Download or read book First Principles Study of Double Perovskites and Group III V Compounds written by Rohan Mishra and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We have then used our understanding of the magnetic interactions that result due to antisites disorder in Sr2FeMoO6 to predict Ca2MnRuO6 as a material which should allow high levels of spin-polarized conduction, even in a complete disordered form.
Download or read book First Principles Studies of New Type Magnetic Semiconductor in Double Perovskites Structure and 2 dimension Honeycomb Structure Compounds written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book First principle Studies of Half metallic Materials in Sr and IV Group Element Based on Double Perovskites Structure Compounds written by 劉雲平 and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book First Principle Study of the Electronic Structure of Semiconductors for Photovoltaic Applications written by Brendan Morningstar and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The ill effects of climate change affect all trends, and the steps taken in the drive to reduce global emissions will reverberate for thousands of years. It is among the most significant and urgent problems we face, and so it is immensely important to call upon existing and near future technologies for generating clean electricity. For now, the most talked-about renewable energy source is solar. It is a massive resource by any standard and it has the potential to play an essential role in decreasing the dependency on crude oil and reducing fossil fuel emissions. Today, the best-performing perovskite cell has reached a power conversion efficiency of 22.1%. This unprecedented rise in efficiency for a photovoltaic technology suggests a sunny outlook, but before a large-scale deployment of the technology, there are still some real questions that must be addressed. The best performing perovskite cells contain lead, which is very toxic and damaging to the environment, and are unstable in humid conditions. Also, the fundamental working of these materials is still largely unknown. The technological base of photovoltaics is becoming progressively dependent on complicated materials, and so it is important to systematically investigate the nature of the electronic structure. In the present work, the electronic structure of five perovskite compounds, MAPbBr3, CsPbX3 (X=Cl, Br, I) and RbPbI3, are systematically studied from first principles using the all-electron, full potential, linearized augmented plane wave ((L)APW) + local orbitals (lo) method as implemented in the WIEN2k code. It is noted that: (i) the band gap of ABX3 increases when A changes from MA to Cs; (ii) as X changes from Br to Cl to I, the band gap increases; and (iii) as A changes from Cs to Rb, the band gap mostly remains the same.
Download or read book A First Principles Study of Highly Anharmonic and Dynamically Disordered Solids written by Johan Klarbring and published by Linköping University Electronic Press. This book was released on 2020-05-06 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is a first-principles theoretical investigation of solid materials with high degrees of anharmonicity. These are systems where the dynamics of the constituent atoms is too complex to be well-described by a set of uncoupled harmonic oscillators. While theoretical studies of such systems pose a significant challenge, they are under increasing demand due to the prevalence of these sytems in next-generation technological applications. Indeed, very anharmonic systems are ubiquitous in envisioned materials for future solid-state batteries and fuel-cells, thermoelectrics and optoelectronics. In some of these cases, the anharmonicity is a “side-effect” that simply has to be dealt with in order to accurately model certain properties, while in other cases the anharmonicity is the origin of the high-performance of the material. There are two main parts to the thesis: The first is on materials with perovskite-related structures. This is a very large class of materials, members of which are typically highly anharmonic, not least in relation to a series of complex phase transformations between different structural modifications. In the thesis, I have studied a specific class of such phase-transformations that relate to tilting of the framework of octahedra that make up the structure. The oxide CaMnO3 and a set of inorganic halide perovskites were taken as model systems. The results shed some light on the experimentally observed differences between the local and average atomic structure in these systems. I have further studied Cs2AgBiBr6, a member of the so-called lead-free halide double perovskites. I rationalized its temperature induced phase transformation and found high degrees of anharmonicity and ultra-low thermal conductivity. Finally, I studied the influence of nuclear quantum effects, which are often ignored in computational modelling, on the structure and bonding in the hybrid organic-inorganic lead-halide perovskite, CH3NH3PbI3. The second part of the thesis deals with theoretical studies of the phase stability of dynamically disordered solids. These are solids which have some sort of time-averaged long-range order, characteristic of a crystalline solid, but where the anharmonicity is so strong that the basic concept of an equilibrium atomic position cannot be statically assigned to all atoms. Examples include certain solids with very fast ionic conduction, so called superionics, and solids with rotating molecular units. This absence of equilibrium atomic positions makes many standard computational techniques to evaluate phase-stability inapplicable. I outline a method to deal with this issue, which is based on a stress-strain thermodynamic integration on a deformation path from an ordered variant to the dynamically disordered phase itself. I apply the method to study the phase stability of the high-temperature ?-phase of Bi2O3, which is the fastest know solid oxide ion conductor, and to Li2C2, whose high temperature cubic phase contains rotating C2 dimers. The thesis exemplifies the need to go beyond many of the standard approximations used in first-principles computational materials science if accurate theoretical predictions are to be made. This is true, in particular, for many emerging material classes in the field of energy materials. I den konventionella teoretiska modellen för ett (kristallint) fast material antags varje atom kunna tillordnas en jämviktsposition. Rörelsen av atomerna runt dessa jämviktspositioner antags sedan ofta vara harmoniskt, d.v.s. hyfsat kunna beskrivs i termer av en samling (kvantmekaniska) fjädrar. Denna avhandling behandlar teori- och beräkningsstudier av material där ett eller båda av dessa antaganden inte är giltiga, så kallade anharmoniska material. En nogrann teoretisk behandling av sådana material är ofta ordentligt utmanande. I takt med en snabb teknologiska utveckling ställs allt mer specifika och stränga krav på de material som behövs för diverse applikationer. Inom flertalet områden dyker då denna typ av komplexa och anharmoniska material upp som potentiella kandidater. Till exempel som fastelektrolyter för batterier och bränsleceller eller som solcellsmaterial. Inom vissa applikationer är denna anharmonicitet en bieffekt som man helt enkelt måste ta hänsyn till för att kunna göra noggranna teoretiska förutsägelser om diverse materialegenskaper, i andra fall är anharmoniciteten själva ursprunget för materialets goda egenskaper. I den första delen av avhandlingen behandlar jag material som har, eller är nära relaterade till, den så kallade perovskitstrukturen. Detta är en väldigt stor klass av material, och strukturen dyker därför upp inom en mängd olika tillämpningar, inte minst i lovande solcellsmaterial. Dessa material är ofta mycket anharmoniska, vilket tar sig uttryck bland annat i en rad komplexa fastransformationer mellan olika typer av perovskitmodifikationer. I perovskitoxiden CaMnO3, samt i en samling halogenperovskiter, har jag har studerat en specifik typ av fastransformationer som tillkommer på grund av rotationer av de oktaedrar som utgör en del av strukturen. Jag har fortsatt studerat den väldigt kraftiga anharmoniciteten i den så kallade blyfria halogendubbelperovskiten Cs2AgBiBr6, och slutligen har jag studerat hur en kvantmekanisk behandling av atomkärnorna, något som oftast inte görs, påverkar materialegenskaper i CH3NH3PbI3, en så kallad hybrid organisk-inorganisk bly-halogenperovskit, som är ett extremt lovande solcellsmaterial. I den andra delen av avhandlingen studerar jag dynamiskt oordnade fasta material. I dessa material är atomernas rörelse för komplex för att varje atom ska kunna tilldellas en statisk jämviktsposition. Material i denna klass är, till exempel, lovande som fastelektrolyter i bränsleceller och batterier. Mer specifikt studerar jag en typ av fasövergång, från en ordnad fas till en fas med dynamisk oordning, som ofta sker när dessa material värms upp. Jag introducerar en beräkningsmetod för att utvärdera deras fasstabilitet. Metoden är baserad på en så kallad termodynamisk integration, utförd mellan en ordnad variant och den dynamiskt oordnade fasen själv. Metoden gör det möjligt att beräkna fastransformationstemperaturer i denna typ av material. Jag applicerar metoden på Bi2O3, som i sin ?-fas är det fasta material med högst känd syrejonledningsförmåga, samt på Li2C2 vars kubiska fas innehåller roterande C2 molekyler. Resultaten stämmer bra överens med kända experimentella mätningar.
Download or read book First principles Study of Electromechanical and Polar Properties in Perovskite Oxides and Half Heusler Semiconductors written by Anindya Roy and published by . This book was released on 2011 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis discusses electromechanical and polar properties in two well-known classes of materials, perovskite oxides and half-Heusler compounds, using first-principles calculations. Certain features of the ab initio codes, such as the capability to calculate polarization based on the modern theory of polarization, or to apply a finite electric field, are central to the problems presented in this thesis. Hence these formalisms are discussed, following a brief opening section on the basic methodology of density-functional theory. The first problem presented in this thesis concerns the nonlinear piezoelectric response of ferroelectric PbTiO3 for the case of a polarization-enhancing electric field applied along the tetragonal axis. The dependence of the c/a ratio on electric field is found to be almost linear in the range up to 500 MV/m, contrary to what expected from Landau-Devonshire theory, but in qualitative agreement with a recent experiment. In the second problem we study the energy landscape and ferroelectric states of double perovskites of the form AA'BB'O6 in which the atoms on both the A and B sites are arranged in rock-salt order. If a ferroelectric instability occurs, the energy landscape will tend to have minima with the polarization along tetrahedral directions, leading to a rhombohedral phase, or along Cartesian directions, leading to an orthorhombic phase. We are not aware of compounds naturally occurring in this structure, although they might be synthesized experimentally. In the final problem, we use a first-principles rational-design approach to search a large materials family, half-Heusler compounds to identify semiconductors, and then compute their piezoelectric properties. This previously-unrecognized class of piezoelectrics may benefit greatly from calculations such as those presented here. Our work may provide guidance for experimental verification of existing compounds and for the experimental realization of other potential candidates.
Download or read book First Principles Study of Electronic and Magnetic Structures in Double Perovskites written by Molly Ball and published by . This book was released on 2017 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: At present, electronic devices are reaching their storage and processing limit causing a major push to find materials that can be used in the next generation of devices. Double perovskites with A2BB'O6 stoichiometry form one of the leading classes of materials currently being studied as a potential candidate because of their extremely wide range and tunability of functional properties, along with economic and highly scalable synthesis routes. Having a thorough understanding of their electronic and magnetic structure and their dependence on composition and local structure is the basis for targeted development of novel and optimized double perovskites. While the body of knowledge and rules within the field of materials chemistry has enabled many previous discoveries, recent developments within density functional theory (DFT) allow by now a rather realistic description of the electronic and magnetic properties of materials and especially identification of their origin from geometry and orbital structure. This thesis details computational work based on DFT within several collaborative studies to better understand the electronic and magnetic properties of double perovskites and related materials that show promise for future use in multifunctional devices. First, we will begin with a general introduction to the double perovskite structure, their properties, and the computational methods used to study them. In the next section, we will look at the case of the antiferromagnetic, insulating double perovskite Sr2CoOsO6, where measurements showed that the transition metal ions in the two sublattices undergo magnetic ordering independently of each other, indicating weak magnetic short-range coupling and a dominance of longer-range interactions, which has previously not been observed. Here, we performed DFT calculations to extract the exchange strengths between the ions and explain this unique dominance of the long-range interactions. Then, we will look at studies done on thin films of Sr2CrReO6, where our experimental collaborators found extraordinarily large anisotropy fields and record-breaking strain-tunable magnetocrystalline anisotropy (MCA). We employed first principles calculations that examine the dependence of MCA on strain and could identify orbital magnetism on the Re atoms as the origin of this unique phenomenon. In the last section, we introduce double perovskites as novel lead-free halide solar cell materials, with current focus on Cs2AgBiBr6 and Cs2AgBiCl6. While organic Pb based halides that can be synthesized without expensive clean rooms have achieved within record time efficiencies that rival that of traditional semiconductor based materials, creating quite a buzz within the field of photovoltaics, their Pb content and lacking air stability represented severe roadblocks towards market introduction. Here, we show with band structure calculations that spin-orbit coupling is a much more dominant interaction than in traditional semiconductors and thus needs to be considered when designing novel materials for maximum efficiency. The results of this study have given momentum to investigate additional halides double perovskites. Finally, we will summarize and discuss the importance of computational modeling in order to explore the wide and to date little explored composition space of double perovskites, one of the currently most promising materials classes for novel devices with unique and extremely tunable properties.
Download or read book Quantum Dots and Nanowires written by Supriyo Bandyopadhyay and published by . This book was released on 2003 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum Dots and Nanowires provides coverage on various emerging aspects of quantum dots and nanowires. This book covers recent advances in physical and chemical synthetic approaches, processing and fabrication of semiconductor quantum-dot arrays, superlattices, self-assemblies, nanowires, nanotubes and nanobelts, computational modeling approaches, spectroscopic characterization, their unique electrical, optical, magnetic and physical properties associated with size effect, transport phenomena, quantum computing, and other potential applications.
Download or read book Bibliography written by Pierre Villars and published by Walter de Gruyter. This book was released on 2012-12-21 with total page 1827 pages. Available in PDF, EPUB and Kindle. Book excerpt: By browsing about 10 000 000 scientific articles of over 200 major journals mainly in a 'cover to cover approach' some 200 000 publications were selected. The extracted data is part of the following fundamental material research fields: crystal structures (S), phase diagrams (also called constitution) (C) and the comprehensive field of intrinsic physical properties (P). This work has been done systematically starting with the literature going back to 1900. The above mentioned research field codes (S, C, P) as well as the chemical systems investigated in each publication were included in the present work. The aim of the Inorganic Substances Bibliography is to provide researchers with a comprehensive compilation of all up to now published scientific publications on inorganic systems in only three handy volumes.
Download or read book Spin Current written by Sadamichi Maekawa and published by Oxford University Press. This book was released on 2017 with total page 541 pages. Available in PDF, EPUB and Kindle. Book excerpt: In a new branch of physics and technology, called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called "spin current", are manipulated and controlled together. This book is intended to provide an introduction and guide to the new physics and applications of spin current.
Download or read book Heyd Scuseria Ernzerhof Screened exchange Hybrid Functional for Complex Materials written by Martin Schlipf and published by Forschungszentrum Jülich. This book was released on 2013 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Materials for Energy Conversion Devices written by C C Sorrell and published by Elsevier. This book was released on 2005-10-30 with total page 433 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the finite capacity and pollution problems of fossil fuels grow more pressing, new sources of more sustainable energy are being developed. Materials for energy conversion devices summarises the key research on new materials which can be used to generate clean and renewable energy or to help manage problems from existing energy sources.The book discusses the range of materials that can be used to harness and convert solar energy in particular, including the properties of oxide materials and their use in producing hydrogen fuel. It covers thermoelectric materials and devices for power generation, ionic conductors and new types of fuel cell. There are also chapters on the use of such materials in the immobilisation of nuclear waste and as electrochemical gas sensors for emission control.With its distinguished editors and international team of contributors, Materials for energy conversion devices is a standard reference for all those researching and developing a new generation of materials and technologies for our energy need. Detailed coverage of solar energy and thermoelectric conversion Comprehensive survey of new developments in this exciting field Edited by leading experts in the field with contributions from an international team of authors
Download or read book Properties of Aluminium Gallium Arsenide written by Sadao Adachi and published by IET. This book was released on 1993 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: The alloy system A1GaAs/GaAs is potentially of great importance for many high-speed electronics and optoelectronic devices, because the lattice parameter difference GaAs and A1GaAs is very small, which promises an insignificant concentration of undesirable interface states. Thanks to this prominent feature, a number of interesting properties and phenomena, such as high-mobility low-dimensional carrier gases, resonant tunnelling and fractional quantum Hall effect, have been found in the A1GaAs/GaAs heterostructure system. New devices, such as modulation-doped FETs, heterojunction bipolar transistors, resonant tunnelling transistors, quantum-well lasers, and other photonic and quantum-effect devices, have also been developed recently using this material system. These areas are recognized as not being the most interesting and active fields in semiconductor physics and device engineering.
Download or read book Hybrid Organic Inorganic Perovskites written by Li Wei and published by John Wiley & Sons. This book was released on 2020-10-19 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hybrid organic-inorganic perovskites (HOIPs) have attracted substantial interest due to their chemical variability, structural diversity and favorable physical properties the past decade. This materials class encompasses other important families such as formates, azides, dicyanamides, cyanides and dicyanometallates. The book summarizes the chemical variability and structural diversity of all known hybrid organic-inorganic perovskites subclasses including halides, azides, formates, dicyanamides, cyanides and dicyanometallates. It also presents a comprehensive account of their intriguing physical properties, including photovoltaic, optoelectronic, dielectric, magnetic, ferroelectric, ferroelastic and multiferroic properties. Moreover, the current challenges and future opportunities in this exciting field are also been discussed. This timely book shows the readers a complete landscape of hybrid organic-inorganic pervoskites and associated multifuctionalities.
Download or read book Perovskites written by Maxim Borowski and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Perovskite is a calcium titanium oxide mineral species composed of calcium titanate. This book discusses perovskite thin films, which are widely employed in today's advanced technology. The broad range of physical properties in such category of materials has offered various functionalities in devices ranging from dynamic random access memories and ferroelectric nonvolatile memories to piezoelectric and optical devices. The structural, magnetic and electron transport properties of ordered-disordered perskovite cobaltites is discussed as is perovskite-type oxides, ferroelectric PbTiO3 from a single-domain state to composite components, and others.
Download or read book First principles Modeling of Functional Perovskite Materials and Superlattices written by Qibin Zhou and published by . This book was released on 2014 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis discusses first-principles modeling of functional perovskite oxides and perovskite superlattices. In the past few decades, first-principles density functional theory has driven tremendous advances in the theoretical study of materials. However, it does not give us a conceptual understanding of the physics of these materials, which makes the first-principles modeling necessary. In the first project, we use the first-principles method to study the epitaxial strain-induced ferroelectricity in the orthorhombic CaTiO$_3$ structure and construct the energy expansion from first principles to illustrate the mechanism of the induced ferroelectricity. We also discover an unexpected polar phase of CaTiO$_3$ with in-plane polarization under compressive strain. Symmetry analysis shows that this phase is a realization of a new mechanism of geometric ferroelectricity. In the second project, we collaborate with an experimental group at SUNY Stony Brook to study the perovskite superlattices PbTiO$_3$/BaTiO$_3$. A variety of properties, including electric polarization, tetragonality, piezoelectricity and dielectric constant, have been studied from first principles. We also construct a slab model, in which different constituents are treated as bulk-like materials with appropriate electrostatic constraints, to investigate the origin of the enhanced piezoelectricity in PTO/BTO superlattices. The third project is our first-principles study of the BaTiO$_3$/CaTiO$_3$ superlattices, in which the oxygen octahedron rotations play a substantial role. We observe the phase transitions among three competing phases and enhanced piezoelectricity in all of the three phases at intermediate BaTiO$_3$ concentration. The slab models of BTO/CTO superlattices consistently underestimate the polarization, which indicates the interfacial enhancement of polarization.
Download or read book Fundamentals of Semiconductors written by Peter YU and published by Springer Science & Business Media. This book was released on 2007-05-08 with total page 651 pages. Available in PDF, EPUB and Kindle. Book excerpt: Excellent bridge between general solid-state physics textbook and research articles packed with providing detailed explanations of the electronic, vibrational, transport, and optical properties of semiconductors "The most striking feature of the book is its modern outlook ... provides a wonderful foundation. The most wonderful feature is its efficient style of exposition ... an excellent book." Physics Today "Presents the theoretical derivations carefully and in detail and gives thorough discussions of the experimental results it presents. This makes it an excellent textbook both for learners and for more experienced researchers wishing to check facts. I have enjoyed reading it and strongly recommend it as a text for anyone working with semiconductors ... I know of no better text ... I am sure most semiconductor physicists will find this book useful and I recommend it to them." Contemporary Physics Offers much new material: an extensive appendix about the important and by now well-established, deep center known as the DX center, additional problems and the solutions to over fifty of the problems at the end of the various chapters.
