Submitted by MAICON CARLONE DA SILVA null (maicon.carlone@gmail.com) on 2017-05-23T16:56:49Z No. of bitstreams: 1 Dissertação - Maicon Carlone da Silva .pdf: 5898245 bytes, checksum: dcaea8b738bb0b5c8699c89bc40d8b7a (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-05-23T18:30:12Z (GMT) No. of bitstreams: 1 silva_mc_me_bauru.pdf: 5898245 bytes, checksum: dcaea8b738bb0b5c8699c89bc40d8b7a (MD5) / Made available in DSpace on 2017-05-23T18:30:12Z (GMT). No. of bitstreams: 1 silva_mc_me_bauru.pdf: 5898245 bytes, checksum: dcaea8b738bb0b5c8699c89bc40d8b7a (MD5) Previous issue date: 2017-04-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Compostos do tipo Ca1-xRxB6 (onde R representa o elemento de terra rara) tem sido estudados durantes os últimos anos principalmente no que se refere as suas características magnéticas e de transporte, porem elas ainda são controversas. Em particular a técnica de Ressonância Magnética tem sido usada para estudar compostos de Ca1-xEuxB6 (EPR) para diversas concentrações de Eu, o qual sugere a existência de uma transição metal isolante quando mudamos a concentração de Eu. Neste trabalho deveremos analisar teoricamente os espectros experimentais deste composto, em função da concentração deste elemento de terra rara. Os espectros de EPR foram simulados usando o modelo de Plefka para diversos valores de concentração x em Ca1-xEuxB6 monocristalino, isto é, 7%, 10%, 15%, 30%, 60% e 100%, visando elucidar a evolução das fases isolantes e semimetálicas, além do colapso do espectro com o aumento da concentração da impureza magnética. Tendo em vista que formas de linha simétricas são características de matrizes isolantes e assimétricas de matrizes metálicas, focaremos o nosso estudo na assimetria dos espectros de EPR. Para procurar pelo conjunto de parâmetros que melhor ajusta o espectro teórico ao experimental utilizamos o método de Simulated Annealing (SA), onde minimizamos a diferencia média quadrática entre os espectros. Ao longo deste trabalho foram reproduzidos as principais características dos espectros experimentais. Também obtivemos parâmetros importantes como o de Campo Cristalino, valor de g, parâmetros de troca da interação Eu-Eu e o parâmetro de assimetria do espectro de absorção. Conseguimos mostrar que ao aumentar a concentração o espectro evolui de uma forma Lorentziana para Dysoniana, mostrando a existência da transição metal-isolante. / Compounds of the type Ca1-xRxB6 (where R represents the element of rare earth) have been studied during the last years mainly as regards their magnetic and transport characteristics, but they are still controversial. In particular the Magnetic Resonance technique has been used to study compounds of Ca1-xEuxB6 (EPR) for several concentrations of Eu, which suggests the existence of an insulating metal transition when we change the concentration of Eu. In this work we will theoretically analyze the spectra Experimental results of this compound, depending on the concentration of this element of rare earth. In the present case, the EPR fine structure spectra were simulated using the Plefka model for various values of concentration (x) in monocrystalline Ca1-xEuxB6, that is, 7%, 10%, 15%, 30%, 60% and 100%, aiming to elucidate the evolution of the insulating and semi-metallic phases, besides the collapse of the spectrum with the increase of the concentration of magnetic impurities. Considering that symmetrical line shapes are characteristic of insulating and asymmetric matrices of metal matrices, we will focus our study on the asymmetry of RPE spectra. To find for the set of parameters that best adjusts the theoretical spectrum to the experimental, we used the Simulated Annealing (SA) method, where we minimize the mean square difference between the spectra. Throughout this work the main characteristics of the experimental spectra were reproduced. We also obtained important parameters such as the Crystalline Field, g value, Eu-Eu interaction exchange parameters and the asymmetry parameter of the absorption spectrum. We show that by increasing the concentration the spectrum evolves from a Lorentzian to Dysonian form, showing the existence of the metal-insulating transition.

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Des films minces de pérovskites NdNiO3 et SmxCa1-xMnO3 ont été synthétisés par co-pulvérisation magnétron et leurs propriétés thermochromes ont été étudiées dans le domaine infrarouge. Dans un premier temps, l'étude du nickelate NdNiO3 a montré la possibilité de synthétiser la phase pérovskite en utilisant un recuit de cristallisation sous air à basse température (550°C). Nous avons mis en évidence une cristallisation compétitive entre la phase orthorhombique thermochrome et une phase rhomboédrique non thermochrome qui est largement influencée par les paramètres d'élaboration : pression de dépôt, épaisseur des couches, température de recuit... L'obtention de ces deux phases a permis d'étudier plus précisément les mécanismes d'oxydation et de réduction intervenant lors du dépôt et lors du traitement thermique respectivement. Parallèlement à cette étude, des couches minces de SmxCa1-xMnO3, ont été également synthétisées par co-pulvérisation. Après une optimisation des conditions expérimentales permettant d'obtenir des films stoechiométriques et des analyses structurales (MEB, DRX), les comportements électriques et optiques des films ont été suivis en fonction de la température (mesure 4 pointes et IRTF). Le composé Sm0,5Ca0,5MnO3 présente une température de transition proche de la température ambiante ainsi qu'un contraste optique dans le très proche et le moyen infrarouge. Les mesures de la transmittance optique dans le domaine visible-proche infrarouge ont permis d'évaluer la dépendance du gap optique avec la température. A 20°C, celui-ci est proche de 0,7 eV. Le manganite SmxCa1-xMnO3 est donc un bon candidat pour la régulation thermique et la furtivité infrarouge / NdNiO3 and SmxCa1-xMnO3 perovskites thin films were synthesized by magnetron co-sputtering process and the thermochromic properties have been studied in the infrared range. At first, the study of the NdNiO3 nickelate has established the timeliness to synthesise the perovskite phase using a subsequent annealing crystallisation in air at moderate temperature (550°C). We have demonstrated a competitive crystallisation between the thermochromic orthorhombic phase and a non-thermochromic rhombohedral phase largely influenced by experimental parameters: deposition pressure, layer thickness, annealing temperature... The presence of these two phases allowed to clarify more precisely the oxidation mechanisms involved during the deposition process and the reduction mechanisms occurring during the heat treatment. At the same time, the SmxCa1-xMnO3 system was synthesised also as thin films. The first step includes developing the experimental conditions to obtain stoichiometric films using two separate targets. After structural analyses (SEM, XRD), the electrical and optical behaviours of films were analysed using the four probe configuration and the FTIR spectroscopy versus temperature respectively. As result, the metal-insulator transition of the Sm0,5Ca0,5MnO3 compound is close to the room temperature and the film shows an interesting optical contrast in the near and mid-infrared ranges. The optical transmittance measurements in the visible-near infrared range were used to evaluate the optical gap dependence with temperature. At room temperature, the optical gap is close to 0.7 eV. Finally, SmxCa1-xMnO3 manganite is a good candidate for thermal regulation and infrared furtivity