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Söderlind, P.

Publications and source records attributed to Söderlind, P..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Improving equations of state calibrations in the toroidal DAC—The case study of molybdenum

We report an updated isothermal equation of state (EoS) of molybdenum (Mo) obtained by compression in beveled and toroidal diamond-anvil cells (DACs). For an improved compression environment, we developed a copper (Cu) pressure-transmitting medium (PTM) for the toroidal diamond-anvil cell samples, as it is a soft metal compared to Mo with a well calibrated EoS. A Ne PTM was used for the conventional beveled DAC samples. The unit-cell volumes of Mo were measured to 336(1) GPa in the Cu PTM and 231.2(6) GPa in the Ne PTM at room temperature. We additionally calculated elastic stiffness and compliance constants and evaluated the uniaxial stress of Mo and Cu with pressure. A new EoS for Mo is presented from data collected in all sample environments and compared to our theoretical predictions as well as previous compression studies of Mo. The (200) lattice plane of Mo produced the lowest volumes across the pressure range of this study for all compression environments, suggesting that it is less affected by nonhydrostatic stresses in the DAC compared to the other observed diffraction planes. The presented Mo EoS is compatible with extrapolations of EoS fits of Mo in helium (He) within ~1% at 330 GPa. Results from this work demonstrate that compressing a sample in a softer metal in the toroidal DAC can improve the compression environment and result in measured sample volumes comparable to those collected in noble-gas media at multi-megabar conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Ramp compression of tantalum to multiterapascal pressures: Constraints of the thermal equation of state to 2.3 TPa and 5000 K

We report measurements of the compressibility of ramp compressed tantalum to a final stress of 2.3 TPa corresponding to threefold volumetric compression. Using these data, we extended the experimental constraint on the Ta cold compression curve by an order of magnitude in pressure. Furthermore, by combining the resulting data with previous measurements of shock compression and ambient pressure heating, we construct an experimentally bounded and thermodynamically consistent equation of state model for Ta which has 2% uncertainty in pressure at 1 TPa. We therefore propose Ta as an in situ pressure scale for laser-heated static compression experiments which were recently able to reach terapascal pressures and thousands of degrees Kelvin. Our new equation of state of Ta is experimentally constrained at extreme pressures and temperatures relevant to a wide range of planetary interiors and will allow for more accurate comparison between experimental measurements and theory at extreme conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

High pressure stability of β-Zr: no evidence for isostructural phase transitions

Isostructural transitions have been reported to occur in several pure elements; however, most of these have been disproven. Zr is one of those elements which remains controversial with two reports of an isostructural bcc-to-bcc transition at ~56–60 GPa at an ambient temperature and a more recent report proposing a second bcc-to-bcc transition at 110 GPa. Here, we report a detailed experimental and theoretical study of zirconium in the pressure region of the proposed isostructural transition(s). We conducted three room temperature static compression experiments using Ne as a pressure transmitting medium up to 80 GPa. We see no evidence for an isostructural transition finding a smooth compression curve for β-Zr. We determined the theoretical volume, elastic parameters, and Poisson’s ratio for β-Zr up to 717 GPa and no obvious anomalies are identified. Furthermore, our new results join the growing body of evidence that does not find evidence of isostructural transitions in β-Zr.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The ultrahigh pressure stability of silver: An experimental and theoretical study

We measured the atomic volume of Ag in a toroidal diamond anvil cell to a maximum pressure of 416 GPa and calculated the atomic volume and elastic constants of Ag up to 750 and 460 GPa, respectively. Our density functional theory calculations at 0 K utilize an all-electron fully relativistic method and agree well with our volume measurements, particularly at pressures above ~75 GPa. In this work, we corrected our experimental results for non-hydrostaticity using a line shift analysis, and the resulting Vinet equation of state (EOS) parameters are reported. We find that the uniaxial stress sustained by Ag increases linearly up to 4.5 GPa at a pressure of 416 GPa. Our experimental results indicate that the fcc structure of Ag remains stable to at least 416 GPa at room temperature. Our theoretical results show that C44 increases as pressure increases and reaches a maximum at ~100 GPa above which it begins to decrease, a sign that the fcc structure of Ag is becoming unstable, and at V/V 0 = 0.30, the bcc structure is lower in energy than fcc.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Phonon dispersion of Mo-stabilized γ -U measured using inelastic x-ray scattering

We have measured the room-temperature phonon spectrum of Mo-stabilized γ–U. The dispersion curves show unusual softening near the H point, q = [1/2,1/2,1/2], which may derive from the metastability of the γ–U phase or from strong electron-phonon coupling. Near the zone center, the dispersion curves agree well with theory, though significant differences are observed away from the zone center. The experimental phonon density of states is shifted to higher energy compared to theory and high-temperature neutron scattering. As a result, the elastic constants of γ-UMo are similar to those of body-centered cubic elemental metals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Pressure-dependent intermediate valence behavior in YbNiGa 4 and YbNiIn 4

We report here a comprehensive structural and valence study of the intermediate valent materials ${\mathrm{YbNiGa}}_{4}$ and ${\mathrm{YbNiIn}}_{4}$ under pressures up to 60 GPa. ${\mathrm{YbNiGa}}_{4}$ undergoes a smooth volume contraction and shows steady increase in Yb valence with pressure, though the Yb valence reaches saturation around 25 GPa. In ${\mathrm{YbNiIn}}_{4}$, a change in pressure dependence of the volume and a peak in Yb valence suggest that a pressure-induced electronic topological transition occurs around 10-14 GPa. In the pressure region where ${\mathrm{YbNiIn}}_{4}$ and ${\mathrm{YbNiGa}}_{4}$ possess similar Yb-Yb spacings, the Yb valence reveals a precipitous drop. This drop is not captured by density functional theory calculations and implies that both the lattice degrees of freedom and the chemical environment play an important role in establishing the valence of Yb.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗