exato e também o limite de acoplamento forte. Se mostra também a construção de um Hamiltoniano efetivo que desacopla a interação el etron-bipolaron com o fim de abordar o problema coletivo de infinitos corpos e vemos como o modelo proposto prediz a formação de ondas de densidade para uma região especifica dos parâmetros físicos do Hamiltoniano estudado. / High-temperature superconductors have different properties than conventional superconductors, one of these important properties is non-isotropic symmetry of the order parameter. In this work we present a model that shows the presence of symmetry d-wave in a class of superconductors of high Tc , as well as the condition for the existence of density waves in the states of equilibrium. We first analyze a three-body system, a bipolaron and two electrons, in order to study the effect of local and non-local Coulomb repulsion on the symmetry of the order parameter for the exact case and also the strong coupling limit. It is also shown the construction of an effective Hamiltonian that decouples the electron-bipolaron interaction in order to approach the collective problem of infinite bodies and we see how the proposed model predicts the formation of density waves for a specific region of the physical parameters of the studied Hamiltonian.

Orientador: Hermes Adolfo de Aquino / Banca: José Antônio Malmonge / Banca: Rinaldo Gregório Filho / Resumo: Os polímeros são muito conhecidos por serem materiais de fácil processamento, leveza, isolantes elétricos e até mesmo térmicos. Essas propriedades viabilizaram várias aplicações tecnológicas desde utensílios domésticos à indústria. No fim do século passado as pesquisas voltaram-se em busca de energias renováveis e novos materiais que associassem as vantagens dos polímeros com as propriedades elétricas dos metais. Com essas pesquisas surgiu uma nova classe de polímeros chamada de Polímeros Condutores Intrínsecos (PCIs) que dispõem de boas propriedades de condução elétrica inerente ao material. Esses PCIs podem ser sintetizados em forma de fibras ou filmes, sozinhos ou com vários outros polímeros para formar blendas com diferentes propriedades. O polipirrol (PPy) é um PCI que proporciona altas condutividades elétricas e boa estabilidade oxidativa, algo difícil de se conseguir com essa classe de polímeros. Esse trabalho teve como objetivo sintetizar amostras de PPy por dois métodos de síntese química: convencional (em solução aquosa) e microemulsão com dodecil sulfato de sódio (SDS - surfactante e dopante). No primeiro método foi variada a razão molar de monômero/oxidante e no segundo variou-se as razões molares de monômero/oxidante/dopante. Para o estudo dessas amostras foram realizadas análises estruturais, morfológicas, térmicas, ópticas e elétricas. De maneira geral, as amostras que apresentaram melhores características morfológicas, ópticas e de condutividade elétrica, foram as obtidas no processo químico em microemulsão, de tal maneira que, quanto maior a quantidade de SDS e menor a temperatura, menor foi o tamanho das partículas de PPy, maior a conjugação das cadeias e maior a dopagem com SDS. / Abstract: The polymers are known to be materials easy processed, slight, electrical insulators and even heat. These properties made possible many technological applications, from household items to the industry. At the end of last century the polls turned in search of renewable energy and new materials that combines the benefits of polymers with the electrical properties of metals. With these studies emerged a new class of polymers called Intrinsic Conducting Polymers (PICs) that have good electrical conduction properties inherent to the material. These PICs can be synthesized in the form of fibers or films, either alone or with various other polymers to form blends with different properties. The polypyrrole (PPy) is a PIC that provides high electrical conductivity and good oxidative stability, something difficult to achieve with this class of polymers. This study aimed to synthesize PPy samples by two methods of chemical synthesis: conventional (aqueous solution) and microemulsion SDS (dodecilsulfate of sodium - surfactant and dopant). In the first method was varied the molar ratio of monomer/oxidant and the second was varied molar ratios of monomer/oxidant/dopant. For the study of these samples were performed structural analyses, morphological, thermal, optical and electrical. In general, samples that showed better morphological characteristics, optical and electrical conductivity were obtained in the chemical process of microemulsion, such a way that the larger the amount of SDS and the lower the temperature, the smaller the particle size of PPy, the greater the conjugation of chains and the higher the doping with SDS. / Mestre

Organic conducting polymers are essential for the development of various electronic devices, including field-effect transistors, light-emitting diodes, solar cells, and thermoelectric devices. Understanding the charge transport mechanisms within these materials, particularly the roles of polarons and bipolarons as charge carriers, is crucial. Despite the recognized importance of these carriers, there are ongoing debates regarding the interpretation of their mid-IR absorption spectral signatures in the 0.3-0.7 eV range. This is mainly due to challenges in applying the conventional mid-gap state model, especially in the context of doped P3HT (poly(3-hexylthiophene)) films. The conventional model predicts a blueshift for the mid-IR P1 band of bipolarons compared to polarons, yet recent experiments reveal both blueshifted and redshifted bands, at elevated oxidation levels, leading to confusion about the true mid-IR spectral hallmark of spinless singlet bipolarons. This thesis aims to resolve these inconsistencies by proposing a Holstein-style model for singlet bipolarons in π-conjugated polymers with nondegenerate ground states. The model incorporates hole hopping, electron−vibration coupling involving the prominent aromatic-quinoidal mode, and Coulombic interactions between (hole) polarons and between polarons and dopant anions. In contrast to the conventional interpretation where bipolaron formation results from self-trapping, our findings indicate that it is primarily driven by attractive electrostatic interactions with dopant anions. Without these anions, two holes would not pair to form singlet bipolarons. More importantly, our results indicate that the observed blueshift at lower oxidation levels signifies the increased localization of Coulombically interacting polarons, whereas at higher oxidation levels, the simultaneous emergence of both redshifted and blueshifted bands is indeed the spectral signature of spinless singlet bipolarons formation. Furthermore, we find that the binding energy of bipolarons in π-stacks of P3HT chains is significantly higher, nearly threefold, than in a single chain, highlighting the profound influence of long-range order and chain stacking on bipolarons formation. This work contributes to resolving the theoretical ambiguities surrounding charge carrier dynamics in organic conjugated polymers and enhances our understanding of their optoelectronic properties. / Chemistry

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-18Bitstream added on 2014-06-13T18:28:58Z : No. of bitstreams: 1 santim_rh_me_ilha.pdf: 3013361 bytes, checksum: 9c0ba8507c697ecca7db1980615ec2b6 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os polímeros são muito conhecidos por serem materiais de fácil processamento, leveza, isolantes elétricos e até mesmo térmicos. Essas propriedades viabilizaram várias aplicações tecnológicas desde utensílios domésticos à indústria. No fim do século passado as pesquisas voltaram-se em busca de energias renováveis e novos materiais que associassem as vantagens dos polímeros com as propriedades elétricas dos metais. Com essas pesquisas surgiu uma nova classe de polímeros chamada de Polímeros Condutores Intrínsecos (PCIs) que dispõem de boas propriedades de condução elétrica inerente ao material. Esses PCIs podem ser sintetizados em forma de fibras ou filmes, sozinhos ou com vários outros polímeros para formar blendas com diferentes propriedades. O polipirrol (PPy) é um PCI que proporciona altas condutividades elétricas e boa estabilidade oxidativa, algo difícil de se conseguir com essa classe de polímeros. Esse trabalho teve como objetivo sintetizar amostras de PPy por dois métodos de síntese química: convencional (em solução aquosa) e microemulsão com dodecil sulfato de sódio (SDS – surfactante e dopante). No primeiro método foi variada a razão molar de monômero/oxidante e no segundo variou-se as razões molares de monômero/oxidante/dopante. Para o estudo dessas amostras foram realizadas análises estruturais, morfológicas, térmicas, ópticas e elétricas. De maneira geral, as amostras que apresentaram melhores características morfológicas, ópticas e de condutividade elétrica, foram as obtidas no processo químico em microemulsão, de tal maneira que, quanto maior a quantidade de SDS e menor a temperatura, menor foi o tamanho das partículas de PPy, maior a conjugação das cadeias e maior a dopagem com SDS. / The polymers are known to be materials easy processed, slight, electrical insulators and even heat. These properties made possible many technological applications, from household items to the industry. At the end of last century the polls turned in search of renewable energy and new materials that combines the benefits of polymers with the electrical properties of metals. With these studies emerged a new class of polymers called Intrinsic Conducting Polymers (PICs) that have good electrical conduction properties inherent to the material. These PICs can be synthesized in the form of fibers or films, either alone or with various other polymers to form blends with different properties. The polypyrrole (PPy) is a PIC that provides high electrical conductivity and good oxidative stability, something difficult to achieve with this class of polymers. This study aimed to synthesize PPy samples by two methods of chemical synthesis: conventional (aqueous solution) and microemulsion SDS (dodecilsulfate of sodium – surfactant and dopant). In the first method was varied the molar ratio of monomer/oxidant and the second was varied molar ratios of monomer/oxidant/dopant. For the study of these samples were performed structural analyses, morphological, thermal, optical and electrical. In general, samples that showed better morphological characteristics, optical and electrical conductivity were obtained in the chemical process of microemulsion, such a way that the larger the amount of SDS and the lower the temperature, the smaller the particle size of PPy, the greater the conjugation of chains and the higher the doping with SDS.

Die vorliegende Arbeit behandelt die elektrochemische Synthese (elektrochemische Polymerisation und Copolymerisation) und die Charakterisierung der Redox- und sensorischen Eigenschaften neuer funktionalisierter Polymere für die Ionensensorik. Die Funktionalisierung wird sowohl in der Polymer-Hauptkette (Polysalene) als auch in der Polymer-Seitenkette (ein Thiophen-Copolymer: 3-Methylthiophen/6-Hydroxy-2-(2-(3-thienyl)-ethoxy)-acetophenon) dargestellt. Die Redox-Prozesse der funktionalisierten Polymere wurden mit spektroelektrochemischen Methoden: ESR-, UV-Vis-NIR- und FTIR-Spektroelektrochemie charakterisiert. Durch diese Methoden konnten während der elektrochemischen Oxidation von funktionalisierten leitfähigen Polymeren verschiedene Polymer- bzw. Copolymer-Ladungsträger nachgewiesen werden: Polaronen, Bipolaronen beim Thiophen-Copolymer, zwei Polaronen auf einer Polymerkette im Singulettezustand beim Poly(3-methylthiophen) und eine diamagnetische Spin-Spin-Wechselwirkung zwischen ungepaarten Elektronen der Cu(II)-Ionen und der ungepaarten Elektronen von bisphenolischen Ligand-Kationradikalen beim Poly[Cu(II)-salen]. Sensorische Eigenschaften gegenüber Ni(II)-Ionen wurden durch Potentiometrie an einem Poly[Ni(II)-salen]-Derivat getestet. Es zeigt eine gute potentiometrische Ni(II)-Ionenselektivität (der Logarithmus des potentiometrischen Selektivitätskoeffizienten liegt im Bereich von -0.5 bis -1.5) in Anwesenheit von Cd(II), Mn(II), Zn(II) und Na(I).

Die vorliegende Arbeit behandelt die elektrochemische Synthese (elektrochemische Polymerisation und Copolymerisation) und die Charakterisierung der Redox- und sensorischen Eigenschaften neuer funktionalisierter Polymere für die Ionensensorik. Die Funktionalisierung wird sowohl in der Polymer-Hauptkette (Polysalene) als auch in der Polymer-Seitenkette (ein Thiophen-Copolymer: 3-Methylthiophen/6-Hydroxy-2-(2-(3-thienyl)-ethoxy)-acetophenon) dargestellt. Die Redox-Prozesse der funktionalisierten Polymere wurden mit spektroelektrochemischen Methoden: ESR-, UV-Vis-NIR- und FTIR-Spektroelektrochemie charakterisiert. Durch diese Methoden konnten während der elektrochemischen Oxidation von funktionalisierten leitfähigen Polymeren verschiedene Polymer- bzw. Copolymer-Ladungsträger nachgewiesen werden: Polaronen, Bipolaronen beim Thiophen-Copolymer, zwei Polaronen auf einer Polymerkette im Singulettezustand beim Poly(3-methylthiophen) und eine diamagnetische Spin-Spin-Wechselwirkung zwischen ungepaarten Elektronen der Cu(II)-Ionen und der ungepaarten Elektronen von bisphenolischen Ligand-Kationradikalen beim Poly[Cu(II)-salen]. Sensorische Eigenschaften gegenüber Ni(II)-Ionen wurden durch Potentiometrie an einem Poly[Ni(II)-salen]-Derivat getestet. Es zeigt eine gute potentiometrische Ni(II)-Ionenselektivität (der Logarithmus des potentiometrischen Selektivitätskoeffizienten liegt im Bereich von -0.5 bis -1.5) in Anwesenheit von Cd(II), Mn(II), Zn(II) und Na(I).

Cette thèse concerne la réalisation des films minces d’oxydes et l’étude de leurs propriétés physiques pour les cellules photovoltaïques (PV) et les modules thermoélectriques. Dans une première partie, les propriétés de l’oxyde de titane TiOx (1,45<x<2) sont mises en évidence pour une utilisation en tant qu’oxyde transparent conducteur optiquement actif à disposer en face avant des cellules PV ou, comme couche de couplage optique à intercaler entre le métal réflecteur et la couche absorbante d’une cellule PV. Les couches sont déposées par ablation laser pulse (PLD). Cette méthode permet d’obtenir des couches stoechiométriques ou déficitaires en oxygène grâce au contrôle de la pression d’oxygène pendant le dépôt. Les couches sont dopées par Nb pour un gain en conductivité électrique et/ou par Nd pour la conversion des photons UV en photons du Proche IR. Les films d’une part, isolants, transparents et luminescents ou d’autre part, conducteurs et absorbants ont été obtenus. La présence de polarons et/ou de bipolarons dans les couches TiO₁,₄₅₋₁,₆₀ explique la discontinuité observée sur leurs courbes de thermoconductivité. Une seconde partie du manuscrit concerne la thermoelectricité ou il est question de modifier les propriétés des cobaltites de calcium pour la conversion en énergie électrique des gradients de température faibles, centres autour de 300-365 K. Le contrôle de la concentration en oxygène des films a permis d’obtenir les phases polymorphes CaxCoO₂, Ca₃Co₄O₉, et Ca₃Co₄O₆,₄₋₆,₈ présentant des comportements semiconducteurs ou métalliques en fonction de la température de dépôt. Les films Ca₃Co₄O₆,₄₋₆,₈ montrent de faibles résistivités (3,8-6 mΩ.cm) et des coefficients de Seebeck élevés (S) ≥ 1000 μV/K qui doivent être confirmes pour que de tels films soient utilisés dans les thermogénérateurs. / This thesis concerns the realization of oxide thin films and the study of their properties for photovoltaic or thermoelectric devices. In the first part, the TiOx properties are studied for use as an optically active transparent conductive oxide to put in front of the PV cells or, as optical coupling layer to interpose between the metal reflector and the absorbent layer of a PV cell. The layers are deposited by pulsed laser deposition (PLD). This method allows to get stoichiometric or oxygen deficient layers by controlling the oxygen partial pressure during the growth. The layers are doped with Nb to enhance electrical conductivity and/or with Nd for the conversion of Ultra-Violet photons to Near Infra-Red photons. Insulating and transparent layers, luminescent layers or conducting and absorbent layers are obtained. The TiO₁,₄₅₋₁,₆₀ films show polaronic or bipolaronic conductivity and exhibited the jump of electrical conductivity with jump height and temperature depending on the nature of the dopants. A second part of the manuscript concerns thermoelectricity in which the properties of cobalt calcium oxide are modulated for an efficient conversion of low temperature gradients centered at 300-365K. The control of the oxygen concentration of films allows to obtain the polymorphic phases CaxCoO₂,Ca₃Co₄O₉ and Ca₃Co₄O₆,₄₋₆,₈ having metallic or semiconducting behavior depending on the deposition temperature. The Ca₃Co₄O₆,₄₋₆,₈ films show high Seebeck coefficients (S) ≥ 1 000 μV/K and low electrical resistivity (3.8 to 6 mΩ.cm). Such interesting values have to be confirmed by additional experiments in order to be used as thermoelectric films.