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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

First principles materials design of novel functional oxides

We review our efforts to develop and implement robust computational approaches for exploring phase stability to facilitate the prediction-to-synthesis process of novel functional oxides. These efforts focus on a synergy between (i) electronic structure calculations for properties predictions, (ii) phenomenological/empirical methods for examining phase stability as related to both phase segregation and temperature-dependent transitions and (iii) experimental validation through synthesis and characterization. We illustrate this philosophy by examining an inaugural study that seeks to discover novel functional oxides with high piezoelectric responses. Lastly, our results show progress towards developing a framework through which solid solutions can be studied to predict materials with enhanced properties that can be synthesized and remain active under device relevant conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Iron Alloying on the Properties of Vanadium Dioxide

Results of investigations of the x-ray structural parameters of the crystal lattice and their temperature dependences in the vicinities of the metal-dielectric phase transition for V{sub 1–x}Fe{sub x}O{sub 2} solid solutions are reported together with results of comparison of x-ray and pycnometric densities of these materials. The defect concentration in the materials under study is estimated at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Pair distribution function analysis of La(Fe{sub 1−x}Ru{sub x})AsO compounds

The local structures of La(Fe{sub 1−x}Ru{sub x})AsO (0.00≤x≤0.80) compounds were investigated by means of pair distribution function analysis at room temperature; as a result, no phase separation or clustering takes place. Local distortions are no longer correlated beyond ∼15 Å for both pure and substituted samples, indicating that the presence of Ru atoms does not determine a notable variation in the length scale of the local distortion. Different types of short range correlation between Fe and Ru atoms do not produce significant changes in the pair distribution function. - Graphical abstract: Fe–As and Ru–As bond length distributions as obtained by pair distribution function analysis of La(Fe{sub 0.70}Ru{sub 0.30})AsO; As atoms (purple spheres) undergo a random shifting around their crystallographic positions (red spheres: Fe/Ru atoms). - Highlights: • No phase separation or clustering takes place in La(Fe{sub 1−x}Ru{sub x})AsO solid solutions. • Local distortions are no longer correlated beyond ∼15 Å. • Ru displays a tendency towards local enrichment in the transition metal sublattice.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Dislocation-Related Photoluminescence in Silicon Implanted with Germanium Ions

The influence exerted by the conditions of the post-implantation annealing of silicon implanted with germanium ions on how luminescence centers are formed is studied. Measurements by the technique of the Rutherford backscattering of medium- and high-energy ions demonstrates that implantation with 1-MeV germanium ions at a dose of 1.5 × 10{sup 14} cm{sup –2} does not lead to the amorphization of single-crystal silicon. It is found that subsequent high-temperature annealing of the implanted samples in a chlorine-containing atmosphere at a temperature of 1100°C for 0.5–1.5 h gives rise to so-called D1 and D2 dislocation-related luminescence lines with wavelengths of 1.54 and 1.42 μm. With increasing annealing duration, the intensity of the D1 line decreases and that of D2 remains constant, but the D1 line dominates in all the spectra. The possible factors responsible for a decrease in the intensity of the D1 line and, in particular, the diffusion of germanium atoms and the formation of a silicon–germanium solid solution are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

On the Combined Application of Raman Spectroscopy and Photoluminescence Spectroscopy for the Diagnostics of Multilayer Heterostructures

The results of studying GaInAs/GaInP/GaAs photodiode structures grown by metal–organic vapor-phase epitaxy are reported. A procedure for the diagnostics of such multilayer structures is developed. The procedure is based on the application of Raman spectroscopy in combination with photoluminescence spectroscopy in the mode of the lateral scanning of transverse cleavages. The compositions of the GaInAs and GaInP solid solutions are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mechanical property and microstructure evolution of nitrogen-modified Ti-6Al-4V alloy with core-shell structure by hot compression

Highlights: • Core-shell structured Ti-6Al-4 V is composed of α shells and α + β cores. • Nitrogen solution and core-shell structure significantly enhances the strength. • Core-shell structural alloy performs inhomogeneous deformation. - Abstract: Core-shell (CS) structured Ti-6Al-4 V (Ti64) alloy with single α shells and duplex α + β cores was fabricated by powder nitriding and spark plasma sintering. The mechanical property and microstructure evolution of CS-Ti64 alloy was investigated by compression at temperatures of 950–1100 °C and strain rates of 0.001–1 s{sup −1}. The nitrogen-induced solid solution strengthening and the nitrogen-stabilized CS structure significantly enhanced the compressive strength. Microstructure evolution of CS-Ti64, involved inhomogeneous deformation of the core and shell, which was quite different from that of the commercial Ti64. Regions adjacent to shells and central locations of cores suffered large strain and therefore preferentially underwent dynamic recrystallization (DRX). The deformation mechanism of the novel CS-Ti64 alloy was discussed in terms of the α shells, α laths and DRX.

36 MATERIALS SCIENCE↗
DOE OSTI2018

AlInPSbAs/InAs Heterostructures for Thermophotoelectric Converters

Using the method of floating-zone recrystallization with a temperature gradient, AlInPSbAs/InAs heterostructures for thermophotoelectric converters operating in the wavelength range of 500–3200 nm are obtained. The use of the AlInPSbAs quinary solid solutions as an active region thermophotoconverters allows one to increase the external quantum yield up to 0.9 in the spectral range of 520–2800 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural-Phase States of Fe–Cu and Fe–Ag Bimetallic Particles Produced by Electric Explosion of Two Wires

X-ray phase analysis, transmission electron microscopy, and X-ray microanalysis were used to examine the structural-phase states of Fe–Cu and Fe–Ag bimetallic nanoparticles. The nanoparticles were obtained by the electric explosion of two twisted metal wires in argon atmosphere. It was demonstrated that the nanoparticles have the structure of Janus particles. Presence of the Janus particle structure in the samples indicates formation of binary melt under conditions of combined electric explosion of two wires. Phases based on supersaturated solid solutions were not found in the examined samples. The data obtained allow arguing that it is possible to achieve uniform mixing of the two-wire explosion products under the described experiment conditions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Remarkable enhancement of La{sub (1-x)}Sm{sub x}CrO{sub 3} nanoperovskite properties: An influence of its doping concentrations

Highlights: • LSCO solid solutions have been synthesized using ball milling method for first time. • Highly polycrystalline single phase LSCO with tolerance factor 0.8 < T > 0.9. • Effective occupancy of dopants onto the respective lattice site is analyzed. • Exhibits dendritic morphology and aggregates with decreasing dopant concentrations. • Synthesized LSCO nanoperovskites exhibit room temperature antiferromagnetism. - Abstract: Rare earth orthochromites of type La{sub (1-x)}Sm{sub x}CrO{sub 3} ((LSCO) x = 0, 0.1, 0.3, 0.5) have been synthesized through solid state reaction. These polycrystalline samples exhibit orthorhombic crystal structure and its corresponding distortion depends on the dopant concentrations. With increasing dopant stoichiometry, the A-O bond length changes resulting in the augmentation of perovskite’s physical properties. The occupancy of relatively less ionic radii dopant influences the decrease in crystallite size, blue shift in emission spectrum and intensification of the phonon characteristic vibrations. The finer particles aggregate to form dendritic morphology and become distinct on Sm/La ratio increments as identified from electron micrographs and atomic force microscopy. Ambient temperature magnetization analysis reveals the enhancement of antiferromagnetic nature upon dopant increments.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Hot Rolling on the Microstructure and Mechanical Properties of Nitrogen Alloyed Austenitic Stainless Steel

In the present investigation, the effect of multi-pass hot rolling in the temperature range of 700–1000 °C on the microstructure and mechanical properties of nitrogen alloyed austenitic stainless steel was studied with the aid of optical microscopy, tensile testing and x-ray diffraction measurements. The microstructural changes that occurred in the hot rolled specimens were elongation of grains in rolling direction, nucleation of new grains at the grain boundaries of elongated grains and growth of nucleated grains to form fully recrystallized grains. Elongated grains formed at lower rolling temperature (700–800 °C) due to inadequate strain/temperature for the initiation of dynamic recrystallization. At higher rolling temperature (900–1000 °C), fine grains formed due to dynamic recrystallization. Tensile properties showed strong dependency on the rolling temperature. Tensile strength increased with the decrease in the rolling temperature at the cost of ductility. Maximum strength was observed in samples hot rolled at 700 °C with yield strength of 917 MPa and ductility of 25%. This variation in the tensile properties with the rolling temperature is attributed to changes in the dislocation density and grain structure. The estimated yield strength from the dislocation density, solid solution and grain boundary strengthening closely matched with experimentally determined yield strength confirming the role of dislocation density and grain size in the strengthening.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Investigations of Ba{sub x}Sr{sub 1−x}TiO{sub 3} ceramics and powders prepared by direct current arc discharge technique

Ba{sub x}Sr{sub 1−x}TiO{sub 3} ceramics with x ranging from 0 to 1 were prepared by direct current arc discharge technique and studied by means of x-ray diffraction (XRD) and Raman spectroscopy. The cubic-tetragonal ferroelectric phase transition in Ba{sub x}Sr{sub 1−x}TiO{sub 3} ceramics was found to occur at x ≈ 0.75. XRD investigation of as-grown BaTiO{sub 3} ceramics revealed co-existence of tetragonal and hexagonal modifications with a small amount of impurity phase BaTi{sub 4}O{sub 9}. No evidences of hexagonal phase were observed in Raman spectra of as-grown BaTiO{sub 3} ceramics, while Raman peaks related to hexagonal phase were clearly observed in the spectrum of fine-grain powders prepared from the same ceramics. A core-shell model for BaTiO{sub 3} ceramics prepared by direct current arc discharge technique is proposed. Absence of the hexagonal phase in any Ba{sub x}Sr{sub 1−x}TiO{sub 3} solid solution with x < 1 is discussed in the frame of specific atomic arrangement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Exponential Increase in the Resistivity upon Cooling and Superconductivity in Indium-Doped Pb{sub 0.45}Sn{sub 0.55}Te

We have analyzed the temperature and magnetic-field dependences of resistivity ρ(T, H) of semiconducting compound Pb{sub 0.45}Sn{sub 0.55}Te doped with 5 at % In under a hydrostatic compression at P < 12 kbar. It is found that the temperature dependence ρ(T) at all pressures at T < 100 K is exponential with the activation energy decreasing upon an increase in pressure; this is accompanied with a superconducting transition on the ρ(T) and ρ(H) dependences at P > 4.8 kbar at T > 1 K (T{sub c} = 1.72 K at a level of 0.5ρ{sub N} at P = 6.8 kbar). We consider the model describing the low-temperature “dielectrization” of the semiconducting solid solution and the formation of the superconducting state upon an increase in the hydrostatic compression P > 4 kbar.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Ferrotorryweiserite, Rh 5 Fe 10 S 16 , a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series

Ferrotorryweiserite, Rh 5 Fe 10 S 16 , occurs as small grains (≤20 µm) among droplet-like inclusions (up to 50 μm in diameter) of platinum-group minerals (PGM), in association with oberthürite or Rh-bearing pentlandite, laurite, and a Pt-Pd-Fe alloy (likely isoferroplatinum and Fe-Pd-enriched platinum), hosted by placer grains of Os-Ir alloy (≤0.5 mm) in the River Ko deposit. The latter is a part of the Sisim placer zone, which is likely derived from ultramafic units of the Lysanskiy layered complex, southern Krasnoyarskiy kray, Russia. The mineral is opaque, gray to brownish gray in reflected light, very weakly bireflectant, not pleochroic to weakly pleochroic (grayish to light brown tints), and weakly anisotropic. The calculated density is 5.93 g·cm –3 . Mean results (and ranges) of four WDS analyses are: Ir 18.68 (15.55–21.96), Rh 18.34 (16.32–20.32), Pt 0.64 (0.19–1.14), Ru 0.03 (0.00–0.13), Os 0.07 (0.02–0.17), Fe 14.14 (13.63–14.64), Ni 13.63 (12.58–14.66), Cu 4.97 (3.42–6.41), Co 0.09 (0.07–0.11), S 29.06 (28.48–29.44), and total 99.66 wt.%. They correspond to the following formula calculated for a total of 31 atoms per formula unit: (Rh 3.16 Ir 1.72 Pt 0.06 Ru 0.01 Os 0.01 ) Σ 4.95 (Fe 4.48 Ni 4.11 Cu 1.38 Co 0.03 ) Σ10.00 S 16.05 . The results of synchrotron micro-Laue diffraction studies indicate that ferrotorryweiserite is trigonal; its probable space group is $R\bar{3}m$ (#166) based on its Ni-analog, torryweiserite. The unit-cell parameters refined from 177 reflections are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å 3 , and Z = 3. The c:a ratio is 4.8502. The strongest eight peaks in the X-ray diffraction pattern derived from results of micro-Laue diffraction study [d in Å(hkil)(I)] are 2.7950 ($20\bar{2}5$) (100); 5.7143 (0006) (60); 1.7671 ($22\bar{4}0$) (44.4); 3.0486 ($20\bar{2}1$) (39.4); 5.7650 ($10\bar{1}2$) (38.6); 2.5956 ($20\bar{2}7$) (37.8); 3.0058 ($11\bar{2}6$) (36.5); and 1.5029 ($4\bar{2}\bar{2}12$) (35.3). Ferrotorryweiserite and the associated PGM crystallized from microvolumes of residual melt at late stages of crystallization of grains of Os- and Ir-dominant alloys occurred in lode zones of chromitites of the Lysanskiy layered complex. In a particular case, the residual melt is disposed peripherally around a core containing a disequilibrium association of magnesian olivine (Fo 72.9–75.6 ) and albite (Ab 81.6–86.4 ), with the development of skeletal crystals of titaniferous augite: Wo 40.8–43.2 En 26.5–29.3 Fs 20.3–22.6 Aeg 6.9–9.5 (2.82–3.12 wt.% TiO 2 ). Ferrotorryweiserite represents the Fe-dominant analog of torryweiserite. We also report occurrences of ferrotorryweiserite in the Marathon deposit, Coldwell Complex, Ontario, Canada, and infer the existence of the torryweiserite–ferrotorryweiserite solid solution in other deposits and complexes.

58 GEOSCIENCES↗
DOE OSTI2018

Electrocaloric Effect in a Lead Magnoniobate–Scandoniobate Relaxor

The electrocaloric effect and also the dielectric, pyroelectric, acoustic, and piezoelectric properties of a lead magnoniobate–scandoniobate solid solution in a biasing electric field have been studied. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructure and Wear Performance of Cobalt-Containing Iron-Based Slag-Free Self-shielded Flux-Cored Wire

A new type of cobalt-containing iron-based slag-free self-shielded flux-cored wire was developed for hardfacing. The influence of cobalt additions on the microstructure and wear performance of the hardfacing was investigated. The cobalt-containing iron-based hardfacing alloy has a typical hypereutectic microstructure consisting of primary M{sub 7}(C, B){sub 3} carbide, and a eutectic of M{sub 3}(C, B) carbide and austenite (part of which subsequently transformed into martensite). Cobalt promoted the formation of austenite and changed the morphology of the primary carbide and eutectic colonies. The morphology of primary carbide became fragmented with increasing cobalt due to the possible impeding effect of cobalt to the movement of the M{sub 7}(C, B){sub 3}/liquid interface. Different structures of the eutectic carbides were observed—the chrysanthemum structure for 1.42 wt.% cobalt, the skeleton form for 2.88 wt.% cobalt, the radial stripe 4.37 wt.% cobalt and the discrete stripe for 5.75 wt.% cobalt. Wear loss of the hardfacing alloy containing 2.88 wt.% cobalt was the smallest among all the alloys, owing to the large primary large carbide and skeleton-shaped eutectic carbides, the proper amount of austenite phase separating the M{sub 7}(C, B){sub 3} and M{sub 3}(C, B) carbides, the solid solution strengthening by cobalt in the matrix, and the high hardness of the alloy. Moreover, the wear resistance has a tendency to decrease with the increase in velocity as well as load.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Different Heat Treatments on the Microstructural Evolution and Mechanical Properties of Ni-Cr-Si Alloy Fabricated by Laser Additive Manufacturing

Ni-Cr-Si alloy samples were fabricated on mild steel via laser additive manufacturing technology. The microstructural evolution and mechanical properties of the samples were studied systematically in as-deposited conditions and under three different types of heat-treated conditions. The scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction results showed that the structures of the as-deposited samples were mainly dendritic matrices of γ(Ni, Fe), continuous interdendritic eutectics of γ + Ni{sub 3}B and discrete Cr-rich carbides and borides. After solid solution treatment, carbides (Cr{sub 7}C{sub 3}) and borides (CrB) precipitated on the boundary of the eutectic structure, distributing discretely in the matrix. In the solution plus aging heat-treated conditions, the interdendritic eutectics formed Ni{sub 3}Fe intermetallic compounds with a layered distribution. After annealing, the grains were refined, and the hard phases (CrB) were uniformly dispersed along the grain boundary. Among the tested samples, the as-deposited specimens exhibited the highest microhardness and good wear ability at room temperature; however, the wear resistance of the as-deposited sample obviously decreased at 250 °C. The mechanical properties of the specimens were not greatly improved by solution treatment or solution plus aging treatment. The sample subjected to annealing treatment exhibited excellent wear resistance both at room temperature and at a service temperature of 250 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced strength and electrical conductivity of ultrafine-grained Al-Mg-Si alloy processed by hydrostatic extrusion

Highlights: • Al-Mg-Si alloy was subjected to hydrostatic extrusion combined with aging treatment. • UFG Al-Mg-Si alloy with UTS of 332 MPa and conductivity of 58% IACS was obtained. • Precipitation process depended on applied strains and crystallographic texture. • Strengthening effect was achieved by UFG structure and needle-like β″ precipitates. • Precipitation of β″ and spherical β′/β particles at GB provided high conductivity. - Abstract: The effect of hydrostatic extrusion combined with an artificial aging on microstructure, mechanical and electrical properties of 6101 Al-Mg-Si alloy was investigated. It has been shown that such thermo-mechanical treatment is an effective method for producing of long wires with an ultrafine-grained microstructure (grain size of 300–400 nm) and enhanced ultimate tensile strength (> 330 MPa) and electrical conductivity (up to 58% IACS). The mechanical behavior of 6101 Al-Mg-Si alloy depended strongly on applied strains by hydrostatic extrusion and crystallographic texture. Higher accumulative strain accelerated the precipitation kinetics but decreased the age hardening response. The double fiber <100> and <111> texture was observed for hydrostatically extruded samples. The <001> grains with homogenously distributed needle-like β″ precipitates provided precipitation strengthening of material while <111> grains resulted in more efficient grain boundary strengthening. Quantitative microstructure characterization allowed adjusting physical model to estimate the electrical conductivity and compare it with experimental data. The high conductivity was provided mainly by decomposition of solid solution due to precipitation of needle-like β″ precipitates in the grain interior and spherical β′ or β particles located at grain boundaries.

36 MATERIALS SCIENCE↗