Les multiferroïques sont des matériaux dans lesquels plusieurs propriétés ferroïques peuvent coexister, e. g. ferromagnétisme et ferroélectricité. La recherche de tels matériaux fait l'objet d'une activité croissante en raison de l’enjeu majeur qu’ils représentent dans de nombreux domaines (mémoires, spintronique…). Les matériaux qui possèdent les propriétés nécessaires pour des applications futures sont cependant peu nombreux. Des niobates de formule Ba2LnFeNb4O15 (Ln = lanthanide), de structure bronze quadratique (TTB) susceptibles de présenter un ordre ferroélectrique et un ordre magnétique ont été synthétisés. Les propriétés magnétiques des céramiques proviennent d'une phase secondaire, faisant d’eux des composites multiferroïques. Leur souplesse cristallochimique permet de contrôler les propriétés composites par substitutions cationiques dans la matrice TTB. Afin de compléter l'étude cristallochimique, la croissance de monocristaux de TTB a été entreprise avec succès. / Multiferroics are materials which possess several ferroic properties, e.g. ferroelectricity, ferromagnetism. The search for multiferroics arises a growing activity, due to their potential applications in memories, spintronic… Yet the materials displaying the adequate properties for future application are very few. Niobates with the formula Ba2LnFeNb4O15, potentially ferroelectric and ferromagnetic, have been synthesized. The magnetic properties of the ceramics are related to a secondary phase, thus making them composite multiferroics. Their crystal-chemical flexibility allows for the composites properties tuning by cationic substitutions into the TTB framework. To complete the crystal-chemical study, the growth of TTB single-crystals was successfully engaged.

Les travaux présentés dans ce manuscrit concernent des niobates de formulation Ba2LnNb4O15 (Ln = La ou Nd) et de structure "Tetragonal Tungsten Bronze" (TTB). Ces travaux se situent à la charnière de la chimie et de la physique des matériaux diélectriques et visent à mettre en relation structure cristalline et propriétés diélectriques. L'étude a été menée sur des TTB élaborés sous forme céramique et monocristalline. Après détermination de conditions optimales de croissance, par fusion de zone en four à image, des sections monocristallines ont été obtenues et caractérisées. Les résultats obtenus suggèrent des liens étroits entre composition, modulations structurales apériodiques et comportement diélectrique. Dans le même temps, deux nouvelles solutions solides céramiques ont été explorées, avec des schémas de substitution différents menant notamment à une réflexion très large sur les liens cristallochimie-ferroélectricité dans cette famille de TTB. Ces solutions solides présentent un crossover relaxeur-ferroélectrique, un comportement original et déjà observé dans d'autres solutions solides issues de cette famille de TTB. Des caractérisations avancées (mesures pyro- et piézoélectriques, cycles de polarisation) et des études structurales résolues en composition et en température ont permis d'établir des diagrammes de phases diélectriques montrant l'existence d'un état ferroélectrique métastable. Finalement, la présence d’une modulation structurale bidimensionnelle a pu être confirmée, dans les monocristaux et dans les céramiques, et l'ensemble des résultats obtenus pointent son implication dans les comportements cristallochimiques originaux rencontrés dans ces TTB. / The present work deals with Ba2LnNb4O15 (Ln = La ou Nd) niobates crystallizing with the "Tetragonal Tungsten Bronze" (TTB) structure. These researches, at the interface of chemistry and physics of dieletrics, aim at establishing structure / dielectric properties relationships. They were performed on TTB materials elaborated in ceramic and single crystal forms. Following optimization of growth parameters with an image furnace, single crystals were obtained and characterized. The results obtained suggest that composition, aperiodically modulated structure and dielectric behavior are closely tied in TTBs. Meanwhile, two new ceramic solid solutions with different substitutions schemes were investigated, deepening the insight on crystal-chemistry and ferroelectricity of TTBs. These solid solutions exhibit a relaxor-ferroelectric crossover, an original behaviour previously observed in solid solutions derived from the same family of TTB niobates. Advanced physical characterization (ferro-, pyro- and piezoelectric measurements, polarization loops), and composition/temperature resolved structural studies, allowed for the determination of a dielectric phase diagrams showing the presence of a metastable ferroelectric state. Finally, the existence of a two-dimensional structural modulation in single crystals and ceramics has been confirmed, and the whole set of experimental results points towards its implication in the original dielectric behavior observed in these TTBs.

Le renouvellement de la documentation lié au dynamisme de l’archéologie préventive, ainsi que la reprise systématique des données issues de fouilles anciennes et inédites ont permis de poser un regard neuf sur le Bronze moyen du sud de la plaine du Rhin supérieur. Le corpus, réuni pour ce travail, offre des données variées (objets métalliques, résineux et céramiques) d’origines diverses (habitats, sépultures, dépôts, objets isolés) qui ne se résument plus uniquement au matériel des nécropoles de la forêt de Haguenau. Les mobiliers métalliques et céramiques ont fait l’objet d’une étude distincte. Leur classement typologique associé à des analyses statistiques ont révélé sept étapes depuis fin du Bronze ancien (BA III/Bz A2b) jusqu’au début du Bronze final (BF 1/Bz D2). La phase moyenne du Bronze moyen (fin du BM I-début du BM II/Bz B2-C1) reste mal définie et semble quasi absente dans la région. La corrélation avec les dates absolues disponibles pour la région indique un intervalle chronologique situé entre 1600 et 1300 avant notre ère environ. Durant la phase ancienne, les contacts extérieurs sont centrés sur le sud du Bade-Wurtemberg, le Jura souabe et la Suisse occidentale. Puis les échanges gagnent en intensité, se diversifient et se tournent également en direction du nord, vers la région du Rhin moyen. / The renewal of documentation about the preventive archaeology dynamism, as well as the systematic recovery of datas from old or unpublished excavations have resulted in a fresh perspective at the Middle Bronze Age of the upper Rhine’s south plain. The corpus, joined in this work, gives varied datas (metallic, resinous objects, pottery), from various sources (settlements, graves, deposits, isolated objects), which is not limited to Haguenau’s cemeteries, anymore. Metallic materials and pottery had been examined individually. The determined typology, combined with statistical analysis show seven stages since the end of the Early Bronze Age (BA III/Bz A2b) to the beginning of Late Bronze Age (BF 1/Bz D2). The middle phase of the Middle Bronze Age (end of BM I-beginning of BM II/Bz B2-C1) remains uncleared and seems not to be in the Upper Rhine. The correlation with well-known absolute dates in the Upper Rhine comes to a time interval between 1600 and 1300 Before J-C, approximately. During the first stage, the interactions are located in the South of Baden-Württemberg, in the Swabian Alb and in the western Switzerland. Then, interactions continue to intensify, become more diverses towards the North, near the Middle Rhine.

This thesis work concerns about the importance of the cast surfaces, surface phenomenon such as the formation of the oscillation marks and exudation and related defects including cracks and segregation that happened during the continuous casting. All of the investigated materials were collected during the plant trials while an in-depth analysis on these materials was performed at the laboratory scale with certain explanations supported by the schematic and theoretical models. The work consists on different material classes such as steels and phosphor bronzes with a focus on the surface defects and their improvements. In order to facilitate the theoretical analysis which could be capable of explaining the suggested phenomenon in the thesis, a reduced model is developed which required lesser computational resources with lesser convergence problems. / <p>QC 20160527</p> / Oscilation mark formation during continous casting of steel

Estudou-se a evolução morfológica de precipitados .. em matriz .. Cu-Al, através de tratamentos isotérmicos interrompidos por têmpera, em amostras previamente solubilizadas desde o início da precipitação, até o crescimento competitivo. Caracterizou-se a forma dos precipitados após tratamentos em diversas temperaturas, por microscopia ótica e microscopia eletrônica de varredura, de estruturas atacadas profundamente. A forma dos precipitados após tratamentos prolongados a 700 ºC tende a ser esférica, enquanto nos tratamentos a 600 ºC, tende a ser facetada. Com temperaturas decrescentes de 700 º para 600 ºC a forma passa gradualmente de esférica para facetada. Verificou-se que a distribuição espacial dos precipitados depende da velocidade de aquecimento. Com altas velocidades (tratamento em banho de sal), a distribuição é homogênea; com velocidade de aquecimento lentas (tratamento em forno de mufla) os precipitados apresentam-se alinhados, indicando nucleação heterogênea. O crescimento competitivo foi caracterizado através de medidas das distribuições de tamanhos de precipitados. Esta medida foi realizada utilizando micrografias de secções polidas, com um equipamento semi-automático. As medidas de distribuição de tamanhos das secções de precipitados foram processadas para a obtenção da distribuição de diâmetros reais dos precipitados através de um programa de computador utilizando o algoritmo de Saltykov. ......... / The morphological evoluation of .. precipitates in a . Cu-Al matrix has been studied from the beginning of precipitation until coarsening, using isothermal treatments on previously solubilized samples. The shape of precipitates after treatments at many temperatures was studied using Optical Microscopy and Scanning Electron Microscopy of deep etched samples. The precipitates treated for long periods at 700 ºC approach an spherical shape, while treatments at 600 ºC the precipitates become faceted. The special distribution of the precipitates are determined by the heating rate from room temperature to isothermal treatment temperature. With high heating rates the distribution is homogeneous. With low heating rate the precipitates are arranged in rows, due to heterogeneous nucleation. Coarsening was studies by measuring the distribution of precipitate sizes on microphotographs of polished sections using a semi-automatic device. The mesures of section sizes were processed to obtain the real diameter distribution using a computer program based on Saltykov\'s algoritm. .....

No description available.

這篇論文以出土青銅禮器為主要研究對象，結合傳世文獻，嘗試對西周到 春秋時期周人貴族階層的婚姻加以討論。鑒於婚姻在周代禮儀制度當中具有相 當突出的地位，考察婚姻在一個以宗族為主體、以禮儀為規範的社會當中如何 運作和演變，就成了本文最為關切的問題。依據「西周」和「春秋」的分期，論文被分為「上編」和「下編」兩部分 進行撰寫。在整理和考察出土文獻中所記載的婚姻關係之後，文章著重討論了西周貴族婚姻所奠基的社會和政治基礎，由此揭示了西周時期兩大貴族群體在 婚姻方面的不同習慣與特點。儘管在西周時期，一系列植根於獨特政治和社會 土壤的婚姻原則已經開始形成，但隨著宗周覆滅，春秋時期已無法在原有的政 治、社會機制上維持周人貴族固有的婚姻習慣。即便在諸侯國地區延續和維持 了一部分西周的婚姻原則及婚姻禮儀，但這種維持實際為了應對新的時代局勢， 其中依然包含了許多對舊有婚姻制度和禮儀的改造。最後，通過討論在「禮儀」 框架下兩個時代在安置婚姻事務方面所呈現出來的不同特點，本論文進而試圖 對「禮儀」在這一階段婚姻活動中所起到的作用進行回顧。

This thesis is an aetiological investigation of the Hellenistic and Roman figural bronze statuettes in the round that form part of the Ashmolean Museum's antiquities collection. The collection serves as a lens through which to study aspects of ancient and modern receptions of Classical sculptural forms. This approach is based on the premise that the collection's composition has been historically determined not only by how the modern parties responsible for its creation and growth responded to the sculptural forms and images recovered from antiquity, but also by how sculptural forms developed in Greece during the Classical and early Hellenistic periods were received by makers and users of bronze statuettes in antiquity. The thesis has three primary objectives: firstly, to produce a useful and informative catalogue of the Ashmolean Museum's collection of Hellenistic and Roman figural anthropomorphic bronze statuettes in the round; secondly, to determine not only how that collection came to have the characteristics that it does, but also how the reception of ancient sculpture has historically affected the formation of collections of bronze statuettes and their compositions; thirdly, to use archaeological evidence of bronze statuettes to reconstruct possible contexts and to determine in greater detail the reception of canonical sculptural figure types in the form of small bronzes during the Hellenistic and Roman periods. Part I of the thesis deals with the modern contexts for the statuettes, investigating the collection history, pulling out its salient characteristics and then comparing these to other major collections to make informed observations about how and why specific types of statuettes have survived from antiquity and the roles that modern reception of antiquity has played in shaping collections. This leads to Part II, which attempts to reconstruct possible ancient contexts for the Ashmolean bronzes by looking at the archaeological evidence for their production, movement use and display. Part III uses some of the figures of dwarfs, Herakles and Hermes in the collection to develop case studies that examine aspects of the visual relationships that existed between small bronzes and classical sculpture from the Classical and early Hellenistic periods.

Estudou-se a evolução morfológica de precipitados .. em matriz .. Cu-Al, através de tratamentos isotérmicos interrompidos por têmpera, em amostras previamente solubilizadas desde o início da precipitação, até o crescimento competitivo. Caracterizou-se a forma dos precipitados após tratamentos em diversas temperaturas, por microscopia ótica e microscopia eletrônica de varredura, de estruturas atacadas profundamente. A forma dos precipitados após tratamentos prolongados a 700 ºC tende a ser esférica, enquanto nos tratamentos a 600 ºC, tende a ser facetada. Com temperaturas decrescentes de 700 º para 600 ºC a forma passa gradualmente de esférica para facetada. Verificou-se que a distribuição espacial dos precipitados depende da velocidade de aquecimento. Com altas velocidades (tratamento em banho de sal), a distribuição é homogênea; com velocidade de aquecimento lentas (tratamento em forno de mufla) os precipitados apresentam-se alinhados, indicando nucleação heterogênea. O crescimento competitivo foi caracterizado através de medidas das distribuições de tamanhos de precipitados. Esta medida foi realizada utilizando micrografias de secções polidas, com um equipamento semi-automático. As medidas de distribuição de tamanhos das secções de precipitados foram processadas para a obtenção da distribuição de diâmetros reais dos precipitados através de um programa de computador utilizando o algoritmo de Saltykov. ......... / The morphological evoluation of .. precipitates in a . Cu-Al matrix has been studied from the beginning of precipitation until coarsening, using isothermal treatments on previously solubilized samples. The shape of precipitates after treatments at many temperatures was studied using Optical Microscopy and Scanning Electron Microscopy of deep etched samples. The precipitates treated for long periods at 700 ºC approach an spherical shape, while treatments at 600 ºC the precipitates become faceted. The special distribution of the precipitates are determined by the heating rate from room temperature to isothermal treatment temperature. With high heating rates the distribution is homogeneous. With low heating rate the precipitates are arranged in rows, due to heterogeneous nucleation. Coarsening was studies by measuring the distribution of precipitate sizes on microphotographs of polished sections using a semi-automatic device. The mesures of section sizes were processed to obtain the real diameter distribution using a computer program based on Saltykov\'s algoritm. .....

Metal-insulator transition is one of the most important properties observed in certain materials which has been studied widely using a wide range of experimental techniques as well as theoretical models. This kind of a transition, observed in several systems, can take place by tuning several parameters such as pressure, temperature or the composition itself. In this thesis we study a few selected transition metal oxide bronzes exhibiting such phenomenon, each of which has a different cause for undergoing the transition. In Chapter 1, we discuss briefly several mechanisms and models that have been used to understand metal-insulator transitions. We also briefly discuss the role of disorder, electron-electron correlations or both to understand the different ways in which such transitions can occur. In Chapter 2, we describe the different experimental as well as theoretical techniques that have been used in this thesis. In Chapter 3, we study the fermi-edge of the NaxWO3 systems, as a function of x, to understand the origin of the metal-insulator transition occurring in this series of compounds. The system undergoes a metal-insulator transition at the critical composition xc=0.25, below which it is found to be insulating. At the lowest temperature, the very low x compounds behave as disordered and correlated materials. Above the transition composition, the compounds behave as disordered and correlated metals. In the insulating regime, close to the critical composition, we find that the system behaves in a way that cannot be described by any known theories for metals or insulators. We have also done a systematic analysis of the Fermi-edge data for the insulating samples as a function of temperature and we find that they cannot be described by any of the known theories for solid-state systems. Further development is necessary in the theoretical side to understand and interpret our data. In Chapter 4, we study the angle-resolved photoemission data for the highly metallic sodium tungsten bronze Na0.8WO3. We have synthesized the single-crystals by high-temperature electrochemical synthesis and we have performed angle-resolved photoemission experiments to understand the band structure of this system. The experimental results have been supported by theoretical calculations. We find that the rigid band model is valid in describing the electronic structure in these systems. We also find the existence of electron-like pockets along certain symmetry directions. Further, photon energy dependent studies on the x=0.8 sample suggest that there is a difference in the surface with the bulk of the sample. The bulk is perfectly periodic and ordered, whereas the surface shows a distortion due to the rotation or deformation of the WO6 octahedra. In Chapter 5, we have studied the electronic structure of the low dimensional molybdenum oxide La2Mo2O7, which is expected to have a charge density wave(CDW)driven metal-insulator transition around 125K. We indeed observed the presence of CDWs in this system, which was observed in the angle-resolved photoemission spectra as back-folding of bands below the transition temperature. We have also studied the temperature evolution of the bands close to the Fermi level and we see a gradually weakening and finally disappearance of the back-folded bands close to and above the transition temperature. We have studied the angle-integrated spectra of this system from which we conclude that La2Mo2O7 is a CDW non-Fermi liquid system. We have also evaluated the total and partial density of states in this system using Vienna ab-initio simulation package. We find the results consistent with our experimental findings. In Chapter 6, we study the metal-insulator transition in another low-dimensional molybdenum oxide KMo4O6, which is expected to show a metal-insulator transition around 120K due to the formation of spin-density waves. We observed back-folding of bands with lower intensities at low temperature, suggesting the formation of spin density waves in the system. The angle-integrated spectra suggested that the system is a non-CDW non-Fermi liquid system. We have also evaluated the density of states and the results are in agreement with our experimental findings. In conclusion we have investigated the electronic structure of different classes of systems and we have given clue to the origin of the metal-insulator transition in these systems.