京都大学 / 新制・課程博士 / 博士(工学) / 甲第23216号 / 工博第4860号 / 新制||工||1759(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 阿部 竜, 教授 陰山 洋, 教授 藤田 晃司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

abstract: A Fundamental study of bulk, layered, and monolayers bromide lead perovskites structural, optical, and electrical properties have been studied as thickness changes. X-Ray Diffraction (XRD) and Raman spectroscopy measures the structural parameter showing how the difference in the thicknesses changes the crystal structures through observing changes in average lattice constant, atomic spacing, and lattice vibrations. Optical and electrical properties have also been studied mainly focusing on the thickness effect on different properties where the Photoluminescence (PL) and exciton binding energies show energy shift as thickness of the material changes. Temperature dependent PL has shown different characteristics when comparing methylammonium lead bromide (MAPbBr3) to butylammonium lead bromide (BA2PbBr4) and comparing the two layered n=1 materials butylammonium lead bromide (BA2PbBr4) to butylammonium lead iodide (BA2PbI4). Time-resolved spectroscopy displays different lifetimes as thickness of bromide-based perovskite changes. Finally, thickness dependence (starting from monolayers) Kelvin Probe Force Microscopy (KPFM) of the layered materials BA2PbBr4, Butylammonium(methylammonium)lead bromide (BA2MAPb2Br7), and molybdenum sulfide (MoS2) were studied showing an exponential relation between the thickness of the materials and their surface potentials. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

Solid oxide fuel cells (SOFCs) offer the advantages of (i) employing less expensive catalysts compared to the expensive Pt catalyst used in proton exchange membrane fuel cells and (ii) directly using hydrocarbon fuels without requiring external fuel reforming due to the high operating temperature. However, the conventional high operating temperatures of 800 - 1000 °C lead to interfacial reactions and thermal expansion mismatch among the components and limitations in the choice of electrode and interconnect materials. These problems have prompted a lowering of the operating temperature to an intermediate range of 500 - 800 °C, but the poor oxygen reduction reaction kinetics of the conventional La[subscript 1-x]Sr[subscript x]MnO₃ perovskite cathode remains a major obstacle for the intermediate temperature SOFC. In this regard, cobalt-containing oxides with perovskite or perovskite-related structures have been widely investigated, but they suffer from large thermal expansion coefficient (TEC) mismatch with the electrolytes. With an aim to lower the TEC and maximize the electrochemical performance, this dissertation focuses on perovskite-related and trigonal RBaCo₄O₇-based oxide cathode materials. First, the effect of M = Fe and Cu in the perovskite-related layered LnBaCo₂₋xMxO₊[delta] (Ln = Nd and Gd) oxides has been investigated. The Fe and Cu substitutions lower the polarization resistance and offer fuel cell performance comparable to that of La[subscript 1-x]Sr[subscript x]CoO₃₋[delta] perovskite due to improved chemical stability with the electrolyte and a better matching of the TEC with those of standard electrolytes. Second, the perovskite-related intergrowth oxides Ln(Sr,Ca)₃Fe₁.₅Co₁.₅O₀ and La₁.₈₅Sr₁.₁₅Cu[subscript 2-x]Co[subscript x]O[subscript 6 +delta] and their composites with gadolinia-doped ceria (GDC) have been investigated. The electrical conductivity, TEC, and catalytic activity increase with increasing Co content. The composite cathodes exhibit enhanced electrochemical performance due to lower TEC and increased triple-phase boundary. Third, RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) oxides with a trigonal structure and tetrahedral-site Con+ ions have been investigated. The chemical instability normally encountered with this class of oxides has been overcome by appropriate cationic substitutions as in (Y₀.₅Ca₀.₅)Ba(Co₂.₅Zn₁.₅)O₇ and (Y₀.₅In₀.₅)BaCo₃ZnO₇. With an ideal matching of TEC with those of standard electrolytes, the RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) + GDC composite cathodes exhibit low polarization resistance and electrochemical performance comparable to that of perovskite oxides. / text

Cette thèse porte sur la synthèse et la caractérisation de nouvelles phases d’oxydes multifonctionnels de la famille Ln2B2O7 avec Ln = lanthanide, B = Ti ; Zr. Ces oxydes présentent de nombreuses propriétés : photocatalytiques, ferroélectriques, piézoélectriques, de luminescence... Sous forme massive, des solutions solides (La1-xLnx)2Ti2O7 avec Ln = Pr à Lu et La2(Ti1-xZrx)2O7 ont été synthétisées par réaction solide-solide. L’étude portant sur la substitution du site Ln a permis de déterminer les limites de stabilité de la phase pérovskite en feuillets en fonction de la nature du lanthanide. Des analyses menées par spectrométrie Raman, ainsi que par spectrofluorimétrie ont mis en évidence des propriétés de luminescence dans les solutions solides (La1-xEux)2Ti2O7 et (La1-xTbx)2Ti2O7, suggérant ainsi la possibilité d’utiliser ces composés pour la fabrication de nouveaux systèmes luminophores. Des couches minces de Ln2Ti2O7 ont été élaborées par ablation laser pulsé, puis caractérisées par diffraction de rayons X haute résolution et par microscopie électronique à transmission haute résolution. Les nouvelles limites de stabilité des films minces à structure pérovskite en feuillets ont pu être déterminées dans le cas de dépôts réalisés sur des substrats de SrTiO3 et LaAlO3 orientés (100) et (110). Le caractère piézoélectrique/ferroélectrique des films de Ln2Ti2O7 cristallisés dans la phase α monoclinique a été confirmé à l’échelle locale par la microscopie à force piézoélectrique. Enfin, nous avons montré que la croissance épitaxiale d’un film de La2Zr2O7 déposé sur SrTiO3-(110) pouvait conduire à l'existence de la ferroélectricité en raison d'une structure pyrochlore géométriquement frustrée et la perte de la symétrie cubique. Ces résultats prometteurs font de ces composés Ln2B2O7 des candidats de premier choix en vue du développement de nouvelles phases oxydes multifonctionnelles. De plus, l’absence de plomb au sein de ces structures, ainsi que leur formidable résistance à la température et à l’irradiation ouvrent des perspectives intéressantes quant à l’utilisation de ces matériaux dans les équipements électroniques et en milieux extrêmes. / This thesis focuses on the synthesis and characterization of new multifunctional Ln2B2O7 oxides phases with Ln = lanthanide, B = Ti, Zr. These oxides possess many properties, including photocatalysis, ferroelectricity, piezoelectricity and luminescence. In bulk form, solid solutions of (La1-xLnx)2Ti2O7 with Ln = Pr to Lu and La2(Ti1-xZrx)2O7 were synthesis by solid-solid reaction. Study on the Ln site substitution highlighted the limits of stability of the layered perovskite depending on the nature of the lanthanide. Analysis carried out by Raman spectroscopy and spectrofluorimetry also permit the detection of luminescence in (La1-xEux)2Ti2O7 and (La1-xTbx)2Ti2O7 solid solutions, suggesting the possibility to use such compounds for fabrication of new phosphor systemes. Ln2Ti2O7 thin films were grown by pulsed laser deposition, and characterized by high resolution X-rays diffraction and high resolution transmission electron microscopy. The new limits of stability of films with layeredperovskite structure have been determined in the case of samples grown on (100)- and (110)-oriented SrTiO3 and LaAlO3 substrates. The piezoelectric/ferroelectrique properties of Ln2Ti2O7 thin films crystallized in the monoclinic α phase were confirmed at the local level by piezoelectric force microscopy measurements. Finally, we have shown the the epitaxial growth of La2Zr2O7 films deposited on (110)-oriented SrTiO3 substrate can induce ferroelectricity for geometrically frustrated pyrochlore structure with the loss of cubic symmetry. These interesting results make Ln2B2O7 compounds promising candidates for the development of new multifunctional oxides. Moreover, the absence of lead in these structures and their resistance to the temperature and irradiation open interesting perspectives for the use of such materials in electronic equipments and in extreme environments.