Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 632

Get Book Here

Book Description

Author: Udo Schwingenschlögl
Publisher:
ISBN: 9783832505301
Category :
Languages : en
Pages : 0

Get Book Here

Book Description
In this thesis electronic structure calculations are applied to gain fundamental insight into physical mechanisms giving rise to specific material properties. The metal-insulator transitions of the vanadium Magneli phases VnO2n-1 are studied by identifying the relevant electronic states and analyzing their response to structural modifications. This investigation is based on a systematic understanding of the various crystal structures, including those of VO2 and V2O3. It is possible to study the relations between structural and electronic properties at the metal-insulator transitions of the latter oxides on a common basis. Similar crystal structures allow for the knowledge of the phase transitions in the vanadium oxides to be transferred to the titanium Magneli phases. Octahedral tiltings, as found in the ruthenates ACu3Ru4O12, are the most important class of structural distortions affecting perovskites. Analyzing the relationship between tiltings and electronic features paves the way for a universal picture of octahedral tilting. Furthermore, a family of quasi one-dimensional materials characterized by extraordinary magnetic properties is addressed. Motivated by band structure calculations for Ca3Co2O6 the related compounds Ca3CoRhO6 and Ca3FeRhO6 are investigated, allowing for insight into the details of the magnetic coupling. In der vorliegenden Dissertation werden Bandstrukturrechnungen eingesetzt, um Einblicke in physikalische Mechanismen zu erlangen, welche charakteristische Materialeigenschaften zur Folge haben. Zur Untersuchung der Metall-Isolator-Ubergange der Vanadium Magneli Phasen VnO2n-1 werden zuerst die relevanten elektronischen Zustande identifiziert und anschlieaend deren Reaktionen auf strukturelle Modifikationen analysiert. Dieses Vorgehen basiert auf einem systematischen Verstandnis der einzelnen Kristallstrukturen, einschliealich derjenigen von VO2 sowie V2O3. Es ist moglich die Beziehungen zwischen den strukturellen und elektronischen Eigenschaften am Metall-Isolator-Ubergang letztgenannter Oxide zu vergleichen. Ahnlichkeiten in der Kristallstruktur erlauben es, Erkenntnisse zu den Phasenubergangen der Vanadiumoxide auf die Titan Magneli Phasen zu ubertragen. Oktaederverkippungen, wie sie in den Ruthenaten ACu3Ru4O12 vorzufinden sind, bilden die wichtigste Klasse struktureller Verzerrungen der Perowskite. Eine detaillierte Analyse der Beziehungen zwischen solchen Verzerrungen und der elektronischen Struktur fuhrt zu einem umfassenden Verstandnis der zugrunde liegenden Mechanismen. Weiterhin wird eine neue Familie quasi-eindimensionaler Materialien mit ungewohnlichen magnetischen Eigenschaften betrachtet. Motiviert durch Bandstrukturrechnungen fur den Vertreter Ca3CoO6 gilt das Interesse den Verbindungen Ca3CoRhO6 sowie Ca3FeRhO6. Eine vergleichende Untersuchung dieser Substanzen gestattet Einblicke in die Details der magnetischen Kopplung.

Author: P.A. Cox
Publisher: Oxford University Press
ISBN: 0199588945
Category : Science
Languages : en
Pages : 295

Get Book Here

Book Description
Transition metal oxides form a series of compounds with a uniquely wide range of electronic properties. The main aim of this book is to describe the varied electronic behaviour shown by transition metal oxides, and to discuss the different types of theoretical models that have been proposed to interpret this behaviour.

Author: Julie Elizabeth Millburn
Publisher:
ISBN:
Category : Transition metal oxides
Languages : en
Pages : 0

Get Book Here

Book Description

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 492

Get Book Here

Book Description

Author: Shenggang Li and
Publisher: Elsevier Inc. Chapters
ISBN: 0128081511
Category : Science
Languages : en
Pages : 79

Get Book Here

Book Description

Author: H.H. Kung
Publisher: Elsevier
ISBN: 0080887422
Category : Science
Languages : en
Pages : 299

Get Book Here

Book Description
In this book the author presents an up-to-date summary of existing information on the structure, electronic properties, chemistry and catalytic properties of transition metal oxides. The subjects covered in the book can be divided into three sections. The first (chapters 1 to 3) covers the structural, physical, magnetic, and electronic properties of transition metal oxides. Although the emphasis is on surface properties, relevant bulk properties are also discussed. The second section (chapters 4 to 7) covers surface chemical properties. It includes topics that describe the importance of surface coordinative unsaturation in adsorption, the formation of surface acidity and the role of acidity in determining surface chemical properties, the nature and reactivities of adsorbed oxygen, and the surface chemistry in the reduction of oxides. The third section (chapters 8 to 14) is on the catalytic properties. Various catalytic reactions including decomposition, hydrogenation, isomerization, metathesis, selective oxidation, and reactions involving carbon oxides are discussed. Emphasis is placed more on reaction mechanisms and the role of catalysts than on kinetics and processes. Chapters on the preparation of oxide catalysts and on photo-assisted processes are also included. Whenever appropriate, relationships between various topics are indicated. Written for surface physicists, chemists, and catalytic engineers, the book will serve as a useful source of information for investigators and as a comprehensive overview of the subject for graduate students.

Author: Keith Michael Glassford
Publisher:
ISBN:
Category :
Languages : en
Pages : 270

Get Book Here

Book Description

Author: Tsezar F. Seman
Publisher:
ISBN:
Category :
Languages : en
Pages : 148

Get Book Here

Book Description
The following studies are presented: theory of K-edge resonant inelastic x-ray scattering and its application for La0.5Sr1.5MnO4, effects of rare earth ion size on the stability of the coherent Jahn-Teller distortions in undoped perovskite manganites, and symmetry-mode-based classical and quantum mechanical formalism of lattice dynamics. The formula based on tight-binding approach for the calculation of K-edge resonant inelastic x-ray scattering (RIXS) spectrum for transition metal oxides is presented first, by extending the previous existing result to include explicit momentum dependence and a basis with multiple core-hole sites. This formula is applied to layered charge, orbital and spin ordered manganites, La0.5Sr1.5MnO4, and good agreement with experimental data was obtained, in particular, with regard to the large variation of the intensity with momentum. As a consequence, it is established that the electron screening in La0.5Sr1.5MnO4 is highly localized around the core hole site and demonstrates the potential of K-edge RIXS, as a probe for the screening dynamics in materials. Theoretical study is then introduced on the relation between the size of the rare earth ions, often known as chemical pressure, and the stability of the coherent Jahn-Teller distortions in undoped perovskite manganites. Using a Keating model expressed in terms of atomic scale symmetry modes, it is shown that there exists a coupling between the uniform shear distortion and the staggered buckling distortion within the Jahn-Teller energy term. It is found that this coupling provides a mechanism by which the coherent Jahn-Teller distortion is more stabilized by smaller rare earth ions. Further analysis shows the appearance of the uniform shear distortion below the Jahn-Teller ordering temperature; the Jahn-Teller ordering temperature is estimated and its variation between NdMnO3 and LaMnO3, and the relations between distortions are obtained. A good agreement is found between theoretical results and the experimental data. Finally, the classical and quantum mechanical descriptions of lattice dynamics are presented, from the atomic to the continuum scale, using atomic scale symmetry modes and their constraint equations. This approach is demonstrated for a one- dimensional chain and a two-dimensional square lattice on a monatomic basis. For the classical description, it is found that rigid modes, in addition to the distortional modes found before, are necessary to describe the kinetic energy. The long wavelength limit of the kinetic energy terms expressed in terms of atomic scale modes is shown to be consistent with the continuum theory, and leading order corrections are obtained. For the quantum mechanical description, conjugate momenta for the atomic scale symmetry modes are presented. In direct space, graphical rules for their commutation relations are obtained. Commutation relations in the reciprocal space are also calculated. As an example, phonon modes are analyzed in terms of symmetry modes. The approach presented here based on atomic scale symmetry modes could be useful for the study of complex emerging materials, in which competing structural phases and non-linearity of the lattice energy play an important role.

Author: Gang Cao
Publisher: World Scientific
ISBN: 9814522457
Category : Science
Languages : en
Pages : 328

Get Book Here

Book Description
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.