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Novokhatska, A. O., G. Ya Akimov, A. V. Zhebel, O. I. Linnik, V. T. Dovgiy, and V. V. Burkhovetskiy. "Forming of Nanoscale Structure in Manganite Ceramics with Superstoichiometric Manganese." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35335.
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The new method for obtaining of the nanoscale structure by means of superstoichiometric manganese
in lanthanum manganite (La0.65Sr0.35)1 – xMn1 + xO3 +_ Δ (x = 0, 0.1, 0.2) ceramics sintered at 1500 °C is developed.
The increasing of x content from 0.1 to 0.2 leads to forming internal nanosize multilayer structure of
ceramic grains with layer size of 190 and 280 nm, respectively. The correlation between such nanostructure
and magnetoresistive properties is revealed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35335
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Chen, Chun-che. "Correlation between electrical and magnetic properties in alkali and alkaline earth metal doped lanthanum manganites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Cooper, Celeste Eaton. "Degradation in Performance of Lanthanum Strontium Manganite Based Solid Oxide Fuel Cell Cathodes Under Accelerated Testing." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1485524881843845.
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Yang, Jun. "Studies on Polarization Behavior and Microstructure of Strontium-doped Lanthanum Manganite Cathodes for Solid Oxide Fuel Cells." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/151984.
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Mishra, Snigdharaj K. "Mean-field and density-functional studies of charge ordering and magnetic transitions in lanthanum manganites /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841176.
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Jin, Tongan. "Interactions of the Air Electrode with Electrolyte and Interconnect in Solid Oxide Cells." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/39223.
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The interactions between different components of solid oxide cells (SOCs) are critical issues for achieving the tens of thousands of hourâ s goal for long-term performance stability and lifetime. The interactions between the ceramic electrolyte, porous ceramic air electrode, and metallic interconnect materials â including solid state interfacial reactions and vaporization/deposition of some volatile elements â have been investigated in the simulated SOC operating environment. The interactions demonstrate the material degradation mechanisms of the cell components and the effects of different factors such as chemical composition and microstructure of the materials, as well as atmosphere and current load on the air electrode side. In the aspect of materials, this work contributes to the degradation mechanism on the air electrode side and provides practical material design criteria for long-term SOC operation.
In this research, an yttria-stabilized zirconia electrolyte (YSZ)/strontium-doped lanthanum manganite electrode (LSM)/AISI 441 stainless steel interconnect tri-layer structure has been fabricated in order to simulate the air electrode working environment of a real cell. The tri-layer samples have been treated in dry/moist air atmospheres at 800°C for up to 500 h. The LSM air electrode shows slight grain growth, but the growth is less in moist atmospheres. The amount of Cr deposition on the LSM surface is slightly more for the samples thermally treated in the moist atmospheres. At the YSZ/LSM interface, La enrichment is significant while Mn depletion occurs. The Cr deposition at the YSZ/LSM interface is observed.
The stoichiometry of the air electrode is an important factor for the interactions. The air electrode composition has been varied by changing the x value in (La0.8Sr0.2)xMnO3 from 0.95 to 1.05 (LSM95, LSM100, and LSM105). The enrichment of La at the YSZ/LSM interface inhibits the Cr deposition. The mechanisms of Cr poisoning and LSM elemental surface segregation are discussed.
A 200 mA·cm-2 current load have been applied on the simulated cells. Mn is a key element for Cr deposition under polarization. Excessive Mn in the LSM lessens the formation of La-containing phases at the YSZ/LSM interface and accelerates Cr deposition. Deficient Mn in LSM leads to extensive interfacial reaction with YSZ forming more La-containing phase and inhibiting Cr deposition.Ph. D.
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Esteve, David. "Développement d'une technique de caractérisation optique appliquée au suivi in situ de la croissance d'oxydes fonctionnels par ablation laser pulsé." Paris 11, 2010. http://www.theses.fr/2010PA112385.
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Une instrumentation optique entièrement statique permettant le suivi in situ de la croissance d'oxydes fonctionnels par ablation laser pulsé, est présenté. Au travers de l'étude de deux système modèles, que sont la croissance de films minces de La₀. ₆₇Sr₀. ₃₃LMnO₃ sur des pseudo-substrats de SrTiO₃/Si et de couches minces de SrRuO₃ déposées sur des substrats de SrTiO₃ vicinaux, le dispositif proposé permet d'obtenir une précision de mesure sur les épaisseurs de l'ordre de la maille atomique (4Å), d'extraire les paramètres physiques de diffusion des espèces en surface (énergie d'activation de diffusion), mais aussi d'observer et d'identifier les modes de croissance. Ces résultats sont en parfait accord avec la simulation numérique développée, reposant sur des modèles de traitement de réflectivité de systèmes multi couches combiné avec la théorie des milieux effectifsA fully static set up allowing in situ observation of the growth of functionnal oxides grown by pulsed laser deposition, is presented. Through the study of two model systems, those are the growth of thin films of La₀. ₆₇Sr₀. ₃₃LMnO₃ on pseudo-substrate of SrTiO₃/Si and thin layers of SrRuO₃ grown on vicinal substrate of SrTiO₃, the proposed instrumentation permit to achieve a precision about one unit cell (4Å) on thickness measurments, to extract physical parameters of the diffusion of species on the surface (activation energy of diffusion), but also observing and identifying growth modes. These results are in good agreement with the numerical simulation developped, based on the treatment of the reflectivity of multi-layers systems combined with effective medium theory
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Devenson, Jelena. "Fabrication and investigation of heterostructures based on lanthanum manganites." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091008_155508-20318.
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In this dissertation application of the lanthanum manganite films and their heterostructures for fabrication of new spintronic devices is discussed. The main subjects of this work are the junctions between lanthanum manganite oxide thin films doped by divalent (Ca, Ba, Sr) and tetravalent (Ce) ions as well heterojunctions formed between lanthanum manganites and n-type SrTiO3Disertacijoje nagrinėjamos įvairios galimybės panaudoti feromagnetinių oksidų – manganitų sluoksnius bei jų darinius naujų spintronikos prietaisų gaminimui. Šio darbo pagrindiniu tyrimo objektu pasirinktos sandūros, sudarytos tarp dvivalenčiais (Ca, Ba, Sr) ir keturvalenčiais (Ce) jonais legiruotų lantano mangano oksidų plonųjų sluoksnių, o taip pat tarp manganitų ir elektroninio laidumo SrTiO3
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Beyreuther, Elke. "Photon-assisted spectroscopy of electronic interface states in perovskite oxide heterostructures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1198071350768-13837.
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Complex oxides are an intriguing field of solid-state research, as they can exhibit a wide variety of functional properties, such as ferroelasticity, ferroelectricity, ferro- and antiferromagnetism or an even more complicated type of magnetic ordering, the combination or interaction of those ferroic properties (multiferroicity), high spin polarization, or high-temperature superconductivity. Thus they are prospective candidates for future materials in microelectronics. It is a matter of fact that the performance of such oxide-based devices depends mainly on transport properties, which in turn depend on the distribution and density of intrinsic or extrinsic electronic interface states across the device structure. The present thesis focuses on the identification and characterization of such electronic properties by two different photoassisted spectroscopy techniques: surface photovoltage spectroscopy and photoelectron spectroscopy. This work especially deals with perovskite oxides, namely with the model perovskite strontium titanate (SrTiO3) as a substrate and three differently doped lanthanum manganite thin films (10-15 nm thickness) grown by pulsed laser deposition (PLD) on the SrTiO3 substrate(La0.7Sr0.3MnO3, La0.7Ca0.3MnO3, La0.7Ce0.3MnO3). The first part aims at the identification of electronic surface and interface states at the free SrTiO3 surface as well as at the three different lanthanum manganite/SrTiO3 interfaces. For that purpose three different experimental realizations of the surface photovoltage spectroscopy technique were implemented and employed: photoelectron spectroscopy under additional optical excitation, the capacitive detection of the photoinduced displacement current in a parallel-plate capacitor geometry under modulated optical excitation, and the classical Kelvin probe technique. The methods are evaluated comparatively with respect to their suitability to analyze the given oxidic interfaces. The main result of this first part is a map of the energetic positions and relaxation time constants of the surface states at the SrTiO3 surface as well as of the interface states at the lanthanum manganite/SrTiO3 interfaces within the SrTiO3 bandgap. The interface states were classified into film- and substrate-induced states and it could be demonstrated that an appropriate annealing procedure can dramatically decrease their densities. The second part tackles the problem of the manganese valence and the doping type of di- and tetravalent-ion-doped LaMnO3. The question whether the insulating parent compound LaMnO3 becomes an electron-doped semiconductor after doping with tetravalent cations such as Ce4+ - which would be in analogy to the well-established hole doping after partial substitution of La3+ by divalent cations such as Sr2+ or Ca2+ - has been discussed controversially in the literature so far. Due to the physics of the manganite crystal lattice the question can also be formulated in a different way: Can part of the manganese ions be driven from the Mn3+ state towards the Mn2+ state without any crystal instabilities or phase separation phenomena? In order to contribute to the clarification of this question, an extensive X-ray- and UV-photoelectron spectroscopy (XPS/UPS) investigation was performed. The three differently doped lanthanum manganite thin films were comparatively studied considering the exchange splitting of the Mn 3s core level line, which is a linear function of the Mn valence, as measured by XPS and the work function as extracted from UPS. All measurements were performed at different states of deoxygenation after heating in ultrahigh vacuum and reoxidation after heating in a pure oxygen atmosphere. Strong evidence for electron doping of the La0.7Ce0.3MnO3 film after deoxygenation was found. Furthermore, the reversible tunability of the Mn valence by variation of the oxygen content could be demonstrated for both tetravalent- and divalent-ion-doped lanthanum manganite filmsOxidische Komplexverbindungen können eine Vielzahl an funktionellen Eigenschaften, wie z.B. Ferroelastizität, Ferroelektrizität, Ferro- und Antiferromagnetismus sowie kompliziertere magnetische Ordnungen, die Kombination und Interaktion solcher ferroischer Eigenschaften (Multiferroizität), hohe Spinpolarisation oder Hochtemperatursupraleitung aufweisen und gelten daher als aussichtsreiche Materialien für die zukünftige Mikroelektronik. Entscheidend für die Funktionsfähigkeit oxidischer Bauelemente sind deren elektronische Transporteigenschaften, die in äußerst sensibler Weise von der Verteilung und Dichte von ex- oder intrinsischen elektronischen Defektzuständen an Grenz- und Oberflächen innerhalb der Bauelementstruktur abhängen. Die vorliegende Arbeit beschäftigt sich mit der Spektroskopie solcher elektronischer Eigenschaften mittels photonenbasierter Methoden. Im Fokus stehen dabei perowskitische Oxide , speziell das Modellperowskit Strontiumtitanat (SrTiO3) als Substrat und darauf mittels gepulster Laserdeposition (PLD) abgeschiedene dünne Filme (10-15 nm Dicke) dotierter Lanthanmanganate (La0.7Sr0.3MnO, La0.7Ca0.3MnO3, La0.7Ce0.3MnO3). Im Rahmen einer halbleiterphysikalischen Interpretation widmet sich der erste Teilder Identifikation elektronischer Ober- und Grenzflächenzustände an der SrTiO3-Oberfläche sowie an verschiedenen Lanthanmanganat/SrTiO3-Grenzflächen mittels dreier unterschiedlicher experimenteller Methoden zur Vermessung der Oberflächenphotospannung: der Photoelektronenspektroskopie unter zusätzlicher optischer Anregung, einer kapazitiven Detektionsmethode in Plattenkondensatorgeometrie unter modulierter optischer Anregung und der optischen Kelvin-Sonde. Neben einem auf die bei oxidischen Ober- und Grenzflächen auftretenden besonderen Herausforderungen zugeschnittenen Methodenvergleich werden Grenzflächenzustände bezüglich ihrer energetischen Position in der Bandlücke des SrTiO3 und ihres Relaxationsverhaltens analysiert, als substrat- oder filminduziert klassifiziert, und die Verringerung ihrer Dichte nach geeigneter Ausheilprozedur wird nachgewiesen. Der zweite Teil der Arbeit befasst sich mit der in der Literatur bisher kontrovers diskutierten Frage, ob sich die isolierende Stammverbindung LaMnO3 durch Dotierung mit tetravalenten Kationen, wie z.B. Ce4+, in einen elektronendotierten Halbleiter verwandeln lässt - analog zur Herstellung lochdotierter Lanthanmanganate durch Dotierung mit divalenten Kationen, wie z.B. Sr2+ oder Ca2+. Die Frage ist äquivalent zur Betrachtung, ob unter Beibehaltung der Stabilität des Kristallgitters ein Teil der Manganionen vom Mn3+-Zustand in den Mn2+-Zustand übergehen kann. Um einen Beitrag zur Klärung dieses Problems zu leisten, wurden als elektronisch sensitive Methoden die Röntgen- und UV-Photoelektronenspektroskopie (XPS/UPS) gewählt. Die oben genannten Lanthanmanganatfilme wurden dazu hinsichtlich der Austauschaufspaltung der Mangan-3s-Linie im XP-Spektrum, die in linearer Weise von der Manganvalenz abhängt, und der anhand der Breite des UP-Spektrums ermittelten Austrittsarbeit jeweils nach Reinigung der Oberfläche im Ultrahochvakuum (UHV) vergleichend untersucht. Die Messungen wurden nach unterschiedlich starker Desoxidation durch Heizen im UHV und Reoxidierung durch Heizen in Sauerstoffatmosphäre durchgeführt. Es konnte nachgewiesen werden, dass eine Elektronendotierung des La0.7Ce0.3MnO3-Films bei geeigneter Einstellung des Sauerstoffgehalts tatsächlich möglich ist. Außerdem wurde gezeigt, dass sich sowohl in di- als auch in tetravalent dotierten Lanthanmanganatfilmen die Manganvalenz und damit der Dotierungstyp reversibel durchstimmen lässt
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Berenov, Andrey Valdimirovich. "Cation deficiency in lanthanum manganites." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322303.
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Turcaud, Jeremy. "Magnetocaloric effect and thermal transport management in lanthanum manganites." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/40889.
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This thesis investigates two challenges associated with the use of manganites for magnetocaloric applications. The first challenge is associated with methods to engineer the thermal conductivity, K. The second challenge is to understand the limits of the entropy change achievable in magnetocaloric manganites. Thermal management has been achieved via different microstructuring routes and their influence on thermal transport properties such as K, resistivity and thermopower, have been studied. A factor of two increase in K is demonstrated by using density and grain size optimization, while three-fold and six-fold increases are seen by employing the introduction of a second highly conductive phase via: (1) silver impregnation and silver particle coating and (2) copper electroplating, respectively. Understanding the magnetocaloric effect (MCE) characteristics in manganites has been achieved by bringing together magnetisation, magneto-structural, magneto-Seebeck, and neutron diffraction independent measurements. We first show that the temperature T* up to which a spontaneous magnetisation is observed in the inverse magnetic susceptibility of La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 above Tc, is related to the transition temperature of the low temperature (high-magnetic field and high-magnetisation) magnetic phase. In the most widely studied La(1-x)CaxMnO3 (x = 0.2, 0.25, 0.3), we then conclude that unlike between the degree of static Jahn-Teller distortion and the interval [T*-Tc]/Tc where we show that there exists a close relationship, there is no apparent correlation between the magnitude of the MCE and [T*-Tc]/Tc . We then unravel the competing strength of the various degrees of freedom and show that the inhibition of a large magnetocaloric response is due to the strong correlations that underpin the collosal magnetoresistance effect: both clustering of magnetic Mn atoms due to polaron formation and the insulator to metal transition. Finally we discuss prospects to improve material properties for application in light of these findings.
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Jorgensen, Mette Juhl. "Lanthanum manganate based cathodes for solid oxide fuel cells." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343243.
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Chiba, Rubens. "Síntese, processamento e caracterização das meia-células de óxido sólido catodo/eletrólito de manganito de lantânio dopado com estrôncio/zircônia estabilizada com ítria." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-29082011-141252/.
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Os filmes cerâmicos de manganito de lantânio dopado com estrôncio (LSM) e de manganito de lantânio dopado com estrôncio/zircônia estabilizada com ítria (LSM/YSZ) são utilizados como catodos das células a combustível de óxido sólido de temperatura alta (CaCOSTA). Estes filmes cerâmicos porosos foram depositados sobre o substrato cerâmico denso de YSZ, utilizado como eletrólito, componente estrutural do módulo, assim conferindo uma configuração de meia-célula denominada auto-suporte. O estudo da meia-célula é fundamental, pois na interface catodo/eletrólito ocorre a reação de redução do oxigênio, conseqüentemente influenciando no desempenho da CaCOSTA. Neste sentido, o presente trabalho contribui para a síntese de pós de LSM e LSM/YSZ e para o processamento de filmes finos, utilizando a técnica de pulverização de pó úmido, adotada para a conformação dos filmes cerâmicos por permitir a obtenção de camadas porosas com espessuras variadas na ordem de micrômetros. Os pós de LSM foram sintetizados pela técnica de citratos e os pós de LSM/YSZ pela técnica de mistura de sólidos. Na etapa de conformação foram preparadas suspensões orgânicas de LSM e LSM/YSZ alimentada por gravidade em um aerógrafo manual. Para a conformação do substrato de YSZ utilizou-se uma prensa uniaxial hidráulica. Foram possíveis a obtenção das meia-células de óxido sólido catodo/eletrólito de estruturas cristalinas hexagonal para a fase LSM e cúbica para a fase YSZ. E as micrografias das meia-células mostram que o substrato YSZ é denso, suficiente para ser utilizado como eletrólito sólido, e os filmes de LSM e LSM/YSZ apresentam-se porosos com espessura de aproximadamente 30 μm e com boa aderência entre os catodos e o eletrólito. A presença do catodo compósito entre o catodo LSM e o substrato YSZ, possibilitou um aumento no desempenho eletroquímico na reação de redução do oxigênio.The ceramic films of strontium-doped lanthanum manganite (LSM) and strontiumdoped lanthanum manganite/yttria-stabilized zirconia (LSM/YSZ) are used as cathodes of the high temperature solid oxide fuel cells (HTSOFC). These porous ceramic films had been deposited on the YSZ dense ceramic substrate, used as electrolyte, structural component of the module, thus conferring a configuration of half-cell called auto-support. The study of the half-cell it is basic, therefore in the interface cathode/electrolyte occurs the oxygen reduction reaction, consequently influencing in the performance of the HTSOFC. In this direction, the present work contributes for the processing of thin films, using the wet powder spraying technique, adopted for the conformation of the ceramic films for allowing the attainment of porous layers with thicknesses varied in the order of micrometers. The LSM powders were synthesized by the citrate technique and the LSM/YSZ powders synthesized by the solid mixture technique. In the stage of formation were prepared organic suspensions of LSM and LSM/YSZ fed by gravity in a manual aerograph. For the formation of the YSZ substrate was used a hydraulical uniaxial press. The attainment of solid oxide half-cells cathode/electrolyte was possible of crystalline structures hexagonal for phase LSM and cubic for phase YSZ. The half-cells micrographs show that the YSZ substrate is dense, enough to be used as solid electrolyte, and the LSM and LSM/YSZ films are presented porous with approximately 30 μm of thickness and good adherence between the cathodes and the electrolyte. The presence of composite cathode between the LSM cathode and YSZ substrate, presented an increase in the electrochemical performance in the oxygen reduction reaction.
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Drevet, Corinne. "Réaction d'électrode à oxygène sous densité de courant et pression d'oxygène élevées : application : compresseur électrochimique à oxygène." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0159.
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La mise au point d'un compresseur electrochimique a oxygene, entierement statique, presente un double interet: d'une part comme generateurs d'oxygene embarques pour l'aviation et, d'autre part, dans des minirefroidisseurs pour applications en optronique dans le domaine militaire ou spatial. Sur le plan pratique, un prototype a ete concu et realise. Il se presente sous forme d'un tube a fond ferme de zircone stabilisee, revetu d'electrodes en platine ; la temperature de fonctionnement est de 800c. Les tests effectues ont confirme la faisabilite d'un tel prototype: une pression de 100 bar a ete obtenue et l'etancheite du systeme a ete verifie sur plus d'un mois. L'augmentation du debit d'oxygene necessite de travailler sous fortes densites de courant. Les resultats permettent d'assurer, qu'avec une optimisation des conditions de preparation et de depot des electrodes en manganite de lanthane, des densites de courant superieures a 1 acm#-#2 peuvent etre utilisees sur de longue duree. Sur le plan theorique, l'etude de la reaction d'electrode sur le platine, l'argent et le manganite de lanthane, presentant des comportements tres differents vis a vis de l'oxygene, a ete effectuee sous tres fortes pressions (jusqu'a 100 bar)
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Marques, Rodrigo Fernando Costa [UNESP]. "Manganita de lantânio dopada com estrôncio obtida por coprecipitação homogênea: magnetorresistência e magnetorrefletividade." Universidade Estadual Paulista (UNESP), 2003. http://hdl.handle.net/11449/102595.
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marques_rfc_dr_araiq.pdf: 3201564 bytes, checksum: 52e1050410ca60bb9191ed79b606558e (MD5)Manganita de lantânio dopada com estrôncio (La1-xSrxMnO3) tem recebido atenção da comunidade científica por apresentar propriedades elétricas e magnéticas, com funções para sensores de campo, catalisadores, eletrodos em células combustíveis, entre outras. A substituição de La3+ por Sr2+ resulta em uma transição de um estado isolante antiferromagnético para um estado metálico ferromagnético em composições de x³0,17 com valência mista Mn3+-Mn4+ responsável pelos portadores de carga. Na presença de campo magnético externo as manganitas dopadas exibem a propriedade magnetoresistência negativa gigante (GMR) e a resistividade do material varia com a temperatura e com o campo magnético aplicado. Este trabalho descreve a síntese de nanopartículas de La1-xSrxMnO3 (x=0,1; 0,2 e 0,3) pelo método da coprecipitação homogênea usando uréia como agente precipitante. Neste método, novos ligantes, tais como NH4 +, OH- e CO3 2-, podem substituir as moléculas de água nas posições de coordenação delas com os íons metálicos. Este método leva a uma nucleação homogênea prevenindo o crescimento das partículas precursoras. A dependência da magnetização DC com a temperatura para as amostras La1-xSrxMnO3 (x=0,1; 0,2 e 0,3) forneceu valores de temperatura crítica (TC) iguais a 140 K, 316 K e 357 K, respectivamente. A dependência da resistividade elétrica com a temperatura para pastilhas destes materiais apresentaram a transição metal-isolante e os valores encontrados para TC são similares aos valores de TC observados em monocristais destas manganitas. Espectroscopia infravermelho foi realizada para estudar as propriedades de transporte...
Lanthanum strontium-doped manganite (La1-xSrxMnO3) has attracted renewed attention at present due to the observation of interesting electrical and magnetic properties such as a giant negative magnetoresistance (GMR), catalytic, oxygen cathode reduction, field-sensing, among others. The substitution of La3+ ions by Sr2+ results in a transition from antiferromagnetic insulating state to a ferromagnetic metallic state at x ³ 0.17 with a Mn3+-Mn4+ mixed valence state responsible for the mobile charge carriers. This work describes the La1-xSrxMnO3 (0.1, 0.2 and 0.3) nanoparticle synthesis by the homogenous coprecipitation method using urea as precipitant agent. In this method, some new ligands like NH4+, OH- and CO3 2- can substitute the water molecules coordinating the metallic ions. This method allows the homogenous nucleation and prevents the particle precursors to grow. The temperature dependence of DC magnetization of the samples La1-xSrxMnO3 and critical temperature (TC) values were found to be 140 K, 316 K and 357 K, respectively for x = 0.1, 0.2 and 0.3. Temperature dependence of the electrical resistivity exhibits a metalinsulator transition at Tc in pellet samples and Tc values were found to be similar to those observed in single crystals of these manganitas. Infrared spectroscopy was performed to study spin dependent transport properties using the magnetorefractive effect (MRE), which probes the change of reflection in the infrared (IR) spectral region due to the change in electrical conductivity in the presence of a magnetic field. In the IR spectral region, the free carrier dispersion mechanism often dominates and MRE have been used to study intraband transitions of the conduction...(Complete abstract, click electronic access below)
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Marques, Rodrigo Fernando Costa. "Manganita de lantânio dopada com estrôncio obtida por coprecipitação homogênea : magnetorresistência e magnetorrefletividade /." Araraquara : [s.n.], 2003. http://hdl.handle.net/11449/102595.
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Resumo: Manganita de lantânio dopada com estrôncio (La1-xSrxMnO3) tem recebido atenção da comunidade científica por apresentar propriedades elétricas e magnéticas, com funções para sensores de campo, catalisadores, eletrodos em células combustíveis, entre outras. A substituição de La3+ por Sr2+ resulta em uma transição de um estado isolante antiferromagnético para um estado metálico ferromagnético em composições de x³0,17 com valência mista Mn3+-Mn4+ responsável pelos portadores de carga. Na presença de campo magnético externo as manganitas dopadas exibem a propriedade magnetoresistência negativa gigante (GMR) e a resistividade do material varia com a temperatura e com o campo magnético aplicado. Este trabalho descreve a síntese de nanopartículas de La1-xSrxMnO3 (x=0,1; 0,2 e 0,3) pelo método da coprecipitação homogênea usando uréia como agente precipitante. Neste método, novos ligantes, tais como NH4 +, OH- e CO3 2-, podem substituir as moléculas de água nas posições de coordenação delas com os íons metálicos. Este método leva a uma nucleação homogênea prevenindo o crescimento das partículas precursoras. A dependência da magnetização DC com a temperatura para as amostras La1-xSrxMnO3 (x=0,1; 0,2 e 0,3) forneceu valores de temperatura crítica (TC) iguais a 140 K, 316 K e 357 K, respectivamente. A dependência da resistividade elétrica com a temperatura para pastilhas destes materiais apresentaram a transição metal-isolante e os valores encontrados para TC são similares aos valores de TC observados em monocristais destas manganitas. Espectroscopia infravermelho foi realizada para estudar as propriedades de transporte...(Resumo completo, clicar acesso eletrônico abaixo)Abstract: Lanthanum strontium-doped manganite (La1-xSrxMnO3) has attracted renewed attention at present due to the observation of interesting electrical and magnetic properties such as a giant negative magnetoresistance (GMR), catalytic, oxygen cathode reduction, field-sensing, among others. The substitution of La3+ ions by Sr2+ results in a transition from antiferromagnetic insulating state to a ferromagnetic metallic state at x ³ 0.17 with a Mn3+-Mn4+ mixed valence state responsible for the mobile charge carriers. This work describes the La1-xSrxMnO3 (0.1, 0.2 and 0.3) nanoparticle synthesis by the homogenous coprecipitation method using urea as precipitant agent. In this method, some new ligands like NH4+, OH- and CO3 2- can substitute the water molecules coordinating the metallic ions. This method allows the homogenous nucleation and prevents the particle precursors to grow. The temperature dependence of DC magnetization of the samples La1-xSrxMnO3 and critical temperature (TC) values were found to be 140 K, 316 K and 357 K, respectively for x = 0.1, 0.2 and 0.3. Temperature dependence of the electrical resistivity exhibits a metalinsulator transition at Tc in pellet samples and Tc values were found to be similar to those observed in single crystals of these manganitas. Infrared spectroscopy was performed to study spin dependent transport properties using the magnetorefractive effect (MRE), which probes the change of reflection in the infrared (IR) spectral region due to the change in electrical conductivity in the presence of a magnetic field. In the IR spectral region, the free carrier dispersion mechanism often dominates and MRE have been used to study intraband transitions of the conduction...(Complete abstract, click electronic access below)
Orientador: Miguel Jafelicci Junior
Coorientador: Carlos de Oliveira Paiva Santos
Doutor
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Maurin, Isabelle. "Effets de non-stoechiometrie et de granularite dans les manganites de lanthane." Palaiseau, Ecole polytechnique, 2000. http://www.theses.fr/2000EPXX0004.
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La magnetoresistance geante (mrg) des manganites de structure perovskite pourrait ouvrir leur champ d'application a la detection magnetique. Les champs necessaires a des variations de resistance consequentes restent cependant trop eleves. L'objet de ce travail est l'etude des proprietes magnetoresistives des manganites granulaires qui revelent une composante mr bas champ au-dessous de leur temperature de curie, effet commun aux materiaux ferromagnetiques polycristallins. Des ceramiques ont ete elaborees par chimie douce, pour des tailles de grains comprises entre 20 nm et 10 m. Ces grains sont assimilables a des heterostructures cur-coquille. Pour les plus faibles tailles de grains, la contribution de la surface domine. Une seconde transition isolant-metal apparait et les courbes de resistivite sous champ presentent une hysteresis differente de celle des cycles d'aimantation. La connexion entre grains a ete modifiee par irradiation aux electrons. Il y a alors endommagement des joints de grains, les paires de frenkel s'y formant preferentiellement ou venant s'y segreguer au recuit. Une partie des jonctions sont rompues, induisant des effets de percolation et une augmentation de la composante mr bas champ au voisinage de la transition ferromagnetique. Les echantillons synthetises a basse temperature presentent des lacunes cationiques. Pour separer les effets de granularite et de non-stchiometrie, le systeme non substitue la 1 xmn 1 xo 3 a ete etudie. Pour des teneurs croissantes en lacunes, les spectres d'absorption des rayons x au seuil k du manganese montrent un deplacement du seuil d'absorption vers les hautes energies, indiquant une augmentation de la densite de porteurs de charge. Ces defauts ne conduisent toutefois pas a un dopage type aliovalent. L'analyse quantitative des spectres demontre le piegeage d'une partie des porteurs pour les fortes teneurs en defauts. Il y a egalement reduction de la mobilite des porteurs libres, d'apres des mesures d'effet seebeck.
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Huber, Anne-Katrin, Sven Ole Steinmüller, Eva Mutoro, Bjoern Luerßen, and Jürgen Janek. "In situ examination of Lanthanum Strontium Manganate (LSM) with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186860.
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Huber, Anne-Katrin, Sven Ole Steinmüller, Eva Mutoro, Bjoern Luerßen, and Jürgen Janek. "In situ examination of Lanthanum Strontium Manganate (LSM) with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)." Diffusion fundamentals 12 (2010) 52, 2010. https://ul.qucosa.de/id/qucosa%3A13889.
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CHIBA, RUBENS. "Obtencao e caracterizacao de manganito de lantanio dopado com estroncio para aplicacao em celulas a combustivel de oxido solido." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11234.
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Dissertacao (Mestrado)
IPEN/D
Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP
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Sun, Zhe. "Angle-resolved photoemission studies on bi-layer colossal magnetoresistive oxides lanthanum(2-2x)strontium(1+2x)manganese(2)oxide(7)." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239456.
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Pajot, Martin. "Nouveaux matériaux à conduction mixte à basse température pour pile à combustible de type SOFC à base de bismuth." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R049.
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Dans le contexte actuel du mix énergétique, les piles à combustible sont des dispositifs prometteurs. Ils permettent de générer de l’énergie électrique à partir d’un combustible par réaction électrochimique mais aussi de produire juste de l’eau comme sous-produit quand le dihydrogène est utilisé comme combustible. Parmi les différents types de pile à combustible actuellement développés, les piles à oxyde solide, Solid Oxide Fuel Cell en anglais, SOFC, présentent l’avantage de fournir une flexibilité importante sur la nature du combustible utilisable (hydrogène, méthane, méthanol, …) ainsi qu’une résistance accrue aux impuretés (monoxyde de carbone, soufre, …) comparé aux autres technologies. Toutefois, l’inconvénient de ce type de système est leur température de fonctionnement trop élevée, typiquement au dessus de 700 °C, qui génère des contraintes et des problèmes de durabilité. Cependant, une étude récente a montré qu’en utilisant un électrolyte bicouche, formé à partir d’une phase stabilisée de l’oxyde de bismuth protégée par une couche de cérine dopée, il serait possible d’abaisser les températures de fonctionnement jusqu’à 350 °C. Néanmoins, pour le développement de ce type de dispositif, l’identification de matériaux de cathode bas coût, compatibles avec l’oxyde de bismuth, reste un verrou à lever. La recherche de matériaux de ce type constitue l’objet de ce travail de thèse. Pour l’électrolyte, au regard des travaux réalisés antérieurement, l’oxyde de bismuth stabilisé à l’erbium de formulation (Bi2O3)0,75(Er2O3)0,25, appelé ESB dans le manuscrit, a été choisi. Après une analyse bibliographique des travaux menés sur ce type de pile, l’élaboration de l’électrolyte est décrite dans le deuxième chapitre avec un accent mis sur l’intérêt d’un broyage des oxydes avec de l’acétone pour permettre un abaissement des températures d’accroche des matériaux d’électrode sur l’électrolyte. Dans un second temps, l’étude du manganite de lanthane de formulation La1-xSrxMnO3 (LSM) en composite avec ESB a été reprise. Alors que les travaux antérieurs portaient essentiellement sur les compositions x = 0,15 - 0,20, une large gamme de compositions (x = 0,15 ; 0,30 ; 0,40 ; 0,50 ; 0,60 et 0,80) a été considérée. Après avoir optimisé l’épaisseur de l’électrode ainsi que la proportion entre les deux matériaux constituant le composite pour la composition x = 0,20 (épaisseur optimale comprise entre 50 µm et 60 µm et proportion optimale de 50 % en masse de chaque constituant), des cellules symétriques de type ESB La1 xSrxMnO3|ESB|ESB La1 xSrxMnO3 ont été élaborées. A basse température, la résistance spécifique surfacique est diminuée de presque 50 % lorsqu’un composite ESB La0,60Sr0,40MnO3 est utilisé en regard d’un composite ESB La0,85Sr0,15MnO3, conventionnellement utilisé à haute température. Enfin dans un troisième temps, un grand nombre de matériaux, choisis en fonction de leur paramètres structuraux tels que Ca3Co4O9, Bi2Ca2Co3O9 ou encore Bi2Sr2Co2O9, ou bien de leurs propriétés de conduction électronique tel que Bi2Sr2-xLaxCuO6+δ pour x = 1 et x = 0,40 ou leur propriété de conduction mixte tel que NaBi25Cr10O78 ou encore Bi38Cr7O68 ont été testés. Bien que ces études n’en soient qu’à un stade préliminaire, plusieurs compositions apparaissent prometteuses, en particulier Bi2Ca2Co3O9 ou encore Bi14CrO24, produit de décomposition de Bi38Cr7O68 lui-même intéressantIn the current context of the energy mix, fuel cells are promising devices. They make it possible to generate electrical energy from a fuel by electrochemical reaction but also to produce just water as a by-product when hydrogen is used as fuel. Of the different types of fuel cells currently being developed, Solid Oxide Fuel Cell (SOFC) offers the advantage of providing significant flexibility on the nature of the usable fuel (hydrogen, methane, methanol, etc.) as well as increased resistance to impurities (carbon monoxide, sulfur, ...) compared to other technologies. However, the disadvantage of this type of system is the too high operating temperature, typically above 700 °C, which generates constraints and durability problems. However, a recent study has shown that by using a bilayer electrolyte, formed of a stabilized bismuth oxide protected by a layer of doped ceria, it would be possible to lower the operating temperatures down to 350 °C. Nevertheless, for the development of this type of device, the identification of low cost cathode materials, compatible with bismuth oxide, remains bottleneck. The search for this type of material is the subject of this thesis work. For the electrolyte, with regard to the work carried out previously, erbium stabilized bismuth oxide of formulation (Bi2O3)0.75(Er2O3)0.25, called ESB in the manuscript, was chosen. After a bibliographic analysis of the work carried out on this type of cells, the elaboration of the electrolyte is described in the second chapter with an emphasis on the interest of grinding the oxides in acetone to allow a lowering of the sintering temperatures of the electrode materials on the electrolyte. In a second step, the study of lanthanum manganite La1-xSrxMnO3 (LSM) in composite with ESB was undertaken. While previous work focused on compositions x = 0.15 - 0.20, a wide range of compositions (x = 0.15, 0.30, 0.40, 0.50, 0.60 and 0.80) was considered. After having optimized the thickness of the electrode as well as the proportion between the two materials constituting the composite for the composition x = 0.20 (optimum thickness between 50 μm and 60 μm and optimal proportion of 50 % by weight of each constituent), ESB La1 xSrxMnO3|ESB|ESB-La1-xSrxMnO3 ESB symmetric cells were developed. At low temperature, the specific surface resistance is reduced by almost 50 % when a composite ESB La0.60Sr0.40MnO3 is used in comparison with a ESB-La0.85Sr0.15MnO3 composite, conventionally used at high temperature. Finally, in a third step, a large number of materials, chosen according to their structural parameters such as Ca3Co4O9, Bi2Ca2Co3O9 or Bi2Sr2Co2O9, or their electronic conduction properties such as Bi2Sr2-xLaxCuO6+δ for x = 1 and x = 0.40 or their mixed conduction property such as NaBi25Cr10O78 or Bi38Cr7O68 were tested. Although these studies are only at a preliminary stage, several compositions appear promising, in particular Bi2Ca3Co2O9 or else Bi14CrO24, decomposition product of Bi38Cr7O68 itself
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Bertrand, Gregory. "Films minces de manganites de lanthane (LaxMnyO 3 + δ) sur zircone yttriée ((100)YSZ) comme modèle de demi-pile à combustible à oxydes solides (SOFC) : élaboration par LP-MOCVD et propriétés interfaciales." Dijon, 2000. http://www.theses.fr/2000DIJOS036.
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Ce travail de thèse a pour objectif la réalisation d'un système modèle de demi-pile à combustible à oxydes solides (SOFC) adapté à l'étude de la réaction de dégradation à haute température de l'interface entre la cathode et l'électrolyte, respectivement LaMnO 3 (LM) et ZrO 2 : 9. 5 mol. % y 2o 3 (YSZ). Ces matériaux sont représentatifs de ceux utilisés dans la technologie SOFC fonctionnant dans un domaine de température compris entre 850 et 1000°C. Les performances et la durée de vie des piles dépendent fortement de la réactivité entre LM et YSZ qui est fonction du rapport cationique La/Mn. Ce travail a pour but de détecter la formation de la phase inhibitrice La2 Zr2 O7 (LZ) à l'interface cathode - électrolyte, en fonction du rapport La/Mn et d'en analyser les mécanismes de formation. Notre approche se singularise par le choix du procédé de synthèse en couche mince de la cathode, par sublimation contrôlée de précurseurs métalloorganiques solides ou LP-MOCVD. La synthèse directe à 600°C et l'utilisation d'un substrat monocristallin de YSZ a permis d'élaborer un système modèle idéal pour l'étude de la réactivité de l'interface LM/(100)YSZ. Cette phase de synthèse s'appuie sur une étude fondamentale des cinétiques de sublimation des précurseurs solides de La et de Mn permettant une optimisation du procédé de dépôt. La réactivité de ces assemblages a été abordée à partir de trois séries de compositions chimiques La/Mn choisies. La microscopie Auger à balayage associée à la diffraction électronique et la diffraction des rayons X en incidence rasante ont permis à la fois de préciser la chimie et les relations cristallographiques de l'interface. Des données concernant les produits de réaction et leur localisation en fonction de La/Mn et d’analyser les mécanismes de cette formation sont présentées.
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CHIBA, RUBENS. "Sintese, processamento e caracterizacao das meia-celulas de oxido solido catodo/eletrolito de manganito de lantanio dopado com estroncio/zirconia estabilizada com itria." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9503.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Hammami, Ramzi. "Les manganites de lanthane LarMnO3+y 0. 8≤ r≥1. 25 : approches théorique et expérimentale des propriétés structurales et superficielle." Paris 6, 2010. http://www.theses.fr/2010PA066041.
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Les oxydes mixtes de manganite de lanthane de formule LarMnO3+y (0. 8≤r≤1. 25) ont été synthétisés avec des rapports atomiques bien contrôlés. Quel que soit le rapport atomique La/Mn compris entre 0. 8 et 1. 25, les structures cristallines sont décrites dans le système rhomboédrique. L’analyse chimique révèle que le manganèse est dans un état d’oxydation supérieur à +III et que selon le rapport La/Mn, les échantillons sont sur ou sous stœchiométriques en oxygène. Les énergies de formation de plusieurs types de défauts ont pu être déterminées à l’aide d’une approche théorique Ces résultats expérimentaux et théoriques ont été mis à profit pour proposer une distribution des défauts en fonction du rapport La/Mn. Les trois défauts qui ont permis de décrire l’écart à la stœchiométrie dans la série d’échantillons sont des vacances cationiques de La et de Mn, des vacances cationiques de Mn et anioniques et des vacances cationiques de La et anioniques. Les concentrations des défauts [VLa3’], [VMn3’] ; [VO. . ] et [h. ] sont déduites et leurs variations en fonction du rapport La/Mn sont étudiées. Les propriétés superficielles des échantillons synthétisés sont étudiées par la technique XPS, l’adsorption de CO2 et le test catalytique de combustion du méthane. L’étude théorique de l’adsorption de CO2 a été entreprise. L’ensemble des résultats obtenus corrobore la présence de plusieurs sites actifs avec un avec un spectre énergétique suffisamment large pour que la surface des manganites de lanthane soit considérée comme hétérogène. Les performances catalytiques déterminées dans la réaction de combustion du méthane se sont avérées sensibles à l'écart à la stœchiométrie.
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Lauret, Hervé. "Propriétés électriques et électrochimiques de manganites de lanthane dopées comme matériau de cathode pour pile à combustible à oxyde électrolyte solide." Grenoble INPG, 1994. http://www.theses.fr/1994INPG0053.
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Ce travail consiste en l'etude de materiaux de cathode pour les piles a combustible haute temperature. Ces materiaux ont pour formule generale la1-xsrxmno3 et (la1-yyy)0,5sr0,5mno3. Dans un premier chapitre nous faisons le point sur l'etat des recherches sur les piles a combustible a oxyde electrolyte solide et leurs constituants. Le deuxieme chapitre presente la synthese des echantillons ainsi que les differents dispositifs de mesures. Le chapitre trois est consacre a la caracterisation physique et electrique des echantillons. Nous avons montre en particulier que le dopage a l'yttrium diminuait le coefficient de dilatation thermique des manganites de lanthane. Pour les echantillons exempts d'yttrium une conductivite maximale est obtenue pour x=0,55. Une etude sur la reaction de reduction de l'oxygene a l'interface la1-xsrxmno3/y2o3-zro2 est menee dans le chapitre quatre. Nous confirmons l'apparition d'un effet electrocatalytique specifique a ce materiau d'electrode. Nous apportons une contribution complementaire a la comprehension du processus d'electrode: l'echantillon qui presente la plus grande activite electrocatalytique est celui qui a la plus forte conductivite electrique. Aux faibles polarisations cathodiques, superieures a -150 mv/air, nous prouvons que l'etape limitante a lieu le long du contact triple. Aux plus fortes polarisations cathodiques nous emettons l'hypothese d'une extension progressive de la reaction sur une zone annulaire autour du perimetre de contact entre le materiau de cathode et l'electrolyte. Enfin, la surface du materiau d'electrode exposee au gaz n'est pas limitante
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Sena, S. P. "An investigation of some magnetic oxides grown by pulsed laser deposition." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287655.
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Ferrandon, Magali. "Mixed metal oxide - noble metal catalysts for total oxidation of volatile organic compounds and carbon monoxide." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3156.
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Bernard, Caroline. "Synthèse hydrothermale d'oxydes La(1-x)Sr(x)MnO(3+8) et ZrO(2)-8%Y(2)O(3) sous forme de poudre et de couches minces et caractérisations." Toulouse 3, 2003. http://www.theses.fr/2003TOU30098.
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Mes travaux de recherche ont pour objectif d'élaborer et d'optimiser les propriétés de matériaux nouveaux sous forme de poudres (ou de couches minces) à rapport surface/volume important. Mon sujet de thèse concerne plus particulièrement la synthèse hydrothermale de manganite de lanthane dopé au strontium La1-xSrxMnO3+d et de zircone yttriée YSZ. En effet cette synthèse à température modérée et sous pression autogène est utilisée depuis longtemps, pour la précipitation ou la cristallisation de poudres alors que son emploi pour le dépôt de films n'est apparu que depuis une dizaine d'années. Dans un premier temps, nous avons abordé la synthèse des poudres. Nous avons ainsi défini les paramètres nécessaires à l'obtention du manganite non dopé monophasé. Les différentes techniques expérimentales classiques ainsi que des méthodes plus originales (W. A. X. S. , S. P. S. , frottement intérieur) utilisées nous ont permis de comprendre les étapes de cristallisation, c'est dire le passage de la poudre brute d'élaboration amorphe à l'oxyde cristallisé. La morphologie et les propriétés des oxydes recuits à différentes températures ont aussi été étudiées. Puis nous avons opté pour la méthodologie de recherches expérimentales, pour la synthèse du manganite de lanthane dopé au strontium et plus précisément La0,7Sr0,3MnO3+d. Ce choix est positif, du fait de l'obtention de l'oxyde désiré après deux plans d'expérimentation originaux. Par la suite, nous avons synthétisé et caractérisé la zircone yttriée. .The aim of my research work was to develop hydrothermal synthesis procedure to get powders and films of strontium doped lanthanum manganite La1-xSrxMnO3+d, (LSMO) and yttrium stabilized zirconia ZrO2-8mol% Y2O3 (YSZ) and to optimize the properties of materials with significiant ratio surface/volume. The use of hydrothermal synthesis at low temperature under homogeneous pressure appeared recently. For the synthesis of powders, first we defined the parameters leading to single phased un-doped manganite samples. We investigated the crystallization stage of the amorphous powder resulting from the hydrothermal synthesis by W. A. X. S. . We also characterized some physical properties by internal friction technique. For LSMO, the procedure was developped involving the methodology of experimental research. This choice is positive, because we obtain the oxide wished after two plans experimentation originals. We optimized the hydrothermal synthesis and characterized 8 mol % Y2O3 stabilized zirconia. In the second time, we investigated the deposition of films: YSZ layers on polycristalline aAl2O3 and LaMnO3+d substrates; LaMnO3+d layers on polycristalline aAl2O3, YSZ and Mn doped YSZ supports. We obtained covering layers but ould not avoid the formation of cracks
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RODRIGUES, RANIERI A. "Estudo da formação de fases secundárias no compósito LSM/YSZ." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11563.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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MONTEIRO, NATALIA K. "Síntese e caracterização de manganita-cromita de lantânio dopada com rutênio para anodos de células a combustível de óxidos sólidos." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10041.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Morel, Constance. "Etude de l'obtention par voie de fusion et solidification controlées des poudres de manganite de lanthane et de strontium pour application dans les couches de cathode de piles à combustible de type SOFC." Thesis, Orléans, 2010. http://www.theses.fr/2010ORLE2002/document.
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Nos travaux portent sur des manganites de lanthane et strontium (LSM), synthétisées par voie de fusion dans un four delévitation aérodynamique. Ce procédé, qui consiste à fondre des échantillons compactés sous impact laser, permetd’atteindre des températures très élevées (2500°C), tout en s’affranchissant des risques de pollution par le creuset. Lamicrostructure des produits obtenus a été caractérisée par DRX et observée au MEB. Leur composition chimique a étédéterminée par analyse EDS et leur stoechiométrie en oxygène, par ATG.L’étude a permis de définir les conditions nécessaires à l’obtention par fusion d’un matériau de composition LSM et destructure pérovskite. Nous avons mis en évidence les paramètres déterminants, montré en quoi ils affectent la nature desphases finales et proposé un mécanisme pour la cristallisation de celles-ci à partir du liquide de composition La1-xSrxMnO3±δ.Une méthode originale de détermination des propriétés élastiques (module d’Young, coefficient de Poisson) a été miseen oeuvre pour caractériser les produits d’un point de vue mécanique : la corrélation d’images enregistrées au cours d’unessai de traction indirecte par fendage. L’effet de l’ajout de différents dopants (Ga, Nb, Mg à raison de 5 et 10% sur lesite B) a été étudié en vue d’améliorer la tenue mécanique du LSMOur study concerns lanthanum and strontium manganites (LSM) synthesized by means of fusion in an aerodynamiclevitation furnace. This process consists in melting compacted samples with lasers, which enables to achievetemperatures as high as 2500°C while avoiding any pollution due to the crucible. The microstructure of the fusedproducts was characterized by XRD and investigated by SEM. Their chemical composition was determined by EDXanalyses and their O-stoichiometry by TGA.The study allowed us to define the conditions demanded in order to get a material exhibiting the LSM composition andthe purely perovskite structure. We evidenced the critical parameters, shew how they affect the final phases andproposed a mechanism for the crystallisation of these phases from a melt with the composition La1-xSrxMnO3±δ.To characterise our products from a mechanical point of view, an original method was used, based on the correlation ofimages recorded during an indirect tensile splitting test. Data on the elastic properties of the fused LSM were collectedand the effects on the mechanical strength of different dopants added on the B-site (Ga, Nb, Mg, 5 and 10%) werecompared
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Llobet, Megias Anna. "Contribution à l'étude du magnéto-transport et aux phénomènes de ségrégation de phase dans les manganites." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10245.
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Les manganites a valence mixte presentent une variete de transitions magnetiques, electroniques et structurales, leur comprehension etant encore un defi pour les physiciens de l'etat solide. La premiere partie de cette these est consacree a l'etude detaillee de la magnetoresistance extrinseque liee au transport dependant du spin a travers les interfaces. La mise en uvre d'une nouvelle chambre d'ablation laser a permis de developper un systeme modele a base des couches de la 2 / 3ca 1 / 3mno 3 deposees sur des substrats non-accordes de mgo (001). La conduction granulaire a ete caracterisee soigneusement et interpretee a partir des mesures de transport tunnel dependant du spin a travers d'interfaces non completement saturees ferromagnetiquement. Nous avons verifie nos hypotheses en developpant un autre systeme a base de joints des grains induits mecaniquement. Le role de la contrainte epitaxiale a ete etudie dans des couches de la 2 / 3ca 1 / 3mno 3 sur srtio 3 (001) et la modification des proprietes magnetiques et de transport a ete discutee et liee a la deformation structurale induite par la croissance epitaxiale. La deuxieme partie de cette these est dediee a l'etude des manganites a l'etat massif presentant des phenomenes d'ordre orbital et/ou de charge, ainsi que de segregation de phase. La diffraction de neutrons et de rayons x synchrotron, la relaxation des muons au champ nul, ainsi que la caracterisation magnetique et de transport ont ete utilisees pour etudier la migration electronique dans les planes ayant un ordre orbital tipe d x 2 - y 2 (pr 1 / 2sr 1 / 2mno 3), l'ordre de charge (pr 1 / 2ca 1 / 2mno 3 et bi 1 / 2ca 1 / 2mno 3) ainsi que la separation electronique de phase (pr 2 / 3ca 1 / 3mno 3) ou l'existence
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Hammouche, Abderrezak. "Contribution à l'étude de La(1-x)Sr(x)MnO3 comme matériau d'électrode à oxygène à haute température." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0075.
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Les composes la#1##xsr#xmno#3 sont utilises comme materiau d'electrode a oxygene utilisables dans les cellules galvaniques mettant en jeu un oxyde d'electrolytes solides. Leur caracterisation physicochimique a porte sur la determination de la structure cristalline et l'etude des proprietes thermiques et electriques
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Najjar, Hend. "Les oxydes type-pérovskite La1-xMxMn1-yM’yO3+δ (M : Pr ; Eu ou M’ : Al, (0≤x,y≤1) ) : synthèse par combustion et études des propriétés physico-chimiques et catalytiques." Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10058/document.
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La synthèse par combustion est un procédé simple et économique qui se base sur une réaction d’oxydoréduction entre un combustible (glycine) et un comburant (nitrates). La synthèse d’une série d’oxydes LaMnO3+δ purs a été optimisée en faisant varier le rapport glycine/nitrate=r de 0,43 à 0,8.Les surfaces spécifiques obtenues varient de 18 à 37 m²/g. Différentes espèces O2 désorbent des solides LMr : celles faiblement liées à la surface (α1-O2) et celles associées au réseau α2-O2 et β-O2 dont la désorption s’accompagne respectivement de la réduction de Mn4+ en Mn3+ et de Mn3+ en Mn2+. Les mélanges riches en glycine (r>0,53) améliorent la surface spécifique et la mobilité des espèces α2-O2 ce qui favorise une activité catalytique importante dans l’oxydation totale de CH4. Le solide obtenu avec un rapport stœchiométrique (r=0,53) est le plus stable thermiquement. La synthèse par combustion s’est avérée aussi efficace pour l’obtention des oxydes LaMn1-yAlyO3+δ (0≤y≤ 1). La substitution progressive de Mn par Al dans le sous réseau B de la structure type-pérovskite améliore la mobilité d’espèces α2-O2 dans le réseau. Le catalyseur le plus actif est obtenu pour y=0,1 en raison de sa surface spécifique et sa concentration superficielle en Mn les plus élevées. Le procédé par combustion a été aussi mis à profit pour préparer des solides type-pérovskite La1-xLnxMnO3+δ (Ln : Pr ;Eu, 0≤x≤1) substitués dans le sous réseau A. La mobilité de l’oxygène α2-O2 est améliorée par cette substitution particulièrement avec l’europium comme substituant. Un taux de substitution de 20% s’est avéré optimum pour l’activité catalytique dans l’oxydation du méthaneCombustion synthesis is a simple and safe-time process. It is based on redox reaction between fuel ( glycine) and oxidant agent (nitrates). A series of nanocristalline powders LaMnO3+δ were successfully obtained by varying glycine/nitrate ratio (r) from 0.43 to 0.8. The obtained specific areas range in 18-37 m²/g. Different desorbed oxygen species from these solids were identified: those weakly adsorbed to the surface (α1-O2) and those diffusing from the bulk (α2-O2 and β-O2 ). The desorption of α2-O2 and β-O2 causes respectively the reduction of Mn4+ to Mn3+ and Mn3+ to Mn2+. The use of fuel rich precursor enhances the specific surface area, the reducibility of manganese and the mobility of desorbed oxygen. This criterion allows interesting catalytic properties in CH4 deep oxidation. The LM0,53 catalyst obtained in stoichiometric conditions exhibits the best thermal stability.The combustion synthesis is also useful to obtain LaMn1-yAlyO3+δ oxides in a large range of Al content (0≤y≤ 1). The Al-substitution for Mn improves α2-O2 mobility. The best catalyst is obtained for the optimal fraction y=0.1 of Al due to their higher surface areas and superficial Mn concentration. A series of substituted lanthanum manganite in the A sublattice of the perovskite-type structure La1-xLnxMnO3+δ (Ln : Pr ;Eu, 0≤x≤1) were obtained by combustion synthesis. The α2-O2 mobility was improved by this substitution. A fraction of 20% was found to be optimum for catalytic activity in deep oxidation of methane
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CASINI, JULIO C. S. "Influência da substituição do cobalto por estanho e cobre na microestrutura e propriedades elétricas em ligas a base de LaMgAlMnCoNi." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/24068.
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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-10-28T11:21:27Z
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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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GALDINO, GABRIEL S. "Influência do PR na microestrutura e propriedades elétricas em ligas à base de LaPrMgAlMnCoNi utilizadas em baterias de Ni-HM." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10080.
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Made available in DSpace on 2014-10-09T12:34:31Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:26Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
38
Wisniewski, Sandra. "Etude et mise en oeuvre de catalyseurs de type perovskite dans un procédé de dénoxification d'effluents gazeux, en présence d'oxygène." Compiègne, 2000. http://www.theses.fr/2000COMP1282.
Full textAbstract:
Ce travail a été effectué dans le cadre de la mise au point de procédés cataliques efficaces pour réduire la pollution atmosphérique induite par les oxydes d'azote (NOx), à partir de sources fixes. La réduction catalique sélective est le procédé le plus couramment utili¬sé sur site industriel. Il s'agit d'employer un réducteur approprié, l'ammoniac, pour réduire les NOx en présence d'oxygène. Cependant, l'utilisation de ce réactif présente un inconvénient majeur en raison de sa toxicité. L'originalité de ce travail est de proposer une réaction de dénitrification (DeN0x) propre, sans pollution induite, en utilisant le carbone comme agent réducteur (celui-ci est soit alimenté directement sous forme de noir de carbone, soit généré in situ sur le catalyseur, à l'aide d'un hydrocarbure) et un catalyseur appartenant à la famille des pérovskites. Les manganites au lanthane substituées par du cuivre en site B (Lao,8 Sro,2Mn1 Cuy03>; Oy(l) ont montré leur efficacité pour une telle réaction. La mise en forme du catalyseur, étape indispensable pour un usage industriel qui ne permet pas l'utilisation de solides pulvérulents, a été étudiée. Celle-ci a consisté à déposer le catalyseur sur un support céramique de type éponge, lui-même préalablement recouvert d'un wash-coat Ce02. Comme l'alimentation en noir de carbone et le contact entre le catalyseur et le noir de carbone sont particulièrement délicats, la génération de réactifs réducteurs carbonés a été réalisée par alimentation en propène sur un catalyseur fabriqué spécialement, constitué de pérovskite et d'alumine dopée au lanthane. De bonnes performances cataliques ont été obtenues grâce à ce catalyseur bifonctionnel.
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RAMIREZ-SALGADO, JOEL. "Contribution à l'étude des électrodes à gaz dans un capteur potentiométrique à CO2 de deuxième espèce." Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10113.
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Ce travail concerne l'etude de materiaux d'electrode utilisables dans des capteurs a gaz bases sur le nasicon, conducteur par ion sodium. Pour une electrode a oxygene, nous avons synthetise par sol-gel des titanates de sodium. Les mesures de conductivite et l'etude des reactions d'electrode par spectroscopie d'impedance ont permis de choisir le materiau le mieux adapte, auquel nous avons melange un lanthanide de manganese pour ameliorer sa reponse. Une premiere etude sur l'electrode a dioxyde de carbone, a base d'un melange de carbonates et d'or, donne un premier apercu sur les mecanismes de la reaction d'electrode. Des tests sur des capteurs realises par serigraphie ont donne des resultats tres encourageants pour le developpement futur des capteurs a oxygene et a dioxyde de carbone. Pour ce devenir, meme si la reponse est sous-nernstien le domaine de sensibilite va de la ppm a quelques pour cent en teneur.
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Karimi, Noureddine. "Etude par diffraction des rayons X in situ des mécanismes d'oxydation de l'acier AISI 304 entre 800°C et 1000°C." Phd thesis, Clermont-Ferrand 2, 2007. http://www.theses.fr/2007CLF21782.
Full textAbstract:
Ce travail a porté sur l'étude des mécanismes d'oxydation de l'acier AISI 304 sur une gamme de température allant de 800 à 1000°C. Nous avons examiné plus particulièrement l'influence des dépôts sol-gel de lanthane et de cérium sur les processus d'oxydation. L' apport de la spectroscopie IR a permis de mieux identifier les oxydes mixtes de type spinelle FeCrO4 et Mn1,5Cr1,5O4 et corindon Fe2O3. L'association des différentes techniques d'analyse telles que la DRX in situ, la spectroscopie IR, le MEB, l'EDS et la microscopie électronique à transmission (MET) ont permis de proposer un nouveau mécanisme d'oxydation de l'acier AISI 304 au cours de son oxydation à 1000°C. Les dépôts sol-gel de lanthane et de cérium conduisent à une diminution importante des constantes de vitesse d'oxydation. Dans le cas de l'AISI 304 recouvert d'un dépôt sol-gel d'oxyde de lanthane, la DRX in situ montre que la croissance de l'oxyde mixte LaCrO3 intervient dès le début de l'oxydation. Cet oxyde est localisé à l'interface interne et bloque la diffusion externe du fer tout en retardant la diffusion externe du manganèse. Ceci peut être dû au fait que le lanthane agit de façon synergique avec le silicium afin de bloquer la diffusion externe du fer et favoriser la formation de la chromine. Le lanthane peut aussi agir en bloquant la diffusion externe des cations métalliques au travers de la couche de chromine selon un processus de ségrégation dynamique au joint de grains. Dans le cas du dépôt sol-gel d'oxyde de cérium le régime linéaire que nous avons observé à toute température est le témoin d'un processus de croissance de la couche d'oxyde limité par la diffusion à travers une couche de CeO2 d'épaisseur constante située à l'interface externe. Dans ce cas l'absence des oxydes contenant du fer dans la couche d'oxyde permet de conclure à un effet synergique avec le silicium qui bloque la diffusion externe du fer. Les essais de cycles thermiques montrent que l'adhérence des couches d'oxyde formées en présence de dépôts sol gel ne s'en trouve pas améliorée
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Iannone, Giuseppina. "Corrélations entre les propriétés cristallographiques, de transport et magnétiques du composé à magnétorésistance colossale La0. 75Ca0. 25Mn03." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10061.
Full textAbstract:
Les oxydes de manganese a structure perovskite sont des composes tres interessants, a cause de la magnetoresistance colossale (mrc) qui consiste en la diminution de la resistivite electrique en presence d'un champ magnetique. Ce phenomene est du a la presence d'une transition paramagnetique-ferromagnetique et d'une transition isolant-metal a la meme temperature t c. La diminution de la resistance electrique a t c est egalement induite par l'application de la pression. Le compose la 0. 7 5ca 0. 2 5mno 3 presente un interet particulier pour l'etude des anomalies structurales correlees aux proprietes de magnetotransport, a cause de sa t c elevee (240k). La technique de diffraction de neutrons sur poudres s'est montree tres puissante pour detecter les variations de la structure a l'echelle microscopique. La technique est aussi adaptee pour un etude en fonction de la temperature, de la pression et du champ magnetique applique. Les resultats obtenus montrent que le domaine de temperatures de la mrc est caracterise par des anomalies structurales qui impliquent l'environnement des atomes de manganese, notamment les distorsions jt, les distorsions de buckling des octaedres mno 6 et de l'angle de liaison mn-o-mn. On a revele aussi le comportement anormal des parametres thermiques des atomes d'oxygene a t c. Les distorsions observees a t c sont defavorisees en presence de la pression et du champ magnetique. Notamment, l'augmentation de l'angle de liaison mn-o-mn a ete associe a la phase magnetique et conductive.
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Zhu, Yuexing. "Synthesis of Lanthanum chromite-Lanthanum manganite and LSCF-Lanthanum manganite core-shell particles via molten salt route." Thesis, 2017. https://hdl.handle.net/2144/27012.
Full textAbstract:
Lanthanum chromite (LaCrO3), Lanthanum manganite (LaMnO3) and 40% strontium doped lanthanum cobalt iron oxide, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF-6428) are perovskite oxides which are widely used as interconnect or cathode materials in solid oxide fuel cells(SOFCs) due to their high electrical conductivity, good oxygen reduction kinetics, and good chemical stability. The solid state reaction route is the most commonly used method for synthesis of these materials. However, the solid state reaction method usually involves long-time mixing and high synthesis temperature (typically, >1200 ºC), which makes it time-consuming and costly. Molten salt synthesis, which occurs at much lower temperatures (350 ºC – 550 ºC) can offer better particle size and compositional control and reduced energy usage during materials synthesis.
In this study, LaCrO3, LaMnO3, and LSCF were synthesized in a molten salt eutectic of LiCl-KCl. A range of reaction temperature from 370 ºC to 600 ºC was investigated. It was found that a pure LaMnO3 perovskite phase can be formed at as 400 ºC using the molten salt method and that LSCF powders were successfully synthesized at 500 ºC. When forming LaCrO3 using the molten salt method, LaOCl was also formed at or above 400 ºC. The X-ray diffraction (XRD) results show this is an attractive alternative route of synthesis to decrease the reaction temperature. Both Scanning Electron Microscopy (SEM) images and XRD patterns for LaCrO3 showed that only cubic structures were formed at low temperature (400 ºC and 450 ºC) and then hexagonal structures started to appear at temperatures above 500 ºC. The molten salt synthesis method was then used to prepare core-shell structures with LaCrO3 or LSCF particles as the core and LaMnO3 as the shell. Core-shell structures were characterized by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscope (STEM) and Energy Dispersive X-ray Spectroscopy (EDS). It was found that the expected core-shell structures were successfully formed with the overall cubic structures.
Therefore, the molten salt synthesis method is a feasible method to decrease the operation temperature and form the core-shell structure.
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Ting-FangYu and 游婷芳. "Unsupported and silica-supported perovskite-type lanthanum manganite and lanthanum ferrite in the conversion of ethanol." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/9t4xfh.
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碩士國立成功大學
化學工程學系
107
This study reports that the Lewis acid-base properties of peroskite-type LaMnO3 and LaFeO3 can be adjusted by immobilizing them on silica. Bulk LaMnO3 and LaFeO3 were strong base catalyst due to unsaturated-coordinated oxygen on the surface, While, after supported them on silica, the basic properties of bulk materials were diluted and simultaneously acidities improved due to the increased amounts of tetravalent B-site cations. Ethanol reactivity was performed to reflect the different acid-base properties of bulk and silica-supported LaMnO3 and LaFeO3. Under differential analysis conditions, bulk perovskites were active in base-catalyzed reactions such as reverse aldolization and Tishchenko reaction, while silica-supported perovskites were active in aldolization and dehydration. We also notice the higher aldolization activity over LaMnO3/SiO2 than that of LaFeO3/SiO2, the different activity was attributed to existence of excess mobile oxygen on the surface of LaMnO3/SiO2, forming aldolization-active Lewis acid (Mn4+)-base (nonstoichiometric oxygen) pair sites while these sites were absent in LaFeO3/SiO2 which was enriched with oxygen vacancies.
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Fun, Yuh-Da, and 范彧達. "Preparation and Characterizations of Lanthanum Manganites." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/46081473350736692265.
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碩士國立成功大學
化學工程研究所
82
The precursors with OH ligands were prepared by coprecipitation and coprecipitation combined with high temperature melting. After freeze drying, the precursors were calcined at 900oC for 8 hrs to obtain corresponding compounds. It indicated from X- ray diffraction patterns that the major compounds are LaMnO3 and La2Zr2O7. In this study, we investigated not only the properties of the ternary system but also the electrical and magnetic properties of the compounds sintered at different tempertures and atmosphere, respectively, for 8 hrs, respectively. X-ray diffraction patterns show that the compounds were the mixture of LaMnO3 and La2Zr2O7 phase. From XRD and bulk density analyses, the compound of La:Mn: Zr=1:0.99:0.01 may be a new compound. But, we could not find the new phase of La(Mn0.99Zr0.01)O3 from analysis of TEM. From the variations of susceptibility with temperature analyzed by SQUID, we found that these compounds are ferromagnetic substances. The compounds are characteristics of polaron mechanism of conductivity from the variations in resistivity with temperature. This semiconductor is a characteristic of resistance changing with electricwave frequency. The powders prepared by coprecipitation combined with high temperature melting,permits sintering at a lower temperature and precisely chemical homogenity and fine paticle size with a narrow size distribution, and is more excellent than those by coprecipitated method.
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Shiu, Ping-chi, and 徐鈵琪. "Preparation and Characterization of Lanthanum Manganese Nickel (Indium) Oxides." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/74905775878030241948.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
96
Chemical coprecipitation has high homogeneity,high reactivity,high quality and exact stochiometry.The goal of this study is that the lanthanum –manganese- nickel/indium oxide powders were prepared by coprecipitation method. The precursors of lanthanum –manganese –nickel and lanthanum –manganese indium oxides with OH- ligands were prepared by coprecipitation.After freeze drying,the precursors were calcined at 800℃ for 10 h and were calcined at 900℃ for 10 h to obtain the corresponding compounds without nickel/indium respectively. It indicated from XRD patterns that the major compound was La0.96MnO3.05,respectively. Laser Particle Size Distribution Analyzer was used to measure the particle size of the samples.It was found that the particle size lanthanum manganese nickel oxide (0.4μm~0.7μm )is low than that of lanthanum manganese indium oxide(0.5μm~0.9μm ). From the electrical resistivity(Ohm-cm) one can obtain that the resistivity of lanthanum manganese nickel oxide (x=0.1mole,ρ=0.76Ω-cm)is low than that of lanthanum manganese indium oxide(x=0.02mole, ρ=1.46Ω-cm). From the variations of susceptibility with temperature analyzed by SQUID,we found that products exhibit Ferromagnetism.
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Hung, Pei-Yu, and 洪珮瑜. "Synthesis and Physical Properties of Nano Lanthanum Strontium Manganese Compounds." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/19008974378215072357.
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碩士國立臺灣大學
材料科學與工程學研究所
92
Different processes for synthesizing the La0.7Sr0.3MnO3/LaMnO3 (LSMO/LMO) powders and films were attempted in this study. The grain sizes of the samples were successfully reduced to 16nm (for powders) and 19nm (for film). The physical properties of samples with different grain sizes were studied, too. At room temperature, the negative MR ratios under a filed of 1 Tesla of the sintered, sol-gel powders and films were 6.25%, 5.95% and 3.69%, respectively. At 20K, however, the negative MR ratios under a field of 1 Tesla were 3.45%, 27.6% and 22.5%, respectively. In addition, the enhanced low field magnetoresistance (LFMR) was observed even at room temperature when LMO is present in the samples. At 20K, all the LSMO/LMO composite samples showed a large LFMR. The negative MR ratios under a field of 0.2T was about 22% for samples with LMO content＞20%. Furthermore, a significant enhancement in MR ratio is also observed in all composite films, especially in the optimal ratio of LMO/LSMO=1/3. Compared with the LSMO single layer sample, the MR ratio at low temperature (20K) can be enhanced up to 31% under an applied field of 0.2 Tesla.
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"Doping effects on the colossal magnetoresistance of lanthanum-calcium- manganese-oxygen." 1998. http://library.cuhk.edu.hk/record=b6073130.
Full textAbstract:
"January 1998."Thesis (Ph.D.)--Chinese University of Hong Kong, 1998.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.
Abstract in Chinese.
48
"Oxygen effects in lanthanum calcium manganese oxide: 氧含量在鑭鈣錳氧化物中的作用." 1997. http://library.cuhk.edu.hk/record=b6073112.
Full textAbstract:
by Yang, Fei.Thesis (Ph.D.)--Chinese University of Hong Kong, 1997.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.
Abstracts in English and Chinese.
by Yang, Fei.
49
"Using silver as a binder for synthesis of magnetoresistive lanthanum calcium manganese oxide =: 用银作粘合剂来合成镧钙锰氧磁致电阻材料." 2000. http://library.cuhk.edu.hk/record=b5890275.
Full textAbstract:
Zhou Lingzhao.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references (leaves 84-85).
Text in English; abstracts in English and Chinese.
Zhou Lingzhao.
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Magnetoresistance effect --- p.1
Chapter 1.2 --- Giant magnetoresistance (GMR) effect --- p.2
Chapter 1.3 --- CMR effect in rare earth manganites --- p.2
Chapter 1.4 --- Main research in this thesis --- p.5
Chapter Chapter 2 --- Synthesis technology
Chapter 2.1 --- Conventional solid state reaction --- p.8
Chapter 2.2 --- Powder preparation --- p.10
Chapter 2.3 --- Shaping --- p.13
Chapter 2.4 --- Sintering --- p.14
Chapter 2.5 --- Fabrication method in this experiment --- p.20
Chapter 2.6 --- Characterization method --- p.22
Chapter Chapter 3 --- Stoichiometry problems in LCMO
Chapter 3.1 --- Doping effects in La2/3Ca1/3MnO3 --- p.24
Chapter 3.2 --- La stoichiometry in La2/3Ca1/3MnO3 --- p.28
Chapter 3.3 --- Mn stoichiometry in La2/3Ca1/3MnO3 --- p.28
Chapter 3.4 --- Oxygen stoichiometry in La2/3Ca1/3MnO3 --- p.32
Chapter Chapter 4 --- Search for binders in the synthesis of La2/3Ca1/3MnO3
Chapter 4.1 --- Solid state reaction --- p.38
Chapter 4.2 --- Density --- p.39
Chapter 4.3 --- Crystal structure --- p.41
Chapter 4.4 --- SEM analyses --- p.48
Chapter 4.5 --- Resistivity and magnetoresistance --- p.54
Chapter 4.6 --- Small polaron transport --- p.72
Chapter 4.7 --- Conclusion --- p.81
50
Behera, Sukanti. "Thermoelectrics and Oxygen Sensing Studies of Selected Perovskite Oxides." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2975.
Full textAbstract:
Perovskite oxides show wide range of applications in the area of magnetism, ferroelectricity, piezoelectricity, thermoelectricity, gas sensing, catalyst development, solid oxide fuel cell, etc. This is due to flexibility in the structure and compositions that can be tuned by specific element doping. In the perovskite oxide (ABO3), large cation (A) is 12 -coordinated and smaller B-cation is 6 coordinated with oxide ions. Oxide materials are considered as better candidates for thermoelectric applications (interconversion of thermal into electrical energy) due to its non-toxicity and thermal stability at elevated temperature. These are insulating in nature and the conductivity can be increased by doping A and / or B –sites. Perovskite oxides are also used for oxygen monitoring in different applications including control and optimization of combustion of fossil fuels in industries and automobiles, biological and defines places, etc.
In the present study, we focused on thermoelectric properties in single perovskite oxides of lanthanum cobaltite and calcium manganite and a double perovskite oxide of dysprosium barium cobaltite. Also, the oxygen sensing behaviour of dysprosium barium cobaltite at elevated temperatures is studied. The thesis contains seven chapters and a summary of respective chapters are given below.
The first chapter outlines the basics of thermoelectric and gas sensing applications of both perovskite and double perovskite oxides. In the initial part, thermoelectric phenomena are explained. Thermoelectric effect is the conversion of thermal energy to electrical energy and vice-versa. Higher thermoelectric efficiency
(η) can be achieved by maintaining a large temperature difference across the material. The efficiency depends on the thermoelectric figure of merit (zT) of material, which depends on thermopower (S), electrical resistivity (ρ) and thermal conductivity
(κ) of the material and hence needs to be optimized. The latter part discusses the oxygen sensing property of distorted double perovskite 112 structure type as it shows advantages over other materials due to oxygen nonstoichiometric. Further, an overview of the relevant literature, objective and scope of the thesis are mentioned.
The second chapter elucidates the materials and methods used for the present work. The materials viz. LaCoO3, CaMnO3-δ and DyBaCo2O5+δ, were selected for thermoelectric and oxygen sensing studies. Both the conventional solid state and soft chemistry methods were adopted for the synthesis of these materials. Powders were densified into pellets by hot uniaxial pressing / cold isostatic pressing and various heat treatments were carried out. Samples thus prepared were phase pure as confirmed using powder x-ray diffraction and Rietveld refinement performed for structural analysis. Morphological studies were carried out using scanning electron microscopy and transmission electron microscopy. Further Raman and x-ray photoelectron spectroscopic characterization of these materials were discussed. The transport properties viz. electrical resistivity, thermopower and thermal conductivity of compact pellets were measured at elevated temperatures. Further, the home-built apparatus for room temperature See beck measurements and chemo resistive oxygen sensing were explained in detail as a part of this work.
The third chapter describes the effect of monovalent ion doping (Na+ and K+) at A-site of lanthanum cobaltite on thermoelectric properties. Lanthanum cobaltite system exhibit exotic behaviour due to commensuration phenomena of spin, lattice, charge and metal insulator transition. The synthesis, followed by structural refinements by Rietveld method using Fullprof suit program are explained. The results of the transport properties indicate that there is no appreciable change in the See beck Coefficient of K-doped samples throughout the studied temperature range.
The Na-doped samples exhibit a decrease in the Seebeck value with increasing Na content at room temperature. At higher temperatures Seebeck value matches with that of the parent sample. This may be due to a change in the ratio of the concentration of Co4+/Co3+ ions which increases the configurational entropy of the system. In conclusion, the highest figure of merit (0.01) found for the Na / K- doped lanthanum cobaltite is for 15 atomic wt. % of doping amongst the studied samples.
The fourth chapter explains about Tb/Nb co-doped calcium manganite for thermoelectric applications. The CaMnO3-δ shows enhanced thermoelectric properties, exhibits n-type behavior and the absolute thermopower is found to be 129 µV/K. Here, we investigated the Terbium and Niobium codoped at Ca and Mn-sites respectively. The presence of oxygen non-stoichiometry was confirmed using Raman spectroscopy (Mn3+ peak at 614 cm-1) and δ value was evaluated by iodometric titration. The thermoelectric properties of cold isostatic pressed (CIP) pellets prepared by the solid state and soft chemistry routes are compared. The non-monotonous behavior of absolute thermopower may be due to the increase of Mn3+ in the Mn4+ matrix and also the presence of oxygen defects in compounds. The thermoelectric figure of merit of solid state sample CaMnO3-δ estimated of 0.036 at 825K.
The fifth chapter describes the thermoelectric properties of double Perovskite AA’B2O6 (112 type): (RE)BaCo2O5+δ. It is a disordered double perovskite with non-stoichiometry in oxygen and exhibits mixed valences of Cobalt. Resistivity of DyBaCo2O5+δ was found to be 0.09 Ω cm and Seebeck coefficient is found to be 42 µV/K. In order to improve the thermopower value, the Fe is substituted at Co-site. This varies the valences of Cobalt that in turn leads to a higher thermopower. Also, the morphology of thermally etched CIP pellets recorded and correlated with the transport properties. It shows the highest thermoelectric figure of merit of 0.25 at 773 K for 20 at wt % of Fe substituted sample.
The sixth chapter explains about oxygen sensing studies of DyBaCo2O5+δ (112 type). The detailed structural and morphological characterization studies were carried out. Thermogravimetric analysis at isothermal temperature 873 K shows fast intake/release of oxygen of this disordered double perovskite structure. The higher chemo resistive oxygen sensitivity at the elevated temperature was measured. Further, the systematic study on the effect of oxygen sensing on the substitution of Fe and Cu at Co-site in DyBaCo2-xM xO5+δ was investigated. The possible bulk diffusion mechanism at higher temperature due to movement of oxygen defects were explained. The highest sensitivity was obtained for x = 0.4 at % of Fe and 0.2 at % of Cu at 973 K and 823 K respectively.
The key findings and future aspects are summarized in the chapter-7.