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Results for “surface phase transitions”

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 OSTI2020

Non-compact oxide-island growth induced by surface phase transition of the intermetallic NiAl during vacuum annealing

Crystal structure and composition are inter-dependent and decoupling their effects on surface reactivity is challenging. Using low-energy electron microscopy to spatially and temporally resolve the oxide film growth during the oxidation of NiAl(100), we differentiate such coupled effects by monitoring oxide growth while simultaneously fine-tuning the surface structure and composition during oxidation. We demonstrate that the oxidation of chemically ordered surfaces results in compact oxide island growth whereas non-compact oxide growth during the surface phase transition. By incorporating the surface phase transition induced chemical disordering into kinetic Monte Carlo simulations, we illustrate that the non-compact oxide growth is induced by the composition effect on the surface diffusion of oxygen, which can be described by the concept of “ant in the labyrinth”.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The Role of Secondary Particle Structures in Surface Phase Transitions of Ni-Rich Cathodes

Nanometer-thick reconstruction layers on layered cathode surfaces have been widely observed on both pristine and cycled materials. However, the mechanisms of reconstruction and the role that these structures play in electrochemical performance are not fully understood. From a crystallographic perspective, such surface reconstruction layers result from cation site-mixing between Li and transition-metal ions, but it remains far from clear as to what the critical factors are that control such cation mixing for various cathode chemistries. In this paper, we report observations on surface transformations during cycling of a Ni-rich cathode-oxide that are governed by direct contact with the liquid electrolyte. Specifically, within a secondary particle, the three-dimensional hierarchical aggregate of primary particles leads to the formation of grain boundaries of different characteristics, including open grain boundaries that allow the permeation of liquid electrolyte, and closed grain boundaries that exclude liquid electrolyte penetration. Upon battery cycling, surfaces in direct contact with the liquid electrolyte showed a surface reconstruction layer while the surfaces that did not have contact with the electrolyte showed no such reconstructions. In addition, the critical role of oxygen in reconstruction of grain boundaries is demonstrated, and the unexpected oxygen depletion at twin boundaries result in severe phase transitions. The present work provides further insights into phase transitions at solid-solid and solid-liquid interfaces within secondary cathode particles and suggests strategies for mitigating surface/interfacial degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries

The energy density of current lithium-ion batteries (LIBs) based on layered LiMO 2 cathodes (M=Ni, Mn, Co: NMC; M=Ni, Co, Al: NCA) needs to be improved significantly in order to compete with internal combustion engines and allow for widespread implementation of electric vehicles (EVs). In this report, we show that atomic layer deposition (ALD) of titania (TiO 2 ) and alumina (Al 2 O 3 ) on Ni-rich FCG NMC and NCA active material particles could substantially improve LIB performance and allow for increased upper cutoff voltage (UCV) during charging, which delivers significantly increased specific energy utilization. Our results show that Al2O3 coating improved the NMC cycling performance by 40% and the NCA cycling performance by 34% at 1C/₋1C with respectively 4.35V and 4.4V UCV in 2Ah pouch cells. High resolution TEM/SAED structural characterization revealed that Al 2 O 3 coatings prevented surface-initiated layered-to-spinel phase transitions in coated materials which were prevalent in uncoated materials. Lastly, EIS confirmed that Al 2 O 3 -coated materials had significantly lower increase in the charge transfer component of impedance during cycling. In conclusion, the ability to mitigate degradation mechanisms for Ni-rich NMC and NCA illustrated in this report provides insight into a method to enable the performance of high-voltage LIBs.

25 ENERGY STORAGE↗
DOE OSTI2020

Controlling Surface Phase Transition and Chemical Reactivity of O3-Layered Metal Oxide Cathodes for High-Performance Na-Ion Batteries

O3-layered metal oxides are promising cathode materials for high-energy Na-ion batteries (SIBs); however, they suffer from fast capacity fade. In this work, we develop a high-performance O3-NaNi 0.68 Mn 0.22 Co 0.10 O 2 cathode for SIBs toward practical applications by suppressing the formation of a rock salt layer at the cathode surface with an advanced electrolyte. The cathode can deliver a high specific capacity of ~196 mAh g –1 and demonstrates >80% capacity retention over 1000 cycles. NaNi 0.68 Mn 0.22 Co 0.10 O 2 –hard carbon full-cells with practical loading (>2.5 mAh cm –2 ) and lean electrolyte (~40 μL) demonstrate ~82% capacity retention after 450 cycles. A 60 mAh single-layer pouch cell has also been fabricated and demonstrated stable performance. This work represents a significant leap in SIB development and brings new insights to the development of advanced layered metal oxide cathodes for alkaline-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

An Investigation of Variables Affecting Plutonium Hydriding (20210946DI): Surface Phase Transitions and Reactions

Tusas was originally developed for phase field simulation of solidification (see [33, 6, 32]) and evolution of polycrystalline solid mechanics (see [16]). Tusas is particularly developed for PDEs compatible with structured or unstructured Lagrange (nodal) finite element discretizations and explicit (Euler) or implicit (Euler, Trapezoid, BDF2) temporal discretizations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Surface phases of the transition-metal dichalcogenide IrTe 2

Transition-metal dichalcogenide IrTe 2 has attracted attention because of its striped lattice, charge ordering, and superconductivity. We have investigated the surface structure of IrTe 2 , using low-energy electron diffraction and scanning tunneling microscopy. A complex striped lattice modulation as a function of temperature is observed, which shows hysteresis between cooling and warming. While the bulk 5 × 1 and 8 × 1 phases appear at high temperatures, the surface ground state has the 6 × 1 phase, not seen in the bulk, and the surface transition temperatures are distinct from the bulk. Here, the broken symmetry at the surface creates a quite different phase diagram, with the coexistence of several periodicities resembling devil's staircase behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

The fate of liquid crystal topological defects on chemically patterned surfaces during phase transitions

Controlling topological defects in liquid crystals (LCs) is an essential element in the development of areas such as directed self-assembly and micropatterning materials. However, during the phase transition on confined patterned surfaces, how the morphologies in one liquid crystalline phase change from deformations or defects into another phase is much less known. Here, we examine the fate of defects in a LC confined on a patterned surface during smectic-A–nematic and nematic–isotropic phase transitions, using experiments and simulation analyses. Upon heating from smectic-A to nematic, a Toric focal conical domain (TFCD) melts into a +1 converging boojum defect, which then transitioned into a concentric configuration as temperature increases, attributed to a steeper decrease of the bend and twist modulus compared to splay modulus. During cooling, TFCDs are developed from two distinct pathways depending on the cooling rates. Our continuum simulation recapitulates these transformations and provides elastic constant-based explanations for the two pathways. Although the phase transition pathways of defects are independent of the geometry of the confined patterns, the arrangement of FCDs is highly dependent on the size and shape of the patterns. Finally, taken together, this simple approach offers promising opportunities for tuning the micro- or nano-patterning of topological defects in liquid crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A sharp interface method for compressible liquid–vapor flow with phase transition and surface tension

The numerical approximation of non-isothermal liquid–vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevant physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Epitaxial TiO x Surface in Ferroelectric BaTiO 3 : Native Structure and Dynamic Patterning at the Atomic Scale

Surfaces and interfaces of ferroelectric oxides exhibit enhanced functionality, and therefore serve as a platform for novel nano and quantum technologies. Experimental and theoretical challenges associated with examining the subtle electro-chemo-mechanical balance at metal-oxide surfaces have hindered the understanding and control of their structure and behavior. Here, we combine advanced electron-microscopy and first-principles thermodynamics methods to reveal the atomic-scale chemical and crystallographic structure of the surface of the seminal ferroelectric BaTiO 3 . Here, we show that the surface is composed of a native < 2-nm thick TiOx rock-salt layer in epitaxial registry with the BaTiO 3 . Using electron-beam irradiation, we successfully patterned artificially TiO x sites with sub-nanometer resolution, by inducing Ba escape. Therefore, our work offers electro-chemo-mechanical insights into ferroelectric surface behavior in addition to a method for scalable high-resolution beam-induced chemical lithography for selectively driving surface phase transitions, and thereby functionalizing metal-oxide surfaces.

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

A Jacobian-free pseudo-arclength continuation method for phase transitions in inhomogeneous thermodynamic systems

Developing phase diagrams for inhomogeneous systems in thermodynamics is difficult, in part, due to the large phase space and the possibility of unstable and metastable solutions arising from first-order phase transitions. Pseudo-arclength continuation (PAC) is a method that allows one to trace out stable and unstable solutions of nonlinear systems. Typically, PAC utilizes the Jacobian in order to implement Newton (or quasi-Newton) steps. In this work, we present a Jacobian-free PAC method that is amenable to the usual workflows in inhomogeneous thermodynamics. We demonstrate our method in systems that have first-order phase transitions, including a novel example of polyelectrolyte complex coacervation in confinement, where multiple surface phase transitions occur and can overlap with one another.

Chemistry↗
NASA NTRS1986

Combustion theory for liquids with a free surface. 3: Special problems

Two special problems concerning the combustion of liquids with a free surface, i.e., flame quenching during the mixing of a burning liquid inside a container and liquid burnout from a porous layer, are analyzed using a quasi-one-dimensional model. The critical parameters corresponding to the quenching of a burning fluid with a free surface are determined. Determinations are also made of the limiting pressure gradients corresponding to the transition from the combustion mode where the liquid evaporates from the surface of a porous layer to the mode where the phase transition surface lies inside the porous layer.

Milkov, S. N.↗
DOE OSTI2019

An isogeometric finite element formulation for phase transitions on deforming surfaces

This paper presents a general theory and isogeometric finite element implementation for studying mass conserving phase transitions on deforming surfaces. The mathematical problem is governed by two coupled fourth-order nonlinear partial differential equations (PDEs) that live on an evolving two-dimensional manifold. For the phase transitions, the PDE is the Cahn–Hilliard equation for curved surfaces, which can be derived from surface mass balance in the framework of irreversible thermodynamics. For the surface deformation, the PDE is the (vector-valued) Kirchhoff–Love thin shell equation. Both PDEs can be efficiently discretized using C 1 -continuous interpolations without derivative degrees-of-freedom (dofs). Structured NURBS and unstructured spline spaces with pointwise C 1 -continuity are utilized for these interpolations. The resulting finite element formulation is discretized in time by the generalized-α scheme with adaptive time-stepping, and it is fully linearized within a monolithic Newton–Raphson approach. A curvilinear surface parameterization is used throughout the formulation to admit general surface shapes and deformations. The behavior of the coupled system is illustrated by several numerical examples exhibiting phase transitions on deforming spheres, tori and double-tori.

42 ENGINEERING↗
DOE OSTI2016

Tuning the Activity of Oxygen in LiNi 0.8 Co 0.15 Al 0.05 O 2 Battery Electrodes

Layered transition metal oxides such as LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) are highly desirable battery electrodes. However, these materials suffer from thermal runaway caused by deleterious oxygen loss and surface phase transitions at highly overcharged and overheated conditions, prompting serious safety concerns. Using in situ environmental transmission electron microscopy techniques, we demonstrate surface oxygen loss and structural changes in the highly overcharged NCA particles are suppressed by exposing them to an oxygen-rich environment. The onset temperature for the loss of oxygen from the electrode particle is delayed to 350 °C at oxygen gas overpressure of 400 mTorr. Similar heating of the particles in a reducing hydrogen gas demonstrated a quick onset of oxygen loss at 150 °C and rapid surface degradation of the particles. Lastly, the results reported here illustrate the fundamental materials science governing the failure processes of electrode particles and highlight possible strategies to circumvent such issues.

25 ENERGY STORAGE↗
DOE OSTI2019

Unveiling the Role of Al 2 O 3 in Preventing Surface Reconstruction During High-Voltage Cycling of Lithium-Ion Batteries

Recent achievements in high-energy batteries have been made by using Ni-rich NMC cathodes (LiNi x Mn y Co 1–x–y O 2 with x > 0.5) in conjunction with higher cell voltages. However, these gains have come at a cost of fast capacity fade and poor rate performace. In our previous study, we showed that Al 2 O 3 ALD coatings on LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) and LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathodes prevented surface phase transitions, reduced impedance, and extended cycle life in high voltage cells. In this work, neutron diffraction (ND), X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS) are used to fully investigate the mechanism by which ALD surface coatings mitigate NMC811 cathode degredation. Refinement of ND patterns indicated no changes in the bulk crystal structure of cycled cathodes with or without the Al 2 O 3 coating. Rather, the improved performance of ALD-coated cathodes is clearly due to surface stabilization. EELS established that all three transition metal oxidation states were reduced at the surface of the uncoated cathode after cycling, whereas the coated cathode showed no changes in surface oxidation states relative to the bulk. The surface coatings also prevented transition metal dissolution and crossover. XPS analysis of the anode harvested from cycled cells with uncoated cathodes showed significant amounts of Mn deposited within the SEI. In contrast, no Mn could be detected on the anodes cycled with coated cathodes. These results affirm that ALD coatings can effectively reduce the reactivity of the NMC surface and prevent detrimental side reactions that shorten battery cycle life.

25 ENERGY STORAGE↗