Solid-state dye-sensitized solar cells (ssDSSCs) and recently developed perovskite solar cells (PSCs) have attracted a great attention in the scientific field of photovoltaics due to their low cost, absence of solvent, simple fabrication and promising power conversion efficiency (PCE). In these types of solar cell, the dye molecule or the perovskite can harvest the light on the basis of electron excitation. Afterwards, the electron and hole are collected at the charge transport materials. Photoelectrochemical polymerization (PEP) is employed in this thesis to synthesize conducting polymer hole transport materials (HTMs) for ssDSSCs. We have for the first time developed aqueous PEP in comparison with the conventional organic PEP with acetonitrile as solvent. This water-based PEP could potentially provide a low-cost, environmental-friendly method for efficient deposition of polymer HTM for ssDSSCs. In addition, new and simple precursors have been tested with PEP method. The effects of dye molecules on the PEP were also systematically studied, and we found that (a) the bulky structure of dye is of key importance for blocking the interfacial charge recombination; and (b) the matching of the energy levels between the dye and the precursor plays a key role in determining the kinetics of the PEP process. In PSCs, the HTM layer is crucial for efficient charge collection and its long term stability. We have studied different series of new molecular HTMs in order to understand fundamentally the influence of alkyl chains, molecular energy levels, and molecular geometry of the HTM on the photovoltaic performance. We have identified several important factors of the HTMs for efficient PSCs, including high uniformity of the HTM capping layer, perovskite-HTM energy level matching, good HTM solubility, and high conductivity. These factors affect interfacial hole injection, hole transport, and charge recombination in PSCs. By systematical optimization, a promising PCE of 19.8% has been achieved by employing a new HTM H11. We believe that this work could provide important guidance for the future development of new and efficient HTMs for PSCs.

This thesis studies parameters influencing both the performance and stability of solid state sensitized solar cells (ssSSCs). ssSSCs benefit from their low materials and manufacturing processing costs, a consequence of using solution processed materials. However, solution processed materials are often structurally and electronically disordered. By characterizing fully operational ssSSCs and their charge transport properties, this thesis elucidates the factors limiting charge transport and proposes routes towards both improved photovoltaic conversion efficiency and long-term stability. Chapter 2 provides an explanation of the operation of ssSSCs, while Chapter 3 discusses the basic methods used in this thesis. Having set this background, Chapter 4 explores the interaction between atmospheric oxygen and charge doping mechanisms in the organic semiconductors used in ssSSCs. To understand the implications of the findings presented in Chapter 4, a new technique, “transient mobility spectroscopy”, was developed to understand the evolution of balanced charge transport behaviour of disordered semiconductors at different operating conditions in ssSSCs. This technique is presented in full in Chapter 5. The understanding gained in Chapters 4 and 5 suggest that alternative light absorbers with higher extinction coefficients may be beneficial to improving the performance of ssSSCs. Chapter 6 discusses the use of an organometal trihalide perovskite, as light absorber in ssSSCs. Using time resolved techniques, the charge transport and recombination mechanisms in various device architectures are explored, allowing suggestions to be made towards future improvements. Chapter 7 uses the technique presented in Chapter 5 to understand a rapid degradation mechanism of working ssSSCs. Particular focus is placed on the titanium dioxide charge-transporting layer. Building on this newfound understanding, two methods for attaining stable photovoltaic performance are provided, a great step forward for this technology.

La plupart des processus géologiques affectant la surface de la Terre sont le reflet des mouvements de convection au sein du manteau terrestre. Ces mouvements sont essentiellement gouvernés par le fluage par dislocations des silicates du manteau et sont à l'origine d'une anisotropie des vitesses des ondes sismiques. Cependant, les mécanismes de déformation de ces minéraux sont mal connus. Les conditions dans les couches les plus profondes sont extrêmes; la température y atteint plusieurs milliers de degrés et la pression est plus d’un million de fois supérieure à la pression atmosphérique. La détermination expérimentale de la plasticité de ces minéraux nécessite des expériences de déformation sous hautes pression et température. Les mécanismes de déformation sont généralement déterminés à partir d'expériences en cellule à enclumes diamants permettant d'atteindre les conditions de pression et de température du manteau. L'objectif de cette thèse visait à développer une nouvelle technique permettant d'étudier les dislocations in situ dans les grains d’un polycristal sous haute pression, directement à partir de leur effet sur les raies de diffraction X. De ce fait, nous avons combiné la diffraction X tridimensionnelle (3D-XRD) à la méthode d'analyse des profils de pics de diffraction (XLPA, X-ray Line Profile Analysis). Les travaux de cette thèse ont été appliqués à la post-perovskite, présente dans la couche D'' à l'interface noyau-manteau et à la stishovite, présente principalement dans les plaques en subduction. Les résultats obtenus sont utiles à la compréhension et la modélisation des mouvements de convection et du développement d'anisotropie sismique dans le manteau. / The Earth mantle and inner core are submitted to large scale movements of solid materials. The physical process allowing the flow of solid materials is connected to plastic properties and, in particular, dislocations. It is the source of seismic wave velocities anisotropy. However, the deformation mechanisms of deep Earth minerals are poorly understood. Deep in the Earth’s interior, minerals are under extreme conditions; the temperature reaches several thousand degrees and the pressure is more than one million times the atmospheric pressure. The experimental study of the plasticity of those minerals requires deformation experiments under high pressure and temperature. High pressure phenomena are often determined from experiments using diamond anvil cell to reach the conditions of pressure and temperature of the mantle. The objective of this thesis was to develop a new technique for studying dislocations in situ in grains inside a polycrystal under high pressure, directly from their effect on the X ray diffraction profiles. To do so, we combine three-dimensional X-ray diffraction (3D-XRD) to X ray Line Profile Analysis method (XLPA). The development done in this thesis was applied to post-perovskite, the main constituent of the D'' layer at the core-mantle boundary and to stishovite, present mainly in subducting slabs. The results obtained are useful for understanding and modeling of convection and the development of seismic anisotropy in the mantle.

There has been significant interest in BiFeO₃ over the past decade. This interest has focused on the magnetic and electrical properties, which in the long term may prove useful in device applications. This thesis focuses on the synthesis, electrical characterisation, and structural origin of the electrical properties of rare earth doped bismuth ferrite. Two systems have been studied: BiFeO₃ doped with lanthanum and neodymium (Bi₁₋ₓREₓFeO₃ RE= La, Nd). Specific examples have been highlighted focusing on a detailed structural analysis of a lanthanum doped bismuth ferrite, Bi₀.₅La₀.₅FeO₃, and a neodymium analogue, Bi₀.₇Nd₀.₃FeO₃. Both adopt an orthorhombic GdFeO₃-type structure (space group: Pnma) with G-type antiferromagnetism. Structural variations were investigated by Rietveld refinement of temperature dependent powder neutron diffraction using a combination of both conventional “bond angle/bond length” and symmetry-mode analysis. The latter was particularly useful as it allowed the effects of A-site displacements and octahedral tilts/distortions to be considered separately. This in-depth structural analysis was complemented with ac-immittance spectroscopy using the multi-formulism approach of combined impedance and modulus data to correlate structural changes with the bulk electrical properties. This approach was essential due to the complex nature of the electrical response with contributions from different electroactive regions. The structural variations occur due to a changing balance between magnetic properties and other bonding contributions in the respective systems. This results in changes in the magnitude of the octahedral tilts, and A-site displacements giving rise to phenomena such as negative thermal expansion and invariant lattice parameters i.e., the invar effect. More specifically, analysis of Bi₀.₅La₀.₅FeO₃ highlights a structural link between changes in the relative dielectric permittivity and changes in the FeO₆ octahedral tilt magnitudes, accompanied by a structural distortion of the octahedra with corresponding A-site displacement along the c-axis; this behaviour is unusual due to an increasing in-phase tilt mode with increasing temperature. The anomalous orthorhombic distortion is driven by magnetostriction at the onset of antiferromagnetic ordering resulting in an Invar effect along the magnetic c-axis and anisotropic displacement of the A-site Bi³⁺ and La³⁺ along the a-axis. This contrasts with the neodymium analogue Bi₀.₇Nd₀.₃FeO₃ in which a combination of increasing A-site displacements in the ac-plane and decrease in both in-phase and anti-phase tilts combine with superexchange giving rise to negative thermal expansion at low temperature. The A-site displacements correlate with the orthorhombic strain. By carefully changing the synthesis conditions, a significant change in bulk conductivity was observed for a number for Bi₁₋ₓLaₓFeO₃ compositions. A series of Bi₀.₆La0.₄FeO₃ samples are discussed, where changes in the second step of the synthesis result in significantly different bulk conductivities. This behaviour is also observed in other compositions e.g. Bi₀.₇₅La₀.₂₅FeO₃. Changes in the electrical behaviour as a function of temperature are discussed in terms of phase composition and concentration gradients of defects. Activation energies associated with the conduction process(es) in Bi₁₋ₓLaₓFeO₃ samples, regardless of composition, fall within one of two broad regimes, circa. 0.5 eV or 1.0 eV, associated with polaron hopping or migration of charge via oxygen vacancies, respectively. The use of symmetry-mode analysis, in combination with conventional crystallographic analysis and electrical analysis using multi-formulism approach, presents a new paradigm for investigation of structure-property relationships in rare earth doped BiFeO₃.

Solid Oxide Fuel Cells could play a key role in energy systems of the future because they can directly convert the chemical energy of fuels into electrical energy in a reliable and energy efficient way. The choice of materials for the components of fuel cells is crucial for the achievement of the high performance and the low price necessary to establish fuel cell technology in the energy market. Current state of the art anodes consisting of nickel and yttria stabilised zirconia (Ni/YSZ) offer good electrochemical performance but suffer from limitations like carbon deposition, redox instability and sulphur poisoning. This thesis explores the properties of composite fully ceramic anodes consisting of a skeleton of yttria stabilised zirconia (YSZ) or cerium gadolinium oxide (CGO) and a perovskite phase based on B-site doped lanthanum strontium titanate. The perovskite phase was fabricated in situ inside the pores of the skeleton material by the infiltration of an aqueous precursor and subsequent firing (impregnation method). Material characterisation of the composite anodes was carried out by X-ray diffraction and the microstructure investigated by electron microscope techniques. The electrochemical performance was tested by IV-curves and impedance spectroscopy. Particularly the investigation of the connection between the microstructure of the impregnated anodes and their electrochemical performance is a main objective of this work. The electrochemical performance of cells with a CGO skeleton and an impregnated lanthanum strontium titanate phase was found to be inferior compared to cells with a YSZ skeleton, even if the ionic conductivity of CGO is known to be higher than the ionic conductivity of YSZ. The difference was assigned to mass transport problems tightly connected to the different microstructure of the composite anodes. A significant improvement of the performance could be achieved by the utilisation of A-site deficient perovskites as impregnated phase in a YSZ skeleton. Cells with composite anodes of YSZ and La₀.₄Sr₀.₄Ti₀.₉₄Mn₀.₀₆O[sub](3-δ) show power densities of 156.2 mW/cm² at a measuring temperature of 750 °C compared to 58.5 mW/cm² measured in a similar cell with A-site stoichiometric LSTM, both cells having an electrolyte thickness of around 60 μm. The superiority of the performance of anodes with A-site deficient perovskites is mainly due to a lower ohmic resistance of only 0.5 Ω*cm², indicating better conductivity of the composite with A-site deficient perovskites. The investigation of the microstructure of composite anodes with A-site deficient perovskites showed the decoration of the surface with nanoparticles after reduction. These nanoparticles originate from exsolution of ions from the B-site of the perovskite and can't be found in A-site stoichiometric perovskites. The influence of fabrication parameters like firing temperature of the skeleton, firing temperature after impregnation or vacuum impregnation on the microstructure and electrochemical performance of the composite anodes was studied. Particularly the increase of the firing temperature of the skeleton from 1400 °C to 1500 °C resulted in an impressive improvement of total cell resistance and maximal power density.

In 2013, the worldwide production of renewable electricity accounted for 22.1% of the total energy production with 0.9% coming from solar photovoltaics (PVs). Recently, there has been a growing interest for Cu2ZnSnS4 (CZTS) quaternary semiconductor due to the abundance and low cost of its precursors. Moreover, this chalcopyrite material has an ideal direct band gap around 1.5 eV, high absorption coefficient (α >104 cm-1) and high conductivity, making it suitable for nanostructured and dye-sensitized solar cell (DSSC) applications. Here, CZTS nanoparticles have been synthesized by pulsed laser deposition (PLD) and simultaneously deposited in the interstitial space of ZnO nanowire arrays to form bulk heterojunction 3D nanostructured solar cells. Secondly, vertically oriented CZTS nanoplates have been synthesized by PLD and used as counter electrode in platinum-free dye-sensitized solar cells. These CZTS nanostructures proved to be suitable in achieving workable solar cells, which could significantly cut down the cell cost and provide environmentally friendly photovoltaic devices. Alternately, hybrid organic–inorganic perovskite solar cells have become one of the most attractive photovoltaic technologies with easy solution fabrication and high conversion efficiencies. However, the devices remain unstable under certain processing and environmental conditions. Herein, formamidinium lead tri-halide perovskite (FAPbI3) planar heterojunction solar cells have been fabricated under a controlled environment. The fabrication parameters (precursor concentration, annealing, etc) and the effect of humidity on the structural, optical, and electrical properties of FAPbI3 thin films and devices have been investigated and proved to be critical in the processing of efficient devices. Solar cells with conversion efficiency of 16.6% have been obtained. Furthermore, in-situ techniques such as in-situ (scanning) transmission electron microscopy and in-situ XRD were performed to understand the crystallization and degradation mechanisms of FAPbI3 thin films.The in-situ data were correlated with planar heterojunction FAPbI3 devices efficiency data in order to improve the device fabrication process.

Neste trabalho, foram desenvolvidos filmes finos de composição SrTi1-xFexO3 (0,00≤ x ≤0,150) nanoestruturados visando sua aplicação como sensor de gás ozônio. Os filmes finos foram depositados através da técnica de deposição por feixe de elétrons (EBD) cujo alvo utilizado foram pastilhas obtidas a partir do pó cristalino SrTi1-xFexO3 (0,00≤ x ≤0,150) sintetizadas através do método dos precursores poliméricos. Foi observado a partir das analises termogravimétrica e térmica diferencial que a incorporação de ferro no sistema diminui a temperatura de queima do pó precursor, sugerindo que o ferro atua como catalisador na cadeia polimérica. Os filmes depositados por DFE apresentam-se no estado amorfo sendo necessário um tratamento térmico ex-situ para que a fase cristalina desejada seja obtida. Todos os filmes apresentaram uma boa aderência aos diferentes tipos de substratos utilizados. Após o processo de cristalização, os filmes depositados sobre diferentes substratos foram caracterizados através das técnicas de difração de raios-X, espectroscopia UV-Vis e microscopia de força atômica (MFA). Foi observado que um aumento na temperatura de tratamento térmico dos filmes leva a um aumento no grau de cristalização e a uma diminuição no valor da energia de gap, calculada a partir dos espectros UV-VIS. A analise por MFA mostrou que a mudança do tipo de substrato utilizado não influencia as propriedades estruturais e microestruturais dos filmes. Através da realização de medidas de resistência elétrica, observou-se que os filmes cristalinos submetidos a um tratamento térmico ex-situ a 500oC por 4 horas apresentaram uma boa sensibilidade ao gás ozônio sendo possível detectar a presença de até 75 ppb de ozônio. / In this study, nanostructured thin films of SrTi1-xFexO3 (0.00 ≤ x ≤ 0.150) compositions were prepared looking their application as ozone gas sensor. The thin films were deposited using the technique of electron beam deposition (EBD) whose targets were obtained from polycrystalline SrTi1-xFexO3 (0.00 ≤ x ≤ 0.150) powders synthesized by the polymeric precursor method. It was observed from the thermogravimetric and differential thermal analysis that the incorporation of iron in the system decreases the calcination temperature of the precursor powders, suggesting that the iron acts as a catalyst in the polymer chain. The as obtained films deposited by EBD present an amorphous state being necessary a ex-situ heat treatment to obtain the desired crystalline phase. All films showed good adhesion to different substrates. After the crystallization process, the films deposited on different substrates were characterized through X-ray diffraction, UV-Vis spectroscopy and atomic force microscopy (AFM) trechniques. It was observed that an increase in the annealing temperature of the film results in an increase in the degree of crystallization and a decrease in the value of band gap energy, which was calculated from the UV-VIS spectra. The AFM analysis showed that changing the type of substrate does not influence the structural properties and microstructure of the films. By carrying out measurements of electrical resistance, it was observed that the crystalline films subjected to a ex-situ heat treatment at 500oC for 4 hours showed a good sensitivity to the ozone gas being possible to detect the presence of up to 75 ppb ozone.

Materiais dielétricos para operação em microondas constituem um ponto importante para usos em sistemas de comunicação móvel/via satélite, incluindo sistemas de monitoramento terrestres, internet/telefonia para celulares, internet das coisas, além do interesse militar para elaboração de radares. Avanços importantes nesse setor tecnológico só foram outorgados, graças ao emprego ostensivo de ressoadores dielétricos (RDs). Esses dispositivos constituem cerâmicas óxidas com baixa perda dielétrica em microondas, com demanda para sua miniaturização. O sistema deverá possuir alta constante dielétrica nesse intervalo e o dispositivo deve ser termicamente estável, ou seja, suas propriedades dielétricas não se alterarão com a temperatura. A busca por materiais de alto desempenho resultou na descoberta das perovskitas ordenadas 1:1 e 1:2, com estequiometria A2BBO6 e A3BB2O9, respectivamente. Tais sistemas ordenam o sítio B, da perovskita ABO3, gerando o empilhamento dos planos cristalinos com B e B, intercalados e na direção [1 1 1]c. Os resultados da literatura mostram que o ordenamento possui papel fundamental na obtenção de ressoadores de baixa perda dielétrica. Ademais, poucos estudos reportam as propriedades dos sistemas contendo os cátions Ca e Nb, no sítio B. Portanto, essa tese dedicou-se à investigação das propriedades dielétricas do sistema Ba3CaNb2O9 e, posteriormente, a modificação desse com a substituição dos cátions Ba2+ por Sr2+ e La3+. As amostras foram preparadas pelo método de reação do estado sólido e, posteriormente, caracterizadas pela difração de raios X, espalhamento Raman, espectroscopia de impedância e desempenho em microondas, além de técnicas complementares como análise térmica, densidade por imersão e microscopia eletrônica de varredura. Os resultados demonstraram a coexistência dos domínios 1:1 e 1:2 no sistema Ba3CaNb2O9, sendo possível manipulá-los mediante condições da sinterização. Microestruturalmente, esses domínios são regiões no cristalito com diferentes ordens catiônicas e, assim, com propriedades cristalográficas e vibracionais diferentes. Pela impedância, notou-se que o ressoador Ba3CaNb2O9 tende a conduzir mais quando possui uma tendência para o domínio 1:1. Tal resultado foi confirmado em microondas, onde a redução da perda dielétrica foi correlacionada à diminuição do domínio 1:1 na estrutura cristalina dos ressoadores. Na solução sólida com Sr2+, uma transição da fase trigonal D3d3 para monoclínica C2h3 foi detectada nos pós-calcinados, sendo oriunda das inclinações octaédricas do sistema de Glazer a0b-b-. As cerâmicas desse sistema foram sinterizadas a 1500 °C por 26 h, cujo resultado ilustrou uma tendência à ordem 1:1 para x ≥ 0,30. No sistema com La3+, observou-se, além da coexistência, os monodomínios 1:1 e 1:2. O sistema com monodomínios 1:1, BaLaCaNbO6 (y = 0,50), evidenciou uma distorção monoclínica intrínseca. Esta distorção foi associada às inclinações octaédricas do sistema de Glazer a0b-b-, reduzindo a simetria da fase cúbica Oh5 para monoclínica C2h3. Por fim, o desempenho como ressoador dielétrico dos sistemas BaLaCaNbO6 e Ba3CaNb2O9 foi avaliado. O primeiro sistema mostrou os seguintes valores: permissividade relativa εg ∼ 26, Qu × fR ∼ 10.506 GHz e coeficiente τf ∼ -55 ppm.K-1. O segundo sistema revelou os dados: permissividade εg ∼ 43, Qu × fR ∼ 15.752 GHz e o coeficiente τf ∼ 278 ppm.K-1. / Dielectric materials for microwave applications play an important role in mobile and satellite communication systems, including terrestrial monitoring, internet/mobile devices, internet of things, as well as the military uses as the radar developments. Advances in this technological field were only possible due to the ostensive use of dielectric resonators (DRs). These devices constitute oxide ceramics with a low dielectric loss in microwave frequency. The system must have high dielectric constant and such a device must be thermally stable. The search for highperformance materials granted the discovery of 1:1 and 1:2 ordered perovskites, with general formula A2BBO6 and A3BB2O9, respectively. These systems depict the B-site ordering of ABO3 perovskite, inducing the crystalline planes stacking in the [1 1 1]c direction. The literature results showed that the ordering plays an essential role in the low loss ceramics. Moreover, few studies reported the features of the systems containing the Ca and Nb cations at the B-site. Therefore, our work drives the dielectric properties of the Ba3CaNb2O9 system and, then, the modification induced by Ba2+ substitution by Sr2+ and La3+. The samples were prepared by the conventional solid-state reaction method and probed by X-ray diffraction, Raman scattering, impedance spectroscopy and microwave performance, as well as other techniques such as thermal analysis, density measurement, and electron microscopy. Our findings elucidated the coexistence of 1:1 and 1:2 domains in Ba3CaNb2O9 ceramics, being possible to manipulate them by sintering conditions. Such an ordered domain denotes regions in the crystallites with different cationic order and with different crystallographic and vibrational behavior. By the impedance spectroscopy, it was observed that Ba3CaNb2O9 ceramics tend to conduct more when they present a tendency towards the 1:1 domains. The earlier result was also confirmed in microwave frequency, in which the dielectric loss decreasing was correlated to the decrease of the 1:1 domain in the crystal structure. In the strontium solid solution, a transition from the D3d3 trigonal phase to the C2h3 monoclinic one was noted in powder samples, being derived from octahedral tilting (a0b-b- Glazer system). In the lanthanum system, besides the coexistence, the monodomains 1:1 and 1:2 were observed. Otherwise, the 1:1 monodomain system, BaLaCaNbO6 (y = 0.50), exhibited an intrinsic monoclinic distortion. This distortion was ascribed to the octahedral tilting (a0b-b- Glazer system), lowering the crystal symmetry from Oh5 cubic phase to the C2h3 monoclinic phase. The dielectric resonator performances of the BaLaCaNbO6 and Ba3CaNb2O9 systems were evaluated. The first system showed the following values: permittivity εg ∼ 26, Qu × fR ∼ 10.506 GHz and coefficient τf ∼ -55 ppm.K-1. The second system exhibited the data: permittivity εg ∼ 43, Qu × fR ∼ 15.752 GHz and coefficient τf ∼ 278 ppm.K-1.

In this study, the financial and economic viable of perovskite-SHJ tandem solar cells were determined using a detailed bottom-up cost model and energy-yield calculations. Attention to specific advancements in perovskite solar cell layer technology and large-scale deposition have been taken into account to create a realistic, viable commercial scale option for tandem production. A reference tandem technology is used to determine the overall manufacturing cost and minimum sustainable price. Models used show that the tandem technology has the potential to be cost competitive with existing silicon technology given the uncertainty and sensitivity of the values used in this study. It was examined further how non-STC energy yield and service life contributes to the overall economic viability of the tandem module within residential, commercial and utility scale of application. Given the reference tandem module, it is expected to be competitive at the residential level with existing silicon technology if perovskite layers' service life is greater than 20 years. In commercial and utility application, the tandem model is not economically viable due to the reductions seen in the area- and project-related installation costs for existing technology. This thesis concludes by presenting the current limitations in perovskite technology that would inhibit adaptation of this into commercial-scale production and presents alternative applications in which tandem modules would be more favourable.

Esta tese apresenta um estudo sistemático da síntese e das propriedades físicas de amostras policristalinas de Nd IND. 1-X R IND. X NiO IND. 3; R = Sm, Eu, 0 < OU = X < OU = 1. Estes materiais apresentam uma transição de fase metal-isolante MI em temperaturas 200 < OU = T IND. MI < OU = 400 K. Amostras foram produzidas a partir do método de precursores sol-gel, sinterizadas a 1000 GRAUSC e sob pressões de O IND. 2 de até 80 bar. O estudo da influência da substituição de R POT. 3+ na matriz de NdNiO IND. 3 foi realizado a partir das caracterizações através de medidas de difração de raios-X DRX, difração de neutrons como função da temperatura DRN, transporte elétrico ro(T), transporte térmico capa(T), coeficiente Seebeck S(T), calorimetria diferencial e susceptibilidade magnética qui(T). Os resultados de DRX revelaram que as amostras são monofásicas e cristalizam-se na estrutura perivskita distorcida ortorrombicamente, grupo espacial Pbnm. As medidas de DRN realizadas nas amostras de Nd IND. 1-XEu IND. X NiO IND. 3 mostraram a evolução dos parâmetros de rede e do volume da cela unitária V como função da temperatura. Estas caracterizações revelaram que, em T DA ORDEM DE T IND. MI, ocorre uma expansão em V, assim como um aumento do ângulo de ligação Ni-O e uma diminuição do ângulo de \"superexchange\" teta. Medidas de ro(T) revelam a ocorrência da transição MI em um amplo intervalo de temperatura 200 < OU = T IND. MI 400 K. Através destas medidas verificou-se também a presença de histerese térmica ocorre decresce continuamente com o aumento de x, até anular-se em x > 0,5 e em x > 0,35 para R=Sm e Eu, respectivamente. Este resultado foi confirmado através das medidas de capa(T) e S(T). Além disso, verificou-se a importância da contribuição da rede na capa(T). As medidas de S(T) indicam que os portadores de carga são elétrons e que a densidade de ) estados no nível de Fermi N(E IND. F) foi estimada ser da ordem de 10 POT. 23 (eVcm POT. 3) POT. -1. Os valores de T IND. MI e a presença ou não de histerese térmica foram verificados através das medidas de DSC. Um estudo foi feito para verificar qual a maneira mais precisa de subtrair a contribuição dos íons terras-raras nas medidas de susceptibilidade magnética qui(T) dos compostos Nd IND. 1-X R IND. X NiO IND. 3. Após estas correções foi possível verificar o ordenamento magnético da sub-rede do Ni POT. 3+ na região de temperatura T IND. n DA ORDEM DE 200 K para as amostras com x < 0,4 e x < 0,25 para R=Sm e Eu, respectivamente. Ajustes lineares feitos em qui(T) acima de temperaturas T > 200 K revelaram valores de momentos magnéticos efetivos müeff variando de 1,7 a 1,8 mü IND. B o que está em concordância com o valor esperado de müeff DA ORDEM DE 1,76 mü IND. B do íon livre de Ni POT. 3+. Adicionalmente, uma separação precisa do termo independente da susceptibilidade magnética foi efetuada e a susceptibilidade de Pauli dos materiais foi encontrada. Foi possível então obter uma estimativa da densidade de estados no nível de Fermi N(E IND. F), que gerou valores similares aos obtidos via medidas do coeficiente Seebeck. Entretanto, o comportamento de qui(T) corrigido abaixo de T IND. n revelou características de um antiferromagnetismo não convencional devido a um aumento monotônico de qui(T) com o decréscimo da temperatura e a presença de irreversibilidade nas curvas resfriadas a campo magnético zero ZFC e do refinamento de estrutura estimou-se que a valência no Ni nas amostras de Nd IND. 1-X R IND. X NiO IND. 3 DA ORDEM DE 3. Estimativas grosseiras da largura de bando W do O 2ro e da energia de transferência de carga delta para a série de compostos Nd IND. 1-X R IND. X NiO IND. 3 revelaram valores compatíveis com aqueles ) encontrados na literatura. De maneira geral, as caracterizações das propriedades estruturais, de transporte e magnéticas sugerem que os compostos Nd IND. 1-X R IND. X NiO IND. 3 podem ser classificados como sistemas onde correlações eletrônicas e flutuações dessas correlações ocorrem. Foram discutidas algumas limitações acerca da aplicabilidade dos modelos vigentes para a explicação da transição metal-isolante nos niquelatos aqui estudados. / This work reports a systematic study on the synthesis and general physical properties of polycrystalline samples of Nd IND. 1-X R IND. X NiO IND. 3; R = Sm, Eu, 0 < OU = X < OU = 1. These compounds exhibit a metal-insulator MI phase transition in a broad range of temperature 200 < OU = T IND. MI < OU = 400 K. The samples were prepared through sol-gel precursors and sintered at extreme conditions: high temperatures 1000 GRAUSC and under oxygen pressures up to 80 bar. These samples were characterized by several techniques including X-ray powder diffraction XRD, neutron diffraction as a function of temperature NRD, electrical resistivity ro(T), thermal conductivity capa(T), Seebeck coefficient S(T), differential scanning calorimetry DSC, and magnetic susceptibility qui(T). The results of XRD revealed that all samples are single phase and crystallize in an orthorhombic structure, space group Pbnm. The NRD data, combined with the Rietveld analysis, indicated small changes in the lattice parameters a, b, and c and in the volume V of the unit cell T DA ORDEM DE T IND. MI. Such a small change in these parameters is accompained by either a little decrease of the superexchange angle teta and a small expansion of the Ni-O bond-length. The ro(T) data exhibit interesting features such as: (1) a metallic-like behavior of ro(T) at high temperatures; (2) a huge increase of the magnitude of ro(T) at T DA ORDEM DE T IND. MI; and (3) a thermal hysteresis occurring just below T DA ORDEM DE T IND. MI in a temperature interval as large as 100K. Such a thermal hysteresis is characteristic of a first order MI transition and was found to vanish with increasing substitution of x. This strongly suggests that increasing x modify the character of this transition to second order. Thermal properties were carried out and confirmed the change of this MI transition with increasing x. In addition, an analysis of the capa(T) data indicate that phonons are the major thermal carriers in these nickelates. Also, the Seebeck coefficient S(T) data revealed features of a conventional metal at higher temperatures with electrons as carriers. An accurate analysis of the S(T) data based on simple band structure arguments indicate a density of states at the Fermi level of 10 POT. 23 (eVcm POT. 3) POT. -1 and energy gaps in the insulating regime close to 20 meV. The character of the first order transition in lightly substituted samples at T DA ORDEM DE T IND. MI was also inferred from the DSC data. The S(T) data confirmed the occurrence of the metal-insulator transition and the already observed change from first to second order character with increasing x. The magnetic susceptibility ípsilon(T) data have been precisely corrected by a systematic subtraction of the R POT.3+-ion contribution of the measured qui(T). Linear adjusts of the corrected curves above 150K where found to fit the Curie-Weiss law with effective magnetic moment of mü IND. EFF ~ 1.76 mü IND. B, which is close to the free-ion value of mü IND. EFF ~ 1.76 mü IND. B (Ni POT. 3+). These results indicate that the Ni POT. 3+ array displays an antiferromagnetic ordering below a well-defined temperature T IND. N, which is close to T IND.MI for Nd IND. 1-X R IND. X NiO IND. 3 and lightly substituted samples. However, the evolution of the susceptibility of the Ni POT. 3+ array displays features which are fingerprints of unconventional antiferromagnetic state. These features, observed mostly below T IND. N, include a field independent irreversibility of qui(T) and a systematic increase of qui(T) with decreasing temperature, resembling that of a paramagnet. An analysis of the electronic contribution to ípsilon(T) resulted in a density of states at the Fermi level close to the one estimated from the S(T) data. These results are discussed within the context of recent experimental results and theories employed to explain the origin of the metal-insulator transition in these nickelates.