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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Pressure dependence of the melting temperature of solids - Rare-gas solids

A method presented by Schlosser et al. (1989) for analyzing the pressure dependence of experimental melting-temperature data is applied to rare-gas solids. The plots of the logarithm of the reduced melting temperature vs that of the reduced pressure are straight lines in the absence of phase transitions. The plots of the reduced melting temperatures for Ar, Kr, and Xe are shown to be approximately straight lines.

Schlosser, Herbert↗
DOE OSTI2016

A first principle study of the pressure dependent elastic properties of monazite LaPO{sub 4}

DFT based ab-initio simulations have been performed to study the effect of pressure on the elastic properties of monazite LaPO{sub 4} which is a promising host material for immobilization of high level nuclear waste. The phase is found to be stable up to 30 GPa. The calculated polycrystalline bulk, shear and Young moduli show an increasing trend as a function of pressure. The ductility and anisotropy in shear modulus of the material have been found to increase with pressure; whilethe bulk modulus anisotropy decreases with pressure.

36 MATERIALS SCIENCE↗
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↗
DOE OSTI2015

Investigation of the pressure dependent thermodynamic and elastic properties of 1,3,5-triamino-2,4,6-trinitrobenzene using dispersion corrected density functional theory

The influence of pressure on the thermodynamic, structural, and elastic properties of the 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) molecular crystal at T = 0 is systematically studied. Calculations are carried out using density functional theory methods in a plane wave basis set with dispersion corrections for the exchange-correlation part of total energy, and ultrasoft pseudopotentials. The equilibrium unit cell parameters, the cold compression curve in the pressure range of 0–50 GPa and the sound speeds are computed. The effect of finite pressure on the molecular structure of TATB is elucidated from the analysis of relative changes in the intra- and intermolecular geometrical parameters. For the first time, the full set of elastic constants of this crystal at zero and non-zero pressures is determined from ab initio calculations. The resulted structural, elastic, and acoustic properties of TATB are shown to be in a good agreement with available experimental and theoretical data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Pressure dependence of electronic properties of BaI{sub 2}

We present Density Functional Theoretical (DFT) calculations of the electronic properties of scintillator material BaI{sub 2} under pressure which were carried out using Perdew-Burke-Ernzerhof genralized gradient approximation. We found that BaI{sub 2} is a direct band gap material with band gap calculated as 3.35 eV. The pressure effect on BaI{sub 2} indicates a linear monotonously decreasing band gap and increasing valence band width with pressure. We have observed the shifting of band extrema from the Γ point with pressure. The pressure coefficient of band gap is found to be −0.047 eV/GPa. The interatomic ionicity factor of BaI{sub 2} is found to be 0.51. Trends in bonding and ionicity under pressure are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pressure-dependent rate constants for PAH growth: formation of indene and its conversion to naphthalene

Unraveling the mechanisms for growth of polycyclic aromatic hydrocarbons (PAHs) requires accurate temperature- and pressure-dependent rate coefficients for a great variety of feasible pathways. Even the pathways for the formation of the simplest PAHs, indene and naphthalene, are fairly complex. These pathways provide important prototypes for modeling larger PAH growth. In this work we employ the ab initio RRKM theory-based master equation approach to predict the rate constants involved in the formation of indene and its conversion to naphthalene. The reactions eventually leading to indene involve C9Hx (x = 8–11) potential energy surfaces (PESs) and include C6H5 + C3H4 (allene and propyne), C6H6 + C3H3, benzyl + C2H2, C6H5 + C3H6, C6H6 + C3H5 and C6H5 + C3H5. These predictions allow us to make a number of valuable observations on the role of various mechanisms. For instance, we demonstrate that reactions which can significantly contribute to the formation of indene include phenyl + allene and H-assisted isomerization to indene of its major product, 3-phenylpropyne, benzyl + acetylene, and the reactions of the phenyl radical with propene and the allyl radical, both proceeding via the 3-phenylpropene intermediate. 3-Phenylpropene can be activated to a 1-phenylallyl radical, which in turn rapidly decomposes to indene. Next, indene can be converted to benzofulvene or naphthalene under typical combustion conditions, via its activation by H atom abstraction and methyl substitution on the five-membered ring followed by isomerization and decomposition of the resulting 1-methylindenyl radical, C10H9 → C10H8 + H. Alternatively, the same region of the C10H9 PES can be accessed through the reaction of benzyl with propargyl, C7H7 + C3H3 → C10H10 → C10H9 + H, which therefore can also contribute to the formation of benzofulvene or naphthalene. Benzofulvene easily transforms to naphthalene by H-assisted isomerization. An analysis of the effect of pressure on the reaction outcome and relative product yields is given, and modified Arrhenius fits of the rate constants are reported for the majority of the considered reactions. Ultimately, the implementation of such expressions in detailed kinetic models will help quantify the role of these reactions for PAH growth in various environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

On the propagation of a quasi-static disturbance in a heterogeneous, deformable, and porous medium with pressure-dependent properties

Using an asymptotic technique, valid when the medium properties are smoothly-varying, I derive a semi-analytic expression for the propagation velocity of a quasi-static disturbance traveling within a nonlinear-elastic porous medium. The phase, a function related to the propagation time, depends upon the properties of the medium, including the pressure-sensitivities of the medium parameters, and on pressure and displacement amplitude changes. Thus, the propagation velocity of a disturbance depends upon its amplitude, as might be expected for a nonlinear process. As a check, the expression for the phase function is evaluated for a poroelastic medium, when the material properties do not depend upon the fluid pressure. In that case, the travel time estimates agree with conventional analytic estimates, and with values calculated using a numerical simulator. For a medium with pressure-dependent permeability I find general agreement between the semi-analytic estimates and estimates from a numerical simulation. In this case the pressure amplitude changes are obtained from the numerical simulator.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Pressure Dependence of Creep in Forsterite Olivine: Comparison of Measurements From the D-DIA and Griggs Apparatus

We present measurements of the creep strength of forsterite olivine at 1200°C from 1 to 7.5 GPa made using a Griggs apparatus at low pressures and a D-DIA apparatus at high pressures. The same starting material is used for all experiments allowing us to compare measurements made with the two instruments. We find that results from the two apparatus are comparable if the stress measurements made from the alumina piston in the D-DIA experiments are used as a proxy for the load that the olivine sample supports. The reproducibility of the D-DIA experiments are improved if microstructural observations of the post experimental integrity of the sample and piston are used to judge experimental validity. Interpretation of the joint dataset indicate that the pressure dependence of creep (ΔV*) for our sample material cannot be described by a constant value over this pressure range, but changes from ~15 cm 3 /mol at low pressure to closer to ~4 cm 3 /mol at high pressure. These results are consistent with changes in the mix of deformation mechanisms operating in forsterite as pressure increases.

58 GEOSCIENCES↗
DOE OSTI2017

Pressure-Dependent Light Emission of Charged and Neutral Excitons in Monolayer MoSe 2

Tailoring the excitonic properties in two-dimensional monolayer transition metal dichalcogenides (TMDs) through strain engineering is an effective means to explore their potential applications in optoelectronics and nanoelectronics. Here we report pressure-tuned photon emission of trions and excitons in monolayer MoSe 2 via a diamond anvil cell (DAC) through photoluminescence measurements and theoretical calculations. Under quasi-hydrostatic compressive strain, our results show neutral (X 0 ) and charged (X – ) exciton emission of monolayer MoSe 2 can be effectively tuned by alcohol mixture vs inert argon pressure transmitting media (PTM). During this process, X – emission undergoes a continuous blue shift until reaching saturation, while X 0 emission turns up splitting. Furthermore, the pressure-dependent charging effect observed in alcohol mixture PTM results in the increase of the X – exciton component and facilitates the pressure-tuned emission of X – excitons. This substantial tunability of X – and X 0 excitons in MoSe 2 can be extended to other 2D TMDs, which holds potential for developing strained and optical sensing devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pressure dependence of carbonate exchange with [NpO 2 (CO 3 ) 3 ] 4– in aqueous solutions

Here, the rates of ligand exchange into the geochemically important [NpO 2 (CO 3 ) 3 ] 4– aqueous complex are measured as a function of pressure in order to complement existing data on the isostructural [UO 2 (CO 3 ) 3 ] 4– complex. Experiments are conducted at pH conditions where the rate of exchange is independent of the proton concentration. Unexpectedly, the experiments show a distinct difference in the pressure dependencies of rates of exchange for the uranyl and neptunyl complexes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Evaluating the pressure dependence of PZT structures using a virtual reality environment

Pb–Zr–Ti–O (PZT) perovskites span a large solid-solution range and have found widespread use due to their piezoelectric and ferroelectric properties that also span a large range. Crystal structure analysis via Rietveld refinement facilitates materials analysis via the extraction of the structural parameters. These parameters, often obtained as a function of an additional dimension (e.g., pressure), can help to diagnose materials response within a use environment. Often referred to as “ in-situ ” studies, these experiments provide an abundance of data. Viewing structural changes due to applied pressure conditions can give much-needed insight into materials performance. However, challenges exist for viewing/presenting results when the details are inherently three-dimensional (3D) in nature. For PZT perovskites, the use of polyhedra (e.g., Zr/Ti–O 6 octahedra) to view bonding/connectivity is beneficial; however, the visualization of the octahedra behavior with pressure dependence is less easily demonstrated due to the complexity of the added pressure dimension. We present a more intuitive visualization by projecting structural data into virtual reality (VR). We employ previously published structural data for Pb 0.99 (Zr 0.95 Ti 0.05 ) 0.98 Nb 0.02 O 3 as an exemplar for VR visualization of the PZT R3c crystal structure between ambient and 0.62 GPa pressure. This is accomplished via our in-house CAD2VR™ software platform and the new CrystalVR plugin. The use of the VR environment enables a more intuitive viewing experience, while enabling on-the-fly evaluation of crystal data, to form a detailed and comprehensive understanding of in-situ datasets. Discussion of methodology and tools for viewing are given, along with how recording results in video form can enable the viewing experience.

Rodriguez, Mark A. (ORCID:0000000269405044)↗
DOE OSTI2024

Pressure-dependent phase transitions in hybrid improper ferroelectric Ruddlesden-Popper oxides

The temperature-dependent phase transitions in Ruddlesden-Popper oxides with perovskite bilayers have been under increased scrutiny in recent years due to the so-called hybrid improper ferroelectricity that some chemical compositions exhibit. However, little is currently understood about the hydrostatic pressure dependence of these phase transitions. Herein we present the results of a combined high-pressure powder synchrotron x-ray diffraction experiment and a b i n i t i o study on the bilayered Ruddlesden-Popper phases Ca 3 Mn 2 O 7 and Ca 3 Ti 2 O 7 . In both compounds we observe a first-order phase transition, that in combination with our density functional theory calculations, we can confidently assign as being between polar A 2 1 a m and nonpolar A c a a structures. Interestingly, we show that while the application of pressure ultimately favors a nonpolar phase, as is commonly observed for proper ferroelectrics, regions of response exist where pressure actually acts to increase the polar mode amplitudes. The reason for this can be untangled by considering the varied response of octahedral tilts and rotations to hydrostatic pressure and their trilinear coupling with the polar instability. Published by the American Physical Society 2024

Materials Science↗
NASA NTRS1996

Pressure-Dependent Yields and Product Branching Ratios in the Broadband Photolysis of Chlorine Nitrate

The photolysis of chlorine nitrate was studied using broadband flash photolysis coupled with long-path ultraviolet-visible absorption spectroscopy. Branching ratios for the Cl + NO3 and ClO + NO2 product channels were determined from time-dependent measurements of ClO and NO3 concentrations. Yields of the ClO and NO3 products displayed a dependence on the bath gas density and the spectral distribution of the photolysis pulse. Product yields decreased with increasing bath gas density regardless of the spectral distribution of the photolysis pulse; however, the decrease in product yield was much more pronounced when photolysis was limited to longer wavelengths. For photolysis in a quartz cell (lambda > 200 nm) the yield decreased by a factor of 2 over the pressure 10-100 Torr. In a Pyrex cell (lambda > 300 nm), the yield decreased by a factor of 50 over the same pressure range. When photolysis was limited to lambda > 350 nm, the yield decreased by a factor of 250. Branching ratios for the photolysis channels [ClONO2 + h.nu yields ClO + NO2 (1a) and ClONO2 + h.nu yields Cl + NO3 (lb)] were determined from the relative ClO and NO3 product yields at various pressures. Although the absolute product yield displayed a pressure dependence, the branching between the two channels was independent of pressure. The relative branching ratios (assuming negligible contributions from other channels) are 0.61 +/- 0.20 for channel 1a and 0.39 +/- 0.20 for channel lb for photolysis with lambda > 200 nm and 0.44 +/- 0.08 for channel 1a and 0.56 +/- 0.08 for channel 1b for photolysis with lambda > 300 nm. The implications of these results for the chemistry of the lower stratosphere are discussed.

Nickolaisen, Scott L.↗
DOE OSTI2015

Anisotropic H c 2 , thermodynamic and transport measurements, and pressure dependence of T c in K 2 Cr 3 As 3 single crystals

We present a detailed study of single crystalline K 2 Cr 3 As 3 and analyze its thermodynamic and transport properties, anisotropic H c2 (T), and initial pressure dependence of T c . In zero field, the temperature-dependent resistivity is metallic. Deviation from a linear temperature dependence is evident below 100 K and a T 3 dependence is roughly followed from just above T c (~10K) to ~40K. Anisotropic H c2 (T) data were measured up to 140 kOe with field applied along and perpendicular to the rodlike crystals. For the applied field perpendicular to the rod, H c2 (T) is linear with a slope ~–70 kOe/K. For field applied along the rod, the slope is about –120 kOe/K below 70 kOe. Above 70 kOe, the magnitude of the slope decreases to ~–70 kOe/K. The electronic specific heat coefficient γ, just above T c , is 73 mJ/mol K 2 ; the Debye temperature Θ D is 220 K. As a result, the specific heat jump at the superconducting transition ΔC~2.2γT c . Finally, for hydrostatic pressures up to ~7 kbar, T c decreases under pressure linearly at a rate of –0.034K/kbar.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Pressure Dependences of Elastic Constants of AMg6 Aluminum–Magnesium Alloy and n-AMg6/С{sub 60} Nanocomposite Alloy

The ultrasonic study results for dependence of the elastic wave velocities and second-order elasticity coefficients of the polycrystalline aluminum alloy AMg6 and its nanocomposite n-AMg6/C{sub 60} on hydrostatic pressure up to 1.6 GPa have been described. The ultrasonic research has been carried out using a highpressure ultrasonic piezometer based on the piston-cylinder device. The pressure derivatives of the secondorder elastic constants of these materials established in the present study have been compared with the results of the third-order elastic constants measurements of the test alloys using the Thurston–Brugger method. Involving available literature data, we determined the relationships between the pressure derivatives of the second-order elastic constants of the AMg6 alloy and the Mg-content and nanostructuring.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Non-monotonic pressure dependence of the thermal conductivity of boron arsenide

Recent experiments demonstrate that boron arsenide (BAs) is a showcase material to study the role of higher-order four-phonon interactions in affecting heat conduction in semiconductors. Here we use first-principles calculations to identify a phenomenon in BAs and a related material - boron antimonide, that has never been predicted or experimentally observed for any other material: competing responses of three-phonon and four-phonon interactions to pressure rise cause a non-monotonic pressure dependence of thermal conductivity, κ, which first increases similar to most materials and then decreases. The resulting peak in κ shows a strong temperature dependence from rapid strengthening of four-phonon interactions relative to three-phonon processes with temperature. Our results reveal pressure as a knob to tune the interplay between the competing phonon scattering mechanisms in BAs and similar compounds, and provide clear experimental guidelines for observation in a readily accessible measurement regime.

36 MATERIALS SCIENCE↗