Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P49: Metals: Actinide, Nuclear Related and Rare Earth Physics |
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Sponsoring Units: DCMP DMP Chair: Krzysztof Gofryk, Idaho National Laboratory Room: Mile High Ballroom 1B |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P49.00001: Plutonium in high magnetic fields. Mark Wartenbe, Paul H Tobash, Neil Harrison, John Singleton, Laurel E Winter High magnetic field studies of plutonium have been limited up until now. The complex behavior |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P49.00002: Ab initio study of the properties of liquid uranium for temperatures up to 2050 K Luis Gonzalez, Beatriz Gonzalez del Rio, David Gonzalez Uranium compounds are used as fissile materials in nuclear reactors. Nowadays the most used nuclear fuel is UO2, but in generation-IV reactors other compounds are being considered, such as UC and UN [1]. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P49.00003: Theoretical investigations of the tritium diffusion pathways in γ-LiAlO2 pellets Hari P Paudel, Ting Jia, Yuhua Duan In tritium-producing burnable absorber rods (TPBAR), γ-LiAlO2 is used in the form of an annular ceramic pellet enriched with 6Li isotope and is located between the zircaloy-4 liner and nickel-plated zircaloy-4 tritium getter with a gas gap in between. When irradiated in a pressurized water reactor (PWR), the 6Li pellets absorb neutrons and produce tritium (3H) through 6Li+ n → 3H + α. However, accurate analysis of the 3H transport through the ceramic pellets and the barrier/cladding system is hampered by the lack of fundamental data about the hydrogen isotope solubility and diffusivity. For TPBARs to enable effective tritium production in PWRs and to improve the performances of these components, we are investigating the 3H solubility and diffusion pathways in the bulk and surface of γ-LiAlO2 with different concentrations of lithium defects. The calculated results for bulk and low-index surfaces properties, thermal conductivity, 3H activation energy barriers, and the diffusion coefficients in γ-LiAlO2 are in good agreement with the available experimental values. With a better knowledge of 3H transport properties within γ-LiAlO2 pellets through our modeling, its performances and higher 3H production rate can be further evaluated experimentally with a higher confidence. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P49.00004: Complex Phase Behavior of U3O8 Andrew Miskowiec, Jennifer Niedziela, Tyler Spano, Sarah Finkeldei, Rodney Hunt, Michael Ambrogio Oxidation of UO2 produces U3O8. During oxidation, the unit cell undergoes a significant expansion (approx. 17%). This reaction must be considered in technological applications of UO2 (such as nuclear fuel). U3O8 itself has multiple crystal phases, including an orthorhombic Amm2 phase that occurs below 300 oC, and a hexagonal P-62m phase above 300 oC. Although these phases are nearly isomorphic, one fact is that the Amm2 phase has two crystallographic uranium sites, and the oxidation configuration is 2U(V) + U(VI). But, the P-62m phase has only one crystallographic site, and so each of the three uranium atoms must carry 16/3 charge. We present preliminary investigations into possible resolutions of this observation, including temperature dependent Raman and x-ray diffraction measurements. Coupled with density functional theory calculations, we show an intimate relationship between phonon softening and local U-O structural re-arrangements. In particular, softening of one strong Raman-active mode near 420 cm-1 appears to be the driving effect in the orthorhombic-to-hexagonal phase transition. We also explore the possibility of coupling between this phonon and the electronic structure and whether this phonon facilitates an electron-hopping mechanism. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P49.00005: Crystal-field states of UO2 probed by directional dependence of nonresonant inelastic x-ray scattering Martin Sundermann, Gerrit Van der Laan, Andrea Severing, Laura Simonelli, Gerard H Lander, Maurits Haverkort, Roberto Caciuffo Core-level nonresonant inelastic x-ray scattering (NIXS) [1-3], also called x-ray Raman scattering, has been performed on single crystals of UO2 to study the directional dependence of higher-order multipole scattering from the uranium O4,5 edges (90–110 eV). By comparing the experimental results with theoretical calculations the symmetry of the ground state is confirmed directly as the crystal-field Γ5 triplet state within the J = 4 manifold [4] as had been suggested by inelastic neutron scattering [5]. The results demonstrate that the directional dichroism of the NIXS spectra is sensitive to the CF strength and establish NIXS as a tool for probing crystal-field interactions quantitatively. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P49.00006: Excess Electrons on Reduced AnO2 (111) Surfaces (An = Th, U, Pu) and Their Impacts on Catalytic Water Splitting Gaoxue Wang, Enrique Batista, Ping Yang Exess electrons from intrinsic oxygen vacancies play a key role in the surface chemistry and catalytic properties of metal oxides. This effect is particularly critical in actinide dioxides (AnO2), the most common nuclear fuels, where radiation can induce the formation of vacancies. However, the behavior of excess electrons on AnO2 surfaces has not been fully explored. In this talk, I will discuss our first-principle study of the electronic structure of excess electrons from oxygen vacancies on AnO2 (111) surfaces. The low-energy electronic structure is searched via U-ramping and occupation matrix control. The excess electrons are found to localize at the vacancy site on ThO2, move to the metal 5f orbitals on PuO2 surface, with UO2 as an intermediate case. In the presence of water, the excess electrons lead to the exothermic splitting of H2O and formation of H2 on ThO2 and UO2 surfaces, while on PuO2 surface the formation of H2 is thermodynamically unfavorable. This work has important implications in the surface chemistry and corrosion of AnO2, and hence the handling and long-term storage of spent nuclear fuels. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P49.00007: First Principles Investigation of the electronic and magnetic structure of Pu6Fe Sarah Hernandez, John M Wills Chemical impurities within δ-plutonium (Pu) arises due to the casting and processing of the material. One impurity, iron (Fe), is believed to segregate to the grain boundaries and forms an intermetallic compound ζ-Pu6Fe. This compound was determined by X-ray diffraction (XRD) to be body-centered tetragonal with a space group of I4/mcm and to date, very little is known about its physical properties, other than it has a low melting temperature at 410°C. Using density functional theory, we can predict equilibrium properties and begin to understand the fundamental electronic and magnetic structure of Pu6Fe. This work will present density functional theory calculations using the all-electron full-potential linearized augmented-plane-wave plus local orbital basis method as implemented in the WIEN2k code. Calculations included a non-magnetic, ferromagnetic, and anti-ferromagnetic arrangement at the respective optimized structures with no-spin-orbit-coupling, spin-orbit-coupling, and spin-orbit-coupling with orbital polarization to gauge the different level of theories. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P49.00008: Magnetic torque of USb single crystals Xiaxin Ding, Keshav Shrestha, Ingrid Zimmermann, Ross McDonald, Franziska Weickert, Neil Harrison, Marcelo Jaime, Myron B Salamon, J-C. Griveau, James L Smith, Krzysztof Gofryk Over 40 years, uranium monoantimonide (USb) has been investigated by a variety of experimental and theoretical methods. This compound crystallizes in the cubic NaCl-type of crystal structure and is known to order antiferromagnetically with a non-collinear triple-k magnetic structure below T_N∼214 K. This high-symmetry complex magnetic structure consists of three equivalent <0 0 1>-type of wave vectors, with spins that point along <1 1 1> direction. During the talk we will present results of our recent magnetic torque measurements performed on high-quality single crystals of USb at temperatures below and above T_N. The measurements have been carried out in both DC and pulsed magnetic fields up to 60 T. The results obtained are crucial in understanding of magnetic interactions, anisotropy, and their coupling to the lattice in this material. We will discuss implications of these results. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P49.00009: 5f-electron localization in metallic PuPdSn Krzysztof Gofryk, J-C. Griveau, Eric Colineau, Roberto Caciuffo, James L Smith While the effect of electronic correlations is relatively well studied in Ce, Yb and U based materials, there is still lack of knowledge on how these collective phenomena impact magnetic, transport, and thermodynamic properties in transuranium intermetallics. Depending upon the strength of the interactions, many unusual properties such as complex magnetism, Kondo effect, heavy fermion ground state, valence fluctuations, and/or unconventional superconductivity have been observed in these materials. Here we present our detailed studies on the structural, magnetic, thermal, and transport properties of PuPdSn. This compound crystalizes in the hexagonal ZrNiAl-type of structure [space group P62m]. It orders antiferromagnetically at TN = 21 K that is followed by another AF-like transition at 9.6 K. The low-temperature linear specific heat coefficient is small, γ∼8 mJ/mol K2. All the results obtained strongly suggest the presence of well localized 5f-states in this material, which is rare among U and Pu intermetallics. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P49.00010: Electronic structure of GdNi and HoNi Chien Wen Chuang, Hong-Ji Lin, F. M. F. de Groot, F. H. Chang, Chien-Te Chen, Y. Y. Chin, Y. F. Liao, Ku-Ding Tsuei, J. Arout Chelvane, R. Nirmala, Ashish Atma Chainani Equiatomic GdNi and HoNi are ferromagnetic materials with a Curie temperature Tc= 69 K and Tc =36 K, respectively. These compounds exhibit a large magnetocaloric effect and are suitable for low temperature magnetic refrigerator applications. We investigate the electronic structure of GdNi and HoNi using Hard hard X-ray photoemission spectroscopy (HAXPES). HAXPES of the Gd and Ho 3d, 4d, 4s and 5p core level spectra confirm the atomic multiplets of Gd3+ and Ho3+. Valence band HAXPES of GdNi and HoNi shows Ni 3d features at the Fermi level, confirming a partially filled 3d band, while the Gd 4f/ Ho 4f states occur at high binding energies away from the Fermi level. For GdNi, we have also carried out XAS and XMCD studies in the ferromagnetic phase at T = 25 K. We analyze the Gd M4,5-edge and Ni L2,3-edge spectra using atomic multiplet and cluster model calculations, respectively. The Gd M4,5-edge XMCD spectrum is consistent with a ground state configuration of S = 7/2 and L=0. The Ni L2,3-edge XMCD results indicate that the antiferromagnetically aligned Ni moments exhibit a small but finite magnetic moment ( mtot ∼ 0.19 μB ). The results indicate that the Ni 3d band is not fully occupied and invalidates the charge-transfer model for GdNi and HoNi. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P49.00011: The structural and mechanically properties of alloyed Zr-50Nb and Zr-22Nb systems with Sn and Co at varied temperature Magoja Malebati, Phuti Ngoepe, Hasani Chauke Zirconium and its alloys are considered as the principal cladding materials due to their good irradiation stability, high mechanical strength, as well as oxidation and corrosion resistance. These alloys play a significant role in various fields and are suitable for extensive applications in the nuclear power and chemical industry. Recently, advanced Zr-based alloys are aimed for service in more severe operating conditions such as higher burn-up, increased operation temperature, and high-PH operation. In this work, density functional theory was used to investigate the structural and mechanical properties of Zr-50Nb-X and Zr-22Nb-X with alloying elements Sn and Co. Their dependence on temperature was evaluated using Dmol3 for 1 to 3 atomic percentages of Sn and Co. It was found that ternary additions with Co and Sn have significant impact on Zr-Nb alloy, and revealed enhanced mechanical strength at higher temperature. The Co and Sn addition on Zr-22Nb are more promising for high temperature applications, with Sn being more preferable. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P49.00012: Magnetic frustration and magnetic correlations in YbMn2Sb2 single crystals Raquel Ribeiro, Julian Munevar, Fabiana R Arantes, Leticie Mendonça-Ferreira, Marcos a Avila, Elvezio Morenzoni The crystal growth and the structural, transport and magnetic characterization of the magnetically frustrated YbMn2Sb2 single crystals are reported. The crystals show a trigonal symmetry, where corrugated honeycomb layers of MnSb are separated by Yb atoms. No structural transition was observed down to 22 K. The resistivity measurements show a predominantly insulating behavior. The combined resistivity, dc and ac susceptibility, and heat capacity measurements confirm successive transitions at 230 K, 116 K and 40 K, being the transition at TN =116 K due to the Mn+2 lattice antiferromagnetic ordering. Muon spin rotation experiments (µSR) reveal a more complicated scenario, with a complex temperature dependence of the magnetic volume fraction and a several order of magnitude variation of the relaxation rate, with its maximum at approximately 40 K. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P49.00013: Study of the Band Structure and the Origin of the XMR Effect in La1-xCexBi Yujie Hao, Xiao-Ming Ma, Bin Li, Yanping Guo, Feng Yue, Rui'e Lu, Chang Liu Extremely high magnetoresistance (XMR) [1] in the rare earth monopnictides LnX (Ln = La, Ce, X = Sb, Bi) has recently received considerable interest [2-3]. These compounds with simple rock salt structure and electronic band structure are ideal model systems to search for the origin of the XMR effect. In this work, La1-xCexBi single crystals with x ranging from 0 to 0.2 is studied. By combining transport, magnetic and angle-resolved photoemission measurements, we performed a systematic investigation on the magnetotransport property and electronic structure of La1-xCexBi. We clearly observe that the XMR effect in LaBi is gradually suppressed with increasing Ce doping level. The field-induced resistivity upturn and plateau disappear before the XMR effect is completely suppressed. On the other hand, the band structures near the Fermi surface barely changed with increasing Ce doping level. According to our results, whether the XMR effect originates from particular bands near the Fermi surface still needs further investigation. |
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P49.00014: The interplay of electronic, magnetic and structural properties of GdB6 from first principles Shaowen Xu Gadolinium hexaboride (GdB6) is a well-known field emitter material that has been investigated for more than three decades. We perform a systematical density-functional theory (DFT) study of GdB6 by using the generalized-gradient approximation and considering the electron interaction parameter U. The basic structural and electronic properties are carefully revised, as well as a strong U-value dependence in determining the antiferromagnetic (AFM) magnetic structures of Gd 4f electronic states. We found a small U (0~3eV) showing the most consistent experimental ground-state properties, which gives rise to a magnetic structure with a ground state of C-AFM and a second stable E-AFM. Moreover, we find the distortion modes of boron octahedron play an important role in the interaction between spin and lattice structures in this system. These results will deepen our understanding of the boron-based correlated rare earth compounds. |
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