AVS 70 Session AC+MI-FrM: Actinide and Rare Earth Chemistry and Physics
Session Abstract Book
(320KB, Jul 23, 2024)
Time Period FrM Sessions
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Abstract Timeline
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8:15 AM | Invited |
AC+MI-FrM-1 Structure, Stability, and Chemistry of Actinide Nanoparticles
Ping Yang, Gaoxue Wang, Enrique Batista (Los Alamos National Laboratory) Nanoscale materials bearing heavy elements have a wide range of applications from the nuclear fuel cycle to environment and health. Nanocrystals (NCs) with size and shape dependent properties are a thriving research field and remarkable progress has been made in the controlled synthesis and characterization of NCs composed of stable elements in the past three decades. In this context, interfacial chemistry of nano-sized materials is critical for controlling the morphology that drives their unique associated chemical and physical properties. The understanding of NCs containing f-elements is comparatively limited due to difficulties in handling them both experimentally and theoretically. In this talk, I will share some recent progress in understanding the interplay between surface energy, surfactant ligands, and the chemistry in determining the morphology of 5f-element nanoparticles. Quantum simulations provide a molecular-level picture of the relevant driving forces and dynamic properties. To push for larger lengthscale, we recently developed the density functional theory tight-binding (DFTB) parameters for actinide systems, that enabled the microsecond quantum MD simulations of actinide nanoparticle systems. [1]G Wang, ER Batista, P Yang. Phys Chem Chem Phys2018, 20, 17563 [2]G Wang, ER Batista, P Yang, J. Phys Chem C, 2019, 123, 30245 [3]RK Carlson, MJ Cawkwell, ER Batista, P Yang, J. Chem. Thoery Compt2020, 16, 3073 [4]NF Aguirre, J Jung, P Yang, Phys Chem Chem Phys2020, 22, 18614 [5]G Wang, ER Batista, P Yang, Appl Sci2020, 10, 4655 [6]D G Gonzalez, G Wang, ER Batista, P Yang, Inorg Chem2023, in press |
8:45 AM | Invited |
AC+MI-FrM-3 The Use of Ligand Modified Electrodes as Electrocatalysts for Actinide Redox Chemistry
Christopher Dares (Florida International University); Travis Grimes (Idaho National Laboratory); Jeffrey McLachlan (University of California at Berkeley); Xiangyang Hou (University of Utah); Alberto Ruiz Reyes (Florida International University) The lanthanides are most stable in the trivalent oxidation state, and with few exceptions, are difficult to generate in higher or lower oxidation states. In contrast the early actinides are redox active and can be generated and studied in a variety of oxidation states ranging from +7 to +2. This variety can complicate separations processes since oxidation state and can have a profound influence on ligand binding and solvent extraction. Separations schemes can also exploit the differences in binding preferences in different oxidation states to make selective extraction more efficient. In an aqueous acidic environment, the Am(IV/III) couple is at 2.6 V vs. the standard hydrogen electrode (SHE). This is nearly at the limit of what is possible in an aqueous solution where the 1-electron oxidation of water to hydroxyl radical is only about 0.3 V more positive. The subsequent potentials to generate penta- and hexavalent americium are lower though the high Am(IV/III) couple renders Am effectively redox-inert. Ligand coordination can be used to reduce the Am(IV/III) couple and/or facilitate the proton-coupled electron transfer (required to make the americyl cation). These can be organic ligands including N-donors or inorganic ligands such as lacunary polyoxometalates. Ligands anchored to metal oxide electrodes serve as good electrocatalysts to generate Am(V) or Am(VI) and operate at potentials as low as 1.6 V vs. SCE (nearly 1 V below the Am(IV/III) couple). Ligands are attached to the surface using either organic functional groups like phosphonic acids, or, through a combination of attractive interactions including hydrogen-bonding. They form well-packed monolayers on mesoporous thin layers of conductive oxides. The development of these ligand modified electrodes (LMEs) will be introduced along with characterization of their ability to adjust actinide oxidation states. |
9:15 AM | Invited |
AC+MI-FrM-5 Observation of Flat Bands in Rare-Earth Based Kagome Metals
Madhab Neupane (University of Central Florida) Quantum materials with kagome lattice – comprised of corner-sharing triangles forming a hexagon in the crystal structure - have been studied as the potential playgrounds for exploring the interplay among parameters such as geometry, topology, electronic correlations, magnetic, and charge density orders. Recent report on a family of kagome metals of the form ReTi3Bi4 (Re = rare-earth) has generated interest due to the combination of highly anisotropic magnetism and a rich electronic structure. We use angle-resolved photoemission spectroscopy measurements in combination with density functional theory calculations to investigate the electronic structure of newly discovered kagome metals ReTi3Bi4. Our results reveal multiple van Hove singularities (VHSs), some of which are in the vicinity of the Fermi level. We clearly observe multiple flat bands, which originate from the destructive interference of wave functions within the Ti kagome motif. These flat bands and VHSs originate from Ti d-orbitals and are very responsive to the polarization of the incident beam. These results demonstrate that of Ti based kagome materials system is an excellent material platform for studying kagome induced flat band physics and its connection with magnetism. |
9:45 AM |
AC+MI-FrM-7 Kinetics and Mechanism of Plutonium Oxycarbide Formation
Paul Roussel (AWE plc) Plutonium is both electropositive and highly reactive, such that an oxide film of varying thickness is always present on metal samples.It is of interest from a safety point of view (reduced handling/processing) to investigate methods that either prevent or slow down the rate of corrosion reaction of the metal. Plutonium oxycarbide, PuC1-xOx, surface films on plutonium metal have shown the ability to slow the rate of oxidation [1]. Favart et al. have reported the rate of plutonium oxycarbide formation at 350 °C [2] as measured using X-ray Diffraction. In the theoretical study reported by Qiu et al. the authors proposed four different mechanisms for the formation of plutonium oxycarbide [3]. Two of the proposed mechanisms involved the reaction of a gas with plutonium sesquioxide, Pu2O3, and the other two involved a solid state reaction of this oxide to form plutonium oxycarbide. Using a combination X-ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry and X-ray Diffraction the kinetics and mechanism of plutonium oxycarbide formation have been investigated and will be presented. [1] Retardation of plutonium oxidation by a PuO surface film, D. T. Larson, D. L. Cash, J. Vac. Sci. Technol. 9, 800 (1972). [2] Characterization of PuO/PuCO phase and its influence on the oxidation kinetics of d-plutonium, N. Favart, B. Ravat, L. Jolly, B. Oudot, L. Berlu, F. Delaunay, I. Popa, S. Chevalier, Oxid. Met., 96, 271 (2021) [3] Thermodynamical stability of plutonium monoxide with carbon substitution, R. Qiu, X. Wang, Y. Zhang, B. Ao, K. Liu, J. Phys. Chem. C 122, 22821 (2018). |
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10:00 AM |
AC+MI-FrM-8 Layered f-Metal Zintl Phases - EuZn2P2 and UCu2P2
LADISLAV HAVELA (Charles University, Czech Republic); Volodymyr Buturlim (Idaho National Laboratory); Oleksandra Koloskova (Charles University, Prague); Dominik Legut, Jiri Prchal (Charles University, Czech Republic); Jindrich Kolorenc, Jiri Kastil, Martin Misek (Institute of Physics CAS, Prague) Zintl phases consisting of an electropositive element, cation, and covalently bonded polyanion, offer a large variability of electronic structure, bridging the gap between semiconducting and metallic behavior and offering interesting functionalities. In case of magnetic cation, properties can be further tuned by magnetic fields. Here we compare compounds based on lanthanide (Eu) and actinide (U) cations. We selected layered compounds, crystallizing in the trigonal structure CaAl2Si2, which exhibit pronounced magnetic anisotropy. EuZn2P2 is a narrow band-gap semiconductor. Antiferromagnetic ordering of Eu2+ moments sets in at TN = 23 K. Rapid increase of TN with applied pressure, which reaches 43 K at p = 9.5 GPa, can be associated with reduction of the band gap, indicated by transport properties as well as by ab-initio calculations. Ferromagnetic alignment of Eu moments, achieved in fields of several Tesla, can reduce electrical resistivity by several orders of magnitude, which is classified as Colossal Magnetoresistance Effect. At p = 18 GPa (still within the same structure type), EuZn2P2 becomes semi-metallic. The compression by hydrostatic pressure is anisotropic, with soft c-axis direction. UCu2P2 with a smaller unit-cell volume is semi-metallic (and probably half-metallic) at ambient conditions. Also here the magnetic order (ferromagnetic) is supported by applied pressure, reaching 290 K at 6 GPa. The situation of 5f states is dramatically different comparing with the 4f states in the Eu counterpart. The indications given by large spontaneous magnetostriction, softer a-axis direction (nearest U-U links), or extremely strong uniaxial magnetocrystalline anisotropy point to an involvement of the 5f states in bonding, i.e. delocalization, although they do not contribute to the Fermi level, located in a pseudo-gap. Tuning by composition changes is not straightforward for single crystals grown by Chemical Vapor Transport method, nevertheless certain routes have been attempted with a positive outcome and properties of doped UCu2P2 will be discussed. |
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10:15 AM | BREAK | |
10:30 AM |
AC+MI-FrM-10 Experimental Electronic Structure Measurements of Actinide-Containing Samples Using Scanning Tunneling Spectroscopy
Benjamin Heiner, Miles Beaux (Los Alamos National Laboratory) The many difficulties performing experiments on plutonium-containing samples makes the prospect of studying them using computational methods enticing. The lag in collection of experimental data using modern techniques, especially related to electronic structure, has made validating computational methods challenging. With the establishment of a scanning tunneling microscope at Los Alamos National Laboratory with the capacity to study plutonium and other radioactive samples, the ability to probe electronic structure seamlessly across the Fermi energy is now possible. In a first of its kind experiment, scanning tunneling spectroscopy data on plutonium-containing samples, especially gallium-stabilized δ-phase plutonium, has been collected. The spectra reveal a surface with semimetal characteristics instead of a computationally predicted semiconductor band gap. LA-UR-24-24274 |
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10:45 AM |
AC+MI-FrM-11 Unconventional Superconductivity in UBe13 - Investigation via Variation of Impurity Level - and Comparison to the Conventional Superconductor LuBe13
Greg stewart, Jungsoo Kim (University of Florida) We have prepared and characterized down to T=0.40 K three arc-melted samples each of MBe13, M = Lu, U, using threedifferent purities (99.999%, 99.96%, and 99.8%) of Be but with the same high purity M (Lu or U) for all three.The measurements down to 0.40 K allow the detection of the maximum in the specific heat in all three LuBe13samples. The resulting superconducting properties strongly depend on impurity level in UBe13 (40% decrease inΔC/Tc, 15% decrease in Tcmid) while the three LuBe13 samples exhibit significantly smaller changes (10% and 5%respectively) with purity. The comparison of properties at the first two levels of purity (99.999% vs 99.96%) iseven more disparate: 12% decrease in Tcmid in UBe13 vs no change in LuBe13. These results are consistent withprevious results that argue for unconventional superconductivity in UBe13, and are consistent with assignment of LuBe13 as a conventional, BCS superconductor. As will be discussed in more detail, this example of comparing superconducting properties vs controlled gradations in impurity levels with two compositionally and structurally “matched” superconducting compounds (one conventional and one of to-be-determined coupling behavior) offers a new method - versus the already existing ones - for determining unconventional superconducting behavior. |
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11:00 AM |
AC+MI-FrM-12 Strong Magnetoelastic Interactions in HoSb Probed by High-Resolution Dilatometry and X-Ray Diffraction
Volodymyr Buturlim (Glenn T. Seaborg Institute, Idaho National Laboratory); Narayan Poudel (Idaho National Laboratory); Dariusz Kaczorowski (Polish Academy of Sciences); Marcelo Jaime (Physikalisch Technische Bundesanstalt); Zahir Islam (Argonne National Laboratory); Krzysztof Gofryk (Center for Quantum Actinide Science and Technology, Idaho National Laboratory) Rare-earth (RE) monopnictides, which crystallize in a cubic structure similar to NaCl have drawn considerable interest due to their diverse transport, magnetic, and structural properties. The non-magnetic compounds are known for the transition from topological to trivial electronic states (e.g. LaPn where Pn = Bi and As [1]). Magnetism of the compounds with long-range order brings complexity to their topological properties. However, the topological nature of these materials undergoes intense debates and investigation. HoSb is a topologically trivial semimetal, which orders antiferromagnetically below TN = 5.7 K [2]. Application of magnetic field leads to the change of its magnetic structure from MnO-type antiferromagnetic (AFM) arrangement to HoP-type arrangement, then to ferromagnetic (FM) arrangement. There are also reports which, suggest a transition to tetragonal structure taking place at TN [3]. The variety of the low-temperature phenomena makes HoSb a good platform to investigate the role of magnetic ordering and the strength of spin-phonon coupling on the crystal structure of this system. We will present the results of low-temperature high-resolution dilatometry as well as X-ray diffraction studies performed at static and pulsed magnetic fields. Heat capacity studies and the presence of latent heat agree with the structural distortion that occurs at TN. The lowering of the symmetry is further supported by detailed low-temperature X-ray diffraction measurements under magnetic fields. Strong spin-lattice coupling in HoSb results in giant magnetostriction of the order of 1500 ppm. Furthermore, our detailed dilatometry studies allow us to construct a magnetic phase diagram of HoSb. We will discuss the implications of these results in the context of the strong magnetoelastic properties in HoSb and other rare-earth monopnictides. [1] H. Y. Yang et al., Phys. Rev. B 98, 045136 (2018). [2] M. M. Hosen et al., Sci. Reports 2020 101 10, 1 (2020). [3] F. Lévy, Phys. Kondons. Mater. 10, 85 (1969). KG acknowledges the support from the Division of Materials Science and Engineering, Office of Basic Energy Sciences, Office of Science of the U. S. Department of Energy (U.S. DOE). VB acknowledges the support from the Idaho National Laboratory's Laboratory Directed Research and Development (LDRD) program under DOE Idaho Operations Office Contract DE-AC07-05ID14517. |
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11:15 AM |
AC+MI-FrM-13 Electronic Structure in a Rare-Earth-Based Intermetallic System TbNi3Ga9
Sabin Regmi, Volodymyr Buturlim (Idaho National Laboratory); Binod K. Rai (Savannah River National Laboratory); Tomasz Durakiewicz, Krzysztof Gofryk (Idaho National Laboratory) Rare-earth-based intermetallics provide flexibility to study the electronic, magnetic, superconducting, and topological properties by tuning the crystal structure, composition, and spin-orbit coupling. Recently, RNi3(Ga/Al)9 intermetallic materials have been studied for their richness in broad range of exotic crystal, magnetic, heavy fermion, and quantum criticality behaviors. However, momentum-resolved electronic structure studies are lacking. Here, we present results of the angle-resolved photoemission spectroscopy measurements to reveal the underlying electronic structure and topology in TbNi3Ga9, both above and below the Néel temperature. This study will open up exciting avenues towards exploration of electronic properties in the chiral family of RNi3(Ga/Al)9 materials with wide range of intriguing properties. |
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11:30 AM |
AC+MI-FrM-14 Catalytic Activities of Defected Actinide Dioxide Ano2 Surface: A First Principles Study
Shukai Yao, Gaoxue Wang, Enrique Batista, Ping Yang (Los Alamos National Laboratory) Actinide dioxides AnO2 play an important role as nuclear fuels in commercial nuclear reactors. Understanding the surface chemistry of AnO2 is crucial in various aspects such as safe operations, recycling, and storage of nuclear fuels. Actinide materials have shown to be highly efficient catalyst for the activation of H2, CO, NH3, etc., mainly due to valent 5f electrons of actinides characterized by strong electron correlations and various oxides states. However, experimental studies of actinide systems are limited by their high safety requirement associated with radioactivity. In this computational study, we employed first principles electronic structure calculations based on density functional theory (DFT) to reveal the catalytic behavior of AnO2 surface with O vacancies. We will show that O vacancies significantly change the electronic structure of AnO2 surfaces, and act as the active sites of small molecules adsorption. As a result, defected AnO2 surface leads to an enhanced reactivity compared to the pristine AnO2 surface. |
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11:45 AM |
AC+MI-FrM-15 Thin Film Synthesis of Rare Earth and Actinide Nitrides Using Molecular Beam Epitaxy
Keivn Vallejo, Brelon May, Zachery Cresswell, Voldymyr Buturlim, Sabin Regmi, Krzysztof Gofryk (Idaho National Laboratory) Lanthanide- and actinide-based nitride compounds are an understudied group of materials compared to their oxide counterparts, which provide new avenues for nuclear reactor designs. Their 4f and 5f electron shell gives rise to a variety of interesting physics such as magnetism and unconventional superconductivity. Samarium nitride (SmN) has been recently identified as a material where ferromagnetic order and potential p-type superconductivity coexist. Our team will present results on the growth conditions in a molecular beam epitaxy chamber of pure and doped SmN using molecular beam epitaxy, and its electronic transport properties as a function of temperature and magnetic field. CeN and UN thin films are also explored. The presence of SmN(111) peaks on (001) substrates indicates an orientation-preference for some material systems. The electrical resistivity and magnetic susceptibility studies have shown a range of magnetic behaviors, including paramagnetic and ferromagnetic. With a potential superconductive transition around ~10 K, SmN and its doping effects on crystal structure and electronic properties are characterized. |