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1
Martin, Airton Abrahao. "Preparação e caracterização de cerâmicas supercondutoras nos sistemas Y-Ba-Cu-O e Tm-Ba-Cu-O." Universidade de São Paulo, 1988. http://www.teses.usp.br/teses/disponiveis/54/54132/tde-18122013-112538/.
Abstract:
Neste trabalho estudamos a influencia da temperatura e tempo de reação e sinterização na preparação de amostras cerâmicas supercondutoras pelo método de reação no estado sólido. Os resultados indicam claramente que algumas propriedades destes supercondutores, tais como: temperatura crítica (Tc), susceptibilidade magnética (X), resistividade (ρ), microestruturas, densidade e porosidade aparente, sofrem forte influencia das condições de tratamento térmico. Foram preparadas várias amostras dos sistemas YBa2Cu3O6.5+x e TmBa2Cu3O6.5+x, sendo que a temperatura e tempo ideal de reação encontrados foram de 950°C por 6 horas e 925°C por 48 horas, respectivamente; ambas tratadas em fluxo de oxigênio. A caracterização destas amostras foram feitas pelas técnicas de difração de raios-x, técnica de quatro-pontas (medida da variação da resistividade pela temperatura), ponte de Hartshorn (para a medida da variação da susceptibilidade magnética pela temperatura), microscopia eletrônica de varredura (para análise das microestruturas) e método de imersão (para a medida da densidade e porosidade aparente). A maior temperatura crítica encontrada foi de aproximadamente 94K para YBa2Cu3O6.5+x e de aproximadamente 91K para o TmBa2Cu3O6.5+xThe influence of the temperature and time in the reaction and sinterization of superconducting ceramics prepared by a solid state reaction was determined. The results clearly showed that some of its properties, such as critical temperature (Tc), magnetic susceptibility (X), resistivity (ρ), microstructure, apparent density, and porosity undergo a strong influence of the preparation conditions. Some samples in the YBa2Cu3O6.5+x and TmBa2Cu3O6.5+x systems were prepared. The ideal reaction temperature and time were 950°C for 6 hours and 925°C for 48 hours, respectively. Both annealed in O2 flow. The sample characterization was made by using X-ray diffraction, standard four probe (measures the variation of resistivity versus temperature), Bridge of Hartshorn (the variation of susceptibility versus temperature), scanning electron micrograph (microstructure analysis), and immersion method (measures the apparent density and porosity). The greatest critical temperature was approximately 94K for YBa2Cu3O6.5+x and 91K for TmBa2Cu3O6.5+x
2
Heffernan, Shane. "Nanostructured CU₂O solar cells." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709220.
3
Seibel, B. [Verfasser]. "Berechnungen von Röntgenabsorptionsspektren an YBa₂Cu₃O₇, PrBa₂Cu₃O₇ und Sr₂RuO₄ / B. Seibel." Karlsruhe : KIT-Bibliothek, 1997. http://d-nb.info/1108447422/34.
4
Sene, Abdoulaye. "Formation et fonctionnement des sites actifs des catalyseurs d'hydrogénation Cu-Zn-O et Cu-Zn-Al-O." Lille 1, 1990. http://www.theses.fr/1990LIL10166.
Abstract:
Thermogravimétrie, spectroscopies SPX et AUGER, mesures cinétiques ont été utilisées pour caractériser très finement différents catalyseurs Cu-Zn-Al-O couramment utilisés en synthèse du méthanol. A l'état réduit à 523 k, les principaux éléments dégagés de notre étude sont : 1) la présence de cuivre métal et d'une fraction de cuivre à l'état partiellement oxyde et inséré dans le réseau Zn-Al-O ; 2) la présence d'une espèce hydrogène extractible, localisée dans le réseau des oxydes résiduels ; 3) l'existence d'ions hydroxyles relativement mobiles auxquels nous avons attribué un phénomène de blocage des sites hydrogénants. La prise en compte de ces différents points associée à une étude cinétique d'hydrogénation de l'isoprène en l'absence d'hydrogène nous ont amené à établir un modèle de sites actifs et un modèle cinétique d'extraction des espèces hydrogène. Ces modèles sont transposables à toute une classe de catalyseurs à base de cuivre. Le modèle cinétique a permis d'évaluer la quantité d'espèces hydrogène localisées à la surface et qui interviennent dans la détermination des aires métalliques et dans le processus catalytique d'hydrogénation. Enfin, l'influence de la nature des phases sur les caractéristiques et performances des catalyseurs a été discutée.
5
Brito, Juliana Ferreira de [UNESP]. "Estudo da redução fotocatalítica e fotoeletrocatalítica de 'CO IND. 2' em meio aquoso sobre 'CU'/'CU IND. 2 'O'', 'TI' 'O IND. 2'/'PT', 'CU''NB' 'O IND. 3' - 'CU''O' e 'CU IND. 0,85''ZN IND. 0,15''NB IND. 2''O IND.6' como catalisadores para formação de metanol." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/110841.
Abstract:
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000775296.pdf: 2220721 bytes, checksum: 20bda960969f72c4be9130ed074b0799 (MD5)O presente trabalho reporta os principais resultados obtidos na construção e caracterização de eletrodos de titânio recobertos com nanotubos de óxido de titânio modificados com nanopartículas de platina (TiO2/Pt) e eletrodos de cobre recobertos com nanopartículas de óxido de cobre (Cu/Cu2O) com vistas a sua aplicação na redução fotoeletrocatalítica de CO2 em meio aquoso e semicondutores em pó de CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 e ZnNb2O6-Nb2O5 construídos e testados na redução fotocatalítica de CO2, com vistas a geração de produtos com maior valor agregado, tal como metanol. Os eletrodos TiO2/Pt e Cu/Cu2O foram construídos por meio de técnicas de eletroquímicas, enquanto que os semicondutores em pó CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 e ZnNb2O6-Nb2O5 foram preparados utilizando a técnica de síntese por combustão e calcinação posterior. A redução fotoeletrocatalítica e fotocatalítica de CO2 não foi satisfatória sobre eletrodos de TiO2/Pt e semicondutor ZnNb2O6-Nb2O5, respectivamente. No entanto, o eletrodo de Cu/Cu2O apresentou grande eficiência na redução de CO2, atingindo 80% de remoção em meio de Na2CO3 0,3 mol L-1 pH 9 a +0,2 V, em solução tampão de NaHCO3/Na2CO3 0,1 mol L-1 pH 8, utilizando luz UV 125 W e potencial de +0,2 V mostrou uma reação praticamente seletiva para metanol, gerando 5,63 mmol L-1, correspondendo a 20% de conversão. Os semicondutores em pó CuNbO3-CuO e Cu0,85Zn0,15Nb2O6 também se mostraram bastante eficientes para a geração de metanol por redução de CO2 dissolvido em Na2CO3 0,1 mol L-1 pH8 utilizando luz visível de 450 W, chegando a formar 7,0 mmol L-1 e 3,2 mmol L-1 de metanol respectivamente. Os resultados obtidos neste trabalho mostram que ambas as técnicas podem ser empregadas para a redução do CO2, usando para isto os semicondutores Cu/Cu2O, CuNbO3-CuO e Cu0,85Zn0,15Nb2O6 e, poderia ser uma potencial alternativa para os problemas ambientais além de contribuir como fonte...
This present work reports the main results obtained with the construction and characterization of TiO2 nanotubes modified by platinum nanoparticle electrode (TiO2/Pt) and copper covered by copper oxide nanoparticles electrode (Cu/Cu2O) for application in the photoelectrocatalytic reduction of dissolved CO2 and CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 and ZnNb2O6-Nb2O5 powders semiconductors constructed and applied in the photocatalytic reduction of dissolved CO2 for the generation of products with higher added value. The TiO2/Pt and Cu/Cu2O electrodes were prepared by electrochemical techniques, whereas the CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 and ZnNb2O6-Nb2O5 powder semiconductors were prepared using the combustion synthesis technique and submitted to annealed. The CO2 reduction by photoelectrocatalysis and photocatalysis were not satisfactory when using the TiO2/Pt electrode and the ZnNb2O6-Nb2O5 semiconductor, respectively. However, the Cu/Cu2O electrode shows a high efficiency in the CO2 reduction obtaining 80% of removal in 0.3 mol L-1 Na2CO3 pH 9 and +0.2 V, and, it showed a practically selective reaction to methanol (producing 5.63 mmol L-1), corresponding to 20% of conversion at ambient of 0.1 mol L-1 NaHCO3/Na2CO3 butter solution pH 8, using UV light of 125 W and +0,2 V. The CuNbO3-CuO and Cu0,85Zn0,15Nb2O6 powder semiconductors also showed a good efficiency to the methanol formation throughout dissolved CO2 reduction in 0.1 mol L-1 Na2CO3 pH 8 using visible light of 450 W, and forming 7 mmol L-1 and 3.2 mmol L-1 of methanol, respectively. The results obtained in this work show that both techniques can be employed for the CO2 reduction, using for this the Cu/Cu2O, CuNbO3-CuO and Cu0,85Zn0,15Nb2O6 semiconductors, and it could be a potential alternative to the environmental problems and contribute as raw material source for the production of fuels, for instance.
6
Brito, Juliana Ferreira de. "Estudo da redução fotocatalítica e fotoeletrocatalítica de 'CO IND. 2' em meio aquoso sobre 'CU'/'CU IND. 2 'O'', 'TI' 'O IND. 2'/'PT', 'CU''NB' 'O IND. 3' - 'CU''O' e 'CU IND. 0,85''ZN IND. 0,15''NB IND. 2''O IND.6' como catalisadores para formação de metanol /." Araraquara, 2014. http://hdl.handle.net/11449/110841.
Abstract:
Orientador: Maria Valnice BoldrinBanca: Mário César Guerreiro
Banca: Luiz Henrique Dall'antonia
Resumo: O presente trabalho reporta os principais resultados obtidos na construção e caracterização de eletrodos de titânio recobertos com nanotubos de óxido de titânio modificados com nanopartículas de platina (TiO2/Pt) e eletrodos de cobre recobertos com nanopartículas de óxido de cobre (Cu/Cu2O) com vistas a sua aplicação na redução fotoeletrocatalítica de CO2 em meio aquoso e semicondutores em pó de CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 e ZnNb2O6-Nb2O5 construídos e testados na redução fotocatalítica de CO2, com vistas a geração de produtos com maior valor agregado, tal como metanol. Os eletrodos TiO2/Pt e Cu/Cu2O foram construídos por meio de técnicas de eletroquímicas, enquanto que os semicondutores em pó CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 e ZnNb2O6-Nb2O5 foram preparados utilizando a técnica de síntese por combustão e calcinação posterior. A redução fotoeletrocatalítica e fotocatalítica de CO2 não foi satisfatória sobre eletrodos de TiO2/Pt e semicondutor ZnNb2O6-Nb2O5, respectivamente. No entanto, o eletrodo de Cu/Cu2O apresentou grande eficiência na redução de CO2, atingindo 80% de remoção em meio de Na2CO3 0,3 mol L-1 pH 9 a +0,2 V, em solução tampão de NaHCO3/Na2CO3 0,1 mol L-1 pH 8, utilizando luz UV 125 W e potencial de +0,2 V mostrou uma reação praticamente seletiva para metanol, gerando 5,63 mmol L-1, correspondendo a 20% de conversão. Os semicondutores em pó CuNbO3-CuO e Cu0,85Zn0,15Nb2O6 também se mostraram bastante eficientes para a geração de metanol por redução de CO2 dissolvido em Na2CO3 0,1 mol L-1 pH8 utilizando luz visível de 450 W, chegando a formar 7,0 mmol L-1 e 3,2 mmol L-1 de metanol respectivamente. Os resultados obtidos neste trabalho mostram que ambas as técnicas podem ser empregadas para a redução do CO2, usando para isto os semicondutores Cu/Cu2O, CuNbO3-CuO e Cu0,85Zn0,15Nb2O6 e, poderia ser uma potencial alternativa para os problemas ambientais além de contribuir como fonte...
Abstract: This present work reports the main results obtained with the construction and characterization of TiO2 nanotubes modified by platinum nanoparticle electrode (TiO2/Pt) and copper covered by copper oxide nanoparticles electrode (Cu/Cu2O) for application in the photoelectrocatalytic reduction of dissolved CO2 and CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 and ZnNb2O6-Nb2O5 powders semiconductors constructed and applied in the photocatalytic reduction of dissolved CO2 for the generation of products with higher added value. The TiO2/Pt and Cu/Cu2O electrodes were prepared by electrochemical techniques, whereas the CuNbO3-CuO, Cu0,85Zn0,15Nb2O6 and ZnNb2O6-Nb2O5 powder semiconductors were prepared using the combustion synthesis technique and submitted to annealed. The CO2 reduction by photoelectrocatalysis and photocatalysis were not satisfactory when using the TiO2/Pt electrode and the ZnNb2O6-Nb2O5 semiconductor, respectively. However, the Cu/Cu2O electrode shows a high efficiency in the CO2 reduction obtaining 80% of removal in 0.3 mol L-1 Na2CO3 pH 9 and +0.2 V, and, it showed a practically selective reaction to methanol (producing 5.63 mmol L-1), corresponding to 20% of conversion at ambient of 0.1 mol L-1 NaHCO3/Na2CO3 butter solution pH 8, using UV light of 125 W and +0,2 V. The CuNbO3-CuO and Cu0,85Zn0,15Nb2O6 powder semiconductors also showed a good efficiency to the methanol formation throughout dissolved CO2 reduction in 0.1 mol L-1 Na2CO3 pH 8 using visible light of 450 W, and forming 7 mmol L-1 and 3.2 mmol L-1 of methanol, respectively. The results obtained in this work show that both techniques can be employed for the CO2 reduction, using for this the Cu/Cu2O, CuNbO3-CuO and Cu0,85Zn0,15Nb2O6 semiconductors, and it could be a potential alternative to the environmental problems and contribute as raw material source for the production of fuels, for instance.
Mestre
7
TROUILLEUX, LIONEL. "Elaboration et etude des proprietes electriques et magnetiques de ceramiques supraconductrices texturees dans les systemes la-sr-cu-o, nd-ce-cu-o et bi-sr-ca-cu-o." Paris 11, 1991. http://www.theses.fr/1991PA112031.
Abstract:
Des ceramiques supraconductrices texturees ont ete elaborees par solidification dirigee, dans les systemes la-sr-cu-o, nd-ce-cu-o et bi-sr-ca-cu-o. L'existence d'une transformation eutectique entre la#2##xsr#xcuo#4 (ou nd#2##xce#xcuo#4) et cuo, nous a permis d'obtenir des materiaux biphases a microstructures orientees. Dans le systeme bi-sr-ca-cu-o, des materiaux textures quasiment monophases, constitues de plaquettes supraconductrices orientees parallelement a l'axe de croissance ont ete elabores a partir de compositions voisines de la stchiometrie du compose bi#2sr#2cacu#2o#8. L'etude par diffraction x revele une direction de croissance preferentielle 110 pour la phase supraconductrice dans les trois systemes. Les densites de courant critique jc, evaluees a partir de cycles d'aimantation en utilisant le modele de bean, sont respectivement de 3 10#5, 10#3 et 10#6 a?cm##2 a 4 k pour les composes la#2##xsr#xcuo#4 (x0,14), nd#2##xce#xcuo#4 (x0,17) et bi#2sr#2cacu#2o#8. Une anisotropie jc#a#b/jc#c30 a ete determinee pour les composes la#2##xsr#xcuo#4 et bi#2sr#2cacu#2o#8. Les temperatures de milieu de transition supraconductrice, determinees par des mesures de resistivite, sont respectivement 36 k, 21 k et 92 k pour ces trois composes. Les densites de courant critique jc, determinees par transport selon l'axe de solidification sont de 800 a?cm##2 a 18 k pour la#2##xsr#xcuo#4 et de 3000 a?cm##2 a 77 k pour bi#2sr#2cacu#2o#8. Ces valeurs sont tres superieures a celles obtenues dans des materiaux polycristallins isotropes. Ceci resulte de l'orientation des joints de grains et des plans de conduction (cu-o) de la phase supraconductrice selon l'axe de solidification
8
Porch, Adrian. "Microwave surface impedance of YBa₂Cu₃O₇." Thesis, University of Cambridge, 1992. https://www.repository.cam.ac.uk/handle/1810/283677.
9
Teruzzi, Tiziano. "Investigation of the vortex dynamics in the high-temperature superconductors Bi₂Sr₂CaCu₂O₈, YBa₂Cu₃O₇₋{delta} and YBa₂Cu₄O₈ /." Zürich, 1993. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10361.
10
Schorne, Pinto Juliano. "Etude expérimentale et modélisation thermodynamique de systèmes de delafossites à base de cuivre." Thesis, Toulouse, INPT, 2020. http://www.theses.fr/2020INPT0006.
Abstract:
Ce travail de thèse multidisciplinaire a été dédié à l’étude des phases CuMO2 avec M = {Cr et Fe} de la famille structurale delafossite. Dans le but principal d’élargir les connaissances et de combler les lacunes autour des propriétés thermodynamiques de ce type de phases, une étude expérimentale approfondie des systèmes Cu-Fe-O et Cu-Cr-O a été menée. Les principaux résultats obtenus sont : a) pour la première fois, une non-stœchiométrie cationique pour la phase delafossite du type CuFe1-yO2- avec y 0.12 a été démontrée, b) les coordonnées du point eutectique du système Cu-Fe-O sous air ont été mesurées à 1049(3) °C pour une composition x(Fe) = 0.105, c) le domaine de stabilité de la phase CuFeO2 sous air est compris entre 1022(2) °C et 1070(2) °C, d) une absence de solution solide à structure delafossite CuCrO2 a été constatée pour les teneurs x(Cr) < 0.50, e) une légère solubilité de chrome dans la phase delafossite avec une valeur maximale de x(Cr) = 0.524(8) a été mesurée dans cette phase, f) la phase spinelle CuCr2O4 est stœchiométrique du fait de l’invariance des paramètres structuraux et de la composition chimique et g) les propriétés thermodynamiques de la phase delafossite CuCrO2 ont été déterminées pour la première fois et les valeurs retenues pour cette phase sont : fH298(CuCrO2) = 670 800 ± 1 400 J/mol, S°298(CuCrO2) = 88.89 J/mol et cp = 102.564 2.872.10-73 128 5421.5 entre [298 < T < 1300]. Ces résultats ont été couplés avec ceux issus de la bibliographie pour la construction d’un modèle thermodynamique générique décrivant les propriétés des phases delafossite, liquide et spinelles dans les sous-systèmes du quaternaire Cu-Cr-Fe-O. La solution liquide a été modélisée par le Modified Quasichemical Model ((Cu1+,Cu2+,Cr1+,Cr2+,Cr3+,Fe1+,Fe2+,Fe3+)(O2-,Va1-)) et les binaires Cu-O et Cr-O ont été réévalués. Une description simplifiée de la solution solide à structure delafossite selon le modèle Compound Energie Formalism a été proposée selon (Cu1+,Cu2+)1 [Cr3+,Fe3+,Cu2+]1 O2 (Va0,O2-)1. Enfin, les systèmes ternaires ont été modélisés par la méthode Calphad, en complétant un modèle existant pour Cu-Fe-O et en établissant un modèle pour Cu-Cr-O. Une projection pour le système quaternaire Cu-Cr-Fe-O a même été proposéeThis multidisciplinary thesis work was dedicated to the study of CuMO2 phases with M = {Cr and Fe} of the delafossite structural family. With the main aim of broadening knowledge and filling the gaps around the thermodynamic properties of this type of phase, an in-depth experimental study of the Cu-Fe-O and Cu-Cr-O systems was carried out. The main results obtained are: a) for the first time, a cationic non-stoichiometry for the delafossite phase of the CuFe1-yO2- type with y 0.12 has been found, b) the coordinates of the eutectic point of the Cu-Fe-O system in air were measured at 1049(3) °C for a composition x(Fe) = 0.105, c) the CuFeO2 phase is stable between 1022(2) ° C and 1070(2) ° C in air, d) an absence of solid solution with a delafossite structure CuCrO2 was observed for x (Cr) < 0.50, e) a slight solubility of chromium in CuCrO2 with a maximum value of x (Cr) = 0.524(8) was measured in this phase, f) the spinel phase CuCr2O4 was defined as stoichiometric by the invariance of the structural parameters and the chemical composition, at last g) the thermodynamic properties of the delafossite phase CuCrO2 were determined for the first time, with the selected values for this phase being: fH298(CuCrO2) = 670 800 ± 1400 J / mol, S°298(CuCrO2) = 88.89 J/mol and cp = 102.564 2.872.10-73 128 5421.5 between [298 <1300]. These results were coupled with those from the bibliography for the construction of a generic thermodynamic model describing the properties of the delafossite, liquid, and spinel phases in the quaternary Cu-Cr-Fe-O subsystems. The liquid phase was modeled by the Modified Quasichemical Model ((Cu1+,Cu2+,Cr1+,Cr2+,Cr3+,Fe1+,Fe2+,Fe3+)(O2-,Va1-)) and the binaries Cu-O and Cr-O were re-evaluated . A simplified description of the delafossite solid solution by the Compound Energy Formalism model has been proposed according to (Cu1+,Cu2+)1 [Cr3+,Fe3+,Cu2+]1 O2 (Va0,O2-)1. Finally, the Cu-Fe-O and Cu-Cr-O ternary systems have been modeled by the Calphad method with good experimental agreement. A projection for the Cu-Cr-Fe-O quaternary system has even been proposed
11
Raichle, Markus. "Neutron scattering studies of doped cuprates: Na 8 Cu 5 O 10 and YBa 2 Cu 3 O 6+x." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-35797.
12
Delap, Martin Richard. "Thermal conductivity studies of YBa₂Cu₃O₇₋δ." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/9301/.
Abstract:
Apparatus to measure the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) at temperatures between 20K and 120K has been designed and constructed. The thermal conductivity is measured using a longitudinal steady state heat flow technique. Thermal conductivity measurements have been performed upon a sample of YBa(_2)Cu(_3)O(_7-δ) which has been subjected to a series of heat treatments in order to remove oxygen from the material. The measurements show conclusively that the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) is very strongly influenced by the oxygen content of the material. A reduction of the oxygen content of the material results in a substantial lowering of the thermal conductivity. To explain this result, a quantitative model has been constructed; the model demonstrates that consideration of the changes in phonon interactions alone cannot account for the differences in the behaviour of the thermal conductivity of YBa(_2)Cu(_3)O(_6) and YBa(_2)Cu(_3)O(_7). In addition; the model, shows that there must be a significant carrier contribution to the thermal conductivity in both the normal and superconducting states. A physical process has been proposed which provides the required large carrier contribution below T(_c). Further studies have been performed on a series of samples of YBa(_2)Cu(_3)O(_7-δ) which were sintered at slightly different temperatures. Qualitative analysis of the physical properties, of these samples has been performed.
13
Caillard, Renaud. "Synthèse, propriétés supraconductrices et thermomécaniques de céramiques texturées des systèmes Y-Ba-Cu-O et Bi-Pb-Sr-Ca-Cu-O." Caen, 2002. http://www.theses.fr/2002CAEN2016.
Abstract:
Au cours de leur cycle d'utilisation, les céramiques supraconductrices sont soumises à des contraintes mécaniques et / ou thermiques qui peuvent entraîner une dégradation rédhibitoire des performànces électriques, voire la destruction des dispositifs. Dans ce travail, nous avons élaboré puis évalué les caractéristiques thermomécaniques de céramiques texturées des systèmes Y-Ba-Cu-O et Bi-Pb-Sr-Ca-Cu-O. Pour assurer une stoechiométrie et une homogénéité constantes et maîtrisées des matières de départ, nous avons synthétisé les poudres précurseurs par voie sol-gel pour Bi2223 et par voie solide pour Y123. Les conditions optimales de formation (température et durée de frittage sous air) de la phase Bi2223 ont été déterminéess et les produits finaux caractérisés par diffraction RX, granulométrie et par des observations au MEB. L'influence des paramètres majeurs de frittage-forgeage (cycles thermiques et de pressage, durée de maintien sous charge) a été étudié et un cycle optimisé sous air a ainsi été défini par une température de 845° C et une contrainte de 23,6 MPa appliquée pendant 20 heures. La texturation du système Y-Ba-Cu-O a été effectuée par la méthode de Top Seeding Melt Texture growth (TSMTG) [etc]
14
Gauzzi, Andrea. "Disorder and fluctuations in superconducting YBa₂Cu₃O₆.₉ films /." Lausanne, 1993. http://library.epfl.ch/theses/?nr=1184.
15
Li, Qiang. "Theoretical calculation of muon site in YBa₂Cu₃O." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29415.
Abstract:
The muon is a useful probe of magnetic fields in superconductors, but knowing the field seen by the muon is often of limited value until we know where the muon is in the crystal lattice. In this thesis I employ two independent theoretical methods to search for candidate muon sites: the potential energy field method, which seeks the minimum of the electrostatic potential of the μ⁺, and the magnetic dipolar field method, which compares the calculated magnetic field (due to the host electronic, atomic or nuclear dipolar fields) with the observed local fields at the muon.Science, Faculty of
Physics and Astronomy, Department of
Graduate
16
Poisl, W. Howard. "Sintering kinetics of the superconducting YBa₂Cu₃O compound." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/29752.
Abstract:
The effect of oxygen partial pressure and temperature on the solid state sintering kinetics of the superconducting ceramic YBa₂Cu₃O₇₋₈ has been investigated. The isothermal contraction behavior of YBa₂Cu₃O₇₋₈ in the temperature range 930 - 960°C with oxygen partial pressures varying from 0.001 to 1.0 atmospheres was studied. The change in the unit cell lattice parameters of YBa₂Cu₃O₇₋₈ over this oxygen partial pressure range was also determined in order to evaluate its effect on the sintering behavior.
The sintering kinetics of YBa₂Cu₃O₇₋₈ were investigated through the variation of the isothermal steady state contraction rate with respect to oxygen partial pressure at different temperatures. Isothermal contraction rates between 930 and 955°C reached a maximum at some critical oxygen partial pressure, PO₂CRIT, with decreasing contraction rates both above and below this oxygen partial pressure. This behavior was not observed for YBa₂Cu₃O₇₋₈ sintered at 960°C. SEM micrographs of the fracture surface of these samples suggest that a liquid phase was formed at this temperature. The unit cell volume and a-lattice parameter of YBa₂Cu₃O₇₋₈ decreased with decreasing oxygen partial pressure, while the c-lattice parameter increased.
The activation energy for sintering at oxygen partial pressures above PO₂CRIT has been estimated to be approximately 191 kJ/mole, which is similar to oxygen ion diffusion in this compound, indicating that for oxygen partial pressures above PO₂CRIT, oxygen diffusion is the rate controlling mechanism for mass transport. The activation energy for sintering below PO₂CRIT was found to be ∽130 kJ/mole, which could also be due to oxygen ion diffusion. Several possible factors have been considered for the sintering behavior of YBa₂Cu₃O₇₋₈ for oxygen partial pressures below PO₂CRIT. These are formation of copper vacancies, positive hole creation, and lattice strain effect. However, although the oxygen
partial pressure dependence on the sintering rate can be correlated with either the formation of Cu²⁺ vacancies in the lattice or hole formation, neither of these mechanisms are considered to be probable.
Mathematically, the contraction rate was found to depend exponentially on the lattice strain (Δɛlat), ie. έ∞еΔɛlat. The significance of this relationship is not clearly understood. Intuitively, it appears that as the vacancies are created due to the removal of oxygen ions from the lattice, the lattice is not contracting to the extent needed to accommodate the vacancies. This elastic strain hinders the migration of the oxygen vacancies through the lattice, thus affecting the sintering rate of the YBa₂Cu₃Ox compound below PO₂CRIT.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
17
Siah, Sin Cheng. "Defect Engineering in Cuprous Oxide (Cu₂O) Solar Cells." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100143.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 105-109).
This thesis is focused on the development of a cuprous oxide (Cu₂O) thin-film (TF) solar cell that is fabricated by manufacturing-friendly methods such as electro-deposition, sputtering and atomic layer deposition. Due to its bandgap of close to 2 eV, it has the potential of being applied as top cell in a tandem configuration. Firstly, I perform bottom-up cost and price analysis to investigate the economic feasibility of TF and c-Si based tandem photovoltaic modules. Next, I investigate the formation of good ohmic back contacts on Cu₂O absorber layer and demonstrate that low contact resistivity can be achieved with a variety of metals on heavily doped Cu₂O films by forming a tunnel junction. Then, I apply synchrotron-based X-ray absorption spectroscopy (XAS) to characterize two front contact buffer materials: amorphous Zn-Sn-O (a-ZTO) and Sndoped Ga₂O₃. I elucidate a fundamental loss mechanism in the amorphous Zn-Sn-O (a-ZTO) electron-blocking layer that has origin in local structural disorder and establish the structure-process- property relationship of a-ZTO so that the front buffer layer can be optimized for photovoltaics. Then, I investigate the doping mechanism of Sn dopant atoms in TFs and single crystalline Ga₂O₃:Sn by revealing the doping mechanism so that Ga₂O₃:Sn can be optimized for photovoltaics. Lastly. I apply bulk defect engineering to manipulate the intrinsic point defect structure of Cu₂O towards improved device performance. The key results will inform the processing conditions for improving mobility and minority carrier lifetime in Cu₂O. Keywords - Earth-abundant, thin-film solar cells, tandem, defect engineering, cost modeling, synchrotron.
by Sin Cheng Siah.
Ph. D.
18
Gershon, Talia. "Strategies for improving solution-processed ZnO/Cu₂O photovoltaics." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610663.
19
Fauth, François. "Etude par diffusion neutronique des composés orientés HoBa₂Cu₃Ox (x=7, 6.2), ErBa₂Cu₃O₇ et d'un cristal Nd₁₊xBa₂₋y₋zSrzCu₃O₆.₇ /." Zürich, 1996. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=11583.
20
Ludwig, H. [Verfasser]. "Unaxiale Druckexperimente an YBa₂Cu₃O₆₊ₓ-Einkristallen / H. Ludwig." Karlsruhe : KIT-Bibliothek, 1998. http://d-nb.info/1198220201/34.
21
Marin, Andrew. "Electrical characterization of atmospherically deposited ZnO/Cu₂O photovoltaic devices." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608206.
22
Withnell, Thomas David. "Flux trapping properties of bulk RE-Ba-Cu-O superconductors." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612195.
23
Souza, Junior Edvaldo Alves de. "Filmes Cu-V-O para aplicações em catodos de microbaterias." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277289.
Abstract:
Orientador: Annette GorensteinTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-05T23:58:57Z (GMT). No. of bitstreams: 1 SouzaJunior_EdvaldoAlvesde_D.pdf: 2701192 bytes, checksum: 949e8dd1afc482f52e573f2b9fbca63a (MD5) Previous issue date: 2006
Resumo: O pentóxido de vanádio é um dos compostos de intercalação mais conhecidos na área de baterias de lítio. Dada sua estrutura lamelar, íons de lítio podem ser inseridos e extraídos de forma reversível, o que torna o pentóxido de vanádio promissor para uso como catodo. No entanto, o armadilhamento de parte dos íons de lítio a cada ciclo de carga e descarga provoca a perda gradativa da capacidade. A incorporação de íons metálicos na estrutura do V2 >O5 é uma das alternativas para melhorar seu desempenho nos ciclos de carga e descarga. Por outro lado, foi demonstrado que o óxido de cobre nanoparticulado é capaz de fornecer alta capacidade de carga em processos reversíveis de inserção e extração de íons lítio. Esta tese se propõe estudar a inserção/extração de íons de lítio em filmes finos de óxidos de cobre-vanádio objetivando sua aplicação em catodos de microbaterias. Um conjunto de amostras foi obtido iniciando-se com o pentóxido de vanádio, e através de acréscimos de cobre e decréscimos de vanádio, atingindo o óxido de cobre II. Óxidos bronzes, complexos, mistos e puros foram obtidos. As amostras foram depositadas através da técnica de sputtering. Na caracterização das amostras foram utilizadas técnicas de difração de raios-X, retroespalhamento Rutherford, emissão de fotoelétrons de raios-X, absorção de raios-X (XANES) e microscopia de força atômica. A inserção de íons de lítio foi realizada através da cronopotenciometria. Cada classe de óxidos apresentou características eletroquímicas próprias. Óxidos de cobre apresentaram uma capacidade de inserção de carga quatros vezes maior que a capacidade do pentóxido de vanádio (109 µAh/cm 2-µm). Bronzes de vanádio apresentaram maior estabilidade entre todos óxidos, e melhor capacidade, quando comparado com o V2 O5. A introdução de átomos de vanádio na matriz CuO permitiu a formação de óxidos mistos com maior estabilidade eletroquímica quando comparados à filmes CuO
Abstract: In the field of lithium batteries, vanadium pentoxide is one of the most studied intercalation compound. Due to its lamellar structure, lithium ions can be reversibly inserted and extracted, and the material is a promising candidate for use as a cathode. However, trapping of part of the lithium ions in each charge/discharge cycle causes a gradative loss of capacity. The incorporation of metallic ions in the V22O5host structure is one of the alternatives to improve its cycling behavior. On the other hand, it was recently demonstrated that nanosized copper oxide is capable of providing high charge capacity in reversible lithium insertion/extraction processes. The aim of the present work is to study the insertion/extraction of lithium ions in thin films of copper-vanadium oxides for application as cathode in microbatteries. A range of samples was produced, starting from pure vanadium pentoxide. By increasing the amounts of copper and decreasing the amount of vanadium in the film, the copper oxide II composition was attained. Different classes of oxides, such as bronzes, complex oxides, mixed oxides and the pure oxides were obtained. The samples were deposited by sputtering. The characterization was performed using X-Ray diffraction, Rutherford Backscattering spectrometry, X-Ray Photoemission Spectroscopy, X-Ray Absorption Spectroscopy (mainly XANES) and Atomic Force Microscopy. The electrochemical behavior was analyzed mainly by chronopotentiometry. Each class of oxides presented distinct electrochemical properties. Copper oxide films presented an insertion capacity four times greater than the capacity of the vanadium pentoxide films (109 µAh/cm 2-µm). Vanadium bronzes presented the best stability among all of the investigated materials, and a higher capacity in comparison to vanadium pentoxide. The insertion of vanadium atoms in the CuO structure allowed the obtention of mixed oxides films with higher electrochemical stability if compared to pure CuO films
Doutorado
Superfícies e Interfaces ; Peliculas e Filamentos
Doutor em Ciências
24
Touron, Rivadulla José Luis. "Equilibrio termodinámico y caminos de solidificación del sistema CU-O-H-Pb." Doctoral thesis, Universitat Autònoma de Barcelona, 2001. http://hdl.handle.net/10803/3334.
25
PAPILLON, STEPHANE. "Etude de la production du j/psi dans les reactions p-cu, p-u, o-cu, o-u et s-u a 200 gev par nucleon." Paris 7, 1991. http://www.theses.fr/1991PA077069.
Abstract:
L'experience na38 etudie la production de dimuons dans des collisions induites par des ions lourds a 200 gev par nucleon. Quand la densite d'energie augmente, une suppression de la production du meson j/psi par rapport aux paires de muons dans le continuum a ete observee. Cet effet est attendu en cas de formation d'un plasma de quarks et de gluons, etat de la matiere nucleaire predit par la chromodynamique quantique. La principale difficulte de cette analyse reside dans l'evaluation de l'important bruit de fond genere par les desintegrations de pions et de kaons. Le present travail reprend l'analyse de l'ensemble des donnees de l'experience, sur la base d'une methode statistique d'estimation du bruit de fond. Cette methode, qui s'appuie sur l'information tiree des muons simples deduits des paires de muons mesurees dans l'appareillage, permet une amelioration sensible de la precision sur le signal. Cette analyse montre que la suppression relative du j/spi par rapport au continuum est plus importante dans les reactions noyau-noyau que dans les reactions proton-noyau. De plus, elle montre que la production de dimuons dans le continuum depend de l'isospin du projectile, ce qui rend delicate la comparaison aux collisions induites par des protons. Efin l'etude de la production du j/psi en fonction de la densite d'energie ne permet pas de favoriser une interpretation de la suppression en termes de plasma plutot qu'en termes d'absorption dans le gaz de mesons, bien que la valeur absolue de l'effet ne soit pas totalement comprise
26
Choi, Siyoung. "Synthesis and Magnetic Properties of ZrO2 or MgO-containing Y-Ba- Cu-O and Bi-Sr-Ca-Cu-O Superconductors prepared by self-propagating chemical decomposition /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487859313343754.
27
Morgan, Benjamin. "Microwave surface impedance of YBa₂Cu₃O₆.₉₅ in the mixed state." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615118.
28
Derro, David Joseph. "A scanning tunneling microscopy investigation of YBa₂Cu₃O₇-[subscript x] /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
29
Kearney, Jonathan. "Cu/CeₓZr(₁₋ₓ)O₂ catalysts for solid oxide fuel cell anodes." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1845.
Abstract:
Ce[subscript(x)]Zr[subscript(1-x)]O₂ mixed oxides of varying compositions were prepared by a sol-gel citrate complexion technique. In order to improve the catalytic activity of the oxides they were impregnated with copper using two different impregnation techniques. The bare oxides and copper impregnated samples were investigated using a range of Temperature Programmed (TP) techniques, in an attempt to establish their effectiveness as anode materials for solid oxide fuel cells (SOFCs) run on hydrocarbon fuels. In order to conduct the TP experiments a novel system was designed and constructed. The high Ce containing mixed oxides were shown to be reduced at lower temperature than high Zr content samples. TPRx experiments were employed to investigate which of the oxides was most prone to carbon deposition when reacted in methane, with the high ceria sample displaying the lowest level of carbon deposition. Lightoff experiments were undertaken to establish which oxide composition was the most active for methane oxidation. The activity of the oxides increased with ceria content up to 75 mole% (ZCe75), before decreasing for ZCe90. All the mixed oxides were shown to be more active for methane oxidation than CeO₂.
30
Frison, Jean-Claude. "Cristallogenèse et caractérisations d'oxydes supraconducteurs du système Tl-Ba-Ca-Cu-O." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1990. http://tel.archives-ouvertes.fr/tel-00170306.
Abstract:
Les cristaux de phases supraconductrices de formulation générale, TlmBa2Can-1CunO2n+m+2 (avec m=1, 2 et n=1, 2, 3) ont été préparés par une technique de croissance en flux. Chaque phase a été caractérisée par diffraction X (Weissenberg, Buerger, cristal tournant) et par micro-spectroscopie Raman. L'analyse par microsonde électronique a révélé des déficits cationiques par rapport a la formulation idéale. Une étude par HREM a montré dans la plupart des cristaux l'absence d'intercroissance à l'échelle atomique. La température critique a été mise en évidence par mesures électriques, mesures sous champ magnétique continu et susceptibilite alternative. Le comportement magnétique révèle une très forte anisotropie entre les propriétés supraconductrices dans la direction de l'axe c et dans le plan (a, b) (Hc1(c)/Hc1(a,b)=1000 pour la phase 2212). Les courbes d'effet Meissner et d'effet d'écran révèle que l'aimantation est réversible près de Tc et irréversible a plus basse température. La ligne d'irréversibilite (H*, T*) a été caractérisée pour la phase 2212.
31
Bradley, Alistair David. "Fabrication and characterisation of joins in melt-textured YBa₂Cu₃O₇-δ." Thesis, University of Cambridge, 2000. https://www.repository.cam.ac.uk/handle/1810/251484.
Abstract:
The development of bulk superconductors for engineering applications, where large critical current densities (Jc's) must be supported over large areas and at relatively high fields and temperatures, is one of the key issues in current superconductivity research. Melt-textured YBa2Cu2O7-δ (YBCO) offers the greatest potential for such applications, however the limited size of single grains which can be grown and the limited Jc supported by grain boundaries (GBs) have presented major hurdles. This thesis describes the fabrication of joins between YBCO grains, which opens up the possibility of producing larger samples of any shape and orientation. The joining technique uses a barium-cuprate 'liquid phase' released from the grains themselves above 920°C to mediate the epitaxial growth of YBCO across the interface between two grains. The microstructure and composition of joins fabricated with different orientations were investigated using optical, transmission electron and secondary electron microscopy. Extensive electrical measurements were made in order to determine the electromagnetic properties of the joins. Measurement of resistance as a function of temperature revealed information about the GB formed at the join. The maximum field dependent temperatures at which a Jc could be supported by different joins was determined (the 'irreversibility line') and compared directly with that of the adjoining grain material. The results have shown that joins with well defined GBs are formed, generally behaving like those found in other bulk and thin-film YBCO samples. Further optimisation of the joining technique is required, however great promise is shown for scale-up of the process to produce samples suitable for engineering applications.
32
Mingard, Kenneth Philip. "Stucture and properties of sputter deposited Y-Ba-Cu-O thin films." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276884.
33
Ramsay, Jonathan M. "A theoretical study of helium diffraction from the O/Cu(100) surface." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363604.
34
Harrison, Neil. "The de Haas-van Alphen effect in Y-Ba-Cu-O superconductors." Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317152.
35
Daniels, Michael W. (Michael William). "Radio-frequency properties of melt-recrystallized YBa₂Cu₃O₇â[delta] fibers." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32616.
Abstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.On t.p., "[delta]" appears as the lower case Greek letter, in subscript. Vita.
Includes bibliographical references (p. [67]-69).
by Michael W. Daniels.
M.S.
36
Moya, Bonhomme Alejandro. "YBa₂CU₃O₇₋δ d.c.SQUID magnetometers : from film deposition to field imaging." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624375.
37
Pathak, Sandeep Kumar. "Processing, flux pinning and recycling of Y-Ba-Cu-O bulk superconductors." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609209.
38
Maritz, E. J. (Erasmus Jacobus). "Flux creep in pulsed laser deposited superconducting YBa₂Cu₃O₇ thin films." Thesis, Stellenbosch : University of Stellenbosch, 2002. http://hdl.handle.net/10019.1/6394.
Abstract:
Thesis (PhD (Physics))--University of Stellenbosch, 2002.Includes bibliography.
ENGLISH ABSTRACT: High temperature superconductivity is an important topic in contemporary solid state physics, and an area of very active research. Due to it’s potential for application in low temperature electronic devices, the material has attracted the attention of researchers in the electronic engineering and material science fields alike. Moreover, from a fundamental point of view, several questions remain unanswered, related to the origin of superconductivity of this class of materials and the nature of quantised magnetic flux present in magnetised samples. In this work, flux creep phenomena in a thin superconducting YBa₂Cu₃O₇ film deposited by pulsed laser deposition, is investigated near the critical temperature 0 ≤ Tc – T ≤ 10 K. Creep activation energy U0 and critical current density jc were determined as a function of temperature close to Tc, providing important data to a problem of high-Tc superconductivity which is still a matter of debate. In particular it is still an open question whether restoring the temperature in a creep freezing experiment in fact restores the film to it's original state before the freezing. The most important novel results concern the regime of critical fluctuations in the vicinity Tc - T < 1 K. We studied the isothermal relaxation of trapped magnetic flux, and determined that the long time decay follows a power law, where the exponent is inversely proportional to the creep activation energy. The temperature dependence of the critical current density jc(T) of the YBa₂Cu₃O₇ film close to Tc was obtained during warming runs. It was determined that jc(T) follows a square root dependence on T to high accuracy in the range 0.2 ≤ Tc – T ≤ 1.5 K. During flux creep experiments an interesting phenomenon called creep freezing related to the strong temperature dependence of the relaxation rate was observed. A pronounced slowing of relaxation with only a small drop in temperature from a starting temperature close to Tc was detected. Experiments were conducted by initiating an isothermal flux decay run. At a certain point the temperature was slightly lowered, and the flux decay stopped within experimental accuracy. When the temperature was restored to the initial value, the flux decay resumed at the previous rate before cooling. An argument based on vortex drift velocity was employed to explain the phenomenon qualitatively. During the course of this investigation, a pulsed laser deposition (PLD) system was designed and built from scratch. PLD involves the interaction of a focussed laser pulse with a multielemental solid target material. Material ablated from the target forms a fast moving plume consisting of atomic and molecular particles, directed away from the target, and towards a usually heated substrate on which the particles condense layer by layer to form a thin film. The substrate temperature and background gas are carefully controlled to be conductive to the growth of a desired phase of the multi-elemental compound. The PLD system proved to be quite versatile in the range of materials that could be deposited. It was used to deposit thin films of different materials, most notable were good quality superconducting YBa₂Cu₃O₇, thermochromic VO2, and magnetoresistive LaxCa1-xMnO3. Metallic Au and Ag layers were also successfully deposited on YBa2Cu3O7 thin films, to serve as protective coatings. The critical temperatures of the best superconducting films were 90 K as determined by resistivity measurement. The optimal deposition conditions to deposit high quality superconducting YBa₂Cu₃O₇ thin films was found to be: deposition temperature 780°C, laser energy density 2-3 J/cm2, oxygen partial pressure 0.2 mbar, and target-substrate distance 35 mm. This yields film with Tc ~ 90 K. It was found that deposition temperature plays the predominant role in determining the quality of YBa₂Cu₃O₇ thin films deposited by PLD.
AFRIKAANSE OPSOMMING: Hoë temperatuur supergeleiding is tans ’n aktuele onderwerp van vastetoestandfisika en dit is ’n gebied van baie aktiewe navorsing. Weens die potensiaal vir toepassings van hoë temperatuur supergeleiers in elektronika, het dié klas materiale die aandag van fisici and elektronici getrek. Verskeie fundamentele vraagstukke bly steeds onbeantwoord, veral met betrekking tot die oorsprong van supergeleiding in hierdie materiale en die gedrag van gekwantiseerde magnetiese vloed (“vortekse”) in gemagnetiseerde monsters. In hierdie werk word diffusie van vortekse in dun supergeleidende YBa₂Cu₃O₇ films ondersoek naby die kritieke temperatuur (0 ≤ Tc - T ≤ 10 K). Die temperatuur afhanklikheid van die diffusie aktiveringsenergie U0 en die kritieke stroomdigtheid jc word bepaal naby Tc. Dit verskaf belangrike inligting tot probleme in hoë temperatuur supergeleiding wat tans nog onbeantwoord bly. In die besonder is dit steeds ’n ope vraag of die herstel van die aanvanklike temperatuur in ’n vloedstollings eksperiment waarlik die film tot die oorspronklike toestand herstel. Die belangrikste nuwe resultate hou verband met die gebied van kritieke fluktuasies van die orde parameter in die omgewing 0 < Tc - T < 1 K. Ons het die isotermiese ontspanning van vortekse verstrik in die kristalstruktuur bestudeer, en bepaal dat die lang tydsverval ’n magsverwantskap handhaaf, waar die eksponent omgekeerd eweredig is aan U0. Die temperatuur afhanklikheid van die kritieke stroomdigtheid jc(T) van die YBa₂Cu₃O₇ film naby Tc is bepaal tydens verhittingslopies. Daar is bevind dat naby Tc, jc ’n vierkantswortel verband met T volg, tot hoë noukeurigheid in die gebied 0.2 ≤ Tc – T ≤ 1.5 K. Gedurende vorteksdiffusie eksperimente is ’n interessante verskynsel naamlik vloedstolling (“flux freezing”) waargeneem. Dit hou verband met die sterk temperatuur afhanklikheid van die vervaltempo van die magnetiese moment van ’n gemagnetiseerde film. ’n Skerp daling van die vervaltempo, weens slegs ’n klein temperatuurdaling vanaf die begin temperatuur naby Tc, is waargeneem. Gedurende eksperimente is daar aanvanklik ’n isotermiese vloedontspanning teweeg gebring. Op ’n sekere tydstip is die temperatuur effens verlaag, waarby die vloedontspanning tot stilstand gekom het binne grense van waarneming. Wanneer die temperatuur weer herstel is na die oorspronklike, het die vloedontspanning voortgegaan teen die tempo voor die temperatuurverlaging. ’n Verklaring wat gebaseer is op vorteks dryfsnelheid was aan die hand gedoen om hierdie gedrag te verklaar. ’n Groot komponent van die projek was om die dun YBa₂Cu₃O₇ films self te vervaardig. Tydens hierdie ondersoek, is ’n gepulseerde laser deposisie (“PLD”) sisteem eiehandig ontwerp en gebou. PLD behels die interaksie van ’n gefokuseerde laser puls met ’n teiken bestaande uit ’n multi-element vastestofverbinding. Materiaal wat verdamp (“ablate”) word, vorm ’n snelbewegende pluim bestaande uit atomiese en molekulêre deeltjies. Dit beweeg vanaf die teiken na ’n verhitte substraat, waarop die deeltjies kondenseer om laag vir laag ’n dun film te vorm. Die substraat temperatuur en agtergrond gas word sorgvuldig beheer om die groei van die verlangde fase van die multi-element verbinding teweeg te bring. Die PLD sisteem is baie veeldoelig ten opsigte van die verskeidenheid materiale wat suksesvol neergeslaan kan word. Dit was aangewend om verskillende materiale neer te slaan, onder andere supergeleidende YBa₂Cu₃O₇, termochromiese VO2, en magnetoresistiewe LaxCa1-xMnO3. Geleidende Au en Ag lagies is ook suksesvol neergeslaan op YBa₂Cu₃O₇ dun films, om te dien as beskermingslagies. Die kritieke temperatuur van die beste supergeleidende films was 90 K soos bepaal deur weerstandsmetings. Die optimale neerslaan toestand vir hoë kwaliteit YBa₂Cu₃O₇ dun films was: substraat temperatuur 780°C, laser energiedigtheid 2 - 3 J/cm2, suurstofdruk 0.2 mbar, en teiken-substraat afstand 35 mm. Daar is bevind dat die substraat temperatuur die deurslaggewende rol speel tydens die neerslaan proses om die kwaliteit van die supergeleidende films te bepaal.
39
Cheng, Show-Jye. "Cu NQR and NMR study of metal-substituted YBa Cu O and YBa Cu O." Thesis, 1995. http://hdl.handle.net/1957/34494.
40
Tolstova, Yulia. "Cu₂O Heterojunction Photovoltaics." Thesis, 2016. https://thesis.library.caltech.edu/9820/7/tolstova_yulia_2016_thesis.pdf.
Abstract:
Cuprous oxide (Cu2O) is an earth abundant semiconductor that has several promising photovoltaic properties, including high absorption in the visible range, high minority carrier diffusion length, and high majority carrier mobility. Cu2O can be easily synthesized by oxidation of copper foils in air. One important advantage that makes Cu2O highly relevant to today's solar cell markets dominated by crystalline silicon is its wide bandgap of 1.9 eV at room temperature, which makes it an ideal candidate for a top cell in tandem with a crystalline silicon bottom cell. The detailed balance efficiency of such a device exceeds 44%.
In this work we aim to understand and address several issues that have limited Cu2O solar cell efficiency. We address the intrinsic p-type nature and chemical instability of Cu2O by pairing it with an appropriate n-type heterojunction partner Zn(O,S), which allows us to achieve devices with open circuit voltages exceeding 1 V. We identify presence of a current blocking layer and reduce it, which results in more than doubling the short circuit current to exceed 5 mA/cm2. Light beam induced current measurements highlight some of the issues inherent to polycrystalline Cu2O solar cells, including grain dependent collection and current losses due to presence of grain boundaries.
In order to address the issues affecting Cu2O made by thermal oxidation we also develop thin film growth of Cu2O by molecular beam epitaxy on several substrates including MgO and heteroepitaxial noble metal templates that act as ohmic back contacts. These studies culminate in achievement of the first Cu2O/Zn(O,S) solar cells incorporating an absorber layer grown by molecular beam epitaxy.
41
Darvish, Davis Solomon. "Cu₂O Substrates and Epitaxial Cu₂O/ZnO Thin Film Heterostructures for Solar Energy Conversion." Thesis, 2013. https://thesis.library.caltech.edu/7834/7/main.pdf.
Abstract:
Future fossil fuel scarcity and environmental degradation have demonstrated the need for renewable, low-carbon sources of energy to power an increasingly industrialized world. Solar energy with its infinite supply makes it an extraordinary resource that should not go unused. However with current materials, adoption is limited by cost and so a paradigm shift must occur to get everyone on the same page embracing solar technology. Cuprous Oxide (Cu₂O) is a promising earth abundant material that can be a great alternative to traditional thin-film photovoltaic materials like CIGS, CdTe, etc. We have prepared Cu₂O bulk substrates by the thermal oxidation of copper foils as well Cu₂O thin films deposited via plasma-assisted Molecular Beam Epitaxy. From preliminary Hall measurements it was determined that Cu₂O would need to be doped extrinsically. This was further confirmed by simulations of ZnO/Cu₂O heterojunctions. A cyclic interdependence between, defect concentration, minority carrier lifetime, film thickness, and carrier concentration manifests itself a primary reason for why efficiencies greater than 4% has yet to be realized. Our growth methodology for our thin-film heterostructures allow precise control of the number of defects that incorporate into our film during both equilibrium and nonequilibrium growth. We also report process flow/device design/fabrication techniques in order to create a device. A typical device without any optimizations exhibited open-circuit voltages Voc, values in excess 500mV; nearly 18% greater than previous solid state devices.
42
DeBenedictis, Jennifer Jean. "Resistivity in Y Ba₂Cu₃O₆₃̣₃₃:." Thesis, 2005. http://hdl.handle.net/2429/16402.
Abstract:
The resistivity of two high quality YBa₂Cu₃O₆.₃₃₃ single crystals was measured, the first via
the Montgomery method, which allows the determination of all three components of the resistivity
tensor, and the second via a colinear arrangement of contacts that allows the determination of
pa. A comparison of ρ[sub a] between the two crystals allowed the intrinsic behaviour to be separated
from the extrinsic behaviour. The intrinsic behaviour of the resistivity was found to be a quadratic
temperature dependence, subject to two abrupt and doping independent changes in the fitting
parameters, which occurred at 45 K and 206 K (these changes were most visible in the derivatives
of the resistivity). A low temperature Ln(1/T) behaviour, reported elsewhere in the literature, was
found to be sample dependent, and thus extrinsic. The intrinsic behaviour of the resistivity showed
a very weak upturn at low temperatures, but the ground state appears to be essentially metallic.
ρ[sub c] was fit to a model having two components added in series, one component being of the form
of one over a quadratic expression. This inverse quadratic term contained almost all the doping
dependence of the c-axis resistivity, with the remaining term (dominant at low temperatures) proving
to be almost doping independent. The derivative of one over the inverse quadratic term showed a
remarkable similarity to the derivatives of the intrinsic in-plane resistivities, implying that the inverse
quadratic term is also intrinsic behaviour. Most notably, the derivative of the inverse quadratic
showed discontinuous changes of slope at 45 K and 206 K again. However, a further two changes
of slope, occurring at 172 K and 239 K, were seen as well. It is suggested that all four of these
changes in behaviour affect the resistivity along all three principal axes, but that the ones at 172 K
and 239 K are too subtle to be seen above the experimental noise in the in-plane data. These
changes of behaviour cannot be due to the charge carriers alone or associated with the CuO₂ planes
only. It is conjectured that they may be due to subtle structural changes in the unit cell that
alter either the charge carrier-phonon coupling in the crystal, or the shape of the Fermi surface. A
model due to Rojo and Levin was found to fit both the in-plane and out-of-plane resistivity data
very well, provided that the low temperature (possibly extrinsic) contribution to the resistivity is
neglected, and the temperature dependence of boson-assisted hopping along the c-axis is taken to
be proportional to T². This model is consistent with the metallic ground state suggested by the
in-plane data, and further suggests that the ρ[sub a] ~ 1/ρ[sub c] behaviour seen in the data is to be expected
ρ[sub c]
for underdoped YBa₂Cu₃O₆[sub +x].Science, Faculty of
Physics and Astronomy, Department of
Graduate
43
Yu, Chueh-Yuan, and 尤玨元. "Study on Microstructure and Nanoindentation of Sputtered Cu/Cu(O) Multilayered Films." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/75258899863193714048.
Abstract:
碩士海洋大學
材料工程研究所
96
Abstract In this study, the nano-scale multilayered films with two alternating individual layers, copper (Cu) and copper oxide (CuOx) were prepared by the radio frequency sputtering system deposited on Si and stainless steel substrates. The individual layer thicknesses were 38nm, 53nm, 73nm and 82 nm. The nanoindentation results indicate the hardness increases with decreasing individual layer thickness and the modulus decreases with increasing hardness. For multilayers manufactured by depositing Cu with interruption time about 10 minutes between each Cu layer, the individual layer thicknesses were 8 nm, 28 nm and 70nm. The enhancement in hardness is not apparent with increasing number of layers or decreasing individual layer thickness. The layer structure in Cu/Cu multilayer is not observed in SIMS results, but is clearly seen in AES results for Cu/Cu2O multilayer. In XRD results, the Cu(111) and Cu2O(220) are the major components in the multilayered and samples are consistent with TEM results. For the cold rolling study, the hardness and modulus increase with increasing reduction ratios. SEM and FIB results show the distribution and size of crack and the changes of layer structure in different reduction ratios in the cold rolled samples. The cold rolling is helpful in densing film structure such as eliminations of voids, layer and grain boundary. For the micropillars, the FIB images show the micropillar diameters were in a range of 611-686 nm and the height-to-diameter aspect ratios were from 1.94:1 to 4.09:1. The stress of micropillar is ~0.4-0.5 GPa and the FIB images obtain that the micropillars were fractured interface between film and substrate.
44
Guan-JieChen and 陳冠捷. "Thermal Chemistry of Thiazole on Cu(100) and O/Cu(100) Surfaces." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/x4239u.
Abstract:
碩士國立成功大學
化學系
107
Temperature-programmed reaction/desorption (TPR/D), X-ray photoelectron spectroscopy (XPS) and reflection-absorption infrared spectroscopy (RAIRS), with the aid of density-functional-theory calculations, to analyze the adsorption and thermal chemistry of thiazole on Cu(100) and oxygen-precovered Cu(100). At 120 K, thiazole is predominantly adsorbed on Cu(100), via N-Cu interaction and with the aromatic ring perpendicular to the surface. At 200 K, the ring begins to rupture, and forms a small amount of sulfur atoms (S(ad)) on the surface. As the temperature further increases, C2H2(~290 K), H2(~597, 737 K) and HCN(~525 K, ~610 K, ~737 K) evolve as the reaction products. -SCHNCHCH-, -SCHCHNCH- and/or -CHNCHCH- are proposed to be the surface intermediates formed in the thiazole reaction on Cu(100). The adsorption of thiazole on O/Cu(100) at 120 K is similar to case of Cu(100). In the presence of oxygen atoms on Cu(100), thiazole also reacts on the surface and eventually generates S(ad), but the product distribution is different from that of Cu(100) with evolution of H2(~388 K, ~604 K) H2O (~438 K), C2H2 (279 K), CO (~373 K, 604 K), CO2 (~373 K, ~604 K) and N2 (~834 K). In addition to the three reaction intermediates proposed in the case of Cu(100), 〉C=C=O, NCO and another surface intermediate with C-O group are possibly formed in the thiazole reaction on O/Cu(100).
45
LUO, RUI-CHENG, and 羅瑞成. "Growth of Y-Ba-Cu-O and Y-Ba-Sr-Cu-O high Tc superconductor single crystals." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/03656249874208581441.
46
Jyun-Yi, Jhuang, and 莊君毅. "Thermal Chemistry of 1H-Pyrazole on Cu(100) and O/Cu(100) Surfaces." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/41280904998465135777.
47
Tai-YouChen and 陳泰佑. "Thermal Chemistry of 2-Chloropyrazine on Cu(100) and O/Cu(100) Surfaces." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/87sbme.
48
Sheng-HsunChan and 詹昇勳. "Thermal Chemistry of 2-Chloropyrimidine on Cu(100) and O/Cu(100) Surfaces." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/r9cfd7.
49
Lai, Xu-Feng, and 賴許鳳. "YBaCuO-x及PrBaCuO-x薄膜光學性質之研究." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/98551077620281858508.
50
Szabová, Lucie. ""Ab initio" studium rozhraní Cu-Ce-O." Master's thesis, 2009. http://www.nusl.cz/ntk/nusl-278131.
Abstract:
"Ab initio" study of interface Cu-Ce-O Abstract: The present work is a theoretical analysis based on the numerical DFT+U simulations investigating the structural and electronic properties of Cu/CeO2 model systems, which have important applications as heterogeneous catalysts for environment protection and energy sources. We provide a detailed insight into the cohesion of the interface between metal Cu nanoparticles supported on CeO2 substrates. This issue is analyzed both in context of small supported Cu clusters as well as for the extended interface underneath Cu nanoparticles on ceria surfaces. These cases were modelled with a Cu(111)/CeO2(111) interface and with a Cu adatom adsorbed at the oxidized and reduced CeO2(111) surface, respectively. The thesis provides a direct correlation between the cohesive and electronic properties mediated by the charge transfer process. The reduction of surface cerium atoms in the presence of copper either in form of adatom, thin copper layer or a slab of copper is predicted to result from charge transferred from the metal. Since cerium reduction is suggested to play an important role into the catalytic activity of ceria-based catalysts, by predicting the reduction of cerium ions in the presence of copper it can be expected that Cu/CeO2 systems will have important...