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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Anomalous magneto-structural behavior of MnBi explained: A path towards an improved permanent magnet

Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation and magnetic susceptibility maximum near 90 K, and, importantly for high-temperature magnetic applications, an increasing coercivity (unique to MnBi) above 180 K. We calculate the total energy and magneto-anisotropy energy (MAE) versus (a, c) using DFT+U methods. We reproduce and explain all the above anomalies. We predict that coercivity and MAE increase due to increasing a, suggesting means to improve MnBi permanent magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Evolution of structural and magnetic properties due to nanocrystallization of mechanically milled amorphous Pr-Co-B powders

Pr{sub 2}Co{sub 14}B permanent magnet powders were prepared by mechanical milling of an arc-melted ingot. X-ray diffraction analysis revealed the presence of the 2:14:1 phase after 1 h of milling which transformed into an amorphous phase with additional milling time. Increasing the milling time also lowered the intrinsic coercivity while the saturation magnetization increased up to 105 emu/g. Differential scanning calorimetry measurements revealed a crystallization temperature of around 560 °C. Upon annealing 30 h of as-milled amorphous powders between 500 and 900 °C, we observed the precipitation of the 2:14:1 phase. The optimum post-milling annealing temperature was 600 °C with an intrinsic coercivity of 7 kOe and maximum energy product of 6 MGOe.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Binary pseudo-random patterned structures for modulation transfer function calibration and resolution characterization of a full-field transmission soft x-ray microscope

We present a modulation transfer function (MTF) calibration method based on binary pseudo-random (BPR) one-dimensional sequences and two-dimensional arrays as an effective method for spectral characterization in the spatial frequency domain of a broad variety of metrology instrumentation, including interferometric microscopes, scatterometers, phase shifting Fizeau interferometers, scanning and transmission electron microscopes, and at this time, x-ray microscopes. The inherent power spectral density of BPR gratings and arrays, which has a deterministic white-noise-like character, allows a direct determination of the MTF with a uniform sensitivity over the entire spatial frequency range and field of view of an instrument. We demonstrate the MTF calibration and resolution characterization over the full field of a transmission soft x-ray microscope using a BPR multilayer (ML) test sample with 2.8 nm fundamental layer thickness. We show that beyond providing a direct measurement of the microscope’s MTF, tests with the BPRML sample can be used to fine tune the instrument’s focal distance. Our results confirm the universality of the method that makes it applicable to a large variety of metrology instrumentation with spatial wavelength bandwidths from a few nanometers to hundreds of millimeters.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Structure Sensitivity of Acrolein Hydrogenation by Platinum Nanoparticles on Ba x Sr 1- x TiO 3 Nanocuboids

The structure sensitivity of Pt nanoparticles (Pt N ) for gas-phase acrolein (AC) hydrogenation was probed for Pt N on Ba x Sr 1- x TiO 3 nanocuboid supports with (0 0 1) facets in a combined theoretical and experimental study. The in situ selectivity for allyl alcohol increased with the increase of the Sr concentration in the support, which corresponds to modifications in the stable Winterbottom shape and lattice strain of the Pt nanoparticles as a result of the interfacial energy between Pt and the Ba x Sr 1- x TiO 3 supports. “Local model” nanofacets of the Pt surface, edge, and corner morphologies were developed as compact representations of adsorption and reaction sites. DFT was used as the primary modeling tool for the equilibrium adsorption states. We argue that adsorption on edge sites is critically important for the overall allyl alcohol selectivity of Pt N catalysts. A simple model was developed to represent Pt N strain effects caused by its interaction with the substrate. Bader topological atom, spherical volume averaging charge, and modified bond valence sum analyses were used to understand the bonding structure. Density of states analysis was performed for the structures of Pt N , adsorbed AC, and intermediate products to examine adsorbate–particle interactions. The simulated hydrogenation of AC on Pt N nanofacets was compared to the in situ hydrogenation of AC by Pt N on Ba x Sr 1- x TiO 3 to examine the effects of facet, edge, and corner sites on the overall selectivity.

bio-inspired↗