Recent advances in third generation photovoltaics, particularly the rapid increase in perovskite power conversion efficiencies, may provide a cheap alternative to silicon solar cells in the near future. A key component to these devices is the transparent front electrode, and in the case of Dye Sensitized Solar Cells, it is the most expensive part. A lightweight, cost-effective, robust, and easy-to-fabricate new generation TCE is required to enable competition with silicon. Indium Tin Oxide, commonly used in touchscreen devices, Organic Light Emitting Diodes (OLEDs), and thin film photovoltaics, is widely used and commonly referred to as the industry standard. As the global supply of indium decreases and the demand for this TCE increases, a similar alternative TCE is required to accompany the next generation solar cells that promise energy with lighter and significantly cheaper modules. This alternative TCE needs to provide similar sheet resistance and optical transmittance to ITO, while also being mechanically and chemically robust. The work in this thesis begins with an exploration of several synthesized ITO replacement materials, such as copper nanowires, conductive polymer PEDOT:PSS, zinc oxide thin films, reduced graphene oxide and combinations of the above. A guiding philosophy to this work was prioritizing cheap, easy deposition methods and overall scalability. Shortcomings of these TCEs were investigated and different materials were hybridized to take advantage of each layers strengths for development of an ideal ITO replacement. For CuNW-based composite electrodes, ~85% optical transmittance and ~25 Ω/sq were observed and characterized to understand the underlying mechanisms for optimization. The second half of this work is an examination of many different perovskite synthesis methods first to achieve highest performance, and then to integrate compatible methods with our CuNW TCEs. Several literature methods investigated were irreproducible, and those that were successful posed difficulties integrating with CuNW-based TCEs. Those shortcomings are discussed, and how future work might skirt the issues revealed here to produce a very low cost, high performance perovskite solar cell.

A series of oxide materials were modified with different nanoparticles (NPs). Novel cobalt@H4Nb6O17 nanopeapod structures were fabricated and magnetic NPs modified oxide nanosheets and nanoscrolls were prepared. Both aqueous method and two-phase method were applied to prepare gold NPs onto oxide nanosheets, nanoscrolls and other nanocrystals. The combination of H4Nb6O17 nanoscrolls and cobalt NPs generate a novel method to fabricate nanopeapod structures. Cobalt NPs were synthesized in the presence of exfoliated H4Nb6O17 nanosheets and the resulting magnetic chain structures, formed due to the dipole-dipole interaction, were captured within scrolled lamella. The yield of peapod structures can be improved by using proper reagents and reaction temperatures. As similar method with iron oxide NPs also produced peapod-like structures in a low yield. Exfoliated Dion-Jacobson phase layered perovskite HLaNb2O7 (HLN), its organic derivate propoxyl-HLaNb2O7 (pHLN), Ruddlesden-Popper phase perovskite H2SrTa2O7 (HSTO) and Aurivillius phase perovskite H2W2O7 (HWO) were synthesized and functionalized with gold NPs by in-situ methods. Gold NPs were prepared by both an aqueous method and two-phase method. The size of NPs can be adjusted by different reaction times. Overall, the latter method shows a narrower size distribution and better dispersion. In addition, most gold NPs prepared by the two-phase method were attached on the surface of nanosheets and almost no free gold NPs were observed in solution. This approach should be applicable to most layered perovskites. The aqueous and two-phase methods were also applied on the preparation of gold NPs onto H4Nb6O17 nanosheets and nanoscrolls. H4Nb6O17 nanosheets were prepared by two approaches and showed similar gold NPs attachment. LiNbO3 nanocrystals can be also modified with gold NPs by the two-phase method though free gold NPs were observed. Further studies involved the functionalization of layered perovskites and related compounds with magnetic NPs. Iron oxide and cobalt NPs were synthesized in the presence of layered perovskite and modified perovskite nanosheets were obtained.

Orientador: Alexandre Mesquita / Resumo: O titanato de cálcio CaTiO3 é um material com estrutura de tipo perovskita que tem sido aplicado como luminóforo. É bem estabelecido que a inserção de íons de terra rara no sítio ocupado pelo Ca2+ provoca mudanças significativas nas suas propriedades estruturais e produz efeitos luminescentes na faixa do visível. Entretanto não existem trabalhos reportando a inserção do La3+ no sítio do Ca2+ no que se refere às características estruturais e luminescentes desses materiais. Portanto, o presente trabalho estuda as propriedades fotoluminescentes apresentadas pela matriz à base de titanato de cálcio dopada com praseodímio, lantânio e alumínio. O material foi sintetizado a partir do método Pechini, que se mostrou um método eficaz na preparação de acordo com a caracterização estrutural realizada. A técnica de difração de raio X permitiu identificar que todas as amostras de CaTiO3 apresentam-se na fase cristalina com simetria ortorrômbica. Através da espectroscopia de absorção de raio X na borda K do Ti4+ constatamos a ocorrência de maior simetria do Ti4+ em relação aos átomos ao seu redor quando aumentamos a temperatura de calcinação e que a substituição de íons no sítio do Ca2+ não altera essa simetria. Em razão do aumento da concentração dos dopantes, tanto no sítio do Ca2+ quanto no sitio do Ti4+, foram observados alterações nos modos de vibração dos espectros Raman. Constatou-se o aumento da torção entre os octaedros de TiO6 em relação ao aumento da concentração dos dopantes. No... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The calcium titanate CaTiO3 is a perovskite structure material which has been used as phosphor. It is well established that the incorporation of rare earth ions in the place occupied by Ca2+ cause significant changes in their structural properties and produce luminescent effects in the visible range. However, there are no studies reporting the insertion of La3+ on the Ca2+ site with respect to structural and luminescent characteristics of these materials. So, this work studies the photoluminescent properties presented by the matrix based on calcium titanate doped with praseodymium, lanthanum and aluminum. The material was synthesized by the Pechini method, which proved an effective method of preparation according to the structural characterization performed. The technique of X-ray diffraction showed that all samples are organized and exhibit orthorhombic symmetry. Using X-ray absorption spectroscopy at the K edge of Ti4+, we found that the occurrence of major symmetry of Ti4+ with respect to the neighbor atoms when the calcination temperature was increased and that the substitution of ions Ca2+ by Pr3+ does not change this symmetry. With the concentration of dopants increasing at the Ca2+ and Ti4+ sites, changes of the vibration modes in the Raman spectra were observed. It was found an increased torque between the TiO6 octahedra as a function of the increase in concentration of dopants. In the luminescence spectra, increasing the structural defect density enhanced the light e... (Complete abstract click electronic access below) / Mestre

Cette thèse est entièrement consacrée à l'étude par la théorie de la fonctionnelle de la densité des composés pérovskites halogénés, matériaux prometteurs pour de nombreux domaines applicatifs. Le caractère « hybride » de ce type de matériau est illustré par différentes études de leurs propriétés structurales et électroniques. Le composé tridimensionnel MAPbBr₃ est tout d'abord présenté. Les propriétés électroniques fondamentales telles que les structures de bandes, les états de densité projetée ou les fonctions d'ondes sont discutées. De plus, l'importance du couplage spin-orbite est mise en évidence. L'analyse des symétries est appliquée pour comprendre la symétrie des états électroniques et pour interpréter les propriétés optiques des différents matériaux. Les reconstructions structurales à la surface des cristaux entraînent l'apparition d'effets Rashba-Dresselhaus. Par ailleurs les défauts de surface et leurs passivations sont également étudiés. Des travaux sur les matériaux sans plomb potentiellement moins toxiques sont proposés dans un second temps. Ces études ont pour but d'analyser leurs potentiels pour le photovoltaïque du point de vue des structures électroniques. Différentes stratégies de substitution sont envisagées allant du simple remplacement du plomb à d'autres alternatives plus élaborées comme les pérovskites doubles ou les pérovskites de basse dimensionnalité. / This actual work is entirely devoted to the study of halide perovskite materials, promising materials in many fields of application, by means of the Density Functional Theory. The "hybrid" feature of this type of material is illustrated through various studies of their structural and electronic properties. The three-dimensional compound CH₃NH₃PbBr₃ is firstly presented. Basic electronic properties such as band structures, projected density of states or wave functions are discussed. In addition, the importance of spin-orbit coupling is highlighted. Symmetry analysis is applied to understand and interpret the optical properties of different materials. Structural reconstructions on the surface of the crystals lead the Rashba-Dresselhaus effects. In addition, surface defects and their passivations are also studied. Studies on lead-free materials that are potentially less toxic are proposed in a second step. These studies aim to analyze their potentials for photovoltaic devices from the point of view of electronic structures. Different substitution strategies, ranging from the simple replacement of lead to other more elaborate alternatives such as double perovskites or low-dimensional perovskites are investigated as well.

O mundo moderno é extremamente dependente de combustíveis fósseis como fonte de energia primária e essa forte dependência leva a problemas políticos, econômicos e ambientais. Como possível solução a esses problemas tem-se as células combustíveis, pois são dispositivos que geram energia elétrica limpa diretamente de reações eletroquímicas produzindo, além da energia elétrica, apenas calor e água. Logo, percebe-se que essas células são fontes de energia confiáveis, renováveis e não poluentes, que contribuem para o desenvolvimento sustentável. Devido a isso, este trabalho teve como objetivo principal a síntese (por um método inédito) e a caracterização de materiais porosos a base de cromita de lantânio, LaxSr1-xCryFe1-y(Mn1-y)O3-?, para possível implementação como material de anodo e catodo de célula a combustível de óxido sólido (SOFC). Particularmente, estudos com anodos nos quais o transporte eletrônico é feito por materiais cerâmicos ao invés de metais são a área mais promissora na pesquisa recente. Além disso, materiais a base de manganita de lantânio dopadas com estrôncio são na atualidade os materiais mais usados na construção do catodo da SOFC. Nesta tese os materiais foram sintetizados pelo método sol-gel com agentes direcionador e dilatador de estrutura, resultando em materiais porosos em forma de esponja e com a estrutura perovskita, porém com fases espúrias. Foi estudada a influência do processamento de calcinação e de dopagem sobre as estruturas cristalográficas e porosas dos materiais. A maior temperatura de calcinação favoreceu a formação da estrutura perovskita com a retenção da fase romboédrica e reduziu a presença das fases espúrias, porém reduziu a porosidade, principalmente dos menores mesoporos, e a área superficial dos materiais. Por outro lado, ao dopar o sítio B os materiais com 75 %mol de La e calcinação a 1000 °C, observou-se a formação de um maior volume de mesoporos, ao mesmo tempo, que produziu uma maior quantidade de mesoporos menores e favoreceu a retenção da fase romboédrica da estrutura perovskita. Quanto ao comportamento eletrocatalítico, as células com eletrodos confeccionados a partir de La0,33Sr0,66Cr0,33Mn0,33O3-? apresentaram os melhores resultados tanto para anodo como para catodo entre as amostras avaliadas na tese. Além do mais, foram obtidos dois materiais, um cerâmico (La0,33Sr0,66Cr0,33Mn0,33O3-?) e um compósito cerâmico (La0,33Sr0,66Cr0,33Mn0,33O3-? + ZrO2 8%mol Y2O3) bons candidatos a catodo da SOFC. Esses materiais possuem uma composição química não encontrada na literatura para tal finalidade, ou seja, são inéditos. / The modern world is extremely dependent on fossil combustibles as primary source of energy and, this dependence brings political, economic and ambient problems. As a possible solution to these problems are the fuel cells, because they are devices that generate clean electric energy directly from electrochemical reactions, producing besides electric energy, heat and water. Therefore, these cells are reliable, renewable and non-pollutant sources, that contribute to the sustainable development. Related to it, this work had the main goal the synthesis (by a new method) and characterization of porous materials based on lanthanum chromite, LaxSr1-xCryFe1-y(Mn1-y)O3-?, for possible use as anode and cathode material of Solid Oxide Fuel Cell (SOFC). In particular, studies of anodes in which the electronic transport is performed by ceramic materials instead of metals are the most promising recent research area. Moreover, materials based on lanthanum manganite doped with strontium are now a days the more used materials for SOFC cathodes. In this thesis, the materials were synthesized by the sol-gel method with directing and swelling structure agents, resulting in porous sponge materials with perovskite structure, but having spurious phases. The influence of the calcination and doping of the materials upon the crystallographic and porous structures were studied. Higher calcination temperature favored the formation of the perovskite structure and reduced the presence of spurious phases, but reduced the porosity, mainly of smaller mesopores and the surface area. On the other hand, doping the B site in materials with 75 %mol of La and the calcination at 1000 oC produced a higher mesopore volume, a higher amount of small mesopores and favored the retention of the rhombohedral perovskite structure. Regarding the catalytic behavior, the cells with electrodes of La0,33Sr0,66Cr0,33Mn0,33O3-? presented the best results as anode and cathode among the evaluate samples. Moreover, two materials were obtained, a ceramic one, (La0,33Sr0,66Cr0,33Mn0,33O3-?) and a ceramic composite, (La0,33Sr0,66Cr0,33Mn0,33O3-? + ZrO2 8%mol Y2O3), good candidates as SOFC cathodes. These materials have a chemical composition, which were not reported in the literature for this application, being unique.

This thesis focuses on the phase transitions, including ferro-magnetic, anti-ferromagnetic, metal to "Mott" insulator and structural transitions in perovskite and Ruddlesden-Popper ruthenates. The thesis is mainly composed of two parts. The first half presents Density Functional Theory (DFT)+Dynamical Mean Field Theory (DMFT) studies of the electronically driven phase transitions in various ruthenate materials. We study cubic perovskite BaRuO$_3$ via DFT add DMFT method using interaction parameters which were found in previous studies to be appropriate for the related materials, CaRuO$_3$ and SrRuO$_3$. The calculated variation in transition temperature between the Ba and Sr compounds is consistent with experiment, confirming the assignment of the compounds to the Hund's metal family of materials, the appropriateness of the single-site dynamical mean field approximation for these materials as well as confirming the appropriateness of the values for the interaction parameters. The results provide insights into the origin of magnetism and the role of the van Hove singularity in the physics of Hund's metals. We also study the metal-insulator transition (MIT) and magnetic transitions in Ca$_2$RuO$_4$. The Ru-O bonds lengths are found to be the most important control parameters for the metal-insulator transitions and rotations are found to be less important. The calculation successfully captures the important features of the para-magnetic (PM) "Mott" insulating state, including the orbital occupancy disproportionation and the orbitally resolved electron spectral function. It shows the advantage of single set DFT+DMFT in dealing with strongly correlated multi-orbital systems without the assumption of spin symmetry breaking. In the second half, we present a Landau free energy model that incorporates the electronic energetics, the coupling of the electronic state to local distortions and the coupling of local distortions to long-wavelength strains. The model is used to elucidate important experimental features in thermal and current-induced MIT in Ca$_2$RuO$_4$ and Ca$_3$Ru$_{2-x}$Ti$_x$O$_7$ materials. The investigation of lattice and electronic energetics and determination of parameters using DFT+DMFT methods is explained. The change in lattice energy across the metal-insulator transition is shown to be comparable to the change in electronic energy. Important consequences are a strongly first order transition, a sensitive dependence of the phase boundary on pressure and that the geometrical constraints on in-plane lattice parameter associated with epitaxial growth on a substrate typically change the lattice energetics enough to eliminate the metal-insulator transition entirely. The change in elasto-resistance across the MIT is determined. The DFT+U relaxation study shows the octahedron relaxation with respect to uniaxial strain on a and b axes are very different. This sensitive a and b axes dependence is observed in calculations on both Ca$_2$RuO$_4$ and Ca$_3$Ru$_2$O$_7$. The theory model is also generalized to investigate spatially non-homogeneous solutions. Important features of the stripe patterns at the domain boundaries of metallic and insulating phases are discussed and compared with experiments.

Highly efficient LEDs and photovoltaic cells based on spin coated films of layered Ruddlesden-Popper hybrid perovskites (RPP) have been recently reported. The electronic structure and phase composition of these films remains an open question, with diverse explanations offered accounting for the excellent device performance. Here we report x-ray and optical characterization of hot cast RPP thin films, emphasizing the distribution of structural and electronic properties through the film depth. Our results indicate an at least 70% phase pure n=3 film results from casting a stoichiometric solution of precursors, with minor contributions from n=2 and n=4 phases. We observe a strong correspondence between the predicted single-crystal RPP reciprocal lattice and measured RPP film wide angle scattering pattern, indicating a highly ordered [101] oriented film. This correspondence is broken at the air-film interface where new scattering peaks indicate the existence of a long wavelength structural distortion localized near the films surface. Using transient absorption spectroscopy, we show that the previously detected luminescent mid-gap states are localized on the films surface. Investigating films of varying thickness, we determine the photo-excited carrier dynamics are dominated by diffusion to this interface state, and extract an excitonic diffusivity of 0.18cm2s-1. We suggest that the observed surface distortion is responsible for the creation of luminescent mid-gap states.

Historically, the interfaces and charge transportation layers dictate the performance in heterojunction solar cells. This thesis addresses the interface behaviours and the interfacial layers within perovskite solar cells (PSCs), and provides insights and practicable solutions to facilitate the realisation of efficient PSCs. To achieve efficient charge collection with interlayer fabricated with low-temperature processes, a graphene-TiO₂ nanocomposite is demonstrated; By investigating the carrier transport, we found the insertion of graphene improved the electron collection efficiency with its high surface area and ballistic carrier conduction properties, and in conjunction with pre-synthesised TiO₂, we have successfully circumvented the need for high-temperature annealing, enabling the whole device to be fabricated at under 150 °C. While the anomalous hysteresis behaviour which is widely observed in regular PSCs structure is a significant problem, the quest of stable PSCs seems to be answered by the use of inverted PSCs structures. We show a detailed development of inverted PSCs which are deconstructed layer by layer. Numerous approaches have been tailored to improve interfaces, and energy levels between layers, leading to an efficient and hysteresis-free perovskite solar cells. Lastly, an in-depth study of impurity doping is investigated using Al³⁺. The doping with small metal ions in the perovskite precursor has been found to influenced the crystallisation and optoelectronic properties of the perovskite crystals. Here, for the first time, the correlation between reduced structural crystal defects is clearly linked to enhanced photovoltaic properties, with the best performance for the lowest electronic disorder in the CH₃NH₃PbI₃ crystal.

The work presented involved simulation and experimental studies aimed at improving the methodology of positron annihilation lifetime spectroscopy (PALS), and applied PALS to gain a better understanding of doping mechanisms in ABO3 perovskite oxide materials. Reliable decomposition of PALS spectra requires an accurate description of the instrument resolution function (IRF) and the extrinsic, source component, annihilation events. The source terms include annihilations with the crystallites of the radionuclide and in the thin foil normally used to support the source. In principle both the IRF and the source correction terms can accurately be determined if samples exhibiting a true single lifetime component are measured. A series of annealing studies was performed on commercially available high purity polycrystalline metal samples to reduce the defect concentration below the approximate 0.1 ppm detection limit of PALS. The study showed that despite the numerous reports in literature it was not possible to reproduce the results with similar annealing conditions or sample purity. The possibility of utilising two-lifetime materials to enable the extraction of source correction terms is analysed using simulations, and by experiments on commercially available pure polycrystalline metals. The positron source is commonly deposited on, and supported by, a thin Kapton foil. As part of this work variable energy PALS (VE-PALS) performed at the Munich Research Reactor FRMII on Kapton foils were analysed. This enabled one of the source correction terms to be unambiguously determined. In consequence, the source correction terms for a Kapton supported positron source were extracted from measurements using annealed nickel exhibiting two positron lifetime components. PALS was applied to a study on donor doping of PbTiO3 ceramics using a series of lanthanide-ions. It has been proposed that the smaller Ln-ions may act as amphoteric dopants substituting either on the A-site as a donor, or on the Bsite as an acceptor. In this study Ln-ions in size from La down to Er were studied. A systematic variation in the average positron lifetime was observed where the value was constant from La to Gd and then reduced for the smaller ions. The decrease in average lifetime provides evidence for a reduction in the fraction of trapping to A-site related vacancy defects. The onset of a reduction in the average lifetime between Gd and Dy provides evidence for a change in the doping mechanism resulting in a relative reduction in the fraction of A-site vacancy positron trapping. In contrast to PbTiO3, donor doping of SrTiO3 normally results in electron charge compensation. Recently this has been very clearly demonstrated for La3+ doped SrTiO3 thin films grown by molecular beam epitaxy (MBE) which exhibit exceptional electron mobilities. A series of MBE films grown at University of California Santa Barbara were measured by VE-PALS at FRMII and have been analysed here. Strontium vacancies were identified, and a reduced bulk lifetime component was also observed. This enabled bulk lifetime values to be obtained from two of the films which were in good agreement with the previously obtained values from single crystal samples. A PALS study was also performed on a series of B-site donor, Nb, doped SrTiO3 crystals. High intensity reduced bulk components were observed and enabled measurements of the bulk lifetime. The highest Nb doping level samples showed the most intense reduced bulk lifetime but also clearly demonstrated the presence of Sr vacancies. The observation of A-site vacancy defects for both Nb-doped and La-doped SrTiO3 suggest that formation of these defects is preferred and are independent of the site of incorporation of the donor ion. Studies were also performed on acceptor doped SrTiO3. PALS measurements were made on a series of Fe-doped SrTiO3 ceramic samples, and VE-PALS measurements on pulsed laser deposition of Fe-doped SrTiO3 thin film samples were analysed. The positron lifetime measurements on the ceramic samples showed a dominant 166(3) ps component, a value less than the Ti-vacancy lifetime. It is proposed that the component contains a contribution from positrons trapping at oxygen vacancy substitutional Fe impurity complexes with a local charge that is neutral or negative. The measurements on the series of Fe-doped PLD SrTiO3 films suggest a complex relation between the vacancy defect content of a film and both the Fe-doping and PLD growth conditions. Films grown with higher laser fluence values contained Sr vacancy defects, in contrast to previous studies of acceptor doped perovskites. Films grown with low laser fluence or with high Fe-content showed dominant trapping to Ti-vacancy related defects.

Wai, Kwai Fong = 錳氧化物 - 鈮摻雜之鈦酸鍶異構結的電流電壓關係測量 / 韋桂芳. / "Sept 2007." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Wai, Kwai Fong = Meng yang hua wu - ni shan za zhi tai suan si yi gou jie de dian liu dian ya guan xi ce liang / Wei Guifang. / Acknowledgement / Abstract / 論文摘要 / Table of content / List of Figures / List of Tables / Appendix A / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Structure and properties of perovskite manganites / Chapter 1.2 --- Magnetoresistance (MR) / Chapter 1.3 --- Giant Magnetoresistance (GMR) / Chapter 1.4 --- Colossal Magnetoresistance (CMR) / Chapter 1.4.1 --- Exchange interaction and CMR / Chapter 1.5 --- p-n junction / Chapter 1.5.1 --- Fundamentals of a p-n homojunction / Chapter 1.5.2 --- Deviations from the Ideal Diode / Chapter 1.5.2.1 --- Zener breakdown / Chapter 1.5.2.2 --- Avalanche / Chapter 1.5.3 --- Heterojunction / Chapter 1.6 --- Research motivation / Chapter 1.7 --- Scope of the thesis / References / Chapter Chapter 2 --- Experimental details / Chapter 2.1 --- Thin film deposition / Chapter 2.1.1 --- Facing target sputtering / Chapter 2.1.2 --- Vacuum system / Chapter 2.1.3 --- Deposition procedure / Chapter 2.2 --- Oxygen annealing system / Chapter 2.3 --- Silver electrode coating apparatus / Chapter 2.4 --- Characterization / Chapter 2.4.1 --- Alpha-step profilometer / Chapter 2.4.2 --- X-ray diffractometer / Chapter 2.4.3 --- Electrical transport property measurement / Chapter 2.4.3.1 --- Measurement of resistance as a function of temperature (RT) / Chapter 2.4.3.2 --- Measurement of I-V characteristics of a junction / References / Chapter Chapter 3 --- Epitaxial LSMO/STON heterojunction / Chapter 3.1 --- Sample preparation / Chapter 3.2 --- Results and Analysis / Chapter 3.2.1 --- Structural analysis / Chapter 3.2.2 --- R-T measurement / Chapter 3.2.3 --- I-V measurement / Chapter 3.2.3.1 --- Analysis of diffusion voltage and breakdown voltage / Chapter 3.2.3.2 --- Construction of energy band diagram of LSMO/STON at room temperature / Chapter 3.2.3.3 --- Investigating how the energy band structure varies with the temperature / Chapter 3.2.3.4 --- Further development of the energy band analyzing method to wide-p/narrow-n heteroj unction / Chapter 3.2.3.5 --- Forward-biased deviations from ideal / Chapter 3.2.3.6 --- Discussion on the reasons for deviations from ideal / Chapter 3.2.4 --- MR determination / References / Chapter Chapter 4 --- Epitaxial [LSMO/PCMO] multilayers and p-n junction / Chapter 4.1 --- [LSMO/PCMO]/NGO multi-layered thin films / Chapter 4.1.1 --- Sample preparation / Chapter 4.1.2 --- Results and analysis / Chapter 4.1.2.1 --- Structural analysis / Chapter 4.1.2.2 --- R-T measurement / Chapter 4.2 --- [LSMO/PCMO]/STON multi-layered junction / Chapter 4.2.1 --- Sample preparation / Chapter 4.2.2 --- Results and analysis / Chapter 4.2.2.1 --- Structural analysis / Chapter 4.2.2.2 --- R-T measurement / Chapter 4.2.2.3 --- I-V measurement / Chapter 4.2.2.3.1 --- Analysis of diffusion voltage and breakdown voltage / Chapter 4.2.2.3.2 --- Investigating the energy band structure as a function of temperature / Chapter 4.2.2.3.3 --- Forward-biased deviations from an ideal junction diode / Chapter 4.2.2.3.4 --- Review on MR calculation / Chapter 4.2.2.3.5 --- Analysis of MR of [LSMO(8 A ) /PCMO(8 A)]/STON and LSMO/STON / References / Chapter Chapter 5 --- [La0 4Ca0.6MnO3/La0.8Ca0.2MnO3］p-n junction / Chapter 5.1 --- Sample preparation / Chapter 5.2 --- Result and analysis / Chapter 5.2.1 --- Structural analysis / Chapter 5.2.2 --- R-T measurement / Chapter 5.2.3 --- I-V measurement / Chapter 5.2.3.1 --- Analysis of diffusion voltage and breakdown voltage / Chapter 5.2.3.2 --- Investigating the energy band structure as a function of temperature / Chapter 5.2.3.3 --- Forward-biased deviations from ideal / Chapter 5.2.3.4 --- MR analysis / Chapter Chapter 6 --- Conclusion / Chapter 6.1 --- Conclusion / Chapter 6.2 --- Future outlook