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Author: Graham Missell King
Publisher:
ISBN:
Category :
Languages : en
Pages : 148
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Book Description
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.
Author: Graham Missell King
Publisher:
ISBN:
Category :
Languages : en
Pages : 148
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Book Description
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.
Author: Asish K Kundu
Publisher: Springer
ISBN: 8132227611
Category : Technology & Engineering
Languages : en
Pages : 174
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Book Description
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.
Author: Molly Ball
Publisher:
ISBN:
Category :
Languages : en
Pages : 159
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Book Description
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.
Author: Labib Ali Awin
Publisher:
ISBN:
Category : Oxides
Languages : en
Pages :
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Author: Francis S. Galasso
Publisher: Elsevier
ISBN: 1483146022
Category : Science
Languages : en
Pages : 228
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Book Description
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.
Author: Andrew Izumi
Publisher:
ISBN: 9781339260808
Category :
Languages : en
Pages :
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Book Description
Studies into a class of materials known as complex oxides have evoked a great deal of interest due to their unique magnetic, ferroelectric, and superconducting properties. In particular, materials with the ABO3 perovskite structure have highly tunable properties because of the high stability of the structure, which allows for large scale doping and strain. This also allows for a large selection of A and B cations and valences, which can further modify the material's electronic structure. Additionally, deposition of these materials as thin films and superlattices through techniques such as pulsed laser deposition (PLD) results in novel properties due to the reduced dimensionality of the material. The novel properties of perovskite oxide heterostructures can be traced to a several sources, including chemical intermixing, strain and defect formation, and electronic reconstruction. The correlations between microstructure and physical properties must be investigated by examining the physical and electronic structure of perovskites in order to understand this class of materials. Some perovskites can undergo phase changes due to temperature, electrical fields, and magnetic fields. In this work we investigated Nd0.5Sr0.5MnO3 (NSMO), which undergoes a first order magnetic and electronic transition at T=158K in bulk form. Above this temperature NSMO is a ferromagnetic metal, but transitions into an antiferromagnetic insulator as the temperature is decreased. This rapid transition has interesting potential in memory devices. However, when NSMO is deposited on (001)-oriented SrTiO3 (STO) or (001)-oriented (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrates, this transition is lost. It has has been reported in the literature that depositing NSMO on (110)-oriented STO allows for the transition to reemerge due to the partial epitaxial growth, where the NSMO film is strained along the [001] surface axis and partially relaxed along the [11̄0] surface axis. This allows the NSMO film enough freedom of movement to undergo a shear strain along the [11̄0] axes, allowing the NSMO film to switch phases. It was found that the desired magnetic and electrical properties were closely tied to the structural properties, which were highly sensitive to the precise growth conditions. These perovskite oxides can be further geometrically constrained by patterning, resulting in additional novel magnetic and electrical properties. One such method of patterning involves implanting Ar into a film to locally destabilize the ordered perovskite structure, therefore suppress the magnetic and electrical properties. However, to fully integrate this technique into devices which require multi-planar processes, the ability for a patterned perovskite film to withstand high temperature anneals is crucial in creating more advanced structures. The stability of Ar-implanted La0.7Sr0.3MnO3 (LSMO) thin films was studied upon annealing at 400°C, 500°C, and 600°C. The LSMO retained its amorphous structure with little ferromagnetism after a 400°C anneal, but anneals at 500°C and 600°C resulted in partial recrystallization and a return of the ferromagnetic properties. This recrystallized film displayed semiconducting properties with a lower Curie temperature than the as deposited film. The deposition of an La0.7Sr0.3FeO3 (LSFO) film onto an Ar implanted LSMO film at 400°C caused the LSMO film to almost fully recrystallize, suggesting that the deposition process also recrystallizes the Ar-implanted film. In conclusion, two perovskites films were explored in this thesis. NSMO films proved to be very sensitive to growth conditions, and Ar-implanted LSMO films quickly recrystallized past 400°C or a subsequent film deposition. These studies provide useful information on the structural and electronic transformations these films go through during heat treatment and strain engineering.
Author: Nina Orlovskaya
Publisher: Springer Science & Business Media
ISBN: 1402023499
Category : Technology & Engineering
Languages : en
Pages : 315
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Book Description
Advanced mixed ionic electronic conducting (MIEC) perovskites play an important role in many electrochemical systems for advanced energy technologies. They are major components in such devices as solid oxide fuel cells (SOFCs), oxygen separation membranes, chemical sensors and catalysts. In addition to energy technology, the development of these multifunctional materials is of crucial importance for transportation, aerospace engineering, and electronics. The use of these materials as chemical sensors is also important for anti-terrorism initiatives. The present book discusses progress and problems in the development of ionic, electronic, and MIEC materials as active materials in advanced energy systems; the development and design of solid-oxide fuel cells (SOFCs) for next-generation vehicles, chemical sensors and oxygen separation membranes; and identifies directions for future research, such as conducting mechanisms, stability and reliability of devices, degradation problems, crystal structure, classification of phase transitions exhibited by the materials.
Author: Rhian-Mari Thomas
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Richard J. D. Tilley
Publisher: John Wiley & Sons
ISBN: 1118935640
Category : Technology & Engineering
Languages : en
Pages : 328
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Book Description
Uniquely describes both the crystallography and properties of perovskite related materials. Practical applications in solar cells, microelectronics and telecommunications Interdisciplinary topic drawing on materials science, chemistry, physics, and geology Contains problems and answers to enhance knowledge retention
Author: Maxim Borowski
Publisher:
ISBN: 9781616685256
Category : Oxide minerals
Languages : en
Pages : 0
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Book Description
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.
