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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 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Partial-wave analysis of γ p → K + Λ using a multichannel framework

Results from a partial-wave analysis of the reaction γp→K+Λ are introduced. The reaction is dominated by the S 11 (1650) and P 13 (1720) resonances at low energies and by P 13 (1900) at higher energies. There are small contributions from all amplitudes up to and including G 17 , with F 17 necessary for obtaining a good fit of several of the spin observables. We present evidence for P 11 (1880), D 13 (2120), and D 15 (2080) resonances, as well as a possible F 17 resonance near 2300 MeV, which is expected from quark-model predictions. Some predictions for γn→K 0 Λ are also covered.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Bootstrap-determined p values in lattice QCD

We present a general method to determine the probability that stochastic Monte Carlo data, in particular those generated in a lattice QCD calculation, would have been obtained were that data drawn from the distribution predicted by a given theoretical hypothesis. Such a probability, or p -value, is often used as an important heuristic measure of the validity of that hypothesis. The proposed method offers the benefit that it remains usable in cases where the standard Hotelling T 2 methods based on the conventional χ 2 statistic do not apply, such as for uncorrelated fits. Specifically, we analyze q 2 , defined as the correlated χ 2 statistic obtained using an arbitrary covariance matrix estimator, and show how to use the bootstrap as a data-driven method to determine the expected distribution of q 2 for a given hypothesis with minimal assumptions. This distribution can then be used to determine the p -value for a fit to the data. We also describe a bootstrap approach for quantifying the impact upon this p -value of estimating population parameters from a single ensemble of N samples. The overall method is accurate up to a 1 / N bias which we do not attempt to quantify. Published by the American Physical Society 2025

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Probing C P Violation with Neutrino Disappearance Alone

The best way to probe C P violation in the lepton sector is with long-baseline accelerator neutrino experiments in the appearance mode: the appearance of ν e in predominantly ν μ beams. Here we show that it is possible to discover C P violation with disappearance experiments only, by combining JUNO for electron neutrinos and DUNE or Hyper-Kamiokande for muon neutrinos. While the maximum sensitivity to discover C P is quite modest ( 1.6 σ with 6 years of JUNO and 13 years of DUNE), some values of δ may be disfavored by > 3 σ depending on the true value of δ . Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Optical and electronic properties of doped p -type CuI: Explanation of transparent conductivity from first principles

In this paper, we report the properties of the reported transparent conductor CuI, including the effect of heavy p-type doping. The results, based on first-principles calculations, include an analysis of the electronic structure and calculations of optical and dielectric properties. We find that the origin of the favorable transparent conducting behavior lies in the absence in the visible of strong interband transitions between deeper valence bands and states at the valence-band maximum that become empty with p-type doping. Instead, strong interband transitions to the valence-band maximum are concentrated in the infrared with energies below 1.3 eV. This is contrast to the valence bands of many wide-band-gapmaterials. Turning to the mobility,we find that the states at the valence-band maximum are relatively dispersive. This originates from their antibonding Cu d–I p character. We find a modest enhancement of the Born effective charges relative to nominal values, leading to a dielectric constant ε(0) = 6.3. This is sufficiently large to reduce ionized impurity scattering, leading to the expectation that the properties of CuI can still be significantly improved through sample quality.

14 SOLAR ENERGY↗
DOE OSTI2018

Metastable rocksalt ZnO is p -type dopable

Despite decades of efforts, achieving p-type conductivity in the wide band gap ZnO in its ground-state wurtzite structure continues to be a challenge. Here we detail how p-type ZnO can be realized in a known metastable, high-pressure rocksalt phase (also wide-gap) with Li as an external dopant. Using modern defect theory, we predict Li to dope the rocksalt phase p-type by preferentially substituting for Zn and introducing shallow acceptor levels, resulting in predicted hole concentrations to exceed 1019cm-3. Formation of compensating donors like interstitial Li and unintentional hydrogen, ubiquitous in wurtzite phase, is inhibited by the close-packed nature of the rocksalt polymorph. Also, relatively high absolute valence band edge of rocksalt ZnO benefits low hole effective masses and hole delocalization. In addition to the technological significance, our results reveal polymorphism as a promising route to overcome strong doping asymmetry of wide band gap oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Boron phosphide as a p-type transparent conductor: Optical absorption and transport through electron-phonon coupling

Boron phosphide has recently been identified as a potential high-hole-mobility transparent conducting material. This promise arises from its low hole effective masses. However, boron phosphide has a relatively small, 2 eV, indirect bandgap which will affect its transparency. In this study, we computationally study both optical absorption across the indirect gap and phonon-limited electronic transport to quantify the potential of boron phosphide as a p-type transparent conductor. We find that phonon-mediated indirect optical absorption is weak in the visible spectrum and that the phonon-limited hole mobility is very high (around 900 cm 2 /Vs) at room temperature. This exceptional mobility comes from the combination of a low hole effective mass and very weak scattering by polar phonon modes. We rationalize the weak scattering by the less ionic bonding in boron phosphide compared to oxides. We suggest that this could be a general advantage of nonoxides for p-type transparent conducting applications. Using our computed properties, we assess the transparent conductor figure of merit of boron phosphide and show that it exceeds by one order of magnitude that of established p-type transparent conductors, confirming the potential of this material.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ab initio modeling and experimental investigation of Fe 2 P by DFT and spin spectroscopies

Fe 2 P alloys have been identified as promising candidates for magnetic refrigeration at room-temperature and for custom magnetostatic applications. The intent of this study is to accurately characterize the magnetic ground state of the parent compound, Fe 2 P, with two spectroscopic techniques, μSR and NMR, in order to provide solid bases for further experimental analysis of Fe 2 P-type transition metal based alloys. Herein, we perform zero applied field measurements using both techniques below the ferromagnetic transition T C = 220 K. The experimental results are reproduced and interpreted using first principles simulations, validating this approach for quantitative estimates in alloys of interest for technological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Magnetic order in the S eff =1/2 triangular-lattice compound NdCd 3 ⁢P 3

Here, we present and characterize a new member of the R⁢Cd 3 ⁢P 3 (R=rare earth) family of materials, NdCd 3 ⁢P 3 , which possesses Nd 3+ cations arranged on well-separated triangular lattice layers. Magnetic susceptibility and heat capacity measurements demonstrate a likely S eff =1/2 ground state, and also reveal the formation of long-range antiferromagnetic order at T N =0.34K. Via measurements of magnetization, heat capacity, and electrical resistivity, we characterize the electronic properties of NdCd 3 ⁢P 3 and compare results to density functional theory calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Lead apatites: structural variations among Pb 5 ( B O 4 ) 3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite)

The crystal structure of four Pb apatite samples, Pb 5 ( B O 4 ) 3 Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space group P 6 3 / m and Z = 2. For this isotypic series, B = P 5+ is pyromorphite, B = As 5+ is mimetite and B = V 5+ is vanadinite. The ionic radius for As 5+ (0.355 Å) is similar to that of V 5+ (0.335 Å), and this is twice as large as that for P 5+ (0.170 Å). However, the c unit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes, V , are almost equal to each other. No explanation was available for this peculiar c -axis value for mimetite. Structural parameters such as average $\langle$ B —O$\rangle$ [4], $\langle$Pb1—O 9 $\rangle$ [9] and $\langle$Pb2—O 6 Cl 2 $\rangle$ [8] distances increase linearly with V (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2—O1 distance, so the O1 oxygen atom interacts with the 6 s 2 lone-pair electrons of the Pb 2+ cation that causes the Cl—Cl distance (= c /2) to increase to the largest value in the series because of repulsion, which causes the c -axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.

chemistry↗
DOE OSTI2019

Investigation of Rear-Emitter GaAs 0.75 P 0.25 Top Cells for Application to III–V/Si Tandem Photovoltaics

A rear-emitter (rear-junction) n-on-p+ device design was investigated for use in metamorphic monolithic III-V/Si tandem solar cells as an alternative to the traditional front-emitter (front-junction) n+-on-p design for potentially greater resistance to threading dislocation-induced performance degradation. A comparison of MOCVD-grown rearversus front-emitter 1.7-eV bandgap GaAs 0.75 P 0.25 top cell isotypes demonstrated as 30-mV advantage in WOC for the rear-emitter design. Here, this reduction in WOC was determined to be nearly equally caused by a reduction in junction recombination current as well as reduced reverse saturation current from improved quasi-neutral region transport. These results suggest that the rear-emitter design may indeed be a promising pathway for application to metamorphic cells, including III-V/Si tandems, where achieving maximum voltage output is often hindered by elevated dislocation densities. However, further optimization of short-circuit current collection is needed to overcome suboptimal collection probability profiles that could limit the efficacy of such structures.

14 SOLAR ENERGY↗
DOE OSTI2018

A Datasheet Driven Unified Si/SiC Compact IGBT Model for N-Channel and P-Channel Devices

This paper presents a unified physics-based insulated-gate bipolar transistor (IGBT) compact model for circuit simulation that predicts the performance of both Si and SiC, n- and p-channel devices. The model can predict the detailed switching waveforms of these technologies based on its charge-based formulation. Further, this compact IGBT model is presented alongside a unique datasheet-driven parameter extraction process. The parameter extraction process enables users to quickly extract model parameters from data typically published without the need of taking physical measurements. The model has been validated with both Si and SiC devices for static and dynamic characteristics. The SiC IGBTs used for validation are a 12.5-kV n-channel device and a 13-kV p-channel device, while the Si IGBT chosen was IXDH30N120 from IXYS Corp. (Milpitas, CA, USA). This is the only IGBT model that predicts the performance of both n- and p-channel, Si and SiC devices, providing more freedom for the development of complex power electronics circuit designs. The convergence of the model has been verified by implementing a complex circuit consisting of both a dc-dc converter and a dc-ac inverter. The results presented here show that the unified model can be used to describe the behavior of a wide range of Si and SiC IGBT circuits. This paper is accompanied by a Verilog-A source code and a power point file demonstrating the model parameter extraction sequence.

42 ENGINEERING↗
DOE OSTI2024

Nitrogen availability and summer drought, but not N:P imbalance, drive carbon use efficiency of a Mediterranean tree-grass ecosystem

All ecosystems contain both sources and sinks for atmospheric carbon (C). A change in their balance of net and gross ecosystem carbon uptake, ecosystem-scale carbon use efficiency (CUE ECO ), is a change in their ability to buffer climate change. However, anthropogenic nitrogen (N) deposition is increasing N availability, potentially shifting terrestrial ecosystem stoichiometry towards phosphorus (P) limitation. Depending on how gross primary production (GPP, plants alone) and ecosystem respiration (R ECO , plants and heterotrophs) are limited by N, P or associated changes in other biogeochemical cycles, CUE ECO may change. Seasonally, CUE ECO also varies as the multiple processes that control GPP and respiration and their limitations shift in time. We worked in a Mediterranean tree-grass ecosystem (locally called ‘dehesa’) characterized by mild, wet winters and summer droughts. We examined CUE ECO from eddy covariance fluxes over 6 years under control, +N and + NP fertilized treatments on three timescales: annual, seasonal (determined by vegetation phenological phases) and 14-day aggregations. Finer aggregation allowed consideration of responses to specific patterns in vegetation activity and meteorological conditions. We predicted that CUE ECO should be increased by wetter conditions, and successively by N and NP fertilization. Milder and wetter years with proportionally longer growing seasons increased CUE ECO , as did N fertilization, regardless of whether P was added. Using a generalized additive model, whole ecosystem phenological status and water deficit indicators, which both varied with treatment, were the main determinants of 14-day differences in CUE ECO . The direction of water effects depended on the timescale considered and occurred alongside treatment-dependent water depletion. Overall, future regional trends of longer dry summers may push these systems towards lower CUE ECO .

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Description of Differential Cross Sections for {sup 63}Cu + p Nuclear Reactions Induced by High-Energy Cosmic-Ray Protons

The results of calculation of {sup 63}Cu + p differential cross sections at incident-proton energies between 10 and 200 MeV and a comparative analysis of these results are presented as a continuation of the earlier work of our group on developing methods for calculating the contribution of nuclear reactions to radiative effects arising in the onboard spacecraft electronics under the action of high-energy cosmic-ray protons on {sup 63}Cu nuclei (generation of single-event upsets) and as a supplement to the earlier calculations performed on the basis of the TАLYS code in order to determine elastic- and inelastic-scattering cross sections and charge, mass, and energy distributions of recoil nuclei (heavy products of the {sup 63}Cu + p nuclear reaction). The influence of various mechanisms of the angular distributions of particles emitted in the {sup 63}Cu + p nuclear reaction is also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Multiparticle Photonuclear Reactions in the p-Process at Temperatures between 1 and 10 GK

The role of (γ, 2n), (γ, pn), and (γ, 2p) multiparticle photonuclear reactions in processes that lead to the nucleosynthesis of p-nuclides is considered. The library of rates of multiparticle photonuclear reactions that was developed for the temperature range between 1 and 10 GK and which is intended for use in stellar-evolution models and in calculations of nucleosynthesis is described. A simulation of the p-process in the course of an SN-IIa core-collapse event reveals that, within the scenario being considered, a dominant effect of multiparticle photonuclear reactions consists in enhancing the rate of photodisintegration of p-nuclides at temperatures above 6 to 7 GK.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Experimental studies of the effects of atomic ordering in epitaxial Ga{sub x}In{sub 1–x}P alloys on their structural and morphological properties

The properties of epitaxial Ga{sub x}In{sub 1–x}P alloys with an ordered arrangement of atoms in the crystal lattice are studied by a number of structural and microscopic methods. The alloys are grown by metal-organic chemical vapor deposition onto single-crystal GaAs(100) substrates. It is shown that, under conditions for the coherent growth of an ordered Ga{sub x}In{sub 1–x}P alloy on a GaAs(100) substrate, atomic ordering results in radical modifications of the structural properties of the semiconductor compared to the properties of disordered alloys. Among these modifications are a change in the crystal-lattice parameter and, as a consequence, lowering of the crystal symmetry and the formation of two different types of surface nanorelief. With consideration for elastic strains, the parameters of Ga{sub x}In{sub 1–x}P alloys with ordering as functions of the order parameter are calculated for the first time. It is shown that all experimental data are in good agreement with the developed theoretical concepts.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Experimental studies of the effects of atomic ordering in epitaxial Ga{sub x}In{sub 1–} {sub x}P alloys on their optical properties

The properties of epitaxial Ga{sub x}In{sub 1–} {sub x}P alloys with an ordered arrangement of atoms in the crystal lattice are studied by a number of spectroscopic methods. The alloys are grown by metal-organic chemical vapor deposition onto single-crystal GaAs(100) substrates. It is shown that, under conditions of the coherent growth of an ordered Ga{sub x}In{sub 1–} {sub x}P alloy on a GaAs(100) substrate, atomic ordering results in radical modifications of the optical properties of the semiconductor compared to the properties of disordered alloys. Among these modifications are a decrease in the band gap and an increase in the luminescence intensity. From the data of dispersion analysis of the infrared dispersion spectra and from ultraviolet spectroscopy data obtained in the transmittance–reflection mode of measurements, the basic optical characteristics, specifically, the dispersion of the refractive index and the high-frequency permittivity of Ga{sub x}In{sub 1–} {sub x}P alloys with ordering are determined. All of the experimental data are in good agreement with the developed theoretical concepts.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Calculation of the T–P Phase Diagrams for the Halogenomethane Compounds (CCl{sub 4 –} {sub n}Br{sub n}, n = 0, 1, 2, 4) Using the Mean Field Theory

The T–P phase diagrams of the halogenomethane compounds (CCl{sub 4 –} {sub n}Br{sub n}, n = 0, 1, 2, 4) are calculated using a mean field model. By expanding the free energy in terms of the order parameters for the transitions of the liquid (L), rhombohedral (R), face-centered cubic (FCC) and monoclinic (M) phases in those compounds, the phase line equations are derived and they are fitted to the experimental data from the literature. This method of calculating the T–P phase diagram is satisfactory to explain the T–P measurements for the halogenomethane compounds and it can also be applied to two-component systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microplasticity of Amorphous and Crystallized Fe{sub 78}P{sub 20}Si{sub 2} Alloy

In order to determine the mechanism of plastic deformation, the hardness and local plasticity of amorphous Fe{sub 78}P{sub 20}Si{sub 2} alloy are compared at different stages of its crystallization activated by thermal treatment at 300–750°C or short-term photon treatment with a radiation dose coming to the sample of 10–60 J/cm{sup 2}. The phase composition and structure were investigated by X-ray diffractometry and high-resolution transmission electron microscopy. With the same sequence of structural changes, the crystallization rate under photon treatment is more than two orders of magnitude higher than that under thermal treatment, which indicates the effect of a high rate of input of the process activation energy. The nonmonotonic dependence of the hardness, elastic modulus, and the proportion of plastic strain in the indentation work is found, depending on the annealing temperature or radiation dose received by the sample, as a result of structural changes in the alloy. The local plasticity of the initial alloy and fully crystallized alloy are close in magnitude. Based on the features of the crystal structure of the Fe{sub 3}P phase (the impossibility of the dislocation mechanism of plastic deformation) and assuming that the structural unit (tetrahedral Fe{sub 3}P cluster) of the crystallized and amorphous alloy is identical, a conclusion was formulated about the cluster mechanism of plastic deformation of the amorphous alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗