D-Orbital Occupancy Of Transition Metal Oxides By X-Ray Absorption Near Edge Structure (Xanes), 2020 Seton Hall University

#### D-Orbital Occupancy Of Transition Metal Oxides By X-Ray Absorption Near Edge Structure (Xanes), Eric Kurywczak

*Seton Hall University Dissertations and Theses (ETDs)*

XANES *L*_{2} and *L*_{3}-edge X-Ray Absorption Near Edge Spectra (XANES) for 4*d* and 5*d* row transition metals (TM) oxides are assumed to be directly reflecting unoccupied *d* orbitals influenced by the local symmetry of the metal ion. XANES *L*_{2}- and *L*_{3}-edge data analysis through non-linear curve fitting allows for a unique, efficient look at the structural eccentricities of transition metal oxides. In this way it is possible to determine the oxidation state of a material as well as its site symmetry. We have used non-linear least-squares fitting across the near-edge region of ...

Studies Of Maximum Supercooling And Stirring In Levitated Liquid Metallic Alloys, 2020 Washington University in St. Louis

#### Studies Of Maximum Supercooling And Stirring In Levitated Liquid Metallic Alloys, Mark Edward Sellers

*Arts & Sciences Electronic Theses and Dissertations*

Nucleation—or the formation of some cluster in a medium undergoing a phase transition—is usually the initial step in a phase transition. However, this process is still not fully understood, as outstanding questions related to the role of structure, local order, and diffusion remain unanswered. Systematic supercooling studies on metallic liquids performed using electrostatic and electromagnetic (ESL and EML, respectively) will be presented and discussed within the context of several nucleation theories, such as the Classical Nucleation Theory, Diffuse Interface Theory, and Coupled-Flux theory. To study the role of diffusion on nucleation, studies on the International Space Station using ...

First-Principles Studies Of Anion Engineering In Functional Ceramics, 2020 Washington University in St. Louis

#### First-Principles Studies Of Anion Engineering In Functional Ceramics, Steven Timothy Hartman

*Engineering and Applied Science Theses & Dissertations*

Ceramic materials display a wide variety of valuable properties, such as ferroelectricity, superconductivity, and magnetic ordering, due to the partially covalent bonds which connect the cations and anions. While many breakthroughs have been made by mixing multiple cations on a sublattice, the equivalent mixed-anion ceramics have not received nearly as much attention, despite the key role the anion plays in the materials’ properties. There is great potential for functional ceramics design using anion engineering, which aims to tune the materials properties by adding and removing different types of anions in existing classes of ceramic materials. In this dissertation, I present ...

Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, 2020 Iowa State University and Ames Laboratory

#### Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield

*Ames Laboratory Accepted Manuscripts*

We report temperature-dependent measurements of ambient-pressure specific heat, magnetic susceptibility, anisotropic resistivity, and thermal expansion as well as in-plane resistivity under pressure up to 20.8 kbar on single crystals of EuAg4As2. Based on thermal expansion and in-plane electrical transport measurements at ambient pressure this compound has two, first-order, structural transitions in the 80–120 K temperature range. Ambient-pressure specific heat, magnetization, and thermal expansion measurements show a cascade of up to seven transitions between 8 and 16 K associated with the ordering of the Eu2+ moments. In-plane electrical transport is able to detect the more prominent of these transitions ...

Ground-State Properties Of The Hubbard Model In One And Two Dimensions From The Gutzwiller Conjugate Gradient Minimization Theory, 2020 Iowa State University and Ames Laboratory

#### Ground-State Properties Of The Hubbard Model In One And Two Dimensions From The Gutzwiller Conjugate Gradient Minimization Theory, Zhuo Ye, Feng Zhang, Yong-Xin Yao, Cai-Zhuang Wang, Kai-Ming Ho

*Ames Laboratory Accepted Manuscripts*

We introduce Gutzwiller conjugate gradient minimization (GCGM) theory, an *ab initio* quantum many-body theory for computing the ground-state properties of infinite systems. GCGM uses the Gutzwiller wave function but does not use the commonly adopted Gutzwiller approximation (GA), which is a major source of inaccuracy. Instead, the theory uses an approximation that is based on the occupation probability of the on-site configurations, rather than approximations that decouple the site-site correlations as used in the GA. We test the theory in the one-dimensional and two-dimensional Hubbard models at various electron densities and find that GCGM reproduces energies and double occupancies in ...

Thermophysical Properties And Phase Transformations In Metallic Liquids And Silicate Glasses, 2020 Washington University in St. Louis

#### Thermophysical Properties And Phase Transformations In Metallic Liquids And Silicate Glasses, Daniel Christian Van Hoesen

*Arts & Sciences Electronic Theses and Dissertations*

The first quantitative measurements of the electrical resistivity in binary metallic liquids, used to probe local order in the liquid, are reported in this dissertation. The electrical resistivity is very sensitive to short and medium range ordering because the electron mean free path is approximately the same length scale as the atomic spacing. Particular attention is given to the resistivity value at a crossover temperature that, based on molecular dynamics (MD) simulations, is the onset of cooperative motion in liquid alloys. Experimental evidence for the crossover is found in measurements of the shear viscosity, a dynamical property. An indication of ...

Measurement, Dissipation, And Quantum Control With Superconducting Circuits, 2020 Washington University in St. Louis

#### Measurement, Dissipation, And Quantum Control With Superconducting Circuits, Patrick Harrington

*Arts & Sciences Electronic Theses and Dissertations*

The interaction between a superconducting circuit and its environment can cause decoherence. However, interactions with an environment are necessary for quantum state preparation and measurement. Through the dynamics of open quantum systems, the environment is a resource to control and readout superconducting circuit states. I present an experimental result demonstrating qubit state stabilization from engineered dissipation with a microwave photonic crystal. In addition, I discuss the statistical arrow of time in the dynamics of continuous quantum measurement. These results demonstrate an interplay between open quantum system dynamics and statistics, which highlights the role of both dissipation and measurement for quantum ...

Density Functional Theory Calculations Of Al Doped Hafnia For Different Crystal Symmetry Configurations, 2020 Seton Hall University

#### Density Functional Theory Calculations Of Al Doped Hafnia For Different Crystal Symmetry Configurations, Joshua Steier

*Seton Hall University Dissertations and Theses (ETDs)*

Dogan et al.[1], investigated the causes of ferroelectricity in doped hafnia using ab initio methods. Similarly, we investigated the stability of Al doped hafnia using quantum mechanical methods.

There are many different phases of Hafnia: monoclinic, tetragonal, cubic and orthorhombic. Starting with the monoclinic phase of Hafnia, Hafnia undergoes phase transitions which result in different space groups. The temperature at which the tetragonal phase is induced is 2000 K and cubic phase is induced at 2900 K[1]. Different dielectric constants vary from phase to phase. The average dielectric constants are highest for the cubic and tetragonal phases. In ...

Applied-Force Oscillations In Avalanche Dynamics, 2020 University of lllinois at Urbana-Champaign

#### Applied-Force Oscillations In Avalanche Dynamics, Louis W. Mcfaul, Gregory Sparks, Jordan Sickle, Jonathan T. Uhl, Wendelin J. Wright, Robert Maass, Karin A. Dahmen

*Faculty Journal Articles*

Until now most studies of discrete plasticity have focused on systems that are assumed to be driven by a monotonically increasing force; in many real systems, however, the driving force includes damped oscillations or oscillations induced by the propagation of discrete events or “slip avalanches.” In both cases, these oscillations may obscure the true dynamics. Here we effectively consider both cases by investigating the effects of damped oscillations in the external driving force on avalanche dynamics. We compare model simulations of slip avalanches under mean-field dynamics with observations in slip-avalanche experiments on slowly compressed micrometer-sized Au specimens using open-loop force ...

Nitrogen Vacancy Center Optical Magnetometry Of A Barium-Iron-Cobalt Superconductor, 2020 Macalester College

#### Nitrogen Vacancy Center Optical Magnetometry Of A Barium-Iron-Cobalt Superconductor, William Setterberg

*Macalester Journal of Physics and Astronomy*

Experimentally probing the intrinsic properties of superconductors—such as the London penetration depth λ and the critical fields H_{c1} and H_{c2}—poses a difficult task. Various sample- and measurement-related factors can impact the efficacy of results obtained for λ or H_{c1}, such as perturbations to the magnetic properties of a superconducting sample or crystalline defects. One measurement technique that can minimize the impact of both of these issues is known as Nitrogen Vacancy (NV) center magnetometry. In this work, we use NV center magnetometry to perform minimally-invasive measurements of the lower critical field H_{c1} and the ...

Electron Irradiation Effects On Superconductivity In Pdte2 : An Application Of A Generalized Anderson Theorem, 2020 Iowa State University and Ames Laboratory

#### Electron Irradiation Effects On Superconductivity In Pdte2 : An Application Of A Generalized Anderson Theorem, Erik I. Timmons, S. Teknowijoyo, M. Konczykowski, O. Cavani, Makariy A. Tanatar, Sunil Ghimire, Kyuil Cho, Yongbin Lee, Liqin Ke, Na Hyun Jo, Sergey L. Bud’Ko, Paul C. Canfield, Peter P. Orth, Mathias S. Scheurer, Ruslan Prozorov

*Physics and Astronomy Publications*

Low-temperature (∼20 K) electron irradiation with 2.5 MeV relativistic electrons was used to study the effect of controlled nonmagnetic disorder on the normal and superconducting properties of the type-II Dirac semimetal PdTe2. We report measurements of longitudinal and Hall resistivity, thermal conductivity and London penetration depth using the tunnel-diode resonator technique for various irradiation doses. The normal-state electrical resistivity follows the Matthiessen rule with an increase of the residual resistivity at a rate of ∼0.77μΩcm/(C/cm2). London penetration depth and thermal conductivity results show that the superconducting state remains fully gapped. The superconducting transition temperature is suppressed ...

Curvature In Compressed Thin Cylindrical Shells Approaching The Isometric Limit, 2020 James Madison University

#### Curvature In Compressed Thin Cylindrical Shells Approaching The Isometric Limit, Nicole Voce

*Senior Honors Projects, 2020-current*

The ability to manipulate surface elastic instabilities finds many applications in engineering smart interfaces, e.g. in fluid-structure interaction and micro-fabrication. We study the buckling of a thin cylindrical shell constrained to slide onto an inner non-deformable pipe. Our goal is to characterize the relationship between the shell thickness and the localization of stresses by using curvature measurements. First, we induce surface buckling by immobilizing one end of the shell and applying force to the other end. Then, we obtain a virtual reconstruction of the surface from 3D optical scanning and compute the Gaussian curvature for every point on the ...

Exploring The Role Of Electronic Structure On Photo-Catalytic Behavior Of Carbon-Nitride (C3n4) Polymorphs, 2020 University of Calcutta and Lady Brabourne College

#### Exploring The Role Of Electronic Structure On Photo-Catalytic Behavior Of Carbon-Nitride (C3n4) Polymorphs, Sujoy Datta, Prashant Singh, Debnarayan Jana, Chhanda B. Chaudhuri, Manoj K. Harbola, Duane D. Johnson, Abhijit Mookerjee

*Materials Science and Engineering Publications*

A fully self-consistent density-functional theory (DFT) with improved functionals is used to provide a comprehensive account of structural, electronic, and optical properties of C3N4 polymorphs. Using our recently developed van Leeuwen-Baerends (vLB) corrected local-density approximation (LDA), we implemented LDA + vLB within full-potential N*th*-order muffin-tin orbital (FP-NMTO) method and show that it improves structural properties and band gaps compared to semi-local functionals (LDA/GGA). We demonstrate that the LDA + vLB predicts band-structure and work-function for well-studied 2D-graphene and bulk-Si in very good agreement with experiments, and more exact hybrid functional (HSE) calculations as implemented in the Quantum-Espresso (QE) package ...

First-Principles Prediction Of Incipient Order In Arbitrary High-Entropy Alloys: Exemplified In Ti0.25crfenialx, 2020 Ames Laboratory

#### First-Principles Prediction Of Incipient Order In Arbitrary High-Entropy Alloys: Exemplified In Ti0.25crfenialx, Prashant Singh, Andrei V. Smirnov, Aftab Alam, Duane D. Johnson

*Materials Science and Engineering Publications*

Multi-principal-element alloys, including high-entropy alloys, experience segregation or partially-ordering as they are cooled to lower temperatures. For Ti0.25CrFeNiAl*x*, experiments suggest a partially-ordered B2 phase, whereas CALculation of PHAse Diagrams (CALPHAD) predicts a region of L21+B2 coexistence. We employ first-principles density-functional theory (DFT) based electronic-structure approach to assess stability of phases of alloys with arbitrary compositions and Bravais lattices (A1/A2/A3). In addition, DFT-based linear-response theory has been utilized to predict Warren-Cowley short-range order (SRO) in these alloys, which reveals potentially competing long-range ordered phases. The resulting SRO is uniquely analyzed using concentration-waves analysis for occupation probabilities ...

Development Of Co2 Laser-Heating For The Study Of Wide Band Gap Oxide Materials, 2020 University of Nevada, Las Vegas

#### Development Of Co2 Laser-Heating For The Study Of Wide Band Gap Oxide Materials, Christian Matthew Childs

*UNLV Theses, Dissertations, Professional Papers, and Capstones*

The ability to access a vast region of the pressure-temperature landscape using energy density tuning enables exotic states of matter to be probed. A well documented method for such exploration, under static conditions, is the use of the laser-heated diamond anvil cell (LH-DAC), accessing a combination of high pressure (>300 GPa) and high temperature (>5000 K). This thesis presents our development of direct CO2 laser heating techniques to study a series of wide band gap insulators, La2Sn2O7, ZrO2, and CeO2, under high pressure conditions. The lasing frequency of CO2 lasers is such that these wide band gap materials absorb the ...

Symmetry And Interface Considerations For Interactions On Mos2, 2020 University of Nebraska–Lincoln

#### Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans

*Theses, Dissertations, and Student Research: Department of Physics and Astronomy*

The critical role of symmetry, in adsorbate-MoS_{2} interactions, has been demonstrated through a variety of electronic structure, topology, and catalytic studies of MoS_{2} and MoS_{2 }composites.A combination of density functional theory and experiment exhibiting diiodobenzene isomer dependent adsorption rates highlight frontier orbital symmetry as key to adsorption on MoS_{2}. It is clear that the geometry and symmetry of MoS_{2} influences the creation and stability of surface defects, that in turn affect catalytic activity and a myriad of other applications. We have shown that surface reactions such the methanol to methoxy reaction can create defects ...

Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, 2020 Iowa State University and Ames Laboratory

#### Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa

*Ames Laboratory Accepted Manuscripts*

The sulfur-substituted FeSe system, FeSe1−xSx, provides a versatile platform for studying the relationship among nematicity, antiferromagnetism, and superconductivity. Here, by nuclear magnetic resonance (NMR) and resistivity measurements up to 4.73 GPa on FeSe0.91S0.09, we established the pressure- (p-) temperature (T) phase diagram in which the nematic state is suppressed with pressure showing a nematic quantum phase transition (QPT) around p=0.5GPa, two superconductivity (SC) regions separated by the QPT appear, and antiferromagnetic (AFM) phase emerges above ∼3.3GPa. From the NMR results up to 2.1 GPa, AFM fluctuations are revealed to be characterized by ...

Computational Simulations Of Temperature-Dependent Dynamics In Type Ii Superconductors Using A Material Specific Formulation Of Ginzburg Landau Theory, 2020 William & Mary

#### Computational Simulations Of Temperature-Dependent Dynamics In Type Ii Superconductors Using A Material Specific Formulation Of Ginzburg Landau Theory, Aiden Harbick

*Undergraduate Honors Theses*

Superconducting Radio Frequency (SRF) cavities play a fundamental role in particle accelerators. Efficient operation depends on expelling magnetic flux from the cavity, and any residual flux that remains trapped after cooling below the critical temperature can have a significant impact on performance. Experimental evidence suggests that material defects as well as cooling protocols can have a strong impact on subsequent performance. To better understand these phenomena, we use time-dependent Ginzburg-Landau theory implemented as finite-element simulations. We adapt the theory to allow spatial variation of material-specific parameters along with realistic temperature dependencies. We report on numerical experiments for different configurations of ...

Investigations Of Technetium Metal And The Synthesis Of Binary Technetium Nitrides Under Extreme Conditions, 2020 University of Nevada, Las Vegas

#### Investigations Of Technetium Metal And The Synthesis Of Binary Technetium Nitrides Under Extreme Conditions, Emily Siska

*UNLV Theses, Dissertations, Professional Papers, and Capstones*

Technetium (Tc) is the lightest of the radioactive elements and has no stable isotopes. Significant quantities of Tc are not naturally occurring on earth. However, technetium is found in high fission yield in nuclear reactors and produced for medical imaging. With its long half life, and high mobility in the environment make it of particular interest. To that end, the fundamental chemistry of Tc and Tc compounds is not as well understood compared to neighboring elements on the periodic table. Therefore, fundamental studies designed to better understand this transition metal, coupled with more targeted investigation at high temperature and pressure ...

First-Order Ferromagnetic Transitions Of Lanthanide Local Moments In Divalent Compounds: An Itinerant Electron Positive Feedback Mechanism And Fermi Surface Topological Change, 2020 Max-Planck-Institut für Eisenforschung and University of Warwick

#### First-Order Ferromagnetic Transitions Of Lanthanide Local Moments In Divalent Compounds: An Itinerant Electron Positive Feedback Mechanism And Fermi Surface Topological Change, Eduardo Mendive-Tapia, Durga Paudyal, Leon Petit, Julie B. Staunton

*Ames Laboratory Accepted Manuscripts*

Around discontinuous (first-order) magnetic phase transitions, the strong caloric response of materials to the application of small fields is widely studied for the development of solid-state refrigeration. Typically strong magnetostructural coupling drives such transitions and the attendant substantial hysteresis dramatically reduces the cooling performance. In this context, we describe a purely electronic mechanism which pilots a first-order paramagnetic-ferromagnetic transition in divalent lanthanide compounds and which explains the giant nonhysteretic magnetocaloric effect recently discovered in a Eu2In compound. There is a positive feedback between the magnetism of itinerant valence electrons and the ferromagnetic ordering of local f-electron moments, which appears as ...