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| Author | : James George Vale |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2017 |
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| Author | : J. G. Vale |
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| Release | : 2017 |
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| Author | : Gang Cao |
| Publisher | : World Scientific |
| Total Pages | : 328 |
| Release | : 2013 |
| Genre | : Science |
| ISBN | : 9814374865 |
This book is aimed at advanced undergraduates, graduate students and other researchers who possess an introductory background in materials physics and/or chemistry, and an interest in the physical and chemical properties of novel materials, especially transition metal oxides.New materials often exhibit novel phenomena of great fundamental and technological importance. Contributing authors review the structural, physical and chemical properties of notable 4d- and 5d-transition metal oxides discovered over the last 10 years. These materials exhibit extraordinary physical properties that differ significantly from those of the heavily studied 3d-transition metal oxides, mainly due to the relatively strong influence of the spin-orbit interaction and orbital order in 4d- and 5d materials. The immense growth in publications addressing the physical properties of these novel materials underlines the need to document recent advances and the current state of this field. This book includes overviews of the current experimental situation concerning these materials.
| Author | : Andrew O'Hara |
| Publisher | : |
| Total Pages | : 444 |
| Release | : 2015 |
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Transition metal oxides have received significant attention in recent decades due to their ability to display a wide range of novel functional properties. In particular, many oxides are able to undergo metal-to-insulator transitions as a function of external stimuli such as temperature, pressure, and electric field or through doping and defect formation. In the present dissertation, density functional theory is used to explore these phenomena in three systems: (1) the Peierls transition in NbO2, (2) defect formation necessary for HfO2’s resistive switching, and (3) La-doping of SrTiO3 and trap states that may limit conductivity. For NbO2, we use successive improvements to the exchange-correlation energy combined with experiment to improve understanding of the material’s band gap in the insulating phase and show it to be close to 1.2 eV for the direct gap with an indirect gap just below 1.0 eV. Furthermore, we are able to explain the orbital contributions to the dielectric function. Using a combination of transition state theory and phonon dispersion, we demonstrate that the phase transition is driven by a second-order structural transition of the Peierls type. For HfO2, we explore the nature of the metallic gettering layer used to create substoichiometric HfO2-x for resistive switching via an atomistic model of the hafnia-hafnium interface and use transition state theory to study the ability for oxygen to diffuse across the interface. Our investigation shows that the presence of hafnium lowers the formation energy of oxygen vacancies in hafnia, but more importantly the oxidation of hafnium through oxygen migration is energetically favored. In La-doped SrTiO3, the calculations are first used to corroborate optical and electrical measurements by giving values for the density of states effective mass as well as understanding the effect of La-doping on the conductivity and DC relaxation time. Motivated by the experimental observation that even after annealing in oxygen rich environments, heavily n-type doped SrTiO3 shows carrier concentrations inconsistent with dopant concentration, we explore the role that interstitial oxygen may play as a trapping state in SrTiO3. We find three meta-stable sites and that for n-type SrTiO3, interstitials with mid-gap states are favored.
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| Release | : 2015 |
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In this study, the insulating ground state of the 5d transition metal oxide CaIrO3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t2g states to open an insulating gap. These results indicate that CaIrO3 can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.
| Author | : Gang Cao |
| Publisher | : Oxford University Press |
| Total Pages | : 176 |
| Release | : 2021-06-14 |
| Genre | : Science |
| ISBN | : 0192555510 |
This book is aimed at graduate students, post docs and senior researchers with preliminary expertise in materials physics or chemistry, and with an interest in the physical and chemical properties of 4d- and 5d transition metal oxides, especially ruthenates and iridates. The 4d- and 5d-transition metal oxides are among the most current and interesting quantum materials. This book reviews recent experimental and theoretical evidence that the physical and structural properties of these materials are decisively influenced by strong spin-orbit interactions that compete with comparable Coulomb, magnetic exchange and crystalline electric field interactions. This competition often leads to unusual ground states and magnetic frustration that are unique to this class of materials. Novel coupling between the orbital/lattice and spin degrees of freedom, which seriously challenge current theoretical models and are not addressed by traditional textbooks, are of particular interest, This book also reviews a few techniques for single-crystal growth that are most suitable for the 4d- and 5d-transition metal oxides. The discussion is intended to help fill an existing void in the literature describing relevant synthesis techniques for 4d- and 5d-materials, which is a daunting experimental challenge.
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| Release | : 1994 |
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| Author | : Alexander Pergament |
| Publisher | : Nova Science Publishers |
| Total Pages | : 0 |
| Release | : 2014 |
| Genre | : Oxides |
| ISBN | : 9781633214996 |
MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) for a long time have been the workhorse of the modern electronics industry. For the purpose of a permanent integration enhancement, the size of a MOSFET has been decreasing exponentially for decades in compliance with Moore's Law, but nowadays, owing to the intrinsic restrictions, the further scaling of MOSFET devices either encounters fundamental (e.g. quantum-mechanical) limits or demands for more and more sophisticated and expensive engineering solutions. Alternative approaches and device concepts are being currently designed both in order to sustain an increase of the integration degree, and to improve the functionality and performance of electronic devices. Oxide electronics is one such promising approach which could enable and accelerate the development of information and computing technology. The behavior of d-electrons in transition metal oxides (TMOs) is responsible for the unique properties of these materials, causing strong electron-electron correlations, which play an important role in the mechanism of metal-insulator transition. The Mott transition in vanadium dioxide is specifically the effect that researchers consider as one of the most promising phenomena for oxide electronics, particularly in its special direction known as a Mott-transition field-effect transistor (MTFET).
| Author | : Likun Pan |
| Publisher | : BoD – Books on Demand |
| Total Pages | : 652 |
| Release | : 2016-02-03 |
| Genre | : Technology & Engineering |
| ISBN | : 9535122452 |
The book summarizes the current state of the know-how in the field of perovskite materials: synthesis, characterization, properties, and applications. Most chapters include a review on the actual knowledge and cutting-edge research results. Thus, this book is an essential source of reference for scientists with research fields in energy, physics, chemistry and materials. It is also a suitable reading material for graduate students.
| Author | : Jennifer Eleanor Lam |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 1997 |
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A study of the temperature dependence of the resistivity of gated SiGe quantum well structures has revealed a metal-insulator transition as a function of carrier density at zero magnetic field. Although early scaling theories (Abrahams et al., 1979) have argued against the existence of a metal-insulator transition at zero temperature in infinite 2D and 1D systems, more recent theoretical results using a random set of two-dimensional point potentials have shown that such a transition is allowed in two dimensions (Az'bel, 1992). Mounting experimental evidence for such a transition in 2D systems with short range scattering has accumulated in both semiconducting and superconducting structures (Kravchenko et al., 1995, and others). Pseudomorphic, CVD-grown p-type Si/Si$\sb{0.87}$Ge$\sb{0.13}$/Si quantum wells of various widths (65-200 A) have been studied. The samples were gated using a Ti-Au Schottky gate to allow for carrier density variation. Measurement of the transport to quantum lifetime ratio indicates that the transport is dominated by short range scattering. In the temperature range from 400 mK - 4.2 K, the temperature dependence shows a transition from a metallic phase in the high density regime to an insulating phase in the low density regime with a transition boundary close to 2.2 $\times$ 10$\sp $ cm$\sp{-2}$. The scaling properties of the observed metal-insulator transition will be discussed, and compared to previous scaling results from silicon MOSFETs. Below 400 mK, the onset of another transition is accompanied by a sharp drop in resistivity with temperature followed by a monotonic decrease in resistivity below 115 mK. The phase diagram was explored using temperature and density dependences of the current-voltage characteristics.
