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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Role of target-substrate distance on the growth of CuInSe{sub 2} thin films by pulsed laser ablation technique

CuInSe{sub 2} thin films have been deposited on corning glass substrates by pulsed laser ablation technique. The chamber pressure and substrate temperature was maintained at 1 × 10{sup −6} torr and 550°C respectively during deposition of the films. The influence of target to substrate (T-S) distance on the structural and optical properties of thin films have been investigated by grazing incidence x-ray diffraction, Raman spectroscopy, scanning electron microscope and UV-Vis-NIR spectroscopy. The study reveals that thin films crystallized in a chalcopyrite structure with highly preferential orientation along (112) plane. Optimum T-S distance has been attained for the growth of thin films with large grain size. An intense Raman peak at 174 cm{sup −1} corresponding to dominant A{sub 1} vibration mode is gradually shifted to smaller wavenumber with the increase in T-S distance. The optical bandgap energy of the films was evaluated and found to vary with the T-S distance. The bandgap tailing was observed to obey the Urbach rule and the Urbach energy was also calculated for the films. Scanning electron micrographs depicts uniform densely packed grains and EDAX studies revealed the elemental composition of CuInSe{sub 2} thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Study of the Kinetics of the Phase Transition of the First Order in Tetracosane C{sub 24}H{sub 50} by Fourier-Transform IR Spectroscopy

The kinetics of the development of the structural phase transition of the first order in monodisperse samples of tetracosane C{sub 24}H{sub 50} has been studied using Fourier-transform IR spectroscopy. Temperature dependences of frequencies and intensities of rocking (in the region of ν ~ 720 cm{sup –1}) and bending (in the region of ν ~ 1470 cm{sup –1}) vibration modes of CH{sub 2} groups in trans methylene sequences in crystalline cores of elementary lamellae has been analyzed. It has been shown that the solid-phase transition of the first order develops by the heterogeneous mechanism in a narrow temperature interval ΔT ~ 2 K according to the theory of diffuse phase transitions of the first order and is caused by changes in the symmetry of crystallographic cells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Nonlinear instability saturation due to quasi-particle trapping in a turbulent plasma

We consider the problem of a single wave mode stability, dispersion, and nonlinear saturation in a turbulent plasma background. We adopt a wave kinetic description for the quasi-particle turbulence and assume a low frequency perturbation of both the plasma and the turbulent spectrum. We describe an improved theoretical approach, which goes beyond the geometric optics approximation and retains the recoil effects associated with the emission and absorption of low frequency waves by nearly resonant quasi-particles. We illustrate the present approach by considering the case of zonal flow excited by drift wave turbulence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Synthesis and characterization of Fe{sub 2}O{sub 3} nanoparticles by simple precipitation method

A simple and efficient synthesis of Iron-oxide nanoparticles was carried out by precipitation method using ferric chloride as precursor and ammonium hydroxide as a stabilizing agent at different calcination temperatures. The synthesized powder was characterized by powder X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscope (FE-SEM) and Transmission Electron Microscopy (TEM). X-ray diffraction indicated the formation hematite Fe{sub 2}O{sub 3} structure. FTIR showed various functional groups of particles and absorption bands related to metal oxygen vibration modes. The heating temperatures were varied at 100 °C, 200°C, and 300°C. The Fe{sub 2}O{sub 3} nanostructures with the average particle size of about 36.22 nm were prepared at 300°C for 4h. TEM study is also confirming the nanosize of Fe{sub 2}O{sub 3} particle. This aqueous precipitation method gives a large scale production of Fe{sub 2}O{sub 3} nanoparticles easily.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Control of liquid crystal molecular orientation using ultrasound vibration

We propose a technique to control the orientation of nematic liquid crystals using ultrasound and investigate the optical characteristics of the oriented samples. An ultrasonic liquid crystal cell with a thickness of 5–25 μm and two ultrasonic lead zirconate titanate transducers was fabricated. By exciting the ultrasonic transducers, the flexural vibration modes were generated on the cell. An acoustic radiation force to the liquid crystal layer was generated, changing the molecular orientation and thus the light transmission. By modulating the ultrasonic driving frequency and voltage, the spatial distribution of the molecular orientation of the liquid crystals could be controlled. The distribution of the transmitted light intensity depends on the thickness of the liquid crystal layer because the acoustic field in the liquid crystal layer is changed by the orientational film.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Overview of recent HOM coupler development

Higher Order Mode (HOM) damping is important for SRF applications, especially for high-intensity machines. A good HOM damping design will help to reduce power load to the cryogenic system and to reduce the risk of beam breakup. The design of HOM damping, including antenna/loop HOM couplers, beam pipe HOM absorbers and waveguide HOM couplers, is to solve a multi-physics problem that involves RF, thermal, mechanical, and beam-cavity interaction issues. In this talk, the author provides an overview on the latest advances of the HOM couplers for high-intensity SRF applications.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Electrical properties and conduction mechanism study by OLPT model of NaZnPO4 compound

Highlights: • The crystal structure was resolved using Fullproof program. • The conduction in NaZn PO{sub 4} is insured by OLPT model. • Ac conductivity of NaZn PO{sub 4} compound obeys the Joncher’s law. - Abstract: A polycrystalline sample with NaZnPO{sub 4} stoichiometry was synthesized by the conventional solid-state reaction and then identified and characterized by X-ray powder diffraction, Raman spectroscopy and impedance spectroscopy. The X-ray diffraction pattern revealed that the composite represents a single phase that crystallizes in the monoclinic system with a P2{sub 1}/n space group. All vibration modes of tetrahedral PO{sub 4} appeared in the Raman spectrum. Besides, the electrical conductivity behavior of the title compound was analysed as a function of frequency ranging from 209 Hz to 1 MHz and at a temperature interval ranging from 578 K to 728 K by means of impedance spectroscopy to elucidate the conduction mechanism in this compound. The temperature dependence of frequency exponent ′s′ showed that the conduction in NaZnPO{sub 4} is insured by the overlapping large polaron tunneling (OLPT) model. A correlation between electrical and structural properties was also depicted.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Quantifying the agreement between observed and simulated extratropical modes of interannual variability

Using historical simulations of the Coupled Model Intercomparison Project-5 (CMIP5) and multiple observationally-based datasets, we employ skill metrics to analyze the fidelity of the simulated Northern Annular Mode, the North Atlantic Oscillation, the Pacific North America pattern, the Southern Annular Mode, the Pacific Decadal Oscillation, the North Pacific Oscillation, and the North Pacific Gyre Oscillation. We assess the benefits of a unified approach to evaluate these modes of variability, which we call the common basis function (CBF) approach, based on projecting model anomalies onto observed empirical orthogonal functions (EOFs). The CBF approach circumvents issues with conventional EOF analysis, eliminating, for example, corrections of arbitrarily assigned, but inconsistent, signs of the EOF’s/PC’s being compared. It also avoids the problem that sometimes the first observed EOF is more similar to a higher order model EOF, particularly if the simulated EOFs are not well separated. Compared to conventional EOF analysis of models, the CBF approach indicates that models compare significantly better with observations in terms of pattern correlation and root-mean-squared-error (RMSE) than heretofore suggested. In many cases, models are doing a credible job at capturing the observationally-based estimates of patterns; however, errors in simulated amplitudes can be large and more egregious than pattern errors. In the context of the broad distribution of errors in the CMIP5 ensemble, sensitivity tests demonstrate that our results are relatively insensitive to methodological considerations (CBF vs. conventional approach), observational uncertainties in pattern (as determined by using multiple datasets), and internal variability (when multiple realizations from the same model are compared). The skill metrics proposed in this study can provide a useful summary of the ability of models to reproduce the observed EOF patterns and amplitudes. Additionally, the skill metrics can be used as a tool to objectively highlight where potential model improvements might be made. Finally, we advocate more systematic and objective testing of simulated extratropical variability, especially during the non-dominant seasons of each mode, when many models are performing relatively poorly.

58 GEOSCIENCES↗
DOE OSTI2019

Synthesis, Characterization, and Magnetic Properties of A{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} (A = Ag or Na) Alluaudite-Type Vanadates

We successfully synthesized the polycrystalline form of vanadates A{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} (A = Ag or Na) using sol–gel method. Powder X-ray diffraction analysis allowed the identification of the alluaudite-type vanadate structure. The morphology and the elemental composition of the synthesized powders were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). The two vanadates A{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} (A = Ag or Na) were further characterized by infrared and Raman spectroscopies to get complementary structural information. The infrared and Raman spectroscopy-observed bands were assigned to VO{sub 4}{sup 3−} vibration modes. The room temperature {sup 57}Fe Mössbauer spectroscopy confirmed the +III oxidation state of iron. Magnetic properties of these vanadates were investigated. The magnetic susceptibility data reveal that the predominant interactions in these vanadates are antiferromagnetic with a Curie−Weiss constant of θ = − 125.6 K for Na{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} and θ = − 104.5 K for Ag{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3}. The magnetic interactions in these vanadates were discussed according to semiempirical Goodenough–Kanamori–Anderson rules (GKA).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Crystal structure, Raman spectra, infrared spectra and microwave dielectric properties of Li2Mg3Ti1-X(Mg1/3Ta2/3)XO6 (0 ≤ x ≤ 0.2) solid solution ceramics

Highlights: • Microwave properties of ε{sub r} = 14.70, Q·f = 200,600 GHz and τ{sub f} = −11.83 ppm/°C were obtained. • A small amount of (Mg{sub 1/3}Ta{sub 2/3}){sup 4+} can obviously improve properties. • Rietveld refinement and spectra were used to analyze properties. • Relationships between intrinsic parameters and properties were established. - Abstract: Li{sub 2}Mg{sub 3}Ti{sub 1-X}(Mg{sub 1/3}Ta{sub 2/3}){sub X}O{sub 6} (x = 0.00, 0.05, 0.10, 0.15, 0.20) solid solution ceramics were prepared by the conventional solid-state reaction method. Rietveld refinements, Raman spectra, infrared spectra, polarizability and bond energy were used to research the changes of microwave dielectric properties of these solid solutions. With the increase of x values from 0 to 0.2, dielectric constants (ε{sub r}) gradually increased, which could be explained by the variations of the polarizability, infrared resonant modes and Raman vibration modes. The variations of the quality factor (Q·f) could be explained by the changes of the bond valences. The temperature coefficient of resonant frequency (τ{sub ƒ}) correlated with the bond energy of TiO bonds. A small quantity of (Mg{sub 1/3}Ta{sub 2/3}){sup 4+} can obviously improve the microwave dielectric properties. Excellent microwave dielectric properties of ε{sub r} = 14.70, Q·f = 200,600 GHz and τ{sub f} = −11.83 ppm/°C were obtained for Li{sub 2}Mg{sub 3}Ti{sub 0.95}(Mg{sub 1/3}Ta{sub 2/3}){sub 0.05}O{sub 6} ceramic sintered at 1550 °C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Correlation of atomic packing with the boson peak in amorphous alloys

Boson peaks (BP) have been observed from phonon specific heats in 10 studied amorphous alloys. Two Einstein-type vibration modes were proposed in this work and all data can be fitted well. By measuring and analyzing local atomic structures of studied amorphous alloys and 56 reported amorphous alloys, it is found that (a) the BP originates from local harmonic vibration modes associated with the lengths of short-range order (SRO) and medium-range order (MRO) in amorphous alloys, and (b) the atomic packing in amorphous alloys follows a universal scaling law, i.e., the ratios of SRO and MRO lengths to solvent atomic diameter are 3 and 7, respectively, which exact match with length ratios of BP vibration frequencies to Debye frequency for the studied amorphous alloys. This finding provides a new perspective for atomic packing in amorphous materials, and has significant implications for quantitative description of the local atomic orders and understanding the structure-property relationship.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Bandgaps and directional properties of two-dimensional square beam-like zigzag lattices

In this paper we propose four kinds of two-dimensional square beam-like zigzag lattice structures and study their bandgaps and directional propagation of elastic waves. The band structures are calculated by using the finite element method. Both the in-plane and out-of-plane waves are investigated simultaneously via the three-dimensional Euler beam elements. The mechanism of the bandgap generation is analyzed by studying the vibration modes at the bandgap edges. The effects of the geometry parameters of the xy- and z-zigzag lattices on the bandgaps are investigated and discussed. Multiple complete bandgaps are found owing to the separation of the degeneracy by introducing bending arms. The bandgaps are sensitive to the geometry parameters of the periodic systems. The deformed displacement fields of the harmonic responses of a finite lattice structure subjected to harmonic loads at different positions are illustrated to show the directional wave propagation. An extension of the proposed concept to the hexagonal lattices is also presented. The research work in this paper is relevant to the practical design of cellular structures with enhanced vibro-acoustics performance.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Depth profile characterization with noncollinear beam mixing

Noncollinear beam mixing is an ultrasonic approach to quantify elastic nonlinearity within a subsurface volume of material. The technique requires interaction between two beams of specific frequency, angle, and vibration mode to generate a third beam propagating from the intersection volume. The subsurface depth to interaction zone is controlled by changing the separation distance between the two input transducers, and the amplitude of the third generated beam is proportional to the elastic nonlinearity within the interaction zone. Therefore, depth profiling is possible if a suitable parameter is established to normalize the detected signal independent of propagation distances and input amplitudes. This foundational effort has been conducted toward developing such a parameter for depth profile measurements in homogeneous aluminum that includes corrective terms for attenuation, beam overlap noise, beam spread, and input amplitudes. Experimental and analytical results are provided, and suggested applications and improvements are discussed toward characterizing subsurface material property profiles.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electronic structures and magnetic/optical properties of metal phthalocyanine complexes

Electronic structures and magnetic / optical properties of metal phthalocyanine complexes were studied by quantum calculations using density functional theory. Effects of central metal and expansion of π orbital on aromatic ring as conjugation system on the electronic structures, magnetic, optical properties and vibration modes of infrared and Raman spectra of metal phthalocyanines were investigated. Electron and charge density distribution and energy levels near frontier orbital and excited states were influenced by the deformed structures varied with central metal and charge. The magnetic parameters of chemical shifts in {sup 13}C-nuclear magnetic resonance ({sup 13}C-NMR), principle g-tensor, A-tensor, V-tensor of electric field gradient and asymmetry parameters derived from the deformed structures with magnetic interaction of nuclear quadruple interaction based on electron and charge density distribution with a bias of charge near ligand under crystal field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Stability of gyrotron operation in very high-order modes

This study was motivated by the desire to increase the power, which can be delivered by gyrotrons in long pulse and continuous regimes. Since the admissible power level is determined by the density of ohmic losses in resonator walls, to increase the radiated power a gyrotron should operate in higher order modes. Using an existing gyrotron developed for plasma experiments in the International Thermonuclear Experimental Reactor as a base model, the stability of operation of such a gyrotron in modes with larger number of radial variations was studied. It is shown that the power level achievable in such gyrotrons in stable single mode regimes is close to 1.5 MW. The power level 1.7-1.8 MW can be realized in regimes where the oscillations of the desired mode are accompanied by excitation of distant sidebands whose power is about 1% level of the power of the operating mode. Finally, in the case of operation at the 2-MW level, either the desired mode loses its stability and is replaced by less efficient oscillations of a mode with a smaller azimuthal index or oscillations of the operating mode are accompanied by excitation of sidebands with equally spaced frequencies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Structures and thermoelectric properties of double-filled (Ca{sub x}Ce{sub 1−x})Fe{sub 4}Sb{sub 12} skutterudites

The structures and thermoelectric properties of the double-filled (Ca{sub x}Ce{sub 1−x})Fe{sub 4}Sb{sub 12} series (x=0, 0.25, 0.5, 0.75, and 1) have been studied using a combined experimental and computational methods. Compounds of (Ca{sub x}Ce{sub 1−x})Fe{sub 4}Sb{sub 12} were obtained only for x=0, 0.5, and 1. Composition with x=0.25 was found to be a mixture of x=0 and 0.5 compounds, and composition with x=0.75 was found to be a mixture of x=1 and 0.5 compounds, respectively. Our conclusions on phase formation are supported by density functional theory (DFT) calculations. In Ca{sub 0.5}Ce{sub 0.5}Fe{sub 4}Sb{sub 12,} Ca substitution in the Ce site of CeFe{sub 4}Sb{sub 12} leads to high hole concentrations, resulting in stronger semimetal transport as compared to CeFe{sub 4}Sb{sub 12}. Ca{sub 0.5}Ce{sub 0.5}Fe{sub 4}Sb{sub 12} yields a slightly higher ZT value than that of CeFe{sub 4}Sb{sub 12}, which is attributed to its lower lattice thermal conductivity. Phonon mode calculations adopting a three-particle bending model suggest that thermal conductivity is reduced upon Ca substitution because of an additional vibration mode which involves both Ca and Ce atoms. - Graphical abstract: Detailed structural information to correlate with thermoelectric properties in a series of double-filled (Ca{sub x}Ce{sub 1−x})Fe{sub 4}Sb{sub 12} skutterudite samples were obtained using synchrotron X-ray diffraction and first principle calculations. - Highlights: • Research focus on phase stability of CaCe double-filled p-type skutterudite. • Stable structure forms for an equiatomic occupancy of the voids by Ca and Ce. • Samples feature two-phase mixtures with variations of filling atoms ratio. • Phase stablility is investigated by DFT total energy calculations. • Sample with Equiatomic occupancy of Ca and Ce show higher ZT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ultrasonic fingerprint sensor using a piezoelectric micromachined ultrasonic transducer array integrated with complementary metal oxide semiconductor electronics

This paper presents an ultrasonic fingerprint sensor based on a 24 × 8 array of 22 MHz piezoelectric micromachined ultrasonic transducers (PMUTs) with 100 μm pitch, fully integrated with 180 nm complementary metal oxide semiconductor (CMOS) circuitry through eutectic wafer bonding. Each PMUT is directly bonded to a dedicated CMOS receive amplifier, minimizing electrical parasitics and eliminating the need for through-silicon vias. The array frequency response and vibration mode-shape were characterized using laser Doppler vibrometry and verified via finite element method simulation. The array's acoustic output was measured using a hydrophone to be ∼14 kPa with a 28 V input, in reasonable agreement with predication from analytical calculation. Pulse-echo imaging of a 1D steel grating is demonstrated using electronic scanning of a 20 × 8 sub-array, resulting in 300 mV maximum received amplitude and 5:1 contrast ratio. Because the small size of this array limits the maximum image size, mechanical scanning was used to image a 2D polydimethylsiloxane fingerprint phantom (10 mm × 8 mm) at a 1.2 mm distance from the array.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗