Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V31: Metals and Metal Physics I 
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Sponsoring Units: DMP Chair: Michael Osofsky, Naval Research Lab Room: LACC 407 
Thursday, March 8, 2018 2:30PM  2:42PM 
V31.00001: Direct Observation of the Wind Force in Aluminum Nanowires Matthew Mecklenburg, Brian Zutter, William Hubbard, Shaul Aloni, Brian Regan Using recently developed techniques based on in situ mapping of valence electron energy loss spectra (EELS) in a transmission electron microscope (TEM), it is now possible to efficiently determine electron density changes in nanowires with partsperthousand precision. By mapping the bulk plasmon energy we quantify density changes throughout an aluminum wire with sub10 nm spatial resolution, both while it carries electric current and after the current has been switched off. We observe changes in the wire density that are both even and odd in the sign of the applied current, which we attribute to thermal expansion and an electron wind force respectively. Our measurements are the first direct observation of the Blech effect, whereby strain in a currentcarrying wire is induced to balance an applied force. 
Thursday, March 8, 2018 2:42PM  2:54PM 
V31.00002: Revisiting the PhotonDrag Effect in Thin Metal Films Jared Strait, Glenn Holland, Bojan Ilic, Amit Agrawal, Domenico Pacifici, Henri Lezec Current flow in metal films can be induced by the photon momentum carried by an obliquelyincident electromagnetic wave, a phenomenon known as photon drag. The prevailing intuition for the sign of this current is based on the assumption that the absorbed light transfers momentum to the free electrons of the metal, generating electron flow in the direction of the inplane incident photon momentum. However, the direction of this flow has been reported to puzzlingly vary with polarization state, surface morphology, and excitation of surface plasmons. Here we demonstrate that for a smooth gold film, spolarized light unequivocally produces a photon drag current proportional to the Minkowski photon momentum and unrelated to plasmonic effects. But the sign of the observed current is opposite to that implied by the intuitive model above, requiring a reimagination of the microscopic processes of lightmetal interaction to include momentum transfer to all the electrons of the metal, free and bound. To this end, we propose a new model which also accounts for an observed marked change in amplitude and sign of the photon drag current upon polarization rotation. 
Thursday, March 8, 2018 2:54PM  3:06PM 
V31.00003: Largescale firstprinciples calculations of high entropy alloys Tetsuya Fukushima, Hiroshi KatayamaYoshida, Kazunori Sato, Masako Ogura, Rudolf Zeller, Peter Dederichs High entropy alloys show a variety of fascinating properties like high hardness, wear resistance, corrosion resistance, etc. They are random solid solutions of many components with rather high concentrations. We perform abinitio calculations for the high entropy alloy CrFeCoNi, which equal concentration of 25% for each element. By the KKRnano program package, which is based on an orderN screened KorringaKohnRostoker Green's function method, we consider a facecentered cubic (FCC) supercell with 1372 randomly distributed elements. It is found from our calculations that the local moments of the Cr atoms show a large environmental variation. We present a new method to calculate "local energies" of all atoms. This is based on the partitioning of the whole space into Voronoi cells and allows to calculate the energetic contribution of each atomic cell to the total energy of the supercell. The supercell calculations show very large variations of the local energies, analogous to the variations of the local moments. This shows that the random solid solution is not stable and has a tendency to form an L12structure with the Cratoms ordered at the corner of the cube and the elements Fe, Co and Ni randomly distributed on the three other FCC sublattices. 
Thursday, March 8, 2018 3:06PM  3:18PM 
V31.00004: Predicting the Stability of an HEA: a FirstPrinciples Analysis Meha Bhogra, Srinivas Ranganathan, Umesh V Waghmare In the quest of engineering new materials with superior strength and ductility, there has been an upsurge in the design and synthesis of multicomponent alloys (known as highentropy alloys) consisting of 45 elements in almost equiatomic proportions. These alloys have shown significant solidsolution strengthening and excellent hightemperature properties, and have been found to exist primarily as a single phase, either in FCC or BCC structure. With the formation of a medley of innumerable configurations at the atomic scale, the complex interactions among the coexisting elements, the stability of HEA in such simple structural forms (FCC or BCC) is still enigmatic. Here, in this work, we use a combination of firstprinciples analysis, cluster expansion method and machine learning algorithms to understand the origin of the structural stability of a solid solution of 5 elements in a particular structure at the atomic scale, in terms of the relative energies of vast number of configurations. The energy of a configuration is then disintegrated into its elementary clusters, the number densities of which are regarded as the descriptors in our neural network. This network obtains the relative weights of each cluster in local stabilization or destabilization of an HEA. 
Thursday, March 8, 2018 3:18PM  3:30PM 
V31.00005: Experimental Search for Avalanches of Entangled Dislocations as a Source of Dissipation and Mechanical Noise Morgan Shaner, Marina Mondin, Riccardo DeSalvo, Samavarti Gallardo, Nicole Araya, Greta O'Dea, Hope Hamamoto Recent measurements using highly sensitive instruments have shown increased dissipation and the appearance of random low frequency noise in metal flexures. These effects have been attributed to avalanches of dislocations, a phenomenon supposedly controlled by selforganized criticality (SOC) statistics. This experiment is attempting to detect these subtle effects using a variation on the rotating beam KimballLovell 1927 experiment that was used to measure the loss angle of materials above 1Hz. We have demonstrated the feasibility of making measurements of loss angle with μradian precision at arbitrarily low frequencies. If dislocation avalanches are the source of the 1/f noise in these flexures, we expect to see them using this experiment. 
Thursday, March 8, 2018 3:30PM  3:42PM 
V31.00006: Inelastic Neutron Scattering and Density Functional Theory for Uranium Compounds Andrew Miskowiec, Ashley Shields, Marie Kirkegaard Modern computational tools, specifically density functional theory (DFT), have enhanced the utility of many experimental techniques. Here, we discuss the application of DFT to inelastic neutron scattering (INS) phonon density of states measurements of two Ubearing compounds, UO_{2}F_{2} and UF_{4}. Neutrons offer an exceptional advantage for UO_{2}F_{2}, whose hygroscopic nature localizes environmental water, because of the relative sensitivity of neutrons to H compared to the high Z U crystal backbone. Likewise, UF_{4 }has a weak Raman and infrared activity, but a reasonable neutron crosssection. Combined with a novel computational approach developed at the Spallation Neutron Source, we can directly calculate the dynamic structure factor from DFT calculations and identify regions of special interest based on agreement or disagreement between experiment and theory. 
Thursday, March 8, 2018 3:42PM  3:54PM 
V31.00007: Insights into pointdefects of δPu and δPuGa alloys using density functional theory Sarah Hernandez, Franz Freibert, John Wills, Blas Uberuaga Aging of fcc δPu is becoming a forefront challenging problem in Pu science, as we try to understand the effects of radiological decay on the phase stability. The most influential drivers of δPu aging include He and U ingrowth, radiationinduced lattice defect accumulation, and phase instability, which may affect the overall integrity in mechanical and electronic properties. Due to multiple processes that occur while δPu ages, computational efforts, such as DFT, may provide fundamental insight and guidance into the most prominent defects that will impact the stability of the lattice and the electronic properties. We have explored a variety of point defects in unalloyed and Gaalloyed δPu, which include vacancies, selfinterstitials, and defects containing the radioactive daughter decay product, U. Formation energies and binding energies of these defects, and migration barriers of selective defects will be discussed, along with corresponding radial distribution functions (RDFs). 
Thursday, March 8, 2018 3:54PM  4:06PM 
V31.00008: Ab initio calculation of static and dynamic properties of liquid uranium dioxide. Luis Gonzalez, Beatriz Gonzalez del Rio, David Gonzalez A detailed knowledge of the structural and dynamic behavior of molten UO_{2} is essential in order to improve the safety of fission power reactors. 
Thursday, March 8, 2018 4:06PM  4:18PM 
V31.00009: Implementation of density functional theory for studies of trivacancies in unalloyed plutonium Elliot Kisiel, Sarah Hernandez, Franz Freibert Studying vacancy clusters in fcc plutonium using density functional theory will provide further understanding in the stability of extended defects. We investigated trivacancies in unalloyed δplutonium using the generalized gradient approximation (GGA) exchange correlation functional using the projector augmented wave method in VASP. Ionic relaxation of a series of permutations of trivacancies in the δPu matrix yielded only 8 unique ground state structures. Results indicate that the one of the most energetically stable structure is a DamaskDienesWeizer stacking fault tetrahedron (SFT), which has been predicted by MEAM calculations, while disperse vacancies are calculated to be thermodynamically unstable. A slightly lower energetic state than the SFT is calculated and is shown to be dependent on the magnetic configuration in the structure. 
Thursday, March 8, 2018 4:18PM  4:30PM 
V31.00010: First Principles Calculations on Grain Boundary and Corrosion Effects in Nuclear Materials Ember Sikorski, Eric Nelson, Simon Middleburgh, Brian Jaques, Lan Li We studied defects in amorphous UO2 and corrosion at UN and Zr surfaces. Amorphous UO2 was investigated to simulate grain boundary behavior. Effects of irradiation damage were calculated via formation enthalpies of O adatom and vacancy defects in the most stable amorphous structure, and the vacancy was found to be favorable. Fission products I, Te, and Xe were also considered. The stable defects occurred for fission products at O vacancies. Unlike UO2, UN is susceptible to corrosion when exposed to air. We studied the energetics of UN (100) and (110) surfaces and their stability in the presence of dissociated water with and without added oxygen content. Similar studies were applied to cladding component Zr. This presentation will discuss the effects of defects at the grain boundary in UO2 and the interactions of UN and Zr surfaces with dissociated water on the atomic scale. 
(Author Not Attending)

V31.00011: HighTemperature Oxidation Mechanism of Uranium Mononitride: A Study from Ab Initio Molecular Dynamics Bo Sun Uranium mononitride (UN) is the promising advanced fuel for future reactors. However, the surface oxidation of metallic UN might jeopardize its safety and utility in storage and in use. The knowledge of the initial oxidation behavior of UN has been limited by now. Based on the van der Waals density functional (vdWDF) scheme, we have carried out the ab initio molecular dynamics (AIMD) simulations to explore the surface oxidation dynamics and mechanism of UN. Our studies have revealed that UN can be readily oxidized due to the strong affinity of U and O atoms. During the initial oxidation at high temperatures, U will segregate out of UN surface to bond with O, forming an ultrathin uniform UO_{2} film. The residual N atoms will migrate into the deep layers of UN driven by high temperatures. The current theoretical conclusions have strong implications to the interpretation of experimental observations. 
Thursday, March 8, 2018 4:42PM  4:54PM 
V31.00012: Static structure, microscopic dynamics and electronic properties of the liquid LiPb alloy. An ab initio molecular dynamics study. David Gonzalez, Manuel Alemany, Jaime SoutoCasares, Luis Gonzalez We report an abinitio molecular dynamics study of several structural and dynamic 
Thursday, March 8, 2018 4:54PM  5:06PM 
V31.00013: Growth and characterization of BaZnGa Paul Canfield, Na Hyun Jo, Qisheng Lin, Manh Cuong Nguyen, Udhara Kaluarachchi, William Meier, Soham Manni, Savannah Downing, Anna Boehmer, Tai Kong, Yang Sun, Valentin Taufour, CaiZhuang Wang, KaiMing Ho, Sergey Bud'ko We report the growth, structure and characterization of BaZnGa, identifying it as the sole known ternary compound in the BaZnGa system. Single crystals of BaZnGa, which adopts a new structural type (Pearson symbol tI36), can be grown out of excess BaZn liquid as selflux. The structure contains three unique Ba sites and three M=Zn/Ga sites. Using DFT calculations we can argue that whereas one of these three M sites is probably solely occupied by Ga, the other two M sites, most likely, have mixed Zn/Ga occupancies. Temperature dependent resistivity and magnetization measurements suggest that BaZnGa is a poor metal with no electronic or magnetic phase transitions between 1.8 and 300 K. As time allows, societal implications of this discoverry will also be discussed. 
Thursday, March 8, 2018 5:06PM  5:18PM 
V31.00014: A New Ion Diffusion Model Applied to Leadfree Solder Tom Ichibha, Genki Prayogo, Kenta Hongo, Ryo Maezono The spread of Leadfree solder based on SnCu alloy has been long prevented by the joint cracking on Cu board, which is known to be caused by Kirkendall effect. This work evaluated the diffusion coefficient of Cu ion in εCu_{3}Sn from ab initio approach, which has been realized, for the first time, by introducing our own modeling. So far the applications of ab initio calculation for ion vacancy diffusion have been restricted to just simplest crystals like FCC, BCC, and HCP. εCu_{3}Sn has, however, rather complex structure and also longrange periodicity. To overcome the difficulties coming from them, we reached a new understanding for the longrange structure and then established an insightful approximation to reduce the complexity of the structure based on the diffusion barriers for the possible ion jumps, calculated by climbingNEB (nudged elastic band) method. Finally, our model succeeded to give better estimation of the Cu diffusion coefficient than MD, when referring to the experimental values. 
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