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Title: Atomic displacements in transition metals.
Creator: Moghadam, Nassrin Y., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Using the order-N locally-self-consistent multiple scattering (LSMS) method, we carry out first-principles studies of the displacement of atoms from their average sites in the vicinity of a vacancy and transition metal impurities in copper. Our approach is to relax the first nearest neighbor distance and to calculate total energy for a number of relaxed geometries. We then obtain the equilibrium configuration of the nuclei from minimization of the total energy.
Date Issued: 1998
PURL: http://purl.flvc.org/fcla/dt/12546
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: Computational methods in metallic alloys within multiple scattering theory.
Creator: Rusanu, Aurelian, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Designing materials, particularly at the nano-scale, is an important scientific research area. It includes a large spectrum of basic science and technological developments. In order to provide results that are relevant to real materials, quantum mechanical simulations involving thousands to millions of atoms must be carried out. The locally self-consistent multiple scattering (LSMS) method is the method of choice for such calculations because it has a technical feature called order-N scaling....
Show moreDesigning materials, particularly at the nano-scale, is an important scientific research area. It includes a large spectrum of basic science and technological developments. In order to provide results that are relevant to real materials, quantum mechanical simulations involving thousands to millions of atoms must be carried out. The locally self-consistent multiple scattering (LSMS) method is the method of choice for such calculations because it has a technical feature called order-N scaling. We describe an implementation of the LSMS for massively parallel supercomputers using k-space and real-space methods. For magnetic materials, the constrained local moment approach and the exchange interaction method are used. We demonstrate our approach by calculating the electronic and magnetic structure of an iron nano-particle embedded in an iron aluminide crystal matrix.
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Date Issued: 2005
PURL: http://purl.flvc.org/fcla/dt/12176
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: The electronic structure and properties of equi-atomic CuAu.
Creator: Xu, Xumou, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The electronic structure of equi-atomic CuAu has been investigated by a combination of photoelectron spectroscopy and first-principles band structure calculations. The study includes the first ever ARUPS and ARAES measurements from a single crystal of CuAu I. We have studied in detail the energy dispersion and shifts of a Tamm state on the (001) and (100) surfaces and we determined the surface lattice constants and the dependencies of the energy shifts on atomic concentration and geometry....
Show moreThe electronic structure of equi-atomic CuAu has been investigated by a combination of photoelectron spectroscopy and first-principles band structure calculations. The study includes the first ever ARUPS and ARAES measurements from a single crystal of CuAu I. We have studied in detail the energy dispersion and shifts of a Tamm state on the (001) and (100) surfaces and we determined the surface lattice constants and the dependencies of the energy shifts on atomic concentration and geometry. Two new surface states were found on the two surfaces and their properties have been investigated. Comparisons between the valence band spectra from the two samples of CuAu I have been carried out and the results show that the different atomic arrangements in the crystal do not have a significant effect on the band structure. We also compared spectra from the alloy with those from the parent metals. A series of calculations of the electronic structure of CuAu I has been carried out by the SCF-LMTO-ASA and RKKR methods. We found that the superzone boundaries that are created when the CuAu II phase is formed destroy appreciable regions of Fermi surface, thus, favoring the latter phase. The positions of the new boundaries are related directly to the period of the long period superlattice and we have investigated their dependence on the e/a ratio and pressure. The results are in very good agreement with previous experimental measurements. We also calculated the Fermi surfaces of three disordered Cu-Au alloys near the equi-atomic composition using the KKR-CPA scheme. The results have shown strong evidence that the Fermi surface topology may play an important role in stabilizing and determining the modulation of the LPS in CuAu II.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/12423
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: The electronic structure and properties of silver-magnesium alloys.
Creator: Liu, Yan, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The electronic structures of beta'-AgMg and Ag3Mg alloys have been investigated by a combination of photoelectron spectroscopy and first-principles band structure and photocurrent calculations. The study includes the first ever XPS and UPS measurements from the ordered and disordered phases of Ag3Mg. We concentrated mainly on measurements of the valence bands and the core level binding energies for these alloys and their parent metals. The band structures of the ordered alloys and pure metals...
Show moreThe electronic structures of beta'-AgMg and Ag3Mg alloys have been investigated by a combination of photoelectron spectroscopy and first-principles band structure and photocurrent calculations. The study includes the first ever XPS and UPS measurements from the ordered and disordered phases of Ag3Mg. We concentrated mainly on measurements of the valence bands and the core level binding energies for these alloys and their parent metals. The band structures of the ordered alloys and pure metals have been calculated by the SCF-LMTO-ASA method, and the KKR and KKRCPA calculational schemes have been used in order to determine the electronic structures of both ordered and disordered phases of Ag3Mg on an equal footing. For the purpose of interpreting the core level shifts due to alloying, a modified LMTO scheme has been applied, in a supercell geometry, to allow for relaxation effects. In addition, we have shown that the Fermi surface topology may well be an important factor in determining the relative stability of the long period superlattice structure in Ag3Mg. In general, the calculations are in very good agreement with the experimental results. We conclude that the combination of theoretical calculations and photoemission measurements provides a detailed understanding of the electronic structures and the properties of Ag-Mg alloys.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12332
Subject Headings: Physics, Condensed Matter, Engineering, Metallurgy
Format: Document (PDF)

Title: Electronic structure calculations for alloys using the polymorphous coherent potential approximation.
Creator: Pella, Silvia, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The Polymorphous Coherent Approximation (PCPA) plays the central role in this study. The PCPA represents an extension of the Coherent Potential Approximation (CPA) in the sense that it treats an alloy model in which all of the atoms are allowed to have distinct charges and potentials. It makes use of the supercells that contain hundreds of atoms. The Madelung potentials at all sites are calculated exactly. The present calculations demonstrate the advantages of the PCPA over the CPA in...
Show moreThe Polymorphous Coherent Approximation (PCPA) plays the central role in this study. The PCPA represents an extension of the Coherent Potential Approximation (CPA) in the sense that it treats an alloy model in which all of the atoms are allowed to have distinct charges and potentials. It makes use of the supercells that contain hundreds of atoms. The Madelung potentials at all sites are calculated exactly. The present calculations demonstrate the advantages of the PCPA over the CPA in explaining experiments that depend critically on the charge transfer in an alloy.
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Date Issued: 2003
PURL: http://purl.flvc.org/fau/fd/FADT12029
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: The electronic structure of beta'-nickel-aluminum and its low-index, high-symmetry surfaces.
Creator: Hines, Eric Lawrence, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The electronic structure of beta'-NiAl alloy and its low-index high-symmetry surfaces has been studied with a combination of photocurrent and first-principles electronic structure calculations. Bulk calculations have been performed with both the LMTO and LSMS computational codes, and the core level shifts upon alloying are discussed in detail. Defect formation and bonding mechanisms in off-stoichiometric NiAl are investigated. The electronic structure of the (110), (100) and (111) surfaces...
Show moreThe electronic structure of beta'-NiAl alloy and its low-index high-symmetry surfaces has been studied with a combination of photocurrent and first-principles electronic structure calculations. Bulk calculations have been performed with both the LMTO and LSMS computational codes, and the core level shifts upon alloying are discussed in detail. Defect formation and bonding mechanisms in off-stoichiometric NiAl are investigated. The electronic structure of the (110), (100) and (111) surfaces are investigated using the LMTO and LSMS, and electronic potentials for input to the photocurrent code are evaluated in the surface geometry. Photocurrent calculations for the (110), (100) and (111) surface are presented and compared with high quality experimental measurements. The (100) surface is found to have a double Ni termination. This defect layer is predicted to sustain a magnetic moment. The rippling of the (110) surface is modelled in the photocurrent calculations, and is found to effect the spectral profile in significant ways. The calculated photocurrent spectra are used to predict the surface composition for the (100), (111) and (110) surfaces, and the rippling value of the (110) surface. Agreement with experiment is good. A method for utilizing computational photoemission spectra to predict the structure and composition of metallic surfaces is presented, and its strengths and weaknesses are discussed.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12492
Subject Headings: Physics, Electricity and Magnetism, Physics, Condensed Matter
Format: Document (PDF)

Title: Epitaxial bain paths and metastable phases of tetragonal iron and manganese.
Creator: Ma, Hong, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Epitaxial Bain paths and metastable states of tetragonal Fe and Mn have been studied by first-principles total-energy calculations using the full-potential linearized-augmented-plane-wave method. The main accomplishments are as follows. (1) We have performed the first ever EBP calculation of tetragonal antiferromagnetic (AF) Mn showing that when grown epitaxially on Pd(001), the AF Mn film is strained gamma-Mn, but grown on V(001) the film is strained delta-Mn, which could not be determined...
Show moreEpitaxial Bain paths and metastable states of tetragonal Fe and Mn have been studied by first-principles total-energy calculations using the full-potential linearized-augmented-plane-wave method. The main accomplishments are as follows. (1) We have performed the first ever EBP calculation of tetragonal antiferromagnetic (AF) Mn showing that when grown epitaxially on Pd(001), the AF Mn film is strained gamma-Mn, but grown on V(001) the film is strained delta-Mn, which could not be determined using the available crystallographic and elastic data because they were obtained from unstrained states. (2) We have calculated the EBP's of Fe at zero pressure in four magnetic phases, i.e., ferromagnetic (FM), nonmagnetic (NM), type-I antiferromagnetic (AF1), and type-II antiferromagnetic (AF2), which show that the AF2 is the phase of the bulk of epitaxial Fe films on Cu(001) and it is unstable for [110] and [010] shears in the (001) plane, but it can be stabilized by epitaxy on Cu(001). (3)We have unified and simplified the theory of elasticity under hydrostatic pressure p at zero temperature using the Gibbs free energy G, rather than the energy E. The minima of G, but not E, with respect to strains at the equilibrium structure give the zero temperature elastic constants; the stability of a phase at p is then determined by the same Born stability conditions used at p = 0 when applied to the elastic constants from G. The EBP's of FM Fe under hydrostatic pressure show that the bcc phase exists up to 1500 kbar. A bct phase is shown to come into existence at 1300 kbar and becomes stable at 1825 kbar and above. (4) Based on this dissertation research five papers have been published in refereed journals.
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Date Issued: 2002
PURL: http://purl.flvc.org/fau/fd/FADT12021
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: Magnetic, thermodynamic, and structural studies of manganese oxides.
Creator: Terashita, Hirotoshi, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Magnetic, thermodynamic, and structural properties of the manganese oxides La1-xCa xMnO3 are studied. Neutron powder diffraction reveals two distinct crystallographic phases as well as two magnetic (ferromagnetic and antiferromagnetic) phases for 0.08
Show moreMagnetic, thermodynamic, and structural properties of the manganese oxides La1-xCa xMnO3 are studied. Neutron powder diffraction reveals two distinct crystallographic phases as well as two magnetic (ferromagnetic and antiferromagnetic) phases for 0.08 < x < 0.14. Details of the compositional dependence of the phase fractions is discussed in the context of local ferromagnetism. Comparisons of magnetic and crystallographic properties are made to the analogous electron-doped Ca1- yLayMnO3 (0 < y < 0.20) system. Thermodynamic properties of La1- xCaxMnO 3 (0 < x < 0.54) are investigated for possible applications in magnetic refrigeration. A maximum magnetic entropy change of 5.5 J/kg K and a corresponding temperature change of 2 K are estimated for x = 0.28. The magnetocaloric effect in antiferromagnetic and charge-ordering compounds is found to be small.
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Date Issued: 2005
PURL: http://purl.flvc.org/fau/fd/FADT12133
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: Massively parallel molecular dynamics simulation of crack initiation and growth in a copper-nickel alloy.
Creator: Morrey, Willard C., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics, Wille, Luc T.
Abstract/Description: We developed code in MasPar Fortran (an extension of Fortran 90) to conduct molecular dynamics simulations on a MasPar MP-1 massively parallel computer. The code is portable to other Single-Instruction Multiple-Data (SIMD) platforms with minor modifications. We used a two dimensional grid containing over 220,000 atoms to simulate a high strain-rate fracture growth in Cu-Ni alloys. The atoms are arranged in a triangular lattice corresponding to an fcc (111) surface and a Lennard-Jones (LJ)...
Show moreWe developed code in MasPar Fortran (an extension of Fortran 90) to conduct molecular dynamics simulations on a MasPar MP-1 massively parallel computer. The code is portable to other Single-Instruction Multiple-Data (SIMD) platforms with minor modifications. We used a two dimensional grid containing over 220,000 atoms to simulate a high strain-rate fracture growth in Cu-Ni alloys. The atoms are arranged in a triangular lattice corresponding to an fcc (111) surface and a Lennard-Jones (LJ) potential with a spline cutoff is used for the inter-atomic potential. The location of the spline cutoff can be adjusted to simulate either brittle or ductile fracture. The atomic positions are spatially decomposed on each Processor Element, the data are shared with adjacent PEs, and atoms are transferred as they move. Free boundary conditions are used, and the appropriate techniques for applying strain and damping unwanted reflections are developed. We report variations in the critical applied strain with increasing temperature, and propose a novel method for characterizing the location of a crack tip. This method lends itself to algorithmic calculation and reporting by the fracture code. Our results represent the first microscopic analysis of fracture in an alloy system and extend recent work on pure metals. During the investigation, we introduced a Sigma 5 grain boundary (36.9) into the sample, with appropriate grain-boundary segregation. We developed a technique for rapidly quenching the high-energy particles at an artificially constructed grain boundary. We demonstrate crack blunting at the grain boundary. We also report on flyer/target impact simulations in an alloy with an LJ inter-atomic potential.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12445
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Molecular dynamics study of atomic displacements in disordered solid alloys.
Creator: Puzyrev, Yevgeniy S., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The effects of atomic displacements on the energetics of alloys plays important role in the determining the properties of alloys. We studied the atomic displacements in disordered solid alloys using molecular dynamics and Monte-Carlo methods. The diffuse scattering of pure materials, copper, gold, nickel, and palladium was calculated. The experimental data for pure Cu was obtained from diffuse scattering intensity of synchrotron x-ray radiation. The comparison showed the advantages of...
Show moreThe effects of atomic displacements on the energetics of alloys plays important role in the determining the properties of alloys. We studied the atomic displacements in disordered solid alloys using molecular dynamics and Monte-Carlo methods. The diffuse scattering of pure materials, copper, gold, nickel, and palladium was calculated. The experimental data for pure Cu was obtained from diffuse scattering intensity of synchrotron x-ray radiation. The comparison showed the advantages of molecular dynamics method for calculating the atomic displacements in solid alloys. The individual nearest neighbor separations were calculated for Cu 50Au50 alloy and compared to the result of XAFS experiment. The molecular dynamics method provided theoretical predictions of nearest neighbor pair separations in other binary alloys, Cu-Pd and Cu-Al for wide range of the concentrations. We also experimentally recovered the diffuse scattering maps for the Cu47.3Au52.7 and Cu85.2Al14.8 alloy.
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Date Issued: 2005
PURL: http://purl.flvc.org/fcla/dt/12137
Subject Headings: Physics, Condensed Matter, Physics, Atomic
Format: Document (PDF)

Title: The multiple scattering approach to the electronic structure of ordered solids, impurities, and alloys.
Creator: Wang, Yang, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: In this dissertation, multiple scattering theory (MST) plays a fundamental role. It is applied to develop the electronic structure calculation techniques for ordered solids, single impurities and binary alloys. The most accurate fast-band-theory technique based on the MST is the quadratic Korringa-Kohn-Rostoker (QKKR) method. A method for carrying out the self-consistent QKKR calculation for ordered compounds is derived and applied to palladium hydride. The application of the QKKR method to...
Show moreIn this dissertation, multiple scattering theory (MST) plays a fundamental role. It is applied to develop the electronic structure calculation techniques for ordered solids, single impurities and binary alloys. The most accurate fast-band-theory technique based on the MST is the quadratic Korringa-Kohn-Rostoker (QKKR) method. A method for carrying out the self-consistent QKKR calculation for ordered compounds is derived and applied to palladium hydride. The application of the QKKR method to single impurity problems is also examined. In order to study phase diagrams of binary alloys, a new approach, called the embedded cluster Monte Carlo (ECMC) method, is developed. It is used to calculate the miscibility gap in the Pd-Rh alloy phase diagram to an accuracy that has never before been achieved. A non-magnetic calculation for Cu-Ni alloys is also provided. These calculations required the mastery of Korringa-Kohn-Rostoker coherent-potential-approximation methods and the development of embedded cluster codes.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12333
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Narrow and broad band photoluminescence spectroscopy of Cd(x)Zn(1-x)Se semiconductor.
Creator: Sweiti, Ayman, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: In this dissertation I have used photoluminescence (PL) spectrometric analysis to measure the temperature dependence of the spectral features of the direct band gap semiconductor CdxZn1-xSe , for two nominal concentrations x = 0.25, 0.50, in the temperature range 25--300 K. The effective concentrations were obtained from analysis of the spectra. The parameters that describe the temperature dependence of the line width broadening have been evaluated using different models. The PL broadband...
Show moreIn this dissertation I have used photoluminescence (PL) spectrometric analysis to measure the temperature dependence of the spectral features of the direct band gap semiconductor CdxZn1-xSe , for two nominal concentrations x = 0.25, 0.50, in the temperature range 25--300 K. The effective concentrations were obtained from analysis of the spectra. The parameters that describe the temperature dependence of the line width broadening have been evaluated using different models. The PL broadband characteristics of Cd0.22Zn0.78Se and Cd0.41Zn0.59Se are also investigated within the energy range 1.36--2.40 eV and temperature range 25--305 K. Two broad bands are observed, the higher energy band I centered at 1.991 and 1.773 eV, the lower energy band II centered at 1.844 and 1.705 eV for the two samples, respectively. The emission bands are attributed to donor-acceptor pair transitions. The energy scheme shows two donors and two acceptor levels, the binding energies of the donors for Cd 0.22Zn0.78Se are 29 and 208 meV below the conduction band, the binding energies of the acceptors 472 and 511 meV above the valence band. The binding energies of the donors for Cd0.41Zn 0.59Se are 27 and 137 meV, the binding energies of the acceptors 393 and 423 eV. A significant blue shift in energy with increasing temperature was observed for the lower energy band. The ionization temperatures for the deep donors are 279 and 287 K for Cd0.22Zn0.78Se and Cd0.41Zn0.59Se, respectively.
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Date Issued: 2003
PURL: http://purl.flvc.org/fau/fd/FADT12075
Subject Headings: Chemistry, Analytical, Physics, Condensed Matter
Format: Document (PDF)

Title: Physical properties of ferrimagnetic bioceramics.
Creator: Kis, Antonella C., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The structural, magnetic and microstructural properties of ferrimagnetic bioglass ceramics (FBC) in the system {0.45(CaO,P2O5) x (0.52-x)SiO2 x xFe 2O3 x 0.03Na2O} with x = 0.05, 0.10, 0.15, 0.20 were studied as a function of composition and heat-treatment temperature. Specimens from each samples series were heattreated at temperatures in the range 600--1000C. X-ray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy...
Show moreThe structural, magnetic and microstructural properties of ferrimagnetic bioglass ceramics (FBC) in the system {0.45(CaO,P2O5) x (0.52-x)SiO2 x xFe 2O3 x 0.03Na2O} with x = 0.05, 0.10, 0.15, 0.20 were studied as a function of composition and heat-treatment temperature. Specimens from each samples series were heattreated at temperatures in the range 600--1000C. X-ray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy dispersive x-ray spectroscopy were used in our studies. Calcium phosphate [Ca3PO4)2], which is the biocompatible component of the materials, and magnetite Fe3O 4 are the two major crystalline phases that were developed in all samples series. In the two series of samples with x = 0.15 and 0.20, calcium phosphate undergoes a gradual transition from the monoclinic to the rhombohedral crystal system (Space Group P21/a, R3c) as the heat-treatment temperature increases from 800 to 1100C. It crystallizes only in R3c in the samples series with x = 0.05 and x = 0.10. Magnetite crystallizes in the orthorhombic system (SG Imma) in weight fractions determined by the heat-treatment temperature. In the system with x = 0.20, magnetite partially converts to hematite (SG R3c) in weight fractions that increase with the heat-treatment temperature. The saturation magnetization of all specimens depends on the starting composition in Fe2O3 while it becomes maximum in samples that were heat-treated at 800°C in all sample series. Magnetization loops show that the energy stored in the material is greatly affected by composition and heat-treatment, but not in a systematic way. SEM and EDX spectra reveal a variety of microstructures that are determined by the processing parameters of each sample. Dendrite structures consisting of Fe and O with crystallites of various sizes form on a glassy matrix of P, Si, Ca and O in the samples series 20G, while very fine surface microstructures are observed in the series 15G.
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Date Issued: 2004
PURL: http://purl.flvc.org/fau/fd/FADT12069
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Spectroscopic studies of ZnWO4 and doped ZnWO4 single crystals.
Creator: Wang, Hong, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Zinc tungstate (ZnWO4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et al. 1986a, 1986b, 1989). A group-theoretical analysis of the characteristic lattice vibrational modes for ZnWO4 single crystals is given. The mode assignments have been made. The temperature dependence of the Raman...
Show moreZinc tungstate (ZnWO4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et al. 1986a, 1986b, 1989). A group-theoretical analysis of the characteristic lattice vibrational modes for ZnWO4 single crystals is given. The mode assignments have been made. The temperature dependence of the Raman spectra has been obtained experimentally in various polarization geometries. Anharmonic contributions and interactions between phonons are discussed. Photoluminescence studies of ZnWO4 (colored, color-free), ZnWO4: Nb and ZnWO4:Sb have been carried out in the temperature range from 11 to 430 K. All samples show the blue emission band. An IR emission band with a zero-phonon line (ZPL) has been found in ZnWO4 colored samples only. The lineshape function of the emission bands has been theoretically studied and compared with the experimental results. Radiative, non-radiative and multiphonon transitions have been investigated in the thermal quenching model. The temperature dependences of the intensity, the frequency and the linewidth of the ZPL have been studied. Using the Single Configurational Coordinate model, the linear coupling between electrons and phonons has been analyzed. The quadratic coupling of electrons and phonons has been studied in the Debye approximation. The coupling of electronic transitions to normal vibrational modes, pseudo-localized vibrational modes and localized modes is also discussed.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12346
Subject Headings: Physics, Condensed Matter, Physics, Optics, Engineering, Materials Science
Format: Document (PDF)

Title: Statistical physics for materials classification.
Creator: Lassalle, Hugues Jean, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Genetic algorithms (GA) and clustering techniques are used to study and classify materials. An analysis of the convergence speed of GA is carried out using advanced probability theory and random walk concepts. The determination of the ground-state of multicomponent alloys and Ising models with long-range interactions is accomplished using a genetic algorithm. A new GA operator, the domain-flip, is introduced and its efficiency is compared to that of traditional GA operators, crossover and...
Show moreGenetic algorithms (GA) and clustering techniques are used to study and classify materials. An analysis of the convergence speed of GA is carried out using advanced probability theory and random walk concepts. The determination of the ground-state of multicomponent alloys and Ising models with long-range interactions is accomplished using a genetic algorithm. A new GA operator, the domain-flip, is introduced and its efficiency is compared to that of traditional GA operators, crossover and mutation. The domain-flip operator destroys phase-boundaries by flipping all bits of a given domain at the same time. This operator turns out to be crucial in extracting the system from low local minima. Therefore its presence is rather essential to speed up the GA convergence. A study of GA convergence in its last stages, where all chromosomes present in the population are assumed to consist of two well-ordered domains, is performed using random walk theory and probability theory. Exact expressions for the average time needed for at least one chromosome to find the ground-state are derived. Also, the probability for two chromosomes to undergo a successful crossover, meaning the result is the ground-state, are given. Finally, clustering techniques, which belong to the field of Data Mining, are applied to the classification of materials. An improved version of the widely-used clustering algorithm, K-means, is developed. A comparison of the two clustering techniques on a two-dimensional data set shows that the guide-point approach is more powerful than the K-means algorithm. The guide-point algorithm is used successfully to partition a materials data set. This clustering results in extracting useful information from the data set for which no a priori knowledge was assumed.
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Date Issued: 2002
PURL: http://purl.flvc.org/fcla/dt/11998
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science, Computer Science
Format: Document (PDF)

Title: Structural, electrical and magnetic properties of transition metal nickel oxides.
Creator: Wu, Guoqing, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Neutron powder diffraction, high pressure, magnetic susceptibility, and heat capacity measurements, as well as x-ray powder diffraction and iodometric titration, have been conducted on transition metal nickel oxides (TMOs), representative Ruddlesden-Popper (RP) phases Lan+1NinO3n+1 (n = 1, 2, ..., infinity) and hole-doped La2-xSr xNiO4 (0
Show moreNeutron powder diffraction, high pressure, magnetic susceptibility, and heat capacity measurements, as well as x-ray powder diffraction and iodometric titration, have been conducted on transition metal nickel oxides (TMOs), representative Ruddlesden-Popper (RP) phases Lan+1NinO3n+1 (n = 1, 2, ..., infinity) and hole-doped La2-xSr xNiO4 (0 < x < 1.2). The first complete study of La 2-xSrxNiO4 (0 < x < 1.2) and La n+1NinO3n+1 (n = 2 and 3) phases under high pressure is produced. Strong direct experimental evidence for polaron dominated electrical conduction in these charge transfer (CT) gap La2-xSr xNiO4 compounds is provided. Temperature evolution of the crystal structure of La2-xSrxNiO4 (x = 1/4 and 1/3) is revealed through neutron powder diffraction, structural relationships among n = 1, 2, and 3 phases are exhibited, and charge density wave (CDW) in multilayer Lan+1NinO3n+1 phases is strongly suggested. No superconductivity is observed at pressures up to 1.6 GPa and temperatures down to 4.2 K.
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Date Issued: 2002
PURL: http://purl.flvc.org/fcla/dt/11997
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: The tight-binding coherent potential approximation embedded cluster method Monte Carlo approach and approximations to the quadratic Korringa-Kohn-Rostoker method.
Creator: Horvath, Eva Antoinette, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The coherent potential approximation (CPA) can yield information about the long-range characteristics of an alloy. However, since it is a single-site theory, the effect of the local environment cannot be taken into account. The CPA can be extended to more than one site using the embedded cluster method, thereby including short-range order effects. The tight-binding coherent-potential approximation embedded cluster method can be used to generate the densities of states corresponding to all...
Show moreThe coherent potential approximation (CPA) can yield information about the long-range characteristics of an alloy. However, since it is a single-site theory, the effect of the local environment cannot be taken into account. The CPA can be extended to more than one site using the embedded cluster method, thereby including short-range order effects. The tight-binding coherent-potential approximation embedded cluster method can be used to generate the densities of states corresponding to all possible configurations of any cluster, but in particular a cluster consisting of an atom and its nearest neighbors. It is then demonstrated that the interaction energies can be calculated and used in conjunction with the Monte Carlo approach to generate the phase diagram of an alloy. In addition, the formalism for two new approximations to the Quadratic Korringa-Kohn-Rostoker method is developed and is applied to a system consisting of one metal.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/12321
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Engineering, Materials Science (5)	+ -
Chemistry, Analytical (1)	+ -
Computer Science (1)	+ -
Engineering, Metallurgy (1)	+ -
Physics, Atomic (1)	+ -

Physics, Electricity and Magnetism (1)	+ -
Physics, Optics (1)	+ -

Department of Physics (17)	+ -
Florida Atlantic University (17)	+ -
Hines, Eric Lawrence (1)	+ -
Horvath, Eva Antoinette (1)	+ -
Kis, Antonella C. (1)	+ -

Lassalle, Hugues Jean (1)	+ -
Liu, Yan (1)	+ -
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