Made available in DSpace on 2014-12-17T14:07:19Z (GMT). No. of bitstreams: 1 DanieleMHM.pdf: 2362797 bytes, checksum: d58bd3fdee9f1e1945af3e9862aa11b8 (MD5) Previous issue date: 2007-04-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Ionic oxides with ABO3 structure, where A represents a rare earth element or an alkaline metal and B is a transition metal from group VIII of the periodic table are potential catalysts for oxidation and good candidates for steam reforming reaction. Different methods have been considered for the synthesis of the oxide materials with perovskite structure to produce a high homogeneous material with low amount of impurities and low calcination temperatures. In the current work, oxides with the LaNiO3 formula had been synthesized using the method of the polymeric precursors. The thermal treatment of the materials took place at 300 ?C for 2h. The material supported in alumina and/or zirconia was calcined at 800 ?C temperature for 4h. The samples had been characterized by the following techniques: thermogravimetry; infrared spectroscopy; X-ray diffraction; specific surface area; distribution of particle size; scanning electron microscopy and thermo-programmed reduction. The steam reforming reaction was carried out in a pilot plant using reducing atmosphere in the reactor with a mixture of 10% H2-Argon, a mass about 5g of catalyst, flowing at 50 mL.min-1. The temperature range used was 50 - 1000 oC with a heating rate of 10 oC.min-1. A thermal conductivity detector was used to analyze the gas after the water trapping, in order to permit to quantify the consumption of hydrogen for the lanthanum nickelates (LaNiO3). The results showed that lanthanum nickelate were more efficient when supported in alumina than when supported in zirconia. It was observed that the methane conversion was approximately 100% and the selectivity to hydrogen was about 70%. In all cases were verified low selectivity to CO and CO2 / ?xidos i?nicos com estrutura ABO3, onde A representa elemento terra rara ou metal alcalino e B ? um metal de transi??o especialmente do grupo VIII da tabela peri?dica s?o potenciais catalisadores para oxida??o e fortes candidatos para reforma a vapor. Diferentes m?todos t?m sido propostos para a s?ntese de ?xidos com estrutura perovisquita visando produzir um material com alta homogeneidade, baixa quantidade de impurezas e baixa temperatura de calcina??o. No presente trabalho, ?xidos do tipo LaNiO3 foram sintetizados utilizando o m?todo dos precursores polim?ricos. Os materiais foram tratados termicamente a 300 ?C por 2h, calcinados a 800 ?C por 4h e suportados em alumina e/ou zirconia. As amostras foram caracterizadas pelas seguintes t?cnicas: an?lise termogravim?trica; espectroscopia na regi?o do infravermelho; difra??o de raios-X; ?rea superficial; distribui??o do tamanho de part?cula; redu??o a temperatura programada e microscopia eletr?nica de varredura. Rea??es catal?ticas de reforma a vapor foram realizadas em uma planta piloto, usando-se atmosfera redutora com uma mistura de 10% H2-Arg?nio, uma massa de cerca de 5g de catalisador, com fluxo total de 50 mL.min-1. A temperatura variou de 50 a 1000 oC com raz?o de aquecimento de 10 oC.min-1. Um detector de condutividade t?rmica foi utilizado para analisar o g?s ap?s trapeamento da ?gua, permitindo assim quantificar o consumo de hidrog?nio para os niquelatos de lant?nio (LaNiO3). Os resultados mostraram que o niquelato de lant?nio, foi mais eficaz quando suportado em alumina que em zirconia, observou-se que a convers?o do metano foi pr?xima a 100% e seletividade ao hidrog?nio em torno de 70%. Em todos os casos verificou-se baixa seletividade ao CO e CO2

Kimberlitos são rochas vulcânicas que, frequentemente, contêm diamante, grafite e/ou carbonato, sendo a presença destes componentes diretamente influenciada pela variabilidade da fugacidade de oxigênio (fO2) do magma durante a sua ascenção. Segundo Chakhmouradian and Mitchell (2000), CaTiO3-perovskitas podem ser usadas para revelar as condições de alguns dos múltiplos estágios de cristalização da história magmática destas rochas. No intuito de estabelecer a fugacidade de oxigênio de magmas kimberlíticos naturais, CaTiO3-perovskitas foram cristalizadas experimentalmente em equilíbrio com um líquido kimberlítico sintético em altas temperaturas e diferentes condições de pressão e de fugacidade de oxigênio. Os experimentos mostraram que a perovskita incorporou maiores quantidades de Fe3+ com o aumento da fO2. A equação do oxigênio barômetro desenvolvida neste estudo pode ser aplicada em rochas kimberlíticas de diferentes condições de fO2, que contêm CaTiO3-perovskita e olivina. Na presente pesquisa, nós aplicamos este oxigênio barômetro em amostras do kimberlito Rosário do Sul, que é um kimberlito transicional localizado no limite sudoeste da Bacia do Paraná. Os dados de minerais deste kimberlito sugerem que sua fonte é um produto da reação de um líquido silicático-carbonatítico com o manto. Idades U-Pb de ~ 128Ma em CaTiO3-perovskitas (Conceição et al., in prep.) revelam que o kimberlito Rosário do Sul provavelmente entrou em erupção logo após o vulcanismo da Província Paraná-Etendeka. Temperaturas de cristalização, pressões e fO2 dos kimberlitos Rosário do Sul e Alfeu-I, outro importante kimberlito situado no sul do Brasil, foram calculadas. As condições de suas fontes foram estimadas usando diferentes métodos a partir das composições de olivinas, espinélios, CaTiO3-perovskitas, granadas, ortopiroxênios e clinopiroxênios. As temperaturas, pressões e condições de fO2 dos kimberlitos Rosário do Sul e Alfeu-I sugerem que eles foram transportados para a superfície em condições nas quais fluidos ricos em CO2 podem reagir com o manto silicático e produzir carbonatos. A composição mineral e as condições de formação do kimberlito Rosário do Sul indicam que a sua fonte pode ter sido metassomatizada por fluidos provenientes da reciclagem de uma placa oceânica subductada durante a quebra do Gondwana e abertura do Atlântico Sul, logo depois do vulcanismo da Província Paraná-Etendeka. As condições de formação dos kimberlitos Rosário do Sul e Alfeu-I são usadas também para estimar o potencial destes kimberlitos em preservar diamantes. / Kimberlites are volcanic rocks which often contain diamonds, graphite and/or carbonate, and the stability of these minerals is directly influenced by the variability of oxygen fugacity (fO2) of the magma during its ascent. Second Chakhmouradian and Mitchell (2000), CaTiO3-perovskites may be used to unravel the conditions of some of the multiple stages of crystallization in the magmatic history of these rocks. In order to establish oxygen fugacities of natural kimberlititic magmas, we experimentally equilibrated CaTiO3-perovskites with synthetic kimberlitic melts at high temperatures, different oxygen fugacities and different pressures. The experiments show that perovskite incorporates increasing amounts of Fe3+ with increasing fO2. The oxygen barometer equation developed in this study can be applied in kimberlite rocks that contain CaTiO3-perovskite and olivine from different fO2 conditions. In the present research, we applied this oxygen barometer in the Rosário do Sul kimberlite samples, which is a transitional kimberlite located in the southwestern edge of the Paraná Basin. The mineral data of this kimberlite suggest that its source is a product of the reaction of a silicate-carbonate liquid in the mantle. U-Pb ages of ~ 128 Ma on CaTiO3-perovskites (Conceição et al., in prep.) reveal that the Rosário do Sul kimberlite probably erupted just after the volcanism of Paraná-Etendeka Province. We calculated crystallization temperatures, pressures and oxygen fugacities (fO2) of Rosário do Sul and Alfeu-I kimberlites, another important kimberlite situated in the South of Brazil. Their source conditions are estimated using different methods from olivines, spinels, CaTiO3-perovskites, garnets, orthopyroxenes and clinopyroxenes compositions. The calculated temperature, pressure and fO2 values of Rosário do Sul and Alfeu-I kimberlites suggest that they were transported to the surface under fO2 conditions in which CO2-rich fluids may react with mantle silicates to produce carbonates. The mineral composition and fO2 conditions of Rosário do Sul kimberlite indicate that its source may have been metasomatized by fluids generated from the recycling of a subducted oceanic plate during the Gondwana breakup and the South Atlantic opening, just after the Paraná-Etendeka Province volcanism. The source conditions of Rosário do Sul and Alfeu-I kimberlites are also used to estimate the potential of these kimberlites to preserve diamonds.

El análisis químico de los meteoritos que más se parecen a la materia que dio lugar a la formación de la Tierra revela que la concentración del gas xenón en la atmósfera de nuestro planeta es menor de la que se debería esperar. Investigaciones recientes parecen indicar que el origen de esta deficiencia podría estar relacionado con la solubilidad de los gases nobles en las vacantes de oxígeno de la estructura perovskita del silicato de magnesio, MgSiO3, principal componente del manto terrestre. / The chemical analysis of the meteorites considered to resemble closely the primordial matter which led to the formation of the Earth indicates that the concentration of xenon gas in our atmosphere is lower than expected. It seems that this deficiency is related to the noble gases’ solubility in the oxygen vacancies present in the perovskite structure of magnesium silicate, MgSiO3, the main constituent of the Earth’s mantle.

Rhombohedral perovskite BiFeO3 is a single phase multiferroic compound exhibiting both magnetic (Neel temperature ~370˚C) and ferroelectric (Curie point ~840˚C) ordering well above the room temperature. Ferroelectricity in BiFeO3 is due to stereochemically active 6slone pair in Biion which causes large relative displacements of Bi and O ions along the [111] direction. Long range spiral modulation of the canted antiferromagnetic spin arrangement in Feeffectively cancels the macroscopic magnetization due to Dzyaloshinskii–Moriya interaction and thereby prevents linear magneto-electric effect. Synthesizing dense pure BiFeO3 by conventional solid state method is difficult due to the formation of thermodynamically stable secondary phases such as Bi2Fe4O9, Bi25FeO39 and Bi46Fe2O72. To stabilize the perovskite phase and to suppress the cycloid several groups have adopted different strategies such as thin film growth, different synthesis methods and chemical substitution. Of the various substitutions reported in the literature, PbTiO3 substitution has shown very interesting features, such as (i) unusually large tetragonality (c/a~1.19), (ii) formation of morphotropic phase boundary (MPB) and (iii) high curie point Tc~650C. MPB ferroelectric systems such as lead zirconate titanate (PZT) are known to exhibit high piezoelectric response due to the coupling between strain and polarization. Hence the existence of magnetic ordering in BiFeO3-PbTiO3 offers an interesting scenario where polarization, strain and magnetization may couple together. The high Curie point also makes the system an interesting candidate for high temperature piezoelectric application. However its potential as a high temperature piezoelectric material has not been realized yet. A detailed review of literature suggests a lack of clear agreement with regards to the composition range of the reported MPB itself. Different research groups have reported different composition range of MPB for this system even for almost similar synthesis conditions. The present thesis deals with broadly two parts, firstly with the preparation of pure BiFeO3 by co-precipitation and hydrothermal methods and its thermal stability and secondly resolving the cause of discrepancy in range of MPB reported in BiFeO3-PbTiO3 solid solution. Detailed examination of this system (BiFeO3-PbTiO3) around the reported MPB composition by temperature dependent X-ray, electron and neutron diffraction techniques, in conjunction with a systematic correlation of sintering temperature and time with microstructural and phase formation behavior revealed the fact that the formation of MPB or the single ferroelectric phase is critically dependent on the grain size. This phenomenon is also intimately related to the abnormal grain growth in this system. Chapter 1 gives the brief overview of the literature on the topics relevant to the present study. The literature survey starts with a brief introduction about the perovskite oxides; their ferroelectric, magnetic and multiferroic properties were discussed in further sections. A brief outline on the grain growth mechanism is described. An overview of BiFeO3 and various synthesis methods, different chemical substitutions and their effect on properties are provided. A brief review of published literature on BiFeO3-PbTiO3 solid solution and its properties is also presented. Chapter 2 deals with the synthesis of pure BiFeO3, heat treatment and characterisation. BiFeO3 was synthesised by (a) co-precipitation and (b) hydrothermal methods. In co-precipitation method, calcination of precipitate at different temperature resulted in the formation of BiFeO3 along with secondary phases (Bi2Fe4O9 and Bi24FeO39). The optimum calcination temperature to prepare pure BiFeO3 was found to be 560C. The synthesized pure BiFeO3 exhibits weak ferromagnetic hysteresis at room temperature, the degree of which increases slightly at 10K (-263C). The hydrothermal treatment was carried out in (a) carbonate and (b) hydroxide precipitates with KOH as mineralizer. BiFeO3 prepared using hydroxide precipitate was stable till 800C whereas with carbonate precipitate it was stable only till 600C. Chapter 3 deals with the stability of phases in (1-x)BiFeO3 -(x)PbTiO3 solid solution. Samples prepared by conventional solid state route sometimes remain as dense pellet and on certain occasions it disintegrate completely into powder observed after sintering. Irrespective of the composition, sintering time and temperature, powder X-ray Diffraction (XRD) pattern of the survived pellet (crushed into powder) shows coexistence of rhombohedral (R3c) and tetragonal (P4mm) phases and the disintegrated powder (without crushing) show 100% tetragonal (P4mm) phase. Very high spontaneous tetragonal strain (c/a-1) ~0.19 at MPB is believed to be the origin for disintegration. But in all the survived pellets at least a minor fraction of rhombohedral phase (5-7%) is present. Systematic sintering studies with the time and temperature shows, decreasing the sintering temperature and time will increase the lifetime of the pellet and by increasing the sintering temperature and time the pellet will disintegrate. In this work we have conclusively proved that the wide composition range of MPB reported in the literature is due to kinetic arrest of the metastable rhombohedral phase and that if sufficient temperature and time is given, the metastable phase disappears. The suppression/formation of minor rhombohedral phase is expected due to the play of local kinetic factors during the transformation process. This makes the system behave in an unpredictable way with regard to the fraction of rhombohedral phase that is observed at room temperature. A systematic X-ray and neutron powder diffraction study of the giant tetragonality multiferroic (1-x)BiFeO3 -(x)PbTiO3 have shown that the compositions close to the morphotropic phase boundary of this system present two different structural phase transition scenarios on cooling from the cubic phase: (i) Pm3m P4mm(T2)+P4mm(T1) P4mm (T1) and (ii) Pm3m P4mm(T2) + P4mm(T1) + R3c P4mm (T1) + R3c. The comparatively larger tetragonality of the T1 phase as compared to the coexisting isostructural T2 phase is shown to be a result of significantly greater degree of overlap of the Pb/Bi-6s and Ti/Fe-3d with the O-2p orbitals as compared to that in the T2 phase. High temperature electron diffraction studies show that the metastable rhombohedral phase is present in the cubic matrix well above the Curie point as nuclei. Life time of the metastable R3c nuclei is very sensitive to composition and temperature, and nearly diverges at x → 0.27. MPB like state appears only if the system is cooled before the metastable R3c nuclei could vanish. Issue of the metastable rhombohedral state is developed further in Chapter 4. A one-to-one correlation was found between the grain size and phase formation behavior. Fine grained (~1µm) microstructure (usually pellets) shows phase coexistence (R3c+P4mm) and the disintegrated coarse grains (~10µm) show tetragonal (P4mm) phase. Microstructural analysis revealed the disintegration was caused by abnormal grain growth along with the disappearance of metastable rhombohedral phase. Abnormal grain growth starts at the periphery/crack i.e., at the free surface and move towards the canter of the pellet. Size reduction of disintegrated coarse grains (~10µm) to fine grains (~1µm) by crushing the sample showed that the system switching form pure tetragonal (P4mm) state to the MPB state comprising of tetragonal and rhombohedral phases (R3c+P4mm). In another approach the smaller sized particles of x=0.20 were synthesized by sol gel method. It was reported that in conventional solid state route x=0.20 exhibits pure rhombohedral phase. The sol-gel sample calcined at 500C (particle size ~15nm) stabilizes tetragonal metastable phase along with the stable rhombohedral phase, the morphotropic phase boundary state. Samples calcined at higher temperature, 800C (particle size ~50nm) also showed stable rhombohedral phase. Ferromagnetic behavior was observed in the sample having phase coexistence and the sample with pure rhombohedral phase showed antiferromagnetic behavior. Hence this material is a promising candidate which can be tuned to exhibit different behavior just by adopting different grain size. Chapter 5 deals with the magnetic structure of (1-x)BiFeO3 -xPbTiO3 solid solution with change in composition and temperature. Magnetic structure was studied using powder neutron diffraction in the composition range x=0.05 -0.35. Rietveld analysis was carried out for the nuclear and magnetic phases, by considering R3c phase for the nuclear structure. To account for the magnetic Bragg peak at d=4.59Å, three antiferromagnetic models were considered for the magnetic structure: (i) helical spin arrangement as in BiFeO3, (ii) commensurate G-type antiferromagnetic ordering with moments in the a-b plane (of the hexagonal cell), and (iii) commensurate G-type ordering with moments parallel to the c-axis (of the hexagonal cell). The third model was found to be suitable to explain the magnetic peak accurately and the better fitting of magnetic peak was observed in this model compared to others. At room temperature the MPB compositions have rhombohedral and tetragonal nuclear phases along with the rhombohedral magnetic phase. Addition of PbTiO3 in BiFeO3 not only changes the magnetic structure but also reduces the magnetic moment due to the substitution of Ti in Fesite. High temperature neutron diffraction studies reveal the magnetic transition at ~300C for x=0.20, ~95C for x=0.27 and ~150C for x=0.35. The Neel temperature observed in neutron diffraction studies were also confirmed by DSC and by temperature dependent dielectric studies. For x=0.20, anomalous variation in the lattice parameters and the octahedral tilt angle was observed across the magnetic transition temperature. In the magnetic phase, the c-parameter was contracted and the octahedral tilt angle slightly increased. This result suggests a coupling between spin, lattice and structural degrees of freedom around the transition temperature. Temperature dependent powder neutron diffraction study at low temperature from 300K (27C) to 4K (-269C) in x=0.35 shows the evolution of tetragonal magnetic phase at 200K (-73C) whose intensity is increasing with decrease in temperature. Below 200K, x=0.35 has rhombohedral and tetragonal magnetic and nuclear phases. While in x=0.27 at low temperature, rhombohedral magnetic and nuclear phases are present along with the tetragonal nuclear phase alone (the tetragonal magnetic phase is absent). We propose this discrepancy in the Neel temperature and the magnetic phase formation can be due to the probabilistic nature of the existence of metastable rhombohedral phase which was discussed earlier.

This thesis is about new ways to experimentally realise materials with desired nano-structures for solution-processable optoelectronic devices such as solar cells and light-emitting diodes (LEDs), and examine structure-performance relationships in these devices. Short exciton diffusion length limits the efficiency of most exciton-based solar cells. By introducing nano-structured architectures to solar cells, excitons can be separated more effectively, leading to an enhancement of the cell’s power conversion efficiency. We use diblock copolymer lithography combined with solvent-vapour-assisted imprinting to fabricate nano-structures with 20-80 nm feature sizes. We demonstrate nanostructured solar cell incorporating the high-performance polymer PBDTTT-CT. Furthermore, we demonstrated the patterning of singlet fission materials, including a TIPS-pentacene solar cell based on ZnO nanopillars. Recently perovskites have emerged as a promising semiconductor for optoelectronic applications. We demonstrate a perovskite light-emitting diode that employs perovskite nanoparticles embedded in a dielectric polymer matrix as the emissive layer. The emissive layer is spin-coated from perovskite precursor/polymer blend solution. The resultant polymer-perovskite composites effectively block shunt pathways within the LED, thus leading to an external quantum efficiency of 1.2%, one order of magnitude higher than previous reports. We demonstrate formations of stably emissive perovskite nanoparticles in an alumina nanoparticle matrix. These nanoparticles have much higher photoluminescence quantum efficiency (25%) than bulk perovskite and the emission is found to be stable over several months. Finally, we demonstrate a new vapour-phase crosslinking method to construct full-colour perovskite nanocrystal LEDs. With detailed structural and compositional analysis we are able to pinpoint the aluminium-based crosslinker that resides between the nanocrystals, which enables remarkably high EQE of 5.7% in CsPbI3 LEDs.

This thesis presents a study of hybrid solar cells, specifically looking at various methods which can be employed in order to increase the power conversion efficiency of these devices. The experiments and results contained herein also present a very accurate picture of how rapidly the field of hybrid solar cells has progressed within the past three years. Chapters 1 and 2 present the background and motivation for the investigations undertaken, as well as the relevant theory underpinning solar cell operation. Chapter 2 also gives a brief review of the literature pertinent to the main types of devices investigated in this thesis; dye-sensitised solar cells, semiconductor sensitized solar cells and perovskite solar cells. Descriptions of the synthetic procedures, as well as the details of device fabrication and any measurement techniques used are outlined in Chapter 3. The first set of experimental results is presented in Chapter 4. This chapter outlines the synthesis of mesoporous single crystals (MSCs) of anatase TiO₂ as well as an investigation of its electronic properties. Having shown that this material has superior electronic properties to the conventionally used nanoparticle films, they were then integrated into low temperature processed dye-sensitised solar cells and achieved power conversion efficiencies of > 3%, exhibiting electron transport rates which were orders of magnitude higher than those obtained for the high temperature processed control films. Chapter 5 further investigates the use of MSCs in photovoltaic devices, this time utilising a more strongly absorbing inorganic sensitiser, Sb₂S₃. Utilising the readily tunable pore size of MSCs, these Sb₂S₃ devices showed an increase in voltage and fill factor which can be attributed to a decrease in recombination within these devices. This chapter also presents the use of Sb₂S₃ in the meso-superstructured configuration. This device architecture showed consistently higher voltages suggesting that in this architecture, charge transport occurs through the absorber and not the mesoporous scaffold. Chapters 6 and 7 focus on the use of hybrid organic-inorganic perovskites in photovoltaic devices. In Chapter 6 the mixed halide, lead-based perovskite, CH₃NH₃PbI_3-xCl_x is employed in a planar heterojunction device architecture. The effects of Lewis base passivation on this material are investigated by determining the photoluminescence (PL) lifetimes and quantum efficiencies of treated and untreated films. It is found that passivating films of this material using Lewis bases causes an increase in the PLQE at low fluences as well as increasing the PL lifetime. By globally fitting these results to a model the trap densities are extracted and it is found that using these surface treatments decreases the trap density of the perovskite films. Finally, these treatments are used in complete solar cells resulting in increased power conversion efficiencies and an improvement in the stabilised power output of the devices. Chapter 7 describes the materials synthesis and characterisation of the tin-based perovskite CH₃NH₃SnI₃ and presents the first operational, lead-free perovskite solar cell. The work presented in this thesis describes significant advances in the field of hybrid solar cells, specifically with regards to improvements made to the nanostructured electrode, and the development and implementation of more highly absorbing sensitizers. The improvements discussed here will prove to be quite important in the drive towards exploiting solar power as a clean, affordable source of energy.

Ce travail de thèse a pour sujet la conception des cellules solaires photovoltaïques à base de pérovskite hybride par le biais de la technologie d’impression jet d’encre. Les deux premiers chapitres font la présentation du contexte de la thèse, à savoir l’alimentation d’un réseau autonome de capteurs, et passent en revue les aspects scientifiques des technologies jet d’encre et photovoltaïque de nouvelle génération. Le troisième chapitre présente la mise au point d’une cellule photovoltaïque à l’état de l’art et son évolution vers une architecture imprimable à basse température de recuit. La problématique de la stabilité des cellules photovoltaïques à pérovskite est aussi abordée. La dernière partie présente les différents aspects et problématiques de l’impression par jet d’encre des trois couches internes d’une cellule solaire pérovskite. Au terme de ce travail la possibilité d’imprimer des cellules solaires pérovskites avec des rendements supérieurs à 10 % a été démontrée, le tout en condition ambiante et à basse température. / This thesis is about the design of photovoltaic solar cells based on hybrid perovskite using inkjet printing technology. The first two chapters present the context of the thesis, namely the powering of an autonomous sensor network, and review the scientific aspects of inkjet and photovoltaic technologies. The third chapter presents the development of a state-of-the-art photovoltaic cell and its evolution towards a printable architecture at low annealing temperatures. The problem of the stability of photovoltaic cells with perovskite is also discussed. The last part presents the different aspects and problems of the inkjet printing of the three inner layers of a perovskite solar cell. At the end of this work the possibility of printing perovskite solar cells with efficiencies higher than 10% has been demonstrated, all in ambient conditions and at low temperature.

SILVA, Eder Nascimento. Propriedades Vibracionais de Perovskitas Complexas Ordenadas. 2008. 181 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-04T19:23:25Z No. of bitstreams: 1 2008_tese_ensilva.pdf: 7886254 bytes, checksum: baaeb81edf0f9b9bff1c7ee1c5ae7c79 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T16:52:15Z (GMT) No. of bitstreams: 1 2008_tese_ensilva.pdf: 7886254 bytes, checksum: baaeb81edf0f9b9bff1c7ee1c5ae7c79 (MD5) / Made available in DSpace on 2015-05-07T16:52:15Z (GMT). No. of bitstreams: 1 2008_tese_ensilva.pdf: 7886254 bytes, checksum: baaeb81edf0f9b9bff1c7ee1c5ae7c79 (MD5) Previous issue date: 2008 / The A2B0B00O6 double perovskites can crystallize in at least 12 different space groups, where the B0O6 and B00O6 octahedra (1:1 order) alternate along the three crystallographic axis. Four perovskites with this order are studied in this work, to know: Sr2CoWO6 (I4/m), Ca2CoWO6, Ca2CoTeO6 and Sr2CoTeO6 (P21/n). In many cases, total or partial disorder due to the random distribution of the B0 and B00 cations in the B sites of the ABO3 perovskites can be observed. An example of compound with total disorder is Pb(Fe1/2Nb1/2)O3 (Cm), where the Fe3+ and Nb5+ cations possess an occupation factor 1/2 in the octahedral sites of the perovskite structure. The compounds: (i) Ba2In(In1/3U2/3)O6, Ba2In(In1/3W2/3)O6 (Fm¯ 3m), Sr2In(In1/3U2/3)O6, Sr2(In0,87W0,13)(In0,46W0,54)O6 (P21/n) and (ii) a2(Fe0,73W0,27)(Fe0,60W0,40)O6 (P21/n) and Sr2(Fe0,79W0,21)(Fe0,54W0,46)O6, Sr2(Fe0.90Te0.10)(Fe0.57Te0.43)O6 (I4/m) possess partial disorder in the sites of the B0 and/or B00 cations, but nevertheless they exhibit 1: 1 order. In the present work, the phonon spectra of the above-mentioned perovskites are studied through the Raman scattering and infrared transmittance and/or diffuse reflectance. To analyze the phonon spectra of these compounds, theory group methods are used based on three ion sub-lattices, to know: A, B0 and B00O6. The vibrational freedom degrees of the 12 ordered perovskites are described in terms of the internal vibrations of the B00O6 octahedron and of the translational modes of the A and B0 cations. This model is valid when the vibrations of the B0O6 octahedron are negligible compared with the one of the B00O6 octahedron. We used crystallographic information to discuss the processes behind the changes in the phonon energies based on the internal modes of the octahedra. Besides, our results of Raman scattering of low temperature in Pb(Fe1/2Nb1/2)O3 ceramic, reveal pronounced anomalies in the phonon spectra around N´eel temperature TN∼150 K. We attributed these anomalies to the magnetoelectric effect in this compound.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Recentemente, vem sendo desenvolvido o uso de catalisadores de metais preciosos suportados por óxidos do tipo perovskita em automóveis. Tais sistemas catalíticos são conhecidos como catalisadores Inteligentes. A tecnologia dos catalisadores inteligentes aponta para um novo futuro na catálise automotiva e surge como um promissor substituinte para os catalisadores convencionais. O entendimento dos principais fatores que levam a auto regeneração destes catalisadores é um passo fundamental no processo de evolução desta tecnologia. O mecanismo de auto regeneração é responsável diretamente pelo aumento considerável do tempo de vida útil destes catalisadores perante aos convencionais. Consequentemente, o seu custo é bem mais baixo comparado ao convencional. Outro fator relevante é a durabilidade estrutural e o grande número de possibilidade de combinações possíveis das perovskita que fazem delas excelentes estruturas para estudo. O objetivo do trabalho é entender o processo auto regenerativo do catalisador automotivo a base de perovskita dopadas com um átomo de cobalto, manganês e níquel e quando expostas a um ambiente com uma molécula de NO e CO , através da análise da interação desses átomos dopantes em relação a estrutura da perovskita e como se comportará o átomo de paládio ao entrar em contato com a molécula de NO e CO / Has been recently developed the use of precious metal catalysts supported on perovskite oxides in automobiles . Such catalyst systems are known as Smart catalysts. The technology of smart catalysts points to a new future in automotive catalysis and appears promising as a replacement for conventional catalysts . The understanding of the main factors that lead to self regeneration of these catalysts is a key step in the evolution of this technology process. The mechanism of self regeneration is directly responsible for the substantial increase in the lifetime of these catalysts towards the conventional . Consequently , the cost is much lower compared to the conventional . Another relevant factor is the structural durability and the possibility of large number of possible combinations of perovskite structures that make them excellent for estudo.o objective is to understand the self regenerative process of the automotive catalyst based perovskite doped with a cobalt atom , MN and nickel and when exposed to an environment with a molecule of NO and CO , by analyzing the interaction of these dopant atoms relative to the perovskite structure and behaves as the palladium atom on contact with the molecule of NO and CO

abstract: Integrated oxide/semiconductor heterostructures have attracted intense interest for device applications which require sharp interfaces and controlled defects. The research of this dissertation has focused on the characterization of perovskite oxide/oxide and oxide/semiconductor heterostructures, and the analysis of interfaces and defect structures, using scanning transmission electrom microscopy (STEM) and related techniques. The SrTiO3/Si system was initially studied to develop a basic understanding of the integration of perovskite oxides with semiconductors, and successful integration with abrupt interfaces was demonstrated. Defect analysis showed no misfit dislocations but only anti-phase boundaries (APBs) in the SrTiO3 (STO) films. Similar defects were later observed in other perovskite oxide heterostructures. Ferroelectric BaTiO3 (BTO) thin films deposited directly onto STO substrates, or STO buffer layers with Ge substrates, were grown by molecular beam epitaxy (MBE) in order to control the polarization orientation for field-effect transistors (FETs). STEM imaging and elemental mapping by electron energy-loss spectroscopy (EELS) showed structurally and chemically abrupt interfaces, and the BTO films retained the c-axis-oriented tetragonal structure for both BTO/STO and BTO/STO/Ge heterostructures. The polarization displacement in the BTO films of TiN/BTO/STO heterostructures was investigated. The Ti4+ atomic column displacements and lattice parameters were measured directly using HAADF images. A polarization gradient, which switched from upwards to downwards, was observed in the BTO thin film, and evidence was found for positively-charged oxygen vacancies. Heterostructures grown on Ge substrates by atomic layer deposition (ALD) were characterized and compared with MBE-grown samples. A two-step process was needed to overcome interlayer reaction at the beginning of ALD growth. A-site-rich oxide films with thicknesses of at least 2-nm had to be deposited and then crystallized before initiating deposition of the following perovskite oxide layer in order to suppress the formation of amorphous oxide layers on the Ge surface. BTO/STO/Ge, BTO/Ge, SrHfTiO3/Ge and SrZrO3/Ge thin films with excellent crystallinity were grown using this process. Metal-insulator-metal (MIM) heterostructures were fabricated as ferroelectric capacitors and then electrically stressed to the point of breakdown to correlate structural changes with electrical and physical properties. BaTiO3 on Nb:STO was patterned with different top metal electrodes by focused-ion-beam milling, Au/Ni liftoff, and an isolation-defined approach. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2018