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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Interfacial dislocations in (111) oriented (Ba 0.7 Sr 0.3 )TiO 3 films on SrTiO 3 single crystal

In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO 3 films grown on (111)-oriented SrTiO 3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrieved the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba 0.7 Sr 0.3 )TiO 3 films.

(Ba 0.7 Sr 0.3 )TiO 3↗
DOE OSTI2015

Determination of 60° polarization nanodomains in a relaxor-based ferroelectric single crystal

We report a determination of monoclinic nanodomains in PMN-xPT with x = 31%PT by using scanning convergent beam electron diffraction (SCBED). We show the presence of 60 ± α degree nanodomains with C m -like symmetry as well as significant variations (α) in local polarization directions across lengths of ~10 nm. The principle of our technique is general and can be applied for the determination of polarization domains in other ferroelectric materials of different symmetry.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Broadband nanophotonic waveguides and resonators based on epitaxial GaN thin films

We demonstrate broadband, low loss optical waveguiding in single crystalline GaN grown epitaxially on c-plane sapphire wafers through a buffered metal-organic chemical vapor phase deposition process. High Q optical microring resonators are realized in near infrared, infrared, and near visible regimes with intrinsic quality factors exceeding 50 000 at all the wavelengths we studied. TEM analysis of etched waveguide reveals growth and etch-induced defects. Reduction of these defects through improved material and device processing could lead to even lower optical losses and enable a wideband photonic platform based on GaN-on-sapphire material system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A device for the application of uniaxial strain to single crystal samples for use in synchrotron radiation experiments

We present the design, construction, and testing of a straining device compatible with many different synchrotron radiation techniques, in a wide range of experimental environments (including low temperature, high field and ultra-high vacuum). The device has been tested by X-ray diffraction on single crystal samples of quasi-one-dimensional Cs{sub 2}Mo{sub 6}Se{sub 6} and K{sub 2}Mo{sub 6}Se{sub 6}, in which microscopic strains up to a Δc/c = 0.12% ± 0.01% change in the c lattice parameters have been achieved. We have also used the device in an inelastic X-ray scattering experiment, to probe the strain-dependent speed of sound ν along the c axis. A reduction Δν/ν of up to −3.8% was obtained at a strain of Δc/c = 0.25% in K{sub 2}Mo{sub 6}Se{sub 6}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Structural and vibrational properties of single crystals of Scandia, Sc{sub 2}O{sub 3} under high pressure

We report the results of single-crystal X-ray diffraction and Raman spectroscopy studies of scandium oxide, Sc{sub 2}O{sub 3}, at ambient temperature under high pressure up to 55 and 28 GPa, respectively. Both X-ray diffraction and Raman studies indicated a phase transition from the cubic bixbyite phase (so-called C-Res phase) to a monoclinic C2/m phase (so-called B-Res phase) at pressures around 25–28 GPa. The transition was accompanied by a significant volumetric drop by ∼6.7%. In addition, the Raman spectroscopy detected a minor crossover around 10–12 GPa, which manifested in the appearance of new and disappearance of some Raman modes, as well as in softening of one Raman mode. We found the bulk modulus values of the both C-Res and B-Res phases as B{sub 0} = 198.2(3) and 171.2(1) GPa (for fixed B′ = 4), respectively. Thus, the denser high-pressure lattice of Sc{sub 2}O{sub 3} is much softer than the original lattice. We discuss possible mechanisms that might be responsible for the pronounced elastic softening in the monoclinic high-pressure phase in this “simple” oxide with an ultra-wide band gap.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A photoluminescence study of excitonic grade CuInSe{sub 2} single crystals irradiated with 6 MeV electrons

High-quality single crystals of CuInSe{sub 2} with near-stoichiometric elemental compositions were irradiated with 6 MeV electrons, at doses from 10{sup 15} to 3 × 10{sup 18 }cm{sup −2}, and studied using photoluminescence (PL) at temperatures from 4.2 to 300 K. Before irradiation, the photoluminescence spectra reveal a number of sharp and well resolved lines associated with free- and bound-excitons. The spectra also show broader bands relating to free-to-bound transitions and their phonon replicas in the lower energy region below 1.0 eV. The irradiation with 6 MeV electrons reduces the intensity of the free- and the majority of the bound-exciton peaks. Such a reduction can be seen for doses above 10{sup 16 }cm{sup −2}. The irradiation induces new PL lines at 1.0215 eV and 0.9909 eV and also enhances the intensity of the lines at 1.0325 and 1.0102 eV present in the photoluminescence spectra before the irradiation. Two broad bands at 0.902 and 0.972 eV, respectively, are tentatively associated with two acceptor-type defects: namely, interstitial selenium (Se{sub i}) and copper on indium site (Cu{sub In}). After irradiation, these become more intense suggesting an increase in the concentration of these defects due to irradiation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO{sub 3}

We report the magnetic properties, of nano-crystalline powders Tb{sub 1−x}Y{sub x}MnO{sub 3} (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO{sub 3}. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below ∼40 K. Furthermore, at T ≤ 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2 K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2 K. However, for the other samples (x = 0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2 K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn{sup 3+} (4μ{sub B}) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392–397 (2010)].

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Roto-translational states of the interstitial molecular hydrogen in silicon: A theoretical study

A theoretical study of the interstitial molecular hydrogen in the silicon single-crystal is reported. H{sub 2} and Si have been approximated as a rigid object and a static matrix, respectively. A five-dimensional numerical-analytical representation of an ab initio potential energy surface of the system has been constructed. This representation has been used to calculate rotational, translational, and roto-translational energy levels of the interstitial hydrogen, where three levels of theory, 2D, 3D, and 5D were considered. The potential energy surface, the band structure of energy levels, and the roto-translational states obtained are presented together with the symmetry analysis of the roto-translational wavefunctions.

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

Non-resonant electromechanical energy harvesting using inter-ferroelectric phase transitions

Non-resonant electromechanical energy harvesting is demonstrated under low frequency excitation (<50 Hz) using [110]{sub C}-poled lead indium niobate-lead magnesium niobate-lead titanate relaxor ferroelectric single crystals with compositions near the morphotropic phase boundary. The efficiency of power generation at the stress-induced phase transition between domain-engineered rhombohedral and orthorhombic ferroelectric states is as much as four times greater than is obtained in the linear piezoelectric regime under identical measurement conditions but during loading below the coercive stress of the phase change. The phase transition mode of electromechanical transduction holds potential for non-resonant energy harvesting from low-frequency vibrations and does not require mechanical frequency up-conversion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Excellent performances of energy harvester using cantilever driving double-clamped 0.7Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.3PbTiO{sub 3} plates and symmetric middle-stops

We present a high performance nonlinear piezoelectric energy harvester constituted by a cantilever with symmetrically middle-stops and double-clamped piezoelectric plates based on piezoelectric single crystal 0.7Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.3PbTiO{sub 3}. Electrical properties of the device under different excitation frequencies, accelerations, and load resistances are studied systematically. Under a low acceleration of 3 m/s{sup 2} (0.3 g), a peak voltage of 26.2 V and a maximum normalized power of 25.6 mW/g{sup 2} were obtained across a matching impedance of 600 kΩ with favorable bandwidths. The low excitation acceleration and excellent performances indicate that the device can be a promising candidate for energy harvesting in low-power electronics and wireless sensors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A modular reactor design for in situ synchrotron x-ray investigation of atomic layer deposition processes

Synchrotron characterization techniques provide some of the most powerful tools for the study of film structure and chemistry. The brilliance and tunability of the Advanced Photon Source allow access to scattering and spectroscopic techniques unavailable with in-house laboratory setups and provide the opportunity to probe various atomic layer deposition (ALD) processes in situ starting at the very first deposition cycle. Here, we present the design and implementation of a portable ALD instrument which possesses a modular reactor scheme that enables simple experimental switchover between various beamlines and characterization techniques. As first examples, we present in situ results for (1) X-ray surface scattering and reflectivity measurements of epitaxial ZnO ALD on sapphire, (2) grazing-incidence small angle scattering of MnO nucleation on silicon, and (3) grazing-incidence X-ray absorption spectroscopy of nucleation-regime Er{sub 2}O{sub 3} ALD on amorphous ALD alumina and single crystalline sapphire.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Sign reversal of transformation entropy change in Co{sub 2}Cr(Ga,Si) shape memory alloys

In situ X-ray diffraction (XRD) measurements and compression tests were performed on Co{sub 2}Cr(Ga,Si) shape memory alloys. The reentrant martensitic transformation behavior was directly observed during the in situ XRD measurements. The high-temperature parent phase and low-temperature reentrant parent phase were found to have a continuous temperature dependence of lattice parameter, therefore suggesting that they are the same phase in nature. Moreover, compression tests were performed on a parent-phase single crystal sample; an evolution from normal to inverse temperature dependence of critical stress for martensitic transformation was directly observed. Based on the Clausius-Clapeyron analysis, a sign reversal of entropy change can be expected on the same alloy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Antiferromagnetic order competing with topological state in Ce{sub x}Bi{sub 2−x}Te{sub 3}

The topological surface states in three-dimensional topological insulators are easily tuned by chemical doping, especially by magnetic impurities. We prepared single crystals of Ce{sub x}Bi{sub 2−x}Te{sub 3} with various x (=0.04, 0.06, 0.08, 0.10, and 0.12). The obtained crystals were characterized by X-ray diffraction and scanning electron microscopy. The magnetic susceptibility data revealed that the Ce atoms are well substituted for Bi into Bi{sub 2}Te{sub 3}. From the Curie-Weiss fits, we observed that the effective magnetic moments μ{sub eff} are close to 2.54 μ{sub B} for free Ce ion, and the paramagnetic Curie-Weiss temperatures θ{sub p} are negatively increased from 2.87 K to −59.3 K with increasing x. The magnetization data clearly showed antiferromagnetic orders around T{sub N} = 4.1 K for x ≥ 0.08, where θ{sub p} suddenly increases, and the electrical resistivity is simply metallic and the magnetoresistance is parabolic. Only for x = 0.06, exotic physical properties arising from the topological states were observed such as non-metallic behavior in the electrical resistivity and linear dependence of the magnetoresistance. Moreover, the carrier concentration of x = 0.06 is one order lower than that of x ≥ 0.08. These observations propose that the antiferromagnetic order is strongly competing with the topological state in Ce{sub x}Bi{sub 2−x}Te{sub 3}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Quantitative and high spatial resolution d{sub 33} measurement of piezoelectric bulk and thin films

A single beam laser interferometer based on a modified Mirau detection scheme with a vertical resolution of ∼5 pm was developed for localized d{sub 33} measurements on patterned piezoelectric films. The tool provides high spatial resolution (∼2 μm), essential for understanding scaling and processing effects in piezoelectric materials. This approach enables quantitative information on d{sub 33}, currently difficult in local measurement techniques such as piezoresponse force microscopy. The interferometer is built in a custom microscope and employs a phase lock-in technique in order to detect sub-Angstrom displacements. d{sub 33} measurements on single crystal 0.67PbMg{sub 0.33}Nb{sub 0.67}O{sub 3}-0.33PbTiO{sub 3} and bulk PbZrTiO{sub 3}-5A ceramics demonstrated agreement within <3% with measurements using a double beam laser interferometer. Substrate bending contributions to out-of-plane strain, observed in thin continuous PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} films grown on Si substrates is reduced for electrode diameters smaller than 100 μm. Direct scanning across room temperature and 150 °C poled 5 μm and 10 μm features etched in 0.5 μm thick PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} films doped with 1% Nb confirmed minimal substrate contributions to the effective d{sub 33,f}. Furthermore, enhanced d{sub 33,f} values were observed along the feature edges due to partial declamping from the substrate, thus validating the application of single beam interferometry on finely patterned electrodes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Mechanical detection of electron spin resonance beyond 1 THz

We report the cantilever detection of electron spin resonance (ESR) in the terahertz (THz) region. This technique mechanically detects ESR as a change in magnetic torque that acts on the cantilever. The ESR absorption of a tiny single crystal of Co Tutton salt, Co(NH{sub 4}){sub 2}(SO{sub 4}){sub 2}⋅6H{sub 2}O, was observed in frequencies of up to 1.1 THz using a backward travelling wave oscillator as a THz-wave source. This is the highest frequency of mechanical detection of ESR till date. The spectral resolution was evaluated with the ratio of the peak separation to the sum of the half-width at half maximum of two absorption peaks. The highest resolution value of 8.59 ± 0.53 was achieved at 685 GHz, while 2.47 ± 0.01 at 80 GHz. This technique will not only broaden the scope of ESR spectroscopy application but also lead to high-spectral-resolution ESR imaging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Deformation mechanisms, defects, heat treatment, and thermal conductivity in large grain niobium

The physical and mechanical metallurgy underlying fabrication of large grain cavities for superconducting radio frequency accelerators is summarized, based on research of 1) grain orientations in ingots, 2) a metallurgical assessment of processing a large grain single cell cavity and a tube, 3) assessment of slip behavior of single crystal tensile samples extracted from a high purity ingot slice before and after annealing at 800 °C / 2 h, 4) development of crystal plasticity models based upon the single crystal experiments, and 5) assessment of how thermal conductivity is affected by strain, heat treatment, and exposure to hydrogen. Because of the large grains, the plastic anisotropy of deformation is exaggerated, and heterogeneous strains and localized defects are present to a much greater degree than expected in polycrystalline material, making it highly desirable to computationally anticipate potential forming problems before manufacturing cavities.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Mechanical properties as an indicator of interstitials in niobium for superconducting accelerator cavities

A preliminary investigation was conducted into the feasibility of using simple mechanical properties experiments to evaluate interstitial impurity uptake from processing environments. Two types of tests were examined: tensile tests and complex modulus measurements using a dynamic mechanical analyzer (DMA). For the tensile tests, samples were cut from a single crystal of niobium, with the same orientation, and then prepared following different procedures. Significant differences were observed during tensile tests, with yielding strength and strain-to-failure clearly related to interstitial uptake. When the strain rate was reduced by an order of magnitude, the strain-to-failure was reduced by 18 % indicating that interstitial hydrogen is responsible for this behavior. For the complex modulus measurement, polycrystalline samples from different locations of two different ingots were examined at a frequency of 1.0 Hz while the temperature was increased at the rate of 1.0 °C per minute. Anaelastic peaks were found for C, N, and O in all samples, but the lower limit of the system did not allow for detection of a peak for H. It is concluded that mechanical properties could be developed as a measurement tool to guide the development of processing methods for producing reduced interstitial content material, but additional research, and uncertainty analysis, is required for these tools to be reliable in this application.

36 MATERIALS SCIENCE↗
DOE OSTI2015

SRF niobium characterization using SIMS and FIB-TEM

Our understanding of superconducting radio frequency (SRF) accelerator cavities has been improved by elemental analysis at high depth resolution and by high magnification microscopy. This paper summarizes the technique development and the results obtained on poly-crystalline, large grain, and single crystal SRF niobium. Focused ion beam made possible sample preparation using transmission electron microscopy and the images obtained showed a very uniform oxide layer for all samples analyzed. Secondary ion mass spectrometry indicated the presence of a high concentration of hydrogen and the hydrogen content exhibited a relationship with improvement in performance. Depth profiles of carbon, nitrogen, and oxygen did not show major differences with heat treatment. Niobium oxide less than 10 nm thick was shown to be an effective hydrogen barrier. Niobium with titanium contamination showed unexpected performance improvement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗