Este trabalho descreve a construção e operação de dois fornos especiais para crescimento de monocristais pelas técnicas de Bridgmann e Czochralski. Vários cristais de LiF puros e dopados foram crescidos nesses fornos e suas propriedades testadas. O forno para crescimento pela técnica de Bridgmann pode operar até 1800&#176C em atmosferas agressivas não oxidantes (por exemplo HF seco). Com esses fornos podem ser crescidos monocristais de MnF2 e PbF2. O forno para crescimento pela técnica de Czochralski permite a preparação de monocristais de Nitreto de Litio (Li3N) partindo do Lítio metálico e de Nitrogênio gasoso sob pressão. Os fornos e sua operação são descritos em detalhes permitindo sua reprodução. / This work describes the construction and operation of two special furnaces for crystal growth using Bridgmann and Czochralski techniques. Several LiF single crystals, pure and doped, were grown in these furnaces and their properties tested. The Bridgmann furnace allows operation at temperatures as high as 1800&#176C and no-oxidational agressive growing conditions (dry HF gas for example). In this furnace it is possible to grow MnF2 and PbF2 single crystals. The Czochralski furnace allows the growth of Li3N starting from Li metal and gaseons N2 under pressure. The furnaces and their operation are described in details allowing their reproduction.

Este trabalho descreve a construção e operação de dois fornos especiais para crescimento de monocristais pelas técnicas de Bridgmann e Czochralski. Vários cristais de LiF puros e dopados foram crescidos nesses fornos e suas propriedades testadas. O forno para crescimento pela técnica de Bridgmann pode operar até 1800&#176C em atmosferas agressivas não oxidantes (por exemplo HF seco). Com esses fornos podem ser crescidos monocristais de MnF2 e PbF2. O forno para crescimento pela técnica de Czochralski permite a preparação de monocristais de Nitreto de Litio (Li3N) partindo do Lítio metálico e de Nitrogênio gasoso sob pressão. Os fornos e sua operação são descritos em detalhes permitindo sua reprodução. / This work describes the construction and operation of two special furnaces for crystal growth using Bridgmann and Czochralski techniques. Several LiF single crystals, pure and doped, were grown in these furnaces and their properties tested. The Bridgmann furnace allows operation at temperatures as high as 1800&#176C and no-oxidational agressive growing conditions (dry HF gas for example). In this furnace it is possible to grow MnF2 and PbF2 single crystals. The Czochralski furnace allows the growth of Li3N starting from Li metal and gaseons N2 under pressure. The furnaces and their operation are described in details allowing their reproduction.

Lead halide perovskite solar cells (PSCs) are considered the next generation of photovoltaic technology, reaching an outstanding certified power conversion efficiency of 25.7% in just 20 years. The best-performing PSCs are based on polycrystalline films, where the presence of grain boundaries and a tremendous number of defects limit stability and efficiency and thus further industrial development. Compared to their polycrystalline counterparts, single crystals of lead halide perovskites have been shown to possess much lower trap-state densities, long diffusion lengths, high stability, and near-IR absorption. This thesis describes the use of a confined space and inverse temperature method to grow perovskite single crystals of MAPbI3 directly on PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) films. This method allowed the fabrication of p-i-n inverted solar cells with the structure ITO/PTAA/perovskite single-crystal thin film/C60 (fullerene)/BCP (bathocuproine)/Cu (copper). A key requirement in achieving high photoconversion efficiency (PCE) is avoiding iodine oxidation, which forms triiodide impurities that function as defects in perovskites and that can seriously hinder the performance of perovskites. By suppressing the formation of triiodide, high-quality perovskite photodetectors and solar cells can be realized. For single crystals, orientation has a strong effect on device performance. Here, (100)- and (001)-facet single-crystal thin films were fabricated into solar cells. Unlike traditional (100)-facet films, which exhibit high PCE in a glovebox environment, (001)-facet single-crystal thin films show high stability under ambient conditions.

In this thesis, work hardening and latent hardening behaviours of pure Mg single crystals were mainly studied under uniaxial deformation tests at room temperature, 298K. By uniaxial tensile/compression tests, work hardening behaviours of Mg single crystals with different orientations favoured for single and double basal <a> slip, {10-12}<10-11> twin, 2nd order pyramidal <c+a> slip and basal <a> slip + {10-12}<10-11> twin were studied. In order to investigate latent hardening behaviours among slip and twin systems, the Jackson-Basinski type latent hardening experiments in Mg single crystals at room temperature have been carried out under different types of dislocation interactions, which included: (i) the self-interactions, (ii) the co-planar interactions on the basal plane, (iii) basal <a> slip / {10-12}<10-11> twin dislocation interactions, (iv) {10-12}<10-11> twin / basal <a> slip dislocation interactions and (v) basal <a> slip / 2nd order pyramidal <c+a> slip dislocation interactions. The microstructure and micro-texture of the deformed single crystals was observed by optical microscopy (OM), scanning electron microscopy (SEM), and SEM/EBSD methods. In addition, micro- and nano-indentation measurements were performed on adjacent matrix and {10-12}<10-11> twin regions of deformed Mg single crystals and the hardness values were analyzed by the Oliver-Pharr method. The results from the Ph.D. work provided framework for the discussion of the plastic flow in Mg single crystals and quantitative values for hardening parameters used in the crystal plasticity modelling. / Thesis / Doctor of Science (PhD)

<p> Single crystals of sodalite have been studied by means of electron paramagnetic resonance (E. P.R.) both at 0.8 cm. and 3 cm. wavelength. The existence of at least four different E. P. R. spectra was established of which one was attributed to the manganese impurity and a possible model for two other spectra is proposed. It was found that two of the observed spectra disappear upon heat treatment although the bleaching of the characteristic blue colour of sodalite crystals does not appear to be related to any of the spectra studied. </P> / Thesis / Master of Science (MSc)

<p> The theoretical formulation of the electronic transport properties (in the absence of a magnetic field) of pure single crystals of simple metals is extended to incorporate the effect of a non~spherical Fermi surface, using a multiple orthogonalized plane wave description of the conduction electrons. Two approaches are considered, one using a variational principle, and the other employing a scattering time approximation. </p> <p> Formal results for the electrical resistivity and the electronic contribution to the thermal resistivity are expressed in terms of effective phonon frequency distributions. These distributions are particularly convenient for numerical computations and are generalization: of those previously used for the case of a spherical Fermi surface. </p> <p> The generalization of the scattering time method to dilute nonmagnetic substitutional alloys is applied to hexagonal close~packed metalsc It is shown that the addition of small amounts of impurities to pure Zn leads to measurable changes in the temperature dependence of the electrical resistivity ratio (see text for ratio with symbols). The corresponding deviations front Matthiessen's rule for polycrystalline samples are also calculated. </p> / Thesis / Master of Science (MSc)

In order to understand and predict the fracture behaviour of polycrystalline materials from a fundamental perspective, it is important to first investigate plastic deformation at a crack tip in a ductile single crystal. In this context, it may be noted that when the crack opening displacement is much less than the grain size, the crack tip fields are entirely contained in a single grain. Further, some key structural components are being fabricated in single crystal form. For example, blades in high pressure turbines of jet engines are made of single crystals of Nickel-based superalloys. In view of the above considerations, a combined experimental and computational study of the crack tip stress and strain fields in FCC single crystal is carried out in the present work. The effect of constraint level, which is characterized by the T-stress under mode I, plane strain small scale yielding conditions, on the near-tip response is first analyzed for a crystal orientation in which the crack plane coincides with (010) and ¯the crack front lies along[101]direction. A family of finite element solutions are generated by employing a boundary layer approach within continuum crystal plasticity framework. The results show that the near-tip deformation field, especially the development of kink and slip shear bands, is sensitive to the constraint level. On imposition of negative T-stress, a significant drop in the hydrostatic stress level is noticed in the region ahead of the tip. This suggests loss of crack tip constraint with negative T-stress, which is akin to isotropic plastic solids. The reason for the loss of crack tip constraint is traced to the occurrence of an elastic sector near the notch tip. The results also show that a two-parameter (such as K-T or J-Q) characterization of near-tip fields is necessary to accommodate different constraint levels in FCC single crystals. The results of the boundary layer formulation are used to guide the construction of asymptotic solutions near the crack tip corresponding to various constraint levels in elastic-perfectly plastic FCC single crystal. Two families of alternate asymptotic solutions are constructed by introducing an elastic near-tip sector. These families of stress fields are parameterized by the normalized opening stress ahead of the tip, τA22/τo, where τo is the critical resolved shear stress, and a quantity (p) which characterizes the coordinates of the point where elastic unloading commences in stress plane. The results show that the stress distribution corresponding to each member of these families, as well as the trajectories in stress plane as the crack tip is traversed, agree well with finite element results for a certain value of T-stress. In order to validate the above numerical and analytical solutions, the nature of crack tip deformation in aluminium single crystals is examined experimentally in a high constraint three point bend (TPB) specimen and in a low constraint single edge notch tensile (SENT) geometry. These experiments provide evidence, based on in-situ Electron Back Scattered Diffraction (EBSD) of the existence of kink shear bands (involving lattice rotation) exactly as predicted by Rice [J.R. Rice, Mech. Mater. 6 (1987) 317] and the present finite element analysis. The experimental investigation of a low constraint SENT geometry is also supplemented by 3D finite element computations based on continuum crystal plasticity. These computational results enable assessment of 3D effects near the tip. Finally, the effects of different lattice orientations (especially ones for which the slip systems are not symmetric with respect to the notch line) on the near-tip fields are studied pertaining to various constraint levels. The results obtained for different orientations show that the near-tip deformation field is sensitive to the constraint level. The stress distribution and the size and shape of plastic zone near the notch tip are also strongly influenced by the level of T-stress. It is clearly established that ductile single crystal fracture geometries, would progressively lose stress triaxiality with increase in negative T-stress irrespective of lattice orientation. Also, the near-tip field is shown to be part of a family which can be characterized by two parameters (such as K – T or J - Q).

An understanding of crack tip fields and fracture mechanisms in single crystals can help in developing better polycrystalline alloys and manufacturing processes. To this end, the effects of loading rate, material inertia and strain rate sensitivity on crack tip fields and their influence on fracture mechanisms in FCC single crystals are examined in this work by performing finite element analysis. It is shown that, in the absence of inertial effects, high loading rates elevate the stresses ahead of a crack tip and decrease the plastic strains in rate dependent single crystals. Also, it is found that the quasi-static near-tip stress field can be adequately characterized by the energy release rate J and a constraint parameter Q. Similar two-parameter characterization is possible even under dynamic loading. It is observed that if a suitable reference solution is used, the role of inertia manifests as a loss of constraint with increasing loading rate irrespective of strain rate sensitivity and lattice orientation. Thus, at very high loading rates, inertial effects oppose the role of rate sensitivity and cause a decrease in stresses near the tip. The relative influence of these two factors depends on rate sensitivity index. For a mildly rate dependent single crystal, the predicted cleavage fracture toughness remains constant up to a certain loading rate and thereafter increases sharply. On the other hand, for a strongly rate dependent single crystal, fracture toughness drops initially up to a certain loading rate beyond which it increases marginally. The loss of crack tip constraint is found to retard the ductile fracture mechanisms of void growth and coalescence. However, this is dependent on lattice orientation. In-situ experimental observation of void growth near a notch tip also shows strong orientation dependence. In addition, 3D finite element results indicate though-thickness dependence of equivalent plastic slip and hydrostatic stress leading to variations in void growth along the thickness direction of the specimens. The predicted load-displacement curves, lattice rotation, slip traces and void growth using finite element analysis are found to be in good agreement with the experimental observations. Thus, the present study has provided an understanding of the role of several factors such as constraint level, rate sensitivity, material inertia, lattice orientation and 3D effects on the mechanics of fracture of ductile single crystals.

There is a critical need for inspection and condition monitoring of high temperature critical components such as pipelines and welds in electrical power generation and other plants operating at temperatures as high as 580°C. The high temperatures and pressures experienced in these pipelines, particularly for ageing plants lead to creep, fatigue and corrosion type defects. Safety of these plants is of paramount importance, and regular maintenance is carried out during planned outages at ambient temperatures. Ultrasonic non-destructive testing can be used to detect defects in the weld at ambient temperatures. However, at high operational temperatures, this technique cannot be applied due to the lack of high temperature transducers. This research has achieved significant advances towards enabling ultrasonic inspection and condition monitoring of high temperature critical points, by developing an ultrasonic transducer around an advanced piezoelectric single crystal material, called Gallium Orthophosphate (GaPO4), which can operate at the required temperature of 580°C. Based on its reported piezoelectric and other properties, and its commercial availability, GaPO4 was chosen as a candidate active material for application in a prototype high temperature transducer. In a series of confidence building tests with the selected piezoelectric material (electrical characterisation via the impedance method), it has been demonstrated that the GaPO4 piezoelectric elements are stable when subjected to 580°C for more than 600 hours. Ultrasonic thickness gauging has shown that GaPO4 works as a functional transducer generating and receiving ultrasound waves at 580°C for at least 360 hours. Furthermore, the sensitivity of the GaPO4 transducer to detect defects with simple geometry was successfully tested through measurements on steel blocks containing artificial defects (side-drilled holes) up to the same high temperatures. Based on the characterisation results from the impedance and ultrasonic measurements, a prototype ultrasonic transducer for operation at high temperatures has been designed and manufactured. The new ultrasonic transducer was tested in a laboratory environment using a steel calibration block, high temperature couplant, SONO 1100, and an electric furnace. In the range from ambient temperatures up to the target of 580°C, the ultrasonic transducer kept a signal-to-noise (SNR) level sufficiently high, above the threshold of 6 dB, which is high enough for practical non-destructive testing and condition monitoring.

O titanato de estrôncio é um dielétrico com elevada energia de gap entre a banda de va-lência e a banda de condução, porém quando alguns íons de oxigênio são removidos de sua estrutura cristalina, o composto se torna um semicondutor dopado do tipo n com um regime de ionização de impurezas diferente dos outros semicondutores convencionais. Além disto, o composto exibe uma supercondutividade anômala que diverge da teoria BCS no que diz respeito às interações elétron-fônon. Na medida em que o oxigênio é removido do cristal, a resistividade elétrica diminui no composto, sendo assim, este trabalho tem o objetivo de estudar a evolução do tratamento térmico que transforma o estado isolante em um semicondutor através de medidas de resistividade elétrica in situ durante o tratamento de desoxigenação de monocristais de titanatos de estrôncio crescidos pelo método Floating zone. Com o interesse de estudar as propriedades físicas do sistema Sr1-xCaxTiO3, amostras com diferentes teores de cálcio na faixa entre x = 0 e x = 0,05 foram preparadas e caracteriza-das por difratometria de raios X e medidas de calor específico. A cinética de desoxigena-ção é descrita por modelos matemáticos ajustados sobre pontos experimentais adquiridos nas medidas de resistividade elétrica in situ durante o tratamento térmico. Foi observado que a cinética de desoxigenação é de primeira ordem com energia de ativação de 1,4±0,1 eV, que concorda com os dados previamente reportados na literatura. / Strontium titanate is a dielectric material with large energy gap between valence and con-duction bands. However, when some oxygen ions are removed from the crystal structure it becomes n-type semiconductor with an impurity ionization regime which differs from conventional semiconductors. Furthermore, this compound exhibits non-conventional su-perconductivity which can not be described by electron-phonon interaction predicted by BCS theory. When oxygen gets out from the sample electrical resistivity decreases. The goal of this work is study the deoxygenation kinetics during annealing which turns an insulator into a semiconductor using in situ electrical resistivity measurements during the thermal an-nealing of titanate single crystals grown by Floating zone Method. In order to study physical properties of Sr1-xCaxTiO3 system, samples with different cal-cium contents between x = 0 and 0.05 were prepared and characterized by X-ray difratom-etry and heat capacity. Deoxygenation kinetics were analyzed by models with fits the experimental data acquired at in situ electrical resistivity measurements. It was observed that deoxygenation kinetics is of first order with energy activation of 1,4±0,1 eV The estimated value for activation energy agrees with previously reported data.