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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Enhanced microwave dielectric properties of Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics doping by metal Fe powders

Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics by adding mental Fe powders have been fabricated via the solid-state reaction method. The microstructures and optical properties of samples are systematically studied in order to establish the effects of Fe powder additives on microwave dielectric properties of Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics by x-ray diffraction, x-ray photoelectron spectroscopy, and optical reflective spectrum. The results show the coexistence of Fe{sup 2+} and Fe{sup 3+} in Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics, the decrease of O vacancy concentrations, and their incorporation into the B-site (Ti) of the Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} host lattice give rise to excellent microwave dielectric properties. All samples have a higher Q value above 290 while maintaining relatively high tunability above 16.6%. In particular, the sample with the composition of x = 0.035 mol has the dielectric constant of 889, Q Multiplication-Sign f value of 826 (at 1.370 GHz), and tunability of 24%, which are very promising for high power tunable devices. In comparison, Fe{sub 2}O{sub 3} oxide doped Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics with the same molar ratios of Fe exhibit inferior microwave properties. It indicates that additives of the metal Fe powders can more effectively improve dielectric properties of Ba{sub x}Sr{sub 1-x}TiO{sub 3} system than Fe{sub 2}O{sub 3} oxide.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Electrical and optical properties of Ta-Si-N thin films deposited by reactive magnetron sputtering

The electrical and optical properties of Ta{sub x}Si{sub y}N{sub z} thin films deposited by reactive magnetron sputtering from individual Ta and Si targets were studied in order to investigate the effects of nitrogen and silicon contents on both properties and their correlation to the film microstructure. Three sets of fcc-Ta{sub x}Si{sub y}N{sub z} thin films were prepared: sub-stoichiometric Ta{sub x}Si{sub y}N{sub 0.44}, nearly stoichiometric Ta{sub x}Si{sub y}N{sub 0.5}, and over-stoichiometric Ta{sub x}Si{sub y}N{sub 0.56}. The optical properties were investigated by near-normal-incidence reflectivity and ellipsometric measurements in the optical energy range from 0.375 eV to 6.8 eV, while the d.c. electrical resistivity was measured in the van der Pauw configuration from 20 K to 300 K. The optical and electrical measurements were interpreted using the standard Drude-Lorentz model and the so-called grain boundary scattering model, respectively. The electronic properties were closely correlated with the compositional and structural modifications of the Ta{sub x}Si{sub y}N{sub z} films due to variations in the stoichiometry of the fcc-TaN{sub z} system and the addition of Si atoms. According to the nitrogen and silicon contents, fcc-Ta{sub x}Si{sub y}N{sub z} films can exhibit room temperature resistivity values ranging from 10{sup 2} {mu}{Omega} cm to about 6 Multiplication-Sign 10{sup 4} {mu}{Omega} cm. The interpretation of the experimental temperature-dependent resistivity data within the Grain Boundary Scattering model, combined with the results from optical investigations, showed that the mean electron transmission probability G and the free carriers concentration, N, are the main parameters that control the transport properties of these films. The results indicated that the correlation between electrical and optical measurements with the chemical composition and the nanostructure of the Ta{sub x}Si{sub y}N{sub z} thin films provides a pertinent and consistent description of the evolution of the Ta-Si-N system from a solid solution to a nanocomposite material due to the addition of Si atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Bipolar resistive switching properties of Ti-CuO/(hexafluoro-hexa-peri-hexabenzocoronene)-Cu hybrid interface device: Influence of electronic nature of organic layer

This study reports the change in the structural and junction properties of Ti-CuO-Cu structure on incorporation of a 2-dimensional (2D) organic layer comprising of n-type hexafluoro-hexa-peri-hexabenzocoronene (6F-HBC). A bipolar resistive switching is observed in the device having interface between sputter deposited copper oxide (CuO) and vacuum sublimated 6F-HBC hybrid interface. The CuO/6F-HBC hybrid interface exhibits rectifying I-V characteristics in complete contrast to the ohmic and rectifying characteristics of junctions based on individual 6F-HBC and CuO layers. Large change in resistive switching property from unipolar resistive switching in CuO/HBC to bipolar resistive switching in CuO/6F-HBC interface was observed. At the CuO/6F-HBC interface, C1s peak corresponding to fluorinated carbon is shifted by 0.68 eV towards higher binding energy (BE) side and O1s peak due to non-lattice oxygen is shifted by 0.6 eV towards lower BE, confirming the interaction of O{sup 2-} ion in CuO with fluorinated carbon atoms in 6F-HBC at the hybrid interface. Correlation between conductive atomic force microscopy images and atomic force microscopy topography images, I-V characteristics in conducting, non-conducting, and pristine regions along with x-ray photoelectron spectroscopy results establishes the important role of hybrid interface to determining the resistive switching properties. This study demonstrates that the resistive switching and interface properties of a hybrid device based on inorganic and organic 2D materials can be modified by changing the electronic properties of organic layer by attaching suitable functional groups.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The adsorption properties of CO molecules on single-layer graphene nanoribbons

The adsorption properties of CO molecules on graphene nanoribbons (GRNs) are studied through the molecular dynamics (MD) method. The AIREBO and LJ potentials are used to describe the C-C bonds in GNR and the interactions between the carbon atoms in GNR and CO molecules, respectively. The influences of the environmental pressure and charge density on the adsorption properties of CO molecules on GRNs are taken into account in this study. The effects of charges carried by GNRs on the adsorption properties are investigated in two aspects: atom distribution and energy evolution. Its observation from the results shows that the Coulomb force plays a more important role in the adsorption phenomenon than the van der Waals force, and the higher the charge density is, the larger the amount of the adsorbed CO molecules becomes. Low charge densities (<3.291 C/m{sup 2}) do little for the system, that is to say, the GNRs present similar properties to the ones with no charges. However, relatively high charge densities (>4.937 C/m{sup 2}) have an obvious effect on the whole system. The results also indicate that the environmental pressure has great influence on the adsorption properties of COs on GRN, and the higher the pressure is, the greater the adsorption energy becomes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Comparative studies of optical and elastic properties of ZrO{sub 2} thin films prepared under normal and oblique incidence deposition geometries

Oblique angle deposited optical thin films have attracted recent researcher’s interest because of their attractive optical, micro-structural, mechanical properties and more importantly because of their great potential in achieving tunability in refractive index. These properties in turn make it important in case of designing different optical devices. In the present work, ZrO{sub 2} thin films have been deposited on fused silica substrate by electron beam evaporation technique in normal as well as oblique angle deposition configurations. Optical properties, especially refractive index of the films have been estimated by fitting the measured transmission spectra with suitable theoretical dispersion models. Atomic force microscopy has been employed to characterize morphological properties of samples. The elastic properties of both the films are estimated by Atomic Force Acoustic Microscopy, a new and highly sensitive technique for thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A non-destructive method for measuring the mechanical properties of ultrathin films prepared by atomic layer deposition

The mechanical properties of ultrathin films synthesized by atomic layer deposition (ALD) are critical for the liability of their coated devices. However, it has been a challenge to reliably measure critical properties of ALD films due to the influence from the substrate. In this work, we use the laser acoustic wave (LAW) technique, a non-destructive method, to measure the elastic properties of ultrathin Al{sub 2}O{sub 3} films by ALD. The measured properties are consistent with previous work using other approaches. The LAW method can be easily applied to measure the mechanical properties of various ALD thin films for multiple applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

On how differently the quasi-harmonic approximation works for two isostructural crystals: Thermal properties of periclase and lime

Harmonic and quasi-harmonic thermal properties of two isostructural simple oxides (periclase, MgO, and lime, CaO) are computed with ab initio periodic simulations based on the density-functional-theory (DFT). The more polarizable character of calcium with respect to magnesium cations is found to dramatically affect the validity domain of the quasi-harmonic approximation that, for thermal structural properties (such as temperature dependence of volume, V(T), bulk modulus, K(T), and thermal expansion coefficient, α(T)), reduces from [0 K-1000 K] for MgO to just [0 K-100 K] for CaO. On the contrary, thermodynamic properties (such as entropy, S(T), and constant-volume specific heat, C{sub V}(T)) are described reliably at least up to 2000 K and quasi-harmonic constant-pressure specific heat, C{sub P}(T), up to about 1000 K in both cases. The effect of the adopted approximation to the exchange-correlation functional of the DFT is here explicitly investigated by considering five different expressions of three different classes (local-density approximation, generalized-gradient approximation, and hybrids). Computed harmonic thermodynamic properties are found to be almost independent of the adopted functional, whereas quasi-harmonic structural properties are more affected by the choice of the functional, with differences that increase as the system becomes softer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Equations of state and transport properties of mixtures in the warm dense regime

We have performed average-atom molecular dynamics to simulate the CH and LiH mixtures in the warm dense regime, and obtained equations of state and the ionic transport properties. The electronic structures are calculated by using the modified average-atom model, which have included the broadening of energy levels, and the ion-ion pair potentials of mixtures are constructed based on the temperature-dependent density functional theory. The ionic transport properties, such as ionic diffusion and shear viscosity, are obtained through the ionic velocity correlation functions. The equations of state and transport properties for carbon, hydrogen and lithium, hydrogen mixtures in a wide region of density and temperature are calculated. Through our computing the average ionization degree, average ion-sphere diameter and transition properties in the mixture, it is shown that transport properties depend not only on the ionic mass but also on the average ionization degree.

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

Production of Ni-Cr-Ti-natural fibres composite and investigation of mechanical properties

Intermetallic materials such as Ni{sub 2}Ti, Cr{sub 2}Ti are among advanced technology materials that have outstanding mechanical and physical properties for high temperature applications. Especially creep resistance, low density and high hardness properties stand out in such intermetallics. The microstructure, mechanical properties of (%50Ni-%48Cr-%2Ti)-%10Naturel Fibres and (%64Ni-%32Cr-%4Ti)-%10Naturel Fibres powders were investigated using specimens produced by tube furnace sintering at 1000-1200-1400°C temperature. A composite consisting of ternary additions, a metallic phase, Ti,Cr and Ni have been prepared under Ar shroud and then tube furnace sintered. XRD, SEM (Scanning Electron Microscope), were investigated to characterize the properties of the specimens. Experimental results carried out for composition (%64Ni-%32Cr-%4Ti)-%10Naturel at 1400°C suggest that the best properties as 112.09HV and 5,422g/cm{sup 3} density were obtained at 1400°C.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A critical appraisal of the zero-multipole method: Structural, thermodynamic, dielectric, and dynamical properties of a water system

We performed extensive and strict tests for the reliability of the zero-multipole (summation) method (ZMM), which is a method for estimating the electrostatic interactions among charged particles in a classical physical system, by investigating a set of various physical quantities. This set covers a broad range of water properties, including the thermodynamic properties (pressure, excess chemical potential, constant volume/pressure heat capacity, isothermal compressibility, and thermal expansion coefficient), dielectric properties (dielectric constant and Kirkwood-G factor), dynamical properties (diffusion constant and viscosity), and the structural property (radial distribution function). We selected a bulk water system, the most important solvent, and applied the widely used TIP3P model to this test. In result, the ZMM works well for almost all cases, compared with the smooth particle mesh Ewald (SPME) method that was carefully optimized. In particular, at cut-off radius of 1.2 nm, the recommended choices of ZMM parameters for the TIP3P system are α ≤ 1 nm{sup −1} for the splitting parameter and l = 2 or l = 3 for the order of the multipole moment. We discussed the origin of the deviations of the ZMM and found that they are intimately related to the deviations of the equilibrated densities between the ZMM and SPME, while the magnitude of the density deviations is very small.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Communication: Multiple-property-based diabatization for open-shell van der Waals molecules

We derive a new multiple-property-based diabatization algorithm. The transformation between adiabatic and diabatic representations is determined by requiring a set of properties in both representations to be related by a similarity transformation. This set of properties is determined in the adiabatic representation by rigorous electronic structure calculations. In the diabatic representation, the same properties are determined using model diabatic states defined as products of undistorted monomer wave functions. This diabatic model is generally applicable to van der Waals molecules in arbitrary electronic states. Application to locating seams of conical intersections and collisional transfer of electronic excitation energy is demonstrated for O{sub 2} − O{sub 2} in low-lying excited states. Property-based diabatization for this test system included all components of the electric quadrupole tensor, orbital angular momentum, and spin-orbit coupling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Synthesis, microstructure and dielectric properties of zirconium doped barium titanate

We report on synthesis, microstructural and relaxor ferroelectric properties of Zirconium(Zr) doped Barium Titanate (BT) samples with general formula Ba(Ti{sub 1-x}Zr{sub x})O{sub 3} (x=0.20, 0.35). These lead-free ceramics were prepared by solid state reaction route. The phase transition behavior and temperature dependent dielectric properties and composition dependent ferroelectric properties were investigated. XRD analysis at room temperature confirms phase purity of the samples. SEM observations revealed retarded grain growth with increasing Zr mole fraction. Dielectric properties of BZT ceramics is influenced significantly by small addition of Zr mole fraction. With increasing Zr mole fraction, dielectric constant decreases while FWHM and frequency dispersion increases. Polarization vs electric field hysteresis measurements reveal ferroelectric relaxor phase at room temperature. The advantages of such substitution maneuvering towards optimizing ferroelectric properties of BaTiO{sub 3} are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A review on ab initio studies of static, transport, and optical properties of polystyrene under extreme conditions for inertial confinement fusion applications

Polystyrene (CH), commonly known as “plastic,” has been one of the widely used ablator materials for capsule designs in inertial confinement fusion (ICF). Knowing its precise properties under high-energy-density conditions is crucial to understanding and designing ICF implosions through radiation–hydrodynamic simulations. For this purpose, systematic ab initio studies on the static, transport, and optical properties of CH, in a wide range of density and temperature conditions (ρ= 0.1 to 100 g/cm 3 and T = 10 3 to 4 × 10 6 K), have been conducted using quantum molecular dynamics (QMD) simulations based on the density functional theory. We have built several wide-ranging, self-consistent material-properties tables for CH, such as the first-principles equation of state (FPEOS), the QMD-based thermal conductivity (Κ QMD ) and ionization, and the first-principles opacity table (FPOT). This paper is devoted to providing a review on (1) what results were obtained from these systematic ab initio studies; (2) how these self-consistent results were compared with both traditional plasma-physics models and available experiments; and (3) how these first-principles–based properties of polystyrene affect the predictions of ICF target performance, through both 1-D and 2-D radiation–hydrodynamic simulations. In the warm dense regime, our ab initio results, which can significantly differ from predictions of traditional plasma-physics models, compared favorably with experiments. When incorporated into hydrocodes for ICF simulations, these first-principles material properties of CH have produced significant differences over traditional models in predicting 1-D/2-D target performance of ICF implosions on OMEGA and direct-drive–ignition designs for the National Ignition Facility. Lastly, we will discuss the implications of these studies on the current small-margin ICF target designs using a CH ablator.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

The strain-induced transitions of the piezoelectric, pyroelectric, and electrocaloric properties of the CuInP 2 S 6 films

Low-dimensional ferroelectrics, ferrielectrics, and antiferroelectrics are of urgent scientific interest due to their unusual polar, piezoelectric, electrocaloric, and pyroelectric properties. The strain engineering and strain control of the ferroelectric properties of layered two-dimensional van der Waals materials, such as CuInP 2 (S,Se) 6 monolayers, thin films, and nanoflakes, are of fundamental interest and especially promising for their advanced applications in nanoscale nonvolatile memories, energy conversion and storage, nano-coolers, and sensors. Here, we study the polar, piezoelectric, electrocaloric, and pyroelectric properties of thin strained films of a ferrielectric CuInP 2 S 6 covered by semiconducting electrodes and reveal an unusually strong effect of a mismatch strain on these properties. In particular, the sign of the mismatch strain and its magnitude determine the complicated behavior of piezoelectric, electrocaloric, and pyroelectric responses. The strain effect on these properties is opposite, i.e., “anomalous,” in comparison with many other ferroelectric films, for which the out-of-plane remanent polarization, piezoelectric, electrocaloric, and pyroelectric responses increase strongly for tensile strains and decrease or vanish for compressive strains.

antiferroelectricity↗
DOE OSTI2024

Properties of photocurrent and metal contacts of highly resistive ultrawide bandgap semiconductors

Ultrawide bandgap (UWBG) semiconductors inherently exhibit very high electrical resistivities. This property presents not only challenges in probing their electrical transport properties but also difficulties to fabricate, understand, and characterize the electrical properties of metal contacts on these materials. Here, we report the measurements and analysis of the applied electric field dependence of photocurrent to reveal the effect of metal contacts on the transport properties of highly resistive h-BN. Our results indicate that even for h-BN with a room temperature resistivity as high as 1014 Ω cm, the as-deposited metal contact is not a completely blocking type as commonly assumed in previous analyses for other large bandgap insulating materials. By modifying the boundary condition between the metal/semiconductor interface, a quantitative description has been obtained, which can be used to determine if the metal contact is Ohmic or blocking type. This quantitative description should be applicable to all UWBG semiconductors with extremely high electrical resistivities. The work also provides a better understanding of how the metal contact type affects the transport properties of UWBG semiconductors in general.

Physics↗
DOE OSTI2019

A Critical Review of the Experimentally Known Properties of U-Pu-Zr Alloys. Part 1: Phases and Phase Diagrams

Each U-Pu-Zr metallic fuel pin contains multiple phases, whose properties and distributions evolve due to factors such as fission, nuclear transmutation, and elemental redistribution under the influence of chemical and thermal gradients. An understanding of experimental data about phases, phase relationships, and phase properties in the U-Pu-Zr system is needed to enable mechanistic modeling of these phenomena and guide future research. Although U-Pu-Zr alloys have been investigated for more than 60 years, relatively little reliable experimental information is available. Information about the technologically important alloy U-20Pu-10Zr (where numbers indicate weight percentages of Pu and Zr and the remainder is U) is even more limited. Many of the experimental results are available only in obscure reports published in the 1950s and 1960s. The quality of the results and experimental documentation varies widely. U-Pu-Zr alloys are difficult materials to study experimentally, and it is therefore useful for researchers to know what results have already been obtained, how reliable they are, and where they were reported. This paper provides a thorough compilation and critical assessment of the available experimental data involving properties of individual phases, phase transitions, and phase diagrams, with particular attention to measurements from alloys with compositions close to U-20Pu-10Zr (wt%). A following paper will review experimental measurements of other properties such as heat capacity, thermal expansion, thermal conductivity, and mechanical properties.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

THE MASS DISTRIBUTION AND ASSEMBLY OF THE MILKY WAY FROM THE PROPERTIES OF THE MAGELLANIC CLOUDS

We present a new measurement of the mass of the Milky Way (MW) based on observed properties of its largest satellite galaxies, the Magellanic Clouds (MCs), and an assumed prior of a {Lambda}CDM universe. The large, high-resolution Bolshoi cosmological simulation of this universe provides a means to statistically sample the dynamical properties of bright satellite galaxies in a large population of dark matter halos. The observed properties of the MCs, including their circular velocity, distance from the center of the MW, and velocity within the MW halo, are used to evaluate the likelihood that a given halo would have each or all of these properties; the posterior probability distribution function (PDF) for any property of the MW system can thus be constructed. This method provides a constraint on the MW virial mass, 1.2{sup +0.7}{sub -0.4} (stat.){sup +0.3}{sub -0.3} (sys.) Multiplication-Sign 10{sup 12} M{sub Sun} (68% confidence), which is consistent with recent determinations that involve very different assumptions. In addition, we calculate the posterior PDF for the density profile of the MW and its satellite accretion history. Although typical satellites of 10{sup 12} M{sub Sun} halos are accreted over a wide range of epochs over the last 10 Gyr, we find a {approx}72% probability that the MCs were accreted within the last Gyr, and a 50% probability that they were accreted together.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE POLARIZATION PROPERTIES OF INVERSE COMPTON EMISSION AND IMPLICATIONS FOR BLAZAR OBSERVATIONS WITH THE GEMS X-RAY POLARIMETER

NASA's Small Explorer Mission GEMS (Gravity and Extreme Magnetism SMEX), scheduled for launch in 2014, will have the sensitivity to detect and measure the linear polarization properties of the 0.5 keV and 2-10 keV X-ray emission of a considerable number of galactic and extragalactic sources. The prospect of sensitive X-ray polarimetry justifies a closer look at the polarization properties of the basic emission mechanisms. In this paper, we present analytical and numerical calculations of the linear polarization properties of inverse Compton scattered radiation. We describe a generally applicable formalism that can be used to numerically compute the polarization properties in the Thomson and Klein-Nishina regimes. We use the code to perform for the first time a detailed comparison of numerical results and the earlier analytical results derived by Bonometto et al. for scatterings in the Thomson regime. Furthermore, we use the numerical formalism to scrutinize the polarization properties of synchrotron self-Compton (SSC) emission, and of inverse Compton radiation emitted in the Klein-Nishina regime. We conclude with a discussion of the scientific potential of future GEMS observations of blazars. The GEMS mission will be able to confirm the synchrotron origin of the low-energy emission component from high-frequency-peaked BL Lac objects. Furthermore, the observations have the potential to decide between an SSC and external-Compton origin of the high-energy emission component from flat spectrum radio quasars and low-frequency-peaked BL Lac objects.

79 ASTRONOMY AND ASTROPHYSICS↗