Les matériaux d’anode pour pile à combustible haute température (Solid Oxide Fuel Cell, SOFC) doivent répondre à un important cahier des charges. L’exigence d’une alimentation directe sous méthane (sans reformage en amont) rajoute des contraintes de fonctionnement au niveau de l’activation catalytique du gaz et le risque de formation de coke. Avec pour objectif la recherche du matériau idéal, l’influence de la dimensionnalité de la structure sur les propriétés catalytiques et électrochimiques a été étudiée. Après synthèse par voie sol-gel de type Pechini et caractérisation structurale par diffraction des rayons X, diffraction des neutrons et diffraction électronique, l’activation catalytique du méthane a été mesurée en condition de vaporeformage (CH4:H2O=10:1). Des mesures de conductivité électrique en température et sous faible pression partielle d’oxygène ont complété cette étude avant d’évaluer l’activité électrochimique en température et sous H2(97%)/H2O(3%) par spectroscopie d’impédance complexe sur cellules à électrodes symétriques ou sur cellule complète, avec ou sans imposition de courant. Parmi l’ensemble des composés testés, le meilleur candidat retenu est le membre x=0.80 de la série LaxSr1-xTiO3+d, composé lamellaire découlant d’une organisation à long ordre de l’oxygène sur-stœchiométrique présent au sein de la structure. Bien que relativement faible par rapport à certains composés 3D (de l’ordre de 10-2 S.cm-1 à 1073K sous Ar/H2(2%)), sa conductivité électrique ne s’avère pas rédhibitoire, étant compensée par une forte activité catalytique et électrochimique. / SOFC anode materials working under methane have to display excellent catalytic properties for fuel oxidation without coke formation. The influence of the structure dimensionnality on catalytic and electrochemical properties was studied. After synthesis of the materials by a Pechini-type method and structural characterization by means of X-ray, neutron and electronic diffraction, the catalytic activation of samples toward methane steam reforming was pursued in slightly humidified methane (CH4:H2O=10:1). Electrical conductivity measurements were carried out in temperature and at low oxygen partial pressure. Then, the electrochemical response of these materials was evaluated by impedance spectroscopy using symmetrical and complete cell under humidified H2, under or without a current bias. Among all tested compounds, the best candidate is the x=0.80-member of the LaxSr1-xTiO3+d family, which displays a lamellar structure exhibiting long range ordered over-stoichiometric oxygen. Low electrical performance when compared to 3D compounds (about 10-2 S.cm-1 at 1073K in Ar/H2(2%)), is compensated by very high catalytic and electrochemical activity.

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Thin films and powders of Ni.Tiï), and CoxTi03 (where x = 0.005 - 0.9) with different stiochiometric ratios were prepared using sol gel techniques. These metal oxides were prepared by spin coating on silicon and titanium substrates followed, by annealing at 400°C and 800°C respectively under a temperature program. A range of films with MxTiOy (where x = 0.005 - 0.9) were prepared and then characterized by optical methods such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Rutherford Backscattering Spectroscopy (RBS). X-ray powder diffraction was also used to determine the structural properties of these metal oxides. XRD pattern peaks showed that the powder forms of these metal oxides were well crystallized. Thin films could be amorphous because strong peaks were not present. For nickel titanates preparation, the best trend is at the low concentration of Ni that is 0.3:1 Ni:Ti. It is pure with no impurities of NiO and Ti02. High concentration of Co ranging from 0.7-1:1 Co:Ti forms a C02Ti04 structure with cubic phase. The best route for the CoTi03 preparation is at the low cobalt concentration that is 0.5:1 Co:Ti. Scanning Electron Microscopy (SEM) shows that a film deposited on silicon or a titanium substrate is smooth, uniform and crack-free. It also shows that a cobalt titanate film deposited on a Si substrate is rough, with cracks, whereas on the Ti substrate, it is smooth, uniform and crack-free. AFM studies show that as the concentration of Ni:Ti is reduced and the roughness of the thin film is increased. SEM, FTIR, XRD and RBS suggest that the 0.3:1 and 0.5:1Ni:Ti films with 10nm and 11nm thickness, respectively, iii Stellenbosch University http://scholar.sun.ac.za iv have the same structure. RBS suggests that the 1:1 and 0.5:1 Co:Ti have C0I.39Ti02.29and CoTi04.2 structures with 13nm and 16nm respectively. XRD reveals that NiTi03 and CoTi03 have rhombohedral crystal structure. / AFRIKAANSE OPSOMMING: Dunlagies en poeiers van NixTi03 en CoxTi03 (waar x = 0.005 - 0.9) met verskillende stoigiometriese verhoudings was voorberei deur gebruik te maak van sol gel tegnieke. Hierdie metaaloksiedes was voorberei deur gebruik te maak van "spin coating" op substrate van silikon en titaan gevolg deur konstante verhitting by 'n 400°C en 800°C temperatuur program onderskeidelik. 'n Reeks van lagies met MxTiOy (waar x = 0.005 - 0.9) was voorberei en gekarakteriseer met optiese metodes soos Skandeer Elektron Mikroskopie (SEM), Atoom Interaksie Mikroskopie (AFM) en "Rutherford Backscattering Spectroscopy (RBS)." X-straal Poeier Diffraksie was ook gebruik om die strukturele eienskappe van hierdie metaaloksiedes te bepaal. XRD patroon pieke wys dat die poeier vorms van hierdie metaaloksiedes goed gekristalliseer was. Dunlagies mag ook amorf wees aangesien sterk pieke nie teenwoordig was nie. Vir nikkel titaniete is hierdie die algemene roete vir die NiTi03 voorbereiding. Die beste tendens is by lae konsentrasies van Ni naamlik 0.3:1 Ni:Ti. Dit is suiwer en het geen onsuiwerhede van NiO en Ti02 nie. Hoë konsentrasies van Co vanaf 0.7 - 1:1 Co:Ti vorm 'n Co2Ti04 struktuur met 'n kubiese fase. Die beste roete vir die CoTi03 voorbereiding is by lae kobalt konsentrasie naamlik 0.5 -1:1 Co:Ti. Skandeer Elektron Mikroskopie (SEM) wys dat 'n NiTi03 laag gedeponeer op silikon en titaan substrate gelyk was, eenvorming en sonder krake. Dit wys ook dat die kobalt titaan laag oppervlakte gedeponeer op 'n silikon substraat grof was en het krake getoon. Vir die Ti substraat het dit gewys dat die oppervlaktes gladwas, univormig en sonder krake. AFM studies wys dat as die konsentrasie Ni:Ti verminder word die grofheid van die dunlaag verminder. SEM, FTIR, XRD en RBS dui aan dat die 0.3:1 en 0.5:1 Ni:Ti dunlaag dieselfde struktuur het met 10nm en 11nm dikte onderskeidelik. RBS dui aan dat die 1:1 en 0.5:1 Co:Ti het C01.39Ti02.29en CoTi04.2 strukture onderskeidelik met 13nm en 16nm diktes. XRD toon aan dat NiTi03 en CoTi03 rhombohedrale kristal strukture het.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiii, 196 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (M.S.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2005. Directed by Robert Snyder. / Shrout, Thomas, Committee Member ; Snyder, Robert, Committee Member ; Speyer, Robert, Committee Chair. Includes bibliographical references.

Orientador: Elson Longo / Banca: Agda Eunice de Souza Albas / Banca: Fenelon Martinho Lima Pontes / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: Titanatos são óxidos com estrutura do tipo perovskita ABO3 que A pode ser um alcalino terroso e B, o cátion metálico Ti. Como é característico da esetrutura perovskita, o átomo de Ti é coordenado por seis oxigênios, dando origem ao que chamamos de cluster octaédrico compartilha seus oxigênios com os sítios cubo-octaedrais AO12, gerando uma forte dependência estrutural entre eles que irão compor a estrutura perovskita. Dentre os titanatos com estrutura perovskita, o sistema ternário BaTiO3 e CaTiO3 é de considerável importância tecnológica tendo em vista seus comportamentos eletro-ópticos. Alterações causadas na estrutura destes titanatos, como distorções de clusters e a presença de defeitos locais ou impurezas, podem modificar consideravelmente as propriedades exibidas por estes compostos. Neste trabalho, são investigadas a microestrutura e as propriedades fofoluminescentes dos sistemas ATiO3, onde o sítio A será parcialmente substituído por átomos Ca2+ e Ba2+ de modo que possamos obter o composto Ba1-xCaxTiO3(BCT) com x variando de 0,00 a 100%. Para obtenção destes materiais, foi utilizado o método de Hidrotermalização Assistido por Micro-Ondas com um tempo de síntese relativamento curto. As amostras são caracterizadas na forma de pós. O intuito principal é observar as mudanças nas propriedades que os sistemas ternários (BaTiO3 e CaTiO3) poderão sofrer com a substituição parcial do cátion A na estrutura perovskita, além de investigar a eficiência do método na obtenção de nanopartículas destes materiais / Abstract: Titanates are oxides with perovskita ABO3-type structure in which A can be an alkaline earth metal and B, the Ti metal cation. As is characteristic of the perovskite structure, the Ti atom is coordinated by six oxygen atoms, giving rise to what we call TiO6 octahedral cluster. Each cluster shares its octahedral oxygens with the cube-octahedral sites AO12, generating a strong structural dependence between them that will compose the perovskite structure. Among the titanates with perovskite structure, the ternary system BaTiO3 and CaTiO3 has considerable technological importance due to ther electro-optical behavior. Induced change in the structure of these titanates, such as distortion of clusters and the presence of local defects or impurities can significantly change the properties displayed by these compounds. Here, we investigated the microsctructure and photoluminescent properties of ATiO3 systems, where the site A is partly substitued by atoms Ca2+ and Ba+ to obtain the compound Ba1-xCaxTiO3 (BCT) with x ranging 0,00 to 100%. To obtain these materials, the method Hydrothermal Microwave Assisted is used with a relatively short time of synthesis. The main purpose is to observe the changes in optical properties in ternary systems (BaTiO3 and CaTiO3) with partial replacement of the cation A in the perovski structure, and investigate the influence of carbonates as secnondary phases in these properties and verify the efficacy of synthesis method in obtaining nanoparticles of these materials / Mestre

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-11-29Bitstream added on 2014-06-13T20:00:20Z : No. of bitstreams: 1 barra_bc_me_bauru.pdf: 1753744 bytes, checksum: 2dd276b0ef03369acfaa92bc888f4673 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Titanatos são óxidos com estrutura do tipo perovskita ABO3 que A pode ser um alcalino terroso e B, o cátion metálico Ti. Como é característico da esetrutura perovskita, o átomo de Ti é coordenado por seis oxigênios, dando origem ao que chamamos de cluster octaédrico compartilha seus oxigênios com os sítios cubo-octaedrais AO12, gerando uma forte dependência estrutural entre eles que irão compor a estrutura perovskita. Dentre os titanatos com estrutura perovskita, o sistema ternário BaTiO3 e CaTiO3 é de considerável importância tecnológica tendo em vista seus comportamentos eletro-ópticos. Alterações causadas na estrutura destes titanatos, como distorções de clusters e a presença de defeitos locais ou impurezas, podem modificar consideravelmente as propriedades exibidas por estes compostos. Neste trabalho, são investigadas a microestrutura e as propriedades fofoluminescentes dos sistemas ATiO3, onde o sítio A será parcialmente substituído por átomos Ca2+ e Ba2+ de modo que possamos obter o composto Ba1-xCaxTiO3(BCT) com x variando de 0,00 a 100%. Para obtenção destes materiais, foi utilizado o método de Hidrotermalização Assistido por Micro-Ondas com um tempo de síntese relativamento curto. As amostras são caracterizadas na forma de pós. O intuito principal é observar as mudanças nas propriedades que os sistemas ternários (BaTiO3 e CaTiO3) poderão sofrer com a substituição parcial do cátion A na estrutura perovskita, além de investigar a eficiência do método na obtenção de nanopartículas destes materiais / Titanates are oxides with perovskita ABO3-type structure in which A can be an alkaline earth metal and B, the Ti metal cation. As is characteristic of the perovskite structure, the Ti atom is coordinated by six oxygen atoms, giving rise to what we call TiO6 octahedral cluster. Each cluster shares its octahedral oxygens with the cube-octahedral sites AO12, generating a strong structural dependence between them that will compose the perovskite structure. Among the titanates with perovskite structure, the ternary system BaTiO3 and CaTiO3 has considerable technological importance due to ther electro-optical behavior. Induced change in the structure of these titanates, such as distortion of clusters and the presence of local defects or impurities can significantly change the properties displayed by these compounds. Here, we investigated the microsctructure and photoluminescent properties of ATiO3 systems, where the site A is partly substitued by atoms Ca2+ and Ba+ to obtain the compound Ba1-xCaxTiO3 (BCT) with x ranging 0,00 to 100%. To obtain these materials, the method Hydrothermal Microwave Assisted is used with a relatively short time of synthesis. The main purpose is to observe the changes in optical properties in ternary systems (BaTiO3 and CaTiO3) with partial replacement of the cation A in the perovski structure, and investigate the influence of carbonates as secnondary phases in these properties and verify the efficacy of synthesis method in obtaining nanoparticles of these materials

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references. Also available in print.

Thesis (M.S. in Materials Science and Engineering)--Washington State University. / Includes bibliographical references.