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 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 First Principles Studies of Surface Energies of Magnetic Full Heuslers and Machine Learning of Hybrid Perovskites written by Joseph Wong and published by . This book was released on 2019 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Materials design is a cornerstone of every device. Historically, the materials selection process was characterized by a time consuming, expensive, Edisonian approach. In recent years however, rapid advancements in computational power and materials simulation software has spawned the field of computational materials science. Computational materials science opens a new avenue to materials discovery called high-throughput materials design. This approach allows for rapid prototyping of materials in a large, complex chemical space. In this work, the scope of highthroughput materials design approach is used in the analysis of several topics: magnetic full-heuslers, hybrid perovskites, and grain boundary structures. Using high-throughput density functional theory (DFT), we study the surface energy of 68 magnetic full heuslers to guide the synthesis of magnetic tunnel junctions for applications in memory storage devices. We employ a high-throughput machine learning approach to explore the chemical space of single and double perovskite materials for applications in stable, high-performance solar cells. We also look deeper into hybrid perovskite materials in a literature review of two-dimensional hybrid perovskites, which demonstrate greater stability and tunable band gaps with simple fabrication routes. In addition, their strong binding energies lead to strong light emitting properties, with potential applications in light emitting diode devices. We also examine the configurational entropy of yttria-stabilized zirconia grain boundaries and provide example usage and applications of AIMSGB, an open-source python library for grain boundary structure generation.

Download or read book First Principles Studies of ABO3 Perovskite Surfaces and Nanostructures written by Ghanshyam Pilania and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book First principle Studies of Half metallic Antiferromagnets in Double Perovskites Structure Compounds written by 陳少華 and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book First Principles Study of Two Dimensional Electron Gas in Perovskite Oxide Heterostructures written by Jianli Cheng and published by . This book was released on 2018 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two-dimensional electron gas (2DEG) formed at the interface between two insulating perovskite oxides has provided a versatile playground to explore emergent interfacial electronic and magnetic properties. In this thesis our efforts centered on studying the electronic and structural properties of different 2DEG heterostructures (HS), with the goal of designing novel 2DEG HS using first-principles methods. In the first project we studied the [delta]-doping effects on the electronic and energetic properties of LaAlO3/SrTiO3 HS with 23 transition-metal (TM) dopants. It has been found that there is a trade-off between achieving small electron effective mass and obtaining an energetically favorable TM-doped LaAlO3/SrTiO3 system. More importantly, in addition to the experimentally confirmed Mn dopant, we proposed that Fe, Co, Ni, Ru, Rh, Pd, Os and Ir elements can also be promising dopants to yield light effective mass bands and good energetic stability. In the second project we compared the electronic and energetic properties of TiO2/LaAlO3 and LaAlO3/TiO2 HS. We found that TiO2/LaAlO3 is intrinsically metallic and has a larger interfacial charge carrier density, smaller electron effective mass and a stronger interface cohesion than LaAlO3/TiO2, which shows an insulator-to-metal transition at 4 unit cells of LaAlO3. In the third project we introduced a hitherto unknown 2DEG formed at the interface between spinel MgAl2O4 and SrTiO3. Our integrated approach combining experimental measurements and first-principles calculations reveals that an atomic-thin interfacial Ti-Al-O layer with a thickness of about 4Å is key to the observed metallic transport. The 2DEG observed at spinel/perovskite interface implies the existence of emergent phenomena at the interfaces between spinel group minerals and perovskite oxides. In the fourth and fifth project we explored the possibility of creating 2DEG in nonpo- lar/nonpolar perovskite oxide HS. We found that the lattice-mismatch-induced compression strain from the substrate leads to a large polarization in the film, which then drives the charge transfer from the film to the substrate and results in a 2DEG at the interface. In addition, by using high-throughput first-principles calculations and a group of combinatory descriptors, we rapidly designed more than 300 novel nonpolar/nonpolar 2DEG HS. In the final project we introduced Grain Boundary Maker (GBMaker), an efficient and open-source Python library for generating atomic coordinates in periodic grain boundary models. It is designed to construct various grain boundary structures from cubic and non-cubic initial configurations. GBMaker is expected to greatly accelerate the theoretical investigation of grain boundary properties and facilitate the experimental analysis of grain boundary structures as well.

Download or read book Structure Properties and Preparation of Perovskite Type Compounds written by Francis S. Galasso and published by Elsevier. This book was released on 2013-10-22 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: Structure, Properties and Preparation of Perovskite-Type Compounds, Volume 5 presents the various methods of preparing powders, single crystals, and thin films of perovskite-type compounds. This book discusses the structure of perovskite-type compounds and their properties. Organized into 11 chapters, this volume begins with an overview of the structure, properties, and preparation of perovskite-type compounds. This text then examines how X-ray diffraction can be used to determine unit cell data and to orient single crystals. Other chapters consider the effect of nuclear radiation on the properties of ferroelectric materials. This book discusses as well the phase transitions in perovskite-type compounds, which are often associated with a change in ferroelectric properties. The final chapter explores the two techniques in the preparation of the ternary carbides with the perovskite structure, which involves melting the appropriate proportions of the two metals and carbon under argon. This book is a valuable resource for solid-state chemists.

Download or read book Halide Perovskite Semiconductors written by Yuanyuan Zhou and published by John Wiley & Sons. This book was released on 2024-03-18 with total page 517 pages. Available in PDF, EPUB and Kindle. Book excerpt: Halide Perovskite Semiconductors Enables readers to acquire a systematic and in-depth understanding of various fundamental aspects of halide perovskite semiconductors Halide Perovskite Semiconductors: Structures, Characterization, Properties, and Phenomena covers the most fundamental topics with regards to halide perovskites, including but not limited to crystal/defect theory, crystal chemistry, heterogeneity, grain boundaries, single-crystals/thin-films/nanocrystals synthesis, photophysics, solid-state ionics, spin physics, chemical (in)stability, carrier dynamics, hot carriers, surface and interfaces, lower-dimensional structures, and structural/functional characterizations. Included discussions on the fundamentals of halide perovskites aim to expand the basic science fields of physics, chemistry, and materials science. Edited by two highly qualified researchers, Halide Perovskite Semiconductors includes specific information on: Crystal/defect theory of halide perovskites, crystal chemistry of halide perovskites, and processing and microstructures of halide perovskites Single-crystals of halide perovskites, nanocrystals of halide perovskites, low-dimensional perovskite crystals, and nanoscale heterogeneity of halide perovskites Carrier mobilities and dynamics in halide perovskites, light emission of halide perovskites, photophysics and ultrafast spectroscopy of halide perovskites Hot carriers in halide perovskites, correlating photophysics with microstructures in halide perovskites, chemical stability of halide perovskites, and solid-state ionics of halide perovskites Readers can find solutions to technological issues and challenges based on the fundamental knowledge gained from this book. As such, Halide Perovskite Semiconductors is an essential in-depth treatment of the subject, ideal for solid-state chemists, materials scientists, physical chemists, inorganic chemists, physicists, and semiconductor physicists.

Download or read book Magnetic Perovskites written by Asish K Kundu and published by Springer. This book was released on 2016-02-11 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic perovskite with multi functional properties (magneto-resistive, magneto-dielectric, multiferroics, spintronics, etc.) have attracted increasing attention due to their possible applications towards storage materials and intriguing fundamental Physics. Despite the numerous investigations on multi functional materials in the past few years, a very few magnetic perovskites have been known to realize as ferromagnetic-insulators. In perovskites centred transition metal oxides strong interplay between lattice, charge, spin and/or orbital degrees of freedom provide a fantastic playground to tune their physical properties. The main purpose of this book is to introduce the phenomenon and physics of complex magnetism (phase separation, spin glass, frustrations, etc.) in perovskite manganites and cobaltites via an experimental approach. The book is organized into four chapters; Chap. 1 gives a brief introduction of various interesting phenomena in magnetic perovskites. Chapter 2 describes the results of the investigations on electronic phase separation and glassy ferromagnetism of the hole-doped perovskite manganites and cobaltites. Ordered and disordered effects and related aspects in hole-doped perovskite cobaltites are described in Chap. 3. Finally, in Chap. 4 the bismuth based magnetic perovskite is discussed.

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 First principles Studies of Perovskite Thin Films and Heterostructures written by Kurt David Fredrickson and published by . This book was released on 2015 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt: The growth of oxides on semiconductors is of great interest for electronics applications; however, the effects of film growth, atomic adsorption, and strain can have fundamental effects on the properties of the oxides in question. In this dissertation, we use density functional theory to calculate the properties of SrTiO3 and BaTiO3, and discover the effects of the environment on the electronic and atomic properties of these systems. We examine the effects of H adsorption on the SrTiO3 and BaTiO3(001) surfaces, and discover the coverage-dependent onset and retreat of metallic surface states. We calculate the effect of Pt film growth on BaTiO3, and study the effects on the polarization of BaTiO3 for different Pt/BaTiO3 interfaces. We study how strain and interfacial chemistry affect the ferroelectricity of BaTiO3/Ge and BaTiO3/SrTiO3/Ge heterostructures. We also discuss the development of two-dimensional conducting states created in BaTiO3/SrTiO3 heterostructures.

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 Investigation of Structural and Magnetic Properties of Perovskite Type Oxides Containing 5d Ions written by Jie Xiong and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this thesis work is to explore the exotic magnetism in perovskite type oxide materials containing 5d transition metal. Strong spin orbit coupling and extended 5d orbitals lay the foundation of unique orbital and spin interactions between 5d ions. Understanding the physics of 5d ions is not only of fundamental interests, but important in the search for new phases of matter such as topological insulators, Weyl semimetals and quantum spin liquids. Chapter 2 and 3 discuss the magnetic behavior of 5d1 and 5d2 ions on a face-centered cubic lattice embedded in the double perovskite structure. The crystal structure, transport and magnetic properties of double perovskites Ba2BReO6 (B=Cd, Zn, Sc, In, Lu, La), Sr2LuReO6 and Ca2ScReO6 are characterized by X-ray diffraction, neutron diffraction, dc electric conductivity, dc magnetometry and heat capacity. Ferromagnetic ground states are prevalent in 5d1 systems. Orbital degree of freedom dominates the magnetic behavior over a wide temperature range before the magnetic ordering, resulting in changing effective moments with temperature and artificial negative Weiss constants. The ground state is a delicate balance sensitive to factors such as spin orbit coupling, metal-oxygen covalency, and subtle structural details. On the other hand, 5d2 systems are dominated by antiferromagnetic ground states. Filling d orbitals on the diamagnetic ion tends to destroy long range magnetic ordering in compounds with cubic symmetry. Strong distortion of the octahedral environment of 5d2 ions can result in ionic singlet states, which is not possible in 5d1 systems. Chapter 4 investigates the superexchange coupling between 5d ions and 3d ions in ordered double perovskites Sr2-xCaxCoOsO6. The crystal structures and magnetic properties are characterized using X-ray diffraction, neutron diffraction and magnetometry. Independent magnetic ordering of Co and Os sublattices are found in Sr-heavy compounds with less structural distortions, stabilized by Co-Co interactions (Co-O-O-Co and Co-O-Os-O-Co superexchange coupling) and Os-Os interactions (Os-O-O-Os and Os-O-Co-O-Os superexchange coupling), respectively. The Os-Os interactions are more sensitive to structural distortions than the Co-Co interactions. As a result, magnetic ordering of the Os sublattice disappear at lower Ca doping level than that of the Co sublattice. The strength of Co-Os superexchange coupling increases as the structure gets more distorted, resulting in ferrimagnetic ordering between Co and Os sublattices on the Ca-heavy compound. Complex glassy behavior is present in a wide compositional range in between due to the presence of competing magnetic interactions.

Download or read book Structural Chemistry and Heterostructures of Lead Halide Perovskite Semiconductors written by Matthew P. Hautzinger and published by . This book was released on 2021 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: The graduate research presented in this thesis describes the discovery of new halide perovskite materials and the relationship of the structure to the physical properties of these materials. Chapter 1 reviews the chemistry of the A-site cation in three-dimensional (3D) and two-dimensional (2D) halide perovskites, including a comprehensive review of the 3D and 2D halide perovskite compounds reported in literature and the A-site cations utilized to form them. The choice of A-site cation in the structure is related to the bonding in the structures, the optical properties, semiconductor behavior, and non-linear properties. Chapter 2 describes the use of a new spacer cation, N,N-dimethylphenylene-p-diammonium (DPDA), to form the 2D perovskite, (DPDA)PbX4 (X = Br, I). The asymmetry of the DPDA dication was the key to the ability to form a 2D perovskite instead of non-perovskite structures. Chapters 3-4, describe the discovery of 2D Ruddlesden-Popper (RP) perovskites ability to incorporate large A-site cations not attainable in 3D perovskites. The crystal structures of (HA)2(GA)Pb2I7 and (HA)2(MA)Pb2I7 (HA = n-hexylammonium, GA = guanidinium, MA = methylammonium) are compared to show the Pb-I bonds are elongated and the PbI64- octahedra are distorted in the GA containing compound. Furthermore, colloidal (HA)2(A)Pb2I7 RP perovskite nanoplates (NPLs) were demonstrated with seven unique cations occupying the A-site cavity. Absorbance and PL measurements compared with the A-site cation size shows a clear parabolic trend of the band edge energy versus the A-site cation size. In addition to structural chemistry, Chapter 5 describes the vapor phase growth of 2D/3D halide perovskite heterostructures. Characterization of the heterostructures showed phase pure 2D perovskite films coating the 3D perovskite. Spectroscopic and electrical measurements of the heterostructures suggest there are competing processes occurring at the interface of the heterostructure. These investigations have enabled a better understanding of the relationship between the structure and properties of halide perovskites and will be valuable in the future pursuit of novel material properties.

Download or read book First principles Study of the Structural Electronic and Magnetic Properties of Double Perovskite Sr2FeReO6 Containing Various Imperfections Project Supported by the National Natural Science Foundation of China Grant No 51501017 written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Design Synthesis Crystal Structure and Magnetic Properties of Novel Osmium based B site Ordered Double Perovskites written by David D. Russell and published by . This book was released on 2016 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Transition metal oxides (TMOs) with face centered cubic arrangement of magnetic ions are composed of triangular sub-lattices. When antiferromagnetic (AFM) interactions of the same strengths between all three pathways in triangular settings are in place, spin constraints cannot be fulfilled simultaneously and the system undergoes geometric magnetic frustration (GMF). The purpose of the work presented in this thesis is to better understand the criteria for a system to undergo GMF. To achieve this, the novel B-site ordered double perovskites Ca2ScOsO6 and Ca2.2Mg0.8 OsO6 were synthesized in polycrystalline form utilizing the conventional solid-state method. The crystal structure of these compounds were characterized through X-ray diffraction, and magnetic properties were explored through magnetic susceptibility measurements. Employing the spin-dimer analysis method, relative magnetic exchange interactions were calculated and modeled. These novel osmium-based B-site ordered double perovskites were then compared to isostructural compounds to study the effects of the osmium oxidation state on crystal structure and the exhibited properties.

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.