Abstract
Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, ...was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd
3
to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature—the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.
A study on zirconium nitride was performed to assess the effect of radiation damage by heavy ions at cryogenic and elevated temperatures. Cross-sectional transmission electron microscopy, grazing ...incidence X-ray diffraction, nanoindentation, and helium desorption studies were used to assess the damage and its effects. Xenon and krypton were used as heavy ions at 300keV to displacement damage as high as 200dpa. Implants were cryogenic, 350°C, 580°C, and 800°C. Amorphization was not observed at low temperatures nor was bubble formation observed at elevated temperatures, however, defect migration was observed at elevated temperatures. Nanoindenter results showed the onset of defect saturation. Helium release studies were performed to show the effect of increasing damage by Xe to 40dpa.
The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls ...the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.
Radiation Tolerance of Complex Oxides SICKAFUS, K. E; MINERVINI, L; GRIMES, R. W ...
Science (American Association for the Advancement of Science),
08/2000, Volume:
289, Issue:
5480
Journal Article
Peer reviewed
The radiation performance of a variety of complex oxides is predicted on the basis of a material's propensity to accommodate lattice point defects. The calculations indicate that a particular class ...of oxides possessing the fluorite crystal structure should accept radiation-induced defects into their lattices far more readily than a structurally similar class of oxides based on the pyrochlore crystal structure. Preliminary radiation damage experiments substantiate the prediction that fluorites are inherently more radiation resistant than pyrochlores. These results may permit the chemical durability and radiation tolerance of potential hosts for actinides and radioactive wastes to be tailored.
Uranium diboride (UB2) and uranium tetraboride (UB4) are candidate constituents for multi-phase accident tolerant fuel due to their anticipated high thermal conductivity. These fuels have high ...uranium density that contributes to fission, and by tailoring the ratio of 10B/11B, can also act as an integrated burnable poison. Understanding the thermophysical and mechanical properties of uranium borides, for which only limited data are available in the literature, is of importance to determine their accident tolerance. In this work UB2 and UB4 have been synthesized via arc melting and sintered to high densities via spark plasma sintering (SPS). High density samples, >90% theoretical density, were used to measure the thermal diffusivity and thermal expansion of UB2 and UB4 and, in conjunction with specific heat literature data, their thermal conductivities were calculated from 298 to 1773 K. Additionally, resonance ultrasound spectroscopy (RUS) and nanoindentation were performed to investigate the mechanical properties of the uranium borides. Our results are discussed in the context of available literature. Both UB2 and UB4 exhibit thermal conductivities higher than that of UO2, with UB2 having the highest. The thermal conductivity of UB2 increases with temperature above 874 K, while for UB4 there is a linear increase over the entire measured range. X-ray diffraction (XRD) results indicate that impurity phases were present in the fabricated materials, which could explain why literature density functional theory (DFT) results predict higher values. This suggests that if impurity phases or any microstructural defects can be eliminated then the thermal conductivity can be further increased.
•Uranium boride phases can be used as secondary phases in composite fuels to increase the overall thermal conductivity. This comes in addition to contributing as fissile and burnable poison phases, when tailoring the ratio of 10B/11B.•The materials were synthesized via arc melting and sintered to high densities via spark plasma sintering.•The measured thermal conductivities were significantly higher than that of UO2 indicating that composites of UO2-UBx would have increased thermal conductivities.•The bulk, shear and Young’s moduli were measured and the results indicate good mechanical integrity for both materials.
Uranium dioxide (UO2) pellets with controlled microstructures were densified up to 93.4% of their theoretical density in less than 25 minutes at a furnace temperature of 873 K, utilizing controlled ...current-rate alternating current (AC) flash sintering (FS). Using this AC-FS method it was possible to control the sintering rate and thermal gradients, resulting in dense pellets with no appreciable hourglassing and good mechanical integrity. Moreover, the apparent sintering activation energy for FS and for conventionally sintered samples was estimated to be 108 kJ mol−1 and 380 kJ mol−1, respectively using the master sintering curve method. The apparent activation energy for FS was remarkably close to those reported in the literature for spark plasma sintering of UO2. Both these field assisted sintering methods utilize fast heating rates and electrical effects that are likely enhancing the grain boundary diffusion mechanism. Finally controlled current-rate AC-FS has been demonstrated as a technological advancement, capable of producing ceramic nuclear fuels in a fraction of the conventional processing time.
•U3Si2 and U3Si5 single crystals were grown using the Czochralski method.•A reference condition for high quality single crystals was established.•Near phase-pure crystals 35 mm in length with limited ...cracking were produced.
Single crystals of U3Si2 and U3Si5 were grown using the modified Czochralski tri-arc growth technique in a gettered argon atmosphere. A variety of growth parameters including seed pull rate, seed rotation rate, crystal size, charge size and stoichiometry were evaluated to determine the best growth conditions in an effort to produce high quality single crystals for property measurements and basic studies. The crystals were characterized for quality, phase purity, density, and axial variations in chemistry. Near phase-pure, single crystals 5 mm in diameter and 35 mm in length were grown with minimal variation in stoichiometry and limited cracking using a crystal rotation rate of 30 rpm, a hearth rotation rate of 22 rpm, and a pull rate of 16 mm/h up to solidified fraction of g = 0.75.
•Machine learning models for scintillator performance require self-consistent data.•High-throughput screening needs a universal preparation technique.•Multi-component aluminate garnets were ...synthesized by quenching of the melt.•Structural and luminescence properties of powder samples were evaluated.•A simplified model was developed for interpretation of radioluminescence intensity.
Quenching from the melt using an Optical Floating Zone furnace was investigated as a possible high-throughput preparation method in order to screen novel scintillating materials. To validate this method, polycrystalline rare-earth aluminum garnets and yttrium gallium aluminum garnets were synthesized and characterized by X-ray diffraction, photoluminescence and radioluminescence emission spectra as well as radioluminescence imaging and compared to the previously reported properties of those materials. In order to achieve rapid, but quantitative comparison of the materials, pellets fabricated from the synthesized powders were sintered; two different sintering conditions were investigated and compared. A simplistic energy deposition and light absorption model for brightness of opaque samples under X-ray irradiation was developed to estimate the relative scintillation efficiency of the materials. Based on the results, Y3Al5O12, LuY2Al5O12 and GdY2Al5O12 seem to have the highest scintillation efficiency among the prepared samples.
Although the effects of the interleukin 13 (IL-13) on goblet cell (GC) hyperplasia have been studied in the gut and respiratory tracts, its effect on regulating conjunctival GC has not been explored. ...The purpose of this study was to determine the major IL-13-producing cell type and the role of IL-13 in GC homeostasis in normal murine conjunctiva. Using isolating techniques, we identified natural killer (NK)/natural killer T (NKT) cells as the main producers of IL-13. We also observed that IL-13 knockout (KO) and signal transducer and activator of transcription 6 knockout (STAT6KO) mice had a lower number of periodic acid Schiff (PAS)+GCs. We observed that desiccating stress (DS) decreases NK population, GCs, and IL-13, whereas it increases interferon-γ (IFN-γ) mRNA in conjunctiva. Cyclosporine A treatment during DS maintained the number of NK/NKT cells in the conjunctiva, increased IL-13 mRNA in NK+ cells, and decreased IFN-γ and IL-17A mRNA transcripts in NK+ and NK- populations. C57BL/6 mice chronically depleted of NK/NKT cells, as well as NKT cell-deficient RAG1KO and CD1dKO mice, had fewer filled GCs than their wild-type counterparts. NK depletion in CD1dKO mice had no further effect on the number of PAS+ cells. Taken together, these findings indicate that NKT cells are major sources of IL-13 in the conjunctival mucosa that regulates GC homeostasis.
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