AVS 69 Session AC+AS+MI+TH-WeA: Emerging Topics and Methods in Actinide/Rare Earth Sciences

Wednesday, November 8, 2023 2:20 PM in Room C124

Wednesday Afternoon

Start	Invited?	Item
2:20 PM	Invited	AC+AS+MI+TH-WeA-1 Chemical Imaging and Applications Using High Energy Resolution Fluorescence Detection for the Actinides Samuel Webb, Nicholas Edwards, Vincent Noel (SLAC National Accelerator Laboratory) Microscale synchrotron radiation-based x-ray fluorescence (SR-XRF) chemical analyses can provide a unique capability for chemical signature recognition and classification capabilities for actinide micro-particle analysis. SR-XRF is well suited to forensic type analyses of small particles because it is rapid, non-destructive, highly sensitive, has good spatial resolution, and can provide chemical information on the elements that are present when combined with x-ray absorption spectroscopy (XAS). The combination of spatially resolved distribution and chemical information, often known as chemical imaging, effectively provides a “chemical morphology” of the sample of interest and can show how chemical states are distributed within and among a series of particles. This type measurement is critical for understanding particle origin and history, as the spectroscopy, and its spatial distribution, can provide unique and complementary chemical signatures that may not be elucidated with other forms of measurement. However, the conventional XAS capability in the near edge region as commonly implemented is often inadequate for systems that require high sensitivity or require a higher detail of spectroscopic information. This can be overcome with the combination of traditional micro SR-XRF and XAS, integrated with a high energy resolution fluorescence detector (HERFD) crystal analyzer. This has been recently implemented at BL 6-2b at SSRL and applied in the determination of the micron-scale oxidation state of uranium in particles. A discussion of the image and data processing techniques that can be applied using spatially resolved HERFD to obtain chemical and structural information, as well as the distribution of phases across different particles at the micro-scale, will also be presented.
3:00 PM	Invited	AC+AS+MI+TH-WeA-3 High Energy X-Ray Characterization of Microstructure at Macroscopic Depths in Pu Alloys Donald Brown, Travis Carver, Reeju Pokharel (los alamos National Laboratory); Alice Smith (los al); Peter Kenesei, Jun-Sang Park (Argonne National Laboratory) High energy (95keV) X-rays were utilized to characterize the microstructure of six PuGa alloy samples. The samples had different gallium content, age, and history (i.e. thermos-mechanical processing). The crystallographic textures, phase fractions, lattice parameters and dislocation densities of each sample were evaluated through distinct analysis techniques. The textures of the samples were modest. In each case, the dislocation densities were relatively high, comparable to cold worked metals, with some attributable to mechanical work and some likely due to self-irradiation damage (aging). The lattice parameters determined in the predominantly single-phase samples were larger than expected based on the nominal Ga concentration. The lattice parameter increase is attributed to self-irradiation induced Ga segregation leaving the matrix Ga lean. Finally, measurements of the lattice parameter were completed as a function of temperature to determine the crystallographic thermal expansion of the material.
3:40 PM		BREAK
4:40 PM		AC+AS+MI+TH-WeA-8 Molecular Beam Epitaxy of Ternary Nitrides: From Transition Metals to Actinoids Kevin Vallejo (Idaho National Laboratory); Sandra Julieta Gutierrez Ojeda (Universidad Nacional Autonoma de Mexico); Gregorio Hernandez Cocoletzi (Benemerita Universidad Autonoma de Puebla); Shuxiang Zhou, Krzysztof Gofryk, Brelon May (Idaho National Laboratory) The exceptional properties of transition metal nitrides for coatings, as well as photo- and electrochemical applications have opened the doors for more detailed studies of their structure and synthesis. Mn- and Cr- nitrides are strong candidates to showcase the application of spintronic and magnetic sensing applications partially because of their ability to form several different metastable phases. Similarly, rare-earth nitrides have been studied for over 50 years due to their optical properties and strong electron correlations, leading to behaviors that range from insulating to metallic. This study uses molecular beam epitaxy to synthesize epitaxial thin films of different Mn-, Cr-, Ga-, and Ce-nitride phases. The electrical and magnetic properties of these films are investigated with the rocksalt MnN and CrN both showing metallic behavior, with the latter showing a magnetic transition ~280K. However, when combining these materials at similar growth conditions, instead of maintaining the rocksalt structure, a new ternary cubic phase of Mn_xCr_yN is obtained which shows narrow-gap semiconducting behavior. Additionally, density functional theory calculations show potential new phases where lanthanoid ternary phases are experimentally realizable. This work presents an avenue for the epitaxial integration of metallic, magnetic, and semiconductor materials via transition metal and lanthanoid compounds, en route to the synthesis of actinoid compounds.
5:00 PM		AC+AS+MI+TH-WeA-9 Formation and Electronic Properties of Uranium Tellurides: A Thin Films Study Evgenia Tereshina-Chitrova, Sony G. Alex (Institute of Physics CAS, Prague, Czechia); Oleksandra Koloskova, Lukas Horak (Charles University, Prague); Oleksandr Romanyuk, Zbynek Soban (Institute of Physics CAS, Prague); Thomas Gouder, Frank Huber (JRC Karlsruhe) Understanding the interaction of 5f electrons with other electrons in actinide compounds presents a significant challenge. Factors such as relativistic effects, strong electron correlations, and hybridization with ligands contribute to the complexity of observed effects. This complexity is exemplified in the case of the recently discovered unconventional superconductor UTe₂ [1]. The ongoing debate surrounding UTe₂ revolves around understanding its unconventional superconductivity, the nature of its electronic correlations [2,3], and the character of the 5f electrons. While it's evident that UTe₂ exhibits intermediate occupancy of the 5f states at ambient pressure, there are two opposing interpretations of experimental findings regarding the degree of localization of the 5f electrons: the model based on 5f²6d¹ states with singlet crystal field states [4,5], and a 5f³-based model with atomic Kramers doublet and greater 5f itinerancy [6,7]. Interestingly enough, ab-initio calculations considering the 4f² U-ion ground state multiplet reproduce bulk experimental observations, such as the Schottky anomaly and magnetic anisotropy at low temperatures [8]. To contribute to this subject, we provide a comprehensive and detailed investigation of thin films of uranium tellurides with various compositions U_xTe_y by means of X-ray Photoelectron Spectroscopy (XPS) and Ultra-violet Photoelectron Spectroscopy (UPS). We also explore the structural and bulk properties of the films, including their magnetic and transport characteristics. This comprehensive approach allows us to correlate the changes in XPS spectra across different compositions and crystal structures with resultant bulk properties, contributing to our understanding of the nature of the 5f electrons within uranium tellurides. The work by E.A. T.-Ch. is supported by the Czech Science Foundation (GAčr) under the grant number 22-19416S. E.A. Ch.-T. is a recipient of the L’Oreal-UNESCO for Women in Science prize. [1] S. Ran et al., Science 365, 684 (2019). [2] I. M. Hayes et al., Science, 373, 797 (2021). [3] C. Duan et al., Phys. Rev. Lett. 125, 237003 (2020). [4] L. Miao et al., Phys. Rev. Lett.124, 076401 (2020). [5] S. Liu et al., Phys. Rev. B 106, L241111 (2022). [6] S. Fujimori et al., J. Phys. Soc. Jpn. 88, 103701 (2019). [7] F. Wilhelm, Commun. Phys. 6, 96 (2023). [8] S. Khmelevsyi et al., Phys. Rev. B 107, 214501 (2023).
5:20 PM		AC+AS+MI+TH-WeA-10 Nanoscale Uranium and Thorium Oxides for Applications in Advanced Nuclear Fuels Matthew Heaney, Liane Moreau, Xiaofeng Guo (Washington State University) Nanomaterials of uranium and thorium oxides and their mixtures are of significance to the development of advanced nuclear fuels with properties such as self-healing and greater fission gas retention. They also serve as a means for furthering our understanding of spent nuclear fuel behaviors. Furthermore, thorium incorporation into the uranium sublattice induces changes in oxidation behavior, which would be a promising means to provide additional redox resistance. Coupling this with the possible application in fast neutron reactors presents a potential fuel for the Th fuel cycle, which is inherently proliferation resistant. However, these possible applications are purely hypothetical given that, compared to nanomaterials from the rest of the periodic table, actinide nanomaterials are heavily understudied. Therefore, it will be imperative to interrogate the properties of these nanomaterials. This work aims to explore three key areas. (1) How careful kinetic control through variations in synthetic methods can be used to produce particles with different sizes, shapes, and heterogeneities of mixing. (2) Elucidation of the structural and thermodynamic properties of these nanomaterials and how characteristic size, shape, and heterogeneity of mixing affect them through a variety of X-ray characterization and calorimetry techniques. X-ray characterization techniques such as X-ray absorption spectroscopy (XAS) is used to evaluate the heterogeneity of mixing, local structure, and oxidation state of particles while small-angle X-ray scattering (SAXS) is used to determine statistical values on particle size, shape, and polydispersity. Calorimetry techniques like high temperature drop calorimetry are used to determine enthalpies of formation for nanoparticles and the contribution surface effects have on the thermodynamics or thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), which can be used to evaluate oxidation behaviors. (3) How sintered nanoparticles behave in in-situ reactor conditions as nuclear fuels and how particle characteristics can be chosen to achieve more desirable radiation-resistance and thermal properties for nuclear fuel, through irradiation studies performed at the 1-MW TRIGA reactor on the campus of Washington State University. Overall, the work presented provides initial evidence for the benefits of nanomaterials in the production of advanced reactor fuels and outlines important fundamental properties of actinides on the nanoscale.