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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

On the photo and thermally stimulated luminescence properties of U doped SrBPO{sub 5}

Highlights: • Synthesis of SrBPO{sub 5}:U phosphor by solid state route. • Confirmed the stabilization of uranium as UO{sub 2}{sup 2+}. • Evaluation of order of kinetics and trap parameters of the system. • ESR-TSL correlation of the observed glow peak. • Probable mechanism proposed for the TSL glow peak. - Abstract: Un-doped and uranium doped SrBPO{sub 5} samples were synthesized using solid-state reaction route and investigated for their photo and luminescence properties. Photoluminescence (PL) spectrum of uranium doped sample showed five peaks at 502, 524, 547, 569 and 597 nm. The average frequency of symmetric stretching of O=U=O in the ground electronic state was found to be about 757 cm{sup −1}. PL decay time measurements on the system confirmed the stabilization of uranium as UO{sub 2}{sup 2+} in the matrix. Thermally stimulated luminescence (TSL) measurements carried out on gamma irradiated SrBPO{sub 5}:U sample showed a glow peak at 390 °K, whose spectral characteristics was found to be typical of UO{sub 2}{sup 2+}. The trap parameters were evaluated using different heating rate method. Room temperature EPR data suggested the formation of borate and oxygen based radical centers in the gamma-irradiated sample. Detailed EPR-TSL correlation studies confirmed the destruction of the oxygen radical to be responsible for the observed glow peak.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Fragility correlates thermodynamic and kinetic properties of glass forming liquids

Graphical abstract: The suggested new fragility parameter correlates viscosity and configurational entropy. - Highlights: • A new fragility function, F=ΔT/ΔC{sub p}×C{sub p}{sup l}/T{sub g} has been proposed. • A three parameter viscosity function using the new F reproduces Angell fragility plot. • A new ΔC{sub p} function is derived which directly relates Adam–Gibbs function with the fragility based viscosity function. - Abstract: In our earlier communication we proposed a simple fragility determining function, ([NBO]/V{sub m}{sup 3}T{sub g}), which we have now used to analyze several glass systems using available thermal data. A comparison with similar fragility determining function, ΔC{sub p}/C{sub p}{sup l}, introduced by Chryssikos et al. in their investigation of lithium borate glasses has also been performed and found to be more convenient quantity for discussing fragilities. We now propose a new function which uses both ΔC{sub p} and ΔT and which gives a numerical fragility parameter, F whose value lies between 0 and 1 for glass forming liquids. F can be calculated through the use of measured thermal parameters ΔC{sub p}, C{sub p}{sup l}, T{sub g} and T{sub m}. Use of the new fragility values in reduced viscosity equation reproduces the whole range of viscosity curves of the Angell plot. The reduced viscosity equation can be directly compared with the Adam–Gibbs viscosity equation and a heat capacity function can be formulated which reproduces satisfactorily the ΔC{sub p} versus ln(T{sub r}) curves and hence the configurational entropy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the photoluminescence of InBO3 and TbBO3 doped by Eu3+ and Ce3+

Highlights: • InBO{sub 3} changes its crystal structure from calcite to high temperature vaterite by the incorporation of Eu{sup 3+} or Tb{sup 3+}. • The intensity of the {sup 5}D{sub 0} → {sup 7}F{sub 2} transitions of Eu{sup 3+} are enhanced due to a reduction of the local symmetry at the activator's lattice site. • Doping Ce{sup 3+} into TbBO{sub 3}:Eu{sup 3+} results in a complete change of the absorption spectra in the near UV range due to the intense 4f-5d transitions of Ce{sup 3+}. • Efficient energy transfer occurs in the chain Ce{sup 3+} → Tb{sup 3+} → Eu{sup 3+}. • Even though a metal-to-metal CT between Ce{sup 3+} and Eu{sup 3+} is known to quench the photoluminescence of Eu{sup 3+}, a quantum yield of about 50% was determined. - Abstract: This work concerns ortho-borates according to the compositions InBO{sub 3}:Eu{sup 3+}, InBO{sub 3}:Eu{sup 3+},Tb{sup 3+}, and InBO{sub 3}:Eu{sup 3+},Tb{sup 3+},Ce{sup 3+}. All samples were investigated with respect to their structure type and spectroscopic properties. It turned out that InBO{sub 3} changes its crystal structure from calcite to high temperature vaterite by the incorporation of Eu{sup 3+} or Tb{sup 3+}. At the same time, novel excitation bands arise caused by optical transitions originating from the presence of Eu{sup 3+} or Tb{sup 3+}. The intensity of the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition of Eu{sup 3+} is enhanced due to the change of the crystal system. Doping Ce{sup 3+} into TbBO{sub 3}:Eu{sup 3+} results in a complete change of the absorption spectra caused by the 4f-5d transition of Ce{sup 3+}. These findings open up the possibility to employ the energy transfer chain Ce{sup 3+} → Tb{sup 3+} → Eu{sup 3+}. Even though a metal-to-metal CT between Ce{sup 3+} and Eu{sup 3+} is well known to quench the photoluminescence of Eu{sup 3+}, we found a quantum yield of about 50%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

TRPM7 channel regulates PDGF-BB-induced proliferation of hepatic stellate cells via PI3K and ERK pathways

TRPM7, a non-selective cation channel of the TRP channel superfamily, is implicated in diverse physiological and pathological processes including cell proliferation. Recently, TRPM7 has been reported in hepatic stellate cells (HSCs). Here, we investigated the contribution role of TRPM7 in activated HSC-T6 cell (a rat hepatic stellate cell line) proliferation. TRPM7 mRNA and protein were measured by RT-PCR and Western blot in rat model of liver fibrosis in vivo and PDGF-BB-activated HSC-T6 cells in vitro. Both mRNA and protein of TRPM7 were dramatically increased in CCl{sub 4}-treated rat livers. Stimulation of HSC-T6 cells with PDGF-BB resulted in a time-dependent increase of TRPM7 mRNA and protein. However, PDGF-BB-induced HSC-T6 cell proliferation was inhibited by non-specific TRPM7 blocker 2-aminoethoxydiphenyl borate (2-APB) or synthetic siRNA targeting TRPM7, and this was accompanied by downregulation of cell cycle proteins, cyclin D1, PCNA and CDK4. Blockade of TRPM7 channels also attenuated PDGF-BB induced expression of myofibroblast markers as measured by the induction of α-SMA and Col1α1. Furthermore, the phosphorylation of ERK and AKT, associated with cell proliferation, decreased in TRPM7 deficient HSC-T6 cells. These observations suggested that TRPM7 channels contribute to perpetuated fibroblast activation and proliferation of PDGF-BB induced HSC-T6 cells via the activation of ERK and PI3K pathways. Therefore, TRPM7 may constitute a useful target for the treatment of liver fibrosis. - Highlights: • Upregulation of TRPM7 mRNA and protein in the fibrotic livers from CCl{sub 4}-treated rats. • Increasing expression of TRPM7 mRNA and protein during HSC activation. • Blockade of TRPM7 inhibited the PDGF-BB induced proliferation of HSC-T6 cells. • Blockade of TRPM7 decreased α-SMA and Col1α1 expressions in activated HSC-T6 cells. • TRPM7 up-regulation contributes to the activation of ERK and AKT pathways.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Resolution of Electronic and Structural Factors Underlying Oxygen-Evolving Performance in Amorphous Cobalt Oxide Catalysts

Non-noble-metal, thin-film oxides are widely investigated as promising materials for catalyzing oxygen evolution reactions (OER). Cobalt oxide thin-films that are electrochemically formed in the presence of borate (CoBi) and phosphate (CoPi) serve as important reference catalysts for assessing correlations between oxyhydroxide domain structures with corresponding electronic properties and OER performance. Here, we present a comparison of CoPi and CoBi thin-film catalysts by a combination of advanced X-ray electronic and vibrational spectroscopies of L-edge synchrotron X-ray absorption (XAS), resonant X-ray emission (RXES), resonant inelastic X-ray scattering (RIXS), resonant Raman (RR) scattering, and high-energy X-ray pair distribution function (PDF) analysis. A detailed spectral analysis is presented and identifies relationships between the OER performance and electronic and molecular-type domain structures. XAS shows that CoBi is composed essentially exclusively of cobalt in octahedral coordination, while CoPi contains approximately 17% tetrahedral Co(II), with the remainder in octahedral coordination. Oxygen-mediated 4 p -3 d hybridization through Co-O-Co bonding was detected by RXES and the inter-site dd excitation was observed by RIXS in CoBi, but not in CoPi. RR shows that CoBi resembles a disordered layered LiCoO 2 -like structure while Co- Pi is amorphous. Distinct domain models in the nanometer range for CoBi and CoPi have been proposed on the basis of the PDF analysis coupled to XAS data. In conclusion, the observed differences provide important implications for the enhancement factors in OEC performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Local structure around rare-earth ions in B{sub 2}O{sub 3} glass at high pressure

Melt quenching of B{sub 2}O{sub 3} with less than 25 mol. % rare-earth oxide (RE{sub 2}O{sub 3}) at ambient pressure results in a milky white glass because of liquid-liquid phase separation into B{sub 2}O{sub 3} and RE{sub 2}O{sub 3}{center_dot}3B{sub 2}O phases. In contrast, we have found that melt quenching under GPa-order pressure realizes a transparent RE-doped B{sub 2}O{sub 3} glass. This study investigates the local structure around the RE ions in the B{sub 2}O{sub 3} glass prepared at 3 GPa using optical measurements and electron-spin-echo envelope modulation spectroscopy. It is shown that the RE-rich microparticles disappear and the RE ions are isolated from each other in a highly symmetric crystal field formed by triangular and tetrahedral boron units. This result is consistent with that extrapolated from the data for RE-doped sodium borate glasses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Glass transition and crystallization kinetics of a barium borosilicate glass by a non-isothermal method

The glass transition and crystallization kinetics of a glass with a molar composition 60BaO-30B{sub 2}O{sub 3}-10SiO{sub 2} were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (T{sub g}) and of the maximum crystallization temperature (T{sub p}) on the heating rate was used to determine the activation energy associated with the glass transition (E{sub g}), the activation energy for crystallization (E{sub c}), and the Avrami exponent (n). X-ray diffraction (XRD) revealed that barium borate (β-BaB{sub 2}O{sub 4}) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba{sub 5}Si{sub 8}O{sub 21}). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (χ) were also examined. When the crystallization fraction (χ) increased from 0.1 to 0.9, the value of local activation energy (E{sub c}(χ)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Photoluminescence properties of Ho{sup 3+} ion in lithium-fluoroborate glass containing different modifier oxides

Trivalent holmium (0.5 mol%) doped lithium fluoro-borate glasses with the chemical compositions 49.5Li{sub 2}B{sub 4}O{sub 7−}20BaF{sub 2−}10NaF−20MO (where M=Mg, Ca, Cd and Pb), 49.5Li{sub 2}B{sub 4}O{sub 7−}20BaF{sub 2−}10NaF−10MgO−10CaO and 49.5Li{sub 2}B{sub 4}O{sub 7−}20BaF{sub 2−}10NaF−10CdO−10PbO were synthesized and investigated their photoluminescence properties. The variation in chemical composition by varying modifier oxides causes changes in the structural spectroscopic behavior of Ho{sup 3+} ions. These changes are examined by UV-VIS- NIR and luminescence spectroscopic techniques. The visible luminescence spectra were obtained by exciting samples at 409 nm radiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Indentation size effect and the plastic compressibility of glass

Oxide glasses exhibit significant densification under an applied isostatic pressure at the glass transition temperature. The glass compressibility is correlated with the chemical composition and atomic packing density, e.g., borate glasses with planar triangular BO{sub 3} units are more disposed for densification than silicate glasses with tetrahedral units. We here show that there is a direct relation between the plastic compressibility following hot isostatic compression and the extent of the indentation size effect (ISE), which is the decrease of hardness with indentation load exhibited by most materials. This could suggest that the ISE is correlated with indentation-induced shear bands, which should form in greater density when the glass network is more adaptable to volume changes through structural and topological rearrangements under an applied pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Synergistic effects of mica and wollastonite fillers on thermal performance of intumescent fire retardant coating

In this study, intumescent fire retardant coatings (IFRC) were developed to investigate the synergistic effects of reinforced mica and wollastonite fillers based IFRC towards heat shielding, char expansion, char composition and char morphology. Ammonium poly-phosphate (APP) was used as acid source, expandable graphite (EG) as carbon source, melamine as blowing agent, boric acid as additive and Hardener H-2310 polyamide amine in bisphenol A epoxy resin BE-188(BPA) was used as curing agent. Bunsen burner fire test was used for thermal performance according to UL-94 for 1 h. Field Emission Scanning Electron Microscopy (FESEM) was used to observe char microstructure. X-Ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to analyse char composition. The results showed that addition of clay filler in IFRC enhanced the fire protection performance of intumescent coating. X-Ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results showed the presence of boron phosphate, silicon phosphate oxide, aluminium borate in the char that improved the thermal performance of intumescent fire retardant coating (IFRC). Resultantly, the presence of these developed compounds enhanced the Integrity of structural steel upto 500°C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

The mechanism of the area negative thermal expansion in KBe{sub 2}BO{sub 3}F{sub 2} family crystals: A first-principles study

A very recent study demonstrated that the KBe{sub 2}BO{sub 3}F{sub 2} (KBBF) family of crystals, including KBBF, RbBe{sub 2}BO{sub 3}F{sub 2}, and CsBe{sub 2}BO{sub 3}F{sub 2}, are the only known borates exhibiting a rarely occurring isotropic area negative thermal expansion (NTE) behavior, over a very large temperature range. In the present work, the NTE mechanism in these crystals is comprehensively investigated using the first-principles calculations. It is revealed that the area NTE behavior mainly originates from the concerted distortion of [BeO{sub 3}F] tetrahedra in the two-dimensional [Be{sub 2}BO{sub 3}F{sub 2}]{sub ∞} framework with respect to temperature, while the [BO{sub 3}] triangles remain almost rigid. Moreover, the different magnitude of NTE effect in the three crystals is attributed to the interaction difference between the alkali metal atoms (K, Rb, or Cs) and the [Be{sub 2}BO{sub 3}F{sub 2}]{sub ∞} layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Synthesis and optical properties of polycrystalline Li{sub 2}Al{sub 2}B{sub 2}O{sub 7} (LABO)

A polycrystalline lithium aluminum borate (Li{sub 2}Al{sub 2}B{sub 2}O{sub 7}, LABO) has been synthesized by using simple solid-state technique. The obtained LABO polycrystalline was characterized by powder X-ray diffraction; Fourier transform infrared (FT-IR) spectroscopy and second harmonic generation (SHG) efficiency measurement. The functional groups were identified using the FT-IR spectroscopic data. The SHG efficiency of the polycrystalline material was obtained by the classic Kurtz powder technique using a fundamental wavelength 1064 nm of Nd:YAG laser and it is found to be 1.4 times that of potassium dihydrogen phosphate (KDP).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Synthesis and optical properties of antimony oxide glasses doped with holmium trioxide

Holmium doped lithium-antimony-lead borate glasses having 1 mol% AgNO{sub 3} with composition 50B{sub 2}O{sub 3}-20PbO-25Sb{sub 2}O{sub 3}-5Li{sub 2}O have been prepared using single step melt quenching technique. The XRD spectrum confirms amorphous nature of glasses. The optical absorbance studies were carried out on these glasses. The optical direct band gap energies were found to be in the range of 3.10 eV to 3.31 eV and indirect band gap energies were found to be in the range of 2.28 eV to 3.00 eV. The refractive indexes have been calculated by using Lorentz-Lorenz formula and the calculated values in the range of 2.31 to 2.37.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Concentration dependent spectroscopic properties of Dy{sup 3+} ions doped boro-phosphate glasses

Dy{sup 3+} ions doped boro-phosphate glasses have been synthesized by melt quenching method and characterized through FTIR, absorption and luminescence spectral measurements. The presence of various stretching and bending vibrations of different borate and phosphate groups were identified from the FTIR spectra. In order to examine the electronic band structure of the studied glasses, Optical energy gap (E{sub opt}) and Urbach energy (ΔE) values were estimated from the absorption spectra. The Judd-Ofelt (JO) intensity parameters were calculated to examine the symmetry of the ligand environment around the Dy{sup 3+} ions site. The emission spectra exhibit two intense emission bands at around 482 nm (blue) and 574 nm (yellow) corresponding to the {sup 4}F{sub 9/2}→{sup 6}H{sub 15/2} and {sup 4}F{sub 9/2}→{sup 6}H{sub 13/2} transitions respectively. The emission spectra were characterized through Commission International d’Eclairage (CIE) 1931 chromaticity diagram to explore its suitability for WLED applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Nonlinear negative refraction by difference frequency generation

Negative refraction has attracted much interest for its promising capability in imaging applications. Such an effect can be implemented by negative index meta-materials, however, which are usually accompanied by high loss and demanding fabrication processes. Recently, alternative nonlinear approaches like phase conjugation and four wave mixing have shown advantages of low-loss and easy-to-implement, but associated problems like narrow accepting angles can still halt their practical applications. Here, we demonstrate theoretically and experimentally a scheme to realize negative refraction by nonlinear difference frequency generation with wide tunability, where a thin Beta barium borate slice serves as a negative refraction layer bending the input signal beam to the idler beam at a negative angle. Furthermore, we realize optical focusing effect using such nonlinear negative refraction, which may enable many potential applications in imaging science.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Microelectromechanical systems integrating molecular spin crossover actuators

Silicon MEMS cantilevers coated with a 200 nm thin layer of the molecular spin crossover complex [Fe(H{sub 2}B(pz){sub 2}){sub 2}(phen)] (H{sub 2}B(pz){sub 2} = dihydrobis(pyrazolyl)borate and phen = 1,10-phenantroline) were actuated using an external magnetic field and their resonance frequency was tracked by means of integrated piezoresistive detection. The light-induced spin-state switching of the molecules from the ground low spin to the metastable high spin state at 10 K led to a well-reproducible shift of the cantilever's resonance frequency (Δf{sub r} = −0.52 Hz). Control experiments at different temperatures using coated as well as uncoated devices along with simple calculations support the assignment of this effect to the spin transition. This latter translates into changes in mechanical behavior of the cantilever due to the strong spin-state/lattice coupling. A guideline for the optimization of device parameters is proposed so as to efficiently harness molecular scale movements for large-scale mechanical work, thus paving the road for nanoelectromechanical systems (NEMS) actuators based on molecular materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Terahertz optical properties of LBO crystal upon cooling to liquid nitrogen temperature

The anisotropy of optical properties of nonlinear lithium borate (LBO) crystals in the range of 0.2 – 2 THz is investigated by time-domain THz spectroscopy at room temperature and at T = 81 K. It is shown that the birefringence dramatically decreases upon cooling, as a result of which phase-matching conditions cannot be implemented. At the same time, the absorption coefficients α{sub x} and α{sub y} are found to decrease significantly with decreasing temperature, due to which the LBO crystal becomes a promising material for generating THz radiation via optical rectification and fabricating periodic structures and optical elements. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Seamless aperture and length enlargement of single crystalline materials for high-energy laser applications

An optically seamless method for increasing the aperture or length of nonlinear materials has been developed, which is suitable for optics in high energy laser systems and other applications. Differences between aperture and length scaling are analyzed. Bonding of component pairs of a nonlinear crystal, lithium tri-borate, is experimentally demonstrated by GAMDAN Optics Inc. and tested at the Laboratory of Laser Energetics at the University of Rochester. Here, a bonded crystal is shown to deliver beam quality and second harmonic conversion efficiency that is equivalent to that of a monolithic crystal of similar dimensions.

aperture scaling↗