A5056152156- High-pressure geophysics and materials
- Nuclear Materials and Properties
- Rare-earth and actinide compounds
- Advanced Condensed Matter Physics
- Thermodynamic and Structural Properties of Metals and Alloys
- Thermal properties of materials
- Magnetic and transport properties of perovskites and related materials
- Advanced Thermoelectric Materials and Devices
- Solid-state spectroscopy and crystallography
- Shape Memory Alloy Transformations
- Radioactive element chemistry and processing
- Acoustic Wave Resonator Technologies
- Nonlinear Photonic Systems
- Ferroelectric and Piezoelectric Materials
- Nuclear reactor physics and engineering
- Nuclear Physics and Applications
- Physics of Superconductivity and Magnetism
- Crystal Structures and Properties
- Advanced Fiber Laser Technologies
- Topological Materials and Phenomena
- Nuclear materials and radiation effects
- 2D Materials and Applications
- Quantum, superfluid, helium dynamics
- Organic and Molecular Conductors Research
- Transition Metal Oxide Nanomaterials
Oak Ridge National Laboratory
2016-2025
Idaho National Laboratory
2022
Iowa State University
2020
Ames National Laboratory
2020
Lawrence Livermore National Laboratory
2008-2012
Beijing Research Institute of Uranium Geology
2012
Dioxide Materials (United States)
2012
Lawrence Livermore National Security
2011
Los Alamos National Laboratory
2001-2009
University of California, Davis
2006-2008
Neutrons spot magnetic fluctuations that propel charges in a novel class of paramagnetic thermoelectrics.
Polar nanoregion vibrations control the ultrahigh piezoelectric response of relaxor-based ferroelectrics used in applications.
The physics of heat conduction puts practical limits on many technological fields such as energy production, storage, and conversion. It is now widely appreciated that the phonon-gas model does not describe full vibrational spectrum in amorphous materials, since this picture likely breaks down at higher frequencies. A two-channel model, which uses harmonic states lattice dynamics a basis, has recently been shown to capture both crystal-like (phonon-gas channel) amorphous-like (diffuson...
Inelastic neutron measurements of the high-temperature lattice excitations in NaI show that thermal equilibrium at 555 K an intrinsic mode, localized three dimensions, occurs a single frequency near center spectral phonon gap, polarized along [111]. At higher temperatures mode gains intensity. Higher energy inelastic and x-ray scattering on room-temperature crystal indicate creation ground state is 299 meV.
Phonon dispersion curves were obtained from inelastic x-ray and neutron scattering measurements on $\ensuremath{\alpha}$-uranium single crystals at temperatures 298 to 573 K. Both showed a softening an abrupt loss of intensity in the longitudinal optic branch along $[00\ensuremath{\zeta}]$ above 450 Above same temperature new dynamical mode comparable emerges $[01\ensuremath{\zeta}]$ zone boundary with energy near top phonon spectrum. The forms without structural transition but coincides...
Measurements of the phonon density states by inelastic neutron time-of-flight scattering and specific-heat measurements along with first-principles calculations, provide compelling evidence for existence an Einstein oscillator (rattler) at ${\ensuremath{\omega}}_{E1}\ensuremath{\approx}5.0\text{ }\text{meV}$ in filled skutterudite ${\text{Yb}}_{0.2}{\text{Co}}_{4}{\text{Sb}}_{12}$. Multiple dispersionless modes measured ${\text{Yb}}_{0.2}{\text{Co}}_{4}{\text{Sb}}_{12}$ intermediate transfer...
Lead chalcogenides have exceptional thermoelectric properties and intriguing anharmonic lattice dynamics underlying their low thermal conductivities. An ideal material for efficiency is the phonon glass-electron crystal, which drives research on strategies to scatter or localize phonons while minimally disrupting electronic-transport. Anharmonicity can potentially do both, even in perfect crystals, simulations suggest that PbSe enough support intrinsic localized modes halt transport. Here,...
Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions crystalline imperfections leads to a non-monotonic trend with temperature. Defect-free crystals that exhibit glassy low monotonic increase temperature are desirable because they intrinsically thermally insulating while retaining useful...
High-entropy oxides (HEOs) have aroused growing interest due to fundamental questions relating their structure formation, phase stability, and the interplay between configurational disorder physical chemical properties. Introducing Fe(II) Mn(II) into a rocksalt HEO is considered challenging, as theoretical analysis suggests that they are unstable in this under ambient conditions. Here, we develop bottom-up method for synthesizing Mn- Fe-containing (FeO-HEO). We present comprehensive...
It is shown that structural disorder-in the form of anisotropic, picoscale atomic displacements-modulates refractive index tensor and results in giant optical anisotropy observed BaTiS
Intrinsic localized modes (ILMs) - also known as discrete breathers are excitations that form without structural defects in nonlinear lattices. For crystals thermal equilibrium ILMs were proposed to randomly, an idea used interpret temperature activated signatures of α-U and NaI. Here, however, we report neutron scattering measurements lattice vibrations NaI provide evidence underlying organization: (i) with small changes move a unit back-and-forth between [111] [011] orientations, (ii) when...
The antiferromagnetic semiconductor MnTe has recently attracted attention for spintronics and high-performance thermoelectric applications. However, little is known about its vibrational thermal transport properties how these might relate to the electronic magnetic structure, particularly as related $3d$ Mn orbital correlations. Here, we calculate a physically justified Coulomb correlation parameter within $\mathrm{DFT}+U$ framework. We couple this framework with Heisenberg Hamiltonian...
Computing thermal transport from first-principles in ${\mathrm{UO}}_{2}$ is complicated due to the challenges associated with Mott physics. Here, we use irreducible derivative approaches compute cubic and quartic phonon interactions first principles, perform enhanced computations by evaluating Green's function via self-consistent diagrammatic perturbation theory. Our predicted lifetimes at $T=600\text{ }\text{ }\mathrm{K}$ agree well our inelastic neutron scattering measurements across...
We investigate and compare the electronic structure of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>OsO</a:mi><a:mn>2</a:mn></a:msub></a:math> with extensively studied <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:msub><b:mi>RuO</b:mi><b:mn>2</b:mn></b:msub></b:math>. Calculations show that <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi>OsO</c:mi><c:mn>2</c:mn></c:msub></c:math> exhibits antiferromagnetism spin splitting driven by crystal...
<title>Abstract</title> We provide experimental evidence for the absence of a magnetic moment in bulk RuO2, candidate altermagnetic material, by using combination Mössbauer spectroscopy, nuclear forward scattering, inelastic X-ray and neutron density functional theory calculations. Using complementary scattering we determine 99Ru hyperfine splitting to be negligible. Inelastic derived lattice dynamics RuO2 are compared calculations varying flavors. Comparisons among with experiments indicate...
Phonon density-of-states curves were obtained from inelastic neutron scattering spectra the three crystalline phases of uranium at temperatures 50 to 1213 K. The alpha-phase showed an unusually large thermal softening phonon frequencies. Analysis vibrational power spectrum that this originates with a harmonic solid, as opposed vibrations in anharmonic potentials. It follows excitations electronic states are more significant thermodynamically than classical volume effects. For alpha-beta and...
A three-dimensional molecular-dynamics model of Pt3Al with L12 order was developed and found to support the excitation discrete breathers (DBs) energy localization on Al sublattice. For an initial lattice temperature 0 K, large-amplitude DBs polarized along [100] are be very weakly damped, retaining most their for more than 1000 cycles, while [111] damped out over ∼15 cycles. Because dissipation channels confined sublattice, long-lived nonequilibrium states large differences between Pt...
We experimentally investigate the symmetry in Hidden Order (HO) phase of intermetallic URu2Si2 by mapping lattice and magnetic excitations via inelastic neutron x-ray scattering measurements HO high-temperature paramagnetic phases. At all temperatures respect zone edges body-centered tetragonal phase, showing no signs reduced spatial symmetry, even phase. The originate from transitions between hybridized bands track Fermi surface, whose feature are corroborated phonon measurements. Due to a...
CHESS, chopper spectrometer examining small samples, is a planned direct geometry neutron designed to detect and analyze weak signals intrinsic cross sections (e.g., mass, magnetic moments, or absorbing materials) in powders, liquids, crystals. CHESS optimized enable transformative investigations of quantum materials, spin thermoelectrics, battery liquids. The broad dynamic range the instrument also well suited study relaxation processes excitations soft biological matter. 15 Hz repetition...