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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Thermal conduction in a composite circular cylinder - A new technique for thermal conductivity measurements of lunar core samples

A technique is described for the measurement of the thermal conductivity of lunar core samples. According to their technique, the core sample is heated radiatively from the outside at a known rate, the temperature is measured at the surface of the core-tube, and the thermal conductivity of the sample is determined by comparing the measured temperature with the theory. The corresponding problems for a composite slab or sphere were solved and the solutions are presented for possible future application to the thermal conductivity measurements. The experimental apparatus construction and procedure are examined as well as the number of precautions taken to preserve the sample from disturbances and to improve the measurement results.

Horal, K.↗
NASA NTRS2001

Method of forming electronically conducting polymers on conducting and nonconducting substrates

The present invention provides electronically conducting polymer films formed from photosensitive formulations of pyrrole and an electron acceptor that have been selectively exposed to UV light, laser light, or electron beams. The formulations may include photoinitiators, flexibilizers, solvents and the like. These solutions can be used in applications including printed circuit boards and through-hole plating and enable direct metallization processes on non-conducting substrates. After forming the conductive polymer patterns, a printed wiring board can be formed by sensitizing the polymer with palladium and electrolytically depositing copper.

Murphy, Oliver J.↗
DOE OSTI2018

Ultralow Thermal Conductivity in Diamond-Like Semiconductors: Selective Scattering of Phonons from Antisite Defects

In this work, we discover anomalously low lattice thermal conductivity (<0.25 W/mK at 300 degrees C) in the Hg-containing quaternary diamond-like semiconductors within the Cu2IIBIVTe4 (IIB: Zn, Cd, Hg) (IV: Si, Ge, Sn) set of compositions. Using high-temperature X-ray diffraction, resonant ultrasound spectroscopy, and transport properties, we uncover the critical role of the antisite defects HgCu and CuHg on phonon transport within the Hg-containing systems. Despite the differences in chemistry between Hg and Cu, the high concentration of these antisite defects emerges from the energetic proximity of the kesterite and stannite cation motifs. Our phonon calculations reveal that heavier group IIB elements not only introduce low-lying optical modes, but the subsequent antisite defects also possess unusually strong point defect phonon scattering power. The scattering strength stems from the fundamentally different vibrational modes supported by the constituent elements (e.g., Hg and Cu). Despite the significant impact on the thermal properties, antisite defects do not negatively impact the mobility (>50 cm2/(Vs) at 300 degrees C) in Hg-containing systems, leading to predicted zT > 1.5 in Cu2HgGeTe4 and Cu2HgSnTe4 under optimized doping. In addition to introducing a potentially new p-type thermoelectric material, this work provides (1) a strategy to use the proximity of phase transitions to increase point defect phonon scattering, and (2) a means to quantify the power of a given point defect through inexpensive phonon calculations.

14 SOLAR ENERGY↗
DOE OSTI2018

Thermoelectric Material SnPb 2 Bi 2 S 6 : The 4,4 L Member of Lillianite Homologous Series with Low Lattice Thermal Conductivity

Although the binary sulfides Bi 2 S 3 , PbS, and SnS have attracted extensive interest as thermoelectric materials, no quaternary sulfides containing Sn/Pb/Bi/S elements have been reported. In this paper, we report the synthesis of a new quaternary sulfide, SnPb 2 Bi 2 S 6 , which crystallizes in the orthorhombic space group Pnma with unit cell parameters of a = 20.5458(12) Å, b = 4.0925(4) Å, c = 13.3219(10) Å. SnPb 2 Bi 2 S 6 has a lillianite-type crystal structure consisting of two alternately aligned NaCl-type structural motifs separated by a mirror plane of PbS 7 monocapped trigonal prisms. In the lillianite homologous series, SnPb 2 Bi 2 S 6 can be classified as 4,4L, where the superscripted numbers indicate the maximum numbers of edge-sharing octahedra in the two adjacent NaCl-shaped slabs along the diagonal direction. The obtained SnPb 2 Bi 2 S 6 phase exhibited good thermal stability up to 1000 K and n-type degenerate semiconducting behavior, with a power factor of 3.7 μW cm -1 K -2 at 773 K. Notably, this compound exhibited a very low lattice thermal conductivity of 0.69-0.92 W m -1 K -1 at 300-1000 K. Theoretical calculations revealed that the low thermal conductivity is caused by the complex crystal structure and the related elastic properties of a low Debye temperature, low phonon velocity, and large Grüneisen parameters. A reasonable figure of merit (ZT) of ~0.3 was obtained at 770 K.

Crystal structure↗
DOE OSTI2018

Influence of Nonstoichiometry on Proton Conductivity in Thin-Film Yttrium-Doped Barium Zirconate

Proton-conducting perovskites have been widely studied because of their potential application as solid electrolytes in intermediate temperature solid oxide fuel cells. Structural and chemical heterogeneities can develop during synthesis, device fabrication, or service, which can profoundly affect proton transport. Here, we use time-resolved Kelvin probe force microscopy, scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations to intentionally introduce Ba-deficient planar and spherical defects and link the resultant atomic structure with proton transport behavior in both stoichiometric and nonstoichiometric epitaxial, yttrium-doped barium zirconate thin films. The defects were intentionally induced through high-temperature annealing treatment, while maintaining the epitaxial single crystalline structure of the films, with an overall relaxation in the atomic structure. As a result, the annealed samples showed smaller magnitudes of local lattice distortions because of the formation of proton polarons, thereby leading to decreased proton-trapping effect. This resulted in a decrease in the activation energy for proton transport, leading to faster proton transport.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Out-of-Plane Conductivity and Photovoltaic Performance in n = 1 Layered Perovskites through Organic Cation Design

Layered perovskites with the formula (R–NH 3 ) 2 PbI 4 have excellent environmental stability but poor photovoltaic function due to the preferential orientation of the semiconducting layer parallel to the substrate and the typically insulating nature of the R–NH 3 + cation. Here, we report a series of these n = 1 layered perovskites with the form (aromatic-O-linker-NH 3 ) 2 PbI 4 where the aromatic moiety is naphthalene, pyrene, or perylene and the linker is ethyl, propyl, or butyl. These materials achieve enhanced conductivity perpendicular to the inorganic layers due to better energy level matching between the inorganic layers and organic galleries. The enhanced conductivity and visible absorption of these materials led to a champion power conversion efficiency of 1.38%, which is the highest value reported for any n = 1 layered perovskite, and it is an order of magnitude higher efficiency than any other n = 1 layered perovskite oriented with layers parallel to the substrate. Furthermore, these findings demonstrate the importance of leveraging the electronic character of the organic cation to improve optoelectronic properties and thus the photovoltaic performance of these chemically stable low n layered perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Significant Reduction of Lattice Thermal Conductivity by the Electron-Phonon Interaction in Silicon with High Carrier Concentrations: A First-Principles Study

The electron-phonon interaction is well known to create major resistance to electron transport in metals and semiconductors, whereas fewer studies are directed to its effect on phonon transport, especially in semiconductors. Herein we calculate the phonon lifetimes due to scattering with electrons (or holes), combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon interaction, all from first principles, and evaluate the effect of the electron-phonon interaction on the lattice thermal conductivity of silicon. Unexpectedly, we find a significant reduction of the lattice thermal conductivity at room temperature as the carrier concentration goes above 1019 cm –3 (the reduction reaches up to 45% in p-type silicon at around 1021 cm –3 ), a range of great technological relevance to thermoelectric materials.

42 ENGINEERING↗
DOE OSTI2014

Ignition Sensitivity and Electrical Conductivity of a Composite Energetic Material with Conductive Nanofillers

The safe handling of powdered composite energetic materials requires an understanding of their response to electrostatic ignition stimuli. A binary composite comprised of Al and polytetrafluoroethylene (PTFE) was tailored for ESD ignition sensitivity with varied concentrations of highly conductive nanofillers. The goal was to control the ESD ignition response of the Al+PTFE with small concentrations of nanofillers that may not significantly affect the overall combustion performance of the mixture. The nanofillers examined include carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). Adding CNTs created percolation at a lower volumetric percentage than GNPs and were found to be the controlling nanofiller, creating percolation for the mixture containing both CNTs and GNPs. Various mixing methods were examined. Ignition was achieved only for adding nanofillers at a volumetric percentage and mixing method that led to a bulk conductivity of approximately 5x10-3 ?S/cm.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High Thermoelectric Performance in PbSe–NaSbSe 2 Alloys from Valence Band Convergence and Low Thermal Conductivity

PbSe is an attractive thermoelectric material due to its favorable electronic structure, high melting point, and lower cost compared to PbTe. Herein, the hitherto unexplored alloys of PbSe with NaSbSe 2 (NaPb m SbSe m+2 ) are described and the most promising p-type PbSe-based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPb m SbSe m+2 exhibits unorthodox semiconducting-like electrical conductivity, despite possessing degenerate carrier densities of ≈10 20 cm -3 . Here, it is shown that the peculiar behavior derives from carrier scattering by the grain boundaries. It is further demonstrated that the high solubility of NaSbSe 2 in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe 2 lowers the energy separation between the L- and Σ-valence bands and enhances the power factors under 700 K. The crystallographic disorder of Na + , Pb 2+ , and Sb 3+ moreover provides exceptionally strong point defect phonon scattering yielding low lattice thermal conductivities of 1–0.55 W m -1 K -1 between 400 and 873 K without nanostructures. As a consequence, NaPb 10 SbSe 12 achieves maximum ZT ≈1.4 near 900 K when optimally doped. More importantly, NaPb 10 SbSe 12 maintains high ZT across a broad temperature range, giving an estimated record ZT avg of ≈0.64 between 400 and 873 K, a significant improvement over existing p-type PbSe thermoelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Circularly Polarized Light-Induced Microwave Conductivity Measurement: Rapid Screening Technique of Electronic Conductivity in Chiral Molecular Materials

Here, we developed circularly polarized light-time-resolved microwave conductivity (CPL-TRMC) for investigation of the CPL-dependent photoinduced charge carrier dynamics in chiral materials with chiroptical properties. Chiral R- or S-perylenediimide (PDI) molecular thin films were paired with handedness-sorted (6,5) and (11,-5) single-walled carbon nanotube (SWCNT) films to compose a donor (D)-acceptor (A) system for the spin-dependent charge separation process, and the D-A system was examined through linear and circular polarization-dependent steady-state and time-resolved measurements. The R-PDI-(6,5) film exhibited strong enhancement in circular dichroism (CD) and revealed a reversed transient conductivity signal, relative to the polarity of CD in CPL-TRMC measurement upon excitation of the E 11 state, which is interpreted as arising from a spin-dependent initial charge separation process. Through linear polarization-dependent flash photolysis TRMC and circular polarization-resolved femtosecond transient absorption, we could deduce that sub-picosecond intertubular charge separation upon E 11 excitation in SWCNT was responsible for the spin-dependent photoconductivity transients observed in CPL-TRMC measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics

Solutions of unbundled and unbroken single-walled carbon nanotubes have been prepared using a reductive dissolution process. Transparent conductive films spray-coated from these solutions show a nearly twofold improvement in the ratio of electrical conductivity to optical absorptivity versus those deposited from conventional aqueous dispersions, due to substantial de-aggregation and sizable nanotube lengths. These transparent electrodes have been utilized to fabricate P3HT-PCBM organic solar cells achieving power conversion efficiencies up to 2.3%, comparable to those of solar cells using indium tin oxide transparent electrodes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Mechanisms of nonequilibrium electron-phonon coupling and thermal conductance at interfaces

We study the electron and phonon thermal coupling mechanisms at interfaces between gold films with and without Ti adhesion layers on various substrates via pump-probe time-domain thermoreflectance. The coupling between the electronic and the vibrational states is increased by more than a factor of five with the inclusion of an ∼3 nm Ti adhesion layer between the Au film and the non-metal substrate. Furthermore, we show an increase in the rate of relaxation of the electron system with increasing electron and lattice temperatures induced by the laser power and attribute this to enhanced electron-electron scattering, a transport channel that becomes more pronounced with increased electron temperatures. The inclusion of the Ti layer also results in a linear dependence of the electron-phonon relaxation rate with temperature, which we attribute to the coupling of electrons at and near the Ti/substrate interface. This enhanced electron-phonon coupling due to electron-interface scattering is shown to have negligible influence on the Kapitza conductances between the Au/Ti and the substrates at longer time scales when the electrons and phonons in the metal have equilibrated. These results suggest that only during highly nonequilibrium conditions between the electrons and phonons (T{sub e} ≫ T{sub p}) does electron-phonon scattering at an interface contribute to thermal boundary conductance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗