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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Synthesis and structural study of 4-(2-chlorophenyl)-2-ethoxy-5,6,7,8,9,10-hexahydrocycloocta[B] pyridine-3-carbonitrile

The novel organic material C{sub 20}H{sub 21}ClN{sub 2}O was synthesized by One-Pot synthesis method and the single crystals were grown by slow evaporation solution growth technique. The crystal structure was elucidated by subjecting the grown crystals to the single crystal x-ray diffraction analysis and was refined by full matrix least-squares method to R=0.039 for 2746 reflections. Crystal system of the grown crystal was found to be monoclinic with the space group P2{sub 1}/a and a=9.196(4) Å, b=13.449(4) Å, c=14.818(4) Å, β= 101.542(3)°, V=1795.6(11) Å{sup 3} and Z=4. In this crystal structure, cyclooctanone prefers to reside in a chair-boat conformation. The structure is stabilized by attractive molecular force such as CH/π interaction called hydrophobic interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural and electrical properties of organic stilbazolium single crystal of DSCHS

Organic nonlinear optical crystal 4-N, N-Dimethyl Amino-4’N’-Methyl-Stilbazolium 3-Carboxy-4-Hydroxy benzenesulfonate (DSCHS) has been successfully grown from aqueous methanol solution by adopting slow solvent evaporation technique. Chemical composition of the sample was confirmed by CHN analysis. Powder X-ray diffraction analysis was carried out and it shows that DSCHS crystal belongs to triclinic structure with Pl space group. It is found that this material exhibits positive photoconductivity. Dielectric studies were also carried out for different temperature by varying the frequency.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Studies on 2-amino-5-nitropyridinium nitrate (2A5NPN): A semi-organic third order nonlinear optical single crystal

2-amino-5-nitropyridinium nitrate (2A5NPN) is a semi-organic nonlinear optical crystal and optically good quality 2A5NPN single crystals were successfully grown by slow evaporation solution growth technique (SEST) at ambient temperature. The crystallographic structure of the grown crystal was determined by single crystal X-Ray diffraction analysis and it belongs to Monoclinic crystal system with centro symmetric crystalline nature. The crystallinity of the grown crystal was confirmed by powder X-ray diffraction analysis. The other physical properties of grown crystals are also characterized using TG-DTA, UV-Visible NIR, chemical etching, photoconductivity and Z-scan measurements. The Z-scan method reveals that the 2A5NPN crystal possesses multi photon absorption behaviour and the significantly higher third order susceptibility and it is a promising potential NLO material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth and microtopographic study of CuInSe{sub 2} single crystals

The CuInSe{sub 2} single crystals were grown by chemical vapour transport (CVT) technique using iodine as transporting agent. The elemental composition of the as-grown CuInSe{sub 2} single crystals was determined by energy dispersive analysis of X-ray (EDAX). The unit cell crystal structure and lattice parameters were determined by X-ray diffraction (XRD) technique. The surface microtopographic study of the as-grown CuInSe{sub 2} single crystals surfaces were done to study the defects, growth mechanism, etc. of the CVT grown crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth, structural, optical, thermal and laser damage threshold studies of an organic single crystal: 1,3,5 – triphenylbenzene (TPB)

Good quality single crystals of pure hydrocarbon 1,3,5-Triphenylbenzene (TPB) have been successfully grown using toluene as a solvent using controlled slow cooling solution growth technique. TPB crystallizes in orthorhombic structure with the space group Pna2{sub 1}. The structural perfection of the grown crystal has been analysed by high resolution X-ray diffraction measurements. The range and percentage of the optical transmission are ascertained by recording the UV-vis spectrum. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder second harmonic generation studies were carried out to explore its NLO properties. Laser damage threshold value has been determined using Nd:YAG laser operating at 1064 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Pressure effects on topological crystalline insulator SnTe and derived superconductor Sn{sub 0.5}In{sub 0.5}Te

We are reporting decrease in superconducting transition temperature accompanied by increased metallicity in indium doped SnTe superconductor. SnTe is a topological crystalline insulator and superconductivity is achieved by indium substitution in place of tin. With application of hydrostatic pressure we find negative dT{sub c}/dP of ~ -0.6K/GPa upto 2.5 GPa. The overall phenomenon is ascribed to unconventional superconductivity. Decrease in resistivity is also seen in single crystal SnTe with application of pressure but no evidence of superconductivity is observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth of high quality single crystals of Bi{sub 2}Se{sub 3} topological insulator via solid state reaction method

Recently discovered, Topological Insulators (TIs) have garnered enormous amount of attention owing to its unique surface properties which has potential applications in the field of spintronics and other modern technologies. For all this, it should require a very good quality samples. There are a number of techniques suggested by people for the growth of good quality TIs. Here, we are reporting the growth of high quality single crystals of Bi{sub 2}Se{sub 3} (a TI) by slow cooling solid-state reaction method. X-ray diffraction measurements performed on a cleaved flake of single crystal Bi{sub 2}Se{sub 3} showed up with proper orientations of the crystal planes. High energy X-ray diffraction has been performed to confirm the stoichiometry of the compound and also recorded Laue patterns prove the single crystalline nature of Bi{sub 2}Se{sub 3}. Moreover, angle resolved photo-emission spectroscopy (ARPES) carried out on a flat crystal flake shows distinct Dirac dispersion of surface bands at the gamma point clarifying it as a 3D topological insulator.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Single crystal growth of Sr{sub 2}TiMnO{sub 6} by optical floating zone technique

Single crystals of Sr{sub 2}TiMnO{sub 6} were grown by optical floating zone technique. Powder X-ray diffraction studies confirmed the single phase nature of the grown crystal. Laue diffraction studies proved the quality of the grown crystal. Neutron diffraction showed no magnetic ordering down to 6 K. Impedance studies showed temperature dependant relaxation which is due to the presence of oxygen vacancies in the grown crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Linear magneto-resistance in Bi{sub 2}SeTe{sub 2} topological insulator

Magnetic field and temperature dependent electronic transport measurements have been carried out on Bi{sub 2}SeTe{sub 2} topological insulator single crystals. The measurements reveal an insulating behavior and the carriers were found to be electrons (n-type) from Hall measurement. Magneto-resistance (MR) measurements in the field range (B) of 15 T to -15 T carried out at 4.2 K showed a cusp like weak anti-localization behavior for lower fields (-5 T 5 T. Upon increasing temperature, MR transforms to linear dependence of B at 40, 50 and 100 K. On further increasing temperatures (> 200 K), a parabolic MR is observed. Temperature dependent Hall data also showed a transition from a nonlinear to linear behavior upon increasing temperatures. Disorder induced changes in the electronic transport characteristics of bulk and surface electrons are believed to cause such changes in the magneto-transport behavior of this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Emergence of superconductivity in topological insulator Bi{sub 2}Se{sub 3} by Sr intercalation

Recently superconductivity wasreported by Sr intercalation in topological insulator Bi{sub 2}Se{sub 3}. In this report we extensively study anisotropic superconducting properties of Sr{sub 0.1}Bi{sub 2}Se{sub 3} with transition at ~2.9 through resistivity and DC magnetization measurement. We also discuss synthesis methodology for growth of single crystal Sr-Bi{sub 2}Se{sub 3}. The anisotropic properties of Sr{sub 0.1}Bi{sub 2}Se{sub 3} single crystals were studied using transport measurements. Using Ginzburg Landau formulas the upper critical field H{sub c2}(0) comes out to be 2.1 T and 1.4 T for magnetic field applied along the ab-plane and c-axis of the single crystalsand corresponding Ginzburg - Landau coherence lengths are ξ{sub ab} = 15.3 nm and ξ{sub c} = 10.2 nm. The sample shows weak electronic anisotropy Γ = 1.5. Hall resistivity is linear with field at 10 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Evolution of magnetism in Ru doped Na{sub 2}IrO{sub 3}

We synthesized Ru doped single crystalline samples of the honeycomb iridate material Na{sub 2}IrO{sub 3} and studied their magnetic properties using AC and DC magnetic susceptibility. The parent compound Na{sub 2}IrO{sub 3} is a spin orbit driven Mott insulator with long range order below T{sub N} = 15 K. We find that even smallest substitution of Ru changes the antiferromagnetic long range order state to a spin glass like state indicating the fragile nature of magnetism in Na2IrO3. We track the freezing temperature Tg as a function of Ru concentration and the shift of T{sub g} with frequency f of the ac modulation in AC susceptibility which is found to be very different from canonical spin-glasses like Cu-Mn.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Tunable bandgap in hybrid perovskite CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) single crystals and photodetector applications

We report the synthesis of CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) (X=Cl and I) single crystals via a stepwise temperature control approach. High-quality CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) crystals with a tunable bandgap from 1.92 eV to 2.53 eV have been prepared successfully in this way. And further experiments revealed the influence of halogen content and preparation temperature on the structural and optical properties of these crystals. It is observed that chlorine can lower the critical nucleation energy, which results in crystallizing at lower temperature with the chlorine content increasing, while the nucleation energy increases slowly with increasing iodine content. Moreover, in contrast to Frank–van der Merwe growth with low heating rate, high heating rate leads to a mass of small size single crystals and Stranski-Krastanov growth. The single crystals with tunable band gap and impressive characteristics enable us to fabricate high performance photodetectors for different wavelengths.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

“Glass-like” thermal conductivity gradually induced in thermoelectric Sr{sub 8}Ga{sub 16}Ge{sub 30} clathrate by off-centered guest atoms

The origin of the “glass-like” plateau in thermal conductivity of inorganic type I clathrates has been debated for more than a decade. Here, it is demonstrated that the low temperature thermal conductivity of Sr{sub 8}Ga{sub 16}Ge{sub 30} can be controlled by the synthesis method: A flux-grown sample has a “glass-like” plateau in thermal conductivity at low temperature, while a zone-melted sample instead has a crystalline peak. A combination of flux-growth and zone-melting produces an intermediate thermal conductivity. In a comprehensive study of three single crystal samples, it is shown by neutron diffraction that the transition from crystalline peak to “glass-like” plateau is related to an increase in Sr guest atom off-centering distance from 0.24 Å to 0.43 Å. By modifying ab initio calculated force constants for the guest atom to an isotropic model, we reproduce both measured heat capacity and inelastic neutron scattering data. The transition from peak to plateau in the thermal conductivity can be modeled by a combined increase of Rayleigh and disorder scattering. Measurement of heat capacity refutes simple models for tunneling of Sr between off-center sites. Furthermore, the electronic properties of the same samples are characterized by Hall carrier density, Seebeck coefficient, and resistivity. The present comprehensive analysis excludes tunneling and charge carrier scattering as dominant contributors to the “glass-like” plateau. The increased guest atom off-centering distance controlled by synthesis provides a possible microscopic mechanism for reducing the low temperature thermal conductivity of clathrates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Solid phase epitaxial growth of high mobility La:BaSnO{sub 3} thin films co-doped with interstitial hydrogen

This work presents the solid phase epitaxial growth of high mobility La:BaSnO{sub 3} thin films on SrTiO{sub 3} single crystal substrates by crystallization through thermal annealing of nanocrystalline thin films prepared by pulsed laser deposition at room temperature. The La:BaSnO{sub 3} thin films show high epitaxial quality and Hall mobilities up to 26 ± 1 cm{sup 2}/Vs. Secondary ion mass spectroscopy is used to determine the La concentration profile in the La:BaSnO{sub 3} thin films, and a 9%–16% La doping activation efficiency is obtained. An investigation of H doping to BaSnO{sub 3} thin films is presented employing H plasma treatment at room temperature. Carrier concentrations in previously insulating BaSnO{sub 3} thin films were increased to 3 × 10{sup 19 }cm{sup −3} and in La:BaSnO{sub 3} thin films from 6 × 10{sup 19 }cm{sup −3} to 1.5 × 10{sup 20 }cm{sup −3}, supporting a theoretical prediction that interstitial H serves as an excellent n-type dopant. An analysis of the free electron absorption by infrared spectroscopy yields a small (H,La):BaSnO{sub 3} electron effective mass of 0.27 ± 0.05 m{sub 0} and an optical mobility of 26 ± 7 cm{sup 2}/Vs. As compared to La:BaSnO{sub 3} single crystals, the smaller electron mobility in epitaxial thin films grown on SrTiO{sub 3} substrates is ascribed to threading dislocations as observed in high resolution transmission electron micrographs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The role of chemical structure on the magnetic and electronic properties of Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/Si(111) interface

We show that Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} film deposited on Si(111) has a single crystal structure and twin related epitaxial relationship with the substrate. Sub-nanometer electron energy loss spectroscopy shows that in a narrow interface region there is a mutual inter-diffusion dominated by Si and Co. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that the film has B2 ordering. The film lattice structure is unaltered even at the interface due to the substitutional nature of the intermixing. First-principles calculations performed using structural models based on the aberration corrected electron microscopy show that the increased Si incorporation in the film leads to a gradual decrease of the magnetic moment as well as significant spin-polarization reduction. These effects can have significant detrimental role on the spin injection from the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} film into the Si substrate, besides the structural integrity of this junction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Hierarchical domain structure of lead-free piezoelectric (Na{sub 1/2} Bi{sub 1/2})TiO{sub 3}-(K{sub 1/2} Bi{sub 1/2})TiO{sub 3} single crystals

We report a unique hierarchical domain structure in single crystals of (Na{sub 1/2}Bi{sub 1/2})TiO{sub 3}-xat. %(K{sub 1/2}Bi{sub 1/2})TiO{sub 3} for x = 5 and 8 by transmission electron microscopy (TEM). A high density of polar nano-domains with a lamellar morphology was found, which were self-assembled into a quadrant-like configuration, which then assembled into conventional ferroelectric macro-domains. Studies by high resolution TEM revealed that the polar lamellar regions contained a coexistence of in-phase and anti-phase oxygen octahedral tilt regions of a few nanometers in size. Domain frustration over multiple length scales may play an important role in the stabilization of the hierarchy, and in reducing the piezoelectric response of this Pb-free piezoelectric solid solution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Photoinduced surface voltage mapping study for large perovskite single crystals

Using a series of illumination sources, including white light (tungsten-halogen lamp), 445-nm, 532-nm, 635-nm, and 730-nm lasers, the surface photovoltage (SPV) images were mapped for centimeter-sized CH{sub 3}NH{sub 3}PbX{sub 3} (X = Cl, Br, I) perovskite single crystals using Kelvin probe force microscopy. The significant SPV signals were observed to be wavelength-dependent. We attribute the appreciable SPV to the built-in electric field in the space charge region. This study shines light into the understanding of photoinduced charge generation and separation processes at nanoscale to help advance the development of perovskite solar cells, optoelectronics, laser, photodetector, and light-emitting diode (LED).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Direct conversion of h-BN into c-BN and formation of epitaxial c-BN/diamond heterostructures

We have created a new state of BN (named Q-BN) through rapid melting and super undercooling and quenching by using nanosecond laser pulses. Phase pure c-BN is formed either by direct quenching of super undercooled liquid or by nucleation and growth from Q-BN. Thus, a direct conversion of hexagonal boron nitride (h-BN) into phase-pure cubic boron nitride (c-BN) is achieved by nanosecond pulsed laser melting at ambient temperatures and atmospheric pressure in air. According to the P-T phase diagram, the transformation from h-BN into c-BN under equilibrium processing can occur only at high temperatures and pressures, as the hBN-cBN-Liquid triple point is at 3500 K/9.5 GPa or 3700 K/7.0 GPa with a recent theoretical refinement. Using nonequilibrium nanosecond laser melting, we have created super undercooled state and shifted this triple point to as low as 2800 K and atmospheric pressure. The rapid quenching from super undercooled state leads to the formation of a new phase, named as Q-BN. We present detailed characterization of Q-BN and c-BN layers by using Raman spectroscopy, high-resolution scanning electron microscopy, electron-back-scatter diffraction, high-resolution TEM, and electron energy loss spectroscopy, and discuss the mechanism of formation of nanodots, nanoneedles, microneedles, and single-crystal c-BN on sapphire substrate. We have also deposited diamond by pulsed laser deposition of carbon on c-BN and created c-BN/diamond heterostructures, where c-BN acts as a template for epitaxial diamond growth. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon, and the impact of this discovery on a variety of applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗