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Results for “FUNCTIONAL ANALYSIS”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Survival function analysis of planet size distribution with Gaia Data Release 2 updates

Applying the survival function analysis to the planet radius distribution of the Kepler confirmed/candidate planets, we have identified two natural divisions of planet radius at 4 Earth radii (R ⊕ ) and 10 R ⊕ . These divisions place constraints on planet formation and interior structure model. The division at 4 R ⊕ separates small exoplanets from large exoplanets above. When combined with the recently discovered radius gap at 2 R ⊕ , it supports the treatment of planets in between 2 and 4 R ⊕ as a separate group, likely water worlds. For planets around solar-type FGK main-sequence stars, we argue that 2 R ⊕ is the separation between water-poor and water-rich planets, and 4 R ⊕ is the separation between gas-poor and gas-rich planets. Here, we confirm the slope of the survival function in between 4 and 10 R ⊕ to be shallower compared to either ends, indicating a relative paucity of planets in between 4 and 10 R ⊕ , namely the sub-Saturnian desert there. We name them transitional planets, as they form a bridge between the gas-poor small planets and gas giants. Accordingly, we propose the following classification scheme: (<2 R ⊕ ) rocky planets, (2–4 R ⊕ ) water worlds, (4–10 R ⊕ ) transitional planets, and (>10 R ⊕ ) gas giants.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Coupled-cluster Green's function: Analysis of properties originating in the exponential parametrization of the ground-state wave function

In this paper we derive basic properties of the Green’s function matrix elements stemming from the exponential coupled cluster (CC) parametrization of the ground-state wave function. We demon- strate that all intermediates used to express retarded (or equivalently, ionized) part of the Green’s function in the ω-representation can be expressed through connected diagrams only. Similar proper- ties are also shared by the first order ω-derivatives of the retarded part of the CC Green’s function. This property can be extended to any order ω-derivatives of the Green’s function. Through the Dyson equation of CC Green’s function, the derivatives of corresponding CC self-energy can be evaluated analytically. In analogy to the CC Green’s function, the corresponding CC self-energy is expressed in terms of connected diagrams only. Moreover, the ionized part of the CC Green’s func- tion satisfies the non-homogeneous linear system of ordinary differential equations, whose solution may be represented in the exponential form. Our analysis can be easily generalized to the advanced part of the CC Green’s function.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Operando pair distribution function analysis of nanocrystalline functional materials: the case of TiO 2 -bronze nanocrystals in Li-ion battery electrodes

Structural modelling of operando pair distribution function (PDF) data of complex functional materials can be highly challenging. To aid the understanding of complex operando PDF data, this article demonstrates a toolbox for PDF analysis. The tools include denoising using principal component analysis together with the structureMining , similarityMapping and nmfMapping apps available through the online service `PDF in the cloud' ( PDFitc , https://pdfitc.org/). The toolbox is used for both ex situ and operando PDF data for 3 nm TiO 2 -bronze nanocrystals, which function as the active electrode material in a Li-ion battery. The tools enable structural modelling of the ex situ and operando PDF data, revealing two pristine TiO 2 phases (bronze and anatase) and two lithiated Li x TiO 2 phases (lithiated versions of bronze and anatase), and the phase evolution during galvanostatic cycling is characterized.

Chemistry↗
DOE OSTI2017

Density functional analysis of fluorite-structured (Ce, Zr)O 2 /CeO 2 interfaces [Density functional analysis of fluorite-structured (Ce, Zr)O 2 /CeO 2 interfaces: Implications for catalysis and energy applications]

The structures and properties of Ce 1–x Zr x O 2 (x = 0–1) solid solutions, selected Ce 1–x Zr x O 2 surfaces, and Ce 1–x Zr x O 2 /CeO 2 interfaces were computed within the framework of density functional theory corrected for strong electron correlation (DFT+ U ). The calculated Debye temperature increases steadily with Zr content in (Ce, Zr)O 2 phases, indicating a significant rise in microhardness from CeO 2 to ZrO 2 , without appreciable loss in ductility as the interfacial stoichiometry changes. Surface energy calculations for the low-index CeO 2 (111) and (110) surfaces show limited sensitivity to strong 4f-electron correlation. The fracture energy of Ce 1–x Zr x O 2 (111)/CeO 2 (111) increases markedly with Zr content, with a significant decrease in energy for thicker Ce 1–x Zr x O 2 films. These findings suggest the crucial role of Zr acting as a binder at the Ce 1–x Zr x O 2 /CeO 2 interfaces, due to the more covalent character of Zr–O bonds compared to Ce–O. Finally, the impact of surface relaxation upon interface cracking was assessed and found to reach a maximum for Ce 0.25 Zr 0.75 O 2 /CeO 2 interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy

Operando pair distribution function (PDF) analysis and ex situ Na-23 magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from Na-23 ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electro-chemically; a-Na3-xSb (x approximate to 0.4-0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na1.7Sb, a highly amorphous structure featuring some Sb-Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na3-xSb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphofis network reacts at higher voltages reforming a-Na1.7Sb, then a-Na3-xSb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na3-xSb without the formation of a-Na3-xSb. a-Na3-xSb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature Na-23 NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes.

Allan, Phoebe K.↗
DOE OSTI2017

Same Precursor, Two Different Products: Comparing the Structural Evolution of In–Ga–O “Gel-Derived” Powders and Solution-Cast Films Using Pair Distribution Function Analysis

Amorphous metal oxides are central to a variety of technological applications. In particular, indium gallium oxide has garnered attention as a thin-film transistor channel layer material. In this work we examine the structural evolution of indium gallium oxide gel-derived powders and thin films using infrared vibrational spectroscopy, X-ray diffraction, and pair distribution function (PDF) analysis of X-ray total scattering from standard and normal incidence thin-film geometries (tfPDF). We find that the gel-derived powders and films from the same aqueous precursor evolve differently with temperature, forming mixtures of Ga-substituted In2O3 and In-substituted β-Ga2O3 with different degrees of substitution. X-ray total scattering and PDF analysis indicate that the majority phase for both the powders and films is an amorphous/nanocrystalline β-Ga2O3 phase, with a minor constituent of In2O3 with significantly larger coherence lengths. This amorphous β-Ga2O3 phase could not be identified using the conventional Bragg diffraction techniques traditionally used to study crystalline metal oxide thin films. The combination of Bragg diffraction and tfPDF provides a much more complete description of film composition and structure, which can be used to detail the effect of processing conditions and structure–property relationships. This study also demonstrates how structural features of amorphous materials, traditionally difficult to characterize by standard diffraction, can be elucidated using tfPDF.

36 MATERIALS SCIENCE↗