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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Room temperature syntheses, crystal structures and properties of two new heterometallic polymers based on 3-ethoxy-2-hydroxybenzaldehyde ligand

Two new heterometallic coordination polymers [ZnNa(ehbd){sub 2}(N{sub 3})]{sub n} (1) and [Cu{sub 3}Na{sub 2}(ehbd){sub 2}(N{sub 3}){sub 6}]{sub n} (2) (Hehbd is 3-ethoxy-2-hydroxybenzaldehyde) have been synthesized under room temperature and structurally characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. Complex 1 crystallizes in the orthorhombic space group Pbca, showing a one-dimensional (1-D) chain. Complex 2 crystallizes in the triclinic space group Pī, constructing a heterometallic 2D layer structure. Luminescent properties and magnetic properties have been studied for 1 and 2, respectively and the fluorescence quantum yield of 1 is 0.077. - Highlights: • Two novel complexes 1 and 2 have been synthesized. • Complex 1 represents a novel qualitative change of luminescence property. • Complex 2 displays ferromagnetic interaction through symmetric μ{sub 1,1}–N{sub 3} bridges. • Complex 2 displays anti-ferromagnetic interaction through asymmetric μ{sub 1,1}–N{sub 3} bridges.

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

Evaluation of microstructure anisotropy on room and medium temperature ECAP deformed F138 steel

The microstructure developed during severe plastic deformation results in improved mechanical properties because of the decrease in domain sizes and accumulation of defects, mainly dislocation arrays. The characteristic deformation stages observed in low stacking fault energy (SFE) face centered cubic (FCC) materials are highly influenced by the development of the primary and secondary twinning that compete with dislocation glide. In this paper, a low SFE F138 stainless steel is deformed by equal channel angular pressing (ECAP) up to 4 passes at room temperature (RT) and at 300 °C to compare the grain refinement and twin boundary development with increasing deformation. Tensile tests were performed to determine the deformation stages reached by the material before and after ECAP deformation, and the resulting microstructure was observed by TEM. X-ray diffraction and EBSD, average technique the first and local the second one, were used to quantify the microstructural changes, allowing the determination of diffraction domain sizes, dislocation and stacking fault densities and misorientation indices, which lead to a complete analysis of the deformation introduced in the material, with comparative correlations between various microstructural parameters. - Highlights: • The microstructure of ECAP pressed F138 steel was studied using TEM, EBSD and XRD. • Increasing deformation reduced domain sizes and increased dislocation densities. • Dislocation array compactness and misorientation increased with higher deformation. • Largest dislocation densities, mostly screw, match with simultaneous activation of twins. • Several correlations among microstructural features and parameters have been disclosed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Characterization of microstructure in hydrogen ion irradiated vanadium at room temperature and the microstructural evolution during post-irradiation annealing

The microstructure of pure vanadium after hydrogen ion irradiation at room temperature to a fluence of 1 × 10{sup 17} ions/cm{sup 2} (and 5 × 10{sup 16} ions/cm{sup 2}) was investigated by transmission electron microscopy (TEM). Small dislocation loops (black spots) and cavities are formed after the irradiation. The nature and Burgers vector of dislocation loops formed in vanadium was characterized using g·b technique and inside–outside method. Interstitial dislocation loops with Burgers vector of 1/2 < 111 > predominantly formed with less than 10% of 1/2 < 110 > type. No < 100 > type or vacancy type dislocation loop formed. The microstructural evolution during the annealing process was also studied. Density and size of dislocation loops changed sharply when the annealing temperature was lifted up to 450 °C. When the annealing temperature was higher than 500 °C, bubble coalescence occurred with some large hydrogen bubbles formed. - Highlights: • Interstitial dislocation loops with Burgers vector of 1/2<111> were predominant. • Less than 10% of 1/2<110> dislocation loops were present in pure vanadium. • No <100> or vacancy type loops were present in pure vanadium. • Density and size of dislocation loops changed sharply at temperature above 450 °C. • Bubble coalescence occurred when annealing temperature was higher than 500 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The microstructure and formation mechanism of face-centered cubic Ti in commercial pure Ti foils during tensile deformation at room temperature

Highlights: • Two variants of fcc-Ti appear in ultra-thin commercial pure Ti foils during tension. • The appearance of obvious yield point may be attributed to the formation of fcc-Ti. • The orientation relationship between fcc-Ti phase and hcp-Ti matrix is determined. • The characteristics of dislocation structure in fcc-Ti are identified. • A model for the formation of fcc-Ti is proposed. - Abstract: Two variants of face-centered cubic (fcc) Ti phase appear in ultra-thin commercial pure Ti foils with hexagonal closed packed (hcp) structure during tensile deformation at room temperature. The orientation relationship between fcc-Ti phase and hcp-Ti matrix is determined as <0001>{sub HCP} // <001>{sub FCC}, <11 2-bar 0>{sub HCP} // <1 1-bar 0>{sub FCC} and <01 1-bar 0>{sub HCP} // <110> {sub FCC}. The fcc-Ti phase with a habit plane of {01 1-bar 0}{sub HCP} usually nucleates at grain boundary and grows along the direction of <11> } } }2 }&<; }0 2-bar 0 </>{sub HCP}. The thickness of fcc-Ti phase with a shape of thin plate ranges from 10 nm to 200 nm. Dislocations, steps and stacking faults with a space of 0.58 nm can be seen in fcc-Ti. The formation of a five-layer fcc-Ti can be accomplished by the formation of stacking faults and gliding of 1/6[11 2-bar 0] Shockley partial dislocations on the prismatic plane of hcp-Ti. The 1/3[11 2-bar 0] dislocations in hcp-matrix can cross the fcc-Ti phase because the Burgers vector of these dislocations is coincidence with 1/2[110] dislocations in the fcc-Ti.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural transition from two-dimensional ZIF-L to three-dimensional ZIF-8 nanoparticles in aqueous room temperature synthesis with improved CO2 adsorption

Highlights: • ZIF-L and ZIF-8 were synthesised with the same molar ratio of reagents (Zn{sup + 2}/Hmim = 8). • TEA threshold loading which was responsible for the phase transition was determined. • The CO{sub 2} desorption was improved due to increase of surface basicity and porosity. - Abstract: A new micron-sized leaf- two-dimensional (2D) structured zeolitic imidazolate framework (ZIF-L) and nano-sized ZIF-8 were successfully synthesised in aqueous basic solution at room temperature with the same molar ratio of reagents (Zn{sup + 2}/Hmim = 8). Both ZIFs have attracted tremendous research interest due to their wide applications including absorption, separation, and catalysis. This phase and morphology change could be tailored by changing the concentration of base-type additive triethylamine (TEA). Also, this morphology change from 2D (ZIF-L) to three-dimensional (3D) (ZIF-8) was observed by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), attenuated total reflectance infrared (ATR-IR) spectroscopy analysis, and surface area and pore textural properties using micromeritics gas adsorption analyser. The total amount of basic sites and carbon dioxide (CO{sub 2}) desorption capacity were also calculated using CO{sub 2} temperature-programmed desorption (CO{sub 2}-TPD) technique. Furthermore, TEA/total mole ratio of 0.0006 was proved as transition loading between two phases. Also, the particle and crystal size of samples decreased with increasing TEA/total mole ratio. The smallest ZIF-L and ZIF-8 particles obtained were 1.6 μm and 177 nm, respectively that showed excellent thermal stability. The basicity and uptakes of CO{sub 2} improved proportionally with TEA and followed this order: ZIF-8 > ZIF-L. This study provides some new insights into zeolitic imidazolate framework by controlling crystal growth and morphology.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Recrystallization and martensitic transformation in nanometric grain size Cu-Al-Ni thin films grown by DC sputtering at room temperature

Highlights: • Polycrystalline Cu-Al-Ni thin films with nanometric grain size are grown by DC sputtering. • Influence of thermal annealing process at low temperatures on the microstructure is analyzed. • Strained martensitic transformation is observed for films with grain size average of 30 nm. - Abstract: We report the recrystallization of metastable hexagonal and body centered cubic BCC phase in free-standing 6 μm thick Cu-Al-Ni films grown by DC sputtering at room temperature. The results show that the BCC phase recrystallizes to L2{sub 1} at around 533 K together with precipitation of γ{sub 2}-phase. Annealing temperatures (533 K–623 K) at short times (0–30 min) produce systematic increment of the fraction of γ{sub 2}-phase. Films with phase coexistence of hexagonal, γ{sub 2} and L2{sub 1} structure display temperature driven martensitic transformation. This transformation is observed for samples with austenite grain size of around 30 nm. In all cases, the martensitic transformation temperature (M{sub S}) notoriously decreases (compared to bulk) and systematically increases with the annealing temperatures and annealing time. In addition, the films display extended transformation and retransformation ranges along with asymmetric hysteresis, which may be associated to restitutive forces due to elastic deformations at martensite – martensite and martensite – austenite interfaces. Annealing temperatures above 623 K produce fast precipitation to equilibrium α- and γ{sub 2}-phases. The austenitic phase can be recovered after annealing over 1000 K and fast quenching in ice-water.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Electrochemical performance of CuO nanocrystal film fabricated by room temperature sputtering

Graphical abstract: High capacity of CuO thin film electrode for all-solid-state thin film batteries. Research highlights: {yields} Nanostructured CuO thin film is prepared by in situ sputtering. {yields} Excellent electrochemical performance with a very high capacity is achieved. {yields} Due to nanostructured grains, the in situ formed CuO possesses good cyclability. -- Abstract: To develop high performance anode materials for thin film batteries, copper oxide (CuO) film is fabricated at room temperature by reactive radio frequency magnetron sputtering. Morphological characterization shows that the CuO film consists of compacted CuO columnar grains of 20 nm in diameter and 200 nm in thickness. The measurement of lithium storage capacity and cyclability of the CuO film show that the first charge capacity of the film is 585 mAh g{sup -1} with an efficiency of 68.3% at a current density of 200 mA g{sup -1}. After the 50th cycle, the capacity retention remains as high as 97.4%. The nanostructured CuO film also shows a good rate capability even being cycled at 3000 mA g{sup -1} (5 C), demonstrating that the CuO film can be a promising material as an anode for high performance thin film batteries, especially for thin film battery with amorphous electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Room temperature oxidative intercalation with chalcogen hydrides: Two-step method for the formation of alkali-metal chalcogenide arrays within layered perovskites

Highlights: ► Topochemical reactions involving intercalation allow construction of metal chalcogenide arrays within perovskite hosts. ► Gaseous chalcogen hydrides serve as effect reactants for intercalation of sulfur and selenium. ► New compounds prepared by a two-step intercalation strategy are presented. -- Abstract: A two-step topochemical reaction strategy utilizing oxidative intercalation with gaseous chalcogen hydrides is presented. Initially, the Dion-Jacobson-type layered perovskite, RbLaNb{sub 2}O{sub 7}, is intercalated reductively with rubidium metal to make the Ruddlesden-Popper-type layered perovskite, Rb{sub 2}LaNb{sub 2}O{sub 7}. This compound is then reacted at room-temperature with in situ generated H{sub 2}S gas to create Rb-S layers within the perovskite host. Rietveld refinement of X-ray powder diffraction data (tetragonal, a = 3.8998(2) Å, c = 15.256(1) Å; space group P4/mmm) shows the compound to be isostructural with (Rb{sub 2}Cl)LaNb{sub 2}O{sub 7} where the sulfide resides on a cubic interlayer site surrounded by rubidium ions. The mass increase seen on sulfur intercalation and the refined S site occupation factor (∼0.8) of the product indicate a higher sulfur content than expected for S{sup 2−} alone. This combined with the Raman studies, which show evidence for an H-S stretch, indicate that a significant fraction of the intercalated sulfide exists as hydrogen sulfide ion. Intercalation reactions with H{sub 2}Se{sub (g)} were also carried out and appear to produce an isostructural selenide compound. The utilization of such gaseous hydride reagents could significantly expand multistep topochemistry to a larger number of intercalants.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Room temperature synthesis and photocatalytic property of AgO/Ag{sub 2}Mo{sub 2}O{sub 7} heterojunction nanowires

Graphical abstract: The AgO nanoparticles are attached on the surface of the Ag{sub 2}Mo{sub 2}O{sub 7} nanowires to form a heterojunction structure. The AgO nanoparticles start embedding into the nanowires with increasing reaction temperature or time. Highlights: ► AgO/Ag{sub 2}Mo{sub 2}O{sub 7} heterojunction NWs were synthesized at room temperature for the first time. ► AgO particles embed into the Ag{sub 2}Mo{sub 2}O{sub 7} NWs with increase in reaction time and temperature. ► The heterojunction NWs display much better photocatalytic activity than the none-heterojunction NWs. ► The catalytic mechanism was proposed. -- Abstract: AgO/Ag{sub 2}Mo{sub 2}O{sub 7} heterojunction nanowires were synthesized at temperatures of 25 °C, 50 °C, 80 °C, and 110 °C, under magnetic stirring in solution reaction. The catalytic activity of AgO/Ag{sub 2}Mo{sub 2}O{sub 7} nanowires was evaluated by the degradation of Rhodmine B dye under the irradiation of the simulated sunlight. The synthesized samples were characterized by X-ray diffractometer, energy dispersive spectrometry, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. The results show that the AgO nanoparticles are attached on the surface of the Ag{sub 2}Mo{sub 2}O{sub 7} nanowires to form a heterojunction structure. The length of the nanowires is up to 10 μm and the size of the AgO nanoparticles is 10–20 nm. The length of nanowires increases with increasing reaction time and temperature while the AgO particles are gradually embedded into the nanowires. The photocatalytic activity is greatly improved for the AgO/Ag{sub 2}Mo{sub 2}O{sub 7} heterojunction nanowires compared with that of the pure Ag{sub 2}Mo{sub 2}O{sub 7} nanowires, indicating a remarkable role of AgO particles on the Ag{sub 2}Mo{sub 2}O{sub 7} nanowires in the photodegradation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

One-step room temperature synthesis of very small γ-Fe{sub 2}O{sub 3} nanoparticles

Graphical abstract: - Highlights: • One-step synthesis of 3 nm maghemite nanoparticles is reported. • Maghemite nanoparticles can be synthesized from a ferric solution. • γ-Fe{sub 2}O{sub 3} NPs can be obtained if the precursor has Fe(III) in tetrahedral interstices. • HR-TEM, Mössbauer, XAFS and magnetometry analysis proved the maghemite existence - Abstract: Very small maghemite nanoparticles (∼3 nm) are obtained through a one-step synthesis at room temperature. The fast neutralization reaction of a ferric solution in a basic medium produces an intermediate phase, presumably two-line ferrihydrite, which in oxidizing conditions is transformed to maghemite nanoparticles. The synthesis of maghemite, as final product of the reaction, was characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-ray Absorption Fine Structure (XAFS), Mössbauer spectroscopy, and magnetometry. The XAFS technique allowed the analysis of the crystallographic variations into maghemite nanoparticles as a result of modification in its surface/volume ratio. Mössbauer spectroscopy at low temperature (4.2 K) confirms the presence of Fe(III) in tetrahedral and octahedral interstices, in the stoichiometry corresponding to maghemite. The specific magnetization, M vs H (3 K and 300 K, up to 7 T) and temperature dependence of the magnetization (50 Oe by ZFC mode, 2 K ≤ T ≤ 300 K) indicate that maghemite nanoparticles of 3 nm are in superparamagnetic state with a blocking temperature close to 36 K.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Facile room temperature synthesis of SrSO{sub 4}:RE (RE = Sm{sup 3+}, Tb{sup 3+}, Ce{sup 3+}) microrods via a precipitation method and its luminescence properties

Graphical abstract: PL emission spectra of SrSO{sub 4}:xSm{sup 3+} powder phosphors under 401 nm excitation. The inset shows Sm{sup 3+} concentration of relative luminescence intensity. - Highlights: • Three SrSO{sub 4} phosphors were synthesized by a facile precipitation reaction. • Rod-like SrSO{sub 4} obtained microcrystals are about 14 μm length and 6 μm width. • In the PL spectrum of SrSO{sub 4}:Ce{sup 3+}, two overlapping bands are observed. • Narrow bands are observed in spectra of SrSO{sub 4}:RE (RE = Sm{sup 3+} and Tb{sup 3+}). • The critical quenching concentrations are 0.8, 2 and 0.8 mol%, respectively. - Abstract: Three SrSO{sub 4}:RE phosphors activated with rare-earth ions (RE = Sm{sup 3+}, Tb{sup 3+} and Ce{sup 3+}) were synthesized by a facile precipitation reaction without using any surfactants or templates. Especially, rod-like SrSO{sub 4} microcrystals with size of about 14 μm length and 6 μm width can be obtained under ambient condition at room temperature. The phase structure, microstructure and luminescence properties were characterized. In the photoluminescence property investigation of SrSO{sub 4}:Ce{sup 3+}, two overlapping bands with peaks at 301 and 320 nm due to Ce{sup 3+} were observed. Narrow bands observed in emission spectra and excitation spectra of SrSO{sub 4}:RE (RE = Sm{sup 3+} and Tb{sup 3+}) phosphors were well identified with the electronic transitions within the 4f{sup n} (n = 5 and 8) configurations of RE{sup 3+}.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Application of E{sub h}-pH diagram for room temperature precipitation of zinc stannate microcubes in an aqueous media

Graphical abstract: - Highlights: • One pot aqueous synthesis of zinc stannate (ZnSnO{sub 3}) particles at low temperature. • Synthesis designed with the assistance of potential-pH diagram. • ZnSnO{sub 3} estimated to be stable between pH 8 and 12 was used for synthesis of the particles. • ZnSnO{sub 3}·3H{sub 2}O were formed during the precipitation of zinc stannate. - Abstract: Potential-pH diagram assisted-design for controlled precipitation is an attractive method to obtain engineered binary and ternary oxide particles. Aqueous synthesis conditions of zinc stannate (ZnSnO{sub 3}) particles at low temperature were formulated with the assistance of potential-pH diagram. The pH of a solution containing stoichiometric amounts of Zn{sup 2+} and Sn{sup 4+} was controlled for the precipitation in a one pot synthesis step at room temperature (25 °C). The effect of the concentration of the reactants on the particle size was studied by varying the concentration of the precursor (Zn{sup 2+} + Sn{sup 4+}) solution. Scanning electron micrographs show that the particles are monodispersed micron sized cubes formed by the self-organization of nano-sized crystallites. The obtained microcubes characterized by X-ray Diffraction and thermo gravimetric analysis (TGA) show that the particles are in ZnSnO{sub 3}·3H{sub 2}O form.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Gas sensor based on three dimensional Bi2S3 nanowires network for ammonia detection at room temperature

Highlights: • Three dimensional Bi{sub 2}S{sub 3} nanowires networks. • High response to NH{sub 3} gas. • Good selectivity. • Wide linear range. • Work at room temperature. - Abstract: A film containing three dimensional Bi{sub 2}S{sub 3} nanowires network was obtained using Bi(NO{sub 3}){sub 3} and thioacetamide as starting materials through three steps, namely the chemical synthesis of Bi{sub 2}S{sub 3}, preparation of its sol under ultrasonic condition and crystal self-assembly at 25 °C. The nanowires had diameters of 20–100 nm. The formation mechanism of the 3D nanowires network is the anisotropic growth of Bi{sub 2}S{sub 3}. The sensor based on 3D Bi{sub 2}S{sub 3} nanowires network with an excellent response to ammonia at 30 °C. The response mechanism of the sensor for ammonia is a weak coordination adsorption of ammonia molecule on the Bi{sub 2}S{sub 3} nanowires and the electron is partially transferred from ammonia molecule to bismuth (III) ion. The maximum response of the sensor to ammonia was up to 82.3 and had a good linear range from 30 to 350 ppm concentration, indicating its potential applications in the determination and leak alarm of ammonia.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Facile room temperature CTAB-assisted synthesis of mesoporous nano-cobalt ferrites for enhanced magnetic behaviour

Highlights: • Synthesis of mesoporous nano-cobalt ferrites are carried out CTAB medium. • Crystalline cobalt ferrite phase was formed below CMC of CTAB. • Bilayer arrangement of CTA-OH-Fe-Co growing units leads to inter-particle pores. • Enhanced magnetic properties (M{sub s} and H{sub c}) were obtained in synthesized cobalt ferrites. - Abstract: We report a facile, room temperature synthesis of nanostructured mesoporous cobalt ferrites using the cationic surfactant, cetyltrimethylammonium bromide (CTAB). The synthesis was carried out at various concentrations of CTAB ranging from its pre- to post-micellar concentrations. The pristine and calcined samples exhibit pure cobalt ferrite phase which are confirmed by XRD studies. The morphology of all uncalcined samples was quasi-spherical as shown by TEM images. Nitrogen adsorption – desorption study on pristine samples indicates the presence of mesopores in them. The magnetic properties of the uncalcined and calcined samples were studied by vibrating sample magnetometry. Coercivity and saturation magnetization were found to vary with the concentration of the CTAB employed. Also, the pristine samples were soft magnets, whereas the calcined samples tended towards exhibiting hard magnetism. We have proposed a mechanism to explain the mesoporosity of nanostructured ferrite based the role of CTAB in the present synthetic method.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Room temperature magnetic ordering and analysis by bound magnetic polaron model of Yb3+ doped nanocrystalline zinc oxide (Zn0.98Yb0.02O)

Highlights: • ZnO and Yb doped ZnO are synthesized by co-precipitation method. • Rietvelt anlysis of XRD patterns confirms the complete substitution of Yb{sup 3+} in ZnO. • Vacancy and defect mediated RTFM is introduced in doped ZnO. • BMP model successfully analyze the magnetic property of Zn{sub 0.98}Yb{sub 0.02}O. - Abstract: Nanocrystalline ZnO and Yb-doped ZnO (Zn{sub 0.98}Yb{sub 0.02}O) are prepared by simple co-precipitation method. The pure crystallographic phases of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are confirmed by Rietveld analyses of XRD patterns. Raman and photoluminescence spectra recorded at room temperature (RT) indicates that lattice defects and oxygen vacancy in Zn{sub 0.98}Yb{sub 0.02}O is more than that of ZnO. Magnetic measurements of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are carried out from 300 to 5 K. Ferromagnetic ordering is observed in Zn{sub 0.98}Yb{sub 0.02}O at RT and the strength of the ordering increases with the lowering of temperature. Ferromagnetism of Zn{sub 0.98}Yb{sub 0.02}O is attributed to the oxygen vacancy introduced by annealing in vacuum. Magnetization vs. temperature curve is well fitted by the combination of 3D spin wave and Curie-Weiss law, which suggest simultaneous presence of para- and ferro-magnetic phases in Zn{sub 0.98}Yb{sub 0.02}O. Ferromagnetic ordering is successfully explained by vacancy mediated bound-magnetic polaron model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Observation of large Rashba spin–orbit coupling at room temperature in compositionally engineered perovskite single crystals and application in high performance photodetectors

Indirect absorption extended below the direct transition edge and increase in carrier lifetime derived from Rashba spin–orbit coupling may advance the optoelectronic applications of metal halide perovskites. Spin-orbit coupling in halide perovskites is due to the presence of heavy elements in their structure. However, when these materials lack an inversion symmetry, for example by the application of strain, spin–orbit coupling becomes odd in the electron’s momentum giving rise to a splitting in the electronic energy bands. Here we report on the observation of a large Rashba splitting of 117 meV at room temperature, as predicted by relativistic first-principles calculations, in halide perovskite single crystals through a facile compositional engineering approach. Partial substitution of organic cations by rubidium in single crystals induces significant indirect absorption and dual peak photoluminescence as a result of a large Rashba splitting. We measured circularly polarized photoluminescence and magneto-photoluminescence in perovskite films printed by single crystals as well as magneto-electroluminescence and magneto-photocurrent in spin-LEDs based on perovskite single crystals. They indicated significant spin-momentum locking due to the large Rashba effect. A hybrid perovskite single crystal photodetector achieved record figures of merit, including detectivity of more than 1.3 × 10 18 Jones which represents a three orders of magnitude improvement compared to the to date record. Furthermore, these findings show that facile compositional engineering of perovskite single crystals holds great promise for further advancing the optoelectronic properties of existing materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unraveling the solvation phenomena of Ln 3+ cations in room-temperature ionic liquids: A computational study

Rare-earth elements (REEs), classified as critical materials, are difficult to separate due to their similar chemical properties and slight differences in ionic radius. Room-temperature ionic liquids (RTILs) have gained significant attention for REE separation because of their unique physicochemical properties and environmental advantages. In this study, we have investigated the solvation mechanisms of two RE cations (Ln 3+ ), Nd 3+ (light REE) and Yb 3+ (heavy REE), in two 1-butyl-3-methylimidazolium ([BMIM] + )-based RTILs using bis(trifluoromethylsulfonyl)imide ([NTf 2 ] − ) and acetate ([OAc] − ) as the respective anions, employing classical molecular dynamics (MD) simulations and density functional theory (DFT) techniques. From MD simulations, it is evident that Ln 3+ cations are primarily solvated by RTIL anions in the first solvation shell, while [BMIM] + cations form the second solvation shell with their numbers depending on the size and composition of the first solvation shell. The neutralizing [NO 3 − ] counterions are mainly solvated by [BMIM] + cations in their first solvation shell. Relative free energy change of solvation calculations using thermodynamic integration (TI) method indicate that Yb 3+ is more strongly solvated than Nd 3+ in both RTILs, a trend further supported by DFT calculations. While both methods predict consistent qualitative behavior, differences in models and energy evaluations lead to variations in absolute values. Overall, this study provides a comprehensive understanding of the solvation behavior of Ln 3+ cations in RTILs, demonstrating a stronger solvation preference for the heavy Ln 3+ cation (Yb 3+ ). In conclusion, these findings have implications for the design of RTIL-based separation processes for REEs.

Ash, Tamalika [Ames Lab., and Iowa State Univ., Am↗
DOE OSTI2016

Diffraction and single-crystal elastic constants of Inconel 625 at room and elevated temperatures determined by neutron diffraction

In this work, diffraction and single-crystal elastic constants of Inconel 625 have been determined by means of in situ loading at room and elevated temperatures using time-of-flight neutron diffraction. Theoretical models proposed by Voigt, Reuss, and Kroner were used to determine single-crystal elastic constants from measured diffraction elastic constants, with the Kroner model having the best ability to capture experimental data. The magnitude of single-crystal elastic moduli, computed from single-crystal elastic constants, decreases and the single crystal anisotropy increases as temperature increases, indicating the importance of texture in affecting macroscopic stress at elevated temperatures. Finally, the experimental data reported here are of great importance in understanding additive manufacturing of metallic components as: diffraction elastic constants are required for computing residual stresses from residual lattice strains measured using neutron diffraction, which can be used to validate thermomechanical models of additive manufacturing, while single-crystal elastic constants can be used in crystal plasticity modeling, for example, to understand mechanical deformation behavior of additively manufactured components.

36 MATERIALS SCIENCE↗