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Transition metal fluorides represent an important family of complex solids displaying a variety of different properties and interesting phenomena. Despite their remarkable behaviour, these classes of materials have not received much attention and the rationalization of their behaviour is still lacking a systematic approach. This thesis aims to contribute to the field by examining previously unknown or understudied complex fluorides. The compounds were selected for their intriguing physical properties that range from superconductivity to multiferroism. The discovery of superconductivity in the iron pnictides sparked new interest in materials with layered ZrCuSiAs-type structure. Herein the properties of one of these systems, namely SrFeAsF, will be discussed. We have found that it behaves as a poor metal and undergoes a tetragonal (P4/nmm) to orthorhombic (Cmma) structural transition at T = 180 K, accompanied by a spin density wave in magnetic susceptibility and electrical resistivity. Below T < 150 K, the Fe moments order in antiferromagnetic spin-stripes. Electron doping with La3+ is a successful route to obtain superconducting phases, with maximum Tc = 27 K (x = 0.2). The isostructural AeMnPnF series (Ae = Sr, Ba; Pn = P, As, Sb) was also investigated to elucidate the influence of transition metal d-electrons and size effects of Ae and Pn on the physical properties. The isoelectronic replacement of Ae and Pn leads to a significant distortion in the tetragonal building blocks. All d5 Mn fluorides investigated here are insulating antiferromagnets with TN ~ 350 K. Due to the coexistence of electronic and magnetic ordering, the tetragonal tungsten bronze (TTB) materials KxM2+ xM3+ 1-xF3 (x = 0.4 – 0.6; M = transition metal) are potential multiferroics. The type of structural distortion adopted by these systems is strongly dependant on the M2+/M3+ ratio. For instance, our high-resolution diffraction study on K0.5Mn0.5Cr0.5F3 has revealed a small orthorhombic distortion, which indicates full chemical order of Mn2+ and Cr3+ on all crystallographic sites. K0.5Mn0.5Cr0.5F3 remains orthorhombic Ccc2 on cooling through the ferromagnetic transition at TN = 23 K. On heating, the structure is acentric up to T = 373 K, where a change to tetragonal P42/mbc symmetry marks the transition from ferroelectric (polar) to paraelectric (apolar) states. High-pressure diffraction experiments have shown that the Ccc2 structure is robust upon pressurization with anisotropic axial compressibility up to the maximum pressure applied p = 18 GPa. The crystal structure of related mixed-valence TTB fluoride K0.6Cr2+ 0.6Cr3+ 0.4F3 is influenced by the presence of Jahn-Teller active Cr2+. The structural analysis described here revealed the presence of a small polar monoclinic distortion (P112) providing a clear signature of full charge order (CO). On heating, the gradual loss of CO leads to two consecutive structural phase transitions to orthorhombic (Pba2, T = 423 K) and then tetragonal (P42/mbc, T = 823 K) lattices, the latter is the signature of the ferro- to paraelectric transition. Below T = 150 K, increased X-ray exposure time leads to CO-melting and the stabilization of a new, charge-disordered orthorhombic phase (Cmm2), with a phenomenology similar to the CO manganites. In highpressure diffraction experiments, a further transition to tetragonal P4bm symmetry is found at p = 6 GPa. The magnetic susceptibility points towards a complex spin arrangement, with two transitions at TN = 33 K and 6 K. The results presented herein show the richness of the structural, electronic and magnetic phase diagrams of transition metal fluorides and clearly demonstrate that systematic studies on these systems will greatly enhance our current understanding of the underlying mechanisms of important phenomena such as superconductivity and ferroelectricity.

Zirconia is a metal oxide with high band gap. It is commonly used as catalysts in many industrial practices. In recent years, its high-energy-gap value and redox properties also render it as an excellent photocatalyst, which can eliminate or reduce a variety of pollutants. The purpose of this work is to prepare and characterize the chromium-doped ordered porous zirconia. The main purpose of doping chromium into the zirconia is to avoid the Martensitic transformation of zirconia under high temperatures by volume change and pore structure change, thus reducing the cracking and inferior mechanical properties. With emulsion-free polymerization for the synthesis of polystyrene (PS) particles, controlling the particle diameter less than 200 nm is possible. A polystyrene template is thus produced by gravity sedimentation of these PS particles. Final Cr-doped zirconia is obtained by infiltration of a precursor solution, a mixture consisting of zirconium n-propoxide, n-propanol, acetylacetone, and chromium (III) nitrate nonahydrate, into the PS template, followed by drying and calcination at elevated temperatures. A systematic study on the pore structure and physical properties by XRD and Raman is conducted by varying the precursor concentration, the calcination temperature, and the dopant concentration. The results show that, unlike the pure zirconia, the pore structure of Cr-doped zirconia remains stable under higher calcination temperatures. Without any phase transformation, the doped Cr, evidenced from the EDS mapping, tends to help stabilize the zirconia at tetragonal phase. The average surface area and pore diameter of Cr-doped zirconia from BET measurement are 19 ~ 21 m2/g and 25 -45 nm, far better than the bulk zirconia. The improved surface properties are also confirmed by SEM observations.

Made available in DSpace on 2014-10-09T12:37:08Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:40Z (GMT). No. of bitstreams: 1 01908.pdf: 6409813 bytes, checksum: a4da653568b2a1fde0228c02cc3838b9 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:37:08Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:40Z (GMT). No. of bitstreams: 1 01908.pdf: 6409813 bytes, checksum: a4da653568b2a1fde0228c02cc3838b9 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The present work was produced as part of the MUZIC consortium, a collaboration between a multi-university team from the UK and industrial partners working on the field of nuclear energy, fabrication of alloys and nuclear research. The aim of the project is to establish a multidiscipline mechanistic understanding of the corrosion and breakaway processes of zirconium alloys used as fuel cladding materials in the nuclear industry. A better understanding of the corrosion mechanism of zirconium alloys will not only aid the development of better performing alloys, but will also allow more accurate models to be developed to reliably predict the service life of existing alloys. This could lead to higher burn-up, increase of energy production and reduction of nuclear waste produced.This work seeks to provide a better understanding of the role of residual stresses in the oxide, which are produced during oxidation due to high Pilling-Bedworth ratio and their impact on oxide phase transformation and oxidation kinetics by employing high energy synchrotron X-ray diffraction techniques. This is achieved by observing how stresses change as oxide growth approaches and passes through transition of the corrosion kinetics, their evolution across the oxide thickness, in situ characterising stresses and phase growth early in oxidation process and how stress changes can affect corrosion properties.It was found that relatively high compressive stresses in the two oxide crystal structures are present. The stresses relax with time up to moments before transition where a possible threshold stress magnitude is reached to aid an extensive tetragonal to monoclinic phase transformation. This generalised tetragonal to monoclinic transformation is believed to produce highly stressed monoclinic crystal structure grains and cause defects in the oxide. The above observation is further supported by a decrease of the tetragonal zirconia content. This is the moment that the oxide looses its protective character and a transition of the corrosion kinetics occurs. By comparing different materials it was observed that the minimum magnitude of the tetragonal phase is lower in better performing alloys while the tetragonal content is some cases was relatively low. It is suggested that the amount of the tetragonal phase, in the oxide layer, is not as important as the rate of it transforming into monoclinic. The extent of tetragonal to monoclinic transformation, that introduces defects in the oxide, defines how protective an oxide layer is. The present work provides a contribution to the available knowledge of the importance of residual stresses in the oxide layer and metal substrate of zirconium alloys and how they can affect corrosion rates or act as a precursor to the corrosion transition.

Made available in DSpace on 2015-05-14T12:56:04Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1306209 bytes, checksum: 7375d4165c06e1945051f54d5a0010de (MD5) Previous issue date: 2014-12-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Purpose: This study evaluated the influence of air-particle-abrasion and different solutions application on the shear bond strength of resin cement to zirconia ceramic (Y-TZP). Materials and method: Sintered zirconia blocks (N=180) (Lava, 3M ESPE), with final dimensions of 5.25 x 3.74 x 4.5 mm, were embedded in acrylic resin, polished and randomly distributed among 18 groups (n=10), according to the factors: "solution (8 levels) and air-particle-abrasion" (2 levels): Ctr (control without treatment), AP- Alloy Primer/Kuraray, MP- Monobond Plus/Ivoclar, MZP- Metal Zircônia Primer/Ivoclar, MZ- MZ Primer/Angelus, ReX- Relyx Ceramic Primer/3M ESPE, Sg- Signum Zirconia Bond/Kulzer, SbU- Scotchbond Universal/3M ESPE and ZP- Z Prime Plus/Bisco. The same solutions were also used after zirconia sandblasting: Ctr.S, AP.S, MP.S, MZ.S, ReX.S, Sg.S, SbU.S and ZP.S (*.S = sandblasting). Prior sandblasting, the zirconia/acrylic resin assemblents were ultrasonic cleaned for 5min (Vitasonic, Germany). The .S groups were air abraised with Al2O3 particles (110μm, 2.5 bar, 20s at 10mm), with an assistance of a chairside air-abrasion device (Bioart, Brazil) and another ultrasonic cleaned was performed. After dry the solutions were applied according to the manufactors´ recommendations. The resin cement (Rely X ARC, 3M ESPE) cylinders were bonded and polymerized to zirconia surface, with the aid of a silicone mold (Ø = 3.5, height = 3 mm). All samples were stored in distilled water (60 days at 370 C), and after were subjected to shear test (1 mm/min). Data were analyzed by ANOVA (e-way) and Tukey test (α=5%). Results: Air-particle abrasion (p=0.0001) and solution (p=0.0001) factors significantly affected the bond strength (ANOVA) All samples of the groups Ctr, Ctr.S, ReX, MZ.S and MZP, MZP.S showed premature failure (debonding). Thus, they were not included in the statistical analysis. In addition, air-abrasion increased the bond strength (With: 110.78A MPa; Without: 70.92B MPa) and the solution SbU (142.91a MPa) promoted higher adhesion between ceramic/resin cement than MP (100.15bc MPa), AP (90.03c MPa), ReX (34.03d MPa) and MZ (23.66d MPa), and was similar to Sg (131.78ab MPa) and ZP (113.37bc MPa) (Tukey). Conclusion: Air-abrasion with 110 μm Al2O3 followed by solutions application increased the bond strength to zirconia, except for SbU, that presented the highest value of bond strength. / Objetivo: Este estudo avaliou a influência do jateamento com partículas de O2Al3 e de diferentes soluções na resistência ao cisalhamento entre um cimento resinoso e à cerâmica de zircônia (Y-TZP). Materiais e método: Blocos de zircônia sinterizados (N = 180) (Lava, 3M ESPE), com dimensões finais de 5,25 x 3,74 x 4,5 mm foram incluídos em resina acrílica, polidos e aleatoriamente distribuídos em 18 grupos (n = 10), de acordo com os fatores: "solução" (8 níveis) e "jateamento" (2 níveis): Ctr (controle sem tratamento), AP- Alloy Primer/Kuraray, MP- Monobond Plus/Ivoclar, MZP- Metal zircônia Primer/Ivoclar, MZ- MZ Primer/Angelus, Rex- Relyx Primer para Cerâmica/3M ESPE, Sg- Signum Zircônia Bond/Kulzer, SbU- Scotchbond Adesivo Universal/3M ESPE e ZP- Z Prime Plus/Bisco. As mesmas soluções também foram utilizadas após o jateamento da zircônia: Ctr.S, AP.S, MP.S, MZ.S, ReX.S, Sg.S, SbU.S e ZP.S(* S = jateamento). Anteriormente ao Jateamento os bloco de zircônia foram submetidos à limpeza em ultrassom por 5min (Vitasonic, Alemanha). Os grupos ".S" foram jateados com Al2O3 (110μm, 2,5 bar, 20s à 10 mm), com o auxílio de um microjateador (Bioarte, Brasil) e outra limpeza ultrassônica foi realizada. Depois de secos, as soluções foram aplicadas de acordo com as recomendações dos fabricantes. Cilindros do cimento resinoso (Rely X ARC, 3M ESPE) foram colados e polimerizados na superfície da zircônia com auxílio de um molde de silicone (Ø = 3,5, altura= 3 mm). Todas as amostras foram armazenadas em água destilada (60 dias a 370 C), e depois submetidas ao teste de cisalhamento (1mm/min). Os dados foram analisados pela análise de variância (dois- fatores) e teste de Tukey (α=5%). Resultados: "Os fatores jateamento com O2Al3" (p = 0,0001) e "solução" (p=0,0001) afetou significativamente a resistência de união (ANOVA). Todas as amostras dos grupos Ctr, Ctr.S, Rex, MZ.S e MZP, MZP.S mostraram uma falha prematura (descolamento). Assim, não foram incluídos na análise estatística. Além disso, o jateamento aumentou a resistência de união (com: 110.78A MPa; sem: 70.92B MPa) e a solução SbU (142.91a MPa) promoveu maior adesão entre cimento resinoso/cerâmica. O MP (100.15bc MPa), AP (90.03c MPa), ReX (34.03d MPa) e MZ (23.66d MPa), e foi semelhante ao Sg (131.78ab MPa) e ZP (113.37bc MPa) (Tukey). Conclusão: Jateamento com O2Al3 seguido pela aplicação de soluções aumentou a resistência de união à zircônia, com exceção do SbU, que apresentou o maior valor de resistência de união

Made available in DSpace on 2015-05-14T13:21:52Z (GMT). No. of bitstreams: 1 parte1.pdf: 2740601 bytes, checksum: 60bd87566aa111195ece86e01435aaf6 (MD5) Previous issue date: 2010-12-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / SrTiO3 is a compound with perovskite structure usually found with cubic phase. This works reports the synthesis of powders and thin films of the undoped and Nd3+ doped SrTiO3, replacing Ti4+ or Sr2+ with the stoichiometries SrTi1-xNdxO3 (x = 0.00; 0.01; 0.02; 0.04) and Sr0.99Nd0.01TiO3. The powders were synthesized by the polymeric precursor method. The thin films were prepared by chemical solution deposition (CSD) using the spin coating technique and by pulsed laser deposition (PLD), being deposited on LaAlO3 (100), MgO (100), SrTiO3 (100), Al2O3-R, and SiO2. The structural and optical properties of these materials were evaluated by infrared spectroscopy, UV-vis spectroscopy, photoluminescent emission, micro Raman spectroscopy and X-ray diffraction (XRD) Rietveld refinement of the XRD patterns was realized for powder samples. Moreover the photocatalytic property was evaluated in the degradation of textile dyes. The coexistence of the cubic and tetragonal phases for SrTiO3 powders was confirmed after calcinations at 550 oC. For doped samples calcined at 700 oC, it was observed that the sites occupied by Nd3+ influenced in the amount of these phases, leading to a direct influence in the photoluminescent emission. Emission in the yellow region was observed, while temperature increase lead to a shift to the green region, with higher energy indicating that short range ordering occurred. Thin films deposited on LaAlO3 substrate showed high quality epitaxial growth by CSD and a very high quality by PLD. On MgO doping changed the film orientation. For deposition on Al2O3-R and SiO2, polycrystalline films were obtained. Photocatalytic degradation efficiency was similar in powders and undoped films, increasing for films doped with 4 % of Nd3+ when synthesis was done by PLD. Key words: / SrTiO3 é um composto de estrutura perovskita comumente encontrado na fase cúbica. Este trabalho reporta a síntese de pós e filmes finos deste composto na sua forma pura e dopada com Nd3+ em substituição a Ti4+ ou Sr2+ nas estequiometrias SrTi1-xNdxO3 (x = 0,00; 0,01; 0,02; 0,04) e Sr0,99Nd0,01TiO3. Os pós foram sintetizados pelo método dos precursores poliméricos. Os filmes finos foram preparados pelo método de deposição de solução química (CSD) utilizando a técnica spin coating e pelo método de deposição por laser pulsado (PLD), sendo depositados em substratos de LaAlO3 (100), MgO (100), SrTiO3 (100), Al2O3-R, e SiO2. As propriedades estruturais e óticas desses materiais foram avaliadas por espectroscopia de infravermelho, espectroscopia UV-Vis, espectroscopia de emissão fotoluminescente, espectroscopia micro Raman e difração de raios-X (DRX). Refinamento Rietveld dos dados de DRX foi realizado para algumas amostras em pó. Além disso, a propriedade fotocatalítica foi estudada frente à degradação de corantes têxteis. A coexistência das fases cúbica e tetragonal para os pós de SrTiO3 foi confirmada, já na temperatura de 550 ºC e foi verificado para as amostras dopadas (700 ºC) que o sítio de ocupação do Nd3+ influenciou na quantidade dessas fases. Esse resultado teve influência direta na propriedade fotoluminescente observada. Os materiais emitiram principalmente na região do amarelo, mas com o aumento da temperatura essa região se deslocou para o verde (maior energia) indicando a organização do sistema. Os filmes finos depositados sobre o substrato de LaAlO3 mostraram crescimento epitaxial de alta qualidade por CSD e de qualidade muita alta por PLD. Sobre MgO a dopagem influenciou na orientação dos filmes. Os filmes depositados em Al2O3-R, e SiO2 foram policristalinos. A eficiência de degradação fotocatalítica foi similar entre pós e filmes puros, sendo aumentada com 4 % de Nd3+ nos filmes depositados por PLD.

X-ray diffraction from protein crystals remains the most reliable way to determine the molecular structure of proteins, and how this structure relates to biological function. However, we still lack the ability to predict solution conditions that support the nucleation and growth of high-quality protein crystals for X-ray diffraction studies. The overall goal of this thesis is two-fold: (a) determine the nucleation behavior and solubilities for lysozyme crystals with two distinct crystal structures (orthorhombic vs. tetragonal) and (b) investigate whether these changes in crystal habit and crystal solubility correlate with any discontinuities in the liquid-liquid phase boundary of lysozyme that occurs under the same solution conditions. We measured lysozyme crystal solubility by nucleating and subsequently dissolving very small lysozyme crystals in highly supersaturated solutions. The presence of crystals in our samples is detected and monitored by measuring the light scattered off the micron-sized crystals. These "turbidity measurements" are repeated across a range of protein concentrations, for pH 4.6 and 5.6, thereby yielding the crystal solubility boundary. Changes in crystal structure are assessed at the end of the experiments by microscopic inspection of the distinct crystal habits. Attractive protein interactions in solution also induce liquid-liquid phase separation. Similar to the crystal solubility measurement, we use the turbidity increase associated with liquid-liquid phase separation to map out this phase boundary. Since both crystal formation and liquid-liquid phase separation are driven by attractive protein interactions, we investigated whether the dramatic changes in crystal solubility associated with different protein crystal structures lead to any discernable “discontinuities” in the liquid-liquid phase boundaries.

<p> The magnetic susceptibility of samarium orthophosphate (SmPO4) has been measured over the temperature range from 0.4 to 270°K. A theoretical expression for the susceptibility has been developed assuming a crystal field of cubic symmetry and fitted to the experimental data. </p> / Thesis / Master of Science (MSc)