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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Navigating Organo-Lead Halide Perovskite Phase Space via Nucleation Kinetics toward a Deeper Understanding of Perovskite Phase Transformations and Structure-Property Relationships

Organo-lead halide perovskite photovoltaics have developed faster than our understanding of the material itself. Using the vast body of work on perovskite processing created in just the past few years, it is possible to create a better picture of this material's complex phase-transformation behavior. This concept article summarizes and correlates the current understanding of structural intermediates, kinetic controls, and structure–property relationships of organo-lead iodide perovskites. To this end, a new way of graphically relating information is developed, allowing the simultaneous mapping of schematic kinetic relationships between all currently prevailing perovskite deposition and growth techniques.

14 SOLAR ENERGY↗
DOE OSTI2025

Insights into the phase stability window, phase transformation behavior, and anisotropic thermal expansion of rhombohedral bismuth oxide

Rhombohedral bismuth oxide has emerged as a promising SOFC electrolyte material, particularly at low-to-intermediate temperatures. The stability window of this phase was explored using a co-doped system, using yttrium and lanthanum or aluminum, over 7.5–25 % total dopant content and 0.907–1.154 Å weighted average dopant cationic radius. The phase transformation behavior of rhombohedral-rich phase mixtures was also investigated in situ from 360 to 656 °C to assess the effects of minor impurity phases and thermal evolution pathways. Our results reveal that low-dopant, rhombohedral-rich compositions exhibit poor structural stability upon heating. Anisotropic thermal expansion behavior was observed over 450–656 °C, serving as a sensitive indicator of sequential phase changes, including the rhombohedral β2-to-β1 transition (∼450 °C), monoclinic phase formation, and delayed or incomplete formation of the cubic phase (∼ 550 °C). These multiple unfavorable phase transitions compromise the mechanical robustness required for SOFC operation. This study underscores the need for compositional tuning to balance ionic conductivity with thermal phase stability in rhombohedral Bi 2 O 3 -based systems.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Comments on 'Kinetic Study on the Hexacelsian-Celsian Phase Transformation'

A value of 20.1 +/- 4 kcal/mole for the activation energy (E) for the hexacelsian to celsian phase transformation in BaAl2Si2O8 was reported in an earlier work. In the present work, the earlier experimental data were reanalyzed and a much higher value of E was obtained. This revised E value is consistent with the transformation mechanism of a layered hexacelsian structure into a three-dimensional feldspar structure of celsian which would necessitate the breaking of the Si-O and/or the Al-O bonds.

Bansal, Narottam P.↗
DOE OSTI2020

Minimization of Atomic Displacements as a Guiding Principle of the Martensitic Phase Transformation

I this article, we present a unifying description for the martensitic transformation of steel that accounts for important experimentally observable features of the transformation, namely, the Neumann bands, the interfacial (habit) plane between the transformed and untransformed phases and their orientation relationship. It is obtained through a simple geometric minimization of the total distance traveled by all the atoms from the austenite (fcc or γ) phase to the martensite (bcc or α) phase, without the need for any explicit energy minimization. Our description unites previously proposed mechanisms but it does not rely on assumptions and experimental knowledge regarding the shear planes and directions, or external adjustable parameters. We show how the Kurdjumov-Sach orientation relationship between the two phases and the {225}$_γ$ habit plane, which have both been extensively reported in experiments, naturally emerge from the distance minimization. We also propose an explanation for the occurrence of a different orientation relationship (Pitsch) in thin films.

CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS↗
DOE OSTI2018

The Phase Transformation Wave and Conditions of Its Realization in Deformable Austenitic Steels Irradiated in a BN-350 Reactor

Experimental data on the influence of neutron irradiation on the plasticity characteristics of chromium–nickel austenite steels have been analyzed. Special attention is devoted to detection of anomalously high plasticity levels attained at some parameters of irradiation and deformation, which is explained by the formation and propagation of a “phase transformation wave” in the metastable steel. Necessary and sufficient conditions for the realization of this wave are formulated.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Titanium α-ω phase transformation pathway and a predicted metastable structure

A titanium is a highly utilized metal for structural lightweighting and its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT + U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We also find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Intergranular precipitation-enhanced wetting and phase transformation in an Al0.4CoCrFeNi high-entropy alloy exposed to lead-bismuth eutectic

We report after exposure to oxygen-poor (10 -13 –10 -14 wt%) liquid lead-bismuth eutectic (LBE) at 500 °C for 500 h, LBE penetrates more than one order of magnitude deeper in an FCC Al 0.4 CoCrFeNi high-entropy alloy (HEA) decorated with a network of BCC (Ni, Al)-rich intergranular (IG) precipitates than in a single-phase, FCC Al 0.3 CoCrFeNi HEA without the IG precipitate network. This deterioration of corrosion resistance is attributed to the energetic nature of the BCC/FCC interphase boundaries (IBs) and resultant IB wetting. The LBE ingress film selectively leaches nickel located at those low-indexed crystalline planes, resulting in phase transformation from FCC to BCC structure.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Phase transformations in ion-irradiated silicides

The present investigation has three objectives. The first is concerned with the phase transformation of CoSi2 under ion implantation and the subsequent crystallization characteristics during annealing, taking into account epitaxial and nonepitaxial recrystallization behavior. The second objective is related to a study of the general trend of implantation-induced damage and crystallization behavior for a number of commonly used silicides. The last objective involves a comparison of the recrystallization behavior of cosputtered refractory silicides with that of the ion-implanted silicides. It was found that epitaxial regrowth of ion-irradiated CoSi2 occurred for samples with an epitaxial seed left at the Si/CoSi2 interface. A structural investigation of CoSi2 involving transmission electron microscopy (TEM) showed that after high-dose implantation CoSi2 is amorphous.

Hewett, C. A.↗
DOE OSTI2023

Phase transformations and thermal expansion coefficients of unirradiated U-X wt.% Zr (X = 6, 10, 20, 30) measured via neutron diffraction

This work characterizes the crystallographic evolution of unirradiated U-X wt.% Zr (X = 6, 10, 20, 30) while cooling from equilibration, single phase γ-U-Zr, at 900 °C to ambient temperature using time-of-flight neutron diffraction. The β-U phase was unobserved during cooling at 1 °C/min in all alloys. All alloys followed the phase transformation pathway of γ-U-Zr→γ-U-Zr+α-U→α-U +δ-UZr2 with an observed miscibility gap in γ-U-Zr. The α-U and δ-UZr2 transformation took place simultaneously in the U-30 wt.% Zr sample. These findings strengthen the need to re-approach the U-Zr phase diagram in entirety. Bulk volumetric CTEs agree well with published data, strengthening the quantification of lattice-specific CTEs reported in this study. A compositionally dependent discontinuity in thermal expansion, increasing in magnitude with decreasing U content, occurs during the γ-U-Zr→α-U+δ-UZr2 transformation. The γ-U-Zr lattice parameter was measured to have a compositional dependency.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermomechanical Analysis of A-TIG and MP-TIG Welding of 2.25Cr-1Mo Steel Considering Phase Transformation

In the present study, a finite element-based 3D mesh model is used to simulate the effect of welding processes on the temperature distribution, residual stress and distortion in 11-mm-thick 2.25Cr-1Mo steel weld joints. Tungsten inert gas (TIG) and activated-TIG (A-TIG) welding processes were employed for the fabrication of weld joints. Austenite-to-bainite phase transformation is taken into account in the numerical analysis. The heat input fitting tool has been used to calibrate the heat source by matching the simulated weld bead with that of the actual weld bead. Peak temperature was higher at the weld center for A-TIG weld joint, and the weld joint exhibited a sharp temperature gradient at the weld interface. There was good agreement between the predicted and measured thermal cycles. A-TIG and multipass-TIG (MP-TIG) weld joints exhibited similar longitudinal residual stresses in heat affected zone with a difference of 50 MPa. Moreover, A-TIG weld joint fabricated by double-side welding technique employing two passes exhibited reduced distortion than MP-TIG weld joints. A higher magnitude of distortion was in MP-TIG weld joint which was attributed to more weld metal volume caused by more number of weld passes required to fill the V-groove. There was good agreement between the predicted and measured residual stress and distortion values.

36 MATERIALS SCIENCE↗
DOE OSTI2017

ε- and β-LiVOPO 4 : Phase Transformation and Electrochemistry

In this paper, ε- and β-LiVOPO 4 were synthesized from the same precursor at different temperatures in an air atmosphere. ε-LiVOPO 4 is obtained at 400 and 700 °C. The 700 °C sample has better purity and crystallinity, but the 400 °C sample has a little better electrochemical performance due to its smaller particle size and the conducting carbon residue in the sample. β-LiVOPO 4 is formed between the above two temperatures, which gives slightly lower capacity than that of the ε-LiVOPO 4 sample, indicating higher kinetics of the lithium reaction for the ε phase than those of the β one. The phase transformation from ε to β then back reversibly to ε was also observed by ex situ X-ray diffraction. Finally, this thermal study verifies that ε-LiVOPO 4 is the more stable phase for LiVOPO 4 ; however, reaction kinetics control the phases formed at lower temperatures.

25 ENERGY STORAGE↗
DOE OSTI2017

TEM study of the martensitic phases in the ductile DyCu and YCu intermetallic compounds [The martensitic phase transformation in ductile DyCu and YCu intermetallic compounds]

DyCu and YCu are representatives of the family of CsCl-type B2 rare earth intermetallic compounds that exhibit high room temperature ductility. Structure, orientation relationship, and morphology of the martensites in the equiatomic compounds DyCu and YCu are examined using transmission electron microscopy (TEM). TEM studies show that the martensite structures in DyCu and YCu alloys are virtually identical. The martensite is of orthorhombic CrB-type B33 structure with lattice parameters a = 0.38 nm, b = 1.22 nm, and c = 0.40 nm. (021¯) twins were observed in the B33 DyCu and YCu martensites. The orientation relationship of B33 and B2 phases is (111¯)[112]B33 || (110)[001]B2. The simulated electron diffraction patterns of the B33 phase are consistent with those of experimental observations. TEM investigations also reveal that a dominant orthorhombic FeB-type B27 martensite with lattice parameters a = 0.71 nm, b = 0.45 nm, and c = 0.54 nm exists in YCu alloy. (11¯ 1) twins were observed in the B27 YCu martensite. As a result, the formation mechanism of B2 to B33 and B2 to B27 phase transformation is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mesocrystalline Ordering and Phase Transformation of Iron Oxide Biominerals in the Ultrahard Teeth of Cryptochiton stelleri

Biological organisms naturally synthesize complex, hierarchical, multifunctional materials through mineralization processes at ambient conditions and under physiological pH. One such example is the ultrahard and wear-resistant radular teeth found in mollusks, which are used to scape against the rock to feed on algae. Herein, the biologically controlled structural development of the hard, outer magnetite-containing shell of the chitin teeth is revealed. Specifically, the formation of a series of mesocrystalline iron oxide phases, templated by chitin-binding proteins, is identified. The initial domains, consisting of ferrihydrite mesocrystals with a spherulite-like morphology, undergo a solid-state phase transformation to form magnetite while maintaining mesocrystallinity, likely via a shear-induced solid-state reaction, without any noticeable architectural changes. Subsequent growth via Ostwald ripening leads to nearly single-crystalline rod-like elements. In addition, an interpenetrating organic matrix is identified that, at early stages of tooth development, potentially contains iron-binding proteins that guide the self-assembly of the mesocrystalline mineral and influence the preferred orientation of the later-formed magnetite nanorods, which ultimately determines the mechanical behavior of the mature chiton teeth.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Revealing the Structural Evolution and Phase Transformation of O3-Type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 Cathode Material on Sintering and Cycling Processes

O-type layered oxide cathode materials can be easily synthesized for a full sodium stoichiometry with high specific capacity, but they all suffer from a capacity fade on cycling. The sintering process control and optimization are critical to ensure a high quality and consistency of the prepared cathode materials with stable structure. Herein, in situ high-energy X-ray diffraction (HEXRD) was first employed to investigate the phase evolution of the oxides during the sintering process of O3-type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 . The in situ HEXRD and both operando Bragg coherent diffraction (BCXD) and coherent multicrystal diffraction (CMCD) were utilized to investigate the phase transformation of the cathode materials during the sodiation/desodiation process. A composite structure comprised of O-type and P-type oxides was formed after the initial electrochemical activation of the cathode material, resulting in good structural and electrochemical stability. This finding implies that strain engineering can be a new design philosophy for the development of next generation high-performance sodium ion cathodes.

25 ENERGY STORAGE↗
DOE OSTI2018

Effects of Heating and Quenching Processing Parameters on Phase Transformation of 55CrMo Steel

Microstructure and mechanical properties after induction hardening have a significant effect on the wear resistance performance and lifetime of 55CrMo steel ball screw. In the paper, the dilatometric curves were recorded at the different heating rate by a Gleeble-1500D thermo-mechanical simulator to determine the effect of heating rate on the austenitizing temperature of 55CrMo steel. Heat treatment of some specimens was performed by the Gleeble-1500D thermal simulator at the different heating temperature, holding time and cooling rate to investigate the effect of induction hardening parameters on the phase transformation, microstructure and microhardness of 55CrMo steel. Microstructure of specimen was analyzed using an optical microscope and a scanning electron microscope. Volume fraction of retained austenite was measured using an x-ray diffractometer. The mechanical properties were evaluated by a microhardness tester. The results show that the austenitizing temperature of 55CrMo steel increases with the increasing heating rate. Increasing the heating temperature, holding time and cooling rate of specimen is helpful in obtaining a uniform cryptocrystalline martensite. Volume fraction of retained austenite is less as the heating temperature is in the range of 900-950 °C. In the induction hardening of 55CrMo steel, the heating temperature should be in the range of 900-1000 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni–Ti–Cu–V Quaternary Thin-Film Library

Ni–Ti–based shape memory alloys (SMAs) have found widespread use in the last 70 years, but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their processed shape as a result of a reversible martensitic transformation, SMAs are highly sensitive to compositional variations. Alloying with ternary and quaternary elements to fine-tune the lattice parameters and the thermal hysteresis of an SMA, therefore, becomes a challenge in materials exploration. Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques. In this study, a composition spread of Ni–Ti–Cu–V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer. Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy, synchrotron X-ray diffraction, and temperature-dependent resistance measurements. Of the 177 compositions in the materials library, 32 were observed to have shape memory effect, of which five had zero or near-zero thermal hysteresis. These compositions provide flexibility in the operating temperature regimes that they can be used in. A phase map for the quaternary system and correlations of functional properties are discussed with respect to the local microstructure and composition of the thin-film library.

42 ENGINEERING↗
DOE OSTI2015

Self-assembly of tin wires via phase transformation of heteroepitaxial germanium-tin on germanium substrate

This work demonstrates and describes for the first time an unusual strain-relaxation mechanism by the formation and self-assembly of well-ordered tin wires during the thermal annealing of epitaxial Ge{sub 0.83}Sn{sub 0.17}-on-Ge(001) substrate. Fully strained germanium-tin alloys (Ge{sub 0.83}Sn{sub 0.17}) were epitaxially grown on Ge(001) substrate by molecular beam epitaxy. The morphological and compositional evolution of Ge{sub 0.83}Sn{sub 0.17} during thermal annealing is studied by atomic force microscopy, X-ray diffraction, transmission electron microscopy. Under certain annealing conditions, the Ge{sub 0.83}Sn{sub 0.17} layer decomposes into two stable phases, and well-defined Sn wires that are preferentially oriented along two orthogonal 〈100〉 azimuths are formed. The formation of the Sn wires is related to the annealing temperature and the Ge{sub 0.83}Sn{sub 0.17} thickness, and can be explained by the nucleation of a grain with Sn islands on the outer front, followed by grain boundary migration. The Sn wire formation process is found to be thermally activated, and an activation enthalpy (E{sub c}) of 0.41 eV is extracted. This thermally activated phase transformation, i.e., 2D epitaxial layer to 3D wires, occurs via a mechanism akin to “cellular precipitation.” This synthesis route of Sn wires opens new possibilities for creation of nanoscale patterns at high-throughput without the need for lithography.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗