Search NASA⌕ Search

SEARCH · Search NASA

Results for “Layered Structures”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Synthesis and electrochemical properties of nanosized LiFeO{sub 2} particles with a layered rocksalt structure for lithium batteries

Highlights: Black-Right-Pointing-Pointer 40-nm-sized O3-LiFeO{sub 2} exhibits higher discharge capacities and rate characteristics than 400-nm-sized O3-LiFeO{sub 2}. Black-Right-Pointing-Pointer The cation disorder of Li and Fe ions might have affected the electrochemical activity of the O3-LiFeO{sub 2} nanoparticles. Black-Right-Pointing-Pointer A phase change from a layered structure to a cubic structure during electrochemical cycling. Black-Right-Pointing-Pointer The new cubic phase allowed a stable electrochemical reaction between 4.5 and 1.0 V. -- Abstract: Layered rocksalt-type LiFeO{sub 2} particles (O3-LiFeO{sub 2}) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from {alpha}-NaFeO{sub 2} precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO{sub 2}. 40-nm LiFeO{sub 2} exhibited a higher discharge capacity (115 mAh g{sup -1}) than 400-nm LiFeO{sub 2} (80 mAh g{sup -1}), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO{sub 2} particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO{sub 2} to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe{sup 2+}/Fe{sup 3+} and Fe{sup 2+}/Fe{sup 0} redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO{sub 2} were ca. 115, 210, and 390 mAh g{sup -1} under cutoff voltages of 4.5-2.0 V, 4.5-1.5 V, and 4.5-1.0 V, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effect of Zn coprecipitation on the structure of layered Mn oxides

Mn oxides (MnOx) are a group of ubiquitous metal oxides in the environment and can significantly affect the biogeochemical cycles of metals, nutrients, and contaminants. Due to their negative surface charge across a wide range of environmental conditions, metal cations have strong affinities for MnOx, and the presence of metal cations during or after the formation of MnO x might significantly affect their structure and reactivity. This study systematically investigates the effects of Zn 2+ presence during mineral formation (i.e. coprecipitation) on the structure of acid birnessite and delta-MnO 2 , two synthetic analogs that are structurally similar to fresh biogenic MnO x but with different crystallinity. For both acid birnessite and delta-MnO 2 , Zn 2+ existed as surface adsorbed species at vacancy sites, interrupted layer stacking along c axis, and caused reductions of the lateral particle size. Zn 2+ also reduced Mn(III) contents in delta-MnO 2 layers, leaving more vacancy sites (capped by adsorbed Zn 2+ ). The reduction of layer stacking was more obvious for acid birnessite, while the modification of layer structure was more significant for delta-MnO 2 . These structural changes will likely lead to modified reactivity of MnO x in natural systems.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Atomic Resolution Structural and Chemical Imaging Revealing the Sequential Migration of Ni, Co, and Mn upon the Battery Cycling of Layered Cathode

Layered lithium transition metal oxides (LTMO) are promising candidate cathode materials for next generation high energy density lithium ion battery. The challenge for using this category of cathode is the capacity and voltage fading, which is believed to be associated with the layered structure disordering, a process that is initiated from the surface or solid-electrolyte interface and facilitated by transition metal (TM) reduction and oxygen vacancy formation. However, the atomic level dynamic mechanism of such a layered structure disordering is still not fully clear. In this work, utilizing atomic resolution electron energy loss spectroscopy (EELS), we map, for the first time at atomic scale, the spatial evolution of Ni, Co and Mn in a cycled LiNi1/3M1/3Co1/3O2 layered cathode. In combination with atomic level structural imaging, we discovered the direct correlation of TM ions migration behavior with lattice disordering, featuring the residing of TM ions in the tetrahedral site and a sequential migration of Ni, Co, and Mn upon the increased lattice disordering of the layered structure. This work highlights that Ni ions, though acting as the dominant redox species in many LTMO, are labile to migrate to cause lattice disordering upon battery cycling; while the Mn ions are more stable as compared with Ni and Co and can act as pillar to stabilize layered structure. Direct visualization of the behavior of TM ions during the battery cycling provides insight for designing of cathode with structural stability and correspondingly a superior performance.

annular bright field image↗
DOE OSTI2022

Novel self-assembled two-dimensional layered oxide structure incorporated with Au nanoinclusions towards multifunctionalities

Two-dimensional (2D) layered oxides have recently attracted wide attention owing to the strong coupling among charges, spins, lattice, and strain, which allows great flexibility and opportunities in structure designs as well as multifunctionality exploration. In parallel, plasmonic hybrid nanostructures exhibit exotic localized surface plasmon resonance (LSPR) providing a broad range of applications in nanophotonic devices and sensors. A hybrid material platform combining the unique multifunctional 2D layered oxides and plasmonic nanostructures brings optical tuning into the new level. Here, a novel self-assembled Bi 2 MoO 6 (BMO) 2D layered oxide incorporated with plasmonic Au nanoinclusions has been demonstrated via one-step pulsed laser deposition (PLD) technique. Comprehensive microstructural characterizations, including scanning transmission electron microscopy (STEM), differential phase contrast imaging (DPC), and STEM tomography, have demonstrated the high epitaxial quality and particle-in-matrix morphology of the BMO-Au nanocomposite film. DPC-STEM imaging clarifies the magnetic domain structures of BMO matrix. Three different BMO structures including layered supercell (LSC) and superlattices have been revealed which is attributed to the variable strain states throughout the BMO-Au film. Owing to the combination of plasmonic Au and layered structure of BMO, the nanocomposite film exhibits a typical LSPR in visible wavelength region and strong anisotropy in terms of its optical and ferromagnetic properties. This study opens a new avenue for developing novel 2D layered complex oxides incorporated with plasmonic metal or semiconductor phases showing great potential for applications in multifunctional nanoelectronics devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Metal chalcogenides for pseudocapacitive applications

A synthetic metal dichalcogenide having a highly defected nanocrystalline layered structure, wherein layer spacing is larger than in perfect crystals of the same material, wherein the defected structure provides access to interlayer crystals of the same material, and wherein the defected structure facilitates a pseudocapacitive charge storage mechanism. The metal dichalcogenide is receptive to intercalation of ions such as Li ions, Na ions, Mg ions, and Ca ions, and does not undergo a phase transition upon intercalation of Li ions, Na ions, Mg ions, or Ca ions. The metal dichalcogenide can be used, for example, as a component of an electrode that also includes a carbon derivative, and a binder, which are intermixed to form the electrode. The resultant composite electrode is highly porous and highly electronically conductive, and is suitable for use in devices such as symmetric capacitors, asymmetric capacitors, rocking chair batteries, and other devices.

25 ENERGY STORAGE↗
DOE OSTI2022

Extreme Fast Charging: Effect of Positive Electrode Material on Crosstalk

Extreme fast charging (XFC) is a key requirement for the adoption of battery-based electric vehicles by the transportation sector. However, XFC has been shown to accelerate degradation, causing the capacity, life, and safety of batteries to deteriorate. We tested cells containing five positive electrode chemistries, LFP (olivine structure), LMO (spinel), LCO (layered), NMC811 (layered) and NCA (layered), using fast-charging protocols. After testing, the negative electrodes from cells containing positive electrodes crystallizing with a layered structure were found to have more lithium deposited on their surfaces. Further, those crystallizing with a layered structure also tended to have a larger increase in impedance than those crystallizing with a spinel or olivine structure. Characterization of the negative electrodes by X-ray photoelectron spectroscopy showed that using the concentrations of LiF and Li x PO y F z as metrics, the concentration of LiF in the SEI from the cell with different positive electrodes is LFP > LMO > LCO ~ NMC811 > NCA; and for Li x PO y F z , the order is LMO > LFP > NCA > NMC811 > LCO. Clearly, the positive-electrode material was influencing the amounts of these materials formed.

25 ENERGY STORAGE↗
DOE OSTI2019

Ti‐Gradient Doping to Stabilize Layered Surface Structure for High Performance High‐Ni Oxide Cathode of Li‐Ion Battery

Abstract High‐Ni layered oxide cathodes are considered to be one of the most promising cathodes for high‐energy‐density lithium‐ion batteries due to their high capacity and low cost. However, surfice residues, such as NiO‐type rock‐salt phase and Li 2 CO 3 , are often formed at the particle surface due to the high reactivity of Ni 3+ , and inevitably result in an inferior electrochemical performance, hindering the practical application. Herein, unprecedentedly clean surfaces without any surfice residues are obtained in a representative LiNi 0.8 Co 0.2 O 2 cathode by Ti‐gradient doping. High‐resolution transmission electron microscopy (TEM) reveals that the particle surface is composed of a disordered layered phase (≈6 nm in thickness) with the same rhombohedra structure as its interior. The formation of this disordered layered phase at the particle surface is electrochemically favored. It leads to the highest rate capacity ever reported and a superior cycling stability. First‐principles calculations further confirm that the excellent electrochemical performance has roots in the excellent chemical/structural stability of such a disordered layered structure, mainly arising from the improved robustness of the oxygen framework by Ti doping. This strategy of constructing the disordered layered phase at the particle surface could be extended to other high‐Ni layered transition metal oxides, which will contribute to the enhancement of their electrochemical performance.

Kong, Defei↗
DOE OSTI2014

Elastodynamic behavior of the three dimensional layer-by-layer metamaterial structure

In this work, we numerically investigate for the first time the elastodynamic behavior of a three dimensional layer-by-layer rod structure, which is easy to fabricate and has already proved to be very efficient as a photonic crystal. The Finite Difference Time Domain method was used for the numerical calculations. For the rods, several materials were examined and the effects of all the geometric parameters of the structure were also numerically investigated. Additionally, two modifications of the structure were included in our calculations. The results obtained here (for certain geometric parameters), exhibiting a high ratio of longitudinal over transverse sound velocity and therefore a close approach to ideal pentamode behavior over a frequency range, clearly show that the layer-by-layer rod structure, besides being an efficient photonic crystal, is a very serious contender as an elastodynamic metamaterial.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Large-area, laterally-grown epitaxial semiconductor layers

Structures and methods for confined lateral-guided growth of a large-area semiconductor layer on an insulating layer are described. The semiconductor layer may be formed by heteroepitaxial growth from a selective growth area in a vertically-confined, lateral-growth guiding structure. Lateral-growth guiding structures may be formed in arrays over a region of a substrate, so as to cover a majority of the substrate region with laterally-grown epitaxial semiconductor tiles. Quality regions of low-defect, stress-free GaN may be grown on silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Interconnected Vertically Stacked 2D-MoS2 for Ultrastable Cycling of Rechargeable Li-Ion Battery

2D layer structured material is often high-capacity ionic storage material with fast ionic transport within the layers. This appears to be the case for non-conversion layer structure, such as graphite. However, this is not the case for conversion-type layered structure such as transition metal sulfide, in which localized congestion of ionic species adjacent to the surface will induce localized conversion, leading to the blocking of the fast diffusion channels and fast capacity fading, which therefore constitutes one of the critical barriers for the application of transition metal sulfide layered structure. In this work, we report the tackling of this critical barrier through nanoscale engineering. We discover that vertically-stacked 2D-MoS2 can dramatically enhance the cycling stability. Atomic level in-situ TEM observation reveals that the MoS2 nanocakes assembled with tangling (100)-terminated nanosheets offer abundant open channels for Li+ insertion through the (100) surface, featuring an enhanced cyclability performance for over 200 cycle with a capacity retention of 90%. In contrast, (001)-terminated MoS2 nanoflowers only retains 10% of original capacity after 50 cycles. The present work demonstrates a general principle and opens a new route of crystallographic design to enhance electrochemical performance for assembling 2D materials for energy storage.

Sun, Congli↗
DOE OSTI2015

Tandem Microwire Solar Cells for Flexible High Efficiency Low Cost Photovoltaics

This project has developed components of a waferless, flexible, low-cost tandem multijunction III-V/Si microwire array solar cell technology which combines the efficiency of wafered III-V photovoltaic technologies with the process designed to meet the Sunshot object. The project focused on design of lattice-matched GaAsP/SiGe two junction cell design and lattice-mismatched GaInP/Si tandem cell design. Combined electromagnetic simulation/device physics models using realistic microwire tandem structures were developed that predict >22% conversion efficiency for known material parameters, such as tunnel junction structure, window layer structure, absorber lifetimes and optical absorption and these model indicate a clear path to 30% efficiency for high quality III-V heterostructures. SiGe microwire arrays were synthesized via Cu-catalyzed vapor-liquid-solid (VLS) growth with inexpensive chlorosilane and chlorogermance precursors in an atmospheric pressure reactor. SiGe alloy composition in microwires was found to be limited to a maximum of 12% Ge incorporation during chlorogermane growth, due to the melting of the alloy near the solidus composition. Lattice mismatched InGaP double heterostructures were grown by selective epitaxy with a thermal oxide mask on Si microwire substrates using metallorganic vapor phase epitaxy. Transmission electron microscopy (TEM) analysis confirms the growth of individual step graded layers and a high density of defects near the wire/III-V interface. Selective epitaxy was initiated with a low temperature nucleation scheme under “atomic layer epitaxy” or “flow mediated epitaxy” conditions whereby the Ga and P containing precursors are alternately introduced into the reactor to promote layer-bylayer growth. In parallel to our efforts on conformal GaInP heteroepitaxy on selectively masked Si microwires, we explored direct, axial growth of GaAs on Si wire arrays as another route to a tandem junction architecture. We proposed axial, lattice-mismatched growth of a GaAs segment that extrude out of a Si wire via a self-aligned SiO 2 hollow cylindrical mask. With this growth strategy, misfit dislocations that would normally form at the GaAs/Si interface during thin film epitaxy may bend over to and thus terminate at the sidewall of the SiO 2 tube. A reactive-ion etching technique was employed 1) to remove Si to form a hollow, self-aligned SiO 2 cylindrical tube as a growth template for GaAs epitaxy using a vertical, showerhead, low-pressure metal-organic chemical-vapor deposition reactor that was operated at 0.1 atm. Successful epitaxy of axial GaAs wires on non-polar, <111>-oriented Si wire substrates was found at temperatures of ~850C. This and the other III-V/Si heterojunction wire synthesis strategies described here are promising approaches to realize future III-V/Si tandem solar cell designs.

14 SOLAR ENERGY↗
DOE OSTI2019

Nanoscale LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode materials for lithium ion batteries via a polymer-assisted chemical solution method

A novel and facile polymer-assisted chemical solution method is successfully developed for the synthesis of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) with unique morphology and nanoparticle nature as cathodes for lithium-ion batteries. At calcination temperature up to 800°C and 900°C, NCM with hexagonal crystal structure of layered α-NaFeO 2 ( R 3 &#xAF; m spacing group) is formed and a lower degree of Ni/Li cation mixing for sample heated at 900°C is determined by XRD Rietveld refinement. SEM and TEM images reveal the uniform size distribution of nanoparticles. HRTEM confirms the single crystalline nature of particles with layered structure. XPS verifies the oxidation state of Co 3+ , Mn 4+ , Ni 2+ and Ni 3+ . As compared with the sample prepared at 800°C, the sample heated at 900°C exhibits a higher initial discharge specific capacity of 189 mAh g -1 being charged to 4.5 V at a current rate of 0.05 C, and better cyclability at 4.3 V cutoff voltage at a current density of 1 C. This method has demonstrated easy tuning compositions and particle sizes of cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2017

Importance of interlayer H bonding structure to the stability of layered minerals

Layered (oxy) hydroxide minerals often possess out-of-plane hydrogen atoms that form hydrogen bonding networks which stabilize the layered structure. However, less is known about how the ordering of these bonds affects the structural stability and solubility of these minerals. Here, we report a new strategy that uses the focused electron beam to probe the effect of differences in hydrogen bonding networks on mineral solubility. In this regard, the dissolution behavior of boehmite (γ-AlOOH) and gibbsite (γ-Al(OH)3) were compared and contrasted in real time via liquid cell electron microscopy. Under identical such conditions, 2D-nanosheets of boehmite (γ-AlOOH) exfoliated from the bulk and then rapidly dissolved, whereas gibbsite was stable. Further, substitution of only 1% Fe(III) for Al(III) in the structure of boehmite inhibited delamination and dissolution. Factors such as pH, radiolytic species, and knock on damage were systematically studied and eliminated as proximal causes for boehmite dissolution. Instead, the creation of electron/hole pairs was considered to be the mechanism that drove dissolution. The widely disparate behaviors of boehmite, gibbsite, and Fe-doped boehmite are discussed in the context of differences in the OH bond strengths, hydrogen bonding networks, and the presence or absence of electron/hole recombination centers.

58 GEOSCIENCES↗
DOE OSTI2014

Balancing high gain and bandwidth in multilayer organic photodetectors with tailored carrier blocking layers

We present detailed studies of the high photocurrent gain behavior in multilayer organic photodiodes containing tailored carrier blocking layers we reported earlier in a Letter [W. T. Hammond and J. Xue, Appl. Phys. Lett. 97, 073302 (2010)], in which a high photocurrent gain of up to 500 was attributed to the accumulation of photogenerated holes at the anode/organic active layer interface and the subsequent drastic increase in secondary electron injection from the anode. Here, we show that both the hole-blocking layer structure and layer thickness strongly influence the magnitude of the photocurrent gain. Temporal studies revealed that the frequency response of such devices is limited by three different processes with lifetimes of 10 μs, 202 μs, and 2.72 ms for the removal of confined holes, which limit the 3 dB bandwidth of these devices to 1.4 kHz. Furthermore, the composition in the mixed organic donor-acceptor photoactive layer affects both gain and bandwidth, which is attributed to the varying charge transport characteristics, and the optimal gain-bandwidth product is achieved with approximately 30% donor content. Finally, these devices show a high dynamic range of more than seven orders of magnitude, although the photocurrent shows a sublinear dependence on the incident optical power.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Controlling structure distortions in 3-layer ferroelectric Aurivillius oxides

Combined Rietveld refinements of x-ray and neutron powder diffraction data were used to understand the subtle structure distortions in 3-layer Aurivillius oxides that yield off-centering displacements in ferroelectric and multiferroic compositions. Ferroelectric phases including Bi{sub 2}A{sub 2}Ti{sub 3}O{sub 12} (A=La, Pr, Nd, La/Pr, La/Nd, Pr/Nd), Bi{sub 2}A{sub 2}TiNb{sub 2}O{sub 12} (A=Ca/Sr, Sr, and Sr/Ba) and Bi{sub 2}A{sub 2}TiTa{sub 2}O{sub 12} (A=Ca/Sr, and Sr/Ba) were studied to separate the effects of cation size and charge on the structure distortions and properties. A new approach to describing the local coordination around the Ti, Nb, and/or Ta ions is presented, where the oxygen octahedra are characterized as containing kinks in three dimensions. The kink angles follow trends with the A-site ionic radius and the ferroelectric polarization. The driving force for extensive cation site mixing between the Bi and A-site cations has been clearly established, with site mixing required to maintain interlayer bonding. - Graphical abstract: Distortion of the oxygen octahedra from planar geometries can be controlled via choice of the perovskite A-site cation, and the kink angle correlates with cation off-centering and ferroelectric polarization. Highlights: Black-Right-Pointing-Pointer A-site cations define the tilt and distortion of the octahedral. Black-Right-Pointing-Pointer Distortions of oxygen octahedra, ignoring the central cation, link to ferroelectric polarization. Black-Right-Pointing-Pointer Bi ion occupancy in the perovskite causes distortion of the oxygen sublattice. Black-Right-Pointing-Pointer We predict multiferroic behavior from off-centering caused by the Bi ion lone pair.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Manipulation by exchange coupling in layered magnetic structures

Exchange coupling in magnetic heterostructures can be modified via introduction of additional magnetic spacer layers at the interfaces. The magnetic characteristics and the spacer layer thickness determine the functional properties of the whole system. We show that the hysteresis loop area of trilayer spring magnets with two different soft magnetic layers (s1, s2) and one hard magnetic layer (h) with the sequence s1/s2/h can be increased as compared to both bilayer structures s1/h and s2/h with the same total thickness of the soft layers and for definite thickness ratios of the soft layers and their sequences. For ferrimagnetic spin valves, the perpendicular exchange bias effect can be tuned via the thickness of non-magnetic spacer layers at the interface, which determine the exchange coupling between ferrimagnets. A simple quasi one-dimensional phenomenological model is able to describe the magnetic hysteresis of even complex layered structures and to predict optimal geometrical and magnetic parameters of such heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗