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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Layer-by-layer growth of graphene oxide multilayers using robust interlayer linking chemistry. 2 Zr–bissulfates

We report on the facile layer-by-layer growth of graphene oxide sulfate (GO-S) multilayer structures. The layers are bonded to a modified planar silica support using Zr 4+ ions. Optical ellipsometry shows step-by-step layer growth with layer thickness consistent with that expected from molecular mechanics calculations. The reaction to form Zr–bissulfate linkages is facile, with multistep layer deposition occurring within six to ten minutes per layer. The GO-S layers can be deposited directly on GO-S underlayer(s) or interlayer spacers can be incorporated to control the spacing with GO-S layers. X-ray photoelectron spectroscopy (XPS) data provides information on the density of the sulfonated groups present at the graphene oxide surface and on the Zr : S ratio. This is the first report we are aware of that demonstrates robust layer-by-layer growth of graphene oxide structures.

Graphene oxide↗
DOE OSTI2020

Materials Data on Pr(MoO2)6 by Materials Project

Pr(MoO2)6 crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. Pr3+ is bonded in a distorted square co-planar geometry to four equivalent O2- atoms. All Pr–O bond lengths are 2.45 Å. There are two inequivalent Mo+3.50+ sites. In the first Mo+3.50+ site, Mo+3.50+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MoO6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of Mo–O bond distances ranging from 2.06–2.23 Å. In the second Mo+3.50+ site, Mo+3.50+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MoO6 octahedra. The corner-sharing octahedra tilt angles range from 49–52°. There are a spread of Mo–O bond distances ranging from 1.95–2.23 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Pr3+ and three Mo+3.50+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to three Mo+3.50+ atoms. In the third O2- site, O2- is bonded in a distorted T-shaped geometry to three Mo+3.50+ atoms. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to three Mo+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2Cu(IF)2 by Materials Project

K2Cu(IF)2 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. K1+ is bonded in a distorted square co-planar geometry to two equivalent I1- and four equivalent F1- atoms. Both K–I bond lengths are 3.76 Å. All K–F bond lengths are 2.65 Å. Cu2+ is bonded in a square co-planar geometry to four equivalent I1- atoms. All Cu–I bond lengths are 2.65 Å. I1- is bonded in a distorted square co-planar geometry to two equivalent K1+ and two equivalent Cu2+ atoms. F1- is bonded in a square co-planar geometry to four equivalent K1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(SiO2)3 by Materials Project

Na(SiO2)3 crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Na is bonded in a distorted hexagonal planar geometry to three equivalent O atoms. All Na–O bond lengths are 2.24 Å. Si is bonded to four O atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.64–1.66 Å. There are three inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to two equivalent Si atoms. In the second O site, O is bonded in a linear geometry to two equivalent Si atoms. In the third O site, O is bonded in a distorted trigonal planar geometry to one Na and two equivalent Si atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1991

International Symposium on Space Terahertz Technology, 1st, University of Michigan, Ann Arbor, Mar. 5, 6, 1990, Proceedings

Problems, proposed solutions, and recent results related to the development of solid-state oscillators, detectors, mixers, diode multipliers, and antennas at THz frequencies are addressed. Individual topics considered include: submillimeter heterodyne remote sensing of upper atmospheric gases, planar dipole array antenna with an elliptical lens, twin slot antenna structures integrated with microbolometer detectors for 94-GHz imaging. Also discussed are: quantum-well and quantum-barrier diodes for generating submillimeter wave power, planar Schottky barrier mixer diodes for space applications at submillimeter wavelengths, GaAs Schottky barrier varactor diodes for submillimeter wavelength power generation, planar doped barrier devices for subharmonic mixers.

Ulaby, Fawwaz↗
NASA NTRS2013

Eliminating Obliquity Error from the Estimation of Ionospheric Delay in a Satellite-Based Augmentation System

Current satellite-based augmentation systems estimate ionospheric delay using algorithms that assume the electron density of the ionosphere is non-negligible only in a thin shell located near the peak of the actual profile. In its initial operating capability, for example, the Wide Area Augmentation System incorporated the thin shell model into an estimation algorithm that calculates vertical delay using a planar fit. Under disturbed conditions or at low latitude where ionospheric structure is complex, however, the thin shell approximation can serve as a significant source of estimation error. A recent upgrade of the system replaced the planar fit algorithm with an algorithm based upon kriging. The upgrade owes its success, in part, to the ability of kriging to mitigate the error due to this approximation. Previously, alternative delay estimation algorithms have been proposed that eliminate the need for invoking the thin shell model altogether. Prior analyses have compared the accuracy achieved by these methods to the accuracy achieved by the planar fit algorithm. This paper extends these analyses to include a comparison with the accuracy achieved by kriging. It concludes by examining how a satellite-based augmentation system might be implemented without recourse to the thin shell approximation.

delay estimation↗
DOE OSTI2023

Nanometer flat blazed x-ray gratings using ion beam figure correction

With the development of nanometer accuracy stitching interferometry, ion beam figuring (IBF) of x-ray mirrors can now be achieved with unprecedented performance. However, the process of producing x-ray diffraction gratings on these surfaces may degrade the figure quality due to process errors introduced during the ruling of the grating grooves. To address this challenge, we have investigated the post-production correction of gratings using IBF, where stitching interferometry is used to provide in-process feedback. A concern with ion beam correction in this case is that ions will induce enough surface mobility of atoms to cause smoothing of the grating structure and degradation of diffraction efficiency. In this study we found however that it is possible to achieve a nanometer-level planarity of the global grating surface with IBF, while preserving the grating structure. The preservation was so good, that we could not detect a change in the diffraction efficiency after ion beam correction. This is of major importance in achieving ultra-high spectral resolution, and the preservation of brightness for coherent x-ray beams.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Mixed finite element formulation for frictionless contact problems

Simple mixed finite element models and a computational procedure are presented for the solution of frictionless contact problems. The analytical formulation is based on a form of Reissner's large-rotation theory of the structure with the effect of transverse shear deformation included. The contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the internal forces (or stress resultants), the generalized displacements, and the Lagrange multipliers associated with the contact conditions. Numerical examples of axisymmetric deformations of a hemispherical shell and planar deformations of a circular ring are presented. Both structures are pressed against a rigid plate. Detailed information about the response of the structures is presented. The numerical studies demonstrate the high accuracy of the mixed models and the effectiveness of the computational procedure based on combining the geometrically nonlinear terms and the contact conditions in one iteration loop.

Noor, Ahmed K.↗
DOE OSTI2020

Materials Data on LiSbP2O7 by Materials Project

LiSbP2O7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Li1+ is bonded in a distorted trigonal planar geometry to three O2- atoms. There are a spread of Li–O bond distances ranging from 1.89–2.62 Å. Sb3+ is bonded to six O2- atoms to form distorted SbO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Sb–O bond distances ranging from 2.15–2.52 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three equivalent SbO6 octahedra and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 30–68°. There are a spread of P–O bond distances ranging from 1.53–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three equivalent SbO6 octahedra and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 23–67°. There are a spread of P–O bond distances ranging from 1.52–1.64 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Li1+, one Sb3+, and one P5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Li1+, one Sb3+, and one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Sb3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Sb3+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Sb3+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to one Li1+, one Sb3+, and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaSn5S11 by Materials Project

CaSn5S11 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ca2+ is bonded in a distorted pentagonal planar geometry to five S2- atoms. There are a spread of Ca–S bond distances ranging from 2.81–3.24 Å. There are five inequivalent Sn4+ sites. In the first Sn4+ site, Sn4+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing SnS6 octahedra. The corner-sharing octahedra tilt angles range from 54–59°. There are a spread of Sn–S bond distances ranging from 2.50–2.65 Å. In the second Sn4+ site, Sn4+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing SnS6 octahedra. The corner-sharing octahedra tilt angles range from 19–59°. There are a spread of Sn–S bond distances ranging from 2.56–2.68 Å. In the third Sn4+ site, Sn4+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing SnS6 octahedra. The corner-sharing octahedra tilt angles range from 4–59°. There are a spread of Sn–S bond distances ranging from 2.47–2.77 Å. In the fourth Sn4+ site, Sn4+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing SnS6 octahedra. The corner-sharing octahedral tilt angles are 59°. There are a spread of Sn–S bond distances ranging from 2.52–2.67 Å. In the fifth Sn4+ site, Sn4+ is bonded to six S2- atoms to form a mixture of distorted edge and corner-sharing SnS6 octahedra. The corner-sharing octahedra tilt angles range from 4–42°. There are a spread of Sn–S bond distances ranging from 2.49–2.92 Å. There are eleven inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted trigonal planar geometry to three Sn4+ atoms. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to one Ca2+ and two Sn4+ atoms. In the third S2- site, S2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Sn4+ atoms. In the fourth S2- site, S2- is bonded in a distorted T-shaped geometry to three Sn4+ atoms. In the fifth S2- site, S2- is bonded in a distorted trigonal planar geometry to one Ca2+ and two Sn4+ atoms. In the sixth S2- site, S2- is bonded in a distorted trigonal pyramidal geometry to one Ca2+ and three Sn4+ atoms. In the seventh S2- site, S2- is bonded in a distorted T-shaped geometry to one Ca2+ and two Sn4+ atoms. In the eighth S2- site, S2- is bonded in a distorted T-shaped geometry to three Sn4+ atoms. In the ninth S2- site, S2- is bonded in a distorted trigonal planar geometry to three Sn4+ atoms. In the tenth S2- site, S2- is bonded in a T-shaped geometry to three Sn4+ atoms. In the eleventh S2- site, S2- is bonded in a distorted trigonal planar geometry to three Sn4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pt3O4 by Materials Project

Pt3O4 crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. Pt+2.67+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Pt–O bond lengths are 2.00 Å. O2- is bonded in a trigonal planar geometry to three equivalent Pt+2.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cu3O4 by Materials Project

Cu3O4 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Cu+2.67+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Cu–O bond lengths are 1.88 Å. O2- is bonded in a trigonal planar geometry to three equivalent Cu+2.67+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Improving stability and strength characteristics of framed structures with nonlinear behavior

In this paper an optimal design procedure is introduced to improve the overall performance of nonlinear framed structures. The design methodology presented here is a multiple-objective optimization procedure whose objective functions involve the buckling eigenvalues and eigenvectors of the structure. A constant volume with bounds on the design variables is used in conjunction with an optimality criterion approach. The method provides a general tool for solving complex design problems and generally leads to structures with better limit strength and stability. Many algorithms have been developed to improve the limit strength of structures. In most applications geometrically linear analysis is employed with the consequence that overall strength of the design is overestimated. Directly optimizing the limit load of the structure would require a full nonlinear analysis at each iteration which would be prohibitively expensive. The objective of this paper is to develop an algorithm that can improve the limit-load of geometrically nonlinear framed structures while avoiding the nonlinear analysis. One of the novelties of the new design methodology is its ability to efficiently model and design structures under multiple loading conditions. These loading conditions can be different factored loads or any kind of loads that can be applied to the structure simultaneously or independently. Attention is focused on optimal design of space framed structures. Three-dimensional design problems are more complicated to carry out, but they yield insight into real behavior of the structure and can help avoiding some of the problems that might appear in planar design procedure such as the need for out-of-plane buckling constraint. Although researchers in the field of structural engineering generally agree that optimum design of three-dimension building frames especially in the seismic regions would be beneficial, methods have been slow to emerge. Most of the research in this area has dealt with the optimization of truss and plane frame structures.

Pezeshk, Shahram↗
NASA NTRS1987

Dynamics and control of a planar truss actuator

The concept of using an active truss actuator to control the vibration of a flexible (space) structure has been investigated. The actuator with a generic beam continuum cantilevered from it has been modeled using energy methods. A time-invariant optimal state feedback scheme was utilized for the control method. A digital simulation of the system dynamic response demonstrated the good vibration control possibilities for the (planar) truss actuator on a large flexible space structure.

Lovejoy, V. D.↗
DOE OSTI2025

Planar Defect Layers Template a High-Pressure InBi Polymorph

The short- and long-range order of III–V materials under high pressure has long been the subject of debate, with advancements in structural characterization leading to significant revisions to the accepted structural models. Despite these revisions, previous high-pressure structural assignments in the In–Bi system include the site-disordered β-Sn structure type, a structure type demonstrated to be nonexistent in analogous III–V systems. While X-ray diffraction is consistent with site disordering in InBi at high pressure, cluster expansion calculations indicate that disordering requires temperatures above 3000 K. Here, we propose InBi as a model material for studying unique high-pressure planar defects due to its highly anisotropic stress-dependent properties and structure. Specifically, we identify two sets of planar defects that mimic the diffraction pattern of a site disordered β-Sn structure type and are compatible with the calculated disorder barrier. We derive these defects by symmetry relations over crystallographic transitions. Density functional theory calculations of the proposed defects suggest that these defects are stabilized by diminishing interlayer separations with pressure. Further, we find that one of the proposed defects closely resembles a bulk high-pressure phase of InBi, InBi-ϵ, and we assert that the proposed defects order upon heating, acting as a template for InBi-ϵ growth. The proposed defects and their electronic structure provide a basis for the trend of superconducting critical temperature with increasing pressure. These methods for identifying defects are generalizable to other materials with reports of site disorder at high pressure, prompting a broader search for related high-pressure defects.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Pressure-induced cation and vacancy disorder-order transition and near-zero τ f in deficient hexagonal perovskite Ba 8 ZnTa 6 O 24 dielectrics

Pressure applications can enable the tuning of atomic/defect ordering and provide access to new functional materials. Here, in this study, we report that pressure-induced structural transformation featuring disorder-order transition of both cations and vacancies in the 8-layer deficient hexagonal perovskite tantalate dielectrics Ba 8 ZnTa 6 O 24 , which transformed the structure from twin to shift and remarkably lowered the temperature coefficient of resonant frequency τ f down to near zero (∼0.56 ppm/°C) from 38 ppm/°C for the twinned precursor. The atomic scale STEM-HAADF and EDS results confirm the ordering of Zn in the Ta host at the nanometer scale in the shifted material featuring well-ordered Ba 8 ZnTa 6 O 24 slabs intergrown with Ba 3 ZnTa 2 O 9 and Ba 5 Ta 4 O 15 monolayers and anti-phase grain boundaries as planar defects. The pressure-induced twin-shift structural transformation of Ba 8 ZnTa 6 O 24 features the rare constant concentration of the hexagonal stacked layers, which is allowed by the vacancy ordering at the central layers of face-shared octahedral (FSO) trimers avoiding the FSO B-B repulsion, and remarkably the faster cationic ordering kinetics compared with the 2:1 ordered complex perovskites. Although the inclusion of numerous planar defects and the oxidizable atomic defects led to significant p-type conduction and inhomogeneous electrical microstructures, resulting in an extraordinarily high extrinsic dielectric loss for the high-pressure shifted Ba 8 ZnTa 6 O 24 pellet, the intrinsically near-zero τ f could make the shifted Ba 8 ZnTa 6 O 24 perovskite an ideal microwave dielectric resonator candidate if the defects could be eliminated.

high pressure↗
DOE OSTI2020

Materials Data on ZrBeSi by Materials Project

ZrBeSi crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Be2+ is bonded in a trigonal planar geometry to three equivalent Si4- atoms. All Be–Si bond lengths are 2.16 Å. Zr2+ is bonded to six equivalent Si4- atoms to form a mixture of corner, edge, and face-sharing ZrSi6 octahedra. The corner-sharing octahedral tilt angles are 45°. All Zr–Si bond lengths are 2.82 Å. Si4- is bonded in a distorted trigonal planar geometry to three equivalent Be2+ and six equivalent Zr2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BC2N by Materials Project

BC2N crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. B3+ is bonded in a trigonal planar geometry to two equivalent C and one N3- atom. Both B–C bond lengths are 1.60 Å. The B–N bond length is 1.42 Å. C is bonded to one B3+, two equivalent C, and one N3- atom to form distorted corner-sharing CBC2N tetrahedra. There is one shorter (1.57 Å) and one longer (1.60 Å) C–C bond length. The C–N bond length is 1.47 Å. N3- is bonded in a trigonal planar geometry to one B3+ and two equivalent C atoms.

36 MATERIALS SCIENCE↗