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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A DFT Study on Structural, Electronic Mechanical and Thermodynamic Properties of 5f-Electron System BaAmO{sub 3}

The structural, electronic, mechanical and thermodynamic properties of the perovskite oxide BaAmO{sub 3} have been predicted using the full-potential linearized augmented plane wave (FP-LAPW) method. The equilibrium lattice constant, bulk modulus and pressure derivative were computed using different exchange correlations. The optimization of structure was carried out in ferromagnetic, anti-ferromagnetic and non-magnetic states, and the compound was found to be stable in the ferromagnetic state. A systematic study on the band structure and density of states was accomplished using generalized gradient approximation (GGA), Hubbard approximation (GGA + U) and modified Becke–Johnson exchange potential (mBJ),and the compound was found to have a half-metallic nature in all the approximations. The calculated total spin magnetic moment was found to be 5 μ{sub B} in all the approximations used. The second-order elastic constants, Young modulus, shear modulus, Poisson ratio and anisotropic factor have also been calculated. In order to have a complete understanding of BaAmO{sub 3}, the thermodynamic properties were studied in the pressure range of 0 to 40 GPa and the temperature range extending from 0 to 600 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation of Electronic, Magnetic, Thermodynamic, and Thermoelectric Properties of Half-Metallic XLiSn (X = Ce, Nd) Alloys

We have investigated the electronic, magnetic, thermodynamic, and thermoelectric properties of half-Heusler CeLiSn and NdLiSn using density functional theory. The materials crystallize in F 4-bar 3mstructure with ferromagnetic state at optimized lattice parameter of 6.73 Å for CeLiSn and 6.74 Å for NdLiSn. The modified Becke-Johnson potential (mBJ) and generalized gradient approximation (GGA) have been used for computation of band structure, where mBJ shows a perfect half-metallic nature of the bands in both the alloys. The calculated magnetic moment of 1.0 μ{sub B} for CeLiSn and 3.0 μ{sub B} for NdLiSn follow Slater-Pauling rule, with ferromagnetic interactions. The temperature variation of the Seebeck coefficient shows the p-type behavior with room temperature values of 27 μV/K (43 μV/K) for CeLiSn (NdLiSn). Pressure-dependent variation of specific heat, Debye temperature, and Gruneisen parameter were calculated to infer the nature of lattice vibration and stability at high pressures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Prediction of a Dynamically Stable New Half-Metallic Phase for the BaN and BaC Compounds

The structural, magnetic, elastic, mechanical, and thermodynamic properties of BaC and BaN compounds in different phases were studied using first-principle calculations based on spin-polarized density functional theory within the generalized gradient approximation (GGA-PBEsol) and the modified Becke–Johnson approach (mBJ-GGA-PBEsol) for the exchange-correlation energy and potential. The following phases—rock-salt (NaCl), CsCl, zinc blende (ZB), NiAs- and WZ-type hexagonal, tetragonal (P4/nmm), and orthorombic (Pnma) phases of BaC and BaN compounds—were considered. We obtained that Pnma phase has the lowest energy configuration as a function of the volume for both the BaN and BaC compounds. The ferromagnetic phase is energetically favored with respect to the non-magnetic phase in the BaN and BaC compounds, except for the CsCl phase in the BaC compound. Considering the phonon dynamics of BaN and BaC compounds in the Pnma, NaCl, ZB, and WZ phases, we observed that the BaN and BaC compounds in the Pnma, NaCl, and ZB phases are dynamically stable. The calculated elastic properties for the Pnma, NaCl, and ZB phases show that they are elastically stable. The Pnma phase for the BaN and BaC compounds, which is a new phase was found to be dynamically and elastically stable. The BaN and BaC compounds exhibit half-metallic behavior in the Pnma, NaCl, and ZB phases. The half-metallic and magnetic character found in the BaN and BaC compounds are attributed to the presence of spin-polarized 2p orbitals of the nitrogen and carbon atoms, respectively. We found that BaN and BaC compounds are half-metallic ferromagnets with magnetic moment of 1 μ{sub B} and 2 μ{sub B} per formula unit, respectively. Using the GGA-PBEsol (mBJ-GGA-PBEsol) approach, our calculated half-metallic gaps for BaN and BaC compounds are 0.22 eV (0.54 eV) and 0.32 eV (0.44 eV) in the Pnma phase, 0.23 eV (1.32 eV) and 0.35 eV (1.00 eV) in the NaCl phase, and 0.38 eV (1.54 eV) and 0.50 eV (1.57 eV) in the ZB phase, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation of New d{sup 0} Half-metallic Heusler Alloy LiCsN{sub 2} Using First-Principle Calculations

Using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method, we predicated a new d{sup 0} half-metallic Heusler compound LiCsN{sub 2} with integer total magnetic moment 4.00 μ B per formula unit based on density functional theory (DFT). Our calculation shows that this alloy has a huge half-metallic gap (1.06 eV) and a wide band gap (4.52 eV). We found the LiCsN{sub 2} alloy is a robust half-metallic material with respect to the lattice compression. It maintains the half-metallic character until the lattice constant is contracted to 6.10 Å. The Curie temperature of LiCsN{sub 2} was estimated to be 6145.4 K within the mean field approximations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Study of Electronic, Magnetic, and Thermoelectric Properties of 24 Valence-Electron Fe{sub 2}TiSn Heusler Compound Using Modified Becke-Johnson Scheme

The first-principle investigation of electronic and transport properties of 24 valence-electron Fe{sub 2}TiSn Heusler compound have been carried out using modified Becke-Johnson scheme. The compound possesses Fm-3m structure configuration in the ground state. Spin-polarized electronic calculations reveal Fe{sub 2}TiSn is a semiconductor in both the spin configurations with a total magnetic moment as 0μ{sub B}, which is consistent with the Slater-Pauling rule. The thermoelectric properties were calculated by means of the semiclassical Boltzmann transport theory. The average values of electrical conductivity, thermal conductivity, and Seebeck coefficient at 300, 600, and 900 K temperatures versus chemical potential are reported and discussed in detail. Further, the results show the possibility to create n-type and p-type thermoelectrics within one type of Heusler compound. The large Seebeck coefficient advocates the compounds to be good for thermoelectric applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetostriction of Hexagonal HoMnO{sub 3} and YMnO{sub 3} Single Crystals

We report on the magnetostriction of hexagonal HoMnO{sub 3} and YMnO{sub 3} single crystals in a wide range of applied magnetic fields (up to H = 14 T) at all possible combinations of the mutual orientations of magnetic field H and magnetostriction ΔL/L. The measured ΔL/L(H, T) data agree well with the magnetic phase diagram of the HoMnO{sub 3} single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO{sub 3} crystal is caused by the Ho{sup 3+} ion; the magnetic moment of the Mn{sup 3+} ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO{sub 3} are consistent with the phase diagram of these compounds. For the isostructural YMnO{sub 3} single crystal with a nonmagnetic rare-earth ion, the ΔL/L(H, T) dependences are described well by a conventional quadratic law in a wide temperature range (4–100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Neutron Spin Rotation at Laue Diffraction in a Weakly Deformed Transparent Crystal with No Center of Symmetry

The effect of neutron spin rotation at Laue diffraction in a weakly deformed neutron-transparent noncentrosymmetric crystal has been described theoretically and studied experimentally. The effect is due to the bending of a Kato trajectory of the neutron in the deformed crystal. At a certain type of deformation, one of two neutron waves excited at Laue diffraction, which propagate in opposite crystal fields in the crystal with no center of symmetry, leaves the crystal. As a result, the spin of the remaining neutron wave is rotated by a certain angle with respect to initial direction due to the interaction of the magnetic moment of a moving neutron with the crystalline electric field. This effect is absent in an undeformed perfect crystal, where only the depolarization of a beam occurs because both waves in opposite electric fields have the same amplitude. A method has been developed for controlled deforming the perfect single crystal by creating a temperature gradient in it. Thereby, a new possibility of measuring electric fields acting on a neutron in noncentrosymmetric crystals, as well as a method of controlling these fields in experiments on studying the fundamental properties of the neutron, has been implemented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Modeling the Deflection of Polarized Electrons with Energies in the Range 3.35–14 GeV in a Bent Silicon Crystal

The evolution of the magnetic moment of a relativistic particle is described with the help of the Bargmann–Michel–Telegdi equation in the planar channels of a bent silicon crystal with allowance for multiple scatteringboth along and transverse to the (111) atomic plane, which consists of <110> chains. Results of numerical simulations demonstrate a strong dependence of the degree of depolarization of the electron beam on the energy since at the energies 3.35 and 4.2 GeV the maximum in the distribution over rotation angles of the electron spin is absent, and at energies from 6.3 to 14 GeV the position of the maximum is in line with the theoretical estimate obtained using the formula of V. L. Lyuboshits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Reorientation of antiferromagnetism in cobalt doped FeSn

FeSn is an itinerant antiferromagnet that hosts electronic Dirac states and ordered magnetic moments lying within its Fe Kagome-lattice planes. We present magnetization measurements of single crystals of (Fe 1-x Co x )Sn, revealing the evolution and suppression of this magnetic order with Co substitution. We interpret the dramatic changes in magnetic anisotropy to indicate a reorientation of the moments from perpendicular to parallel to the hexagonal c axis and confirm this with neutron diffraction. It has been proposed that the Dirac nodes observed in FeSn should become gapped if the moments rotate as our data suggests. We identify Co-substituted compositions that adopt both antiferromagnetic configurations at different temperatures. This system provides a unique opportunity to study how the details of magnetic order impact Dirac electron states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Flavor-violating ALPs, electron g − 2 , and the Electron-Ion Collider

We revisit the possibility that light axionlike particles (ALPs) with lepton-flavor-violating couplings could give significant contributions to the electron’s anomalous magnetic moment g e − 2 . Unlike flavor diagonal lepton-ALP couplings, which are exclusively axial, lepton-flavor-violating couplings can have arbitrary chirality. Focusing on the e − τ ALP coupling, we find that the size of the contribution to g e − 2 depends strongly on the chirality of the coupling. A significant part of the parameter space for which such a coupling can explain experimental anomalies in g e − 2 can be probed at the Electron-Ion Collider, which is uniquely sensitive to the chirality of the coupling using the polarization of the electron beam. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

First Principle Mechanical and Thermodynamic Properties of Some TbX (X = S, Se) Compounds

The mechanical and thermodynamic results of some terbium chalcogenides, TbX (X = S, Se) compounds have been examined using full-potential linear augmented plane wave (FP-LAPW) method based on density functional theory. The local spin density approximation with Hubbard potential (LSDA+U) has been used for proper treatment of 4f-electrons of Tb. The magnetic moment of TbS and TbSe was calculated to be 5.44μ{sub B} and 5.57μ{sub B}, respectively. The ground state properties such as lattice parameter, bulk modulus, and pressure derivative of bulk modulus were obtained and found in good agreement with already available theory and experiment results. The mechanical properties such as Young modulus (E), shear modulus (G), Poisson ratio (υ), Cauchy pressure and B/G ratio were also predicted. Further, in thermodynamic properties, Debye temperatures (θ{sub D}), specific heats at constant volume(C{sub V}), thermal expansion co-efficient (α), and entropies (S) and their behavior with high temperature(0–1200 K) and pressure (0–50 GPa) were also predicted.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magneto-Electronic, Thermodynamic, and Thermoelectric Properties of 5f-Electron System BaBkO{sub 3}

In the present work, the structural, electronic, magnetic, mechanical, thermodynamic, and thermoelectric properties of cubic perovskite BaBkO{sub 3} were investigated within the framework of density functional theory using generalized gradient approximation, onsite Coulomb interaction, and modified Becke-Johnson methods. BaBkO{sub 3} is stable in the ferromagnetic phase with a magnetic moment of 7 μ{sub B}. The spin-polarized electronic band structure reveals 100% spin polarization of the material with metallic character in spin-up state and semiconducting in spin-down state. Pugh and Cauchy relation displays that the material is highly ductile. The quasi-harmonic Debye model was used to determine the thermodynamic properties of BaBkO{sub 3} under high pressure and temperature. BaBkO{sub 3} presents high value of Seebeck coefficient and power factor at room temperature with a value of 135 μVK{sup − 1} and 1.5 × 10{sup 12}μWcm{sup − 1} K{sup − 2} s{sup − 1}, respectively. The possession of half metallicity and high Seebeck coefficient makes BaBkO{sub 3} suitable for spintronic and thermoelectric device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

First-Principles Calculations of Acoustic and Anharmonic Properties of Ferromagnetic Cu{sub 2}MnZ (Z = Al and In) Heusler Alloys

The acoustic and anharmonic properties of ferromagnetic Cu{sub 2}MnZ (Z = Al and In) Heusler alloys have been investigated by first-principles calculations method. The obtained lattice parameters, magnetic moments, elastic properties are found to be in good agreement with the available experimental values. From the elastic properties, the sound velocities and the related Debye temperatures and minimum thermal conductivities have been obtained for the two alloys. The sound velocities and thermal conductivities of both alloys are found to show significant anisotropy, and the Cu{sub 2}MnAl with small density and large elastic constants has large sound velocities, high Debye temperature, and large thermal conductivities. Also, the effective second-order elastic constants, generalized Grüneisen constants, and nonlinear ultrasonic parameters to characterize anharmonic properties have been studied for the two alloys. These predictions on the acoustic and anharmonic properties can provide a valuable guidance or reference for further related investigations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Internal Structure of Charged Particles in a GRT Gravitational Model

With the help of an exact solution of the Einstein and Maxwell equations, the internal structure of a multiply connected space of wormhole type with two unclosed static throats leading out of it into two parallel vacuum spaces or into one space is investigated in GRT for a free electric field and dust-like matter. The given geometry is considered as a particle–antiparticle pair with fundamental constants arising in the form of first integrals in the solution of the Cauchy problem – electric charges ±e of opposite sign in the throats and rest mass m{sub 0} – the total gravitational mass of the inner world of the particle in the throat. With the help of the energy conservation law, the unremovable rotation of the internal structure is included and the projection of the angular momentum of which onto the rotation axis is identified with the z-projection of the spin of the charged particle. The radius of 2-Gaussian curvature of the throat R* is identified with the charge radius of the particle, and the z-projection of the magnetic moment and the g-factor are found. The feasibility of the given gravitational model is confirmed by the found condition of independence of the spin quantum number of the electron and the proton s = 1/2 of the charge radius R* and the relativistic rest mass m* of the rotating throat, which is reliably confirmed experimentally, and also by the coincidence with high accuracy of the proton radius calculated in the model R{sub *p} = 0.8412·10{sup –13} cm with the value of the proton charge radius obtained experimentally by measuring the Lamb shift on muonic hydrogen. The electron in the given model also turns out to be a structured particle with radius R{sub *e} = 3.8617·10{sup –11} cm.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Analysis of mechanical, thermodynamic, and thermoelectric properties of ferromagnetic SrFe{sub 4}As{sub 12} skutterudite

In the present work, the electronic, mechanical, thermal and thermoelectric properties of Sr-filled skutterudite have been investigated in the framework of density functional theory. SrFe{sub 4}As{sub 12} shows a ferromagnet character with a magnetic moment of 1.76 μ{sub B} at an optimized lattice parameter of 8.38 Å. The effect of high-pressures on thermodynamic properties viz. thermal expansion coefficient, specific heat capacity and Grüneisen parameter is also carried out by employing the quasi-harmonic Debye model. Temperature dependence of Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and figure of merit is observed up to 800 K. The lattice thermal conductivity decreases with temperature due to rattling behavior of the filler atom. SrFe{sub 4}As{sub 12} exhibits the high value of the figure of merit equal to 0.76 at 800 K. The present results clearly signify that SrFe{sub 4}As{sub 12} may be a good choice for thermoelectric applications due to its high-power factor and figure of merit.

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

Synthesis and structures of Cu{sup I,II} complexes with a 2,2´-bipyridine derivative bearing a (+)-3-carene moiety

The complex salt {[CuL_2][Cu_4I_6]•MeCN}{sub n} (1) and the compound [Cu{sub 4}L{sub 3}I{sub 4}]•3 MeCN (2) (L is a chiral ligand bearing a natural monoterpene (+)-3-carene moiety) were synthesized. The crystal structures of compounds 1 and 2 were determined by X-ray diffraction. The structure of compound 1 consists of complex cations [CuL{sub 2}]{sup 2+} (N{sub 3}O{sub 2} polyhedron is a trigonal bipyramid) and Cu{sup I} coordination polymers (CuI{sub 4} polyhedron is a tetrahedron) as anions. The experimental magnetic moment μ{sub eff} at 300 K is 1.90 μ{sub B}, which is consistent with the X-ray diffraction data and the assumption that compound 1 is mixed-valence. The structure of compound 2 comprises a tetranuclear Cu{sup I} complex, in which three Cu atoms are coordinated by two N atoms of the ligand L and two I atoms, and the fourth Cu atom is coordinated by four I atoms (coordination polyhedra are distorted tetrahedra). Compounds L and 2 were found to influence the viability of human laryngeal carcinoma cells (Hep2). The IC{sub 50} value for complex 2 (13.0±1.7 μM) is substantially smaller than IC{sub 50} for compound L (30.5±0.5 μM).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Theoretical Study of Mechanical Stability and Physical Properties of Co{sub 2}V{sub 1−x}Zr{sub x}Ga

The mechanical stability and physical properties of Co{sub 2}V{sub 1−x}Zr{sub x}Ga (x = 0, 0.25, 0.50, 0.75, 1) have been predicted by using ab initio calculations based on density functional theory. The exchange-correlation potentials are treated within the generalized gradient approximation-Perdew-Burke and Ernzerhhof (GGA-PBE) and Hubbard coefficient (GGA+U). The investigated minimum lattice parameter of Co{sub 2}VGa is 5.8030 Å, which is in excellent agreement with available experimental and theoretical data and for Co{sub 2}V{sub 1−x}Zr{sub x}Ga (x = 0.25, 0.50, 0.75, 1) are 5.9026, 5.9625, 6.0060 and 6.0021 Å, respectively, which are predicted for the very first time. The total magnetic moments decrease with increasing concentration of x in Co{sub 2}V{sub 1−x}Zr{sub x}Ga, in agreement with the Slater-Pauling rule. Band structure and density of states calculations show that the minority spin channel exhibits band gaps of 0.43, 0.46, 0.52, 0.54 and 1.01 eV for GGA+U scheme around the Fermi level confirming that all the studied composites are half-metallic in nature. In this study, we also studied the elastic constant and it is established that all the materials are mechanically stable and ductile in nature. The Co{sub 2}VGa is stiffer than other materials and all the studied composites have anisotropic behaviour. Moreover, by using a quasi-harmonic Debye model and calculated elastic constant, the Debye temperature and temperature-dependent constant volume heat capacity have been investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Muon spin force

Current discrepancy between the measurement and the prediction of the muon anomalous magnetic moment can be resolved in the presence of a long-range force created by ordinary atoms acting on the muon spin via axial-vector and/or pseudoscalar coupling, and requiring a tiny O⁡(10 –13 eV) spin energy splitting between muon state polarized in the vertical direction. We suggest that an extension of the muon spin resonance (μ⁢SR) experiments can provide a definitive test of this class of models. We also derive indirect constraints on the strength of the muon spin force by considering the muon-loop-induced interactions between nuclear spin and external directions. The limits on the muon spin force extracted from the comparison of 199 Hg/ 201 Hg and 129 Xe/ 131 Xe spin precession are strong for the pseudoscalar coupling but are significantly relaxed for the axial-vector one. These limits suffer from significant model uncertainties, poorly known proton/neutron spin content of these nuclei, and therefore do not exclude the possibility of a muon spin force relevant for the muon g – 2.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗