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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Characterization of raw and burnt oil shale from Dotternhausen: Petrographical and mineralogical evolution with temperature

The Toarcian Posidonia shale from Dotternhausen, Germany, is quarried and burnt in a fluidized bed reactor to produce electricity. The combustion residue, namely burnt oil shale (BOS), is used in the adjacent cement work as an additive in blended cements. The starting material is a typical laminated oil shale with an organic matter content ranging from 6 to 18%. Mineral matter consists principally of quartz, feldspar, pyrite and clays. After calcination in the range, the resulting product, burnt oil shale, keeps the macroscopic layered texture however with different mineralogy (anhydrite, lime, iron oxides) and the formation of an amorphous phase. This one, studied under STEM, reveals a typical texture of incipient partial melting due to a long retention time (ca. 30 min) and quenching. An in-situ high temperature X-ray diffraction (HTXRD) allowed studying precisely the mineralogical changes associated with the temperature increase. - Highlights: • We present oil shale/burnt oil shale characterization. • The Posidonia Shale is burnt in a fluidized bed. • Mineralogical evolution with temperature is complex. • The burnt oil shale is used in composite cements.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure characterization of LAE442 magnesium alloy processed by extrusion and ECAP

The magnesium alloy LAE442 was processed by extrusion and equal channel angular pressing (ECAP) to achieve ultrafine grained microstructure. Detailed characterization of the microstructure was performed by scanning electron microscope, electron back scattered diffraction (EBSD) and transmission electron microscope. The initial, as-cast, microstructure consisted of large grains of ~ 1 mm. The grain refinement due to the processing by severe plastic deformation led to a decrease of the average grain size to ~ 1.7 μm after the final step of ECAP. A detailed characterization of secondary phases showed the precipitation of Al{sub 11}RE{sub 3}, Al{sub 2}Ca and Al{sub 10}RE{sub 2}Mn{sub 7} intermetallic phases. X-ray diffraction measurements proved that Li is dissolved within the magnesium matrix in the as-cast condition. Newly formed Al{sub 3}Li phase was observed after ECAP. The texture formation due to the extrusion and ECAP was different from that in the other magnesium alloys due to the activation of non-basal slip systems as a result of the decrease of the c/a ratio. - Highlights: • Combined extrusion and equal channel angular pressing results in significant grain refinement by factor 1000 approximately. • Al{sub 11}RE{sub 3}, Al{sub 2}Ca and Al{sub 10}RE{sub 2}Mn{sub 7} secondary phases are present in the as-cast material while Li was dissolved in the Mg matrix. • Extrusion and ECAP have no effect on the composition of the secondary phases but they influence strongly their distribution. • Texture evolution is affected by decrease of c/a ratio due to the presence of Li and resulting activation of non-basal slip.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Examining the microtexture evolution in a hole-edge punched into 780 MPa grade hot-rolled steel

The deformation behavior in the hole-edge of 780 MPa grade hot-rolled steel during the punching process was investigated via microstructure characterization and computational simulation. Microstructure characterization was conducted to observe the edges of punched holes through the thickness direction, and electron back-scattered diffraction (EBSD) was used to analyze the heterogeneity of the deformation. Finite element analysis (FEA) that could account for a ductile fracture criterion was conducted to simulate the deformation and fracture behaviors of 780 MPa grade hot-rolled steel during the punching process. Calculation of rotation rate fields at the edges of the punched holes during the punching process revealed that metastable orientations in Euler space were confined to specific orientation groups. Rotation-rate fields effectively explained the stability of the initial texture components in the hole-edge region during the punching process. A visco-plastic self-consistent (VPSC) polycrystal model was used to calculate the microtexture evolution in the hole-edge region during the punching process. FEA revealed that the heterogeneous effective strain was closely related to the heterogeneity of the Kernel average misorientation (KAM) distribution in the hole-edge region. A simulation of the deformation microtexture evolution in the hole-edge region using a VPSC model was in good agreement with the experimental results. - Highlights: •We analyzed the microstructure in a hole-edge punched in HR 780HB steel. •Rotation rate fields revealed the stability of the initial texture components. •Heterogeneous effective stain was closely related to the KAM distribution. •VPSC model successfully simulated the deformation microtexture evolution.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Friction consolidation of gas-atomized Fe−Si powders for soft magnetic applications

Soft magnetic materials are often limited in scalability due to conventional processes that do not retain beneficial microstructures, and their associated physical properties, during densification. In this work, friction consolidation (FC) has been studied to fabricate Fe−Si soft magnetic materials from gas-atomized powder precursors. Fe−Si powder is consolidated using variable pressure and tool rotation speed in an effort to evaluate this unique densification approach for potential improvements in magnetic properties. FC, due to the high shear deformation involved, is shown to result in uniform gradual grain structure refinement across the consolidated workpiece from the center nearest the tool to the edge. Magnetic properties along different orientations indicate little, if any, textural orientation in the refined grain structure. The effect of annealing on the magnetic properties is evaluated and shown to decrease coercivity. FC processing was able to retain the magnetization of the original gas-atomized powders but further process optimization is needed to reach the optimal coercivity for the soft magnetic materials applications. - Highlights: •Friction stir processing was utilized to consolidate Fe−Si soft magnetic powders. •The resultant microstructure and magnetic properties were correlated to the processing conditions. •Friction consolidation refined the grain size of the materials by ~ 40%. •Annealing successfully reduced the coercivity induced by the stress during processing. •The results shine light on the possible scaling up of nanostructured materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The partial substitution of Y with Gd on microstructures and mechanical properties of as-cast and as-extruded Mg-10Zn-6Y-0.5Zr alloy

Highlights: • The as-extruded Mg-10Zn-6Y-0.5Zr and Mg-10Zn-3Y-3Gd-0.5Zr alloys show bimodal microstructure and DRXed microstructure. • In addition to W phase, Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt. %) alloy. • The as-extruded Mg-10Zn-6Y-0.5Zr (wt. %) alloy exhibits TYS of 341 MPa, UTS of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt. %) alloy shows lower TYS of 247 MPa, UTS of 330 MPa and higher elongation to failure of 19.8%. - Abstract: Mg-10Zn-6Y-0.5Zr (wt%) alloy and Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy with medium RE content have been fabricated by conventional casting and indirect extrusion. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy shows a bimodal microstructure containing dynamic recrystallized (DRXed) grains with average grain size of 2 μm and deformed regions. In addition to the fragmented W phase particle bands distributing along the extrusion direction, large amount of nano W phase and small amount of nano β{sub 2}′ phase are precipitated in the matrix. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy exhibits completely dynamic recrystallized microstructure with average grain size of 3 μm. The broken W phase particles are distributed homogeneously in the matrix. Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy exhibits yield strength of 341 MPa, ultimate tensile strength of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy shows lower yield strength of 247 MPa, ultimate tensile strength of 330 MPa and higher elongation to failure of 19.8%. The higher strength in the as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy is mainly attributed to higher area fraction of unDRXed regions with strong texture and the precipitation of nano W and β{sub 2}′ phase. The fully recrystallized microstructure with weak texture and the formation of icosahedral quasicrystal phases with good coherent bond with α-Mg contribute to the good ductility of the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of differential speed rolling ratio on the ridging behavior of ultra purified 17%Cr ferritic stainless steel

Highlights: • Differential rolling process improves ridging resistance of ferritic stainless steel. • Texture orientation inhomogeneity were attributed to non-uniform deformation. • Shear bands results in homogeneous deformation and recrystallization nucleation. • Uniform recrystallization grains and random orientation grains were obtained. - Abstract: The effect of the differential speed rolling on the ridging resistance and the crystallographic texture evolution of ultra purified 17%Cr ferritic stainless steel was investigated in order to select the optimal procedure for improving the surface quality. In the present study, the three different cold rolling processes were carried out: a conventional cold rolling and two different speed ratios asymmetric rolling. In the conventional cold rolling, the ridging of ferritic stainless steel was pronounced due to the band-like clusters of grains with similar crystallographic orientations. For differential speed rolling, ridging depth decreased and ridging was less pronounced when a higher different speed ratio was applied. The results show that severe ridging is attributed to the presence of band-like clusters of γ-fiber (<111>//ND) oriented grains. The shear bands introduced by differential speed rolling can enhance the nucleation for recrystallization both in grain interiors and grain boundaries, which can fragment the band-like clusters of similar orientation effectively, promoting the random grain orientation and improving surface quality.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the improvement of measurement accuracy of retained austenite in steel with X-ray diffraction

Highlights: • Improved procedure to determine austenite in steels with crystallographic texture • Extension to X-ray area detectors • Electropolishing is essential to get correct results. - Abstract: An improved measurement scheme for the determination of the retained austenite fraction with X-ray diffraction is extended to area detectors. The scheme reduces the error due to crystallographic texture in phase analysis of steel by averaging the results of diffraction patterns at different sample positions. The method is based on the standard ASTM E975, but it can be easily extended to other crystal structures, multi-phase materials or X-ray wavelengths. Phase transformation, induced by mechanical sample preparation, may lead to a significant reduction of the retained austenite fraction. Electropolishing before the measurement is beneficial to remove the layer affected by sample preparation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A compositional gradient Ce1−xZrxO2 buffer architecture for producing high-performance YBCO film

Highlights: • The compositional gradient CZO buffer architecture can help improve the biaxial texture of YBCO film. • The high density stacking faults are directly observed via a spherical aberration corrected transmission electron microscope. • The enhanced flux pinning force and current-carrying capacity of YBCO films are achieved as a result of lattice strains. - Abstract: In this work, YBCO films were epitaxially grown on Ce{sub 1−x}Zr{sub x}O{sub 2} (CZO) buffered yttria stabilized zirconia (YSZ) single crystal substrates through a fluorine-free sol-gel process. The influence of two different CZO buffer architectures on the microstructure and superconducting properties of YBCO films was investigated. According to XRD results in combination with (S)TEM analysis, it was confirmed that YBCO film grown on the gradient CZO buffer layer (CZO-G) exhibits better in-plane and out-of-plane texture than YBCO film deposited on the uniform CZO buffer layer (CZO-20). And besides, the superconducting performances especially the current-carrying capacity under magnetic field of the former was much higher than that of the latter, which means that the enhanced flux pinning force will be presented in YBCO film on CZO-G buffer layer. The maximum pinning force of the YBCO film grown on CZO-G buffer architecture is up to 17.67 GN/m{sup 3} @ 65 K. HR-STEM analysis shows that the stacking faults within YBCO matrix gave rise to the considerable nanoscale lattice-strains which may suppress the formation of Copper pairs and produce nanoscale non-superconducting regions served as pinning centers to significantly improve the flux pinning performance of YBCO film. Given the above, it has been implied that high-performance YBCO coated conductor can be developed by using a compositional gradient Ce{sub 1−x}Zr{sub x}O{sub 2} films as buffer architecture.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Quasi in-situ analysis of geometrically necessary dislocation density in α-fibre and γ-fibre during static recrystallization in cold-rolled low-carbon Ti-V bearing microalloyed steel

Highlights: • Average GND density is higher in gamma fibre than alpha fibre. • Higher drop in average GND density in un-recrystallized portion of gamma fibre • Fine precipitates pin the grain boundary at 700 °C 0 s. • Precipitates are coarse at 800 °C and present inside strain-free grains. - Abstract: In the present study, cold-rolled low-carbon steel is annealed at three different conditions: 700 °C for 0 s, 800 °C for 0 s and 800 °C for 2 min at the heating rate of ~10 °C/s. Recrystallization behaviour on sample surface is studied using a heated stage Scanning Electron Microscopy and Electron Backscattered Diffraction. For the lower annealing temperature of 700 °C with no dwell, almost no recrystallization is observed and microstructure resembles the as-received deformed material with the exception of occasional sub-micron sized nuclei. For the annealing conditions of 800 °C 0 s and 800 °C 2 min, onset and evolution of recrystallization is observed in-situ as a function of the initial as-cold rolled texture. Slower recovery rate of alpha fibre than gamma fibre is observed and confirmed by lower drop in average geometrically necessary dislocation (GND) density for un-recrystallized alpha fibres (1.1E+14 m{sup −2} for 700 °C 0 s, 1.4E+14 m{sup −2} for 800 °C 0 s and 4.5E+14 m{sup −2} for 800 °C 2 min) than for un-recrystallized gamma fibre grains (3.0E+14 m{sup −2} for 700 °C 0 s, 6.2E+14 m{sup −2} for 800 °C 0 s and 9.8E+14 m{sup −2} for 800 °C 2 min) during annealing. Strong gamma texture in recrystallized matrix is found for annealing conditions of 800 °C 0 s and 800 °C 2 min. From TEM characterisation it was shown that sub-grain boundaries are decorated with fine precipitates (diameter d < 15 nm) of titanium‑vanadium carbides (Ti,V)C for the annealing condition of 700 °C 0 s, which suggests that these precipitates play a major overall role in retardation of the recrystallization kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microstructural and micro-mechanical analysis of 14YWT nanostructured Ferritic alloy after varying thermo-mechanical processing paths into tubing

Microstructural analyses and micro-pillar compression were conducted on 14YWT nanostructured ferritic alloy (NFA) to compare different processing pathways: hydrostatic extrusion and Pilger processing with varying annealing temperatures into thin walled tubing, and after hot extrusion and cross-rolling into a plate. Hydrostatic extrusion at 815 °C resulted in the smallest grain sizes and highest yield strength of 1.20 GPa. Pilger processing with annealing at 800 °C had fine grained regions and bands of coarse grains, leading to a large variation in yield strength of 0.9–1.40 GPa. Higher annealing temperatures of 1200 °C after pilger processing significantly increased the grain size and lowered the yield strength to 1.01 GPa. These tubes showed a stronger (111) crystallographic texture in the normal direction and elongated grains in the extrusion direction. Characterization of the nano-oxides using TEM reveals more numerous, smaller oxides present in tubing processed at lower temperatures. Overall, this work shows NFA tubing after hydrostatic extrusion and pilger processing can lead to fine grained microstructures and texturing leading to higher yield strengths at lower annealing temperatures (e.g. 800 °C).

14YWT↗
DOE OSTI2021

Direct Observation of Tungsten Oxidation Studied by In Situ Environmental TEM

In this study, in situ environmental transmission electron microscopy (ETEM) was applied, for the first time, to investigate the thermal oxidation of a pristine and a self-ion irradiated polycrystalline tungsten, using a MEMS-based gas cell at 500 oC to 900 oC in a 1 bar 2%O2/N2 gas mixture. By tracking the dynamic evolution of the tungsten oxide scale as it initiates, grows, and sublimates during a consecutive thermal oxidation experiment, we observed two distinctive tungsten oxide microstructure – one nanocrystalline o-WO3 scale grown on W{27-1 } and W{1-1 8} and another o-WO3 scale exhibits a novel highly textured nanostructure. While the two oxide microstructures shared a similar thickness of ~200 nm after 40-minute early-stage oxidation, the nanocrystalline scale on the W{27-1 } grew much more rapidly at 800 oC than the highly textured oxide at a higher temperature of 900 oC. This suggests both the microstructure of these tungsten oxide scales as well as their oxidation kinetics are highly sensitive to the tungsten surface orientation, and such correlations also change dynamically in the course of oxidation. We also discuss the tungsten oxidation mechanism, the effects of the TEM foil thickness, and the focused ion beam (FIB) Ga+ damage on in situ ETEM oxidation.

In situ ETEM, Tungsten, Thermal oxidation, Orienta↗
DOE OSTI2012

Surface and related bulk properties of titania nanoparticles recovered from aramid–titania hybrid films: A novel attempt

Highlights: ► Aramid–titania hybrid films (5 and 10 wt%-TiO{sub 2}) were prepared via sol–gel processing. ► 450 °C calcination of the films yield anatase-TiO{sub 2} nanoparticles of rod-like morphology. ► The titania nanoparticle, crystal structure, high surface area are stable up to 800 °C. ► The novel approach has the advantage of nearly 100% recovery of titania. ► Increasing calcination temperature up to 1100 °C triggers anatase → rutile transition. -- Abstract: 5 and 10 wt%-TiO{sub 2}-containing aramid–titania hybrid films were prepared using sol–gel processing improved by the inclusion of 3-isocyanato-propyltriethoxysilane (ICTOS) to strengthen bonding of the titania species to the polymer backbone and, hence, lessen its agglomeration. The films were thermally degraded by heating at 450 °C in a dynamic atmosphere of air. The solid residues were found by thermogravimetry, X-ray diffractometry and electron microscopy to consist dominantly of uniformly agglomerated rod-like anatase-TiO{sub 2} nanoparticles, irrespective of the titania content of the film. The recovered titania particle morphology and surface microstructure were examined by field emission scanning and high-resolution transmission electron microscopy, respectively. Whereas, the particle surface chemistry and texture were assessed, respectively, by means of X-ray photoelectron spectroscopy and N{sub 2} sorptiometry. The recovered titanias were found, irrespective of the film content of titania, to enjoy not only a high temperature (up to 800 °C) stable nanoscopic anatase bulk structure, but also a high-temperature stable surface chemical composition (lattice Ti{sup 4+} and O{sup 2−}, and adsorbed OH/CH{sub x} species), (101)-faceted microstructure and highly accessible (145–112 m{sup 2}/g), uniform mesoporous texture with average pore diameter in the narrow range of 3.9–6.3 nm. Increasing the calcination temperature up to 1100 °C enhances an anatase → rutile transition, the extent of which is larger the higher the titania content of the film.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Roughness-based monitoring of transparency and conductivity in boron-doped ZnO thin films prepared by spray pyrolysis

Graphical abstract: Display Omitted Highlights: ► We report surface roughness dependent transparency and conductivity in ZnO films. ► The surface roughness with respected to boron doping concentrations is studied. ► Boron doped and pristine Zinc oxide thin films have showed ≥95% transmittance. ► Increased carrier concentration of 9.21 × 10{sup 21} cm{sup −3} revealed from Hall measurement. -- Abstract: Sprayed polycrystalline ZnO and boron-doped ZnO thin films composed of spherical grains of 25–32 nm in diameters are used in roughness measurement and further correlated with the transparency and the conductivity characteristics. The surface roughness is increased up to Zn{sub 0.98}B{sub 0.02}O and then declined at higher boron concentrations. The sprayed ZnO films revealed ≥95% transmittance in the visible wavelength range, 1.956 × 10{sup −4} Ω cm electrical resistivity, 46 cm{sup 2}/V s Hall mobility and 9.21 × 10{sup 21} cm{sup −3} charge carrier concentration. The X-ray photoelectron spectroscopy study has confirmed 0.15 eV binding energy change for Zn 2p{sub 3/2} when 2 at% boron content is mixed without altering electro-optical properties substantially. Finally, using soft modeling importance of these textured ZnO over non-textured films for enhancing the solar cells performance is explored.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nanosized Ni–Al layered double hydroxides—Structural characterization

Highlights: ► The takovite anionic clays were obtained using the sol–gel method. ► The effect of samples’ composition on the structural and textural characteristics has been investigated. ► X-ray analysis. ► FTIR spectroscopy evidenced a disordered interlayer structure. ► FESEM and TEM analysis showed that the samples have high porosity. - Abstract: Takovite, a natural mineral with the formula Ni{sub 6}Al{sub 2}(OH){sub 6}CO{sub 3}·5H{sub 2}O belongs to the large class of layered double hydroxides (LDHs) and contains positively charged Ni(II) and Al(III) layers alternating with layers containing carbonate ions and water molecules. Mesoporous takovite-type layered double hydroxides (LDH) of the general formula [Ni{sub 1−x}Al{sub x}(OH){sub 2}]{sup x+}(CO{sub 3}{sup 2−}){sub x/2}·nH{sub 2}O with different Ni/Al molar ratios (1.9–2.8) have been successfully synthesized by the sol–gel method, followed by anionic exchange using nickel acetylacetonate and aluminum isopropylate as cation precursors. A single LDH phase and an anisotropic growth of very small crystallites (below 4 nm) have been evidenced by X-ray diffraction. The effect of samples’ composition on their structural and textural characteristics has been investigated. The BET surface area values are in the range of 100–122 m{sup 2}/g. BJH pore radius decreased with increase in the Al(III) content in the LDHs. FESEM micrographs show large aggregates of highly porous LDH particles, while TEM analysis reveals irregular agglomerates of crystallites, among which some of them displayed a developing hexagonal shape. The average particle size variation with the Al(III) content in the samples follows the same trend as the pore radius, the sample with the highest Ni/Al ratio displaying also the smallest particle size. This sample becomes even more interesting, since TEM analysis shows agglomerates with inside circular structures, feature not observed for the other Ni/Al ratios investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Facile synthesis of phosphorus doped graphitic carbon nitride polymers with enhanced visible-light photocatalytic activity

Graphical abstract: - Highlights: • P-doped g-C{sub 3}N{sub 4} has been prepared by a one-pot green synthetic approach. • The incorporation of P resulted in favorable textural and electronic properties. • Doping with P enhanced the visible-light photocatalytic activity of g-C{sub 3}N{sub 4}. • A postannealing treatment further enhanced the activity of P-doped g-C{sub 3}N{sub 4}. • Photogenerated holes were the main species responsible for the activity. - Abstract: Phosphorus-doped carbon nitride materials were prepared by a one-pot green synthetic approach using dicyandiamide monomer and a phosphorus containing ionic liquid as precursors. The as-prepared materials were subjected to several characterizations and investigated as metal-free photocatalysts for the degradation of organic pollutants (dyes like Rhodamine B, Methyl orange) in aqueous solution under visible light. Results revealed that phosphorus-doped carbon nitride have a higher photocatalytic activity for decomposing Rhodamine B and Methyl orange in aqueous solution than undoped g-C{sub 3}N{sub 4}, which was attributed to the favorable textural, optical and electronic properties caused by doping with phosphorus heteroatoms into carbon nitride host. A facile postannealing treatment further improved the activity of the photocatalytic system, due to the higher surface area and smaller structural size in the postcalcined catalysts. The phosphorus-doped carbon nitride showed high visible-light photocatalytic activity, making them promising materials for a wide range of potential applications in photochemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microstructural and mechanical characteristics of Ni–Cr thin films

Highlights: • Ni–Cr thin films of varied composition deposited by DC magnetron co-sputtering. • Thin film with Ni–Cr: 80–20 at% composition exhibits most distinct behavior. • The films were tensile tested and exhibited no cracking till the substrate yielding. - Abstract: Ni–Cr alloy thin films have been deposited using magnetron co-sputtering technique at room temperature. Crystal structure was evaluated using GIXRD. Ni–Cr solid solution upto 40 at% of Cr exhibited fcc solid solution of Cr in Ni and beyond that it exhibited bcc solid solution of Ni in Cr. X-ray diffraction analysis shows formation of (1 1 1) fiber texture in fcc and (2 2 0) fiber texture in bcc Ni–Cr thin films. Electron microscopy in both in-plane and transverse direction of the film surface revealed the presence of columnar microstructure for films having Cr upto 40 at%. Mechanical properties of the films are evaluated using nanoindentation. The modulus values increased with increase of Cr at% till the film is fcc. With further increase in Cr at% the modulus values decreased. Ni–Cr film with 20 at% Ni exhibits reduction in modulus and is correlated to the poor crystallization of the film as reflected in XRD analysis. The Ni–Cr thin film with 80 at% Ni and 20 at% Cr exhibited the most distinct columnar structure with highest electrical resistivity, indentation hardness and elastic modulus.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Ferroelectric and dielectric study of strontium tantalum based perovskite oxynitride films deposited by reactive rf magnetron sputtering

Highlights: • Oxynitride perovskite thin films were deposited by reactive sputtering. • Films are textured or epitaxially grown on MgO and Nb-SrTiO{sub 3} substrates. • Local piezoelectric and ferroelectric behavior was highlighted by PFM. • A 1600 nm-thick film presents a permittivity of 175 at 10 kHz and RT. • Permittivity is around 65 in high frequency range. - Abstract: Strontium and tantalum based oxynitride perovskite thin films were deposited by reactive magnetron sputtering. Epitaxial films deposited on Nb-SrTiO{sub 3} substrates show smooth surfaces with roughness values from 1.5 to 3.6 nm for a thickness of films in the range 20–1600 nm. The samples are yellow with band gap values around 2.35 eV. Piezo-force microscopy characterization pointed out the local piezoelectric and ferroelectric behavior of the oxynitride perovskite films. In the low frequency range, the 1600 nm-thick film exhibits a permittivity of 175 at 10 kHz, with dielectric losses of 0.055. Permittivity is lowered in high frequencies with a value around 65 obtained on a 1520 nm-thick film deposited on MgO substrate, which is textured with a preferential c-axis orientation. No accordability of the permittivity was highlighted at a macroscopic scale. The moderate crystallographic strain evidenced in the 20 nm thin film does not induce a high permittivity.

36 MATERIALS SCIENCE↗
DOE OSTI2017

One-pot synthesis of Ni/Ni{sub 3}C/Ni{sub 3}N nanocomposite: Structure, growth mechanism and magnetic properties

Graphical abstract: Ni/Ni{sub 3}C/Ni{sub 3}N nanocomposites were synthesized by a one-pot solution chemistry method at lower temperature of 200 °C. The formation mechanism, magnetic properties and textural structures of Ni/Ni{sub 3}C/Ni{sub 3}N nanocomposite were investigated. - Highlights: • Ni/Ni{sub 3}C/Ni{sub 3}N nanocomposites were synthesized by a one-pot solution chemistry method at lower temperature of 200 °C. • Ni{sub 3}N nanomaterials were generally obtained by two steps, here we use one-step for preparation of Ni{sub 3}N nanomaterials. • The formation mechanism, magnetic properties and textural structures of Ni/Ni{sub 3}C/Ni{sub 3}N nanocomposite were investigated. - Abstract: A one-pot solvothermal synthesis of Ni/Ni{sub 3}C/Ni{sub 3}N nanocomposite, using hydrazine hydrate (N{sub 2}H{sub 4}) as reducing agent and tetraethylene glycol (TEG) as solvent, is reported. The contents of Ni{sub 3}C and Ni{sub 3}N decrease with increasing the amount of N{sub 2}H{sub 4}. The magnetic hysteresis loops at room temperature of the Ni/Ni{sub 3}C/Ni{sub 3}N display ferromagnetic characteristics. Saturation magnetization increases gradually with increasing Ni content of the Ni/Ni{sub 3}C/Ni{sub 3}N. Growth mechanism is discussed based on the characterization results of X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG), nitrogen adsorption desorption, and elemental analysis. Furthermore, Ni{sub 3}N was fabricated by such a solution chemistry method at low-temperature of 200 °C.

36 MATERIALS SCIENCE↗