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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Coolant Pressure Evaluations for a MEMS Sensor-Array Quench Detection in REBCO CICC Superconducting Cables

Here, the initial quench pressure developments for a CICC cable of REBCO tapes have been investigated by numerical analyzing the first law of thermodynamics. The temperature and pressure rise due to the quench has been evaluated for a REBCO CICC conductor operated in helium gas coolant at 26 K. Additionally, a MEMS sensor-in-tube array method has been proposed and discussed for quench detection.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Transverse Tunable Magneto-Plasmonic Kerr Effect in Large Area Micro-Patterned Au/Co/Au Structures

By sputtering the sequence of Au/Co/Au layers on ordered microspheres, two-dimensional plasmonic arrays with sufficient angular tunability and enhanced transverse magneto-plasmonic Kerr effect are fabricated. For confirmation of enhanced optical properties, we simulated the fabricated sample using the finite difference time domain method. In order to investigate the effect of rotation speed on the anisotropy of the samples and their magneto-plasmonic responses, these patterned structures are fabricated under dissimilar holder rotation speeds for inner cobalt layer deposition (i.e., Au (10 rpm)/Co (30 rpm)/Au (10 rpm) and Au (10 rpm)/Co (10 rpm)/Au (10 rpm) structures). Our results show that the transverse magneto-plasmonic Kerr effect measurements can provide unique and useful information about the structure and quality of the fabricated samples. In addition, the ability of the samples as a tunable magnetic field sensor has been investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Features of bicrystal growth during the directional crystallization of metal melts

The factors responsible for the formation of different configurations of boundaries between adjacent crystallites during their growth from melt by Bridgman and Czochralski methods have been considered by an of example Fe–20 wt % Ga alloy and Ni bicrystals. It is found that the configuration of intercrystallite boundary is related to the features of crystallite growth, caused by the strained state of intercrystallite and interphase (crystal–melt) boundaries, the difference in the linear thermal expansion coefficients of the crystallite boundaries and bulk, and the shape (geometry) of the bicrystal cross section. It is suggested that the strained state of boundaries and the formation of substructure in crystallites during directional crystallization from metal melt are significantly affected by their deformation under the melt weight.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superconducting Properties of Indium Nanostructured in Pores of Thin Films of SiO{sub 2} Microspheres

Samples of a superconducting indium nanocomposite based on a thin-film porous dielectric matrix prepared by the Langmuir–Blodgett method are obtained for the first time, and their low-temperature electrophysical and magnetic properties are studied. Films with thickness b ≤ 5 μm were made from silicon dioxide spheres with diameter D = 200 and 250 nm; indium was introduced into the pores of the films from the melt at a pressure of P ≤ 5 kbar. Thus, a three-dimensional weakly ordered structure of indium nanogranules was created in the pores, forming a continuous current-conducting grid. Measurements of the temperature and magnetic field dependences of the resistance and magnetic moment of the samples showed an increase in the critical parameters of the superconductivity state of nanostructured indium (critical temperature T{sub c} ≤ 3.62 K and critical magnetic field H{sub c} at T = 0 K H{sub c}(0) ≤ 1700 Oe) with respect to the massive material (T{sub c} = 3.41 K, H{sub c}(0) = 280 Oe). In the dependence of the resistance on temperature and the magnetic field, a step transition to the superconductivity state associated with the nanocomposite structure was observed. A pronounced hysteresis M(H) is observed in the dependence of the magnetic moment M of the nanocomposite on the magnetic field at T < T{sub c}, caused by the multiply connected structure of the current-conducting indium grid. The results obtained are interpreted taking into account the dimensional dependence of the superconducting characteristics of the nanocomposite.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

A Non-contact Apparatus for Measuring Longitudinal Critical Current of REBCO Tapes Using the Magnetic Circuit Method

This paper details the design and construction of a non-contact apparatus that can measure the longitudinal critical current of REBCO tapes based on magnetic circuit method. A 3D finite element model was proposed to study the relation between I{sub c} (critical current of the REBCO tape) and B{sub H} (magnetic field at the Hall sensor). The proportionality coefficient of I{sub c} and B{sub H} was obtained by using the said model. Several experiments on the REBCO tapes were conducted to determine the repeatability, reliability, and accuracy of the apparatus. Four parameters (average value, minimum value, the range, and the coefficient of critical current variation (COV)) were used to determine the repeatability and accuracy of the apparatus. It was observed that transmission speed affects test results because of relaxation of the magnetic flux. Another tape was tested at different transmission speeds to study the relation between B{sub H} and decay time. From the results, a principle formula was established to explain the relation between B{sub H} and decay time, and it was shown that the test results also take the same form as the principle formula.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Numerical approximations for the molecular beam epitaxial growth model based on the invariant energy quadratization method

The Molecular Beam Epitaxial model is derived from the variation of a free energy, that consists of either a fourth order Ginzburg–Landau double well potential or a nonlinear logarithmic potential in terms of the gradient of a height function. One challenge in solving the MBE model numerically is how to develop proper temporal discretization for the nonlinear terms in order to preserve energy stability at the time-discrete level. In this paper, we resolve this issue by developing a first and second order time-stepping scheme based on the “Invariant Energy Quadratization” (IEQ) method. The novelty is that all nonlinear terms are treated semi-explicitly, and the resulted semi-discrete equations form a linear system at each time step. Moreover, the linear operator is symmetric positive definite and thus can be solved efficiently. We then prove that all proposed schemes are unconditionally energy stable. The semi-discrete schemes are further discretized in space using finite difference methods and implemented on GPUs for high-performance computing. Various 2D and 3D numerical examples are presented to demonstrate stability and accuracy of the proposed schemes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Electronic, Magnetic, and Optical Properties of Half-Heusler Alloys RuMnZ (Z = P, As): a First-Principle Study

Half-Heusler alloys RuMnZ (Z = P, As ) are studied in the framework of Density Functional Theory (DFT). Structural, electronic, magnetic, and optical properties are calculated and analyzed using the WIEN2k simulation code. All the calculations are done using the full potential linearized augmented plane wave (FP-LAPW) method. Equilibrium lattice parameters are found to be in the range 5.5–5.6 Å. Band gaps of the compounds and density of states (DoS) analysis reveal that the minority spin-down states are semi-conducting while the majority spin-up states are conducting confirming the half-metallic nature of the compounds. Hence, at Fermi level, states are 100 % polarized. The value of the total magnetic moment is found to be 2, i.e., M{sub Tot} = 2μ{sub B}. Several optical properties, including dielectric function, reflectivity, refractive index, conductivity, and absorption coefficient are calculated as well. It is revealed from the imaginary part of the dielectric function that the compounds are optically metallic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Geometrical Structures and Magnetic Properties of Charged Aluminum-Doped Platinum Clusters: Aluminum Occupied High Coordination Site

The most stable states of neutral and charged Pt{sub n}Al (n = 1 − 8) clusters have been performed using DFT methods. All the most stable structures of neutral and charged Pt{sub n}Al clusters can be obtained by substituting a Pt atom with an Al atom except Pt{sub 7}Al and the Al atom occupies the vertex position with lager coordination number. The Pt{sub 5}, Pt{sub 4,6}Al, Pt{sub 3}Al{sup +}, and Pt{sub 6}Al{sup −} clusters have higher local relative stability and can be seen as “magic clusters.” The fragmentation energy is the largest when a Pt atom is bonded with an Al atom. The average magnetic moments of Pt{sub n+ 1} cluster reduce due to the addition of Al atoms. The static polarizability has been studied in this paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A First Principle Study of Half-Heusler Compounds CrTiZ (Z = P, As)

Half-Heusler compounds CrTiZ (Z = P, As) are studied in the framework of Density Functional Theory (DFT). Structural, mechanical, elastic, electronic, magnetic, and optical properties are derived using first principles. The full-potential linearized augmented plane wave (FP-LAPW) method is used for these investigations as implemented in the WIEN2k simulation package. We have found that the equilibrium lattice parameters are in the range 5.5–5.9 Å. Small band gaps of 0.5–0.6 eV in the minority spin-down states are observed. On the other hand, in the majority spin-up states, there is no band gap. Hence, the compounds are of half-metallic nature, having 100 % polarization at Fermi level. Comparatively, a higher total magnetic moment of ∼ 3μ{sub B} is found for both the compounds. Furthermore, optical properties are derived using dielectric function. Reflectivity, refractive index, conductivity and absorption coefficient are calculated. It is revealed from the imaginary part of the dielectric function that the compounds are optically metallic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Modeling of Phase Transitions of Graphites to Diamond-Like Phases

The method of the density functional theory is used to study structural transformations between graphites and diamond-like phases. The calculations have been carried out in two approximations: a local density approximation and a generalized gradient approximation. It is found that the phase transitions of hexagonal graphene layers to a cubic diamond and diamond-like phases must occur at uniaxial compressions of ~57–71 GPa, whereas some diamond-like phases can be obtained from tetragonal graphene layers at significantly lower pressures of 32–52 GPa. The X-ray diffraction patterns have been calculated for the phase transition of graphite I4{sub 1}/amd to tetragonal LA10 phase that takes place at the minimum pressure that can be used for experimental identification of these compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Optical Properties of Boron-Doped Gallium Selenide

The electronic-absorption and luminescence spectra and the kinetics of relaxation of photocurrent in GaSe single crystals and thin films doped with boron atoms are experimentally investigated. Crystals are doped either in the course of synthesis or upon growing single crystals by the Bridgman method. Thin GaSe films are obtained by thermal evaporation of the compound preliminarily doped with boron. An absorption band with the maximum at λ = 925 nm, which is attributed to boron contaminations, is revealed from the comparison of the electronic-absorption spectra of a GaSe crystal and thin films doped with boron. When the crystals are excited with Nd:YAG laser pulses of a duration of 12 ns, it is established that recombination of nonequilibrium current carriers in pure crystals occurs through rapid and slow recombination channels and in crystals doped with boron only through rapid channels. In the region near λ = 932 nm, photoluminescence is observed in the crystals doped with boron, and its half-bandwidth is 15 Å.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Multi-mode analysis of surface losses in a superconducting microwave resonator in high magnetic fields

This paper reports on a surface impedance measurement of a bulk metal niobium–titanium superconducting radio frequency (SRF) cavity in a magnetic field (up to 10 T). Here, a novel method is employed to decompose the surface resistance contributions of the cylindrical cavity end caps and walls using measurements from multiple TM cavity modes. The results confirm that quality factor degradation of a NbTi SRF cavity in a high magnetic field is primarily from surfaces perpendicular to the field (the cavity end caps), while parallel surface resistances (the walls) remain relatively constant. This result is encouraging for applications needing high Q cavities in strong magnetic fields, such as the Axion Dark Matter eXperiment because it opens the possibility of hybrid SRF cavity construction to replace conventional copper cavities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Structural, Electronic, Magnetic and Optical Investigations of Half-Heusler Compounds YZSb (Z = Cr, Mn): FP-LAPW Method

Half-Heusler compounds YZSb (Z = Cr, Mn) are theoretically explored in the framework of density functional theory (DFT). We have investigated a number of different properties with the help of the WIEN2k simulation package. Equilibrium lattice constants fall in the range 6.0–7.0 Å for both compounds. Elastic properties are also studied and it is found that the compound YCrSb is of brittle and YMnSb is of ductile nature as indicated by a number of parameters including Cauchy pressure, Pugh’s ratio and Poisson’s ratio. Electronically, these compounds are found to be half-metals as their spin-up states are semiconducting and hence 100% spin polarized at the Fermi level while spin-down states are conducting. The total magnetic moments are equal to 4μ{sub B} and 3.15μ{sub B} for YCrSb and YMnSb, respectively. The optical properties including dielectric function, reflectivity, refractive index, conductivity and absorption coefficients are calculated and discussed. Optical characteristics of the compounds hint that they are more active in the infrared region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Monte Carlo Study of the Mixed-Spin (1/2, 2) Ferrimagnetic Ising System on a Honeycomb Lattice

By means of the Monte Carlo method, we have simulated the mixed-spin-1/2 and spin-2 Ising ferrimagnetic system on a honeycomb lattice. We studied the variations of the magnetization as functions of the crystal field and the temperature and obtained the phase diagram of the system for various crystal field values. We have found that the system cannot display a point of compensation if we consider only nearest-neighbor interactions and the crystal field effect. Also, the tricritical point does not exist. To the best of our knowledge, this system has never been studied using the Monte Carlo method.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Comparative S/TEM study of superconducting Ta quantum resonators by wet and dry etching types

Superconducting resonators play a pivotal role in various quantum technology applications, such as quantum computing and high-frequency communication systems. The performance of these resonators is closely tied to the properties of the superconducting films used in their fabrication. Here, in this study, we investigated the impact of wet and dry etching on tantalum (Ta) films leveraging advanced scanning transmission electron microscopy-based characterization methods and examined the morphological, chemical, and strain changes caused by the etching processes. Consequently, we report the significant differences between the two etching methods, with dry etching resulting in straight slanted sidewalls and a thinner oxidized layer, while wet etching produced curved sidewalls and undercuts. Both methods led to the formation of a residual Ta wedge at the lower part of the sidewall, causing lattice deformation, which could adversely influence the homogeneous operations of superconducting devices. These insights enhance our understanding of how etching influences superconducting films, offering valuable guidance for optimizing resonators and related devices. Our findings mark a significant stride in advancing quantum technologies and high-frequency communication by enhancing our practical understanding of superconducting material fabrication.

36 MATERIALS SCIENCE↗
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 OSTI2022

Langevin dynamics of generalized spins as SU( N ) coherent states

Classical models of spin systems traditionally retain only the dipole moments, but a quantum spin state will frequently have additional structure. Spins of magnitude S have N = 2⁢S + 1 levels. Alternatively, the spin state is fully characterized by a set of N 2 - 1 local physical observables, which we interpret as generalized spin components. For example, a spin with S = 1 has three dipole components and five quadrupole components. Further, these components evolve under a generalization of the classical Landau-Lifshitz dynamics, which can be extended with noise and damping terms. In this paper, we reformulate the dynamical equations of motion as a Langevin dynamics of SU(N) coherent states in the Schrödinger picture. This viewpoint is especially useful as the basis for an efficient numerical method to sample spin configurations in thermal equilibrium and to simulate the relaxation and driven motion of topological solitons. To illustrate the approach, we simulate a nonequilibrium relaxation process that creates CP 2 skyrmions, which are topological defects with both dipole and quadrupole character.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗