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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Electronic and optical properties of crystalline nitrogen versus black phosphorus: A comparative first-principles study

We report crystalline black nitrogen (BN) is an allotrope of nitrogen with the black phosphorus (BP) structure recently synthesized at high pressure by two independent research groups. Here, we present a systematic study of the electronic and optical properties of BN focusing on its comparison with BP. To this end, we use the state-of-the-art quasiparticle self-consistent GW approach with vertex corrections in both the electronic and optical channels. Despite many similarities, the properties of BN are found to be considerably different. Unlike BP, BN exhibits a larger optical gap (2.5 vs 0.26 eV), making BN transparent in the visible spectral region with a highly anisotropic optical response. This difference can be primarily attributed to a considerably reduced dielectric screening in BN, leading to enhancement of the effective Coulomb interaction. Despite relatively strong Coulomb interaction, exciton formation is largely suppressed in both materials. Our analysis of the elastic properties shows exceptionally high stiffness of BN, comparable to that of diamond.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Reporter-Spin-Assisted T 1 Relaxometry

A single-spin quantum sensor can quantitatively detect and image fluctuating electromagnetic fields via their effect on the sensor spin’s relaxation time, thus revealing important information about the target solid-state or molecular structures. However, the sensitivity and spatial resolution of spin relaxometry are often limited by the distance between the sensor and target. Here, we propose an alternative approach that leverages an auxiliary reporter spin in conjunction with a single-spin sensor, a diamond nitrogen-vacancy (N-V) center. We show that this approach can realize a 100-fold measurement sensitivity improvement for realistic working conditions and we experimentally verify the proposed method using a single shallow N-V center. Our work opens up a broad path of inquiry into a range of possible spin systems that can serve as relaxation sensors without the need for optical initialization and readout capabilities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

High-pressure neutron diffraction at ultra-low temperature

Neutron diffraction is a powerful tool in the study of quantum materials and associated emergent phenomena as it allows for direct detection of magnetic structure even at ultra-low temperatures. As pressure can drive systems across quantum critical points and tune emergent behaviors at the quantum scale, coupling neutron diffraction with extreme conditions of high pressure at (ultra-)low temperatures has been a key research target over decades. This has proven challenging as magnetic neutron diffraction typically requires large sample volumes due to flux limitations, whereas high-pressure studies require small sample volumes due to pressure limitations. Combining these two contradictory requirements poses many difficulties, but also brings opportunities in research and development. Here, we address these shortcomings through the use of a diamond anvil cell equipped with polycrystalline anvils with relatively large sample volumes coupled with the high neutron flux made available by the high-pressure diffractometer of the Spallation Neutron Source. This particular diamond anvil cell configuration has previously proven useful for single-crystal samples and is here coupled with the ultra-low temperatures of a dilution refrigerator for the first time. Our study on a single crystal of Yb 2 ⁢O 3 successfully collected magnetic neutron diffraction data at 5.3 GPa below 200 mK inside a dilution refrigerator. We have performed a detailed analysis of the magnetic diffraction data to investigate the magnetic structure under pressure and observed a subtle shift in the transition temperature. This development will open the door for future studies on magnetic materials with these much-desired coupled extremes of high pressure and ultra-low temperatures.

Wu, Yan [Oak Ridge National Laboratory (ORNL), Oak↗
DOE OSTI2020

Pressure-Induced Spectroscopic Changes in a Californium 1D Material Are Twice as Large as Found in the Holmium Analog

Here, in this study, the synthesis, characterization, and pressure response of a 1D californium mellitate (mellitate = 1,2,3,4,5,6-benzenehexacarboxylate) coordination polymer, Cf 2 (mell)(H 2 O) 10 ·4H 2 O (Cf-1), are reported. The Cf–O lengths within the crystal structure are compared to its gadolinium (Gd-1) and holmium (Ho-1) analogs as well. These data show that the average Cf–O bond distance is slightly longer than the average Gd–O bond, consistent with trends in effective ionic radii. UV–vis-NIR absorption spectra as a function of pressure were collected using diamond-anvil techniques for both Cf-1 and Ho-1. These experiments show that the Cf(III) f → f transitions have a stronger dependence on pressure than that of the holmium analog. In the former case, the shift is nearly linear with applied pressure and averages 6.6 cm –1 /GPa, whereas in the latter, it is <3 cm –1 /GPa.

absorption spectroscopy↗
DOE OSTI2021

Strong Correlation Between Superconductivity and Ferromagnetism in an Fe-Chalcogenide Superconductor

The interplay among topology, superconductivity, and magnetism promises to bring a plethora of exotic and unintuitive behaviors in emergent quantum materials. The family of Fe-chalcogenide superconductors FeTe x Se 1–x are directly relevant in this context due to their intrinsic topological band structure, high-temperature superconductivity, and unconventional pairing symmetry. Despite enormous promise and expectation, the local magnetic properties of FeTe x Se 1–x remain largely unexplored, which prevents a comprehensive understanding of their underlying material properties. Exploiting nitrogen vacancy (NV) centers in diamond, here we report nanoscale quantum sensing and imaging of magnetic flux generated by exfoliated FeTe x Se 1–x flakes, demonstrating strong correlation between superconductivity and ferromagnetism in FeTe x Se 1–x . The coexistence of superconductivity and ferromagnetism in an established topological superconductor opens up new opportunities for exploring exotic spin and charge transport phenomena in quantum materials. The demonstrated coupling between NV centers and FeTe x Se 1–x may also find applications in developing hybrid architectures for next-generation, solid-state-based quantum information technologies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Synthesis, Structure, and Electric Conductivity of Higher Hydrides of Ytterbium at High Pressure

While most of the rare-earth metals readily form trihydrides, due to increased stability of the filled 4f electronic shell for Yb(II), only YbH 2.67 , formally corresponding to Yb II (Yb III H 4 ) 2 (or Yb 3 H 8 ), remains the highest hydride of ytterbium. Utilizing the diamond anvil cell methodology and synchrotron powder X-ray diffraction, we have attempted to push this limit further via hydrogenation of metallic Yb and Yb 3 H 8 . Compression of the latter has also been investigated in a neutral pressure-transmitting medium (PTM). While the in situ heating of Yb facilitates the formation of YbH 2+x hydrides, we have not observed clear qualitative differences between the systems compressed in H 2 and He or Ne PTM. In all of these cases, a sequence of phase transitions occurred within ca. 13–18 GPa (P$\bar{31}$m–I4/m phase) and around 27 GPa (to the I4/mmm phase). The molecular volume of the systems compressed in H 2 PTM is ca. 1.5% larger than of those compressed in inert gases, suggesting a small hydrogen uptake. Nevertheless, hydrogenation toward YbH 3 is incomplete, and polyhydrides do not form up to the highest pressure studied here (ca. 75 GPa). As pointed out by electronic transport measurements, the mixed-valence Yb 3 H 8 retains its semiconducting character up to >50 GPa, although the very low remnant activation energy of conduction (<5 meV) suggests that metallization under further compression should be achievable. Finally, we provide a theoretical description of a hypothetical stoichiometric YbH 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structural dynamics of laser-ionized cis-stilbene studied by ultrafast electron diffraction

Stilbene has been a model system for studying photoisomerization upon absorption of a UV photon. Although the dynamics of the first excited state have been investigated in great detail, the structural dynamics of cationic states remains largely experimentally unexplored. In this study, the dynamics following ionization via absorption of two UV photons was captured using ultrafast electron diffraction. cis-stilbene (CS) was optically pumped with 267 nm ultraviolet light with two different pump fluences and probed with 3.7 MeV electrons. We compare our experimental results to ab-initio multiple spawning simulations for single-photon excitation and molecular dynamics simulations for ionization in order to separate the contributions from the two channels. We found that with a fluence of 170 mJ cm −2 both the single and two-photon channels are present, while with higher fluence of 280 mJ cm −2 the two-photon channel dominates. We did not observe isomerization of the CS cation and found the main structural motion a to be a vibration of the phenyl rings about the central C–C bond.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Fabricating Diamond-like Amorphous Carbon

Using a magnetically confined hot hollow cathode PE-CVD, hydrocarbon gas is decomposed under a diluent gas to deposit hydrogenated amorphous carbon onto a sample holder. During the fabrication of the hydrogenated amorphous carbon, the electric potential, electron temperature, and electron density of the plasma are measured with a Langmuir probe. Raman spectroscopy is used to determine the structural and electronic characterization of the final hydrogenated amorphous carbon solid.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

In-situ investigation of the vibrational properties of H 2 O CO 2 -bearing and dry K-rich basaltic glasses at high pressure by mid infrared spectroscopy

Here, the vibrational properties of CO 2 –H 2 O-bearing and dry synthetic K-rich basaltic glasses were investigated at room temperature and pressures between 0.0001–5.5 GPa using the diamond anvil cell combined with in situ reflectance and transmittance Fourier Transform infrared micro-spectroscopy. The absorption coefficient a(v) calculated from the Kramers-Kronig relation shows that glasses are dominated by the Q 2 aluminosilicate unit followed by Q 1 , Q 3 . The variation in Q n concentration upon compression suggests that glasses undergo polymerization from ambient pressure to 2 GPa followed by less marked structural changes up to 4 GPa, above which the structure is further polymerized. Once decompressed, glasses retained a polymerized structure. Our results show that 1.03 wt% CO 2 -1.42 wt% H 2 O in a glass with 3.10 wt% K 2 O and 46.77 wt% SiO 2 prevent the formation of fully polymerized connections when cold-compressed. Our results can be used to explain the effect of volatiles and alkali on the rheology of natural basaltic magmas.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High Pressure Synthesis of Pr 2 O 5 – A Unique Lanthanoid(IV) Oxide Peroxide

Abstract Reacting praseodymium(IV) oxide with oxygen at 27 GPa in a diamond anvil cell yielded the oxide peroxide Pr 2 IV (O 2 )O 3 , which was characterized by single crystal X‐ray diffraction on multi‐grain samples, Raman spectroscopy and quantum theoretical calculations at various pressure points. The presence of tetravalent praseodymium ions is supported by electronic structure calculations, showing a band gap of ca. 1.2 eV, which is consistent with the anticipated chemical model of an ionic solid. Pr 2 (O 2 )O 3 thus far represents the most oxygen rich phase of any binary compound of a lanthanoid and oxygen and is the first example of a peroxide anion next to Pr 4+ . Additionally, these results demonstrate that instead of oxidizing the praseodymium ions past their +IV oxidation state, oxygen undergoes a comproportionation to form peroxide anions. Direct oxidation of the oxide anions by Pr 4+ ‐ions was ruled out by a control experiment in argon instead of oxygen, where no oxidation of oxide ions was observed.

Chemistry↗
DOE OSTI2026

Pressure-Induced Stabilization of Terbium(IV) in CsTb(CrO 4 ) 2 Characterized by X-ray Absorption Spectroscopy

Single crystals of CsTb(CrO 4 ) 2 and CsDy(CrO 4 ) 2 , where the lanthanide metals are in the trivalent state under ambient conditions, have been investigated under high-pressure conditions on the gigapascal scale utilizing a diamond anvil cell. These compounds were characterized by single-crystal X-ray diffraction in addition to high-pressure solid-state UV-vis-NIR spectroscopy, Raman spectroscopy, and Tb L 3 -edge highenergy- resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES). The high-pressure UV-vis-NIR spectra reveal strong broadening of the metal-to-ligand charge transfer band to lower energies, associated with a visible color change from yellow to dark red/black. Clear evidence for the stabilization of Tb 4+ under high pressure is provided by the appearance of a second edge feature characteristic of Tb 4+ , starting at 19.62 GPa in the high-pressure L 3 -edge HERFD-XANES at around 7528 eV. This represents the first example of Tb 4+ being stabilized by high pressure and expands upon the limited chemistry of terbium in the tetravalent state.

Anions↗
DOE OSTI2020

When does turbulence spreading matter?

Few, if any, of the many papers on turbulence spreading address the key question of how turbulence spreading actually affects the profile structure. In this work, we are using a reduced model to answer that question. Turbulence spreading is most relevant near regions where the profiles support a strong intensity gradient ∇I. One such case is at the edge of an L mode ischarge, near a source of turbulence [i.e., either a localized source of edge turbulence or an influx of turbulence from the scrape-off layer (SOL)]. Another is in “No Man’s Land” (NML), which connects the pedestal to the stiff core in H mode. In the case of L mode, without an edge intensity source, the turbulence intensity profile is nearly flat and spreading has a weak effect. An edge localized source increases the edge ∇I, which then drives inward spreading. Invasion of turbulence from the SOL to the edge softens the edge pressure gradient. In H mode, the strong shear suppression of pedestal turbulence necessarily forces a sharp ∇I in NML. This sharp∇I drives a significant flux of turbulence from the core to the pedestal, where it is ultimately dissipated by shearing. Counter-intuitively, the results indicate that spreading actually increases the pedestal height and width and hence the energy content in H mode. This suggests that models of the pedestal structure should include NML turbulence spreading effects. The relation of avalanches to spreading is studied. Spreading weakly affects the avalanche distribution, but the spatiotemporal correlation of intensity increases with spreading.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Combined First-Principles and Experimental Investigation into the Reactivity of Codeposited Chromium–Carbon under Pressure

High-pressure synthesis in the diamond anvil cell suffers from the lack of a general approach for the control of precursor stoichiometry and homogeneity. Here, we present results from a new method we have developed that uses magnetron cosputtering to prepare stoichiometrically precise and atomically mixed amorphous films of Cr:C. Laser-heated diamond anvil cell experiments carried out on a flake of this sample at pressures between 13.5 and 24.3 GPa lead to the observation of Cr 3 C (Pnma) over the entire pressure range–in good agreement with our in-house theoretical predictions–but also reveal two other metastable phases that were not expected: a novel monoclinic chromium carbide phase and the NaCl-type CrC (Fm3̅m) phase. The unexpected stability of CrC is investigated by using first-principles methods, revealing a large stabilizing effect tied to substoichiometry at the carbon site. These results offer an important case study into the current limitations of crystal structure prediction methods with regard to phase complexity and bolster the growing need for advanced theoretical approaches that can more completely survey experimentally unexplored phase space.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

X-Ray Diffraction and Electron Microscopy Studies of the Size Effects on Pressure-Induced Phase Transitions in CdS Nanocrystals

In recent years, investigations of the phase transition behavior of semiconducting nanoparticles under high pressure has attracted increasing attention due to their potential applications in sensors, electronics, and optics. However, current understanding of how the size of nanoparticles influences this pressure-dependent property is somewhat lacking. In particular, phase behaviors of semiconducting CdS nanoparticles under high pressure have not been extensively reported. Therefore, in this work, CdS nanoparticles of different sizes are used as a model system to investigate particle size effects on high-pressure-induced phase transition behaviors. In particular, 7.5, 10.6, and 39.7 nm spherical CdS nanoparticles are synthesized and subjected to controlled high pressures up to 15 GPa in a diamond anvil cell. Analysis of all three nanoparticles using in-situ synchrotron wide-angle X-ray scattering (WAXS) data shows that phase transitions from wurtzite to rocksalt occur at higher pressures than for bulk material. Bulk modulus calculations not only show that the wurtzite CdS nanomaterial is more compressible than rocksalt, but also that the compressibility of CdS nanoparticles depends on their particle size. Furthermore, sintering of spherical nanoparticles into nanorods was observed for the 7.5 nm CdS nanoparticles. Our results provide new insights into the fundamental properties of nanoparticles under high pressure that will inform designs of new nanomaterial structures for emerging applications.

Meng, Lingyao↗
DOE OSTI2022

Ultrahigh-pressure disordered eight-coordinated phase of Mg 2 GeO 4 : Analogue for super-Earth mantles

Mg 2 GeO 4 is important as an analog for the ultrahigh-pressure behavior of Mg 2 SiO 4 , a major component of planetary interiors. In this study, we have investigated magnesium germanate to 275 GPa and over 2,000 K using a laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction and density functional theory (DFT) computations. The experimental results are consistent with the formation of a phase with disordered Mg and Ge, in which germanium adopts eightfold coordination with oxygen: the cubic, Th 3 P 4 -type structure. DFT computations suggest partial Mg-Ge order, resulting in a tetragonal $I\bar{4}2d$ structure indistinguishable from $I\bar{4}3d$ Th 3 P 4 in our experiments. If applicable to silicates, the formation of this highly coordinated and intrinsically disordered phase may have important implications for the interior mineralogy of large, rocky extrasolar planets.

58 GEOSCIENCES↗
DOE OSTI2026

Melting temperature of bismuth to 55 GPa using synchrotron X-ray phase contrast imaging

The melting temperature of elemental bismuth under high pressure has been measured to 55 GPa using synchrotron X-ray phase-contrast imaging in the laser-heated diamond anvil cell. Imaging of solid-liquid interface formation, combined with radiometric temperature and X-ray diffraction measurements, reveals a pronounced reduction in melting boundary slope in Bi-V with pressure. The unusually steep initial slope is attributed to low configurational entropy of melting, arising from structural ordering and coordination matching in the cool liquid, while slope reduction is driven by entropy increase correlated with significant liquid structure changes with rising pressure and temperature. Finally, the data rule out kinetic effects on melting in shock compression experiments and demonstrate the need for improved theoretical phase diagrams.

Materials science↗
DOE OSTI2020

Structure and Behavior of the Ni End-Member Schreibersite Ni 3 P under Compression to 50 GPa

To better understand the potential presence of light element alloys of Fe and Ni in the Earth’s interior, the crystal structure and compressional behavior of the Ni-P binary compound, schreibersite (Ni 3 P), have been investigated using synchrotron X-ray diffraction experiments. Both powder and two single-crystal samples of synthetic Ni 3 P (in different orientations with respect to the loading axis of the diamond anvil cell) were compressed up to approximately 50 GPa at ambient temperature. The compressional data obtained for Ni3P were fitted with a 3rd order Birch–Murnaghan equation of state. All data indicated that the c/a ratio of unit cell parameters remained approximately constant up to about 30 GPa but then increased progressively with pressure, exhibiting a second slight discontinuity at approximately 40 GPa. The changes in unit cell parameters at ~30 GPa and ~40 GPa suggested discontinuous changes in magnetic ordering. Moreover, the threshold of these subtle discontinuities is sensitive to the stress state and orientation of the crystal in the diamond anvil cell. This study is the first report on the compressional behavior of both powder and single-crystal schreibersite at high-pressure (up to 50 GPa). It offers insights into the effects of Ni 3 P components on the compressional behavior of the Earth’s core.

36 MATERIALS SCIENCE↗