Developed rechargeable batteries are urgently required to make more efficient use of renewable energy sources to support our modern way of life. Among all battery types, lithium batteries have attracted the most attention because of the high energy density (both gravimetric and volumetric), long cycle life, reasonable production cost and the ease of manufacturing flexible designs. Indeed, electrode material characteristics need to be improved urgently to fulfil the requirements for high performance lithium ion batteries. TiO2-based anodes are highly promising materials for LIBs to replace carbon due to fast lithium insertion/extraction kinetics, environmentally-friendly behavior, low cost and low volume change (less than 4%) therewith, high structural stability as well as improved safety issues are obtained. Nevertheless, the low ionic and electric conductivity (≈ 10−12 S m−1) of TiO2 represent the main challenge. In short, the present work aims at developing, optimization and construction of novel anode materials for lithium ion batteries using materials that are stable, abundant and environmentally friendly. Herein, both of two-phase Ti80Co20 and single phase Ti-Sn alloys (with different Sn contents of 1 to 10 at.%) were used to fabricate highly ordered, vertically oriented and dimension-controlled 1D nanotubes of mixed transition metal oxides (TiO2-CoO and TiO2-SnO2) via a straight-forward anodic oxidation step in organic electrolytes containing NH4F. Surface morphology and current density for the initial nanotube formation are found to be dependent on the crystal structure of the alloy phases. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. The results reveal the successful formation of mixed TiO2-CoO and TiO2-SnO2 nanotubes under the selected voltage ranges. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at different current densities. The results revealed that TiO2-CoO nanotubes prepared at 60 V exhibited the highest areal capacity of ~ 600 µAh cm–2 (i.e. 315 mAh g–1) at a current density of 10 µA cm–2. At higher current densities TiO2-CoO nanotubes showed nearly doubled lithium ion intercalation and a coulombic efficiency of 96 % after 100 cycles compared to lower effective TiO2 nanotubes prepared under identical conditions. To further improve the electrochemical performance of the TiO2-CoO nanotubes, a novel ternary carbon nanotubes (CNTs)@TiO2-CoO nanotubes composite was fabricated by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO2-CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO2 and TiO2-CoO NTs without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li+ ion diffusivity promoting a strongly favored lithium insertion into the TiO2-CoO NT framework, and hence results in high capacity and extremely reproducible high rate capability. On the other hand, the results demonstrate that TiO2-SnO2 nanotubes prepared at 40 V on a Ti-Sn alloy with 1 at.% Sn display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. The thesis is organized as follows: Chapter 1: General introduction, in which the common situation of energy demand, along with the importance of lithium ion batteries in renewable energy systems and portable devices are discussed. A brief introduction to TiO2-based anode in lithium ion batteries and the genera strategies for developing TiO2 anodes are also presented. The scope of this thesis as well as the main tasks are summarized. Chapter 2: The basic concepts of lithium ion batteries with an overview about their main components are discussed, including a brief information about the anode materials and the crystal structure of TiO2 anode. A detailed review for TiO2 nanomaterials for LIBs including the fabrication methods and the electrochemical performance of various TiO2 nanostructures (nanoparticles, nanorods, nanoneedles, nanowires and nanotubes) as well as porousTiO2 nanostructures is presented. The fabrication of TiO2 nanotubes by anodic oxidation, along with the growth mechanism are highlighted. The factors affecting the electrochemical performance of anodically fabricated pure TiO2, TiO2/carbon composites and TiO2-mixed with another metal oxide are reviewed. Chapter 3: In this chapter, the synthesis of TiO2-CoO, (CNTs)@TiO2-CoO and TiO2-SnO2 nanotubes, along with the characterization techniques and the electrochemical basics and concepts are discussed. Chapter 4: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-CoO nanotubes and ternary (CNTs)@TiO2/CoO nanotube composites are presented. Chapter 5: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of ternary (CNTs)@TiO2-CoO nanotube composites are explained. Chapter 6: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-SnO2 nanotubes are presented. Chapter 7: Summarizes the results presented in this work finishing with realistic conclusions, and highlights interesting work for the future.:1. Introduction and scope of the thesis 15 1.1 Batteries for renewable energy systems and portable devices 15 1.2 TiO2-based anodes in lithium ion batteries 17 1.3 Strategies for developing TiO2 anodes 17 1.4 Scope of work 19 1.5 Tasks 20 2. Basics and literature review 23 2.1 Lithium ion battery system 23 2.2 Anode materials 26 2.3 Crystal structure of TiO2 28 2.4 TiO2 nanomaterials for LIBs 30 2.4.1 TiO2 nanoparticles 30 2.4.2 TiO2 nanoneedles 36 2.4.3 Porous TiO2 nanostructures 39 2.5 TiO2 nanotubes prepared by electrochemical anodization 44 2.6 The mechanism of nanotube formation by anodic oxidation 47 2.7 Anodically fabricated TiO2 nanotubes as anodes in LIBs 49 2.7.1 Anodization electrolyte 50 2.7.2 Amorphous and crystalline TiO2 anodes 50 2.7.3 Influence of the nnealing atmospheres of TiO2 52 2.7.4 Free-standing TiO2 nanotube membranes 54 2.7.5 TiO2 nanotubes/carbon composites 55 2.7.6 Mixed oxide nanotubes 55 3. Materials and methods 61 3.1 Methodology 61 3.1.1 Synthesis of TiO2-CoO and TiO2 nanotubes 61 3.1.2 Synthesis of CNTs@TiO2-CoO NT composite 62 3.1.3 Synthesis of TiO2-SnO2 and TiO2 nanotubes 63 3.2 Characterization techniques 64 3.2.1 X-ray diffraction (XRD 64 3.2.2 Scanning electron microscopy (SEM 65 3.2.3 Energy-dispersive X-ray spectroscopy (EDXS 65 3.2.4 Transmission electron spectroscopy (TEM 66 3.2.5 X-ray photoelectron spectroscopy (XPS 66 3.2.6 Raman spectroscopy 67 3.2.7 Nitrogen sorption isotherms 67 3.2.8 Inductively coupled plasma optical emission spectroscopy (ICP–OES 68 3.3 Basic definitions and electrochemical concepts 68 3.3.1 Faraday’s law 68 3.3.2 Capacity 69 3.3.3 Discharging 69 3.3.4 Charging 69 3.4 Electrochemical techniques 70 3.4.1 Cyclic voltammetry 70 3.4.2 Galvanostatic discharging/charging cycling 70 3.4.3 Electrochemical impedance spectroscopy (EIS 71 3.5 Electrode preparation and measurement conditions 71 3.5.1 TiO2-CoO nanotube electrodes 71 3.5.2 CNTs@TiO2 and CNTs@TiO2/CoO NTs electrodes 72 3.5.3 TiO2-SnO2 nanotube electrodes 73 4. TiO2-CoO as anodes in lithium ion batteries 75 4.1 Introduction 76 4.2 Characterization 76 4.2.1 Phase identification of as cast Ti-Co alloy 76 4.2.2 Time-current density relationship 79 4.2.3 Morphology of the fabricated TiO2-CoO nanotubes 81 4.2.4 Phase identification of the fabricated TiO2-CoO nanotubes 85 4.2.5 Specific surface area of the fabricated TiO2-CoO nanotubes 87 4.2.6 Chemical state in the grown TiO2-CoO nanotubes 89 4.2.7 Raman spectroscopy of TiO2-CoO nanotubes 91 4.3 Electrochemical testing of TiO2-CoO electrodes 92 4.3.1 Cyclic voltammetry 92 4.3.2 Galvanostatic cycling with potential limitation 93 4.3.3 Electrochemical impedance spectroscopy (EIS) 97 4.3.4 Structural stability TiO2-CoO anodes over cycling 98 4.4 Summary of chapter 4 99 5. Ternary CNTs@TiO2-CoO nanotube composites: improved anode materials for LIBs 101 5.1 Introduction 102 5.2 Characterization 103 5.2.1 Morphology and Raman analysis of the fabricated CNTs@TiO2-CoO NTs 103 5.2.2 XRD analysis of the fabricated TiO2-CoO NTs before and after CNTs coating 106 5.3 Electrochemical properties 107 5.3.1 Cyclic voltammetry 107 5.3.2 Galvanostatic cycling with potential limitation 109 5.3.2 Electrochemical impedance spectroscopy (EIS 112 5.4 Summary of chapter 5 114 6. TiO2-SnO2 nanotubes as anodes in lithium ion batteries 115 6.1 Introduction 116 6.2 Characterization 117 6.2.1 ICP-OES analysis of the as-cast Ti-Sn alloys 117 6.2.2 SEM analysis of the as-cast Ti-Sn alloys 117 6.2.3 Phase analysis of the as-cast Ti-Sn alloys 118 6.2.4 Morphology of the fabricated TiO2-SnO2 nanotubes 121 6.2.5 XPS investigation of the grown TiO2-SnO2 nanotubes 127 6.2.6 Raman spectroscopy of TiO2-SnO2 nanotubes 129 6.3 Electrochemical Testing 130 6.3.1 Cyclic voltammetry 130 6.3.2 Galvanostatic cycling with potential limitation132 6.3.3 Specific surface area of the fabricated TiO2-SnO2 nanotubes135 6.3.4 Electrochemical impedance spectroscopy (EIS) and rate performance tests of the fabricated TiO2-SnO2 nanotubes 137 6.4 Summary of chapter 6140 7. Summary and outlook 141 7.1 Summary 141 7.2 Outlook 143 Appendix 145 Bibliography 157 List of figures 183 Glossary 191 Publications 193 Curriculum vitae 195 Acknowledgment 199 Declaration 201 / Um die zur Aufrechterhaltung unserer modernen Lebensweise unabdingbaren erneuerbaren Energiequellen effizient nutzen zu können, werden hochentwickelte wiederaufladbare Batterien dringend benötigt. Lithium-Ionenbatterien gelten aufgrund ihrer hohen Energiedichte (sowohl gravimetrisch als auch volumetrisch), ihrer langen Lebensdauer, moderater Produktionskosten und aufgrund der Möglichkeit, vielfältige Konzepte einfach herstellen zu können, als vielversprechend. Dennoch müssen die Elektrodenmaterialien dringend verbessert werden, um den Ansprüchen an zukünftige hochentwickelte Lithium-Ionenbatterien gerecht zu werden. TiO2-basierte Anoden gelten aufgrund ihrer schnellen Lade- und Entladekinetik, ihres umweltfreundlichen Verhaltens und niedriger Kosten als aussichtsreiche Alternativen zu Kohlenstoffen. Durch die geringe Volumenänderung beim Lithiumeinbau (unter 4%) werden außerdem eine hohe strukturelle Stabilität und erhöhte Sicherheit gewährleistet. Die hauptsächlichen Herausforderungen stellen die niedrige ionische und elektrische Leitfähigkeit (≈ 10−12 S m−1) von TiO2 dar. Zusammengefasst liegt das Ziel der vorliegenden Arbeit in der Entwicklung, Optimierung und Herstellung neuartiger Anodenmaterialien für Lithium-Ionenbatterien unter Verwendung stabiler, verfügbarer und umweltfreundlicher Materialien. In dieser Arbeit wurden sowohl zweiphasiges Ti80Co20 und einphasige Ti-Sn-Legierungen (mit verschiedenen Sn-Gehalten zwischen 1 und 10 at-%) zur Herstellung hochgeordneter, vertikal orientierter eindimensionaler Nanoröhren aus gemischten Übergangsmetalloxiden (TiO2–CoO und TiO2–SnO2) mittels anodischer Oxidation in NH4F-haltigen organischen Elektrolyten genutzt. Dabei wurden Abhängigkeiten der Oberflächenmorphologie und der Stromdichte für die Bildung der Nanoröhren von der Kristallstruktur der zugrundeliegenden Legierung beobachtet. Vielfältige Methoden wie REM, EDXS, TEM, XPS und Ramanspektroskopie wurden genutzt, um die Nanoröhren zu charakterisieren. Die Ergebnisse zeigen, dass gemischte TiO2-CoO und TiO2-SnO2 Nanoröhren in den gewählten Spannungsfenstern erfolgreich gebildet werden konnten. Die so hergestellten Nanoröhren sind amorph und in ihren Dimensionen präzise durch die Wahl der Spannung einstellbar. Eine elektrochemische Beurteilung der Nanoröhren erfolgte durch Tests gegen eine Li/Li+-Elektrode bei veschiedenen Stromdichten. Die Resultate zeigen, dass TiO2-CoO-Nanoröhren, welche bei 60 V hergestellt wurden, die höchsten Flächenkapazitäten von ~ 600 µAh cm–2 (d.h. 315 mAh g–1) bei einer Stromdichte von 10 µA cm–2 aufweisen. Bei höheren Stromdichten zeigen TiO2-CoO-Nanoröhren nahezu verdoppelte Lithiuminterkalation und eine Coulomb-Effizienz von 96 % nach 100 Zyklen, verglichen mit weniger effektiven TiO2–Nanoröhren, welche unter identischen Bedingungen hergestellt wurden. Um die elektrochemischen Eigenschaften der TiO2-CoO-Nanoröhren weiter zu verbessern, wurde ein neuer Komposit aus Kohlenstoff-Nanoröhren und TiO2-CoO-Nanoröhren ((CNT)s@TiO2/CoO) durch eine zweistufige Synthese hergestellt. Die Herstellung beinhaltet zunächst die anodische Bildung geordneter TiO2/CoO-Nanoröhren, ausgehend von einer Ti-Co-Legierung, gefolgt von einem horizontalen Kohlenstoff-Nanoröhren-Wachstum auf dem Oxid mittels einer simplen Sprühpyrolyse. Die einzigartige 1D-Struktur einer solchen hybriden Nanostruktur mit eingebundenen CNTs zeigt deutlich erhöhte Flächenkapazitäten und Belastbarkeiten im Vergleich zu Nanoröhren aus TiO2 und TiO2/CoO-Nanoröhren ohne CNTs, die unter identischen Bedingungen getestet wurden. Die Ergebnisse zeigen, dass die CNTs ein hochleitfähiges Netzwerk bilden, welches die Diffusion von Lithium-Ionen und deren Einbau in die TiO2/CoO-Nanoröhren begünstigt und somit hohe Kapazitäten und reproduzierbare hohe Belastbarkeiten bewirkt. Außerdem zeigen die Resultate, dass TiO2-SnO2 Nanoröhren, welche bei 40 V auf einer Ti-Sn-Legierung mit 1 at.% Sn hergestellt wurden, im Mittel eine 1,4-fache Erhöhung der Flächenkapazität und eine exzellente Zyklenstabilität über mehr als 400 Zyklen, verglichen mit unter identischen Konditionen hergestellten und getesteten TiO2-Nanoröhren, zeigen. Die Arbeit ist wie folgt organisiert: Kapitel 1: Allgemeine Einführung, in der die Energienachfrage und die Bedeutung von Lithium-Ionenbatterien in erneuerbaren Energiesystemen und tragbaren Geräten diskutiert wird. Eine kurze Einleitung zu TiO2-basierten Anoden in Lithium-Ionenbatterien und allgemeine Strategien zur Entwicklung von TiO2-Anoden werden ebenfalls gezeigt. Das Ziel der Arbeit und hauptsächliche Aufgaben werden zusammengefasst. Kapitel 2: Das grundlegende Konzept der Lithium-Ionenbatterie mit einem Überblick über ihre Hauptkomponenten wird diskutiert. Dies beinhaltet auch eine kurze Darstellung der Anodenmaterialien und der Kristallstruktur von TiO2-Anoden. Eine detaillierte Übersicht über TiO2-Nanomaterialien für LIB, welche Herstellungsmethoden und die elektrochemische Performance verschiedener TiO2-Nanostrukturen (Nanopartikel, Nanostäbe, Nanonadeln, Nanodrähte und Nanoröhren) und poröser TiO2-Nanostrukturen beinhaltet, wird gezeigt. Die Bildung von TiO2-Nanoröhren durch anodische Oxidation und der Wachstumsmechanismus werden hervorgehoben. Faktoren, welche die elektrochemische Performance anodisch hergestellter TiO2-Materialien, TiO2/Kohlenstoff-Komposite und TiO2 als Gemisch mit anderen Metalloxiden beeinflussen, werden diskutiert. Kapitel 3: In diesem Kapitel werden die Synthese von TiO2-CoO, (CNTs)@TiO2/CoO und TiO2-SnO2-Nanoröhren, die Charakterisierungsmethoden, elektrochemische Grundlagen und Konzepte diskutiert. Kapitel 4: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der TiO2-CoO- Nanoröhren und der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden gezeigt. Kapitel 5: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden diskutiert. Kapitel 6: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance von TiO2-SnO2-Nanoröhren werden gezeigt. Kapitel 7: Eine Zusammenfassung der Resultate, die in dieser Arbeit gezeigt wurden und Schlussfolgerungen, sowie interessante Ansatzpunkte für zukünftige Arbeiten werden präsentiert.:1. Introduction and scope of the thesis 15 1.1 Batteries for renewable energy systems and portable devices 15 1.2 TiO2-based anodes in lithium ion batteries 17 1.3 Strategies for developing TiO2 anodes 17 1.4 Scope of work 19 1.5 Tasks 20 2. Basics and literature review 23 2.1 Lithium ion battery system 23 2.2 Anode materials 26 2.3 Crystal structure of TiO2 28 2.4 TiO2 nanomaterials for LIBs 30 2.4.1 TiO2 nanoparticles 30 2.4.2 TiO2 nanoneedles 36 2.4.3 Porous TiO2 nanostructures 39 2.5 TiO2 nanotubes prepared by electrochemical anodization 44 2.6 The mechanism of nanotube formation by anodic oxidation 47 2.7 Anodically fabricated TiO2 nanotubes as anodes in LIBs 49 2.7.1 Anodization electrolyte 50 2.7.2 Amorphous and crystalline TiO2 anodes 50 2.7.3 Influence of the nnealing atmospheres of TiO2 52 2.7.4 Free-standing TiO2 nanotube membranes 54 2.7.5 TiO2 nanotubes/carbon composites 55 2.7.6 Mixed oxide nanotubes 55 3. Materials and methods 61 3.1 Methodology 61 3.1.1 Synthesis of TiO2-CoO and TiO2 nanotubes 61 3.1.2 Synthesis of CNTs@TiO2-CoO NT composite 62 3.1.3 Synthesis of TiO2-SnO2 and TiO2 nanotubes 63 3.2 Characterization techniques 64 3.2.1 X-ray diffraction (XRD 64 3.2.2 Scanning electron microscopy (SEM 65 3.2.3 Energy-dispersive X-ray spectroscopy (EDXS 65 3.2.4 Transmission electron spectroscopy (TEM 66 3.2.5 X-ray photoelectron spectroscopy (XPS 66 3.2.6 Raman spectroscopy 67 3.2.7 Nitrogen sorption isotherms 67 3.2.8 Inductively coupled plasma optical emission spectroscopy (ICP–OES 68 3.3 Basic definitions and electrochemical concepts 68 3.3.1 Faraday’s law 68 3.3.2 Capacity 69 3.3.3 Discharging 69 3.3.4 Charging 69 3.4 Electrochemical techniques 70 3.4.1 Cyclic voltammetry 70 3.4.2 Galvanostatic discharging/charging cycling 70 3.4.3 Electrochemical impedance spectroscopy (EIS 71 3.5 Electrode preparation and measurement conditions 71 3.5.1 TiO2-CoO nanotube electrodes 71 3.5.2 CNTs@TiO2 and CNTs@TiO2/CoO NTs electrodes 72 3.5.3 TiO2-SnO2 nanotube electrodes 73 4. TiO2-CoO as anodes in lithium ion batteries 75 4.1 Introduction 76 4.2 Characterization 76 4.2.1 Phase identification of as cast Ti-Co alloy 76 4.2.2 Time-current density relationship 79 4.2.3 Morphology of the fabricated TiO2-CoO nanotubes 81 4.2.4 Phase identification of the fabricated TiO2-CoO nanotubes 85 4.2.5 Specific surface area of the fabricated TiO2-CoO nanotubes 87 4.2.6 Chemical state in the grown TiO2-CoO nanotubes 89 4.2.7 Raman spectroscopy of TiO2-CoO nanotubes 91 4.3 Electrochemical testing of TiO2-CoO electrodes 92 4.3.1 Cyclic voltammetry 92 4.3.2 Galvanostatic cycling with potential limitation 93 4.3.3 Electrochemical impedance spectroscopy (EIS) 97 4.3.4 Structural stability TiO2-CoO anodes over cycling 98 4.4 Summary of chapter 4 99 5. Ternary CNTs@TiO2-CoO nanotube composites: improved anode materials for LIBs 101 5.1 Introduction 102 5.2 Characterization 103 5.2.1 Morphology and Raman analysis of the fabricated CNTs@TiO2-CoO NTs 103 5.2.2 XRD analysis of the fabricated TiO2-CoO NTs before and after CNTs coating 106 5.3 Electrochemical properties 107 5.3.1 Cyclic voltammetry 107 5.3.2 Galvanostatic cycling with potential limitation 109 5.3.2 Electrochemical impedance spectroscopy (EIS 112 5.4 Summary of chapter 5 114 6. TiO2-SnO2 nanotubes as anodes in lithium ion batteries 115 6.1 Introduction 116 6.2 Characterization 117 6.2.1 ICP-OES analysis of the as-cast Ti-Sn alloys 117 6.2.2 SEM analysis of the as-cast Ti-Sn alloys 117 6.2.3 Phase analysis of the as-cast Ti-Sn alloys 118 6.2.4 Morphology of the fabricated TiO2-SnO2 nanotubes 121 6.2.5 XPS investigation of the grown TiO2-SnO2 nanotubes 127 6.2.6 Raman spectroscopy of TiO2-SnO2 nanotubes 129 6.3 Electrochemical Testing 130 6.3.1 Cyclic voltammetry 130 6.3.2 Galvanostatic cycling with potential limitation132 6.3.3 Specific surface area of the fabricated TiO2-SnO2 nanotubes135 6.3.4 Electrochemical impedance spectroscopy (EIS) and rate performance tests of the fabricated TiO2-SnO2 nanotubes 137 6.4 Summary of chapter 6140 7. Summary and outlook 141 7.1 Summary 141 7.2 Outlook 143 Appendix 145 Bibliography 157 List of figures 183 Glossary 191 Publications 193 Curriculum vitae 195 Acknowledgment 199 Declaration 201

Ca2RuO4 is a structurally-driven Mott insulator with a metal-insulator (MI) transition at TMI = 357K, followed by a well-separated antiferromagnetic order at TN = 110 K. Slightly substituting Ru with a 3d transition metal ion M effectively shifts TMI and induces exotic magnetic behavior below TN. Moreover, M doping for Ru produces negative thermal expansion in Ca2Ru1-xMxO4 (M = Cr, Mn, Fe or Cu); the lattice volume expands on cooling with a total volume expansion ratio reaching as high as 1%. The onset of the negative thermal expansion closely tracks TMI and TN, sharply contrasting classic negative thermal expansion that shows no relevance to electronic properties. In addition, the observed negative thermal expansion occurs near room temperature and extends over a wide temperature interval. These findings underscores new physics driven by a complex interplay between orbital, spin and lattice degrees of freedom. These materials constitute a new class of Negative Thermal Expansion (NTE) materials with novel electronic and magnetic functions.

La2Mo2-yWyO9 (y = 1.0 to 2.0) oxides were synthesized by conventional solid state route and studied by XRD, TC-XRD and DTA. A phase diagram of the series was proposed. The thermodynamically stable phases at room temperature are: for 1.0≤ y ≤1.2 a cubic β-La2Mo2O9 type solid solution, for 1.3≤ y ≤1.575 a biphasic mixture of β-La2Mo2O9 type + α-La2W2O9 type phases, and for 1.6≤ y ≤2.0 a triclinic α-La2W2O9 type solid solution. Inhomogeneous distribution of W is suspected in the biphasic samples. It is clear that the compounds above y =1.2 are not suitable for SOFC applications.Cationic diffusion studies were performed using SIMS on La2Mo2O9 (LMO)/La0.8Sr0.2MnO3-δ (LSM) annealed couples. Rod shaped LaMnO3 grains were observed on LMO pellet and SrMoO4 type phases were seen to be growing on LSM pellet. Hypotheses for possible reaction mechanisms are presented. Bulk diffusion coefficients of Sr and Mn in LMO and of Mo in LSM are extrapolated to be around 1x10-20 cm2.s-1 and 1x10-15 cm2.s-1, respectively, at 800oC. Similar diffusion studies were performed by depositing Mn and Sr cation rich solutions on LMO pellets and Mo rich solution on LSM pellet. Mn solution was observed to be forming, upon annealing, LaMnO3 single crystals on the surface of the LMO pellet. Mo in LSM and Sr in LMO diffusion coefficients appear to be much higher than in LMO/LSM couple experiments, namely around 1-2x10-10cm2.s-1 at 1150°C. Because of the reactivity, LMO/LSM couple is not desirable for SOFC applications, unless an appropriate buffer layer separates them.The stability of LMO and W-LMO was studied under reductive atmospheres. Successive structural changes from LMO to La7Mo7O30 (7730), an amorphous reduced phase La2Mo2O7-δ, and partial decomposition to metallic Mo were observed as a function of oxygen loss. The pO2 stability domain of La2Mo2-yWyO9 did not appear to change with W content, but the reduction kinetics varied with y. At reverse, the stability limit of the 7730 phase was found to be dependent on W content. The amorphous reduced phase can accommodate a wide range of oxygen stoichiometry (7-δ from 6.69 to 6.20), but its stability vs. pO2 is questioned. Resistivity measurements performed on a low compacity crack-free amorphous La2Mo2O7-δ sample showed significant increase in the conductivity (> 1 S.cm-1 at 1000 K) relative to La2Mo2O9, with a pseudo activation energy 0.255eV. It is postulated that n-type electronic conductivity arises from partial reduction of hexavalent Mo6+ to a mixture of Mo3+ and Mo4+.

The well-known lanthanide cuprates exist in two principal forms, T and T´, which behave as p-type and n-type conductors, respectively. In order to understand the structural properties and crystal chemistry from the T to T´ phase, the Nd₁.₈₋ₓLaₓPr₀.₂CuO₄ (NLPCO) system was studied varying the La substitution ratio (0≤x≤1.8) and then characterised using high temperature X-ray powder diffraction. From analysis of the X-ray diffraction patterns obtained at room temperature, there are clearly five distinguishable regions for the NLPCO system. They are, (1) monophasic T´ solid–solution (2) two phase mixture T´ + T´´ (3) monophasic T´´solid–solution (4) two phase mixture T´´ + O and finally (5) monophasic O phase solid–solution. The T´´ form has previously been suggested as an ordered form of T´; however here we show via high temperature X-ray diffraction studies that it is a non-transformable metastable phase formed on quenching of the T phase via an orthorhombically distorted variant. Also neutron diffraction and selected area electron diffraction (SAED) studies confirmed that the T ´´phase is 4- fold Cu coordinated. The structural, magnetic and electrical properties of this NLPCO series have been investigated for the selected compositions using X-ray diffraction, magnetization measurements, thermal analysis and conductivity measurements. The aim of the second half of this work was to discover the basic high temperature electrical characteristics of Nd₂₋ₓPrₓCuO₄ and investigate how this matches with those required for components on the SOFC cathode side to identify which dopant level shows highest conductivity and whether it is stable at different temperatures. The idea was to make a new concept in SOFC cathodes and current collector development, using n-type conductors instead of p- type conductors and to try to produce a high conductivity material which is stable under the chemical and thermal stresses that exist while under load that can be used in cathode or current collector applications. The Nd₂₋ₓPrₓCuO₄ (NPCO) series has been studied over a range of dopant levels (x=0.15 - 0.25) and maximum conductivity of 86.7 Scm⁻¹ has been obtained for the composition where x = 0.25. Also NPCO shows n-type semiconductor behaviour which gives operational advantages when operating at mild oxygen deficiency. AC impedance studies have been carried out on symmetrical cells to investigate the performance of NPCO as a cathode material. These studies mainly focused on polarization resistance and the activation energies of the cells. Low Rp values and low activation energies are obtained for a composite cathode compared to pure cathode material. Two configurations of NPCO as cathode materials were tested, pre-fired and in-siu fired. Pre-fired NPCO exhibited better performance than in-situ fired NPCO. Both in-situ and pre-fired current collecting NPCO still showed lowest activation energies which suggest good catalytic activity. From all of these studies, it is evident that the praseodymium doped neodymium cuprate material shows considerable promise as a potential cathode material for solid oxide fuel cell applications.

Ce mémoire de thèse concerne l’étude des composés ternaires Terre rare–magnésium–nickel utilisable pour le stockage de l’hydrogène. Ces composés ont été obtenus par fusion ou par mécanosynthèse. Les intermétalliques YNi4-xAlxMg, dérivant des phases de Laves de structure cubique ont été étudiés. Ils réagissent de manière réversible avec l’hydrogène à P et T ambiantes. Le comportement structural lors d’une hydruration a été étudié par DRX in situ. Le composé conserve sa symétrie cubique mais avec diminution de la cristallinité. Cette étude est complétée par l’étude de composés : (i) riche en terre rare (e.g. Gd4NiMg) qui absorbe l’hydrogène à température ambiante de manière irréversible. La structure de l’intermétallique et de l’hydrure sont déterminées. La décomposition de l’hydrure à température supérieure à 90°C est expliquée. (ii) riche en magnésium. Nous avons pu identifié un nouveau composé de formulation proche de Mg77Gd9Ni14.5 de structure CFC. / This work deals with the study of ternary compounds Rare Earth – magnesium - nickel used ofr hydrogen storage. All the compounds are prepared by fusion and by mechanical alloying method.. The compounds YNi4-xAlxMg, derived from the cubic Laves phases have been studied in the first part. It reacts reversibly towards hydrogen at atmospheric pressure and room temperature. The structural behaviour during the hydrogen sorption has been studied by in situ XRD. The compound remains cubic with a decrease of the crystallinity. This study is completed by the study of compounds : (i) rich in rare earth (e.g. Gd4NiMg) that absorb hydrogen at room temperature but irreversibly. Structures of both the intermetallic and the hydride have been determined. The decomposition of the hydride at temperature higher than 90°C is also explained. (ii) rich in magnesium. A new compounds with a formulation closed to Mg77Gd9Ni14.5 has been identified and it crystallized with a cubic faces centred structure.

Une grande partie du patrimoine bâti provençal a été érigé à l’aide d’un matériau connu sous le nom de « Pierre du Midi ». L’exposition de ces pierres aux intempéries conduit à des dégradations particulières. Parmi celles-ci, la desquamation en plaques a la particularité de se développer en dehors des zones de remontées capillaires ainsi qu’en l’absence des facteurs communs de dégradation. Elle est donc induite par les propriétés intrinsèques du matériau. Ce travail a eu pour objectif d’en comprendre les mécanismes et d’établir le rôle joué par les minéraux argileux. La variabilité du degré de desquamation en plaques a tout d’abord été mise en évidence sur des monuments de périodes de construction équivalentes. Puis, un échantillonnage représentatif de cette variabilité a été mené en carrières. Le cortège argileux de chaque échantillon a été caractérisé en combinant la microscopie électronique en transmission, à la simulation des diffractogrammes de rayons X. La nature et la quantité de chacune des phases argileuses ont ainsi été déterminées et la quantité des feuillets expansifs peut être corrélée au degré de desquamation en plaques. Par ailleurs, les propriétés de stockage et de transfert des fluides de ces matériaux ont été évaluées. Elles ont permis d’appréhender les modalités de transport de l’eau et son impact sur les propriétés mécaniques. La combinaison de la perte de résistance mécanique et d’une forte dilatation au cours de la variation de la teneur en eau semble être à l’origine du processus de desquamation en plaques. Ce travail permet en outre de définir des critères de sélection de pierres de remplacement pertinents du point de vue de leur durabilité. / Most of the Provence built heritage was erected using a material named « Pierre du Midi ». The natural weathering of these limestones leads to specific deterioration patterns. Among these, spalling tends to develop in areas apart from capillary rise and free from the commun decay factors. This phenomenon seems induced by the intrinsic properties of the material. The present study aims to understand the mechanisms at play and to establish the role of the clay minerals. A wide variability of spalling degree has been observed on historical buildings of equivalent construction periods. A representative sampling of the different limestones types has thus been realized in the respective quarries. The clay minerals assemblage of each sample has been defined thanks to an adapted methodological approach combining TEM-EDX characterization to XRD profile modeling. It allowed determining both the nature and the quantity of each clay mineral phase. The link between the expansive layers quantity and the spalling degree has been evidenced. The storage and transport properties of the different types of limestones were also defined. Moreover, the macroscopic behavior upon water content variation was assessed through dilation and compressive strength experiences. The results suggest that the mechanism leading to spalling decay is triggered by the interaction between the expansive clay mineral layers and the water molecules. The hydromechanic behavior of the stone constitutes the macroscopic symptom of this interaction. This behavior is highly controlled by the fluid storage and transport properties that condition the macroscopic transmission of the deformation.

Water is “the matrix of life” for its fascinating properties. The well-known simple water molecule consists of one oxygen atom and two hydrogen atoms, covering most of planet earth’ssurface. It is the most studied element in science; however, its properties are still not fully understood. Another essential building block of life is proteins, which manifest naturally in aqueous environments. The protein activity is controlled by the protein folding process that is dependent on the surrounding environment. It is hypothesized that the hydrogen bond network of water plays an important role in the folding process. Here, we investigate the protein lysozyme in liquid water as well as in the crystalline state ice Ih, exploring various temperatures, using FT-IR and XRD. Our main finding is that a transition occurs at approximately T=210 K, indicative of the hypothesised protein dynamic “glass” transitionobserved by previous studies in supercooled water at similar temperatures.

This study reviews the theoretical and experimental aspects of the X-ray diffraction (XRD) technique and evaluates its use in identifying toxic elements or compounds in waste that has been incinerated. Many industries incinerate materials that contain large significant amounts of toxic elements, and these elements should be identified and re-moved to reduce environmental pollution. The aim of this project is to identify the elemental content of an incinerated ash sample, and to recommend a proper identification method when using XRD. Here, we test two ash samples (raw ash without any treatment and ash that has been stabilized by washing) using the software DIFFRAC.EVA that is integrated into Bruker’s diffractometer D2Phaser to match different diffraction patterns to identify the contents of the ash sample. Finally concluding the results XRF is more suitable than XRD for ash surveil-lance.

A otimização de combustíveis nucleares para uso em reatores a água pressurizada pode ser obtida pelo aumento da taxa de queima do combustível. Para isso, no entanto, é necessário levar em conta o aumento na reatividade inicial no reator, causada pelo maior enriquecimento do combustível. Esse problema, por sua vez, pode ser contornado por meio da introdução dos chamados venenos queimáveis diretamente nas pastilhas combustível de UO2. Alguns elementos do grupo das terras-raras possuem propriedades físicas e químicas que os tornam apropriados para esse uso dentro de reatores. Para caracterizar a microestrutura do combustível UO2 utilizado em reatores a água pressurizada dopado de érbio, pastilhas de UO2-Er2O3 foram preparadas, com teor de Er2O3 variando de 1,0 a 9,8 wt%, e analisadas por difração de raios X (DRX) para determinar se houve a formação de solução sólida pelo composto e determinar a variação do parâmetro de rede da solução em função da concentração de érbia. Apesar da análise por DRX ter mostrado que todo o érbio se incorporou à rede de UO2, ela também evidenciou a emergência de uma segunda fase, de estrutura do tipo fluorita, e cuja fração mássica aumenta em função do teor de érbia, enquanto seu parâmetro de rede diminui. Esses resultados são compatíveis com o fenômeno de segregação de defeitos, que consiste na formação de microdomínios segregados da rede principal nos quais há uma concentração maior dos defeitos i.e. são regiões mais ricas em érbio. Assim, a análise por DRX mostrou que houve formação de solução sólida de (U,Er)O2, mas que são necessários ajustes nos parâmetros de sinterização para que seja obtida uma solução monofásica. / Optimization of nuclear fuel for use in pressurized water reactors can be achieved by obtaining higher burnups. This, however, requires the excess reactivity caused by increasing the fuels enrichment to be taken into account, which can be done by introducing burnable absorbers into the UO2 fuel pellets themselves. Some of the rare earth elements have thermal and mechanical properties that make them appropriate for use inside the reactor. In order to characterize the microstructure of erbium-doped UO2 fuel, sintered UO2-Er2O3 pellets were prepared, with Er2O3 content ranging from 1.0 to 9.8wt%, and analyzed by X-ray diffraction to determine whether the composite formed solid solutions and, if so, evaluate the lattice parameter as a function of erbia concentration. While XRD analysis showed the Er2O3 completely dissolved in the UO2 powder, it also evidenced the emergence of a second fluorite-type phase, whose phase fraction increases and lattice parameter decreases with increasing erbia concentration. Analysis of the diffraction patterns showed this emerging phase has the same crystalline structure as the host lattice, but with a smaller lattice parameter. These results are compatible with the phenomenon of defect segregation, which consists in the formation of microdomains with a higher concentration of defects i.e. rare-earth richer regions. Thus, XRD analysis showed the formation of (U,Er)O2 solid solution, but such that there are still adjustments in the sintering parameters that need to be made in order to achieve a single-phase solid solution.

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