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341	Caractérisation électrique multi-échelle d'oxydes minces ferroélectriques / Multi-scale electrical characterization of ferroelectric thin films Martin, Simon 12 December 2016 (has links) Les matériaux ferroélectriques sont des matériaux qui possèdent une polarisation spontanée en l'absence de champ électrique, leur conférant plusieurs propriétés intéressantes du point de vue des applications possibles. La réduction de l'épaisseur des couches ferroélectriques vers des films minces et ultra-minces s'est avérée nécessaire notamment en vue de leur intégration dans les dispositifs de la micro et nano-électronique. Cependant, cette diminution a fait apparaître certains phénomènes indésirables au sein des couches minces tels que les courants de fuite. La caractérisation électrique de ces matériaux reste donc un défi afin de comprendre les mécanismes physiques en jeu dans ces films, d'autant qu'une information à l'échelle très locale est maintenant requise. Il est donc nécessaire de faire progresser les techniques de mesure électrique pour atteindre ces objectifs. Durant cette thèse, nous mesurons la polarisation diélectrique de l'échelle mésoscopique jusqu'à l'échelle nanométrique en utilisant des caractérisations purement électriques constituées de mesures Polarisation-Tension, Capacité-Tension et Courant-Tension mais aussi des mesures électromécaniques assurées par une technique dérivée de la microscopie à force atomique et nommée Piezoresponse Force Microscopy. Au cours de nos travaux, nous montrons la limite de certaines techniques de caractérisation classiques ainsi que les artéfacts affectant la mesure électrique ou électromécanique et pouvant mener à une mauvaise interprétation des résultats de mesure. Afin de pousser nos investigations plus loin, nous avons développé de nouvelles techniques de mesure pour s'affranchir de certains signaux parasites dont nous exposerons le principe de fonctionnement. Nous présentons les premières mesures directes de polarisation rémanente à l'échelle du nanomètre grâce à une technique que nous nommons nano-PUND. Ces techniques et méthodes sont appliquées à une variété importante de matériaux tels que Pb(Zr,Ti)O3, GaFeO3 ou BaTiO3 dont, pour certains, la ferroélectricité n'a jamais été démontrée expérimentalement sans ambiguïté. / Ferroelectric materials show a spontaneous dielectric polarisation even in the absence of applied electric field, which confers them interesting possibilities of applications. The reduction of the thickness of ferroelectric layers towards ultra-thin values has been necessary in view of their integration in micro and nano-electronic devices. However, the reduction of thickness has been accompanied by unwanted phenomena in thin layers such as tunneling currents and more generally leakage currents. The electrical characterization of these materials remains a challenge which aims at better understanding the physical mechanisms at play, and requires now a nanometric spatial resolution. To do so, it is thus mandatory to enhance the techniques of electrical measurement. In this work, we measure the dielectric polarisation of ferroelectric films from mesoscopic scale down to the nanometric scale using purely electric characterisation techniques (Polarisation vs Voltage, Capacitance vs Voltage, Current vs Voltage), but also electro-mechanical techniques like Piezoresponse Force Microscopy which derives from Atomic Force Microscopy. We show the limits of several classical techniques as well as the artefacts which affect electrical or electro-mechanical measurement and may lead to an incorrect interpretation of the data. In order to push the investigation further, we have developed and we describe new measurement techniques which aim at avoiding some parasitic signals. We present the first direct measurement of the remnent polarisation at the nanoscale thanks to a technique which we call « nano-PUND ». These techniques and methods are applied to a large variety of materials like Pb(Zr,Ti)O3, GaFeO3 or BaTiO3 which (for some of them), ferroelectricity has not been measured experimentally. Microélectronique Nanoelectronique Oxydes ferroélectriques Couches minces Couches minces ferroélectriques Caractérisation électrique Courant de fuite Microscopie à Force Atomique Piezoresponse Force Microscopy - PFM Titano-Zirconate de plomb - Pb(Zr, Ti)O3 Titanate de Baryum - BaTiO3 Ferrite de galium - GaFeO3 Microelectronics Nanoelectronics Ferroelectric oxide Thin Layer Electrical characterisation Leakage current Atomic Force Microscopy Piezoresponse Force Microscopy - PFM 621.381 620 107 2
342	Theoretical investigation of size effects in multiferroic nanoparticles Allen, Marc Alexander 05 August 2020 (has links) Over the last two decades, great progress has been made in the understanding of multiferroic materials, ones where multiple long-range orders simultaneously exist. However, much of the research has focused on bulk systems. If these materials are to be incorporated into devices, they would not be in bulk form, but would be miniaturized, such as in nanoparticle form. Accordingly, a better understanding of multiferroic nanoparticles is necessary. This manuscript examines the multiferroic phase diagram of multiferroic nanoparticles related to system size and surface-induced magnetic anisotropy. There is a particular focus on bismuth ferrite, the room-temperature antiferromagnetic-ferroelectric multiferroic. Theoretical results will be presented which show that at certain sizes, a bistability develops in the cycloidal wavevector. This implies bistability in the ferroelectric and magnetic moments of the nanoparticles. This novel magnetoelectric bistability may be of use in the creation of an electrically-written, magnetically-read memory element. / Graduate bismuth ferrite bfo nanoparticle nanomagnetism multiferroics optimization magnetism ferroelectric bistability anisotropy surface anisotropy weak ferromagnetism antiferromagnetism Dzyaloshinskii-Moriya interaction cycloid numerical methods condensed matter solid state physics magnetoelectric effect room-temperature multiferroic superexchange magnetic memory spin canting g-type antiferromagnetism Heisenberg Hamiltonian Nelder-Mead L-BFGS-B mathematica python ferroelectricity perovskite antiferromagnet bifeo3 rhombohedral pseudocubic r3c trigonal physics magnetic memory electrically-written memory curie temperature néel temperature materials science
343	Design and Analysis of a Fractional-Slot Concentrated-Wound PM-Assisted Reluctance Motor / Konstruktion och analys av en permanent magnetiserade synkronreluktans motor med koncentrerad lindning Marino, Luigi January 2015 (has links) The aim of this master thesis is to design and analyse a FSCW PMaSynRM (Permanent Magnet assisted Synchronous Reluctance Motor) for industrial applications. The design process includes analytical calculations (initial design and PM amount minimization) and nite element method (FEM) based design optimization. An overcompensated design is proved to be advantageous for a 10-pole reluctance motor. A comparative analysis with other rotor topologies was made, where motor performance, temperature e ects and production costs are taken into account. Detailed curves which describe eciency, power factor and current with respect to ambient temperature are studied for the proposed motor designs at di erent working points. The demagnetization risk is also taken into account and the safe working temperature ranges have been dened for all the considered motors. The results show that the initial motor design with 10 poles/12 slots PMaSynRM with NdFeB magnets has poor performance in terms of eciency and power factor, with huge amount of PM inserted. This is mainly due to the lack of reluctance torque for this relatively higher number of poles solution. Moreover, it has been found in literature and conrmed in this investigation that this negative e ect for the 10-pole motor is amplied due to the presence of the concentrated winding. Indeed, it is shown by simulations that the motor performance is improved by employing 8 poles/12 slots PMaSynRM conguration with a relatively lower NdFeB magnet amount, thanks to the improved rotor anisotropy. The 10 poles/12 slots interior permanent magnet (IPM) and surface mounted permanent magnet (SMPM) topologies present higher performance due to the e ective utilization of PM, mainly or completely producing the torque. Hence, IPM and SMPM do not su er the lack of anisotropy. / Syftet med detta examensarbete ar att utforma och analysera en FSCW PMaSynRM (Permanent Magnet assisted Synchronous Reluctance Motor) for industriella applikationer. Designprocessen omfattar analytiska berakningar (ursprungliga konstruktion och PM belopp minimering) och nita elementmetoden (FEM) baserad design optimering. En overkompenserad design visat sig vara fordelaktigt for en 10-polig reluktansmotor. En jamforande analys med andra rotor topologier gjordes, dar motor prestanda, temperature ekter och produktionskostnader beaktas. Detaljerade kurvor som beskriver e ektivitet, e ektfaktor och strom med avseende pa omgivningstemperatur studeras for de foreslagna motorn for vid olika arbetspunkter. Den avmagnetisering risken ocksa beaktas och sakerhetstemperaturomraden har denierats for alla ansag motorerna. Resultaten visar att den initiala motordesign med 10-polig/12 spar PMaSynRM med NdFeB magneter har daliga e ektivitet och e ektfaktor, med enorma mangder PM insatt. Detta ar framst pa grund av bristen pa reluktansvridmomentet for denna relativt hogre poltal losning. Dessutom har man funnit i litteraturen och bekraftat i denna unders okning att denna negativa e ekt for 10-polig motorn forstarks pa grund av narvaron av den koncentrerade lindningen. Faktum ar att det framgar av simuleringar att motorprestanda forbattras med en 8-polig/12 spar PMaSynRM konguration med en relativt lagre NdFeB magnet belopp, tack vare den forbattrade rotor anisotropi. Den 10-polig/12 spar interior permanentmagnet (IPM) och ytmonterade permanent magnet (SMPM) topologier presentera hogre prestanda tack vare ett e ektivt utnyttjande av PM och deras produktion vridmoment, huvudsakligen eller helt anfortrotts PM effekten. concentrated windings demagnetization distributed windings ferrite finite element method loss distribution natural and over compensation overlaod permanent magnets rare earth magnets (NdFeB) reluctance torque temperature effects torque ripple avmagnetisering ferrit finita elementmetoden fördelade lindningar förlust distribution koncentrerade lindningar momentrippel naturligt och överkompensation permanentmagneter reluktansvridmomentet sällsynta jordmagneter (NdFeB) temperatureffekter överbelastning Annan elektroteknik och elektronik
344	Performance characterisation of duplex stainless steel in nuclear waste storage environment Ornek, Cem January 2016 (has links) The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis. 620.1
345	To Make Iron of Iron : A Comprehensive Analytical Study of Spade Shaped Iron Bars Pappas Adlreburg, Nickolas January 2017 (has links) This thesis aims to provide adequate analytical information on the spade shaped iron bars of Norrland and central Sweden. While their significance has been thoroughly debated for decades, analytical research on them has been confined to cases of single artefacts or theoretical interpretations of their value, meaning and origin. In this study a comprehensive approach is taken into consideration. Based on X-Ray fluorescence (XRF), scanning electron microscopy (SEM) and metallographical analysis this thesis seeks to facilitate new interpretations on quality, production centres and usage based on analytical results. Aiming to settle some of the long lasting questions regarding the artefacts while producing results which can further the discussion by raising new questions, previously unasked. Archaeological Science Archaeometallurgy Spade Shaped Iron Bars X-Ray Fluorescence (XRF) Scanning Electron Microscopy (SEM) Metallography Swedish Archaeology Archaeology in Norrland Scandinavian Iron Age Nordic Iron Age Roman Iron Age Migration Period Vendel Period Prehistoric Metallurgy Slag Iron Bar Currency Bar Bloomery Bloom Iron Bog Iron Limonite Mineral Iron Ores Hematite Magnetite Phosphoric Iron/Steel Prehistoric Steel Ferrite Pearlite Nickel Cobalt Phosphorus Arsenic Magnesium Sulfur Manganese Norrland Middle Norrland Uppland Gästrikland Hälsingland Medelpad Jämtland Södermanland Helgö Torsåker Gåcksätter Alborga Offerdal Selånger Villberga Arbrå Laborativ Arkeologi Arkeometallurgi Spadformiga Ämnesjärn Röntgenfluorescens (XRF) Svepelektronmikroskop (SEM) Metallografi Svensk Arkeologi Norrländsk Arkeologi Förnnordisk Arkeologi Skandinavisk Järnålder Nordisk Järnålder Fornnordisk Järnålder Romersk Järnålder Folkvandringstiden Vendeltiden Forhistorisk Metallurgi Slaget Ämnesjärn Blästerugn Blästa Myrmalm Sjömalm Limonit Bergmalm Hematit Magnetit Fosforisk Järn/Stål Förhistorisk Stål Ferrit Pearlit Nickel Kobolt Fosfor Arsen Magnesium Svavel Mangan Norrland Mellannorrland Uppland Gästrikland Hälsingland Medelpad Jämtland Södermanland Helgö Torsåker Gåcksätter Alborga Offerdal Selånger Villberga Arbrå Archaeology Arkeologi

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