Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 30 of 77

Full-Text Articles in Physical Sciences and Mathematics

Topics In Quantum Metrology, Control, And Communications, Bhaskar Roy Bardhan Jan 2014

Topics In Quantum Metrology, Control, And Communications, Bhaskar Roy Bardhan

LSU Doctoral Dissertations

Noise present in an environment has significant impacts on a quantum system affecting properties like coherence, entanglement and other metrological features of a quantum state. In this dissertation, we address the effects of different types of noise that are present in a communication channel (or medium) and an interferometric setup, and analyze their effects in the contexts of preserving coherence and entanglement, phase sensitivity, and limits on rate of communication through noisy channels. We first consider quantum optical phase estimation in quantum metrology when phase fluctuations are introduced in the system by its interaction with a noisy environment. By considering …


Expression Of O-Linked N-Acetylglucosamine Modified Proteins And Production And Characterization Of Chlamydia Trachomatis Ct663, Octavia Y. Goodwin Jan 2014

Expression Of O-Linked N-Acetylglucosamine Modified Proteins And Production And Characterization Of Chlamydia Trachomatis Ct663, Octavia Y. Goodwin

LSU Doctoral Dissertations

O-linked â-N-acetylglucosamine is a regulatory post translational modification. This modification occurs on nearly all functional classes of proteins, in the nucleus and cytoplasm. O-GlcNAc is added to serine or threonine by O-GlcNAc transferase and removed by O-GlcNAcase. Previous attempts to study O-GlcNAc-modified proteins have resulted in low yields, making 3-dimensional structure determination impossible. In this dissertation O-GlcNAc transferase will be co-expressed with domains of human cAMP responsive element-binding protein (CREB1) and Abelson tyrosine-kinase 2 (ABL2) in E. coli, to produce O-GlcNAc-modified protein. The O-GlcNAc-modified protein was expressed in a variety of E. coli cell lines at a variety of conditions, …


Synthesis, Characterization, And Investigation Of The Catalytic Activity Of Nio, Cuo, And Nio-Cuo Nanoparticles On Silica As Surrogates Of Combustion-Generated Nanoparticles, Nuwan Nilanka Balapitiya Liyanage Jan 2014

Synthesis, Characterization, And Investigation Of The Catalytic Activity Of Nio, Cuo, And Nio-Cuo Nanoparticles On Silica As Surrogates Of Combustion-Generated Nanoparticles, Nuwan Nilanka Balapitiya Liyanage

LSU Doctoral Dissertations

Transition metal oxide nanoparticles contained in fly ash are known to catalyze the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) during the waste incineration process. The potential catalytic activity of silica-supported NiO, CuO, and NiO-CuO nanoparticles for the formation of PCDD/Fs will be discussed in this dissertation. The successful synthesis of silica-supported NiO, CuO, and NiO-CuO nanoparticles as surrogates of combustion-generated nanoparticles was important to this study. The synthesis was followed by the characterization of the nanoparticle surrogates by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic …


Parallel Processes In Hpx: Designing An Infrastructure For Adaptive Resource Management, Vinay Chandra Amatya Jan 2014

Parallel Processes In Hpx: Designing An Infrastructure For Adaptive Resource Management, Vinay Chandra Amatya

LSU Doctoral Dissertations

Advancement in cutting edge technologies have enabled better energy efficiency as well as scaling computational power for the latest High Performance Computing(HPC) systems. However, complexity, due to hybrid architectures as well as emerging classes of applications, have shown poor computational scalability using conventional execution models. Thus alternative means of computation, that addresses the bottlenecks in computation, is warranted. More precisely, dynamic adaptive resource management feature, both from systems as well as application's perspective, is essential for better computational scalability and efficiency. This research presents and expands the notion of Parallel Processes as a placeholder for procedure definitions, targeted at one …


A Persistent Storage Model For Extreme Computing, Shuangyang Yang Jan 2014

A Persistent Storage Model For Extreme Computing, Shuangyang Yang

LSU Doctoral Dissertations

The continuing technological progress resulted in a dramatic growth in aggregate computational performance of the largest supercomputing systems. Unfortunately, these advances did not translate to the required extent into accompanying I/O systems and little more in terms of architecture or effective access latency. New classes of algorithms developed for massively parallel applications, that gracefully handle the challenges of asynchrony, heavily multi-threaded distributed codes, and message-driven computation, must be matched by similar advances in I/O methods and algorithms to produce a well performing and balanced supercomputing system. This dissertation proposes PXFS, a storage model for persistent objects inspired by the ParalleX …


Spin-Mediated Transport In Superconducting And Spin-Polarized Systems, Joseph C. Prestigiacomo Jan 2014

Spin-Mediated Transport In Superconducting And Spin-Polarized Systems, Joseph C. Prestigiacomo

LSU Doctoral Dissertations

The effects of spin-imbalance on the electronic transport properties of spin-polarized and superconducting systems have been studied in detail. The transport properties of the quaternary Heusler alloys Co2MnSi1-xAlx (0≤x≤1), which have been theoretically predicted to develop a half-metallic band structure as x→0, were investigated. Resistivity versus temperature measurements as a function of Al concentration (x) revealed a systematic reduction in the residual resistivity ratio as well as a transition from weakly-localized to half-metallic conduction as x→0. From measurements of the ordinary and anomalous Hall effects, the charge carrier concentration was found to increase, while the anomalous Hall coefficient decreased by …


Ito Formula And Girsanov Theorem On A New Ito Integral, Yun Peng Jan 2014

Ito Formula And Girsanov Theorem On A New Ito Integral, Yun Peng

LSU Doctoral Dissertations

The celebrated Ito theory of stochastic integration deals with stochastic integrals of adapted stochastic processes. The Ito formula and Girsanov theorem in this theory are fundamental results which are used in many applied fields, in particular, the finance and the stock markets, e.g. the Black-Scholes model. In chapter 1 we will briefly review the Ito theory. In recent years, there have been several extension of the Ito integral to stochastic integrals of non-adapted stochastic processes. In this dissertation we will study an extension initiated by Ayed and Kuo in 2008. In Chapter 2 we review this new stochastic integral and …


Contractional Tectonics: Investigations Of Ongoing Construction Of The Himalaya Fold-Thrust Belt And The Trishear Model Of Fault-Propagation Folding, Hongjiao Yu Jan 2014

Contractional Tectonics: Investigations Of Ongoing Construction Of The Himalaya Fold-Thrust Belt And The Trishear Model Of Fault-Propagation Folding, Hongjiao Yu

LSU Doctoral Dissertations

This dissertation focuses on the kinematic evolution of contractional tectonics: the Himalayan fold-thrust belt along the collisional orogenic belts, and growth of the basement-cored monoclines in Colorado Plateau. Ongoing Himalayan growth is generally thought to be dominated by duplexing and/or extrusion processes. Duplexing models highlight accretion of material from the subducting plate to the over-riding orogenic wedge, whereas extrusion models focus on up-dip translation of a block bounded by out-of-sequence faults. Here, a primary outstanding question involves the uncertain relationship of the Berinag thrust and the Tons thrust, structures with displacements of >80 km and >40 km, respectively. The uncertainty …


Sign Learning Kink Based Quantum Monte Carlo Applied To Multiple Large Systems H2O, N2, F2, Xiaoyao Ma Jan 2014

Sign Learning Kink Based Quantum Monte Carlo Applied To Multiple Large Systems H2O, N2, F2, Xiaoyao Ma

LSU Doctoral Dissertations

A Sign Learning Kink (SiLK) based Quantum Monte Carlo (QMC) method is used to calculate the ground state energies for H2O, N2 and F2 molecules. This method has two stages. The first (learning stage) reduces the minus sign problem by optimizing the states which are used in the second (QMC stage). I test the method in Single, Double excitations (SD), Single, Double, and Triple excitations (SDT), and Full Configuration Interaction (FCI) vector spaces. I also perform exact diagonalization in those vector spaces as a benchmark. In each vector space and for each molecule, I perform SiLK …


Methods For The Characterization Of Deep-Sea Benthic Megafauna In The Vicinity Of The Deepwater Horizon Macondo Well, Stephanie Marie Sharuga Jan 2014

Methods For The Characterization Of Deep-Sea Benthic Megafauna In The Vicinity Of The Deepwater Horizon Macondo Well, Stephanie Marie Sharuga

LSU Doctoral Dissertations

Soft-sediment benthic environments are amongst the largest marine ecosystems in the world and play important roles in many ecosystem functions. In recent years, exploitation of resources and unintentional impacts on deep-sea benthic environments has increased. The Deepwater Horizon oil spill of 2010 in the northern Gulf of Mexico (GoM) represented a prime example of this. The oil spill not only highlighted deficiencies of data and information on baseline conditions, but also represented an opportunity to learn more and develop better methods for the future. Deep-sea imaging platforms such as autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) have been …


Neutron Scattering Studies Of Unusual Spin Structure And Local Correlation In Complex Oxides, Dalgis Mesa Jan 2014

Neutron Scattering Studies Of Unusual Spin Structure And Local Correlation In Complex Oxides, Dalgis Mesa

LSU Doctoral Dissertations

Complex correlated electron materials (CEMs), such as transition-metal oxides with exotic properties and novel functionalities, present immense opportunities and formidable challenges in condensed matter physics, materials science, and engineering. These systems are characterized by a multitude of competing ground states that result from the close coupling between charge, lattice, orbital, and spin degrees of freedom, which can be tuned by chemical substitution, strain induction, or by the application of external stimulus (e.g. pressure, temperature, electric, or magnetic fields). Interest in CEMs is fueled by the richness of their novel properties (e.g. Colossal Magnetoresistance (CMR), Quantum Criticality, and High Temperature Superconductivity), …


Application Of Scanning Probe Microscopy To Characterize Physical Properties Of Polymer Brushes, Photoactive Polymers And Rare Earth Oxide Nanostructures, Susan Denise Verberne-Sutton Jan 2014

Application Of Scanning Probe Microscopy To Characterize Physical Properties Of Polymer Brushes, Photoactive Polymers And Rare Earth Oxide Nanostructures, Susan Denise Verberne-Sutton

LSU Doctoral Dissertations

A sample stage for characterizing photoactive materials was developed for studies with scanning probe microscopy (SPM). A sample stage was designed that directs light from a solar simulator via a fiber optic cable to illuminate the sample. Current-sensing and photocurrent measurements can be acquired with a conductive tip. The designed photocurrent stage can be used for SPM systems with a tip-mounted scanner. Current-sensing measurements can be taken with or without illumination to measure the current produced from organic photovoltaic (OPV) or photoconductive samples. Topography, lateral force and current-sensing images are acquired simultaneously, providing information of how nanoscale morphology affects the …


Bio-Imprinted Hydro-Gels (Bigs) For Protein And Virus Detection, Wei Bai Jan 2014

Bio-Imprinted Hydro-Gels (Bigs) For Protein And Virus Detection, Wei Bai

LSU Doctoral Dissertations

Detection of bio-markers at low concentration is becoming a more and more important topic in scientific research due to its importance in applications crucially related to people’s life like medical diagnosis, environment protection and national security. In the past decades, as the improvement of the modern analytical technologies progressed, plenty of methodologies have been developed to realize the fast and accurate detection of bio-markers in liquid media. However, some drawbacks still remain like the expensive cost, high requirement of operational environment, and need for skilled operators. Here, a new kind of aptamer-based bio-imprinted hydrogel sensor (BIG) with specific macroscopic volume …


Enhancement Of Gulf Killifish, Fundulus Grandis, Fitness And Reproduction, Joshua Thomas Patterson Jan 2014

Enhancement Of Gulf Killifish, Fundulus Grandis, Fitness And Reproduction, Joshua Thomas Patterson

LSU Doctoral Dissertations

Gulf killifish, Fundulus grandis, shows promise for commercial development as a marine baitfish species. Significant markets for F. grandis already exist throughout the Gulf Coast, with the vast majority of supply coming from wild-harvests, which can be hampered by seasonal availability and inconsistent fish health and size. The genus Fundulus also represents an important group of model vertebrates for biological study. A recent review paper described this genus as the premier teleost model for environmental biology. New information generated as a result of the work contained in this dissertation may be more broadly applicable to sister species of F. grandis, …


Space-Efficient Data Structures For String Searching And Retrieval, Sharma Valliyil Thankachan Jan 2014

Space-Efficient Data Structures For String Searching And Retrieval, Sharma Valliyil Thankachan

LSU Doctoral Dissertations

Let D = {d_1, d_2, ...} be a collection of string documents of n characters in total, which are drawn from an alphabet set Sigma =[sigma] ={1,2,3,...sigma}. The top-k document retrieval problem is to maintain D as a data structure, such that when ever a query Q=(P, k) comes, we can report (the identifiers of) those k documents that are most relevant to the pattern P (of p characters). The relevance of a document d_r with respect to a pattern P is captured by score(P, d_r), which can be any function of the set of locations where P occurs in …


Quantum Optical Metrology, Sensing And Imaging, Kebei Jiang Jan 2014

Quantum Optical Metrology, Sensing And Imaging, Kebei Jiang

LSU Doctoral Dissertations

In this dissertation we begin with a brief introduction to quantum optics concentrating on the topics of the noise of quantum optical states, quantum estimation theory, quantum interferometry and the atom-field interaction. This background is necessary for understanding the discussions in later chapters. In particular, quantum interferometry, which is optical interferometry when the light source is a quantum mechanical state, plays a central role in this dissertation. In Chapter 2 we discuss the phase estimation sensitivity of quantum metrology when photon loss is present. In Chapter 3 we extend the discussion to include the phase fluctuation of the system caused …


Phases Of Bosons In Optical Lattices And Coupled To Artificial Gauge Fields, Qinqin Lu Jan 2014

Phases Of Bosons In Optical Lattices And Coupled To Artificial Gauge Fields, Qinqin Lu

LSU Doctoral Dissertations

Ultracold atoms have emerged as an indispensable setting to study quantum many-body systems. Recent experimental and theoretical work has explored the curious phases and novel properties of Bose-Einstein Condensate with optical lattices, and Bose-Einstein Condensate with light-induced artificial spin-orbit coupling. In this thesis, we report our research on these two types of boson systems. In the first topic, in contrast with calculations of bosons in optical lattices that focus on the tight-binding regime, we note that the single-particle states of bosons in a periodic potential generally satisfy the Mathieu equation, and have developed a formalism for studying bosons in an …


Synthesis, Characterization, And Evaluation Of Novel Bodipy Dyes With Theranostic Applications, Jaime Suzanne Hayes Jan 2014

Synthesis, Characterization, And Evaluation Of Novel Bodipy Dyes With Theranostic Applications, Jaime Suzanne Hayes

LSU Doctoral Dissertations

Boron dipyrromethene (BODIPY) dyes, have garnered much attention in recent decades due to their enticing photophysical properties and their bioimaging applicability. Despite the progression of this field, the development of BODIPY based anti-cancer agents and radioimaging dyes has seen little progress. The utilization of fluorescent BODIPYs as photosensitizers for photodynamic therapy, and as boron delivery agents for boron neutron capture therapy offers promise as theranostic agents. Additionally, BODIPY derivatives that absorb and emit in the near-IR regions of the electromagnetic spectrum and bear radioisotopes suitable for radioimaging techniques are of great interest. Chapter 1 is a concise overview of the …


Ionic Liquids And Gumbos For Biomedical And Sensing Applications, Paul Kipkorir Sang Magut Jan 2014

Ionic Liquids And Gumbos For Biomedical And Sensing Applications, Paul Kipkorir Sang Magut

LSU Doctoral Dissertations

This dissertation is a synopsis of advancements in the field of ionic liquids and a group of uniform materials based on organic salts (GUMBOS) in biomedical applications, especially with regard to cancer research. The toxicity of chemotherapeutic agents to normal tissues and drug resistance are a major concern in cancer treatment. In this dissertation, GUMBOS and nanoGUMBOS as well as ionic liquids and nanodroplets are explored as possible chemotherapeutic agents with minimal toxicity to normal cells. In the first part of my dissertation, exploitation of ionic liquid chemistry to modulate toxicity of rhodamine 6G is reported. Rhodamine 6G-based GUMBOS with …


Species Composition And Spatial Ecology Of Amazonian Understory Mixed-Species Flocks In A Fragmented Landscape, Karl Mokross Jan 2014

Species Composition And Spatial Ecology Of Amazonian Understory Mixed-Species Flocks In A Fragmented Landscape, Karl Mokross

LSU Doctoral Dissertations

With the ongoing advance of the agricultural frontier in the Amazon basin, it is inevitable that heterogeneous landscapes will play a key role in conservation. These landscapes are mostly composed of patchworks of small forest fragments, secondary forests and roads. Conservation, however must take species interactions into consideration as they play a pivotal part the maintenance of several biological processes in the tropics. One of the most conspicuous interspecific interactions are seen in mixed-species flocks of birds, which in the Amazon, represent one of the best organized systems of bird aggregations. In this research, I assess how flock spatial behavior …


Microfluidic And Nanofluidic Devices - Mixed Scale Systems For Bioanalytical Applications, Michael David Vincent Jan 2014

Microfluidic And Nanofluidic Devices - Mixed Scale Systems For Bioanalytical Applications, Michael David Vincent

LSU Doctoral Dissertations

Developments in the field of microfluidics and nanofluidics allow an experimenter to employ new analytical techniques. One direction in which the field is moving towards is developing new devices and or instruments on the smallest scale possible. One way in which this can be achieved is by using a combination of top-down and bottom-up technologies. Some of these top-down techniques have been used in other fields such as the use of photolithography to fabricate semiconductors. Photolithography is a top-down method used to create features normally on the micrometer scale, but in order to create nanometer size features another top-down method …


Combinatorial Minimal Free Resolutions Of Ideals With Monomial And Binomial Generators, Trevor Mcguire Jan 2014

Combinatorial Minimal Free Resolutions Of Ideals With Monomial And Binomial Generators, Trevor Mcguire

LSU Doctoral Dissertations

In recent years, the combinatorial properties of monomials ideals and binomial ideals have been widely studied. In particular, combinatorial interpretations of minimal free resolutions have been given in both cases. In this present work, we will generalize existing techniques to obtain two new results. If Lambda is an integer lattice in the n-dimensional integers satisfying some mild conditions, S is the polynomial ring with n variables and R is the group algebra of S[Lambda], then the first result is resolutions of Lambda-invariant submodules of the Laurent polynomial ring in n variables as R-modules. A consequence will be the ability to …


Effects Of Forest Fragmentation On Central Amazonian Bird Demography, Jared Desmond Wolfe Jan 2014

Effects Of Forest Fragmentation On Central Amazonian Bird Demography, Jared Desmond Wolfe

LSU Doctoral Dissertations

Avian diversity in degraded fragmented Amazonian landscapes depends on the persistence of species in cleared and disturbed areas. Regenerating forest facilitates bird dispersal within degraded Amazonian landscapes and may tip the balance in favor of persistence in previously depauperate habitat patches. Despite the potential value of Amazonian second growth, we lack comparisons of demography among second growth, continuous forest, forest fragments in regenerating landscapes, and truly isolated fragments. Here, we used point-count and capture data to compare Amazonian bird communities among continuous forest plots, 100 ha forest fragments with adjacent second growth, 100 ha forested islands bounded by water, young …


Some Numerical And Phenomenological Studies In Loop Quantum Cosmology, Brajesh Kumar Gupt Jan 2014

Some Numerical And Phenomenological Studies In Loop Quantum Cosmology, Brajesh Kumar Gupt

LSU Doctoral Dissertations

A key feature of the singularity resolution in loop quantum cosmology (LQC) is the occurrence of the quantum bounce when the spacetime curvature becomes comparable to the Planck scale. The presence of quantum bounce greatly modifies the dynamics of the early universe and can have important implications for observational signatures. Although the quantum bounce has been previously studied via numerical methods for initial conditions that correspond to large macroscopic universes at late times, a detailed study of the robustness of the quantum bounce for a generic class of initial condition has so far been missing due to severe computational challenges. …


Synthetic Routes To Therapeutic Agents Via Masked Functionalities: From Orthogonal Peptide Crosslink To Photothermal Cancer Prodrug, Chyree Shantel Batton Jan 2014

Synthetic Routes To Therapeutic Agents Via Masked Functionalities: From Orthogonal Peptide Crosslink To Photothermal Cancer Prodrug, Chyree Shantel Batton

LSU Doctoral Dissertations

The theonellamides are a family of compounds distinguished by their crosslinking ô-histidinoalanine (ô-HAL) residue. Part one of this dissertation details the synthesis of an orthogonally protected ô-HAL building block that will be incorporated into a total synthesis of theonellamide C. Selective deprotection of each amine and acid of this orthogonally protected building block is also demonstrated. Various reaction partners for the assembly of ô-histidinoalanine were explored. One approach involved the coupling of N-Fmoc-â-iodoalanine benzyl ester and (Nðim)-blocked histidine nucleophiles including a fused bicyclic urea and a Boc-His(Nð-Pac)-OMe. While the imidazolium salts were identified by mass spectrometry, elimination of the iodide …


A Standardized Ultrasonography Classification For Channel Catfish Ovarian Development, Noel D. Novelo Jan 2014

A Standardized Ultrasonography Classification For Channel Catfish Ovarian Development, Noel D. Novelo

LSU Doctoral Dissertations

The goal of this dissertation was to develop application of ultrasonography as a decision-making tool in genetic improvement programs for channel catfish Ictalurus punctatus. A literature review on the use of ultrasonography in fish reproduction generated a comprehensive reference data set intended to benefit existing and potential users. It exposed the need for reporting of instrument control settings and standardization of fish handling and imaging procedures. These issues were addressed from the onset of this work by assessing more than 6,300 channel catfish ovaries by use of initial fish handling and imaging procedures developed (2004-2005) at the Louisiana State University …


Reductive Alkylation Of Proteins Towards Structural And Biological Applications, Kevin Jerome Roberson Jan 2014

Reductive Alkylation Of Proteins Towards Structural And Biological Applications, Kevin Jerome Roberson

LSU Doctoral Dissertations

Nuclear magnetic resonance (NMR) spectroscopy is a proven technique for protein structure and dynamic studies, typically requiring the incorporation of stable magnetic isotopes to improve sensitivity and assign resonances. Degenerate levels of 13C-incorporation have been the biggest obstacle for mass spectrometry-assisted assignment of 13C-dimethylamine resonances in nuclear magnetic resonance spectroscopy (NMR). Reductive 13C-methylation is an alternative labeling method for proteins not amenable to bacterial host overexpression. Because reductive 13C-methylation adds sparse, isotopic labels, traditional methods of assigning the NMR signals are not applicable. The research presented in the first part of this dissertation explores several methods used to break the …


Design, Synthesis, And Exploration Of A Chimeric Antioxidant And New Crosslinkers For Molecular Imprinting, Danielle Songe Meador Jan 2014

Design, Synthesis, And Exploration Of A Chimeric Antioxidant And New Crosslinkers For Molecular Imprinting, Danielle Songe Meador

LSU Doctoral Dissertations

The improvement and utility of crosslinkers are important topics of molecular imprinting. Crosslinker significance is evident when molecularly imprinted polymer (MIP) composition related to performance as separation media is examined. Crosslinkers account for the bulk of MIP formulations made through traditional imprinting (80-90%) and is even greater when the One Monomer Molecularly Imprinted Polymer (OMNiMIP) approach is utilized (100%.) It is not surprising that alteration of the bulk component will result in different separation performances. Crosslinkers studied in this work were designed, synthesized, and evaluated toward improvement in OMNiMIP selectivity. In particular, functionality and number of polymerizable groups, addition of …


Surface Chemistry And Growth Of Oxide Supported Metal Nanoparticles, Ziyu Zhang Jan 2014

Surface Chemistry And Growth Of Oxide Supported Metal Nanoparticles, Ziyu Zhang

LSU Doctoral Dissertations

A model heterogeneous catalyst inspired by a real catalyst is synthesized for the purpose of understanding how it works. To make such model catalysts, we choose to evaporate metal atoms on metal oxide single crystals and measure them under UHV conditions. The study of model catalysts could advance the understandings of fundamental catalytic properties of real catalysts and helps to optimize or redesign industrial catalysts. In our experiments, many ultra-high vacuum (UHV) techniques have been employed to investigate the atomic and electronic structure of the surface as well as the interface of the prepared samples. In particular, the surface-sensitive tools …


Substitution And Disorder Effects In Ternary Intermetallics, Larico Juan Treadwell Jan 2014

Substitution And Disorder Effects In Ternary Intermetallics, Larico Juan Treadwell

LSU Doctoral Dissertations

The focal point of this dissertation is the investigation of substitution and disorder effects in ternary intermetallics. The crystal growth, crystal structure, and physical properties are reported on single crystals of Ln6W4-xAl43-yTx+y (Ln = Gd, Yb; T= Mn, Fe), LnCr2FexAl20-x (Ln = Yb, Gd), Sm1.33Pd3Ga8, and CeCo2-xMxAl8 (M = Mn, Fe, Ni; 0 ≤ x < 1). The reported compounds were grown via the flux growth method with the strategic synthetic parameters described. Correlations between the structural and physical properties in relation to substitution and disorder of Ln6W4-xAl43-yTx+y (Ln = Gd, Yb; T= Mn, Fe), LnCr2FexAl20-x (Ln = Yb, Gd), Sm1.33Pd3Ga8, and CeCo2-xMxAl8 (M = Mn, Fe, Ni; 0 ≤ x < 1) are discussed. The synthesis and characterization of Mn- and Fe- substituted Ln6W4Al43 (Ln = Gd, Yb) are reported. The compounds adopt the Ho6Mo4Al43 structure type with lattice parameters of a ~ 11 Å and c ~ 17.8 Å with structural site preferences for Mn and Fe. The magnetization of Yb6W4Al43 is sensitive to Mn and Fe doping, which is evident by an increase in the field dependent magnetization. Gd6W4Al43, Gd6W4Al42.31(11)Mn0.69(11), and Gd6W4Al41.69(12)Fe1.30(12) order antiferromagnetically in the ab- and c-direction at 15, 14, and 13 K, respectively, with positive Weiss constants, suggesting the presence of ferromagnetic exchange interactions. Anisotropic magnetization data of Gd6W4Al43-yTy (T= Mn, Fe) analogs are discussed. Crystal growth, structure determination, and magnetic properties of LnCr2Al20-xFex (Ln = La, Gd, Yb) adopting the CeCr2Al20 structure type with space group Fd3¯ m, a ~ 14.5 Å, type are reported. Single crystal X-ray diffraction and Mössbauer spectroscopy are employed to fully characterize the crystal structure of LnCr2Al20-xFex (Ln = La, Gd, Yb). LnCr2Al20-xFex (Ln = La, Gd, Yb) are the first pseudo-ternaries adopting the CeCr2Al20 structure type with a transition metal occupying the main group site. The Yb analogues are Pauli paramagnets with the Yb ion adopting an electronic configuration close to Yb2+, while the Gd analogues show paramagnetic behavior with no magnetic order down to 3 K. The synthesis and characterization of Sm1.33Pd3Ga8 is reported. Sm1.33Pd3Ga8 adopts a disordered variant of the Er4Pt9Al24-structure type with lattice parameters of a = 4.353(5) and c = 38.98(4) Å and V = 639.70(12) Å3. The structure of Sm1.33Pd3Ga8 is composed of three distinct building blocks: Pd2Ga4, PdGa2, and Sm0.67Ga. The Sm0.67Ga slab does not magnetically order, which directly affect the structure. Sm1.33Pd3Ga8 is a temperature independent paramagnet. Field dependent magnetization of Sm1.33Pd3Ga8 displays anisotropic behavior. Single crystals of CeCo2-xMxAl8 (M = Mn, Fe, Ni; 0 ≤ x < 1) were grown and crystallize in the CaCo2Al8 structure type with space group Pbam. Single crystal X-ray diffraction data suggest that the Ce 4f-state is valence fluctuating as Fe concentration increases, whereas the Ni-doped analogues do not exhibit valence fluctuating. The results suggest that hole doping leads to an admixture of Ce3+/Ce4+.