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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Single crystal growth and variation of thermodynamic and magnetic properties of Pr1−xLaxAlO3 (x = 0, 0.8)

Highlights: • The perovskite Pr{sub (1-x)}La{sub (x)}AlO{sub 3} was grown by two different protocols to control the P{sup 4+} concentration. • Low temperature magnetic properties in bulk single crystals are sensitive to annealing protocols. • Post growth annealing in a reducing atmosphere leads to closest Pr{sub 0.2}La{sub 0.8}AlO{sub 3} stoichiometry. • A possible new magnetic transition for single crystal PrAlO{sub 3} is observed at 6 K. - Abstract: Two approaches to using optical floating zone (OFZ) technique for single crystal growth of the perovskite Pr{sub 1−x}La{sub x}AlO{sub 3} are discussed, along with the influence on the physical properties of the resulting single crystals due to oxidizing and reducing post anneals. In method one (M1) we used pre-reduced Pr{sub 2}O{sub 3} powder starting material, while in the other method, M2, we employed an argon 5% hydrogen reducing environment during the floating zone single crystal growth. Magnetic susceptibility of the low temperature monoclinic phase of Pr{sub 0.2}La{sub 0.8}AlO{sub 3} is shown to be sensitive to the precise annealing protocol followed. For the post-growth reduced single crystal the magnetic susceptibility is flat across the R-3c to C2/m structural transition, whereas the oxidized and as-grown samples display a sharp upturn and downturn, respectively. We attribute the low temperature susceptibility differences to relative proportions of Pr{sup 3+} and Pr{sup 4+}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

PbGa6Te10 crystals for IR laser operated piezoelectricity

Highlights: • High-quality single crystals PbGa{sub 6}Te{sub 10} grown by Bridgman method. • PbGa{sub 6}Te{sub 10} crystals were characterized by X-ray photoelectron spectroscopy. • Temperature dependent thermal conductivity was investigated . • Was discovered a rare possibility to improve piezoelectric features using the external infrared laser beams. • The observed effect opens a new stage for the production of the IR operated devices including piezotronics. - Abstract: A ternary compound PbGa{sub 6}Te{sub 10} grown by Bridgman method was studied with respect to IR induced piezoelectricity. We have found an opportunity to induce piezoelectric features using the external infrared laser (IR) beams for PbGa{sub 6}Te{sub 10} crystals. The three principal wavelengths corresponding to fundamental 10.6 μm, doubled frequency 5.3 μm and third harmonic 3.5 μm laser beams were explored as photoinduced beams. Maximally achieved IR induced piezoelectricity was observed at laser induced wavelength 5.3 μm. The optimal photoinduced power density was varied within 150–160 MW/cm{sup 2} . The observed space gratings are very crucial for the observed photo-induced piezoelectricity, which is indicated, that we deal with interference of the photoinduced coherent beams. The role of the surface states was discussed based on the XPS spectra. Additionally, the temperature dependence of thermal diffusivity was measured. The determined thermal conductivity indicates prevailingly the phonon contribution and possesses very low values in the measured temperature ranges.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electro-analytical method for the quantities evaluation of the silicon solar cell by DC and AC characterization technique

Highlights: • Exact electro-analytical method for evaluation of silicon solar cells. • DC and AC characterization technique to determine the performance limiting parameters of solar cells. • EIS is used to get an insight into the solar cells and parameter optimization. - Abstract: Mono and Poly- crystalline silicon (Si) based solar cell has proven to be the most efficient and matured technology till date. The present work reports an exact electro-analytical method for the evaluation of different performance parameters in the current voltage response of the Si solar cell by DC and AC characterization technique. The extracted solar cell parameters from DC and AC techniques were compared with each other under the proper limiting conditions of low and high forward bias. The DC and AC characterization are used to determine the bias dependence of ideality factor and series resistance, respectively. The current-voltage (J-V) characteristics is combined with the impedance spectroscopy (IS) measurements to reveal the various interfacial, resistive and recombination analysis of the silicon solar cell. Herein the experimentally obtained J-V characteristics under the illumination condition have been reconstructed by individually extracted parameters from DC and AC measurements. Moreover, the present mechanistic provides a simple tool for analysing the commercial Si solar cell with a wide applicability for other solar cells.

14 SOLAR ENERGY↗
DOE OSTI2018

Hydrothermal growth and scintillation properties of γ-CuBr single crystals

Highlights: • Transparent γ-CuBr single crystal with regular shape was successfully grown by hydrothermal method. • The x-ray excited optical luminescence of the γ-CuBr crystal, which exhibits an intensive 430 nm emission, is first reported. • The average decay time of the 430 nm emission is 36.9 ns. - Abstract: A fast scintillation crystal, γ-CuBr, was successfully grown by hydrothermal method with NH{sub 4}Br mineralizer. The element mole ratio of the Cu/Br crystal was about 0.91 caused by the crystal grown in a rich bromine environment. Under ultraviolet excitation, the crystal exhibited an intense 420 nm emission, a shoulder emission at 428 nm and a weak broadband emission at 560 nm, which could be related to free exciton recombination, Cu and Br vacancies, respectively. Furthermore, the X-ray excited optical luminescence of the crystal was first reported, and a strong 430 nm emission was observed. The analysis of luminescence decay kinetics revealed that the 430 nm emission is composed of two components with an average decay time of 36.9 ns. It means that the γ-CuBr crystal is a promising candidate for applications in fast radiation detection.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of oxygen vacancies and Ag deposition on the magnetic properties of Ag/N co-doped TiO2 single-crystal films

Highlights: • Photochemical deposition method to prepare Ag-doped TiO{sub 2} samples. • TiO{sub 2} single crystal films are used for studying room temperature ferromagnetism origin. • Ag element is deposited on TiO{sub 2} single crystal films surface in the form of Ag particles. • Oxygen vacancies and Ag particles synergy influence the ferromagnetism in samples. - Abstract: We employ TiO{sub 2} single-crystal films as a substrate and use a photochemical deposition method to prepare Ag-doped and Ag/N co-doped TiO{sub 2} single-crystal films. We also investigate the optical and magnetic properties of the samples using various measurements. No diffraction peaks related to silver oxide appear in the X-ray diffraction (XRD) spectra, which implies the existence of Ag atoms in Ag-doped TiO{sub 2} single-crystal films. X-ray photoelectron spectroscopy (XPS) spectra indicate the existence of Ti{sup 4+} and Ag° in Ag/N co-doped TiO{sub 2} single-crystal films. It is found that Ag is deposited on a TiO{sub 2} single-crystal film surface in the form of Ag particles. Meanwhile, Ag particles can slightly enhance ferromagnetism in Ag-doped TiO{sub 2} single-crystal films compared with the TiO{sub 2} single-crystal film sample. Oxygen vacancies and Ag particle synergy influence ferromagnetism in Ag/N co-doped TiO{sub 2} single-crystal films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

TiO2 nanotubes grown on Ti substrates with different microstructure

Highlights: • TiO{sub 2} nanotube layers were grown on four different Ti substrates by anodization. • Ti substrates with completely different microstructures were used. • The grain size of the substrates ranged from nanocrystalline to single-crystalline. • Differences between the nanotubes grown on these substrates were evaluated. • Similar nanotube dimensions were received on all Ti substrates. - Abstract: Four Ti substrates with various microstructures were investigated for the anodic growth of TiO{sub 2} nanotube layers: nanocrystalline and single-crystalline ingots as well as microcrystalline thick Ti sheets and microcrystalline thin Ti foils. All substrates were anodized in a conventional ethylene glycol based electrolyte under identical conditions. The resulting TiO{sub 2} nanotube layers were compared in dimensions and the consumption of Ti required for their growth. Unexpectedly, the results showed that on all substrates nanotube layers with a similar thickness and nanotube diameter, as well as a similar degree of ordering and after annealing the same crystallographic orientation of anatase were received, regardless the microstructures. However, the nanotube layers grown on a Ti sheet revealed a slightly higher thickness compared to the other substrates which were assigned to slower field-assisted dissolution rates due to different impurities found in this substrate compared to other ones.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Chemical bath deposition of single crystal SnS nanobelts on glass substrates

Highlights: • Single crystal SnS nanobelts were deposited by CBD method. • The morphologies of SnS nanobelts were regulated by mole ratios of precursors and pH levels. • The photo-electrical properties of SnS nanobelts were characterized. - Abstract: SnS nanobelt thin films were deposited on glass substrates in acidic solution by chemical bath deposition (CBD) method. The belt-like morphologies of as-deposited SnS thin films were characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) and Raman measurements were carried out to confirm the crystal structures and phase purities of SnS nanobelt thin films. The morphologies and phase purities of SnS thin films were influenced greatly by the tin and sulfur precursors. The bandgaps of SnS nanobelts were determined to be 1.39–1.41 eV by UV–vis absorption and photoluminescence (PL) spectra. Current-voltage ((IV)) and current-time ((I-T)) characteristics were studied to demonstrate the photoelectric performances of SnS nanobelt thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

X-ray structure and investigation of molecular motions by dielectric, vibrational and 1H NMR methods for two organic-inorganic hybrid piperazinium compounds: (C4H12N2)2[Sb2Cl10]·2H2O and (C4H12N2)2[Sb2Br10]·2H2O

Highlights: • Bis(piperazine-1,4-diium) decabromodiantimonate(III) (PSB) dihydrate has been synthesized and characterized. • The structural phase transition for PSB at ca. 50 K has been confirmed by the dielectric and {sup 1}H NMR spectroscopy results. • The molecular motion parameters of the organic cations and water molecules have been evaluated and compared for PSB and PSC. - Abstract: Bis(piperazine-1,4-diium) decabromodiantimonate(III) dihydrate, (C{sub 4}H{sub 12}N{sub 2}){sub 2}[Sb{sub 2}Br{sub 10}]·2H{sub 2}O, (abbreviated as PSB) has been synthesized and characterized by single-crystal X-ray diffraction studies. The obtained results indicate that PSB is isostructural with a recently described chloride analogue, (C{sub 4}H{sub 12}N{sub 2}){sub 2}[Sb{sub 2}Cl{sub 10}]⋅2H{sub 2}O (PSC), crystallizing with R{sub 2}MX{sub 5}·nH{sub 2}O stoichiometry and characterized by the discrete zero-dimensional anionic species. The crystal structure of PSB is described by monoclinic symmetry in a P2{sub 1}/n space group. Dielectric measurements (down to 25 K) and IR spectral analyses (measured over a broad temperature range) suggested a much more complicated phase situation below 80 K than for that of PSC. To verify and compare the molecular motions of the organic cations in both analogues, a proton magnetic resonance ({sup 1}H NMR) technique was also applied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

White LED based on CsPbBr3 nanocrystal phosphors via a facile two-step solution synthesis route

Highlights: • The work shows a simple and effective strategy to synthesize perovskite materials. • A LED with CsPbBr{sub 3} nanocrystals as green phosphors was fabricated. • Notable stability of the CsPbBr{sub 3} nanocrystals was verified. - Abstract: All-inorganic CsPbBr{sub 3} perovskite nanocrystals with mean size of ∼300 nm were synthesized via a facile two-step solution synthesis route. High-resolution transmission electron microscopy and X-ray diffraction characterizations confirm the as-prepared CsPbBr{sub 3} nanoparticles are single-crystals with good crystallinity, although a CsPb{sub 2}Br{sub 5} impure phase also exists in the final product. Power-/temperature-dependent and time-resolved photoluminescence measurements reveal the notable and stable excitonic emission feature of these CsPbBr{sub 3} nanocrystals. As a proof-of-concept demonstration, a LED with p-GaN/n-ZnO heterojunction as blue-violet excitation chip and CsPbBr{sub 3} nanocrystals as green phosphors, was fabricated and a white electroluminescence was achieved from this perovskite nanocrystals decorated LED.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO4

Highlights: • TmMgGaO{sub 4} crystallizes in the R-3m space group with the YbFe{sub 2}O{sub 4} structure. • TmMgGaO{sub 4} exhibits geometric magnetic frustration with no ordering down to 1.8 K. • Magnetic properties of TmMgGaO{sub 4} are highly anisotropic. - Abstract: The crystal growth, structure, and basic magnetic properties of TmMgGaO{sub 4} are reported. The Tm ions are located in a planar triangular lattice consisting of distorted TmO{sub 6} octahedra, while the Mg and Ga atoms randomly occupy intermediary bilayers of M-O triangular bipyramids. The Tm ions are positionally disordered. The material displays an antiferromagnetic Curie Weiss theta of ∼−20 −25 K, with no clear ordering visible in the magnetic susceptibility down to 1.8 K; the structure and magnetic properties suggest that ordering of the magnetic moments is frustrated by both structural disorder and the triangular magnetic motif. Single crystal magnetization measurements indicate that the magnetic properties are highly anisotropic, with large moments measured perpendicular to the triangular planes. At 2 K, a broad step-like feature is seen in the field-dependent magnetization perpendicular to the plane on applied field near 2 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Optimization of the CVD parameters for ZnO nanorods growth: Its photoluminescence and field emission properties

Highlights: • Home-made CVD reactor fabricated and successfully used for growing ZnO nanorods. • Growth of nanostructures depends on several CVD process parameters. • CVD parameters, flow rate of carrier gas, substrate temperature, Au catalyst droplet size, growth time duration, etc. optimized. • The mechanism of crystal growth understood by studying FESEM/TEM/XRD. • Photoluminescence and Field emission studies done for defects and applications. - Abstract: Vertically aligned single crystalline ZnO nanorods arrays were grown on a silicon substrate in a CVD reactor using Au as a catalyst. The CVD parameters such as substrate temperature, catalyst layer thickness/morphology and reaction time play a crucial role in the synthesis of nanostructures by the vapor-liquid-solid process. By optimizing these various CVD parameters, highly controlled guided growth of ZnO nanorods was achieved. The structural and morphological properties of resultant ZnO nanorods were studied by means of X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction and field emission scanning electron microscopy. The photoluminescence spectroscopy was also done to investigate the defects in grown ZnO nanorods. The field emission results of nanorods array indicated that the properties of the field emission follow Fowler–Nordheim law. The nanorods (grown for 20 min) are vertically aligned on the substrate surface without entanglements and with good crystal quality as well which is very important for several applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Flux growth and magneto-transport properties of cubic antiperovskite Ca3PbO single crystals

Highlights: • Antiperovskite Ca{sub 3}PbO is predicted to be a three-dimensional Dirac fermion system. • Cubic crystals, 1 mm in size, were obtained by a Ca-self-flux method. • The crucible and sealing method were critical factors to reduce carrier density. • Shubnikov-de Haas oscillations were clearly observed, indicating its high purity. - Abstract: We report the single crystal growth of cubic antiperovskite Ca{sub 3}PbO by a Ca-self-flux method. Cubic crystals, 1 mm in size, were successfully obtained through the use of iron crucibles sealed in stainless steel capsules. The crucible material and sealing method were found to be critical factors for achieving large crystals with low carrier density. The crystals were subsequently characterized by powder and single-crystal x-ray diffraction experiments, electron-probe microanalysis, and Hall effect measurements. Through the use of short stainless steel rods as tight caps for the crucible and fillers to occupy extra space in the capsule, the Ca evaporation loss of the flux, which contributes to Ca vacancy formation, was effectively reduced. Hence, the hole carrier density in the single crystal was reduced to 4.0 × 10{sup 19} cm{sup −3}. The crystal synthesized under optimized growth conditions showed clear Shubnikov-de Haas oscillations, indicating its high purity and homogeneity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Optimization of crystal growth and properties of γ-CuI ultrafast scintillator by the addition of LiI

Highlights: • Large and transparent γ-CuI single crystal with the size over 20 mm was successfully obtained for the first time. • The intensities of near-band-edge emissions of γ-CuI single crystal are greatly enhanced by Li and I dopants. • The 430 nm emission decay time is less than 450 ps under pulsed X-ray irradiation. - Abstract: Large-sized γ-CuI single crystals with ultrafast scintillation property were grown in LiI acetonitrile solvent through evaporation technique. The LiI exhibits unique properties to γ-CuI single crystal preparation. One is that it increases the solubility of CuI in the solvent, which gives rise to a largest-sized (23 × 14 × 2 mm{sup 3}) single crystal with the high optical transmission (over 60%) in the wavelength region of 435–800 nm. The other feature is that it acts as an effective isoelectronic dopant and improves the molar ratio of copper to iodine, which greatly enhances the near-band-edge emissions (411 and 432 nm) and suppresses the broadband emission (680 nm). The decay time of the fast emission under pulsed X-ray excitation is shorter than 450 ps. The results will give a guidance for optimizing the properties of γ-CuI single crystal as an ultrafast scintillator.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Spectroscopic properties and rate equation model of Er doped BaLaGa3O7 crystals

Highlights: • We grew Er{sup 3+} activated BaLaGa{sub 3}O{sub 7} crystal for usage in mid-infrared laser. • The change of Er{sup 3+} doping concentration had significant effect on the fluorescence properties. • The best doping concentration of Er{sup 3+} should be maintained at 10–15at% to obtain 2.7 μm output. • We built and discussed the rate equation model according to the energy transfer diagram. - Abstract: Single crystals of pure and Er{sup 3+} doped BaLaGa{sub 3}O{sub 7} were grown successfully by the Czochralski technique. The absorption spectra, emission spectra including up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves were measured at room temperature. The optical parameters of absorption and emission cross sections, the fluorescence lifetimes were evaluated and compared. Based on the Judde-Ofelt theory, Judde-Ofelt parameters such as the fluorescent branching ratios, the spontaneous transition probabilities and the radiative lifetimes were calculated. According to the energy transfer diagram, the rate equation model was built and discussed. In summary, Er{sup 3+}: BaLaGa{sub 3}O{sub 7} crystal is attractive and significant as laser gain material for realization of ∼2.7 μm laser output.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Compositional dependence of disordered structures in Na½Bi½TiO3-BaTiO3 solid solutions

Highlights: • Diffuse X-ray scattering collected from 4 compositions of Na{sub ½}Bi{sub ½}TiO{sub 3}-x%BaTiO{sub 3}. • Oxygen octahedral tilts, atomic displacements and modulations existed. • All local disordered structures evolved across the morphotropic phase boundary. - Abstract: Disordered structures contribute to the relaxor ferroelectric properties of the lead-free system Na{sub ½}Bi{sub ½}TiO{sub 3}-(x)%BaTiO{sub 3}. Such structures are difficult to characterize with conventional structural analysis techniques. Here, diffuse X-ray scattering was used to analyze the disordered structures from four single-crystals of Na{sub ½}Bi{sub ½}TiO{sub 3}-(x)%BaTiO{sub 3}, with compositions of (x)% = 0%, 4%, 9% and 17%. Such a range of compositions allowed a distinction between the structures that occur across the morphotropic phase boundary, where enhanced electro-mechanical properties have been reported. Throughout the compositional range, the resulting diffuse scattering showed the modification of correlated atomic displacements, transformation of planar defects in the oxygen octahedral tilt-systems, and the presence of modulations of approximately 10 unit cells. The results reported here demonstrate an evolution of the short-range structures across the morphotropic phase boundary that may underpin the electro-mechanical properties of Na{sub ½}Bi{sub ½}TiO{sub 3}-(x)%BaTiO{sub 3}. This information will ultimately assist in tailoring disordered structures for next-generation piezoelectric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Fe0.36(4)Pd 0.64(4)Se 2 : Magnetic Spin-Glass Polymorph of FeSe2 and PdSe2 Stable at Ambient Pressure

We report the synthesis and characterization of Fe 0.36(4) Pd 0.64(4) Se 2 with a pyrite-type structure. Fe 0.36(4) Pd 0.64(4) Se 2 was synthesized using ambient pressure flux crystal growth methods even though the space group Pa3 is high-pressure polymorph for both FeSe 2 and PdSe 2 . Combined experimental and theoretical analysis reveal magnetic spin glass state below 23 K in 1000 Oe that stems from random Fe/Pd occupancies on the same atomic site. The frozen-in magnetic randomness contributes significantly to electronic transport. Electronic structure calculations confirm dominant d-electron character of hybridized bands and large density of states near the Fermi level. Flux-grown single crystal alloys in Pd-Fe-Se atomic system therefore open new pathway for exploring different polymorphs in crystal structures and their novel properties. © 2019 American Chemical Society.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Defectoscopy of ZnGeP{sub 2} single crystals using a strontium vapour laser

A modified method of optical defectoscopy of ZnGeP{sub 2} single crystal plates using a strontium vapour laser (λ = 1.03 and 1.09 μm) is proposed based on shadow imaging of internal defects in plates cut parallel to the (100) plane. It is shown that the use of a strontium vapour laser with a wavelength of 6.45 mm makes it possible to study inhomogeneities in large-size ZnGeP{sub 2} samples. The possibility of fabricating a projection defectoscope for monitoring breakdown development in ZnGeP{sub 2} crystals is considered. (laser applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Modelling of heating and photoexcitation of single-crystal silicon under multipulse irradiation by a nanosecond laser at 1.06 μm

We report a theoretical study of heating and photoexcitation of single-crystal silicon by nanosecond laser radiation at a wavelength of 1.06 μm. The proposed physicomathematical model of heating takes into account the complex nonlinear dynamics of the interband absorption coefficient of silicon and the contribution of the radial heat removal to the cooling of silicon between pulses under multipulse irradiation, which allows one to obtain a satisfactory agreement between theoretical predictions of silicon melting thresholds at different nanosecond pulse durations and experimental data (both under single-pulse and multipulse irradiation). It is found that under irradiation by nanosecond pulses at a wavelength of 1.06 μm, the dynamic Burshtein – Moss effect can play an important role in processes of photoexcitation and heating. It is shown that with the regimes typical for laser multipulse microprocessing of silicon (the laser spot diameter is less than 100 μm, and the repetition rate of pulses is about 100 kHz), the radial heat removal cannot be neglected in the analysis of heat accumulation processes. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗