A5060789828- Nuclear materials and radiation effects
- Advanced Condensed Matter Physics
- Nuclear Materials and Properties
- Radioactive element chemistry and processing
- Electronic and Structural Properties of Oxides
- High-pressure geophysics and materials
- Nuclear and radioactivity studies
- Geological and Geochemical Analysis
- Luminescence Properties of Advanced Materials
- Radioactive contamination and transfer
- Ion-surface interactions and analysis
- Guidance and Control Systems
- High-Temperature Coating Behaviors
- Risk Perception and Management
- High Entropy Alloys Studies
- Nuclear Issues and Defense
- Solid State Laser Technologies
- Gas Dynamics and Kinetic Theory
- Advanced ceramic materials synthesis
- Ferroelectric and Piezoelectric Materials
- Laser-Plasma Interactions and Diagnostics
- Metal and Thin Film Mechanics
- MXene and MAX Phase Materials
- Nuclear reactor physics and engineering
- Semiconductor materials and devices
Stanford University
2016-2025
Center for Strategic and International Studies
2016-2025
Stanford Medicine
2016-2021
Harvard University
2019-2021
Union of Concerned Scientists
2020
Peking University
2020
University of Michigan–Ann Arbor
2012-2016
Abstract High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design materials with properties superior to those conventional alloys. However, their phase space remains constrained, transition metal high-entropy alloys exhibiting only face- body-centered cubic structures. Here, we report high-pressure synthesis hexagonal close-packed prototypical alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed...
Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance fission-based energy systems. As advanced nuclear fuels wasteforms are developed, fundamental understanding processes controlling damage accumulation is necessary. Here we report oxidation state reduction analogue elements caused by high-energy, heavy ion irradiation demonstrate coupling this redox behaviour with structural modifications. ThO2, which...
Atomic disordering in materials alters their physical and chemical properties can subsequently affect performance. In complex ceramic materials, it is a challenge to understand the nature of structural disordering, due difficulty direct, atomic-scale experimental observations. Here we report direct imaging ion irradiation-induced antisite defects Mn+1AXn phases using double CS-corrected scanning transmission electron microscopy provide compelling evidence order-to-disorder phase...
${A}_{2}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{O}}_{7}$ $(A=\mathrm{Nd},\text{Sm},\text{Gd},\text{Er},\text{Yb},\text{and Y})$ materials with the pyrochlore structure were irradiated 2.2 GeV Au ions to systematically investigate disordering of this system in response dense electronic excitation. Structural modifications characterized, over multiple length scales, by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. Transformations amorphous disordered phases observed,...
Complex oxides with the pyrochlore (A2B2O7) and defect-fluorite ((A,B)4O7) structure-types undergo structural transformations under high-pressure. Rare-earth hafnates (A2Hf2O7) form structure for A = La-Tb Dy-Lu. High-pressure in A2Hf2O7 (A Sm, Eu, Gd) Dy, Y, Yb) were investigated up to ~50 GPa characterized by situ Raman spectroscopy synchrotron x-ray diffraction (XRD). spectra at ambient pressure revealed that all compositions, including defect-fluorites, have some pyrochlore-type...
Mn+1AXn phases exhibit unique laminated atomic structures that result in properties typical of both ceramics and metals. Due to their unusual characteristics, these materials have been proposed for use a wide variety industrial applications, including nuclear reactors—both fission fusion systems—where they will be exposed extreme irradiation conditions high temperatures. Recently, numerous studies investigated radiation effects on the phases, revealing complex behavior—phase transformations,...
This paper analyzes hypersonic cruise missiles (HCMs) powered by hydrocarbon-fueled scramjets and compares their capabilities to other systems that might perform the same missions, including boost-glide vehicles (BGVs) maneuverable reentry (MaRVs). Most analysis of weapon has focused on BGVs, while HCMs are a distinct technology with characteristics. We analytically model X-51A HCM vehicle United States flight tested in 2010–13 use as basis for assessing potential performance near-term...
The United States possesses a large stockpile of excess weapons plutonium. Following failed attempt to bilaterally dispose this material under an arms control agreement with Russia, the now plans bury it at Waste Isolation Pilot Plant (WIPP), geologic repository in southeastern New Mexico. This is new mission for WIPP, which was originally designed store radioactive wastes from nuclear production, not It raises questions about whether can safely contain plutonium thousands years remains...
Diverse, multi-stage phase transformations occur in many materials under extreme environments. In response to irradiation, some MAX compositions transform from an initial hexagonal structure intermediate γ-phase, then a face-centered cubic (fcc) structure, while others instead become amorphous. To date, no comprehensive description of the associated transformation mechanisms, or influence composition on this behavior, has been reported. work, we combine situ ion Transmission electron...
Phase transformations induced in the cubic C-type lanthanide sesquioxides, ${\mathrm{Ln}}_{2}{\mathrm{O}}_{3}$ (Ln = Sm, Gd, Ho, Tm, and Lu), by dense electronic excitation are investigated. The structural modifications resulting from exposure to beams of 185 MeV Xe 2246 Au ions characterized using synchrotron x-ray diffraction Raman spectroscopy. formation a B-type polymorph, an X-type nonequilibrium phase, amorphous phase observed. specific formed transformation rate show dependence on...
Cerium dioxide (CeO2) exhibits complex behavior when irradiated with swift heavy ions. Modifications to this material originate from the production of atomic-scale defects, which accumulate and induce changes microstructure, chemistry, properties. As such, characterizing its radiation response requires a wide range complementary characterization techniques elucidate defect formation stability over multiple length scales, such as X-ray neutron scattering, optical spectroscopy, electron...
Neutron total scattering is applied to investigate effects of ion irradiation, which a promising means for improving oxygen conductivity.
China has dominated the global production of rare-earth elements (REE) since 1990s. This market dominance is often described as a Chinese victory over competitors—particularly US—in geopolitical contest, REEs are critical components numerous advanced technologies, including military systems, that great powers compete to control. However, this explanation for recent trends in REE fails account domestic factors—technical, economic, political, and environmental—that significantly impact...