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 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 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 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 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 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 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 Electronic and Magnetic Properties of Double Perovskites and Oxide Interfaces written by Onur Erten and published by . This book was released on 2013 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Transition metal oxides exhibit a wide range of fascinating phenomena ranging from high Tc superconductivity to colossal magnetoresistance. In this thesis, we examine the novel electronic and magnetic properties of double perovskites and oxide interfaces.
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 Magnetic Order and Electronic Structure of 5d3 Double Perovskite Sr2ScOsO6 written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The magnetic susceptibility, crystal and magnetic structures, and electronic structure of double perovskite Sr2ScOsO6 are reported. Using both neutron and x-ray powder diffraction we find that the crystal structure is monoclinic P21/n from 3.5 to 300 K. Magnetization measurements indicate an antiferromagnetic transition at TN=92 K, one of the highest transition temperatures of any double perovskite hosting only one magnetic ion. Type I antiferromagnetic order is determined by neutron powder diffraction, with an Os moment of only 1.6(1) muB, close to half the spin-only value for a crystal field split 5d electron state with t2g^3 ground state. Density functional calculations show that this reduction is largely the result of strong Os-O hybridization, with spin-orbit coupling responsible for only a ~0.1 muB reduction in the moment.
Download or read book Structural Magnetic and Electronic Studies of Complex Perovskites written by Graham Missell King and published by . This book was released on 2009 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: This work describes the synthesis and characterization of a number of new AA'BB'O6 perovskites which possess the unusual combination of rock salt ordering of B/B' and layered ordering of A/A'. These compounds have been structurally characterized by powder X-ray and neutron diffraction as well as transmission electron microscopy. Several of these compounds are found to adopt polar P21 space group symmetry as a result of the cation ordering in combination with a-a-c+ octahedral tilting. A number of other compounds are shown to have a compositional modulation of the A-site cations that is accompanied by a twinning of the octahedral tilt system. Using UV-Vis spectroscopy the band gaps of these compounds have been determined. This analysis shows that NaLnMgWO6 compounds are insulators while NaLnMnWO6 compounds are semiconductors. The dielectric constants are found to be in the range of approximately 20-35. The magnetic properties of the NaLnMnWO6 and NaLnMgWO6 compounds have been measured. All NaLnMnWO6 compounds are found to order antiferromagnetically at temperatures ranging from 6-15 K. The NaLnMgWO6 compounds do not show any indications of magnetic order. The magnetic structures of NaLaMnWO6, NaNdMnWO6, and NaTbMnWO6 have been determined from neutron powder diffraction. NaLaMnWO6 is found to order into a simple commensurate structure. NaNdMnWO6 orders incommensurately due to interactions between the two magnetic ions. NaTbMnWO6 is found to pass through two magnetic phase transitions. Just below its Néel temperature it has an incommensurate modulation of its structure which disappears as it is further cooled.
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 Principles Study of Hybrid Halide Perovskites and Beyond for Optoelectronic Applications written by Yuheng Li and published by . This book was released on 2020 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic-inorganic hybrid lead halide perovskites are promising for next-generation solar cells and light-emitting diodes, and it is of high demand to solve their critical issues and to understand their working mechanisms. In this dissertation, using first-principles calculations, we focus on design of stable and non-toxic alternatives to this class of materials, as well as to understand and optimize their structural, energetic, electronic, and ferroelectric properties for optoelectronic applications. In the first project, we designed novel optoelectronic materials based on 24 perovskite-related prototype structures by high-throughput computing and data mining. Out of 4507 hybrid halide compounds calculated, we selected 29 compounds adopting five prototype structures for light-emitting diodes and solar energy conversion. All these candidates show appropriate electronic properties and robust stability. The approach of exploring a large variety of prototype structures is transformative to computational design of other functional materials. In the second project, we further investigated stability diagrams, defect tolerance, and optical absorption of the 29 hybrid halide compounds by high-throughput first-principles calculations. We calculated 2160 neutral and about 5000 charged defect structures to determine defect formation energies and transition energy levels for all possible point defects. Out of the 29 compounds, 15 candidates show high defect tolerance. This work provides detailed guidance on experimental investigation of these novel lead-free optoelectronic materials. In the third project, we studied ferroelectric dipole ordering in hybrid perovskites. We found that organic cations' rotational energy barrier is dependent on the cell aspect ratio, and that spontaneous ferroelectric dipole ordering exists with small energy advantage. More importantly, we found that by increasing the cell aspect ratio, strain and doping can enhance the dipole ordering, which could boost electron-hole separations for photovoltaic applications. In the fourth project, we studied strained epitaxial growth of halide perovskites. Our calculations demonstrate the epitaxial stabilization by calculating detailed thermodynamic terms in the epitaxial nucleation process. We also show that strains control the crystal structure, the bandgap, and the hole effective mass.
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 Hybrid Functional Study of the Electronic Structure and Charge Carrier Mobility in Perovskite CH3NH3SnI3 Project Supported by the National Natural Science Foundation of China Grant No 51172067 the Hunan Provincial Natural Science Fund for Distinguished Young Scholars China Grant No 13JJ1013 the Specialized Research Fund for the Doctoral Program of Higher Education China Grant No 20130161110036 and the New Century Excellent Talents in University China Grant No NCET 12 0171 D written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: We calculate the electronic properties and carrier mobility of perovskite CH3 NH3 SnI3 as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4 × 10 4 cm 2 ·V −1 ·s −1 along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH3 NH3 SnI3 can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics.
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 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.
