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Results for “Transport Properties”

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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Charge carrier mobility of halide perovskite single crystals for ionizing radiation detection

Halide perovskites have recently emerged as promising semiconductor materials for several applications including solar cells, light-emitting diodes (LEDs), and radiation detectors. The charge carrier transport properties, which could be evaluated by the mobility-lifetime (mu-tau or μ-г) product, serve an important role for the development of halide perovskites for radiation detection applications. In this perspective, we firstly explain the charge transport mechanism and the limiting factors that determine the intrinsic charge carrier mobility in halide perovskite single crystals. Then, we overview the techniques and methods that have been employed for evaluating the charge carrier mobility (for both electrons and holes). Lastly, we discuss the discrepancy between the experimentally determined carrier mobility from the literature for halide perovskite single crystals and a perspective on future developments for carrier mobility enhancement is provided.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Synergistic role of Sn-doping on the thermal and electrical properties of sinnerite Cu 6 As 4 S 9

Sinnerite Cu 6 As 4 S 9 has been identified as a promising material for optoelectronic applications, with potential for other energy-related applications; however, knowledge of the electrical and thermal properties as well as the mechanisms underlying transport in sinnerite is lacking. Here, we present an investigation of the synthesis, structural, thermal and electrical transport properties of stoichiometric and Sn-doped Cu 6 As 4 S 9 . Sinnerite has a triclinic lattice structure, with highly distorted local atomic coordination environments that, in part, results in its complex structure and bonding. Our results and analyses indicate As 4s 2 lone pair-induced distortions and strong lattice anharmonicity that leads to a relatively short phonon mean free path, resulting in intrinsically very low thermal conductivity. The electrical resistivity for both compositions, Cu 6 As 4-x Sn x S 9 (x = 0, 0.2), are relatively high and varies little with temperature, typical of degenerate semiconductors. An increase in mobility and electrical conductivity was obtained by Sn doping in Cu 6 As 3.8 Sn 0.2 S 9 . This work demonstrates an effective route to synthesize bulk sinnerite as well as advances the knowledge of the properties of sinnerite, as this and other ternary chalcogenides continue to be of interest for potential technologically significant applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Probing coherence in nanoscale energy transport with high spatial-temporal resolution. Final Technical Report for DOE Award Number DE-SC0019244

The overarching goal of this project is to understand how the phase coherence of phonons and the interaction of phonons with other microscopic degrees of freedom in nanomaterials, such as 2D materials, can affect the energy transport properties and eventually lead to control of energy transport by manipulating phonon interference and phonon scatterings. On the computational side, we are developing and applying first-principles methods to study emerging phonon properties in nanomaterials, including coherent phonons, resonant bonding and gate-tunable phonon-electron scatterings, which hold the promise of enabling significant tunability of energy transport processes with external fields for a wide range of applications. On the experimental side, we are developing ultrafast transient grating spectroscopy and scanning ultrafast electron microscopy (SUEM) to directly probe the coherent phonon transport and phonon-electron interaction processes in nanomaterials with high combined spatial-temporal resolutions. This program will not only provide new insights into the microscopic transport and interaction processes of fundamental energy carriers, but also open new venue towards energy-relevant applications such as thermal switches and coherent energy harvesters.

42 ENGINEERING↗
DOE OSTI2022

Unconventional Charge Transport in MgCr 2 O 4 and Implications for Battery Intercalation Hosts

Ion transport in solid-state cathode materials prescribes a fundamental limit to the rates batteries can operate; therefore, an accurate understanding of ion transport is a critical missing piece to enable new battery technologies, such as magnesium batteries. Based on our conventional understanding of lithium-ion materials, MgCr 2 O 4 is a promising magnesium-ion cathode material given its high capacity, high voltage against an Mg anode, and acceptable computed diffusion barriers. Electrochemical examinations of MgCr 2 O 4 , however, reveal significant energetic limitations. Motivated by these disparate observations; herein, we examine long-range ion transport by electrically polarizing dense pellets of MgCr 2 O 4 . Our conventional understanding of ion transport in battery cathode materials, e.g., Nernst-Einstein conduction, cannot explain the measured response since it neglects frictional interactions between mobile species and their nonideal free energies. In this work, we propose an extended theory that incorporates these interactions and reduces to the Nernst-Einstein conduction under dilute conditions. This theory describes the measured response, and we report the first study of long-range ion transport behavior in MgCr 2 O 4 . We conclusively show that the Mg chemical diffusivity is comparable to lithium-ion electrode materials, whereas the total conductivity is rate-limiting. Given these differences, energy storage in MgCr 2 O 4 is limited by particle-scale voltage drops, unlike lithium-ion particles that are limited by concentration gradients. Future materials design efforts should consider the interspecies interactions described in this extended theory, particularly with respect to multivalent-ion systems and their resultant effects on continuum transport properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cation uptake by fine aggregate in hardened cement mortar and its effect on electrical properties

Electrical resistivity tests can be used to evaluate the transport properties of concrete and provide a durability assessment. However, the electrical resistivity is largely dependent on the pore solution composition and recent work suggests that some aggregates have the capacity for cation uptake. This study first aims to provide further evidence for adsorption of cations on aggregate surfaces, without formation of reaction products (e.g. alkali-silica reaction). Secondly, hardened mortar samples were prepared using a fine aggregate with a high alkali affinity and a non-reactive fine aggregate as a control. The electrical resistivity of mortars was measured, and the pore solution of these mortars was obtained through high-pressure extraction. The effect of aggregate moisture dilution on the pore solution was decoupled by using a pore partitioning model. The results indicate that aggregate minerology can influence the pore solution composition through cation uptake. Specific minerals of minor quantity, like biotite, may be responsible for cation exchange. While adsorbed cations strongly affected pore solution and formation factor measurement, the bulk resistivity measurements on hardened mortar were only marginally influenced. Research on other implications of similar aggregate interactions with pore solutions are an intriguing area for future research.

Alkali-aggregate reaction↗
DOE OSTI2021

Substituted polynorbornene membranes: a modular template for targeted gas separations

Polynorbornenes are ideal materials for systematic structure–property investigations designed to correlate gas-transport properties to polymer structure. The modular nature of norbornene-based systems provides a facile route towards the synthesis of diverse polymeric materials. Though many valuable correlations between gas-permeability and polynorbornene structure have been summarized in a prior review (2017), many of these efforts focused heavily on the design of materials with high permeabilities. More recently, the design of next-generation polynorbornene membranes has shifted toward the development of materials that are highly selective for multiple targeted gas separations. Since 2017, tremendous progress has been realized in the preparation of stable and highly selective polynorbornenes for membrane-based gas separations. Examples include polynorbornene derivatives that exhibit very high selectivity for CO 2 /N 2 and light hydrocarbon (e.g., C 3 +/C 1 ) separations, some of which exhibit gas separation performances that approach or exceed the 2008 upper bound. In this work, we summarize prior findings, present recent developments in the field of advanced polynorbornene membrane materials for targeted gas separations, and provide an outlook for the future of this field of research.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Metal Complex Molecular Solids Showing Band-like Transport Driven by In Situ Ligand Exchange

Transition-metal complexes exhibit excellent charge transport properties in solid films, rendering them promising for application in modern electronics. Although the charge transport mechanism of metal complex solids with multiple redox states is considered to be governed by self-exchange hole hopping, the effect of additives, such as Lewis bases, has not been identified. Herein, we describe the effect of 4- tert -butylpyridine (TBP) on the charge transport mechanism and film properties of [Cu(dmbpy) 2 ] 2 + / + (dmbpy = 6,6'-dimethyl-2,2'-bipyridine)-based molecular solids. The formation of [Cu(TBP) 4 ] 2 + , excess TBP, and free dmbpy from the ligand-exchange reaction between [Cu(dmbpy) 2 ] 2 + and TBP increases the film conductivity and changes the transport mechanism from hopping to band-like transport through a combination of chemical composition, film morphology, and crystallographic changes. In conclusion, these findings advance our understanding of the fundamental properties of molecular metal complex solids and enable optoelectronic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

MHD-induced beta limits in the Large Helical Device

Using the extended-magnetohydrodynamics code, M3D-C1, we perform a systematic numerical study of the effect of externally applied heating on the achievable plasma beta in a ten field-period heliotron. Heat sources of varying intensity are applied to a vacuum magnetic field that is representative of the standard configuration of the Large Helical Device, with R 0 = 3.66 m, where R 0 is the radial position of the magnetic axis in vacuum. As the system is driven to a state that is unstable to low-n magnetohydrodynamic (MHD) modes, nonlinear mode interactions lead to the formation of chaotic magnetic fields. With sufficiently strong heating, a collapse of the electron temperature profile is observed. This demonstrates the necessity of simulating the self-consistent evolution of plasma profiles, without imposing assumptions on the structure of the magnetic field, to accurately determine transport properties in stellarator plasmas. It also highlights the value of these advanced simulation capabilities for accelerating the development of high-performance stellarator operating scenarios.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Aerosol jet printed 3 omega sensors for thermal conductivity measurement

The 3 omega (3ω) method is a trusted technique for measuring thermal conductivity—a fundamental material property of critical importance in a broad range of applications. However, traditional 3ω sensor processing requires some form of physical vapor deposition, such as metal evaporation or sputtering. These 3ω sensor deposition techniques limit the materials and sample sizes applicable to the 3ω method. This work demonstrates an aerosol jet printing method to directly print silver 3ω sensors that yield accurate temperature-dependent measurement up to 300 °C on materials with thermal conductivity ranging from 1 to 150 W/m K. The interrelationship between printed sensor geometry, sensor thermal stability, and applicability to the 3ω method is examined. Thermal conductivity measurement with 3ω sensors conventionally sintered at 300 °C agrees to independent laser flash measurement within 4% from room temperature to 150 °C. An unconventional rapid high-temperature sintering method is shown to produce sensors that agree within 3% of the laser flash measurements from room temperature to 300 °C. The rapid sintering profiles also reduced the sensor–substrate thermal boundary resistance of the printed sensors by as much as 88%. The direct printing of 3ω sensors creates opportunities for measurement of thermal transport properties in applications previously inapplicable to the 3ω method.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Quantitative modeling of gate-tunable cavity exciton-polaritons in transition-metal dichalcogenides

We performed a comprehensive real-space simulation study of propagative exciton-polaritons (EPs) of tungsten disulfide (WS 2 ) inside a Fabry–Pérot cavity. Through our simulations, we were able to construct the dispersion relation and determine the propagation length (L p ) of EPs, both of which show sensitive dependence on the applied gate voltage. We found that L p increases at higher gate voltages when excited at the exciton energy but shows opposite gate dependence at the trion energy. These observations are direct evidence of the coupling between the cavity mode with excitons and trions of WS 2 . Furthermore, we demonstrate a proof-of-concept device based on the tunable cavity EPs of WS 2 , which is promising for application as photonic transistors, modulators, or electrical-to-optical converters. Furthermore, our work unveils the real-space transport properties of gate-tunable cavity EPs and paves the way for future applications of EPs in nanophotonic devices and circuits.

42 ENGINEERING↗
DOE OSTI2024

Validation of galvanomagnetic and thermomagnetic transport measurements using Standard Reference Material 3451

In the “method of four coefficients,” electrical resistivity (ρ), Seebeck coefficient (S), Hall coefficient (RH), and Nernst coefficient (Q) of a material are measured and typically fit or modeled with theoretical expressions based on Boltzmann transport theory to glean experimental insights into features of electronic structure and/or charge carrier scattering mechanisms in materials. Although well-defined and readily available reference materials exist for validating measurements of ρ and S, none currently exists for R H or Q. We show that measurements of all four transport coefficients—ρ, S, R H , and Q—can be validated using a single reference sample, namely, the low-temperature Seebeck coefficient Standard Reference Material® (SRM) 3451 (composition Bi 2 Te 3+x ) available from the National Institute for Standards and Technology (NIST) without the need for inter-laboratory sample exchange. Here, R H and Q data for NIST SRM 3451 reported here for the temperature range 80–400 K complement the data already available for ρ and S and will therefore be of interest to researchers desiring to validate new or existing galvanomagnetic and thermomagnetic transport properties measurement systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Structural anisotropy in Sb thin films

Sb thin films have attracted wide interest due to their tunable band structure, topological phases, high electron mobility, and thermoelectric properties. We successfully grow epitaxial Sb thin films on a closely lattice-matched GaSb(001) surface by molecular beam epitaxy. We find a novel anisotropic directional dependence on their structural, morphological, and electronic properties. The origin of the anisotropic features is elucidated using first-principles density functional theory (DFT) calculations. The growth regime of crystalline and amorphous Sb thin films was determined by mapping the surface reconstruction phase diagram of the GaSb(001) surface under Sb 2 flux, with confirmation of structural characterizations. Crystalline Sb thin films show a rhombohedral crystal structure along the rhombohedral (211) surface orientation parallel to the cubic (001) surface orientation of the GaSb substrate. At this coherent interface, Sb atoms are aligned with the GaSb lattice along the [1̄10] crystallographic direction but are not aligned well along the [110] crystallographic direction, which results in anisotropic features in reflection of high-energy electron diffraction patterns, misfit dislocation formation, surface morphology, and transport properties. Our DFT calculations show that the preferential orientation of the rhombohedral Sb (211) plane may originate from the GaSb surface, where Sb atoms align with the Ga and Sb atoms on the reconstructed surface. The formation energy calculations confirm the stability of the experimentally observed structures. Our results provide optimal film growth conditions for further studies of novel properties of Bi 1-x Sb x thin films with similar lattice parameters and an identical crystal structure, as well as functional heterostructures of them with III–V semiconductor layers along the (001) surface orientation, supported by a theoretical understanding of the anisotropic film orientation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Collision integrals within the Chapman–Enskog theory for a generalized Lennard-Jones potential

Here we report the values of the collision integrals, needed for the calculation of the macroscopic transport properties such as viscosity (η) and diffusion coefficient (D) of gases within the Chapman–Enskog kinetic gas theory, for a generalized Lennard-Jones potential (gLJ), a more general potential with an adjustable long range 1/r dependence that can describe a wide range of intermolecular interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Investigating Morphology and Diffusion in Simulations of Precise Anion-Conducting Polymers

Using atomistic molecular dynamics simulations, we investigate the morphology and transport properties of a new class of polymers which are functionalized with quaternary ammonium groups for use as anion exchange membranes. The polymers are precision polyolefins with either a trimethylammonium (p5CNMe3) or a dimethyl-hexyl ammonium (p5CNMe2Hx) pendant group at every fifth carbon along a polyethylene backbone. Simulations are performed at hydration levels of 5, 10, 15, and 20 water molecules per ammonium group. The hydrated polymers form nanoscale, percolated hydrophilic domains (water channels) in the hydrophobic polymer matrix that become wider with increasing water content. Water and hydroxide anion diffusion coefficients also increase with increasing water content. The morphology of the water domains is similar in both polymers, while the diffusion coefficients are somewhat lower in p5CNMe2Hx at fixed water content. Furthermore, the diffusion coefficients in both polymers fall on the same curve as a function of the fractal dimension of the percolated water channels, which appears to be a useful scalar measure of the effects of the nanoscale morphology on water and hydroxide anion transport.

Anion exchange membrane↗
DOE OSTI2021

Effective Fragment Potential-Based Molecular Dynamics Studies of Diffusion in Acetone and Hexane

To facilitate more reliable descriptions of transport properties in liquids, molecular dynamics (MD) simulations are performed based on the effective fragment potential (EFP) method derived from first-principles quantum mechanics (in contrast to MD based upon empirically fitted potentials). The EFP method describes molecular interactions in terms of Coulomb, polarization/induction, dispersion, exchange-repulsion, and charge-transfer interactions. The EFP MD simulations described in this paper, performed on hexane and acetone, are able to track the mean-square displacement of molecules for sufficient time to reliably extract translational diffusion coefficients. Finally, the results reported here are in reasonable agreement with experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Robust and Highly Conductive Water-Stable Copper Iodide-Based Hybrid Single Crystals

High conductivity, carrier mobility as well as long diffusion length are critical for highly efficient solar cells. Here, we report new types of crystalline inorganic-organic hybrid semiconductors, 2D-Cu 2 I 2 (L) [L = benzo[c][1,2,5]thiadiazole (bs) and benzo[c][1,2,5] selenadiazole (bse)], composed of one-dimensional (1D) copper iodide staircase-like chain and benzodiazole-based ligands. These compounds possess narrow and tunable band gaps and high conductivity. High-quality large single crystals of 2D-Cu 2 I 2 (bse) were grown and used to evaluate the charge transport properties of the material. State-of-the-art time-resolved microwave conductivity (TRMC) techniques were used to investigate the charge carrier dynamics, from which a high conductivity of 2 × 10 -4 S/cm, a carrier mobility of ~1 cm 2 V -1 s -1 , a maximum doping/carrier density of 2 +/- 1 × 10 15 cm -3 , and a diffusion length of ~0.17 um were obtained. We report the excellent water/chemical stability combined with high conductivity makes this I-VII-based hybrid material family promising candidates for potential optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

THz-range Faraday rotation in the Weyl semimetal candidate Co 2 TiGe

The Co 2 family of ferromagnetic Heusler alloys has attracted interest due to their fully spin-polarized nature, making them ideal for applications in spintronic devices. More recently, the existence of room temperature time-reversal-breaking Weyl nodes near the Fermi level was predicted and confirmed in these systems. As a result of the presence of these Weyl nodes, these systems possess a non-zero momentum space Berry curvature that can dramatically influence transport properties such as the anomalous Hall effect. One of these candidate compounds is Co 2 TiGe. Recently, high-quality molecular beam epitaxy-grown thin films of Co 2 TiGe have become available. In this work, we present a THz-range measurement of MBE-grown Co 2 TiGe films. We measure the THz-range Faraday rotation, which can be understood as a measure of the anomalous Hall effect. We supplement this work with electronic band-structure calculations showing that the principal contribution to the anomalous Hall effect in this material stems from the Berry curvature of the material. Overall, our work shows that this class of Heusler materials shows promise for Weyl semimetal based spintronics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Morphology–Diffusivity Relationships in Fluorine-Free Random Terpolymers for Proton-Exchange Membranes

Here, using atomistic molecular dynamics simulations, we investigate the morphology and transport properties of a new family of fluorine-free terpolymers designed as proton-exchange membranes. Simulated random terpolymers consist of three monomers with a 5-carbon backbone with a phenylsulfonate, phenyl, or no pendant group and have ion exchange capacities (IECs) ranging from 1.06–4.14 mmol/g. At a hydration level of 9, cluster analysis reveals macrophase separation between water and terpolymers with IEC < 2.1 mmol/g and continuous, percolated hydrophilic and hydrophobic nanoscale domains at higher IECs. Channel width distribution analysis of the percolated morphologies revealed that more hydrophobic units produce less uniform channels. Decreasing the surface area per sulfonate group and increasing the fractal dimension of the hydrophilic domains correlate with increased water diffusivity, due to a more acidic interface and more isotropic water channels. Relative to the previously studied phenylsulfonate homopolymer, these terpolymers with lower IECs have only modestly lower water diffusion, and we anticipate other advantages related to processability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗