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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Improvement of Front-Junction GaInP by Point-Defect Injection and Annealing

Traditional front junction GaInP solar cells are radiation tolerant and can have good diffusion length, but have limited voltage and thus efficiency. Here, we investigate the impact of annealing on GaInP device performance. First, Zn-doped GaInP/AlGaInP double heterojunction structures are studied in order to investigate the impact of annealing in a simple structure. While standard anneals lower diffusion length and lifetime, annealing after injecting point-defects improves material quality, presumably by eliminating sources of non-radiative recombination. Atomic ordering is reduced by the anneal, which raises the device bandgap and requires consideration. These results can be used to improve front junction device performance while controlling the bandgap. Then, GaInP front-junction devices are created using anneals with and without point-defect injection. Voc and EQE trends follow the diffusion length and lifetime trends from the DH structures. Baseline devices have Woc of 0.484 V, raising to 0.504 V after a high temperature anneal. However, injecting point defects prior to the anneal results in a front junction device with Woc of 0.405 V and a diffusion length greater than 8 micrometers. Optimized front-junction GaInP devices with an ARC have ~20% efficiency without a rear reflector.

anneal↗
NASA NTRS2018

Energy Analysis Method for Hidden Damage Detection

A method of detecting internal defects in composites or other multilayer materials includes generating a wavefield on a surface of the material. Wavefield data is collected from the wavefield on the surface, and the measured wavefield data is processed to provide measured energy data. The method may include generating simulated or predicted energy data for the multilayer material that is compared to the simulated energy data to determine if the multilayer material has internal defects or damage below the surface. The method can be utilized to detect and/or quantify damage or other defects that are "hidden" by damage that is closer to the surface of the material.

Campbell Leckey, Cara A.↗
DOE OSTI2021

Improvement of Front-Junction GaInP by Point-Defect Injection and Annealing: Preprint

Traditional front junction GaInP solar cells are radiation tolerant and can have good diffusion length, but have limited voltage and thus efficiency. Here, we investigate the impact of annealing on GaInP device performance. First, Zn-doped GaInP/AlGaInP double heterojunction structures are studied in order to investigate the impact of annealing in a simple structure. While standard anneals lower diffusion length and lifetime, annealing after injecting point-defects improves material quality, presumably by eliminating sources of non-radiative recombination. Atomic ordering is reduced by the anneal, which raises the device bandgap and requires consideration. These results can be used to improve front junction device performance while controlling the bandgap. Then, GaInP front-junction devices are created using anneals with and without point-defect injection. Voc and EQE trends follow the diffusion length and lifetime trends from the DH structures. Baseline devices have Woc of 0.484 V, raising to 0.504 V after a high temperature anneal. However, injecting point defects prior to the anneal results in a front junction device with Woc of 0.405 V and a diffusion length greater than 8 micrometers. Optimized front-junction GaInP devices with an ARC have ~20% efficiency without a rear reflector.

anneal↗
DOE OSTI2024

Diffuse scattering from dynamically compressed single-crystal zirconium following the pressure-induced α → ω phase transition

The prototypical α → ω phase transition in zirconium is an ideal test bed for our understanding of polymorphism under extreme loading conditions. After half a century of study, a consensus had emerged that the transition is realized via one of two distinct displacive mechanisms, depending on the nature of the compression path. However, recent dynamic-compression experiments equipped with diffraction diagnostics performed in the past few years have revealed new transition mechanisms, demonstrating that our understanding of the underlying atomistic dynamics and transition kinetics is in fact far from complete. We present classical molecular dynamics simulations of the α → ω phase transition in single-crystal zirconium shock compressed along the [0001] axis using a machine-learning-class potential. The transition is predicted to proceed primarily via a modified version of the two-stage Usikov-Zilberstein mechanism, whereby the high-pressure ω phase heterogeneously nucleates at boundaries between grains of an intermediate β phase. We further observe the fomentation of atomistic disorder at the junctions between β grains, leading to the formation of highly defective interstitial material between the ω grains. We directly compare synthetic x-ray diffraction patterns generated from our simulations with those obtained using femtosecond diffraction in recent dynamic-compression experiments, and show that the simulations produce the same unique, anisotropic diffuse scattering signal unlike any previously seen from an elemental metal. Our simulations suggest that the diffuse signal arises from a combination of thermal diffuse scattering, nanoparticlelike scattering from residual kinetically stabilized α and β grains, and scattering from interstitial defective structures. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2012

Studies on the Bi 2 Te 3 –Bi 2 Se 3 –Bi 2 S 3 system for mid-temperature thermoelectric energy conversion

Bismuth telluride (Bi 2 Te 3 ) and its alloys have been widely investigated as thermoelectric materials for cooling applications at around room temperature. We report here a systematic study on many compounds in the Bi 2 Te 3 –Bi 2 Se 3 –Bi 2 S 3 system. All the samples were fabricated by high energy ball milling followed by hot pressing. Among the investigated compounds, Bi 2 Te 2 S 1 shows a peak ZT ~0.8 at 300 °C and Bi 2 Se 1 S 2 ~0.8 at 500 °C. The results show that these compounds can be used for mid-temperature power generation applications. The leg efficiency of thermoelectric conversion for segmented elements based on these n-type materials could potentially reach 12.5% with a cold side at 25 °C and a hot side at 500 °C if appropriate p-type legs are paired, which could compete well with the state-of-the-art n-type materials within the same temperature range, including lead tellurides, lead selenides, lead sulfides, filled-skutterudites, and half Heuslers.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2014

Optical Broadband Angular Selectivity

Light selection based purely on the angle of propagation is a long-standing scientific challenge. In angularly selective systems, however, the transmission of light usually also depends on the light frequency. Here we tailored the overlap of the band gaps of multiple one-dimensional photonic crystals, each with a different periodicity, in such a way as to preserve the characteristic Brewster modes across a broadband spectrum. We provide theory as well as an experimental realization with an all–visible spectrum, p-polarized angularly selective material system. Our method enables transparency throughout the visible spectrum at one angle—the generalized Brewster angle—and reflection at every other viewing angle.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Influence of point defect accumulation on in-pile thermal conductivity degradation: Fuel rod defect distribution and deviation between in-pile and post irradiation thermal conductivity

As nuclear fuel burn-up increases, its thermal conductivity degrades due to the accumulation of defects that lead to increased phonon scattering rates. This results in a rise in the centerline temperature of the fuel rod, whereby heat generation must be decreased to avoid undesired behavior such as fuel melting and extensive fission gas release. Fuel performance codes are utilized to optimize the fuel's operational conditions; while they are based on established physical principles, their empirical nature limits their predictive capabilities. Recently, an effort has been made to develop predictive fuel performance codes for commonly used nuclear fuels, as well as accelerated qualification of advanced nuclear fuels. In this report, we elaborate on the importance of careful analysis of point defects’ impact on thermal conductivity in fuel performance analysis. Further, a model is presented where point defect concentration is estimated based on Rate Theory modeling and used as input to the Klemens-Callaway model to calculate their contribution to the degradation of thermal conductivity in UO 2 under prototypical irradiation conditions. This analysis suggests that point defect concentration is significant at the rim of the fuel pellet and neglecting this leads to underestimation of the centerline temperature, which may have consequences on fission gas behavior.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

DMOF-1 as a Representative MOF for SO 2 Adsorption in Both Humid and Dry Conditions

The mixed-ligand metal–organic framework (MOF) DMOF-1 has been successfully synthesized via ligand: 2,3,5,6-tetramethylterephthalic acid (TM), 9,10-anthracenedicarboxylic acid (ADC), 1,4-naphthalenedicarboxylic acid (NDC), 2,5-dimethyl terephthalic acid (DM), and metal (Zn, Cu, Ni, Co) substitutions to develop structure–property relationships for adsorption of water and SO 2 , an acid gas commonly found in flue gas streams at ppm-level concentrations. The substitution of bulky ligands, TM and ADC, resulted in not only improved water stability but also stability toward dry SO 2 , whereas substitution with NDC and DM did not provide water or SO 2 stability. ADC-functionalized Zn–DMOF exhibited the greatest stability under humid SO 2 exposure of the ligand-functionalized materials that were tested. Metal substitution of Cu into the DMOF–TM structure resulted in the greatest stability of the M–DMOF–TM samples upon exposure to humid SO 2 , and Ni–DMOF–TM provided the second most stable material. Finally, these results follow the prediction of the Irving–Williams series of metal node/ligand bond strengths.

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

Increased p-type conductivity in GaN{sub x}Sb{sub 1−x}, experimental and theoretical aspects

The large increase in the p-type conductivity observed when nitrogen is added to GaSb has been studied using positron annihilation spectroscopy and ab initio calculations. Doppler broadening measurements have been conducted on samples of GaN{sub x}Sb{sub 1−x} layers grown by molecular beam epitaxy, and the results have been compared with calculated first-principle results corresponding to different defect structures. From the calculated data, binding energies for nitrogen-related defects have also been estimated. Based on the results, the increase in residual hole concentration is explained by an increase in the fraction of negative acceptor-type defects in the material. As the band gap decreases with increasing N concentration, the ionization levels of the defects move closer to the valence band. Ga vacancy-type defects are found to act as positron trapping defects in the material, and the ratio of Ga vacancy-type defects to Ga antisites is found to be higher than that of the p-type bulk GaSb substrate. Beside Ga vacancies, the calculated results imply that complexes of a Ga vacancy and nitrogen could be present in the material.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Phonon anharmonicity and negative thermal expansion in SnSe

In this paper, the anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy, in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. Finally, the origin of the anharmonic phonon thermodynamics is linked to the electronic structure.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Characterization of high-quality kerfless epitaxial silicon for solar cells: Defect sources and impact on minority-carrier lifetime

We investigate the types and origins of structural defects in thin (<100 μm) kerfless epitaxial single crystal silicon grown on top of reorganized porous silicon layers. Although the structural defect density is low (has average defect density < 10 4 cm -2 ), localized areas with a defect density > 10 5 cm -2 are observed. Cross-sectional and systematic plan-view defect etching and microscopy reveals that the majority of stacking faults and dislocations originate at the interface between the porous silicon layer and the epitaxial wafer. Localised dislocation clusters are observed in regions of collapsed/deformed porous silicon and at decorated stacking faults. In localized regions of high extended defect density, increased minority-carrier recombination activity is observed. Evidence for impurity segregation to the extended defects (internal gettering), which is known to exacerbate carrier recombination is demonstrated. In conclusion, the impact of the defects on material performance and substrate re-use is also discussed.

14 SOLAR ENERGY↗
DOE OSTI2017

Butanol Separation from Humid CO 2 -Containing Multicomponent Vapor Mixtures by Zeolitic Imidazolate Frameworks

Butanol is a promising renewable fuel and feedstock. A major challenge in fermentative butanol production is to find a cost-effective butanol separation process from dilute aqueous solutions, usually an acetone-butanol-ethanol (ABE) mixture. Nanoporous zeolitic imidazolate frameworks (ZIFs) have shown potential for alcohol separation from dilute solutions. However, little is known about butanol separation from multicomponent mixtures using ZIFs, including the effects of the humid acid gas (CO 2 ) used to sparge the fermenter and generate the vapor product stream. We present a study of butanol separation by ZIF-8, ZIF-90, ZIF-71 and hybrid ZIF-8–90 and ZIF-8–71 adsorbents with binary butanol/water and multicomponent ABE feeds. To obtain reliable structure–property relations for ZIF adsorbents in realistic conditions, we combine multicomponent vapor breakthrough with structural, textural, and stability characterization techniques in humid CO 2 environments. In the absence of CO 2 , more hydrophobic materials such as ZIF-8, ZIF-8 55 -71 45 , ZIF-8 70 -90 30 , and ZIF-71 are found to be excellent candidates with butanol/water selectivities >10 and butanol capacities >3.5 mmol/g. However, in the presence of humid CO 2 , all the materials except ZIF-71 are found to degrade. The mechanistic aspects of this degradation are studied by FTIR spectroscopy and explained based upon acid gas attack of Zn–N coordinate bonds. ZIF-71 emerges as an excellent candidate owing to its acid gas stability, good butanol adsorption capacity, and selectivity. Vapor breakthrough with a model ABE solution demonstrates the high butanol selectivity of ZIF-71 relative to acetone, ethanol, and water and the recovery of a 65 mol % butanol product by desorption at 453 K. Finally, this study highlights the importance of determining structure–property relationships of MOF/ZIF materials in realistic multicomponent conditions, and the importance of acid gas stability in their applications.

09 BIOMASS FUELS↗
DOE OSTI2014

Multilevel probabilistic approach to evaluate manufacturing defect in composite aircraft structures

In this work it is developed a reliable approach and its feasibility to the design and analysis of a composite structures. The metric is compared the robustness and reliability designs versus the traditional design, to demonstrate the gain that can be achieved with a probabilistic approach. The use of the stochastic approach of the uncertain parameteters in combination with the multi-scale levels analysis is the main objective of this paper. The work is dedicated to analyze the uncertainties in the design, tests, manufacturing process, and key gates such as materials characteristic.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Passive directional sub-ambient daytime radiative cooling

Demonstrations of passive daytime radiative cooling have primarily relied on complex and costly spectrally selective nanophotonic structures with high emissivity in the transparent atmospheric spectral window and high reflectivity in the solar spectrum. Here, we show a directional approach to passive radiative cooling that exploits the angular confinement of solar irradiation in the sky to achieve sub-ambient cooling during the day regardless of the emitter properties in the solar spectrum. We experimentally demonstrate this approach using a setup comprising a polished aluminum disk that reflects direct solar irradiation and a white infrared-transparent polyethylene convection cover that minimizes diffuse solar irradiation. Measurements performed around solar noon show a minimum temperature of 6 °C below ambient temperature and maximum cooling power of 45 W m –2 . Our passive cooling approach, realized using commonly available low-cost materials, could improve the performance of existing cooling systems and enable next-generation thermal management and refrigeration solutions.

14 SOLAR ENERGY↗
DOE OSTI2016

Variational approach to extracting the phonon mean free path distribution from the spectral Boltzmann transport equation

The phonon Boltzmann transport equation (BTE) is a powerful tool for studying nondiffusive thermal transport. Here, we develop a new universal variational approach to solving the BTE that enables extraction of phonon mean free path (MFP) distributions from experiments exploring nondiffusive transport. By utilizing the known Fourier heat conduction solution as a trial function, we propose a direct approach to calculating the effective thermal conductivity from the BTE. We reveal this technique on the transient thermal grating experiment, which is a useful tool for studying nondiffusive thermal transport and probing the MFP distribution of materials. We obtain a closed form expression for a suppression function that is materials dependent, successfully addressing the nonuniversality of the suppression function used in the past, while providing a general approach to studying thermal properties in the nondiffusive regime.

42 ENGINEERING↗
DOE OSTI2017

High Thermoelectric Performance of New Rhombohedral Phase of GeSe stabilized through Alloying with AgSbSe 2

GeSe is a IV–VI semiconductor, like the excellent thermoelectric materials PbTe and SnSe. Orthorhombic GeSe has been predicted theoretically to have good thermoelectric performance but is difficult to dope experimentally. Like PbTe, rhombohedral GeTe has a multivalley band structure, which is ideal for thermoelectrics and also promotes the formation of Ge vacancies to provide enough carriers for electrical transport. Herein, we investigate the thermoelectric properties of GeSe alloyed with AgSbSe 2 , which stabilizes a new rhombohedral structure with higher symmetry that leads to a multivalley Fermi surface and a dramatic increase in carrier concentration. The z T of GeAg 0.2 Sb 0.2 Se 1.4 reaches 0.86 at 710 K, which is 18 times higher than that of pristine GeSe and over four times higher than doped orthorhombic GeSe. Our results open a new avenue towards developing novel thermoelectric materials through crystal phase engineering using a strategy of entropy stabilization of high-symmetry alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Facile synthesis of α-MoO{sub 3} nanorods with high sensitivity to CO and intrinsic sensing performance

Highlights: • α-MoO{sub 3} nanorods were synthesized by facile hydrothermal method at 85 °C for 1.5 h. • α-MoO{sub 3} nanorods exhibit the highest sensitivity of 239.6–40 ppm CO at 292 °C. • XPS and PL confirmed that the gas sensing arises from stoichiometric defect of α-MoO{sub 3}. • The sensing mechanism of α-MoO{sub 3} to CO was postulated from bulk defect of material. - Abstract: Orthorhombic molybdenum trioxide (α-MoO{sub 3}) nanorods with well-defined morphology and high crystalline have been synthesized by a facile and fast hydrothermal method under 85 °C for 1.5 h without employing surfactants or templates. The controlling of stirring time, thermostatic time and HNO{sub 3} amount is crucial for the growth of α-MoO{sub 3} nanorods. The morphology and structure of α-MoO{sub 3} were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The obtained α-MoO{sub 3} nanorods as a novel sensing material exhibit high sensitivity, the highest response to 40 ppm CO is 239.6 at operating temperature of 292 °C. The intrinsic sensing performance arises from the non-stoichiometry of the α-MoO{sub 3} due to the presence of Mo{sup 5+} in MoO{sub 3} lattice, that is, the molecular formula of MoO{sub 3} should be expressed as MoO{sub 3−x} (x = 0.08), which has been confirmed by X-ray photoelectron spectroscopic (XPS) analysis and room temperature photoluminescence (PL). The sensing mechanism of α-MoO{sub 3} to CO was also discussed in terms of lattice oxygen in MoO{sub 3}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗