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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A Change in the Debye Temperature of a Single-Component Substance upon Amorphization

A method for calculating the Debye temperature of a single-component substance in the amorphous state is proposed based on a nonlinear dependence of first coordination number k{sub n} of the given structure on its packing factor k{sub p} as established previously. Proceeding from previously defined parameters of the Mie–Lennard-Jones potential, the Debye temperatures have been calculated for some pure crystalline and amorphous metals, diamond, silicon, and germanium, which are in good agreement with estimations reported by other researchers. It is shown that a minimum specific Helmholtz free energy is attained at k{sub p} = 0.45556, which means that this packing corresponds to a thermodynamically stable amorphous structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Machine learning the relationship between Debye temperature and superconducting transition temperature

Recently a relationship between the Debye temperature $Θ_D$ and the superconducting transition temperature $T_c$ of conventional superconductors has been proposed [Esterlis et al., npj Quantum Mater. 3, 59 (2018)]. The relationship indicates that $T_c$ ≤ $AΘ_D$ for phonon-mediated BCS superconductors, with $A$ being a prefactor of order ~ $0.1$. In order to verify this bound, we train machine learning (ML) models with 10 330 samples in the Materials Project database to predict $Θ_D$. Here, by applying our ML models to 9860 known superconductors in the NIMS SuperCon database, we find that the conventional superconductors in the database indeed follow the proposed bound. We also perform first-principles phonon calculations for $\mathrm{H_3S}$ and $\mathrm{LaH_{10}}$ at 200 GPa. The calculation results indicate that these high-pressure hydrides essentially saturate the bound of $T_c$ versus $Θ_D$.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Layer-dependent Debye temperature and thermal expansion of Ru(0001) by means of high-energy resolution core-level photoelectron spectroscopy

The layer-dependent Debye temperature of Ru(0001) is determined by means of high-energy resolution core-level photoelectron spectroscopy measurements. The possibility to disentangle three different components in the Ru 3d{sub 5/2} spectrum of Ru(0001), originating from bulk, first-, and second-layer atoms, allowed us to follow the temperature evolution of their photoemission line shapes and binding energies. Temperature effects were detected, namely, a lattice thermal expansion and a layer-dependent phonon broadening, which was interpreted within the framework of the Hedin-Rosengren formalism based on the Debye theory. The resulting Debye temperature of the top-layer atoms is 295{+-}10 K, lower than that of the bulk (T=668{+-}5 K) and second-layer (T=445{+-}10 K) atoms. While these results are in agreement with the expected phonon softening at the surface, we show that a purely harmonic description of the motion of the surface atoms is not valid, since anharmonic effects contribute significantly to the position and line shape of the different core-level components.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The effect of rare-earth substitution on the Debye temperature of inorganic phosphors

In the quest to predict photoluminescent efficiency in rare-earth substituted inorganic phosphors, research has shown that materials consisting of ordered, rigid crystal structures tend to possess the highest photoluminescent quantum yields. A compound's Debye temperature (Θ D ), which can be calculated using ab initio calculations, is an ideal proxy for quantitatively comparing structural rigidity among different inorganic compounds, allowing potentially efficient phosphors to be selected from large crystal structure databases. However, the high computational cost of these calculations limits estimating Θ D for unsubstituted host crystal structures only. It is assumed that the low substitution concentration of the rare-earth luminescent center does not significantly influence a material's Debye temperature. This work evaluates the validity of this approximation by examining the effect of luminescent center substitution on a host structure's Θ D . Two well-known phosphors, (Y 1– x Ce x ) 3 Al 5 O 12 ( x = 0 – 0.05) and Ba 1-δ Eu δ MgAl 10 O 17 (δ = 0 – 0.15), were synthesized with varying rare-earth concentrations, while Θ D was computationally estimated and then determined by ultrasonic pulse-echo speed-of-sound and low-temperature heat capacity measurements. Overall, the ensuing results provide key implications for using Θ D as a proxy for structural rigidity in substituted inorganic compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

On the Calculation of the Debye Temperature and Crystal–Liquid Phase Transition Temperature of a Binary Substitution Alloy

A method of estimating the interatomic pair interaction potential parameters for a binary substitution alloy with consideration for the deviation of its lattice parameter from the Vegard law is proposed. This method is used as a basis to calculate the Debye temperature and Grüneisen parameters of a SiGe alloy. It is shown that all these function nonlinearly variate with a change in the germanium concentration. Based on this technique and Lindemann's melting criterion, a method for calculating the liquidus and solidus temperatures of a disordered substitution alloy is proposed. The method is tested on the SiGe alloy and demonstrates good agreement with experimental data. It is shown that when the size of a nanocrystal of a solid substitution solution decreases, the difference between the liquidus and solidus temperatures decreases the more, the more noticeably the nanocrystal shape is deflected from the most energetically optimal shape.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Debye temperature, thermal expansion, and heat capacity of TcC up to 100 GPa

Highlights: • A number of thermodynamic properties of rocksalt TcC are investigated for the first time. • The quasi-harmonic Debye model is applied to take into account the thermal effect. • The pressure and temperature up to about 100 GPa and 3000 K, respectively. - Abstract: Debye temperature, thermal expansion coefficient, and heat capacity of ideal stoichiometric TcC in the rocksalt structure have been studied systematically by using ab initio plane-wave pseudopotential density functional theory method within the generalized gradient approximation. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of Debye temperature, thermal expansion coefficient, constant-volume heat capacity, and constant-pressure heat capacity on pressure and temperature are successfully predicted. All the thermodynamic properties of TcC with rocksalt phase have been predicted in the entire temperature range from 300 to 3000 K and pressure up to 100 GPa.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Softening versus hardening transition in surface bilayer bonding of bismuth nanofilm

We have found that the surface bilayer of Bi(001) undergoes an unusual reversible transition at 350 K, well below the bulk melting temperature. Surface Debye temperature abruptly decreases without an anharmonic signature and the vertical-to-lateral ratio of surface thermal expansion increases in a critical manner, as revealed by high-resolution diffraction measurement. Because of the metallic-covalent bilayer structure of semimetal Bi, the most feasible explanation for the result is that bond softening occurs between the first and second bilayers at 350 K. This softening transition leads to the simultaneous hardening of the topmost intrabilayer bonds.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1989

Equation Of State With Temperature Effects For Solids

Behavior at high temperature predicted from only four parameters. Equations derived to express thermodynamical properties of compressed solids at high temperatures. New equations based on fundamental considerations of thermodynamics, isothermal equation of state, and assumption thermal pressure independent of volume and varies linearly with temperature near and about Debye temperature. Using only four parameters (three are those of isothermal equation of state), new equations describe thermodynamic behavior of material over range of temperatures from approximately Debye temperature to melting point.

Vinet, Pascal↗
DOE OSTI2014

FP-LAPW investigation of electronic, magnetic, elastic and thermal properties of Fe-doped zirconium nitride

Full Potential- Linear Augmented Plane Wave (FP-LAPW) method has been employed to study the electronic, magnetic, elastic and thermal properties of Fe-doped Zirconium nitride. In this work, Fe-atoms were doped into the super cell of ZrN in doping concentrations of 12.5%, 25% and 37.5% to replace Zr atoms. Electronic properties such as band structure and DOS were plotted and compared for the doped compounds. Charge density contours were plotted for all the doped compounds. The non-magnetic ZrN doped in different Fe concentrations were found to be ferromagnetic. Magnetic moments have been calculated and compared. Elastic properties have been studied and compared with electronic properties. Appearance of magnetic ordering and its influence with the elastic properties have been reported. Impact of 3d states of Fe in DOS plot on the elastic nature of the compounds has been highlighted. Thermal properties such as Debye temperature and molar heat capacities at low temperature have been determined. Debye temperature is found to decrease with higher doping concentrations. Molar heat capacities are found to increase with higher concentrations of Fe atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Single crystal elasticity of natural topaz at high-temperatures

Topaz is an aluminosilicate mineral phase stable in the hydrothermally altered pegmatitic rocks and also in subducted sedimentary lithologies. In nature, topaz often exhibits solid solution between fluorine and hydrous end members. We investigated elasticity of naturally occurring single crystal topaz (Al 2 SiO 4 F 1.42 (OH) 0.58 ) using Resonant Ultrasound Spectroscopy. We also explored the temperature dependence of the full elastic constant tensor. We find that among the various minerals stable in the Al 2 O 3 -SiO 2 -H 2 O ternary system, topaz exhibits moderate elastic anisotropy. As a function of temperature, the sound velocity of topaz decreases with \(\frac{{\boldsymbol{d}}{{\boldsymbol{V}}}_{{\boldsymbol{P}}}}{{\boldsymbol{d}}{\boldsymbol{T}}}\) and \(\frac{{\boldsymbol{d}}{{\boldsymbol{V}}}_{{\boldsymbol{S}}}}{{\boldsymbol{d}}{\boldsymbol{T}}}\) being –3.10 and –2.30 × 10 –4 km/s/K. The elasticity and sound velocity of topaz also vary as a function of OH and F content. The effect of composition ( \({{\boldsymbol{x}}}_{{\boldsymbol{O}}{\boldsymbol{H}}}\) ) on the velocity is equally important as that of the effect of temperature. We also note that the Debye temperature ( \({{\boldsymbol{\Theta }}}_{{\boldsymbol{D}}}\) ) of topaz at room temperature condition is 910 K and decreases at higher temperature. The Debye temperature shows positive correlation with density of the mineral phases in the Al 2 O 3 -SiO 2 -H 2 O ternary system.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The surface stability of Cr 2 O 3 (0 0 0 1)

The surface of chromia (Cr 2 O 3 ) has a surface electronic structure distinct from the bulk and a packing density distinct from the bulk. More than a demarcation between the solid and the vacuum, the surface differs from the bulk of chromia, not just because of a partial occupancy of chromium sites, but also because of an increased number of unoccupied surface oxygen sites (vacancy sites), evident in angle-resolved core level photoemission. In spite of the structural differences that exist at the surface, there is, as yet, no evidence that these complications affect the surface Debye temperature beyond the most simple of assumptions regarding the lower coordination of the surface. Using low-energy electron diffraction (LEED), the effective surface Debye temperature (similar to 490 K) is found to be lower than the bulk (similar to 645 K) Debye temperature of Cr 2 O 3 (0 0 0 1). This surface effective Debye temperature, indicative of vibrations along the surface normal, uncorrected for anharmonic effects, has a value reduced from the effective bulk Debye temperature yet close to the value root 2 expected from a simple mean field argument.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of After-Growth Treatments on the Optical Parameters of Teraherz ZnGeP{sub 2} Crystals

Results of investigations are presented of the THz spectra of the refractive index n(v) and of the extinction coefficient k(v) for ZnGeP{sub 2} single crystals with different degrees of technological treatment – after growth by the vertical Bridgman technique, after heat treatment at temperatures above the Debye temperature for the highest-frequency phonons, and after modification of the single-crystal properties under irradiation by fast electrons (~4 MeV).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗