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Oxygen defects are essential building blocks for properties and functionalities of oxides, including electrical conductivity, magnetism, ferroelectricity as well as catalytic and electrocatalytic activity. Therefore, fundamental understanding of how to tune the oxygen defect chemistry is essential for advancing applications based on these defect sensitive properties. This thesis investigated pathways to controlling the concentration and structure of oxygen defects on selected case studies with model oxide systems. Three novel effects were assessed and shown to be operative for obtaining a large impact on the oxygen defect chemistry equilibria. These are heterogeneous chemical doping of the surface for improving surface electrocatalytic activity and stability, electrochemical bias to control phase with drastic changes obtained in electronic and phonon transport properties, as well as strain engineering to alter the oxygen interstitial capacity and oxygen exchange kinetics. Surface chemical modifications were applied to the near-surface regions of Lao.8Sro.2CoO 3 (LSC) by replacing the Co cations locally with less reducible cations, such as Hf and Ti. This strategy was shown to effectively stabilize the LSC surfaces and suppress surface segregation of Sr at elevated temperatures. This introduced surface stability by local chemical doping greatly enhanced the long-term electrochemical performance of LSC electrode, which provides a new route for improving the efficiency of solid oxide fuel and electrolysis cells. Applying electrical bias was investigated as another effective method to tune the oxygen stoichiometry, exemplified by the case studies on SrCoOx (SCO). In situ X-ray diffraction was used to investigate the topotactic phase transition between brownmillerite phase SrCoO2.5 (BM-SCO) and perovskite phase SrCoO 3 6 (P-SCO) triggered electrochemically at elevated temperatures. An electrical bias of merely 30 mV was shown sufficient to trigger the BM-->P phase transition. This is much more feasible than chemically induced phase transition, which requires high pressure (> 1 bar) and specialized pressurized apparatus. Moreover, the evolution of electronic structure during the BM4P phase transition was probed in operando by using ambient-pressure X-ray photoelectron and absorption spectroscopy (AP-XPS/XAS). The similar experimental scheme, which combines in operando surface characterizations and electrochemical controlling of oxygen stoichiometry, was extended to oxide systems beyond perovskites. This allows us to investigate the defect chemistry of oxides in a much broader range of effective oxygen partial pressure than what conventional methods can achieve. Firstly, we showed that the surface defect chemistry equilibrium of fluoritestructured Pro.iCeo.902-6 (PCO) strongly deviated from the bulk counterpart, due to the possibly enhanced defect-defect interactions or lattice strain effect at surfaces. Secondly, we found a novel metal-insulator transition triggered electrochemically in VO, by changing the phase between the metallic dioxide VO2 and the insulating pentoxide V2O5 Lastly, we lowered the operation temperature of this electrochemical control of oxygen stoichiometry down to room temperature by using ionic liquid or ion gels as the electrolyte. We achieved tuning of thermal conductivity in SrCoOx with a range of more than one order of magnitude, by using electrochemically triggered phase transitions at room temperature. We also investigated the effect of lattice strain on oxygen defect formation energy in Ruddlesden-Popper (RP) phase oxide Nd2NiO4+6 (NNO). We found that tensile strain along the c-axis of NNO lattice effectively reduced the formation enthalpy of oxygen interstitials, which can provide a new route for designing the defect chemistry of RP phase oxide for electrocatalytic applications..
Metal oxides and particularly their nanostructures have emerged as animportant class of materials with a rich spectrum of properties and greatpotential for device applications. In this book, contributions from leadingexperts emphasize basic physical properties, synthesis and processing, and thelatest applications in such areas as energy, catalysis and data storage. Functional Metal Oxide Nanostructuresis an essential reference for any materials scientist or engineer with aninterest in metal oxides, and particularly in recent progress in defectphysics, strain effects, solution-based synthesis, ionic conduction, and theirapplications.
Oxide Electronics Multiple disciplines converge in this insightful exploration of complex metal oxides and their functions and properties Oxide Electronics delivers a broad and comprehensive exploration of complex metal oxides designed to meet the multidisciplinary needs of electrical and electronic engineers, physicists, and material scientists. The distinguished author eschews complex mathematics whenever possible and focuses on the physical and functional properties of metal oxides in each chapter. Each of the sixteen chapters featured within the book begins with an abstract and an introduction to the topic, clear explanations are presented with graphical illustrations and relevant equations throughout the book. Numerous supporting references are included, and each chapter is self-contained, making them perfect for use both as a reference and as study material. Readers will learn how and why the field of oxide electronics is a key area of research and exploitation in materials science, electrical engineering, and semiconductor physics. The book encompasses every application area where the functional and electronic properties of various genres of oxides are exploited. Readers will also learn from topics like: Thorough discussions of High-k gate oxide for silicon heterostructure MOSFET devices and semiconductor-dielectric interfaces An exploration of printable high-mobility transparent amorphous oxide semiconductors Treatments of graphene oxide electronics, magnetic oxides, ferroelectric oxides, and materials for spin electronics Examinations of the calcium aluminate binary compound, perovoksites for photovoltaics, and oxide 2Degs Analyses of various applications for oxide electronics, including data storage, microprocessors, biomedical devices, LCDs, photovoltaic cells, TFTs, and sensors Suitable for researchers in semiconductor technology or working in materials science, electrical engineering, and physics, Oxide Electronics will also earn a place in the libraries of private industry researchers like device engineers working on electronic applications of oxide electronics. Engineers working on photovoltaics, sensors, or consumer electronics will also benefit from this book.
The climate crisis that we are facing has galvanized the scientific and engineering communities and has led to the rapid development of new, efficient, environmentally-friendly devices. One of the most promising classes of materials for such applications are transition metal oxides. This is due to the fact that by controlling the oxygen content in these crystals by means of reduction and oxidation, the material properties can be tuned in a wide range of values. Thus, the transition metal oxides, such as the model crystals, titanium dioxide (TiO2) and strontium titanate (SrTiO3), find use in so many different fields, from photocatalysis, to energy storage (solid oxide fuel cells), information technology (memristors) and even healthcare (antibacterial films). This PhD thesis is an investigation into the effect of reduction and oxidation on the electronic properties of transition metal oxides. These processes were studied at nanoscale using a multitude of techniques to provide a thorough characterization of the changes that occur in the studied systems, i.e. TiO2 and SrTiO3. Moreover, the experiments were performed in both ultra high vacuum (UHV) conditions, as well as in oxygen, and even in atmospheric air, in order to comprehensively describe the changes in properties and to bring the results closer to applications. The goal of the dissertation was to study the evolution of the electronic properties, i.e. the work function and conductivity, due to redox processes, and to add to the general understanding of these processes. The experiments revealed that the electronic properties may be tuned. In case of using reduction by means of annealing in UHV, ion sputtering, and repeated ion sputtering and annealing, and for oxidation by exposure to oxygen or air at room temperature, and annealing in oxygen. Using this range of methods, the conductivity of TiO2 can be changed from semiconductive-like to metallic-like. Furthermore, the work function of the transition metal oxides can be tuned in a wide range, from 3.4 eV to 5.0 eV for TiO2, and from 2.9 eV to 4.5 eV for SrTiO3. This is associated with changes in surface and subsurface composition, crystallography, morphology and even with the growth of new oxide phases. The key findings in the field of surface science were the description of the changes in electronic properties due to repeated sputtering and annealing, and the presence of oxygen getter substances. These results are important, because they touch upon the very basis of every experiment in the field, i.e. the preparation of crystals. This work can be used to foster greater reproducibility of experiments, as well to provide new means of designing experiments. Another object of the study was the technologically interesting system of conductive nanowires on semiconductive SrTiO3 substrate. It was shown that the nanostructures are composed of a TiO core covered with a layer of Ti3O5. The evolution of the system, starting from atomically flat strontium titanate, through nanowire-covered substrate to a crystal with a layer of porous titanium suboxides was described. The effect of annealing in oxygen on wire-covered surface was been investigated.
Chemical Solution Synthesis for Materials Design and Thin Film Device Applications presents current research on wet chemical techniques for thin-film based devices. Sections cover the quality of thin films, types of common films used in devices, various thermodynamic properties, thin film patterning, device configuration and applications. As a whole, these topics create a roadmap for developing new materials and incorporating the results in device fabrication. This book is suitable for graduate, undergraduate, doctoral students, and researchers looking for quick guidance on material synthesis and device fabrication through wet chemical routes. Provides the different wet chemical routes for materials synthesis, along with the most relevant thin film structured materials for device applications Discusses patterning and solution processing of inorganic thin films, along with solvent-based processing techniques Includes an overview of key processes and methods in thin film synthesis, processing and device fabrication, such as nucleation, lithography and solution processing
Metal Oxide Defects: Fundamentals, Design, Development and Applications provides a broad perspective on the development of advanced experimental techniques to study defects and their chemical activity and catalytic reactivity in various metal oxides. This book highlights advances in characterization and analytical techniques to achieve better understanding of a wide range of defects, most importantly, state-of-the-art methodologies for controlling defects. The book provides readers with pathways to apply basic principles and interpret the behavior of metal oxides. After reviewing characterization and analytical techniques, the book focuses on the relationship of defects to the properties and performance of metal oxides. Finally, there is a review of the methods to control defects and the applications of defect engineering for the design of metal oxides for applications in optoelectronics, energy, sensing, and more. This book is a key reference for materials scientists and engineers, chemists, and physicists. Reviews advances in characterization and analytical techniques to understand the behavior of defects in metal oxide materials Introduces defect engineering applied to the design of metal oxide materials with desirable properties Discusses applications of defect engineering to enhance the performance of materials for a wide range of applications, with an emphasis on optoelectronics
The proceedings reflect the Twelfth International Conference on Defects in Insulating Materials, covering topics on point defects and extended defects including theory and computer simulation in various insulating materials, as well as applications in laser physics, imaging, data storage and radioactive waste disposal.
Functional oxides are used both as insulators and metallic conductors in key applications across all industrial sectors. This makes them attractive candidates in modern technology ? they make solar cells cheaper, computers more efficient and medical instrumentation more sensitive. Based on recent research, experts in the field describe novel materials, their properties and applications for energy systems, semiconductors, electronics, catalysts and thin films. This monograph is divided into 6 parts which allows the reader to find their topic of interest quickly and efficiently. * Magnetic Oxides * Dopants, Defects and Ferromagnetism in Metal Oxides * Ferroelectrics * Multiferroics * Interfaces and Magnetism * Devices and Applications This book is a valuable asset to materials scientists, solid state chemists, solid state physicists, as well as engineers in the electric and automotive industries.
Developing cost-effective and durable electrocatalysts for the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is at the heart of advancing energy conversion and storage technologies, such as rechargeable metal"â€air batteries. In this thesis, several strategies were investigated for this purpose, with a focus on non-noble transition metal derivatives (Mn, Co, Ni, Fe oxides/hydroxides) and functional carbon substrates (oxidized carbon nanotubes and defective graphene). The enhancement in electrochemical performance was realized by rational design of the hybrid structure. Three series of hybrids were synthesized and analyzed: (1) Manganese cobalt oxide/nitrogen-doped multiwalled carbon nanotubes hybrids were rationally integrated by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, the congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst"â€support interfaces. The hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential difference of 0.93 V. The long-term electrochemical activities are also sustained by rational design of hybrid structures from the nanoscale. (2) Defect-rich graphene was realized by a two-step treatment (thermal reduction and annealing) to enhance the effectiveness of ORR and OER. The dominant mechanism for the enhancement is the increased density of active sites, which can be controlled by the annealing temperature in relation to the O/C ratio, surface area and pore structure. This defective graphene substrate can reduce the amount of manganese cobalt oxide needed to achieve comparable performance against the commercial standard Pt/C, proving an effective strategy of developing cost-effective oxygen electrocatalysts. (3) Nickel-iron layered double hydroxide on defective graphene was developed for highly efficient oxygen evolution electrocatalysis. The hybrids with annealed graphene as the substrate exhibit more efficient oxygen evolution than the other graphene-based materials studied earlier and in this work, in terms of high current response, low overpotential and Tafel slope. The main reason is due to the extensive defects, high electrical conductivity and hierarchical pore size distribution. The morphology, phase and electronic state of the nickel-iron hydroxides were further tuned by the atomic ratio of Ni and Fe and the synthesis conditions, leading to a much reduced low overpotential of 285 mV and 418 mV to achieve 10 mA cm−2 and 100 mA cm−2, respectively, which is among the best oxygen evolution electrocatalysts. The thesis also reviewed the concurrent progress of this subject area, outlined the perspective of this emerging field and proposed further work.