Dissertations / Theses on the topic 'Bismuth Based Materials'

La tesi està basada en la fabricació de nous sensors i biosensors per a la detecció de contaminants. Els micro i nanomateials basats en bismut semblen ser materials molt apropiats per aconseguir aquest objectiu, tanmateix també s’han proposat altres plataformes sensores. En el primer capítol es descriuen detalladament els principals objectius d’aquesta tesi. La introducció d’aquesta tesi descriu les aplicacions més recents i rellevants basades en la utilització de nanomaterials de bismut, com ara en els camps de la medicina, la fotodegradació de contaminants orgànics, la cosmètica, els pigments o els aliatges. Aquesta part precedeix la descripció dels mètodes de síntesi més innovadors, dels sensors més eficients, bàsicament de metalls pesants, i de les aplicacions en el camp dels biosensors. Aquest recull es pot trobar al capítol 2. Les nanopartícules de bismut són una bona plataforma per a sensors i biosensors. En aquest sentit s’ha estudiat la modificació d’elèctrodes serigrafiats amb nanopartícules de bismut. En el capítol 3, s’avaluen diferents mètodes de síntesi de nanopartícules de bismut amb l’objectiu d’obtenir les nanopartícules més eficients en la detecció de metalls pesants; en aquest cas centrat en la detecció de cadmi i plom. Al capítol 4 es presenta una nova estratègia de modificació d’elèctrodes. Aquesta estratègia es basa en la utilització de nanopartícules core-shell. Tenint en compte l’avantatge que dóna el recobriment de bismut, aquestes nanopartícules s’han utilitzat en la detecció de metalls pesants en diferents plataformes sensores. La bona modificació d’aquests elèctrodes es demostra clarament fent cicles de modificat i neteja; el comportament d’aquests elèctrodes modificat es podria considerar com a una resposta digital. L’última plataforma sensora per a metalls pesants proposada es basa en xips de paper. El capítol 5 descriu la fabricació i optimització d’aquests dispositius. Aprofitant la capacitat de filtrar del substrat de paper de filtre, aquestes simples plataformes són capaces de detectar plom i cadmi en diferents matrius, com ara solució tampó, aigua de mar o fangs. En aquest últim capítol es mostra la integració de les nanopartícules de bismut en un biosensor de fenol, basat en l’activitat enzimàtica de la tirosinasa. El capítol 6 inclou la caracterització morfològica i electroquímica del sensor. Aquests elèctrodes modificats amb nanopartícules de bismut i tirosinasa tenen una molt bona resposta en la detecció de fenol i catecol i un baix efecte de les interferències. Finalment al capítol 7 hi ha les conclusions generals i les futures perspectives que obre aquest treball. En els annexos s’hi pot trobar una descripció dels mètodes de fabricació de les diferents plataformes sensores, les abreviatures utilitzades i la producció científica derivada d’aquest treball.
The thesis is focused on the fabrication of new sensing and biosensing platforms for pollutants detection. Although bismuth-based micro and nanomaterials seem to be the appropriated materials to achieve this objective nevertheless new platforms including for example those based on paper are also proposed. In the first chapter the main objectives of this thesis are described in detail. The introduction part (chapter 2) of this thesis is dedicated to the revision of the recent reports / achievements on bismuth-based nanomaterials in different application fields that include medicine, photodegradation of organic pollutants, cosmetics, pigments and alloys. An important section of this part is focused on the description of the effect of bismuth-based materials in heavy metals and biosensing applications. Bismuth nanoparticles are found as an innovative material in heavy metals sensing and biosensing applications. A study on the effect of the modification of screen-printed electrodes with bismuth nanoparticles and its use for the heavy metal detection is shown (chapter 3). Different modifications of polyol based bismuth nanoparticles synthesis have been evaluated in aim to obtain the more efficient nanoparticles with interest in heavy metal sensing. In addition the results obtained for the detection of lead and cadmium is also shown in the same chapter. In the chapter 4 a new electrode modification strategy is presented. This new strategy is based on the use of magnetic core/shell bismuth nanoparticles. Taking advantages of the bismuth oxide presence onto the shell of these nanoparticles, heavy metal detection in different On-Off sensing platforms is shown. The modification of electrodes is clearly demonstrated by doing cycles with both modification and cleaning of the electrodes obtaining a kind of digital (On-Off) response of heavy metals. To solve sampling and sample pretreatment issues a heavy metal sensing platform that uses a paper-based lateral flow chip is also developed and described at chapter 5. Fabrication and the optimization of this new heavy metal sensor are shown; it takes advantage of the use of a filter paper substrate. This new platform is capable to detect lead and cadmium in different matrixes including mud. In the last chapter (chapter 6), the integration of bismuth nanoparticles into a phenol biosensing system is shown. It takes advantages of the use of tyrosinase enzyme which brings certain selectivity in phenolic compounds detection. Morphological and electrochemical characterizations of the developed biosensor also are shown in this chapter. The developed biosensor shows good performance in catechol detection. Finally in the chapter 7 the general conclusions and some future perspectives are given.

L’attività di ricerca oggetto della tesi è focalizzata sullo studio di materiali nanostrutturati e non a base di bismuto e relativi composti aventi proprietà ottiche avanzate. Nello specifico, data la peculiare attività di luminescenza, per i materiali investigati si prevedono interessanti potenzialità per applicazioni come (nano)fosfori per la fotonica, nel bioimaging, come sensori termici, nell’anticontraffazione. La parte preponderante della ricerca ha quindi riguardato la caratterizzazione ottica dei sistemi oggetto di studio e, in particolare, la definizione e la modellizzazione dei meccanismi di luminescenza. Inoltre, al fine di incrementare l’efficienza e di aumentare il controllo della risposta in emissione, è stata sviluppata anche un’approfondita attività in relazione allo studio dell’evoluzione strutturale del materiale e all’ottimizzazione dei processi di sintesi. Nell’ambito della macrotematica relativa ai (nano)materiali a base di bismuto, di seguito vengono specificati i sistemi oggetto della ricerca: a) controllo della struttura in nanoparticelle di bismuta drogata con ioni lantanidi e studio dei processi di upconversion (UC) per l’attivazione delle emissioni di fluorescenza nel visibile tramite pompaggio ottico nell’IR; b) studio del meccanismo di formazione di sistemi core-shell in nanoparticelle di silicato di bismuto drogate con ioni lantanidi; c) studio delle fluorescenze dello ione Cr3+ in Bi2Ga4O9 e definizione delle potenzialità per l’utilizzo come sensore termico luminescente; d) stabilizzazione dei polimorfi della bismuta tramite confinamento quantico in strutture a dimensionalità ridotta e studio delle proprietà ottiche; e) studio della luminescenza “persistente” nel sistema Bi2+/3+ in CaSnO3; f) sintesi di nanoparticelle di Y2O3 drogate con ioni Bi3+ e Er3+ e studio dei processi di energy transfer.

The thermoelectric properties of bismuth telluride based thermoelectric (TE) materials are well-characterized, but comparatively little has been published on the thermomechanical properties. In this paper, dynamic mechanical analysis (DMA) and differential scanning calorimetry data for bismuth telluride based TE materials is presented. The TE materials' tan delta values, indicative of viscoelastic energy dissipation modes, approached that of glassy or crystalline polymers, were greater than ten times the tan delta of structural metals, and reflected the anisotropic nature of TE materials. DMA thermal scans showed changes in mechanical properties versus temperature with clear hysteresis effects. These results showed that the application of DMA techniques are useful for evaluation of thermophysical and thermomechanical properties of these TE materials.

The project is focus on the synthesis and characterization of lanthanide bismuth oxyfluoride particles. The samples are synthesized through homogeneous precipitation using a microwave reactor to heat. Furthermore, by doping with different lanthanides (Tb, Eu, Tb-Eu; Pr; Nd; Yb-Ln, Ln=Er,Yb,Tm) it is tested how the optical response of the systems can be in terms of luminescence spectroscopy. The synthesized Ln3+ NPs are tested for the biological applications as nanothermometer. In recent times Luminescent nanothermometers have been widely investigated because they relate the local temperature of a biological system with their emission, as a result of an external radiation. Through these systems there is the possibility of excitation and / or emission in the so-called first and second biological window. The studies of these project are focused on NPs doped Ln3+ as thermal and emitting probes.

The main goal for this project was to design, manufacture and evaluate a thermoelectric cooler, TEC, prototype. One of the biggest challenges with TECs is that they need to be very reliable and have a long lifetime. The two biggest contributing factors to degradation and breakdown stem from thermal expansion mismatch, resulting in cracks, and from material diffusion between the thermoelectric material and connecting materials. The thermoelectric material in this case is Bismuth telluride, Bi2Te3, obtained from two suppliers. The thermoelectric cooler prototype was successfully manufactured. The prototype, which consisted of 38 thermoelectric elements, showed a maximum temperature difference of 65.1 degrees Celsius. A commercial TEC of the same size had a maximum temperature difference of 68 degrees Celsius. The figure of merit and grain size of p- and n-doped Bismuth Telluride from two different suppliers have been measured as means of testing the thermoelectric material prior to manufacturing, and to compare the suppliers. In this report, the figure of merit is a measure of how well a material converts electrical current to a heat gradient. The figure of merit for bismuth telluride, Bi2Te3, from both suppliers was found to be between 0.4 and 0.8 through the Harman method. Since studies show that smaller grains for Bi2Te3 result in a more durable material, the morphology was investigated. However, no grains could be observed with light optical microscopy with an applied etchant, or scanning electron microscopy. A cohesion tape test showed that Bismuth telluride from one of the suppliers is more fragile than the other.

La recherche de nouveaux matériaux en tant que photocatalyseurs en lumière visible pour la dépollution de l’environnement (eaux, atmosphères) est un domaine de recherche très actif et suscite l’intérêt d’une large communauté scientifique en Physique, Chimie et Sciences des matériaux. Des recherches exhaustives sont actuellement menées pour améliorer l’efficacité photocatalytique de certaines classes de matériaux photoactifs connus, et pour développer la synthèse de nouveaux matériaux fonctionnels. Dans ce contexte, les semiconducteurs oxydes photoactifs à base de vanadates de bismuth (BiVO4) possédant une bande électronique au milieu du spectre visible, offrent une sérieuse alternative aux photocatalyseurs classiques efficaces (TiO2, ZnO) dont la photo-excitation requiert uniquement la fraction UV du spectre solaire. Le travail effectué dans le cadre de cette thèse est donc dédié aux matériaux à base BiVO4 sous forme d’architectures mésoporeuses ou d’assemblages hybrides associant des groupes organiques à transfert de charges.Deux contributions majeures ont été développées dont la première portant sur la réalisation expérimentale d’architectures mésoporeuses inédites, fonctionnalisées par des groupes organiques sensibilisateurs et l’étude de leurs propriétés électroniques et optiques en vue d’optimiser leurs efficacités photocatalytiques. La deuxième partie porte sur des simulations numériques de nanostructures hybrides par des approches exploitant la méthode DFT, ab-initio ou des modèles de chimie quantique. Des systèmes modèles ont été construits associant des nanoclusters (NC) et des groupes organiques (GO). Les propriétés électroniques et optiques ainsi que les caractéristiques structurelles et vibrationnelles des systèmes (NC-GO) ont été déterminées et confrontées aux données expérimentales. Les phénomènes de transfert de charges impliqués entre les groupes organiques et la structure inorganique ont été caractérisés ainsi que leur rôle dans l’efficacité des réponses photo-catalytiques des systèmes hybrides
The search for new materials as photocatalysts invisible light for the depollution of the environment (waters, atmospheres) is a very active field of research and attracts the interest of a large scientific community in Physics, Chemistry and Materials Science. Recent research developpements are conducted to improve the photocatalytic efficiency of certain classes of known photoactive materials, and to develop the synthesis of new functional materials. In this context, photoactive oxide semiconductors based on bismuth vanadate (BiVO4) having an electronic band in the middle of the visible spectrum, offer a serious alternative to efficient conventional photocatalysts (TiO2, ZnO) whose photo-excitation requires only the UV fraction of the solar spectrum.The work done in this thesis is therefore dedicated toBiVO4-based materials in the form of mesoporous architectures or hybrid assemblies associating organic groups with charge transfer processes. Two major contributions have been developed, one of which is the experimental realization of novel mesoporous architectures, functionalized by sensitizing organic groups and the study of their electronic and optical properties in order to optimize their photocatalytic efficiencies. The second part deals with numerical simulations of hybrid nanostructures using approaches as the DFT method, ab-initio or quantum chemistry codes. Model systems have been constructed associating BiVO4nanoclusters (NC) and organic groups (GO). The electronic and optical properties as well as the structural and vibrational characteristics of the systems (NC-GO) were determined and compared with the experimental data. The charge transfer phenomena involved between the organic groups and the inorganic structure were characterized as well as their role in the efficiency of photo-catalytic responses of hybrid systems

This doctoral studies focused on the development of new materials for efficient use of solar energy for environmental applications. The research investigated the engineering of the band gap of semiconductor materials to design and optimise visible-light-sensitive photocatalysts. Experimental studies have been combined with computational simulation in order to develop predictive tools for a systematic understanding and design on the crystal and energy band structures of multi-component metal oxides.

The basis of prosperity of 20th centrury is oil. As oil is going to be used up, people need to find alternatives to meet the earth’s energy demand in 21st centrury. For each second, there are about 1.2×1017 J energy hitting the earth. The energy in 1 hour of sunlight is about 4.32×1020 J, which almost meets the energy consumed on earth in 2016. It determines solar energy may be a potential candidate to solve the energy crisis. As for techniques to utilize solar energy, the most popular one is using photovoltaic (PV) cells. PV cell is a device to convert solar energy into electricity. There are also some other techniques trying to utilize solar energy. Photocatalysis is one of them, which is to convert solar energy into chemical energy. Applications of photocatalysis have extended from hydrogen evolution via water splitting to environemtnal remediation, CO2/ N2 reduction and so on. Photocatalysis, as an advanced oxidation process, has been extensively studied and applied to the purification and remediation of contaminated water and wastewater, and exhibits advantages over conventional treatment technologies. When considering solar energy as an energy source for photocatalysis, it is key to prepare visible light-responsive materials. Bismuth-based semiconductors are promising materials as visible light-responsive photocatalysts primarily due to their suitable band gaps, well-dispersed valence bands, and commercial availabilities at reasonable costs, as well as the possibility of preparing them under mild conditions. Recent work focusing on the preparation, characterization and activity testing of bismuth-based photo-active materials as well as their associated photoreactor designs are introduced herein. In order to enhance the photocatalytic activities of the new materials, different precursors, additives, preparation procedures and process parameters, as well as surface treatments were explored to obtain binary and ternary heterostructures, with different doping, surface modification, nanoparticle sizes and morphologies. It was found that formation of heterojunction and loading metal nanoparticle on the surface are very effective to imrove the photocatalytic activity of the support. In this work, we found that palladium nanoparticles modified BiVO4 exhibited excellent activity in the decomposition of phenol, which was even higher than TiO2. To facilitate the separation process of catalysis particels from a slurry system, magnetically separable composites were also prepared, and it was found that it is very effective to remove the particles from the slurry system using external magnets. To further scale up this process, two different types of immbolized photoreactors (flat-plate and packed beads photoreactor) were also developed. Suggestions were made for further work in this research area.

Mestrado em Ciência e Engenharia de Materiais
Nos dias de hoje são inúmeras as aplicações dadas aos materiais à base de bismuto. As aplicações situam-se em áreas tão distintas como a medicina, metalurgia, cosmética e farmácia, tintas e vernizes. Por exemplo na área dos pigmentos colorantes, prevê-se que o BiVO4 venha a ter uma importância comercial crescente dado ser o mais promissor substituinte dos pigmentos amarelos contendo chumbo e cádmio. O principal problema na utilização de pigmentos à base de bismuto reside no facto destes compostos serem geralmente dispendiosos. Neste trabalho investigam-se métodos alternativos na preparação e utilização destes pigmentos, potenciando a sua utilização de um modo mais competitivo. Investigou-se a preparação de revestimentos de BiVO4 pelo processo de deposição química em solução (CBD: Chemical Bath Deposition) em substratos de vidro. Procurou-se adaptar este novo método de preparação de BiVO4, na formação de partículas compósitas utilizando o ZnO como material de suporte. O processo de deposição química foi investigado pela caracterização detalhada quer dos materiais sólidos obtidos quer pela monitorização espectroscópica das soluções sobrenadantes. Estudou-se a incorporação de Ce (III) na estrutura do BiVO4. Os filmes obtidos foram caracterizados, nomeadamente no que diz respeito às suas propriedades cromáticas, estruturais e morfológicas. Os nanocompósitos polímero-inorgânico têm sido largamente investigados devido às suas potenciais aplicações como materiais compatíveis a elevadas temperaturas ou como revestimentos poliméricos reforçados com partículas. Investigou-se a utilização de nanopartículas de Bi2S3 como cargas no fabrico de nanocompósitos de matriz polimérica. As propriedades térmicas de nanocompósitos de nylon-6.10 foram especialmente estudadas, tendo em conta as potenciais aplicações do Bi2S3 nanodisperso como retardador de chama. O efeito do tratamento prévio das cargas bem como o efeito do método de preparação do nanocompósito nas propriedades finais do material foram igualmente investigadas.
Bismuth based materials have been used in several applications including in medicine, metallurgy, cosmetics and pigments. Bismuth (III) vanadate (BiVO4) is a solid that presents interesting technological properties as a pigment. This compound is the best candidate to replace toxic yellow pigments, such as cadmium and lead compounds, in some applications. Due to restrictions imposed to the industry on the use of Cd and Pb pigments, it is expected that the commercial importance of BiVO4 continues to increase. It is also true that bismuth pigments are relatively expensive materials, lowering the commercial competitiveness of such pigments. Therefore, there is interest in developing new forms of pigmentation, enabling a more competitive use of Bi containing pigments. Chemistry can provide the tools to create innovative forms of BiVO4 pigmentation by synthesizing BiVO4 based materials with specific optical and morphological properties. A chemical bath deposition method to deposit monoclinic-BiVO4 coatings on glass substrates is presented. The reported method involves the controlled growth of BiVO4 monolayers, at mild temperatures, in the presence of a sequestering agent such as ethylenediaminetetracetic acid (EDTA). We used this CBD method to deposit BiVO4 on other types of substrates of technological interest. The encapsulation of hollow ZnO microparticles with the BiVO4 pigment is reported. The CBD process was investigated by the characterization of the solid fase and by the spectroscopic studies of the solutions. Pigments based on BiVO4 doped with Ce (III) were prepared using the CBD developed. The colour, morphological and structural properties of these pigments were studied. Polymer-inorganic nanocomposites have been of interest due to several applications, such as in tough and high-temperature compatible materials or particle-reinforced polymer coatings. This work presents results concerning the preparation of a novel type of polymer nanocomposites, which contain Bi2S3 nanofibers as fillers. The synthetic approaches to prepare Bi2S3/nylon-6.10 nanocomposites will be discussed in light of the final nanocomposites properties, such as the chemical stability and morphological homogeneity. This work aims to investigate the potential use of such nanomaterials as flame retardant pigments for polymeric materials.

Orientador: Oswaldo Luiz Alves
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Doutorado

O objetivo deste trabalho foi desenvolver e caracterizar um cimento endodôntico experimental a base de resina epóxica com a adição de diferentes proporções de três sais de bismuto, seguindo os requisitos das normas ISO 6876 e ISO 4049 em busca da composição que atendesse estas normas. Para isto, foram formulados dezoito grupos com resina epóxica e adição de 20%; 40%; 60%; 80%; 100% e 120% em massa de três diferentes sais de bismuto. Foram realizados ensaios de escoamento, tempo de trabalho, tempo de presa, espessura de película, alteração dimensional, sorção e solubilidade, radiopacidade e citotoxicidade. Os resultados foram comparados com requisitos das normas ISO 6876 e 4049 e submetidos a ANOVA de duas vias (tipo de carga e concentração) e teste de Tukey com nível de significância de 5%. Os cimentos com subnitrato e subcarbonato de bismuto demonstram-se promissores, com especial destaque às formulações contendo subnitrato de bismuto por apresentarem resultados superiores. A adição de carga a partir de 80% conferiu radiopacidade satisfatória para os cimentos com subnitrato e subcarbonato de bismuto. Para os cimentos com subsalicilato de bismuto a única concentração que atendeu à norma foi de 120%. No ensaio de citotoxicidade nenhuma das formulações apresentou diferença estatística significativa quando comparado ao controle. Conclui-se que o subnitrato de bismuto e subcarbonato de bismuto apresentam características para utilização como carga e radiopacificante em cimentos endodônticos a base de resina epóxica.
The aim of this study was the development and evaluating of an experimental endodontic sealer epoxy based after addition of three different bismuth salts, according to the requirements of ISO 6876 and 4049 searching for the composition with better performance. Eighteen groups were formulated with the inclusion of 20%, 40%, 60%, 80%, 100% and 120% of three different bismuth salts, by weight, on epoxy resin. Then, flow tests, working time, setting time, film thickness, dimensional change, sorption and solubility, radiopacity and cytotoxicity were performed. Data were analyzed by two-way ANOVA (type of filler and concentration) and Tukey at a level of significance of 5%. The formulations with bismuth subsalicylate did not show suitable properties. However, cements with bismuth subnitrate and subcarbonate shown to be promising, particularly with regard to formulations containing bismuth subnitrate, wich presented superior results. The addition of 80% salt generated satisfactory radiopacity to subcarbonate and bismuth subnitrate sealers, bismuth subsalicylate had only reached satisfatory radiopacity at 120%. In the cytotoxicity assay none of the formulations showed statistical significance when compared to control. It is concluded that the formulations containing bismuth subnitrate and bismuth subcarbonate have potential use as filler in endodontic sealers.

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As rotas de síntese dos cupratos supercondutores buscam por melhorias em suas propriedades como a obtenção de fases únicas, grãos homogêneos e melhor conectados o que, consequentemente, interfere no aumento da capacidade de transporte de corrente elétrica. Neste trabalho foi estudada a síntese do óxido supercondutor do sistema Bi:Sr:Ca:Cu:O na fase 2212 (BSCCO-2212) que apresenta temperatura crítica em torno de 85 K. Para a síntese desse material, foi utilizada uma variação do método dos precursores poliméricos desenvolvido por Pechini e, em uma segunda rota, foi adicionada, a este método, uma etapa na qual se aplicou o método de hidrotermalização assistida por energia de micro-ondas. Neste último, o material é aquecido de dentro para fora e, devido à interação das micro-ondas com a solução, a temperatura do sistema aumenta rapidamente, influenciando diretamente na velocidade da síntese. Em contraste, no aquecimento convencional, o material é aquecido, primeiramente, na superfície e, só então, ocorre a transferência de calor para o interior do sistema. Os pós resultantes dos dois métodos de síntese ora descritos foram tratados termicamente e, então, prensados para se obter pastilhas. Na sequência, foram feitas caracterizações estruturais, elétricas e magnéticas no intuito de se estudar a influência de cada método sobre as propriedades dos materiais sintetizados.
The synthesis routes of superconducting cuprates seek for the improvement of the proprieties of these materials such as the achievement of pure superconducting phases, homogeneity of the grains, better connectivity between the grains and the increase of the transport current. In this study we synthesized oxide superconductors of the Bi:Sr:Ca:Cu:O system focusing on the 2212 phase (BSCCO-2212) for which the Tc lies on around 85 K. For the productions of this material, it was used two synthesis routes. In one of them it was followed only the polymeric precursor method developed by Pechini and, in the second route, the Microwave-Assisted Hydrothermal method was associated with the Pechini one. For this method the heat of the material is from inside out, i.e., the temperature of the system is increased very fast and, consequently, the velocity of synthesis is increased. In conventional heat treatment the material is heated, firstly, at the surface and then the heat is transferred to the interior of the system. The powders of the materials, which were obtained from the described methods, were heat treated and thus, pressed. After that, structural, electrical and magnetic characterizations were carried out to study the influence of each synthesis method on the properties of the produced superconductors.

Orientador: Rafael Zadorosny
Banca: Agda Eunice de Souza Albas
Banca: Fabiano Colauto
Resumo: As rotas de síntese dos cupratos supercondutores buscam por melhorias em suas propriedades como a obtenção de fases únicas, grãos homogêneos e melhor conectados o que, consequentemente, interfere no aumento da capacidade de transporte de corrente elétrica. Neste trabalho foi estudada a síntese do óxido supercondutor do sistema Bi:Sr:Ca:Cu:O na fase 2212 (BSCCO-2212) que apresenta temperatura crítica em torno de 85 K. Para a síntese desse material, foi utilizada uma variação do método dos precursores poliméricos desenvolvido por Pechini e, em uma segunda rota, foi adicionada, a este método, uma etapa na qual se aplicou o método de hidrotermalização assistida por energia de micro-ondas. Neste último, o material é aquecido de dentro para fora e, devido à interação das micro-ondas com a solução, a temperatura do sistema aumenta rapidamente, influenciando diretamente na velocidade da síntese. Em contraste, no aquecimento convencional, o material é aquecido, primeiramente, na superfície e, só então, ocorre a transferência de calor para o interior do sistema. Os pós resultantes dos dois métodos de síntese ora descritos foram tratados termicamente e, então, prensados para se obter pastilhas. Na sequência, foram feitas caracterizações estruturais, elétricas e magnéticas no intuito de se estudar a influência de cada método sobre as propriedades dos materiais sintetizados.
Abstract: The synthesis routes of superconducting cuprates seek for the improvement of the proprieties of these materials such as the achievement of pure superconducting phases, homogeneity of the grains, better connectivity between the grains and the increase of the transport current. In this study we synthesized oxide superconductors of the Bi:Sr:Ca:Cu:O system focusing on the 2212 phase (BSCCO-2212) for which the Tc lies on around 85 K. For the productions of this material, it was used two synthesis routes. In one of them it was followed only the polymeric precursor method developed by Pechini and, in the second route, the Microwave-Assisted Hydrothermal method was associated with the Pechini one. For this method the heat of the material is from inside out, i.e., the temperature of the system is increased very fast and, consequently, the velocity of synthesis is increased. In conventional heat treatment the material is heated, firstly, at the surface and then the heat is transferred to the interior of the system. The powders of the materials, which were obtained from the described methods, were heat treated and thus, pressed. After that, structural, electrical and magnetic characterizations were carried out to study the influence of each synthesis method on the properties of the produced superconductors.
Mestre

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Nas últimas décadas, o consumo de dispositivos eletrônicos e a alta demanda por armazenamento de dados tem mostrado grandes oportunidades para a criação de novas tecnologias que garantam as necessidades mundiais na área de computação e desenvolvimento. Alguns materiais multiferroicos tem sido amplamente estudados e o BiFeO3, considerado o único material multiferroico em temperatura ambiente, ganhou destaque como candidato para produção de dispositivos lógicos e de memória. O uso de técnicas de crescimento como a deposição por laser pulsado permitiu a produção de filmes finos de BiFeO3 com elevado controle de qualidade. Heteroestruturas de filmes multiferroicos de BiFeO3 e LaBiFeO3 foram crescidas com diferentes espessuras sobre substratos de SrTiO3(100), DyScO3(110) e SrTiO3/Si(100) para avaliação e teste de suas propriedades elétricas e magnéticas. Filmes ferromagnéticos de Co0,9Fe0,1 foram depositados por sputtering sobre os filmes multiferroicos para avaliação da interação interfacial entre ordenamentos magnéticos. Técnicas como fotolitografia foram utilizadas para padronização de microdispositivos gravados sobre as amostras. Tanto os filmes finos de BiFeO3 como os de LaBiFeO3 foram crescidos epitaxialmente sobre os substratos já cobertos com uma camada buffer de SrRuO3 usado como contato elétrico inferior. A estrutura cristalina romboédrica das ferritas de bismuto foi confirmada pelos dados de difração de raios X, bem como a manutenção de tensão estrutural causada pela rede cristalina do substrato para amostras de 20 nm. Os valores de coeficiente do tensor piezelétrico d33 foram da ordem de 0,15 V (∼ 60 kV.cm-2) para amostras com 20 nm de espessura enquanto que os valores de voltagem coerciva para as análises de histerese elétrica foram da ordem de 0,5 V para as mesmas amostras. A relação de coercividade elétrica com a espessura corresponde ao perfil encontrado na literatura pela relação E≈d-2/3. As amostras de CoFe/BFO e CoFe/LBFO depositadas em diferentes substratos apresentam acoplamento interfacial entre ordenamento ferromagnético e antiferromagnético com momento ferromagnético de rede.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
CAPES:99999.009511/2014-08
CNPq:146622/2013-2

L'investigation du système BaBiO3-BaRuO3 a permis de mettre en évidence trois nouvelles phases qui cristallisent dans trois différents polytypes de la perovskite. L'interprétation des propriétés magnétiques de ces phases, ainsi que des considérations cristallochimiques, montrent qu'il s'établit un phénomène de transfert de charge entre le ruthénium et le bismuth selon le schéma réactionnel: 2 Ru4+ + Bi5+->2 Ru5+ + Bi3+. L'activité catalytique de ces composés pour la réduction de NO a été étudiée. Cinq nouveaux composés ont ete isoles dans le système Ba(Sr)-Ru-O. Leurs structures sont caractérisées par des groupements [Ru3O12] ou [Ru2O9], formant des systèmes de basse dimensionnalité (clusters, système 2D). Des modèles structuraux ont été développés et ont permis d'établir des filiations structurales avec des structures type telles que K2NiF4, la perovskite 2H et Sr4PtO6. Les propriétés magnétiques ont été étudiées et pour certaines phases, interpretées en termes d'entités isolées selon un modèle d'Heisenberg.

博士
國立臺灣大學
材料科學與工程學研究所
102
The bismuth-based metal oxides, such as BiFeO3 (BFO) and Bi/B-doped TiO2 are potential candidates for electrolyte of low temperature solid oxide fuel cell and solution processable hybrid solar cell, respectively. In this study, we synthesize bismuth-based metal oxides, and investigate the material characteristics and the cell characteristics. For low temperature solid oxide fuel cells, we prepared BFO as electrolyte. The material was synthesized using solution approach. Bismuth nitrate pentahydrate (Bi(NO3)3．5H2O) and iron nitrate nonahydrate (Fe(NO3)3．9H2O) were dissolved in the mixture of 2-ethoxyethanol and acetic acid at 70°C for 30 min. After evaporating the solvent, the BFO was calcined at 500°C for 2 hrs in air. The air calcined BFO was pressed into a disk which showed a pure BFO perovskite structure after sintered at either 850°C or 900°C. The BFO was coated with 100 micron yttria-stabilized zirconia (YSZ) buffer layer to avoid hydrogen reduction of BFO. This bilayer electrolyte exhibits 1.6 times increasing in maximum power density as compared with pure YSZ due to its perovskite structure, when Ni-YSZ anode and lanthanum strontium cobalt ferrite cathode were used in the fuel cell at 650°C. TiO2 nanorods were synthesized to fabricate hybrid P3HT:TiO2 solar cells. The TiO2 nanorods were synthesized using sol-gel process in the presence of oleic acid surfactant at 98℃ for 9 hrs. The size of TiO2 nanocrystal is about 35 nm in length and 5 nm in diameter. The insulating oleic acid on TiO2 nanorods was replaced by pyridine (as-synthesized TiO2) for good charge transport between P3HT and TiO2 in the application of hybrid P3HT:TiO2 nanorods solar cells. In order to improve the power conversion efficiency (PCE) of P3HT:TiO2 solar cell, we have further increased the crystallinity of anatase TiO2 nanorods. Two novel approaches: (1) ripening and (2) bismuth/boron doping for TiO2 nanorods were explored. The crystallinity of the as-synthesized TiO2 nanorods was increased through ripening (120℃, 24 hrs) by using an autoclave reactor while the size of nanocrystal was not significantly changed. The bismuth doped TiO2 (Bi-doped TiO2) and boron doped TiO2 nanorods (B-doped TiO2) were synthesized using the same sol-gel process of as synthesized TiO2 nanorods. The PCE of P3HT:TiO2 solar cells was increased by 1.31 times and 1.79 times under A. M. 1.5 illumination for ripened and B-doped TiO2, respectively, as compared with as-synthesized TiO2. The B-doped TiO2 has the highest mobility and PCE, mainly due to the presence of partially reduced Ti4+ by boron atom with delocalized electrons. W4-dye is a promising way for modifying the interface between P3HT and TiO2 charge transport further. The Bi-doped TiO2 has higher Jsc as compared with B-doped TiO2, mainly due to the presence of improvement of electron density under TiO2. The PCE of solar cell made of W4-dye modified TiO2 nanorods has been increased by 1.33 times and 1.30 times for Bi-doped TiO2 and B-doped TiO2, respectively, as compared with that of as-synthesized TiO2.

Technologies based on alternative and sustainable energy sources present a vital solution in the present and for the future. These technologies are strongly driven by the increased global energy demand and need to reduce environmental issues created by fossil fuel. Solar energy is an abundant, clean and free-access resource, but it requires harvesting and storage for a sustainable future. Direct conversion and storage of solar energy using heterogeneous photocatalysts have been identified as parts of a promising paradigm for generating green fuels from sunlight and water. This thesis focused on developing semiconductor absorbers in a visible light region for photocatalytic hydrogen production reaction. In addition, theoretical studies are combined with experimental results for a deep understanding of the intrinsic optoelectronic properties of the obtained materials. The study presents a novel family of oxysulfide BiAgOS, produced by applying a full substitution strategy of Cu by Ag in BiCuOS. I was interested to address how the total substitution of Cu by Ag in a BiCuOS system affects its crystal structure, optical and electronic properties using experimental characterizations and theoretical calculations. Single-phase bismuth silver oxysulfide BiAgOS was prepared via a hydrothermal method. Rietveld refinement of the powder confirmed that BiAgOS is an isostructural BiCuOS. The diffraction peak positions of BiAgOS, relative to those of BiCuOS, were shifted toward lower angles, indicating an increase in the cell parameters. BiCuOS and BiAgOS were found to have indirect bandgaps of 1.1 and 1.5 eV, respectively. The difference in the bandgap results from the difference in the valence band compositions. The hybrid level of the S and Ag orbitals in BiAgOS is located at a more positive potential than that of S and Cu, leading to a widened bandgap. Both materials possess high dielectric constants and low electron and hole effective masses, making them interesting for photoconversion applications. BiAgOS has a potential for photocatalytic hydrogen evolution reaction in the presence of sacrificial reagents; however, it is inactive toward water oxidation. BiCuOS and BiAgOS can be considered interesting starting compositions for the development of new semiconductors for PV or Z-scheme photocatalytic applications. The second study investigates the synthesis and characterization of NaBiS2, this contains Bi3+, which belongs to the p-block electronic configuration Bi3+ 6s26p0, and NaLaS2, which contains La3+ with electronic configuration 6s05d0. Solid-state reactions from oxide precursor starting materials were applied for synthesis the materials. The sulfurization process was conducted by pressurizing a saturated vapor of CS2. The obtained black material of NaBiS2 has an indirect transition with high absorption coefficients in the visible region of the spectrum and the absorption edge is determined at 1.21 eV. However, NaBiS2 did not show photocatalytic activity toward hydrogen production. NaLaS2 is characterized by an indirect transition with a bandgap in the UV region at 3.15 eV and can drive the photocatalytic hydrogen evolution reaction in Na2S/Na2SO3 solution. Utilizing the solid solution NaLa1-xBixS2 strategy, the absorption properties and band edge position for photocatalytic hydrogen evolution reaction were optimized. The results indicated that the bismuth content is critical parameter for maintaining the photocatalytic activity. The incorporation of low Bi content up to 6% in NaLaS2 leads to extending the photon absorption from the UV to the visible region and enhancing the photocatalytic activity of hydrogen production. In contrast, all the solid solutions that have Bi content of more than 12% present absorption edges close to that of pure NaBiS2, and they are inactive for photocatalytic hydrogen production. Combining the experimental measurements with density functional theory calculations, such behavior can be explained by the degree of overlapping of Bi and La states on the conduction band minimum (CBM). Finally, self-assembly of Bi2S3 nanorods were grown on FG or FTO substrates. Bi2S3 thin films were prepared by sulfurization of Bi metal layer using the hydrothermal method. The results show that Bi2S3 has absorption up to 1.3 eV and has a moderate absorption coefficient in the visible region. The ultraviolet photoelectron spectroscopy and photoelectron spectroscopy in air results showed that the conduction band minimum of Bi2S3 is located slightly above the hydrogen redox potential. However, Pt/Bi2S3 did not evolve a detectable amount of hydrogen, suggesting the presence of surface states that can hinder the hydrogen reduction reaction.

碩士
國立臺灣大學
材料科學與工程學研究所
104
The effects of nickel, cobalt and manganese doping in bismuth-based ferrite perovskite (Bi0.7Sr0.3FeO3-δ) used as cathode of solid oxide fuel cells have been investigated in this study. The cathode powders were synthesized by EDTA-citric acid method. The phase purity of synthesized perovskites were analyzed by X-ray Diffraction (XRD). The solubility limit of Ni was 3 at%, while Mn can substitute for Fe at least 50 at% in BSF. Electrical conductivity by 2-probe and 4-probe DC methods showed that the 50 mol% doping of Mn on B-site improved the electrical conductivity significantly. The oxygen nonstoichiometry was analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) to reveal the deficiency of oxygen and ionic conductivity in the ferrites. The ionic conductivity of BSF was 4.21 x10-3 S.cm-1 at 800 oC. Anode disk of 300 μm thick coated with thin layer (μm layer thickness) of electrolyte by spin-coating method. The polarization resistance and contact resistance of the half-cell with an 8YSZ-N flat layer and cathode sintered by different sintering temperatures were analyzed by electrochemical impedance spectra analysis (EIS). Finally, the optimal cathode (Bi0.7Sr0.3Fe0.5Mn0.5O 2.88-0.034+20 SDC) was assembled to a full cell and the maximum power output was 119 mW.cm-2 at 800 oC.

博士
國立中山大學
電機工程學系研究所
104
The crisis of energy shortage and carbon reduction has become an important issue; the green technology is getting more and more attention. The thermoelectric power generator exhibits the advantages of environmental protection and renewable energy. The thermoelectric devices can convert heat energy to electric energy and vice versa. Bismuth telluride (Bi-Te) and antimony telluride (Sb-Te)-based compounds, which exhibit the highest figure of merit (ZT), are known to be the best thermoelectric materials within the room temperature region and are widely utilized for thermoelectric cooling and generation. In this study, thermoelectric materials were prepared by different processing methods. The characteristics of the obtained thermoelectric materials are investigated. The powder metallurgy method was adopted to fabricate Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3 thermoelectric materials via the ball milling, cold pressing, and sintering processes. The effects of sintering time and temperature on the thermoelectric properties are investigated and discussed for the Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3 thermoelectric materials. On the other hand, Bi2Te3 and Sb2Te3-based thin films were prepared by thermal evaporation method on the silicon substrates. The influences of substrate temperature and annealing temperature on the surface morphology, crystal structure and thermoelectric properties of thin films are investigated. Further, the Ag-doped Bi2Te3 and Sb2Te3 thin films are also fabricated by co-evaporation and then annealed. The effects of post annealing on the microstructures and thermoelectric properties of the thin films are evaluated. In the study of bulk thermoelectric materials, the Seebeck coefficient of Bi2Te2.7Se0.3 decreased at first and then increased by the increased sintering temperature. Moreover, the results also showed that the thermal conductivity and electrical resistivity exhibited a reversal trend. When the thermal conductivity was increased by the increased sintering temperature, the electrical resistivity was reduced. The calculated PF of 1.074 mW/mK2 was obtained as the sample was sintered at 723K for 2h. The figure of merit (ZT) of 0.31 was obtained at room temperature as the sample was sintered at 648K for 2h. The thermoelectric properties of Bi0.5Sb1.5Te3 showed that the optimal Seebeck coefficient of 300.694 μV/K was obtained as the sample was sintered at 623K for 1h and the resistivity reached the maximum. The figure of merit (ZT) of 0.15 was obtained at room temperature as the sample was sintered at 648K for 3h, in which, the structure showed the rectangular prism crystallization. Besides, n-type Bi2Te3 and p-type Sb2Te3 thin films were deposited on SiO2/Si substrates using thermal evaporation method in this thesis. The influences of substrate temperature and thermal annealing on the structure, composition, morphology and thermoelectric properties of Bi2Te3 and Sb2Te3 thin films were investigated. As the substrate temperature increased to 150°C, the power factors of n-type Bi2Te3-based and p-type Sb2Te3-based thin films were found to be about 4.89 μW/cm⋅K2 and 3.94 μW/cm⋅K2, respectively. Further, the Ag-doped thin films were fabricated by co-evaporation and the thermal annealing treatment was carried out. The results showed that the Ag-doped Bi2Te3 with a maximized value of power factor of 2.16 μW/cm·K2 could be obtained at the substrate temperature of 100°C and annealing temperature of 250°C (0.5hr). In the Ag-doped Sb2Te3, the thin films exhibited a maximized value of power factor of 19.99 μW/cm·K2 at the substrate temperature of 150°C and annealing temperature of 200°C (0.5hr).

碩士
國立臺灣大學
材料科學與工程學研究所
101
Two series perovskites, Bi1-xSrxFeO3-δ (x = 0.1-0.5) and Bi0.5Sr0.5CoyFe1-yO3-δ (y = 0-0.2), have been synthesized by EDTA-citric complexing method and characterized in intermediate-temperature range (600 to 800°C) by X-ray diffraction, electrical property study, thermal analysis and cell testing. The results show single-phase perovskite structure offering CTE values from 10.0 to 19.1 ppmk-1. Two samples S50 and S50C20 perform maximal electrical and ionic conductivities among the series. Polarization resistance from Nyquist plot depicts that S50C20 has a lowest value of 0.10 Ω.cm2. The cells with S50 or S50C20 cathode comparing to the standard cell with La0.6Sr0.4Co0.2Fe0.8O3-δ cathode show the power density 361 mWcm-2,405 mW cm-2 and 353 mW cm-2,respectively. The cells with Bi-base cathodes have a power density higher then that of STD cell.

博士
逢甲大學
環境工程與科學學系
107
Abstract Supercapacitors have been relatives of energy storage devices, which is the conversion of the electrical energy from sustainable energy sources of solar, wind energy and so on. They differentiate from another family of energy storage devices like Li, Na and K ion batteries, for instance, batteries are able to full charging take time meanwhile discharging in seconds. The overall supercapacitor performances of developing electrode materials have been relying on the outstanding electrical conductivity, porous nanostructures with excellent long-term stability and larger surface areas. These properties are attractive and extensive research efforts to move on one-step forward to developing the supercapacitor performances. The scope of this dissertation to design and synthesis of bismuth and molybdenum-based electrode materials, with their application of supercapacitor. Bismuth-based electrode materials, the increasing loading amount of RGO nanosheets to improve the electrical conductivity on Bi2O2CO3 electrode materials at three-electrode configuration. In addition, the anode of Bi2O3/porous-RGO nanosheet has been prepared with the help of catalytic carbon gasification method and then combine with cathode materials of α-MnO2 to exhibits high energy/power density at two-electrode configuration. Molybdenum-based electrode materials, the hexagonal-MoO3 nanoplates have been create the high amount of oxygen vacancy concentration in crystal lattice at high annealing temperature and thereby interlayer distance increases and enhance the electrical conductivity. The highest oxygen vacancy concentration of hexagonal-MoO3 nanoplates is generated the crystal defects in the presence of NH4+ ions such as grain and twin boundaries, amorphous and screw dislocation. This crystal defects to produce the diffusion path for electrolyte ions easily move on the electrode surface and thus improve the charge storage performances. Furthermore, the hetero-atoms of nitrogen doped hallow carbon nanotubes are augmented the electrical conductivity of molybdenum oxy-carbide nanoparticles in acidic condition. The above our synthesized bismuth and molybdenum-based nanostructured electrode materials to make new insight for future work of asymmetric supercapacitor fabrication techniques. Keywords: Porous-RGO, Bismuth, Molybdenum, Crystal defects, Electrical conductivity

Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system. The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation. The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm + P4/mbm → P4/mbm →Pm3 m. The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0