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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Super Large Sn 1– x Se Single Crystals with Excellent Thermoelectric Performance

SnSe single crystals have drawn extensive attention for their ultralow thermal conductivity and outstanding thermoelectric performance. In our paper, we report super large Sn 1– x Se single crystals with excellent thermoelectric properties, fabricated via an advanced horizontal Bridgman technique with great yield and high reproducibility. The obtained single crystals have a super large size of ~70 × 50 × 15 mm with a considerable weight of 148 g, which leads to a record-high mass density of >6.1 g cm –3 . Extensive chemical characterization demonstrates that ~0.3% Sn vacancies are present, which results in a large concentration of holes, ~1.2 × 10 19 cm –3 , and an enhanced power factor of ~6.1 μW cm –1 K –2 at 793 K. Simultaneously, the Sn-vacancy-induced lattice distortions result in a low thermal conductivity of ~0.39 W m –1 K –1 at 793 K, leading to a competitive ZT of ~1.24. This work demonstrates that large-size off-stoichiometric SnSe single crystals hold promise to achieve high thermoelectric performance.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Single crystal micromechanical resonator

A single crystal micromechanical resonator includes a suspended plate of lithium niobate or lithium tantalate. The suspended plate and a support structure are formed from a single crystal.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Compensation mechanism of bromine dopants in cadmium telluride single crystals

We grew single crystals of cadmium telluride, doped with bromine by the Bridgman method, annealed them under a cadmium overpressure (P Cd = 10² - 10⁵ Pa) at 800-1100 K, and investigated their electrical properties at high- and low-temperature. The influence of impurities on the crystals' electrical properties were analyzed using the defect subsystem model; the model includes the possibility of the formation of point intrinsic defects (V²⁻ Cd , Cd²⁺ i , V²⁺ Te , Te²⁻ i ), and substitutional ones (Br⁰ Te , Br⁺ Te ), as well as complexes of point defects, i.e., (Br⁺ Te V²⁻ Cd )⁻ and (2Br⁺ Te V²⁻ Cd )⁰. We established the concentration dependence between free charge carriers and the parameters of the annealing process. Here, n(T) and n(P Cd ) are determined by two dominant defects – Br⁺ Te and (2Br⁺ Te V²⁻ Cd )⁰. Their content varies with the annealing temperature and the vapor pressure of the component; the concentration of other defects is much smaller and almost does not affect the electron density.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Hydrogenation on Magnetostriction and Magnetocaloric Effect in Gadolinium Single Crystal

The gadolinium single crystal obtained by the Czochralski method was hydrogenated to the composition GdH{sub 0.15}, which corresponds to a metal–hydrogen solid solution (α phase). The magnetostriction and magnetocaloric effect were measured for both the initial and hydrogenated samples. It is found that the hydrogen atoms in the hexagonal lattice of gadolinium can affect the magnitude and sign of the magnetostriction constants and cause the anisotropy of the magnetocaloric effect. The main mechanisms responsible for the observed effects are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1976

Rolling-contact deformation of MgO single crystals

Magnesium oxide single crystals were used as a model bearing material and deformed by rolling contact with a steel ball 0.64 cm in diameter. A dependence of depth of slip on rolling velocity which persisted with increasing numbers of rolling-contact cycles was discovered. The track width, track hardness and dislocation interactions as observed by transmission electron microscopy all increased in a consistent manner with increasing cycles. The rolling-contact state of stress produces a high density of dislocations in a localized zone. Dislocation interaction in this zone produces cleavage-type cracks after a large number of rolling-contact cycles. The orientation of the crystal influences the character of dislocation accumulation.

Dufrane, K. F.↗
NASA NTRS1981

Electrical switching in cadmium boracite single crystals

Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed.

Takahashi, T.↗
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 OSTI2013

Hydrostatic pressure (8 GPa) dependence of electrical resistivity of BaCo{sub 2}As{sub 2} single crystal

Graphical abstract: - Highlights: • Single crystals of BaCo{sub 2}As{sub 2} were grown by CoAs self-flux method. • We have studied pressure effects (8 GPa) on dc electrical resistivity of BaCo{sub 2}As{sub 2}. • On applied external pressure BaCo{sub 2}As{sub 2} remains a metallic state up to 8 GPa. • Superconductivity is absent in BaCo{sub 2}As{sub 2} because of its proximity to ferromagnetism. - Abstract: The pressure dependence of the electrical resistivity of BaCo{sub 2}As{sub 2} single crystal as a function of temperature was measured at ambient and high pressures up to 8 GPa for the first time using cubic anvil high pressure cell. It is observed that at room temperature the resistivity monotonically decreases with increasing pressure and it remains in the metallic state even at an applied pressure of 8 GPa. From the temperature dependence of the resistivity measurements under pressure, we found that superconductivity is absent up to 8 GPa. The value of the electron's scattering factor (A) is found to be large at ambient pressure and it decreases with the application of pressure, indicating that the substantial electron correlation effect of BaCo{sub 2}As{sub 2} is reduced under pressure, revealing a dramatic change of density of states at the Fermi energy.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Epitaxial TiN(001) wetting layer for growth of thin single-crystal Cu(001)

Single-crystal Cu(001) layers, 4-1400 nm thick, were deposited on MgO(001) with and without a 2.5-nm-thick TiN(001) buffer layer. X-ray diffraction and reflection indicate that the TiN(001) surface suppresses Cu-dewetting, yielding a 4 x lower defect density and a 9 x smaller surface roughness than if grown on MgO(001) at 25 deg. C. In situ and low temperature electron transport measurements indicate that ultra-thin (4 nm) Cu(001) remains continuous and exhibits partial specular scattering at the Cu-vacuum boundary with a Fuchs-Sondheimer specularity parameter p = 0.6 {+-} 0.2, suggesting that the use of epitaxial wetting layers is a promising approach to create low-resistivity single-crystal Cu nanoelectronic interconnects.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Lightweight optical mirrors formed in single crystal substrate

This invention is directed to a process for manufacturing a lightweight mirror from a single crystal material, such as single crystal silicon. As a near perfect single crystal material, single crystal silicon has much lower internal stress than a conventional material. This means much less distortion of the optical surface during the light weighting process. After being ground and polished, a single crystal silicon mirror is light weighted by removing material from the back side using ultrasonic machining. After the light weighting process, the single crystal silicon mirror may be used as-is or further figured by conventional polishing or ion milling, depending on the application and the operating wavelength.

Bly, Vincent T.↗
DOE OSTI2025

Phase-field predictions of the influence of cooling rates during AM on the Evolution of Microstructures in Nickel-Based Single Crystal Superalloys

Additive manufacturing of single crystals made of Ni-based superalloys offers major cost savings for gas turbine engines with the inclusion of internal cooling channels. However, the lack of understanding of the effect of transient thermal conditions on solidification grain structure during additive manufacturing hinders the potential for process control to maintain the single crystal quality. The use of high-fidelity simulations through high performance computing to predict the evolution of the solidification microstructure will enhance the abilities to tailor the microstructures through process optimization. Phase field simulations are used to determine the effect local thermal conditions and defects on the stability of the solidification morphology, specifically with respect to the onset of columnar-to-equiaxed transition that results in the loss of the single crystal. The results are expected to be instrumental for developing future surrogate models to speed up the integration of design and manufacturing of turbine blades under the harsh in-service conditions.

36 MATERIALS SCIENCE↗