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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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The performance of Cu x In 2−x S y quantum dots in energy harvesting devices is controllable by stoichiometry and the formation of distinct defects.
A series of achiral tricatenar rod-like molecules with a 3,5-disubstitution pattern at one end and a single alkyl chain at the other end of a rod-like azobenzene derived core is reported. Depending on temperature and alkyl chain length, these Y-shaped compounds self-assemble into different types of liquid crystalline (LC) phases, ranging from non-tilted and synclinic tilted hexatic, via non-tilted and anticlinic tilted smectic and bicontinuous cubic LC phases, to a spontaneous mirror symmetry broken isotropic liquid (Iso 1 [*]) or a related achiral liquid network phase (Iso 1 ). An additional tilted, but uniaxial smectic phase was observed at the transition between anticlinic and synclinic tilt correlation and was investigated by soft resonant X-ray scattering with respect to possible helix formation. This work provides a new concept for the design of technological interesting azobenzene based LC materials with anticlinic tilted smectic C phases (SmC a ) and with azobenzene units organized in the long range or short range helical network structures of bicontinuous cubic and chiral isotropic liquid phases, respectively. Core fluorination removes all lamellar phases, leaving only the cubic phase over wide temperature ranges, even at ambient temperature.
Proton-conducting oxides, such as BaZr 0.9 Y 0.1 O 3–δ (BZY10), are receiving significant scientific attention for application in a variety of electrochemical applications. It has been shown that the synthesis route has a significant effect on the ionic behavior of these materials, especially the grain boundaries (GB). In this study, laser-pulsed atom probe tomography (APT) is used to characterize the GB chemistry of BZY10 samples prepared by four different methods: (1) spark plasma sintering (SPS), (2) conventional sintering followed by high-temperature annealing (HT), (3) conventional sintering with NiO used as a sintering aid (SSR-Ni), and (4) solid-state reactive sintering of oxide precursor powders with NiO as a reactive sintering aid (SSRS-Ni). Oxygen depletion (corresponding to oxygen vacancy accumulation) was observed at every GB in this study, consistent with the positive space-charge GB region commonly assigned to these materials. In contrast to the consistent trends associated with oxygen depletion, cation constituents showed varying segregation/depletion behaviors. The samples that used NiO revealed Ni preferentially segregating to the GB. The most common impurities in BZY10 are Al, Fe, Mg, Si, and Sr, all of which generally accumulate at GBs. In order to quantify these chemical trends, the APT method was optimized for this material supplemented with understanding from density functional theory (DFT). Finally, this APT study reveals the complexity of BZY10 GB chemistry and shows that even adjacent GBs in the same material can sometimes show surprisingly different GB chemistry.
Complementary permeation and conductivity relaxation studies reveal the optimal 10% yttrium B-site doping in BaCo 0.4 Fe 0.4 Zr 0.2− X Y X O 3− δ (BCFZY X ) triple ionic-electronic conductors for improved proton conductivity and surface exchange.
A new dianionic bis(amino)phosphine ligand was synthesized and the corresponding metallacyclohexane complexes of Y, La, and Lu were studied using NMR experiments.
Neutron diffraction, thermogravimetry, and high temperature solution calorimetry measurements reveal insights into proton and oxygen-ion kinetics in BaCo 0.4 Fe 0.4 Zr 0.2− X Y X O 3− δ triple ionic–electronic conducting ceramics.
Large configurational disorder in compositionally complex ceramics can lead to unique functional properties that deviate from traditional rules of alloy mixing. In recent years, compositionally complex oxides (CCOs) have shown intriguing magnetic behavior including long-range order, enhanced magnetic exchange couplings, and mixed phase magnetic structures. This work focuses on how large local spin disorder affects magnetic ordering in a CCO. Specifically, we investigated the A-site alloyed perovskite, (Y 0.2 La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 )MnO 3 , or (5A)MnO 3 , using a combination of bulk magnetometry, synchrotron X-ray diffraction, and temperature-dependent neutron diffraction. The five A-site ions have an average spin and ionic radius nearly equal to that of Nd 3+ ions, which minimizes structural distortions and allows for an understanding of the local spin disorder effects through a direct comparison with NdMnO 3 . Our magnetometry data show that (5A)MnO 3 exhibits two distinct phase transitions associated with the A-site and B-site sublattices, as seen in NdMnO 3 , as well as the presence of domain pinning and exchange bias at low temperature, suggesting a mixed phase magnetic ground state, as seen in other magnetic CCOs. Neutron powder diffraction shows clear long-range antiferromagnetic ordering below 67 K and refines to a Pn'ma' magnetic structure at low temperature, in excellent agreement with the well-studied behavior of NdMnO 3 . The two most notable differences in (5A)MnO 3 magnetism apparent from our data are a slight suppression of the B-site ordering temperature, which is explained by a smaller Mn–O–Mn bond angle in (5A)MnO 3 than NdMnO 3 , and the presence of a magnetic susceptibility transition above the B-site ordering, which could indicate the formation of a cluster glass but requires further study. Finally, this work demonstrates a general method of isolated investigation of size and spin disorder in CCOs and motivates future work using local structure probes to better understand the effects of nanoscale clustering and local spin disorder in magnetic CCOs.
Proton exchange kinetics plays an important role in governing the performance of intermediate-temperature protonic ceramic electrolysis cells (PCECs) for hydrogen production. Our understanding of the nature of the surface hydration reaction at the single-cell level, however, remains very limited, hampering further efficiency improvements. Here, in this study, we developed a custom operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) platform that operates under high temperature and steam conditions with applied bias. Quantitative investigations of surface H 2 O/D 2 O isotope exchange in a BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ (BZCYYb1711) protonic electrolyte-based single cell were conducted under different applied voltages using this DRIFTS platform, to gain molecular-level insight into hydration kinetics. The findings show that the application of an external voltage significantly enhances the surface proton exchange rate, decreasing the apparent activation energy from 29.1 kJ mol −1 at open-circuit voltage (OCV) to 6.8 kJ mol −1 at 1.3 V. In addition, distinct voltage-induced spectral shifts in O–D vibrations point to dynamic changes in surface hydration. These findings demonstrate a sensitive spectroscopic platform for probing interfacial proton processes and reveal strong electrochemical control over surface proton kinetics, offering new opportunities for probing electrolyte hydration behavior in PCECs.
Y 3 Fe 5 O 12 (YIG) thin films are well known for their ferrimagnetic insulating property and low Gilbert damping coefficient (α), allowing them to be used for various spintronic applications and as magneto-optical isolators for photonic devices. Instead of doping, incorporation of plasmonic metals as nanoinclusions could be a promising route for improved magneto-optical coupling properties. In this work, YIG–Au nanocomposites have been deposited with ferrimagnetic insulating YIG as the matrix and Au nanoinclusions which introduce plasmonic absorption, optical anisotropy, and hyperbolic properties. Films with varying Au nanoinclusion densities have been processed and annealed to compare with the as-deposited ones. The films that had low Au nanoinclusion density and were annealed presented a lower magnetic damping coefficient of 2.84 × 10 −4 than the pure YIG film (9.66 × 10 −4 ). The as-deposited film with the highest Au density shows the strongest hyperbolic properties among all samples. These results demonstrate that both magnetic damping and optical properties can be tuned through deposition conditions in YIG–Au nanocomposite thin films, allowing for a balance of both properties. This YIG–Au nanocomposite system presents promising potential in next-generation opto-spintronic devices.
Recent reports of the superconductivity in hydrides of two different families (covalent lattice, as in SH3 and clathrate-type H-cages containing La and Y atoms, as in LaH10 and YH6) have revealed new families of high-Tc materials with Tc’s near room temperature values. These findings confirm earlier expectations that hydrides may have very high Tc’s due to the fact that light H atoms have very high vibrational frequencies, leading to high Tc values within the conventional Bardeen–Cooper–Schrieffer phonon mechanism of superconductivity. However, as is pointed out by Ashcroft, it is important to have the metallic hydrogen “alloyed” with the elements added to it. This concept of a metallic alloy containing a high concentration of metal-like hydrogen atoms has been instrumental in finding new high-Tc superhydrides. These new superhydride “room-temperature” superconductors are stabilized only at very high pressures above 100 GPa, making the experimental search for their superconducting properties very difficult. We will review the current experimental and theoretical results for LaH10−x and YH6−x superhydrides.
We report on the successful fabrication of (111) oriented thin films of pyrochlore iridate Y 2 Ir 2 O 7 by means of solid phase epitaxy. Essentially, we developed an entirely in situ annealing protocol, which is superior to the conventional ex-situ routine that requires multi-hour annealing to stabilize the proper pyrochlore structure. The morphological quality of the films has been confirmed by x-ray diffraction, reflectivity, and reciprocal space mapping, demonstrating their high crystallinity with a pure pyrochlore phase and an expected epitaxial relation to the substrate. Strikingly, below the magnetic phase transition, the temperature dependence of resistivity shows a power-law behavior with the power exponent of similar to 3/2, characteristic of a Weyl semimetal in the presence of impurities and electron-electron correlations. Finally, below 10K, the magneto-transport measurements reveal the emergence of a non-saturated negative magnetoresistance up to 9T with a small "valley" around zero field. These findings are further interpreted in relation to the weak anti-localization effect and the non-collinear antiferromagnetic ordering on the Ir sublattice.
Development of a robust, thin, hole-blocking (n+) contact on high purity germanium (HPGe) has been the main challenge in the development of Ge-based radiation sensors. Yttrium has been reported to be a viable hole-blocking contact on HPGe, and detectors with low leakage have been fabricated. Niobium has also been considered as a potential hole-blocking contact due to its low work function. Here, we investigate interface chemistry and the Schottky barrier height of Y and Nb, as well as electron-blocking contacts Au and Pt, on Ge(100) surfaces using hard x-ray photoelectron spectroscopy. We find a barrier height of 1.05 ± 0.10 eV for Y/HPGe, confirming the formation of a hole-blocking barrier. For Nb/HPGe, the barrier height of 0.13 ± 0.10 eV demonstrates that the interface is not hole-blocking. The Schottky barrier of Au and Pt was found to be 0.45 ± 0.10 and 0.51 ± 0.10 eV, respectively.
The high density of aluminum nanocrystals (>10 21 m -3 ) that develop during the primary crystallization in Al-based metallic glasses indicates a high nucleation rate (~10 18 m -3 s -1 ). Several studies have been advanced to account for the primary crystallization behavior, but none have been developed to completely describe the reaction kinetics. Recently, structural analysis by fluctuation electron microscopy has demonstrated the presence of the Al-like medium range order (MRO) regions as a spatial heterogeneity in as-spun Al 88 Y 7 Fe 5 metallic glass that is representative for the class of Al-based amorphous alloys that develop Al nanocrystals during primary crystallization. From the structural characterization, an MRO seeded nucleation configuration is established, whereby the Al nanocrystals are catalyzed by the MRO core to decrease the nucleation barrier. The MRO seeded nucleation model and the kinetic data from the delay time (τ) measurement provide a full accounting of the evolution of the Al nanocrystal density (N v ) during the primary crystallization under isothermal annealing treatments. Moreover, the calculated values of the steady state nucleation rates (J ss ) predicted by the nucleation model agree with the experimental results. Moreover, the model satisfies constraints on the structural, thermodynamic, and kinetic parameters, such as the critical nucleus size, the interface energy, and the volume-free energy driving force that are essential for a fully self-consistent nucleation kinetics analysis. In conclusion, the nucleation kinetics model can be applied more broadly to materials that are characterized by the presence of spatial heterogeneities.
Two-micron lasing is obtained on the {sup 5}I{sub 7} → {sup 5}I{sub 8} transition of Ho{sup 3+} ions in ZrO{sub 2} − Y{sub 2}O{sub 3} −Ho{sub 2}O{sub 3} crystals upon resonance pumping into the {sup 5}I{sub 7} level of these ions by a pulsed laser based on a Tm : LiYF{sub 4} crystal. The efficiency of conversion of pump radiation incident on the crystal to laser radiation and the slope lasing efficiency at a pulse duration of 8 ms and a pulse repetition rate of 10 Hz were 25% and 28%, respectively. (paper)
The GaSb-based diode lasers operating simultaneously at two wavelengths near 2.1 μm have been designed and fabricated. The Y-branch devices used the 6th order distributed Bragg reflectors (DBR) to provide spectrally selective feedback. The laser active region contained two asymmetric quantum wells with allowed optical transitions between two lowest electron (e1 and e2) and top hole (hh1) subbands. The laser emission lines loosely matched the e1-hh1 and e2-hh1 optical transitions with separation corresponding to ~3.1 THz. Finally, the 10 μm wide deeply etched straight ridge DBR lasers demonstrated stable single mode operation with more than 50 mW of output power.
In this work, we report on the evolution of the electronic correlation strength across the nematic critical point in FeySe$_{1-x}$Sx ($0.10\leqslant x \leqslant0.24; y \geqslant0.9$), inferred from the measurements of the slope of the upper critical field $H_{c2}$. Superconducting transition T c and quasiparticle mass $m^*$ exhibit similar reduction with sulfur content x. Our results indicate that electronic correlations from all Fermi surface pockets show strong interconnection with pairing strength and are not governed by the change of nematic fluctuations. The upper critical field anisotropy γH = $H_{c2}^{ab}$/$H_{c2}^c$ exhibits a minimum in the critical region and stronger temperature dependence away from it.
Hydrogen economy is of paramount importance in the global transition to a sustainable, clean energy source that contributes to decarbonization efforts. In particular, the proton conducting proton ceramic fuel cells (PCFCs) play a crucial role in promoting hydrogen energy technology [1-5]. In a PCFC, the electrolyte is typically a solid oxide material that enables proton transport and can operate at temperatures lower than those of traditional oxygen ion conducting fuel cells [6]. The reduced operating temperature of PCFCs contributes to their durability, scalability, and efficiency [7,8]. BaZr 0.8 Y 0.2 O 3-x (BZY) is a promising proton conducting solid oxide electrolyte [9,10]. The emphasis on proton conductivity entails the importance of understanding proton content in the system. However, previous studies have largely relied on bulk techniques such as electrochemical impedance spectroscopy [7,11], Karl-Fischer titration [12,13], and thermogravimetric analysis [14] to obtain proton concentration. This is due to the small atomic size and light mass of hydrogen species making direct detection challenging. Bulk methods may be useful in estimating the proton content; however, it overlooks possible proton concentration gradient or segregation that may occur across or within a nanoparticle, especially when proton incorporation occurs nonuniformly through steam exposure on powder samples. In this paper, BZY is protonated at an estimated 0.15 mol of protons via steam exposure. Electron energy loss spectroscopy (EELS) with nanoscale spatial resolution is explored to identify proxy signals for proton detection using a JEOL ARM300 microscope operated at 300 kV with a Gatan GIF Continuum detector.
Wind energy’s rapid expansion has led to unintended consequences for wildlife, with migratory bats among the species most at risk. The behavioural mechanisms underlying collisions remain poorly understood, but one hypothesis is that bats are attracted to wind turbine structures. Vision is important to bat orientation and obstacle avoidance, yet it has been relatively understudied in the context of bat–turbine interactions. We hypothesize that light reflected off turbine surfaces could attract bats, acting as a sensory pollutant that may increase collision risk. To test whether reflective turbine surfaces elicit attraction, we flew 242 Lasiurus cinereus and 154 Lasionycteris noctivagans through Y-maze assays. Bats were at least twice as likely to fly towards white turbine blade sections compared to less reflective black ones. This attraction intensified when the alternative exit was a dark, empty flyway, with 74% of L. cinereus and 97% of L. noctivagans flying towards the white turbine blade. These findings provide evidence that visual sensory pollutants could underlie bat–turbine interactions, and if so, wind turbines could be ecological traps.