Download or read book Unlocking the Potential of Half metallic Sr2FeMoO6 Thin Films Through Controlled Stoichiometry and Double Perovskite Ordering written by Adam Joseph Hauser and published by . This book was released on 2010 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Sr2FeMoO6 is the most studied half-metallic double perovskite with the potential for room-temperature magnetoelectronic applications due to its Curie temperature above 400 K. Despite its promise, researchers have not yet succeeded in growing films of sufficient quality to realize its potential. By identifying and controlling critical factors that complicate attempts to grow thin films of Sr2FeMoO6, we have overcome the obstacles of non-stoichiometry, impurity phase formation and poor double perovskite ordering, all of which must be overcome to achieve half-metallicity. This dissertation reports an in-depth investigation that addresses several critical issues about the deposition of Sr2FeMoO6 epitaxial films using off-axis ultrahigh vacuum sputtering. High quality Sr2FeMoO6 films have been grown by off-axis ultrahigh vacuum DC magnetron sputtering, and characterized by a wide variety of techniques. We have discovered that sputtering gas pressure plays a dominant role in the stoichiometry and phase formation of Sr2FeMoO6 films. Film stoichiometry was found via Rutherford backscattering spectroscopy (RBS) and electron dispersive x-ray (EDX) spectroscopy to be both position dependent and pressure dependent in off-axis magnetron sputtering, changing from a Mo:Fe ratio of 1.43:1 at PTot = 70 mTorr to 1.12:1 at PTot = 6.7 mTorr. Our Sr2FeMoO6 films exhibit a combination of desired properties expected for its half-metallicity. X-ray-diffractometry (XRD) shows the films to be epitaxial, pure-phase, and well ordered by Reitveld refinement ([Xi]= 85.4%). High angle annular dark field scanning transmission microscopy (HAADF STEM) was performed to give the first direct observation of double perovskite ordering in a film, as well as a low defect level. Magnetic characterization was done via vibrating sample magnetometry (VSM) and superconducting quantum interference device (SQUID) magnetometry to find a saturation magnetization of 2.6 uB per formula unit at T = 5 K and a Curie temperature TC of 380 K, roughly in line with expectation for the film stoichiometry and ordering level. This dissertation also reports the first known report of distinct magnetic shape anisotropy, suggesting a high quality film with long-range magnetic ordering. The Sr2FeMoO6 films with these attributes will provide the material base for magnetoelectronic applications that will eventually achieve its half-metallic potential.

Download or read book Exploration and Engineering of Physical Properties in High quality Sr2CrReO6 Epitaxial Films written by Jeremy M. Lucy and published by . This book was released on 2015 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: Double perovskites have proven to be highly interesting materials, particularly in the past two decades, with many materials in this family exhibiting strong correlations. These materials are some of many novel complex oxides with potential spintronics application. Sr2CrReO6, in particular, is a double perovskite with one of the highest Curie temperatures of its class (> 620 K in bulk and ~510-600 K in thin films), as well as high spin polarization, ferrimagnetic behavior, and semiconducting properties. This dissertation covers recent work in exploring and tuning physical properties in epitaxial films of Sr2CrReO6. It starts by providing a background for the field of spintronics and double perovskites, bulk and thin film synthesis of Sr2CrReO6, and standard and specialized characterization techniques utilized in both university and national laboratories, and then provides reports of work on Sr2CrReO6 epitaxial films. Examples of exploration and engineering of properties of Sr2CrReO6 include: (1) tuning of electrical resistivity, such as at T = 7 K by a factor of 18,000%, via control of oxygen partial pressure during film growth; (2) enhancement of interfacial double perovskite ordering, demonstrated with high-angle annular dark-field scanning transmission electron microscopy, via the use of double perovskite buffer layer substrates; (3) measurement of magnetization suppression near film/substrate interfaces via polarized neutron reflectometry, which reveals a reduction of thickness (from 5.6 nm to 3.6 nm) of the magnetically suppressed interface region due to buffer layer enhancement; (4) strain tunability of atomic spin and orbital moments of Cr, Re, and O atoms probed with x-ray magnetic circular dichroism, which demonstrates ferrimagnetic behavior and reveals important magnetic contributions of the oxygen sites (~0.02 μB/site); (5) strain tunability of large magnetocrystalline anisotropy via applied epitaxial strain, revealing anisotropy fields of up to 10s of tesla; and (6) depth-resolved synchrotron x-ray studies of correlated magnetic and structural relaxation in a thick relaxing film. The utilized techniques and demonstrated results for Sr2CrReO6 will hopefully benefit researchers of complex oxide materials and perhaps stimulate further work on this and other related materials.

Download or read book Growth and Characterization of Sr2FeMoO6 Thin Films on Ceramic Substrates written by Santosh Kumar Myana and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Transition metal oxide heterostructures are known to have shown a wide range of phenomenal properties such as superconductivity, colossal magnetoresistance and multiferroicity. The double perovskite Sr2FeMoO6 (SFMO) is reported to be a ferrimagnetic with high Curie temperature (410 - 450 K), which exhibits an appreciable low field magnetoresistance (LFMR) even at room temperature. Most of the thin film systems are prepared on single crystal substrates such as SrTiO3, LaAlO3, MgO and some limited compositions with few low index orientations available. Here, we used a throughput synthesis technique called Combinatorial Substrate Epitaxy , where we deposit thin films on isostructural polycrystalline substrates, using optimized deposition conditions. We investigate the deposition of SFMO thin films on three different polycrystalline substrates such as Sr2MgWO6 (SMWO), Ba2MgWO6 (BMWO) and Ca2MgWO6 (CMWO), and correlate the structural and electronic properties with the compositions, the strains and nature of defects.

Download or read book Chemical Magnetic and Orbital Order of Polycrystalline and Thin Film Double Perovskites written by Rebecca Ann Ricciardo and published by . This book was released on 2009 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt: The final chapter investigates the possibility of double perovskite materials as thin films for both technological and scientific exploration. Specifically the novel growth of three double perovskites, Sr2CrNbO6, Sr2GaNbO6, and Sr2GaTaO6 are investigated. Pulsed laser deposition on stoichiometric targets is used to grow thin films on single crystal substrates. A number of growth parameters are explored. A detailed X-ray diffraction is carried out to determine the phase purity and lattice constants. Additional techniques are used to further characterize the surface features and metal content.

Download or read book Enhancing Properties of Perovskite Ferroelectrics and Correlated Metals Via Precise Stoichiometry Control written by Tatiana Kuznetsova and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Complex transition metal oxides in the perovskite structure exhibit an abundance of functionalities, such as ferroelectricity, superconductivity, multiferroicity, and many more, making the perovskite structure an ideal playground for engineering such properties and even discovering new ones. Advances in computational materials science simplify this exploration and streamline the process of trial and error in research. However, the need for experimental verification of such predictions is ever-pressing. While advances in thin film synthesis enabled the creation of many nearly-perfect materials with atomic precision, the growth of transition metal oxides still often presents a challenge. This work aims to facilitate thin film synthesis of transition metal oxides with low vapor pressures for ferroelectrics and transparent conductor applications. This dissertation strives to expand the variety of available high-quality transparent conducting oxides with improved electrical and optical properties. While CaVO3 was one of the first correlated metals explored for transparent conducting applications, its electrical performance was hampered by a high stacking fault density in the films. Careful control of the cation stoichiometry and microstructure enabled achieving superior electrical properties, such as room temperature resistivity of (3.7 ± 0.6) x 10-5 [omega] cm and residual resistivity ratio of over 90, in 38 nm thick CaVO3 films grown via hybrid molecular beam epitaxy. A custom effusion cell for preventing reduction of molybdenum oxide in vacuum was designed, which provided a high and stable flux of MoO3. Experimental verification of the growth of SrMoO3 thin films by suboxide molecular beam epitaxy is demonstrated. A very competitive transparent conductor SrMoO3 with room temperature resistivity as low as 5 x 10-5 [omega] cm and high optical transparency in the visible spectrum was grown by suboxide MBE. This work demonstrates the growth of BaTiO3/SrTiO3 superlattices via hybrid molecular beam epitaxy for the first time. The dependence of stabilized domain structure on superlattice periodicity and strain state has been investigated by synchrotron-based X-ray diffraction and optical second harmonic generation. This study deepens the understanding of the energy landscape of ferroelectrics. This dissertation is structured as follows. Chapter 1 introduces the reader to the perovskite structure and properties of transition metal oxides in the perovskite structure. Chapter 2 reviews the fundamentals of oxide thin film synthesis and commonly used deposition techniques. Chapter 3 introduces the characterization techniques used in this dissertation, such as X-ray diffraction, reflection high-energy electron diffraction and atomic force microscopy. Chapter 4 discusses synthesis and properties of correlated metal SrMoO3 grown via suboxide molecular beam epitaxy. Chapter 5 describes the growth and characterization of ultraclean correlated metal CaVO3. Chapter 6 studies the growth and domain structures in BaTiO3/SrTiO3 superlattices with different strain states and periodicity. Finally, Chapter 7 discusses future research directions in the area of ferroelectric superlattices and demonstrates the growth of KTaO3/KNbO3 superlattices by suboxide molecular beam epitaxy. Also, Chapter 7 demonstrates the growth of thin films of a solid solution of two incipient ferroelectrics CaTiO3 and SrTiO3 in attempts to find ferroelectric or highly polarizable phases. Further, preliminary work on integration of a UV transparent conductor SrNbO3 with ferroelectric BaTiO3 thin films for the creation of ferroelectric solar cells is demonstrated.

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 Structure property Correlations in Double Perovskite Systems written by Manisha Dixit and published by . This book was released on 2013 with total page 225 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Double perovskite compounds of the type ABB'O3 where B and B' are transition elements, exhibit a wide range of properties that are useful for various applications. Double perovskites such as Sr2FeMoO6 (SFMO), Sr2CrReO6 (SCRO) are ferrimagnetic materials with properties useful for spintronic applications. The ordering of Fe and Mo atoms in the case of SFMO and Cr and Re atoms in case of SCRO known as B-site ordering is very important. Sputter-deposited thin-films of SFMO and SCRO systems were characterized using various high resolution transmission electron microscopy (TEM) techniques.

Download or read book A Study of Structure Induced Phase Phenomena in Perovskite Oxide Thin Films written by Jason Lapano and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The three core tenants of materials science are theory, synthesis, and characterization. A solid theoretical framework is required for understanding of the problem at hand and using that knowledge to advance new areas of research. Synthesis of pristine materials is required to study the theory in a physical system and prevent misinterpretation of results. Complex structures and compositions are often the most interesting, and when defects and impurities are of interest, perfectly-imperfect samples are required which are often the most challenging to synthesize. Characterization of these materials is equally as important and complex, requiring careful sample preparation and experimental setups. Further, it is not always clear how to observe the property of scientific interest, and new characterization techniques must be developed. This dissertation focuses on using these three tenants to understand and advance the field of transition metal perovskite complex oxides using thin films of the incipient ferroelectrics CaTiO3 and SrTiO3 and antiferromagnetic Mott-Insulators LaVO3 and YVO3. The knowledge gained in this thesis can be applied to other complex oxide materials in better understanding magnetic and electronic transitions, high Tc superconductivity and quantum hall effect. Coupled with the relatively simple structure and ease of integration of multiple different chemical compounds into a single heterostructure leads to near numerous avenues to design functionality into materials.The first sections of this thesis begin with (1) an introduction to the basic science and past work in perovskite oxides, followed by (2) exploring the most common and promising synthesis routes, and finally (3) the various characterization methods used. The 4th chapter addresses the specific challenges of growth of ternary complex oxide thin films in an industrially profitable fashion. The three primary criterion that these deposition methods must adhere to is that they must (a) control film stoichiometry to less than 1% deviations, (b) deposit conformal coatings over standard 8 silicon wafers, (c) and exhibit deposition rates in excess of 1 m/hr. We show that these can be achieved using a hybrid molecular beam (hMBE) epitaxy approach and outline a route for commercially viable growth of complex oxides on silicon. This method is applied directly to the deposition of SrTiO3 on silicon for virtual single crystal perovskite substrates. The 5th chapter of this thesis discusses the effect of epitaxial strain, stoichiometry and interfacial coupling in heterostructures of complex oxides. In the (SrTiO3)n(CaTiO3)n series of superlattices grown by hMBE, it is found that interfacial energies play a large role in dictating the macroscopic properties, particularly ferroelectricity. In coherently strained thin films, both CaTiO3 and SrTiO3 exhibit relaxor-like ferroelectric behavior below room temperature. However, certain superlattices of these materials show nonpolar behavior when probed using second harmonic generation (SHG). High resolution scanning transmission electron microscopy (STEM) reveals that the symmetry in the superlattice is different from the individual parent compounds at the same strain state. It is found these are directly related to the high density of interfacial layers present in the films. Further, interfacial mixing of the constituent layers on certain superlattices leads to the development of a Ca1-xSrxTiO3 alloy which develops a ferroelectric moment at low temperatures, leading to spurious SHG signals. The findings of this experiment highlight the sensitivity of these complex layered structures to strain, stoichiometry, distortion coupling effects, and interfacial mixing.

Download or read book Investigating Quadruple Perovskites written by Amanda Huon and published by . This book was released on 2018 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: The miniaturization trend in conventional electronics is approaching the limits beyond which the reduction of the electronic element is becoming more and more difficult. One way to continue the current trends in computer power and data storage increase without further size reduction is to use new functionalities such as charge-ordering or multiferroic behavior in devices. Complex oxide heterostructures are a materials platform that exhibit an unmatched array of collectively ordered states, including magnetism, ferroelectricity, and charge/orbital ordering, and are being researched for potential device applications. As a member of the quadruple perovskite family, CaMn7O12 exemplifies the rich physics that complex oxides can host. Previous work shows that this material in bulk form exhibits four distinct phase transitions: a charge-ordering transition at 430 K, an orbital ordering transition at 250 K, and two magnetic transitions at 90 K (TN1) and 45 K (TN2). Additionally, the magnetic ordering at TN1 induces ferroelectricity, which is the largest magnetically induced polarization yet reported. Despite the scientific interest and the technological potential for this material, there have been no reports of CaMn7O12 films prior to this thesis work. This dissertation is focused on establishing growth conditions for CaMn7O12 quadruple perovskite thin films using molecular beam epitaxy and pulsed laser deposition methods. By synthesizing thin films using both methods, I identify the key parameters in establishing the growth conditions for phase-pure CaMn7O12 films by evaluating cation stoichiometry and structural properties. To develop insight into the role of thin film structure-property relations, I explore how the electronic and magnetic structures of thin films compare to bulk. Then I develop insight into quadruple manganites by elucidating how the electronic and magnetic properties are tuned by chemical pressure effects through A-site substitution in Ca1-xSrxMn7O12 films. I identified the changes in charge-ordering, magnetic ordering, and helical spin structure through Sr-doping up to x ~ 0.6 by transport, magnetometry, and neutron diffraction measurements. These results provide fundamental insights into quadruple perovskite film synthesis and serve as a catalyst for future studies focused on AMn7O12 thin films. The material understanding of CaMn7O12 films obtained from this dissertation offers new avenues in the search and control of new functionalities in oxide heterostructures.

Download or read book Correlation of Structure and Properties in Perovskite Oxide Thin Films written by Cole Richard Smith and published by . This book was released on 2015 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rare-earth nickelate (RNiO3) materials exhibit metal-to-insulator transitions at given critical temperatures, which are highly correlated to the relative radii of the rare-earth elements to the radius of nickel. In this work, La1-xEuxNiO3 (LENO) single crystal thin films were grown by molecular beam epitaxy for the first time to understand how epitaxial strain correlates to the metal-to-insulator transition. These thin films showed transition temperatures that trended well with previous research on their bulk counterparts. However, it was found that films grown under tensile strain (~1%) transitioned at much higher temperatures than films grown under the same amount of compressive strain, while films under severe amounts of tensile strain (>2.5%) remained insulating from 1.8 K to 400 K. This is due to the elongation of the in-plane Ni-O bonds which dominate the electron conduction path. During the course of this research the tolerance to cationic off-stoichiometry was also studied in LaNiO3 films. Typically it was assumed that films with defects were more resistive than more crystalline films, however it is rare to find a cationic composition study on complex oxide thin films. In this work Rutherford Backscattering Spectrometry and electronic transport measurements were utilized to show that LaNiO3 films with a La:Ni ratio of 0.75 can be more conductive than films with more stoichiometric cation ratios. This non-trivial behavior is attributed to an increase in electronic bandwidth brought on by a shortening of the Ni-O bonds. These Ni-O-Ni bond angles and lengths are heavily correlated to the macroscopic properties, and in all perovskites these B-O-B parameters are critical for understanding physical behavior. A final effort of this work was to develop a program capable of solving for these angles and bond lengths through the use of synchrotron diffraction of half-order Bragg peaks. My program was shown to work with rhombohedral systems and more structurally complex orthorhombic perovskites, in which the origin of the half-order peaks arises from both octahedral rotations and A-site displacements. Using this program the structure of LaGaO3 films strained to SrTiO3 was solved. This program will be available for all perovskite thin film researchers after being thoroughly vetted.

Download or read book Achieving Novel Magnetic States in Perovskite Oxides Through Heteroepitaxy written by Virat Mehta and published by . This book was released on 2012 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation is focused on controlling the spin state and long-range magnetic order in cobaltites by heteroepitaxial thin-film growth. I explore the growth of two different cobaltite materials, LaCoO3 and PrCoO3, on lattice-mismatched substrates to determine the role of epitaxial strain in giving rise to long-range magnetic order. This magnetic order is not found in the bulk cobaltite material and warrants the detailed investigations carried out in this work. I investigate changes in structure and stoichiometry that influence the electronic structure and the long-range magnetic order in these materials. In the LaCoO3 system, I explore the changes in structure in the films under tensile strain and compressive strain by growth on SrTiO3, LaSrAlTaO3, and LaAlO3 substrates and film growth between 8 nm -133 nm thick. Substrate-dependent oxygen vacancy ordering in the films is found using microstructural characterization, presumably related to the amount of stress in each of the films. By carrying out a study of the effects on the film structure from the oxygen growth pressure, I find an overall increase in the out-of-plane lattice parameter with lower oxygen growth pressures. These structural and stoichiometry changes in the LaCoO3 films to trends appear to be related to the stabilization of long-range magnetic order. Highest moment is found in the films in tension (which also have the most defects) on SrTiO3 and LaSrAlTaO3 substrates and the lowest moment is found in films in compression on LaAlO3. Element-specific X-ray absorption techniques reveal contributions from Co in different spin and valence states. I show how strain affects the electronic structure and distribution of these different states and relate these observations to trends observed in the magnetism. Strained films in tension have the highest amount of high spin Co3+ and high spin Co2+, while relaxed films appear to have mostly low spin Co3+ at 25 K.I present some scenarios to explain how these different Co ions combine to give rise to long-range ferromagnetic order in LaCoO3 films. In the PrCoO3 system, I explore whether long-range magnetic order can be observed using heteroepitaxial synthesis similar to the efforts in the LaCoO3 thin film system despite PrCoO3 having a more stable low spin state configuration in the bulk. The PrCoO3 films in tension are ferromagnetic, similar to the LaCoO3 system. Thus, epitaxial strain dominates the effects of chemical pressure which stabilize a low spin state. The strained films have more high spin Co3+. The implication of Co sublattice ordering on the ordering of the Pr sublattice is explored using X-ray magnetic circular dichroism. A rare ordering of the Pr ions anti-parallel to the orientation of the moments on the Co sublattice appears to occur in this system. These studies demonstrate the power of heteroepitaxial synthesis to give rise to new magnetic functionality in perovskite oxide systems.

Download or read book Controlling the Electronic Properties in La1 3Sr2 3FeO33 delta Complex Perovskite Oxides written by Alex L. Krick and published by . This book was released on 2017 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: For nearly 5 decades, the global semiconductor industry has followed Moore's law, which employs the iterative concept of transistor scaling in silicon-based technology. Though this approach has been massively successful at maintaining consistent increases in computational speed and power, silicon technology is quickly approaching its physical limitations with respect to continued scaling. In recent years, a growing effort has been adopted to pursue new materials and technologies as alternative platforms for information processing. Complex oxides are a potential candidate material system for next generation electronic devices due to their rich material properties such as metal-insulator transitions, high Tc superconductivity, and colossal magnetoresistance. In particular, there is growing interest to understand and control the unique electronic properties of complex oxides for applications in transistor-like devices. This dissertation is focused on understanding the growth, characterization and application of La1/3Sr2/3FeO3 (LSFO) thin films, which are known to undergo an abrupt charge ordering phase transition at 190 K in bulk materials. This phase transition is accompanied by an order of magnitude increase in resistivity going from a conductive to insulating state as well as the spontaneous ordering of charge and antiferromagnetic spin structure along the [111] direction. Isocompositional cation-ordered superlattices of LSFO were synthesized via oxygen-assisted molecular beam epitaxy and explored through synchrotron X-ray diffraction, electronic transport, and density functional theory modeling. By adjusting the cation ordering of LaFeO3 (LFO), an antiferromagnetic insulator, and SrFeO3 (SFO), a conductor with a helical magnetic ground state, three isocompositional systems of LSFO were investigated. The superlattices were found to exhibit a charge ordering phase transition similar to LSFO for two of the three structures, as measured by an abrupt discontinuity in the temperature-dependent resistivity. Carrier behavior within the superlattices was also explored by fitting the temperature dependent resistivity to common conduction models. The conduction mechanism fits show that the transport at high temperatures is dominated by weakly insulating behavior due to small polaron conduction and at low temperatures the resistivity can be fit to both a novel power law and 3-dimensional variable range hopping. Additionally, reversible changes of the structural and electronic transport properties of La1/3Sr2/3FeO38́2Îþ/Gd-doped CeO2 (GDC) heterostructures arising from the manipulation of Îþ are presented. Thermally induced oxygen loss leads to a c-axis lattice expansion and an increase in resistivity in an LSFO film capped with GDC. In a three-terminal device where a gate bias is applied across the GDC layer to alter the LSFO oxygen stoichiometry, the ferrite channel is shown to undergo an order of magnitude change in resistance using gate voltages of less than 1 V applied at 500 K. The changes in resistance remain upon cooling to room temperature, in the absence of a gate bias, suggesting solid state ionic gating of perovskite oxides as a promising platform for applications in non-volatile, multistate devices. Along with the experiments of controlling Îþ in a device format, the kinetics of oxygen loss as a function of biaxial strain was investigated.

Download or read book Synthesis and Cation Stoichiometry Effects of MBE Grown Strained Ca2Fe2O5 Thin Films written by Yizhou Yang and published by . This book was released on 2018 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: The physical properties of perovskite oxide (ABO3) thin films can be tailored through cation deficiency, epitaxial strain, and anion substitution. Similar approaches should be applicable to A2B2O5 brownmillerite materials that consist of alternating layers of BO6 octahedra and BO4 tetrahedra, however, such strategies have yet to be explored in detail in brownmillerite films. In this thesis, Ca2Fe2O5 thin films are synthesized using molecular beam epitaxy, and anion substitution is explored through vapor transport fluorination. Cation off-stoichiometric effects, oxygen vacancy channel orientation, and fluorine substitution are studied through characterization methods such as X-ray diffraction, X-ray reflectivity, X-ray photoelectron spectroscopy, ellipsometry, and Rutherford backscattering spectrometry. The results suggest that Ca deficiency leads to minimal changes to the lattice parameter, while Fe deficient films exhibit c-axis expansion. Epitaxial strain is shown to control the orientation of the vacancies, which is consistent with previous reports. For fluorination, the mechanism is depended on the orientation of vacancies. When the oxygen vacancies are oriented parallel to the film/substrate interface, fluorination is dominated by fluorine substitution for oxygen, while the mechanism for perpendicularly oriented oxygen vacancies is a combination of both fluorine substitution and insertion into anion vacancy sites.

Download or read book Semiconductor Spintronics and Quantum Computation written by D.D. Awschalom and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 321 pages. Available in PDF, EPUB and Kindle. Book excerpt: The past few decades of research and development in solid-state semicon ductor physics and electronics have witnessed a rapid growth in the drive to exploit quantum mechanics in the design and function of semiconductor devices. This has been fueled for instance by the remarkable advances in our ability to fabricate nanostructures such as quantum wells, quantum wires and quantum dots. Despite this contemporary focus on semiconductor "quantum devices," a principal quantum mechanical aspect of the electron - its spin has it accounts for an added quan largely been ignored (except in as much as tum mechanical degeneracy). In recent years, however, a new paradigm of electronics based on the spin degree of freedom of the electron has begun to emerge. This field of semiconductor "spintronics" (spin transport electron ics or spin-based electronics) places electron spin rather than charge at the very center of interest. The underlying basis for this new electronics is the intimate connection between the charge and spin degrees of freedom of the electron via the Pauli principle. A crucial implication of this relationship is that spin effects can often be accessed through the orbital properties of the electron in the solid state. Examples for this are optical measurements of the spin state based on the Faraday effect and spin-dependent transport measure ments such as giant magneto-resistance (GMR). In this manner, information can be encoded in not only the electron's charge but also in its spin state, i. e.

Download or read book Superconductivity in D and F band Metals written by David H. Douglass and published by . This book was released on 1976 with total page 676 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book CRC Handbook of Thermoelectrics written by D.M. Rowe and published by CRC Press. This book was released on 2018-12-07 with total page 720 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermoelectrics is the science and technology associated with thermoelectric converters, that is, the generation of electrical power by the Seebeck effect and refrigeration by the Peltier effect. Thermoelectric generators are being used in increasing numbers to provide electrical power in medical, military, and deep space applications where combinations of their desirable properties outweigh their relatively high cost and low generating efficiency. In recent years there also has been an increase in the requirement for thermoelectric coolers (Peltier devices) for use in infrared detectors and in optical communications. Information on thermoelectrics is not readily available as it is widely scattered throughout the literature. The Handbook centralizes this information in a convenient format under a single cover. Sixty of the world's foremost authorities on thermoelectrics have contributed to this Handbook. It is comprised of fifty-five chapters, a number of which contain previously unpublished material. The contents are arranged in eight sections: general principles and theoretical considerations, material preparation, measurement of thermoelectric properties, thermoelectric materials, thermoelectric generation, generator applications, thermoelectric refrigeration, and applications of thermoelectric cooling. The CRC Handbook of Thermoelectrics has a broad-based scope. It will interest researchers, technologists, and manufacturers, as well as students and the well-informed, non-specialist reader.

Download or read book Science and Technology of Rare Earth Materials written by E C Subbarao and published by Academic Press. This book was released on 1980-01-28 with total page 464 pages. Available in PDF, EPUB and Kindle. Book excerpt: Science and Technology of Rare Earth Materials reviews the important aspects of the science and technology of rare earth materials, covering the entire spectrum from occurrence to extraction and purification, phase relationships, electronic structure, and applications. This book is organized into five sections encompassing 19 chapters. The occurrence, extraction, and production of rare earths are discussed in the first section, followed by purification methods employed for rare earths, together with the role of impurities on their behavior. The phase relations among the rare earth alloys, including a particular reference to the technologically important rare earth-cobalt alloys, and phase relations among the rare earth oxides are considered in the second section. The succeeding two sections focus on studies of the electronic structure of rare earth materials, with emphasis on the use of nuclear magnetic resonance and Mössbauer spectroscopy. Theoretical conceptions are set forth as well as the effect of crystal fields and valence fluctuations on the properties of rare earth systems. The final section describes some of the extensive current uses of rare earth materials such as in the steel industry and in permanent magnets, as well as emerging applications in catalysis, hydrogen storage, ferroelectrics, and fast ion conductors. This book is a valuable resource for researchers and students interested in rare earths.