Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L11: Actinides and Complex Metals |
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Sponsoring Units: DCOMP Chair: Shruba Gangopadhyay, University of California, Davis Room: 270 |
Wednesday, March 15, 2017 11:15AM - 11:27AM |
L11.00001: Elastic moduli of $\delta $-Pu$^{\mathrm{239}}$ reveal changes in aging in real time Boris Maiorov, Jonathan Betts, Per Söderlind, Alexander Landa, Sarah Hernandez, Tarik Saleh, Franz Freibert, Albert Migliori We study the time evolution (aging) of the elastic moduli of an eight-year-old polycrystalline $\delta $-Pu 2.0 at {\%} Ga alloy ($\delta $-Pu:Ga ) from 295K to nearly 500K in real time using Resonant Ultrasound Spectroscopy (RUS). After 8 years of aging at 295K, the bulk and shear moduli increase at a normalized rate of 0.2{\%}/year and 0.6{\%}/year respectively. As the temperature is raised, two time dependences are observed, an exponential one of about a week, followed by a linear one (constant rate). The linear rate is thermally activated with an activation energy of 0.33$+$0.06 eV. Above 420K a qualitative change in the time evolution is observed; the bulk modulus decreases with time while the shear modulus continues to stiffen. No change is observed as the $\alpha -\beta $ transition temperature is crossed as would be expected if a decomposition of $\delta $-Pu:Ga to $\alpha $-Pu and Pu$_{\mathrm{3}}$Ga occurred over the temperature range studied. Our results indicate that the main mechanism of aging is creation of defects that are partially annealed starting at $T =$ 420 K. [Preview Abstract] |
Wednesday, March 15, 2017 11:27AM - 11:39AM |
L11.00002: Dynamical stability of plutonium alloys Marc Torrent, Boris Dorado, Jordan Bieder Plutonium sits at the center of the actinide series and marks the transition between localization and delocalization of the $5f$ electrons. From a metallurgical standpoint, the monoclinic $\alpha$ phase (stable at low T) is brittle, not suitable for engineering applications, as opposed to the ductile fcc $\delta$ phase (stable at $580$K). The $\delta -\alpha$ transition can be avoided by alloying $\delta$-Pu with "deltagen" elements. There is a wide unexplored area for Pu when it comes to lattice dynamics. Due to the changes in the composition, the dynamical stability of is constantly challenged. Displ. cascades are created in the material, which in turn produce numerous of point defects. Therefore, the accumulation of defects preclude a thermodynamic equilibrium. Given the importance for engineering applications, it is crucial that we understand the mechanisms that lead to stabilization with respect to the alloy composition. We use first-principles calculations to provide evidence of the effect of defects/impurities (C, O, Al, Fe, Ni, Ga, Ce, U, Am) on the dynamical stability of $\delta$-Pu. We show that this phase is dynamically unstable at low T and that it depends on the $5f$ orbital occupancies. We investigate how defects affect the stability by comparing the phonon DoS. [Preview Abstract] |
Wednesday, March 15, 2017 11:39AM - 11:51AM |
L11.00003: Stability of surface plastic flow in large strain deformation of metals Koushik Viswanathan, Anirduh Udapa, Dinakar Sagapuram, James Mann, Srinivasan Chandrasekar We examine large-strain unconstrained simple shear deformation in metals using a model two-dimensional cutting system and high-speed \textit{in situ} imaging. The nature of the deformation mode is shown to be a function of the initial microstructure state of the metal and the deformation geometry. For annealed metals, which exhibit large ductility and strain hardening capacity, the commonly assumed laminar flow mode is inherently unstable. Instead, the imposed shear is accommodated by a highly rotational flow---sinuous flow---with vortex-like components and large-amplitude folding on the mesoscale. Sinuous flow is triggered by a plastic instability on the material surface ahead of the primary region of shear. On the other hand, when the material is extensively strain-hardened prior to shear, laminar flow again becomes unstable giving way to shear banding. The existence of these flow modes is established by stability analysis of laminar flow. The role of the initial microstructure state in determining the change in stability from laminar to sinuous / shear-banded flows in metals is elucidated. The implications for cutting, forming and wear processes for metals, and to surface plasticity phenomena such as mechanochemical Rehbinder effects are discussed. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L11.00004: Phase stability, crystal structure and magnetism in (U$_{\mathrm{1-x}}$Nb$_{\mathrm{x}})_{\mathrm{2}}$Ni$_{\mathrm{21}}$B$_{\mathrm{6}}$ and (U$_{\mathrm{y}}$Nb$_{\mathrm{1-y}})_{\mathrm{3}}$Ni$_{\mathrm{20}}$B$_{\mathrm{6}}$. Alessia Provino, Amitava Bhattacharya, Sudesh K Dhar, Marcella Pani, Flavio Gatti, Durga Paudyal, Pietro Manfrinetti Ternary phases with composition T$_{\mathrm{2}}$M$_{\mathrm{21}}$X$_{\mathrm{6}}$ and T$_{\mathrm{3}}$M$_{\mathrm{20}}$X$_{\mathrm{6}}$ (T $=$ transition metal; M $=$ 3$d$ metal; X $=$ B, C, P) are reported to crystallize with the W$_{\mathrm{2}}$Cr$_{\mathrm{21}}$C$_{\mathrm{6}}$-type and Mg$_{\mathrm{3}}$Ni$_{\mathrm{20}}$B$_{\mathrm{6}}$-type, respectively (ternary ordered derivatives of the cubic Cr$_{\mathrm{23}}$C$_{\mathrm{6}}$-type, \textit{cF}116). They attract interest due to their refractory, mechanical, and peculiar magnetic properties. Literature data on these compounds only concern apparently stoichiometric 2:21:6 and 3:20:6 phases. Often only nominal composition has been reported, with few structural refinements and no measurements of physical properties. Lack of detailed stoichiometry and crystallographic data does not allow sufficient understanding of the crystal chemistry and properties of these compounds. We studied stability, crystal structure and magnetism of (U$_{\mathrm{1-x}}$Nb$_{\mathrm{x}})_{\mathrm{2}}$Ni$_{\mathrm{21}}$B$_{\mathrm{6}}$ and (U$_{\mathrm{y}}$Nb$_{\mathrm{1-y}})_{\mathrm{3}}$Ni$_{\mathrm{20}}$B$_{\mathrm{6}}$; stable phases are U$_{\mathrm{2}}$Ni$_{\mathrm{21}}$B$_{\mathrm{6}}$ and Nb$_{\mathrm{3}}$Ni$_{\mathrm{20}}$B$_{\mathrm{6}}$, as also confirmed by theoretical calculations. The two pristine compounds solubilize Nb and U, respectively, up to a given extent. The substitution of U by Nb leads to a structural change from the W$_{\mathrm{2}}$Cr$_{\mathrm{21}}$C$_{\mathrm{6}}$- to the Mg$_{\mathrm{3}}$Ni$_{\mathrm{20}}$B$_{\mathrm{6}}$-type. While U$_{\mathrm{2}}$Ni$_{\mathrm{21}}$B$_{\mathrm{6}}$ is a Pauli paramagnet (itinerant non-magnetic state of U-5$f$ electrons), in agreement with literature, magnetization data for (U$_{\mathrm{y}}$Nb$_{\mathrm{1-y}})_{\mathrm{3}}$Ni$_{\mathrm{20}}$B$_{\mathrm{6}}$ show itinerant ferromagnetism with T$_{\mathrm{C}}$ \textgreater 300 K. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L11.00005: Phase Transitions and Water Interactions in Uranyl Fluoride Andrew Miskowiec, Marie Kirkegaard, John Langford, Brian Anderson Uranyl fluoride (UO2F2) is a hygroscopic powder resulting from the hydrolysis of uranium hexafluoride (UF6). Crystal hydrates of the form UO2F2*x(H2O) have previously been identified with X-ray and neutron scattering, but phase transitions between different crystal hydrate structures have not been directly observed. In this work, we present a combined experimental and theoretical approach to determining crystal structures and vibrational modes. We use inelastic neutron scattering to probe vibrational frequencies of powder samples of anhydrous uranyl fluoride (x = 0, anh-UO2F2), and the most stable crystal hydrate (x = 0.4, partially hydrated (ph-UO2F2)). Combined with density functional theory (DFT), we identify and differentiate crystalline phonons and water-coupled phonon modes. Significant shifts in water O-H stretching frequencies are observed as well as lower-energy water librational modes due to water-crystal interactions. Finally, we use temperature-dependent Raman scattering with a custom sample cell, providing constant relative humidity environments, to observe phase transitions between the anhydrous and hydrated states of uranyl fluoride in situ. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L11.00006: On the nature of the phase transition in uranium dioxide K. Gofryk, D. Mast, D. Antonio, K. Shrestha, D. Andersson, C. Stanek, M. Jaime Uranium dioxide (UO$_{2}$) is by far the most studied actinide material as it is a primary fuel used in light water nuclear reactors. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. UO$_{2}$ crystalizes in the face-centered-cubic fluorite structure and is a Mott-Hubbard insulator with well-localized uranium 5$f$-electrons. In addition, below 30~K, a long range antiferromagnetic ordering of the electric-quadrupole of the uranium moments is observed, forming complex non-collinear 3-$\textbf{\textit{k}}$ magnetic structure. This transition is accompanied by Jahn-Teller distortion of oxygen atoms. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion. Here we present results of our extensive thermodynamic investigations on well-characterized and oriented single crystals of UO$_{2+x}$ ($x$ = 0, 0.033, 0.04, and 0.11). By focusing on the transition region under applied magnetic field we are able to study the interplay between different competing interactions (structural, magnetic, and electrical), its dynamics, and relationship to the oxygen content. We will discuss implications of these results. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L11.00007: Stabilizing stored PuO$_{2}$ with addition of metal impurities Shafaq Moten, Muhammad Huda Plutonium oxides is of widespread significance due its application in nuclear fuels, space missions, as well as the long-termed storage of plutonium from spent fuel and nuclear weapons. The processes to refine and store plutonium bring many other elements in contact with the plutonium metal and thereby affect the chemistry of the plutonium. Pure plutonium metal corrodes to an oxide in air with the most stable form of this oxide is stoichiometric plutonium dioxide, PuO$_{2}$. Defects such as impurities and vacancies can form in the plutonium dioxide before, during and after the refining processes as well as during storage. An impurity defect manifests itself at the bottom of the conduction band and affects the band gap of the unit cell. Studying the interaction between transition metals and plutonium dioxide is critical for better, more efficient storage plans as well as gaining insights to provide a better response to potential threats of exposure to the environment. Our study explores the interaction of a few metals within the plutonium dioxide structure which have a likelihood of being exposed to the plutonium dioxide powder. Using Density Functional Theory, we calculated a substituted metal impurity in PuO$_{2}$ supercell. We repeated the calculations with an additional oxygen vacancy. Our results reveal interesting volume contraction of PuO$_{2}$ supercell when one plutonium atom is substituted with a metal atom. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L11.00008: Interstitial-mediated diffusion and clustering for transmutation elements Re and Os precipitation in W Hong-Bo Zhou, Yu-Hao Li, Guang-Hong Lu Under high energy (14 eV) neutrons irradiation in nuclear fusion devoices, tungsten (W) will undergo transmutation to its near-neighbors in the periodic table, such as rhenium (Re), osmium (Os), etc. The transmutation elements Re and Os will precipitate and form new Re/Os-rich phase, and further significantly degrade the mechanical properties of W. Here, we have investigated the mechanism for the irradiation-induced Re/Os clustering in W using the first-principles method and thermodynamic~models. It is found that there is strong attraction between Re/Os and self-interstitial atom (SIA) in W. The SIA can be easily trapped by Re/Os once overcoming a low energy barrier, and form W-Re/Os complex dumbbell. The diffusion energy barrier of W-Re/Os is much lower than that of Re/Os diffusing via mono-vacancy or even vacancy clusters. Further, the W-Re/Os can be easily trapped by the substitutional Re/Os atoms, and form high stable Re-Re/Os-Os dumbbell structure. Most importantly, the Re-Re/Os-Os dumbbell can serve as trapping centre for subsequent interstitial-Re/Os, leading to the growth of Re/Os-rich clusters in W. Our finding suggests an interstitial-mediated mechanism for the irradiation-induced Re/Os clustering in W. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L11.00009: Ab Initio Calculations of Transport in Titanium and Aluminum Mixtures Nicholas Walker, Brian Novak, Ka Ming Tam, Dorel Moldovan, Mark Jarrell In classical molecular dynamics simulations, the self-diffusion and shear viscosity of titanium about the melting point have fallen within the ranges provided by experimental data. However, the experimental data is difficult to collect and has been rather scattered, making it of limited value for the validation of these calculations. By using ab initio molecular dynamics simulations within the density functional theory framework, the classical molecular dynamics data can be validated. The dynamical data from the ab initio molecular dynamics can also be used to calculate new potentials for use in classical molecular dynamics, allowing for more accurate classical dynamics simulations for the liquid phase. For metallic materials such as titanium and aluminum alloys, these calculations are very valuable due to an increasing demand for the knowledge of their thermophysical properties that drive the development of new materials. For example, alongside knowledge of the surface tension, viscosity is an important input for modeling the additive manufacturing process at the continuum level. We are developing calculations of the viscosity along with the self-diffusion for aluminum, titanium, and titanium-aluminum alloys with ab initio molecular dynamics. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L11.00010: Prediction of high entropy alloys with sublattice order Bojun Feng, Michael Widom, Walter Steurer Multicomponent high entropy alloys form simple Bravais lattice structures such as body-centered cubic (Pearson type cI2), in which all species occupy every lattice site equally. Here we seek to generalize this notion to lattices with inequivalent sites, such as with cube vertex and body center favoring different subsets of species (Pearson type cP2), or more complex order with three inequivalent sites (Pearson type cF16). A thorough investigation of stability of Al-TM1-TM2 (TM=Transition Metal) BCC-based ternary alloys is done by means of first principles DFT calculation. Energies of disordered structures are estimated using special quasi-random structures (SQS), where those special quasi-random structures are artificial structures that have the same short range order as cP2 and cI2 up to as many as several nearest neighbors. Application of a simple entropy model predicts sequences of temperatures over which differing degrees of order are stabilized up to the alloy melting point. Comparing with experiment, we find substantial but not complete agreement with experiment in cases where the phase diagrams are known. The source of disagreement is analyzed. Additionally, we find many examples where we predict partially ordered structures that have not yet been reported experimentally. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L11.00011: First-principles Study Of The Residual Resistivity Of Single-Phase Ni-based Concentered Solid Solution and High Entropy Alloys Sai Mu, G. D. Samolyuk, S. N Khan, M. C. Troparevsky, S. Zhao, G. M. Stocks, M. Daene, S. Wimmer Recent discoveries demonstrate that the remarkable electronic, magnetic, mechanical and radiation resistance properties of a novel class of multicomponent concentrated solid solution alloys (of which 5 or more component High Entropy Alloys are exemplars) can be tuned through control of the degree of chemical complexity – number and types of alloying elements. Residual resistivity ($\rho_0$) provides a direct measurement for the effect of chemical disorder on the Fermi surface. Here we use ab-initio KKR-CPA method to access the electronic structure and estimate $\rho_0$ from Kubo-Greenwood formula in a series of 2-5 component equiatomic alloys comprised of Ni and various combinations of other mid $3d$-transion metal elements. In agreement with experiment, for alloys without Cr or Mn, low residual resistivity is observed due to weak disorder scattering in one spin channel. On the contrary, Mn/Cr elements greatly raise $\rho_0$ due to smeared Fermi surface in both spin channels, resulted from the antiparallel spins on Cr/Mn. While chemically induced magnetic disorder is the dominant scattering mechanism, we present additional results that clarify the role of local lattice distortions and magnetic non-collinearity neglected in standard KKR-CPA based transport calculations. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L11.00012: Energy dissipation in Ni-containing concentrated solid solutions. German Samolyuk, Sai Mu, Ke Jin, Hongbin Bei, G. Malcolm Stocks Due to high disorder the diffusion processes are noticeably suppressed concentrated solid solution, so called high entropy alloys. It makes these alloys promising candidate for energy application under extreme conditions. Understanding of the energy dissipation in these alloys during the irradiation or interaction with laser bean is extremely important. In the metals and alloys the main channel of energy dissipation is provided by the electronic subsystem. The first principles approach was used to investigate the electronic structure properties of the alloys. The obtained results were used to calculate the electronic part of thermal resistivity caused by scattering of electrons on atomic disorder, magnetic and phonon excitations The contribution of last two excitations to the temperature dependence of thermal resistivity is discussed. The importance of magnetism in 3d transition metals based alloy was demonstrated. In particular, it was shown that antiferromagnetic ordering of chromium or manganese leads to significant increase of electron scattering in alloy containing these elements. It results in significant reduction of conductivity in chromium or manganese containing alloys. The comparison with the existing experimental data is discussed. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L11.00013: Static structure, microscopic dynamics and electronic properties of liquid titanium near melting. An ab-initio study David J. Gonzalez, Beatriz Gonzalez del Rio, Luis E Gonzalez We present an ab-initio molecular dynamics study of several structural, dynamic and electronic properties of liquid titanium near melting. The obtained structural results are compared with the available experimental data, most notably the static structure factor for which discordant experimental data have been reported [1]. Several dynamical properties have been calculated, such as the velocity autocorrelation function, intermediate scattering functions and dynamic structure factors along with some transport coefficients. The dynamic structure factors show side peaks indicative of collective density excitations and the associated dispersion relation curve has been compared with experiment. The relaxation mechanisms for the density excitations have been analyzed in terms of a model with two decay channels. [1] Y Waseda, The Structure of Non-Crystalline Materials, (New York: McGraw-Hill, 1980); K F Kelton et al, Phys Rev. Lett. 90, 195504 (2003); D Holland-Moritz et al, Mater. Sci. Eng. A, 449-451, 42 (2007) [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L11.00014: Effect of alloying elements on the ideal strength and charge redistribution of $\gamma \prime $-Ni$_{\mathrm{3}}$Al: a first-principles study of tensile deformation Minru Wen, Chong-Yu Wang The ideal strength, which is the minimum stress required to yield a perfect crystal, is fundamental for understanding the mechanical properties of real materials. Using density functional theory, the effect of the alloying elements Ta, W, Re, Mo, and Co on the ideal tensile strength ($\sigma _{\mathrm{IT}})$ of $\gamma \prime $-Ni$_{\mathrm{3}}$Al along three characteristic directions was investigated. By examining the crystal mechanical stability in terms of Born criteria at every single strain during the tensile tests, the $\sigma_{\mathrm{IT}}$ of L1$_{\mathrm{2}}$-Ni$_{\mathrm{3}}$Al along the [001], [110] and [111] directions are determined to be 12.93 GPa, 7.20 GPa and 25.55 GPa, respectively. The effect of alloying elements on $\sigma_{\mathrm{IT}}$ shows obvious directionality because of directional interactions between impurities and host atoms. Doping with Ta, W, Re, Mo, and Co increases $\sigma_{\mathrm{IT}}$ in the [110] direction by 13{\%}, 18{\%}, 21{\%}, 17{\%}, and 5{\%}, respectively. Furthermore, the electronic mechanism underlying the strengthening effect of alloying elements is determined by analyzing the d-orbital partial density of states and charge redistribution. [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L11.00015: Implementation of EAM and FS potentials in HOOMD-blue Lin Yang, Feng Zhang, Alex Travesset, Caizhuang Wang, Kaiming Ho HOOMD-blue$^{\mathrm{[1]}}$ is a general-purpose software to perform classical molecular dynamics simulations entirely on GPUs. We provide full support for EAM and FS type potentials in HOOMD-blue, and report accuracy and efficiency benchmarks, including comparisons with the LAMMPS$^{\mathrm{[2]}}$ GPU$^{\mathrm{[3]}}$ package. Two problems were selected to test the accuracy: the determination of the glass transition temperature of Cu$_{\mathrm{64.5}}$Zr$_{\mathrm{35.5}}$ alloy using an FS potential and the calculation of pair distribution functions of Ni$_{\mathrm{3}}$Al using an EAM potential. In both cases, the results using HOOMD-blue are indistinguishable from those obtained by the GPU package in LAMMPS within statistical uncertainties. As tests for time efficiency, we benchmark time-steps per second using LAMMPS GPU and HOOMD-blue on one NVIDIA Tesla GPU. Compared to our typical LAMMPS simulations on one CPU cluster node which has 16 CPUs, LAMMPS GPU can be 3-3.5 times faster, and HOOMD-blue can be 4-5.5 times faster. [1] Anderson, J. A., Lorenz, C. D., Travesset, A. J Comp Phys, 227(10), 5342--5359, (2008). [2] S. Plimpton, J Comp Phys, 117, 1-19 (1995). [3] W. M. Brown, P. Wang, S. J. Plimpton, A. N. Tharrington, Comp Phys Comm, 182, 898-911, (2011). [Preview Abstract] |
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