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The research work presented in this thesis reports for the first time the fabrication of Titanium Niobium complex oxide (TiNb2O7 (TNO)) thin films by employing pulsed laser deposition and their use as the anode material in Li-ion micro batteries. Chapter 1 provides a brief introduction to complex metal oxides as multifunctional materials. In the first section of this chapter, a brief introduction is given about the history of TNO complex oxide material. The complex structure and properties of TNO oxide are also discussed briefly. In the second section, the importance and need of thin film batteries in emerging applications is discussed. Finally, the specific objectives of the current research are outlined in the last section. Chapter 2 gives the details about various experimental methods and characterization tools used in this research. The first part gives a brief overview about the principles and the use of different experimental methods involved in the growth of TNO thin films using pulsed laser deposition. Details, including the laboratory setup designed for PLD growth, also described briefly. In the second part, the different state-of-the-art characterization tools used in this research are described in terms of their principles and their applications such as measuring structural, morphological, chemical and electrochemical properties. Chapter 3 describes the synthesis and characterization of TNO bulk targets prepared via solid state reaction. In the first part, the detailed descriptions of experimental conditions are given. In the second part, the study of as-prepared TNO targets by various characterization tools such as XRD, Raman, SEM and XPS for understanding its structure, morphology and chemical properties are discussed briefly. The emphasis is made on the preparation of a quality target by careful observations. Chapter 4 mainly describes the comprehensive studies carried out on the fabrication and characterization of TNO thin films using PLD. In the first part, the preliminary experimental conditions for the growth of TNO thin films on Pt (200)/TiO2/SiO2/ Si (100) substrates are explained briefly. The importance of primary understanding about target-laser interaction through the structural, morphology changes observed by various characterization tools is discussed. In the latter part of the chapter, the effects of systematic variation of deposition parameters on the properties of the grown TNO thin films are described extensively. Various advanced characterization tools are used to study the changes in as-grown TNO thin films in terms of their structural, morphological and chemical changes by various advanced characterization tools. Chapter 5 is an account of the state-of-the-art characterization tools that are used on the as-grown TNO thin films for determining structural, compositional and elemental information with nanometer spatial resolution. In the first part, the effects of various processing conditions used during FIB are discussed briefly, along with observed results. An attempt has been made to solve the experimental difficulties during FIB for cross sectional sample preparation for HRTEM analysis. Later, the imaging, diffraction and spectroscopic studies carried out on TNO thin films using HRTEM, STEM HAADF, and EDXS elemental mapping are discussed in detail. Finally, obtained results are correlated to the experimental conditions during PLD growth. Chapter 6 focuses on the usage of as-grown TNO thin films as a new anode material in rechargeable Li-ion micro batteries. The various experimental details, battery cell fabrication, etc are described in the first part of the chapter. Then the comprehensive studies are carried out for demonstrating TNO thin films as anode material in micro batteries. Besides this, the basic cyclic voltammogram and charge-discharge tests carried out on a TNO electrode are discussed in detail. The structural, morphological studies are done before and after the electrochemical cell reaction to understand the crystal stability of TNO as an anode electrode. The effects of important experimental parameters on their electrochemical properties are also described briefly. Finally, the observed results are compared with existing literature. Chapter 7 summarizes the present research reported in this thesis and discusses the future research that could give insight into the understanding and optimization of TNO thin films for better usage in battery applications.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-07-27T23:02:40Z No. of bitstreams: 1 BASÍLIO SERRANO DE SOUSA FILHO – DISSERTAÇÃO (UAEMa) 2015.pdf: 6550059 bytes, checksum: df64991899dee3033f0a17c6e1047024 (MD5) / Made available in DSpace on 2018-07-27T23:02:40Z (GMT). No. of bitstreams: 1 BASÍLIO SERRANO DE SOUSA FILHO – DISSERTAÇÃO (UAEMa) 2015.pdf: 6550059 bytes, checksum: df64991899dee3033f0a17c6e1047024 (MD5) Previous issue date: 2015-08-31 / CNPq / O objetivo deste trabalho é produzir ligas de titânio-nióbio (Ti-Nb) pelo processo de fusão a plasma seguido d emoldagem por injeção em molde metálico (PSPP, plasma skull push-pull). As ligas de Ti-Nb foram produzidas com teores crescentes de nióbio correspondentes a 5, 10, 15, 20 e 30% (em peso). Essas ligas foram caracterizadas quanto a sua composição química, microestrutura, propriedades mecânicas e resistência à corrosão, visando futuras aplicações biomédicas. A microestrutura observada nestas ligas variou em função da concentração de Nb, manifestando-se na variação dos tamanhos de grãos, estando presentes nos contornos de grãos camadas de fase α nucleadas, placas de Widmanstatten e inclusas na matriz intragranular lamelas da fase α ou fase β nucleadas. As análises de difração de raios X revelaram picos característicos das fases α, α’, α” e β. Nas concentrações entre 5 a 10%p de Nb, observou-se predominantemente as fases α e α’. Nas concentrações entre 15 e 20%p de Nb se alternaram as fases α, α’, α” e β. A concentração de 30%p de Nb apresentou as fases α” e β, sendo a β em maiores proporções. Os resultados de microdureza registraram a dependência quanto à microestrutura, presente em cada composição. O módulo de elasticidade (E) foi influenciado pelas fases constituintes, por alterações da microestrutura, apresentando correlação direta com o teor de Nb. As ligas Ti-Nb foram submetidas a ensaios eletroquímicos de corrosão segundo a norma ASTM F2129-15, e utilizando fluido corporal simulado (SBF), à temperatura corpórea (37ºC). Avaliou-se a influência dos teores de Nb sobre as medidas de polarização potenciodinâmica linear (PPL) e a espectroscopia de impedância eletroquímica (EIE). A resistência à corrosão das ligas Ti-10Nb e Ti-30Nb foi superior à das outras composições, embora haja ocorrência de formação de filmes de passivação em todas as ligas estudadas. O circuito elétrico equivalente, obtido dos diagramas de impedância, confirma a formação dos filmes de passivação, mais evidentes nas concentrações anteriormente citadas. / The objective of this work is to produce titanium alloys, niubium (Nb-Ti) by plasma fusion process followed by injection molding metal mold (PSPP, plasma push-pull skull). The Ti-Nb alloys were produced with increasing levels of niobium corresponding to 5, 10, 15, 20 and 30% (by weight). These alloys were characterized for their chemical composition, microstructure, mechanical properties and corrosion resistance, aiming future biomedical applications. The microstructure observed in such alloys varies with the concentration of Nb, manifesting itself in the range of grain sizes being present in the contours of grain layers of α nucleated phase Widmanstätten plates and included in the intragranular array plates of the α phase or phase β nucleated. The analysis of X-ray diffraction showed the characteristic peaks of phases α, α’, α” and β. At concentration of 5 to 10 wt% of Nb, it was observed predominantly the α phase and α’. In concentrations between 15 and 20 wt% Nb alternated phases α, α’, α” and β. The concentration of 30wt% Nb presented phases α’ and β, with the β in higher proportions. The microhardness results reported in dependence on the microstructure present in each composition. The modulus of elasticity (E) is influenced by the constituent phases, changes the microstructure, having a direct correlation with the Nb content. The Ti-Nb alloys were subjected to electrochemical corrosion tests according to ASTM F2129-15, and using simulated body fluid (SBF) at body temperature (37ºC). We evaluated the influence of N levels on linear potendiodynamic polarization measurements (PPL) and electrochemical impedance spectroscopy (EIS). The corrosion resistance of Ti-10Nb and Ti-30Nb alloy was superior to other compositions, although there is occurrence of formation of passivating films on all studied alloys. The electoral equivalent circuit obtained from the impedance diagrams, confirms the formation of passivating films on all studied alloys. The electrical equivalent circuit obtained from the impedance diagrams, confirms the formation of passivation films, most evident in the concentrations mentioned above.

The effect of Laves phase (Fe2Nb) formation on the Charpy impact toughness of the ferritic stainless steel type AISI 441 was investigated. The steel exhibits good toughness after solution treatment at 850°C, but above and below this treatment temperature the impact toughness decreases sharply. With heat treatment below 850°C the presence of the Laves phase on grain boundaries and dislocations plays a significant role in embrittlement of the steel whereas above that temperature, an increase in the grain size from grain growth plays a major role in the impact embrittlement of this alloy. The toughness results agree with the phase equilibrium calculations made using Thermo–Calc® whereby it was observed that a decrease in the Laves phase volume fraction with increasing temperature corresponds to an increase in the impact toughness of the steel. Annealing above 900°C where no Laves phase exists, grain growth is found which similarly has a very negative influence on the steel’s impact properties. Where both a large grain size as well as Laves phase is present, it appears that the grain size may be the dominant embrittlement mechanism. Both the Laves phase and grain growth, therefore, have a significant influence on the impact properties of the steel, while the Laves phase’s precipitation behaviour has also been investigated with reference to the plant’s manufacturing process, particularly the cooling rate after a solution treatment. The microstructural analysis of the grain size shows that there is a steady increase in grain size up to about 950°C, but between 950°C and 1000°C there is a sudden and rapid 60 % increase in the grain size. The TEM analysis of the sample that was annealed at 900°C shows that the Laves phase had already completely dissolved and cannot, therefore, be responsible for “unpinning of grain boundaries” at temperatures of 900°C and higher where this “sudden” increase in grain size was found. The most plausible explanation appears to be one of Nb solute drag that loses its effectiveness within this temperature range, but this probably requires some further study to fully prove this effect. During isothermal annealing within the temperature range of 600 to 850°C, the time – temperature – precipitation (TTP) diagram for the Laves phase as determined from the transformation kinetic curves, shows two classical C noses on the transformation curves. The first one occurring at the higher temperatures of about 750 to 825°C and the second one at much lower temperatures, estimated to possibly be in the range of about 650 to 675°C. The transmission electron microscopy (TEM) analyses show that there are two independent nucleation mechanisms that are occurring within these two temperature ranges. At lower temperatures of about 600°C, the pertaining nucleation mechanism is on dislocations and as the temperature is increased to above 750°C, grain boundary nucleation becomes more dominant. Also, the morphology of the particles and the mis-orientation with the matrix changes with temperature. At lower temperatures the particles are more needle-like in shape, but as the temperature is increased the shape becomes more spheroidal. The effect of the steel’s composition on the Laves phase transformation kinetics shows that by lowering the Nb content in these type 441 stainless steels, had no significance effect on the kinetics on precipitation of the Laves phase. However, a Mo addition and a larger grain size of the steel, retard the formation of the Laves phase, although the optimum values of both parameters still need further quantification. The calculation made for the transformation kinetics of the Laves phase, using the number density of nucleation sites No and the interfacial energy, as the fitting parameters in this work, demonstrated a reasonable agreement with experimental results. / Thesis (PhD)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted