Condensed Matter Physics Commons^™

Structure And Magnetism Of New Rare- Earth-Free Intermetallic Compounds: Fe3+Xco3−Xti2 (0 ≤ X ≤ 3), Balamurugan Balamurugan, Bhaskar Das, Manh Cuong Ngyuen, Xiaoshan Xu, Jie Zhang, Xiaozhe Zhang, Yaohua Liu, Ashfia Huq, Shah R. Valloppilly, Yunlong Jin, Cai-Zhuang Wang, Kai-Ming Ho, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

We report the fabrication of a set of new rare-earth-free magnetic compounds, which form the Fe₃Co₃Ti₂-type hexagonal structure with P-6m2 symmetry. Neutron powder diffraction shows a significant Fe/Co anti-site mixing in the Fe₃Co₃Ti₂ structure, which has a strong effect on the magnetocrystalline anisotropy as revealed by first-principle calculations. Increasing substitution of Fe atoms for Co in the Fe₃Co₃Ti₂ lattice leads to the formation of Fe₄Co₂Ti₂ , Fe₅CoTi, and Fe₆Ti₂ with significantly improved …

Understanding Electrical Conduction In Lithium Ion Batteries Through Multi-Scale Modeling, Jie Pan

Theses and Dissertations--Chemical and Materials Engineering

Silicon (Si) has been considered as a promising negative electrode material for lithium ion batteries (LIBs) because of its high theoretical capacity, low discharge voltage, and low cost. However, the utilization of Si electrode has been hampered by problems such as slow ionic transport, large stress/strain generation, and unstable solid electrolyte interphase (SEI). These problems severely influence the performance and cycle life of Si electrodes. In general, ionic conduction determines the rate performance of the electrode, while electron leakage through the SEI causes electrolyte decomposition and, thus, causes capacity loss. The goal of this thesis research is to design Si …

Innovations In Thermoelectric Materials Research: Compound Agglomeration, Testing And Preselection, Hugo Lopez

Open Access Theses & Dissertations

Thermoelectric materials have the capacity to convert a temperature differential into electrical power and vice versa. They will represent the next revolution in alternative energies once their efficiencies are enhanced so they can complement other forms of green energies that depend on sources other than a temperature differential.

Progress in materials science depends on the ability to discover new materials to eventually understand them and to finally improve their properties. The work presented here is aimed at dynamizing the screening of materials of thermoelectric interest. The results of this project will enable: theoretical preselection of thermoelectric compounds based on their …

A Systematic Study Of The Effect Of Spin-Orbit Interaction On Properties Of Tetravalent And Pentavalent Iridate Compounds, Jasminka Terzic

Theses and Dissertations--Physics and Astronomy

Previous studies of iridates have shown that an interplay of strong SOI, Coulomb interaction U, Hund’s rule coupling and crystalline electric fields result in unexpected insulating states with complex magnetic states. The novel J_eff =1/2 insulating state first observed in Sr₂IrO₄ is a direct consequence of such an intriguing interplay and is one of the central foci of this dissertation study.

The work presented here consists of three projects: (1) Effects of Tb doping on Sr₂IrO₄ having tetravalent Ir⁴⁺(5d⁵) ions; (2) Emergence of unexpected magnetic states in double-perovskite (Ba …

Physical And Electronic Properties Of Nanoscale 2d Materials, Mathias J. Boland

Theses and Dissertations--Physics and Astronomy

There is a great push towards reducing the size scale of both electronic components and machines. Two dimensional materials, such as graphene, are ideal candidates towards this push, as they are naturally atomically thin. In the case of nanoscale machines, the mechanical properties of the material surfaces become increasingly important. The use of laminar materials, such as graphene and MoS₂, to modify the surface properties, yet maintain nanoscale topographical features, are very attractive. Towards this goal, we have investigated the surface properties of MoS₂ at the nanoscale using Lateral Force Microscopy (LFM). In these investigations, we measure …

Stereographic Visualization Of Bose-Einstein Condensate Clouds To Measure The Gravitational Constant, Ed Wesley Wells

College of Graduate Studies: Theses & Dissertations

This thesis describes a set of tools that can be used for the rapid design of atom interferometer schemes suitable for measuring Newton's Universal Gravitation constant also known as "Big G". This tool set is especially applicable to Bose--Einstein--condensed systems present in NASA's Cold Atom Laboratory experiment to be deployed to the International Space Station in 2017. These tools include a method of approximating the solutions of the nonlinear Schrödinger or Gross--Pitaevskii equation (GPE) using the Lagrangian Variational Method. They also include a set of software tools for translating the approximate solutions of the GPE into images of the optical …

First Results Of Magnetic Field Penetration Measurements Of Multilayer Sis Structures, O. B. Malyshev, L. Gurran, R. Valizadeh, S. Pattalwar, N. Pattalwar, K. D. Dumbell, A. Gurevich

Physics Faculty Publications

The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of B_p ≈200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the …

Hexagonal Rare-Earth Manganites As Promising Photovoltaics And Light Polarizers, Xin Huang, Tula R. Paudel, Shuai Dong, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Ferroelectric materials possess a spontaneous electric polarization and may be utilized in various technological applications ranging from nonvolatile memories to solar cells and light polarizers. Recently, hexagonal rareearth manganites, h-RMnO₃ (R is a rare-earth ion), have attracted considerable interest due to their intricate multiferroic properties and improper ferroelectricity characterized by a sizable remnant polarization and high Curie temperature. Here we demonstrate that these compounds can serve as very efficient photovoltaic materials and, in addition, possess remarkable optical anisotropy properties. Using first-principles methods based on density functional theory and considering h-TbMnO₃ as a representative …

Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley

Reports

A model developed by the Materials Research Group that calculates electron penetration range of some common materials, has been greatly expanded with the hope that such extensions will predict the range in other, perhaps, more interesting materials. Developments in this extended model aid in predicting the approximate penetration depth into diverse classes of materials for a broad range of energetic incident electrons (10 MeV, with better than 20% accuracy). The penetration depth—or range—of a material describes the maximum distance electrons can travel through a material, before losing all of its incident kinetic energy. This model has started to predict a …

Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley, Jr Dennison

Senior Theses and Projects

A model developed by the Materials Research Group that calculates electron penetration range of some common materials, has been greatly expanded with the hope that such extensions will predict the range in other, perhaps, more interesting materials. Developments in this extended model aid in predicting the approximate penetration depth into diverse classes of materials for a broad range of energetic incident electrons (<10 eV to>10 MeV, with better than 20% accuracy). The penetration depth—or range—of a material describes the maximum distance electrons can travel through a material, before losing all of its incident kinetic energy. This model has started to predict …

Contact Resistance To Srruo3 And La0.67Sr0.33Mno3 Epitaxial Films, Mohammad Abuwasib, Hyungwoo Lee, Alexei Gruverman, Chang-Beom Eom, Uttam Singisetti

Alexei Gruverman Publications

Contact resistance to the metallic oxide electrodes, SrRuO₃ (SRO) and La_0.67Sr_0.33MnO₃ (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρ_c) for Ti and Pt contact metals and the sheet resistance (R_sh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and …

Hydrogen Bond-Mediated Structural Order In Hydroxylated Bis-Mpa Dendritic Polymers: Experimental And Molecular Dynamics Simulation Study, Maliha N. Syed

Dissertations

Dendritic architectures are echoed throughout nature. While the significance of these pervasive patterns is not entirely clear, connections between their structures and physical properties are fascinating to contemplate. Particular interest has been paid to a family of synthetically manufactured and commercially available dendritic polymers based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) as a monomer. Composed of two hydroxyls and a carboxyl group, bis-MPA based structures hydrogen bond (H-bond) profusely. Given the high concentration and unique spatial orientation of end-groups, as well as the multitude of carbonyl, ester, and ether interior H-bond acceptors, a set of distinct H-bond organizations may be observed …

The Role Of Space Materials Research In Spacecraft Charging And Satellite Survivability, Jr Dennison

Presentations

No abstract provided.

An Overview Of The Dynamic Interplay Between The Space Environment & Spacecraft Materials, Jr Dennison

Presentations

No abstract provided.

Hohenberg-Kohn Theorems In Electrostatic And Uniform Magnetostatic Fields, Xiao-Yin Pan, Viraht Sahni

Publications and Research

The Hohenberg-Kohn (HK) theorems of bijectivity between the external scalar potential and the gauge invariant nondegenerate ground state density, and the consequent Euler variational principle for the density, are proved for arbitrary electrostatic field and the constraint of fixed electron number. The HK theorems are generalized for spinless electrons to the added presence of an external uniform magnetostatic field by introducing the new constraint of fixed canonical orbital angular momentum. Thereby, a bijective relationship between the external scalar and vector potentials, and the gauge invariant nondegenerate ground state density and physical current density, is proved. A corresponding Euler variational principle …

Dependence Of Electrostatic Field Strength On Voltage Ramp Rates For Spacecraft Materials, Krysta Moser

Senior Theses and Projects

No abstract provided.

Effect Of Sm Content On Energy Product Of Rapidly Quenched And Oriented Smco5 Ribbons, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly

Nebraska Center for Materials and Nanoscience: Faculty Publications

The Sm-content dependence of phase composition, anisotropy, and other magnetic properties of Sm_1+δCo₅ (δ ≤ 0.12) ribbons melt spun at 10 m/s has been studied. The samples consist of hexagonal SmCo₅ grains whose c axes are preferentially aligned along the long direction of the ribbon. The lattice parameter a and the cell volume (V) increase with increasing Sm content δ, whereas c decreases. Sm addition appears to improve the degree of the preferred orientation of the c-axis and to increase the mean grain size, which weakens the effective intergranular exchange …

Force-Enhanced Atomic Refinement: Structural Modeling With Interatomic Forces In A Reverse Monte Carlo Approach Applied To Amorphous Si And Sio2, A. Pandey, Parthapratim Biswas, D. A. Drabold

Faculty Publications

We introduce a structural modeling technique, called force-enhanced atomic refinement (FEAR). The technique incorporates interatomic forces in reverse Monte Carlo (RMC) simulations for structural refinement by fitting experimental diffraction data using the conventional RMC algorithm, and minimizes the total energy and forces from an interatomic potential. We illustrate the usefulness of the approach by studying a−SiO₂ and a−Si. The structural and electronic properties of the FEAR models agree well with experimental neutron and x-ray diffraction data and the results obtained from previous molecular dynamics simulations of a−SiO₂ and a−Si. We have shown that the method is more efficient …

Pre-Breakdown Arcing As A Proxy For Dc Dielectric Breakdown Testing Of Polymeric Insulators, Jr Dennison, Allen Andersen

Presentations

No abstract provided.

Mixed Weibull Distribution Model Of Dc Dielectric Breakdowns With Dual Defect Modes, Allen Andersen, Jr Dennison

Journal Articles

This work provides physical insight into common statistical models for DC dielectric breakdown field strengths. Voltage step-up tests were performed on low density polyethylene films. The merits of generalizations to widely-used empirical Weibull models are discussed. The cumulative probability distributions of the breakdown fields were fit to standard two- and three-parameter Weibull distributions. Mixed two-parameter Weibull distributions, sometimes used in the literature to model multiple breakdown modes, were found to yield the best fits to the data. In addition, the same data were fit to a physically-motivated dual-defect mean field model incorporating both low- and high-energy defect modes with different …