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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Experimental Investigation of Microstructure and Phase Transitions in Ag-Cu-Zn Brazing Alloys

Microstructure and phase transitions of selected brazing alloys from the Ag-Cu-Zn ternary system were investigated. Four ternary alloys with silver content in the compositional range from 25 to 60 wt.% were studied using x-ray diffraction (XRD) and scanning electron microscopy coupled with the energy-dispersive spectroscopy (SEM–EDS). Phase transitions of the investigated alloys were measured using differential scanning calorimetry (DSC). Experimentally obtained results were compared with the results of a thermodynamic calculation of the phase equilibria according to the CALPHAD method. The experiments confirmed the optimized thermodynamic parameters for the calculations from the thermodynamic assessment in literature. Phase compositions, liquidus and solidus temperatures were confirmed by the EDS and DTA methods. Additionally, the calculated solidification paths and predicted phase transformations were in agreement with the SEM images.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Observation of stacking engineered magnetic phase transitions within moiré supercells of twisted van der Waals magnets

Abstract Recent demonstrations of moiré magnetism, featuring exotic phases with noncollinear spin order in the twisted van der Waals (vdW) magnet chromium triiodide CrI 3 , have highlighted the potential of twist engineering of magnetic (vdW) materials. However, the local magnetic interactions, spin dynamics, and magnetic phase transitions within and across individual moiré supercells remain elusive. Taking advantage of a scanning single-spin magnetometry platform, here we report observation of two distinct magnetic phase transitions with separate critical temperatures within a moiré supercell of small-angle twisted double trilayer CrI 3 . By measuring temperature-dependent spin fluctuations at the coexisting ferromagnetic and antiferromagnetic regions in twisted CrI 3 , we explicitly show that the Curie temperature of the ferromagnetic state is higher than the Néel temperature of the antiferromagnetic one by ~10 K. Our mean-field calculations attribute such a spatial and thermodynamic phase separation to the stacking order modulated interlayer exchange coupling at the twisted interface of moiré superlattices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

An investigation of shock-induced phase transition in soda-lime glass

There exists a large body of evidence from experiments and molecular dynamics simulations to suggest the occurrence of phase transitions in soda-lime glass (SLG) and other silica glasses subject to shock compression to pressures above 3 GPa. In light of these findings, the current work investigated the existence of phase transition in SLG using shock and release experiments. The experiments employed symmetric SLG–SLG impact to achieve complete unloading to zero stress after shock compression to stresses in the range of 3–7 GPa. The stress–strain response and the Lagrangian release wave speed behavior of SLG obtained from these experiments are seen to reveal a mismatch between the loading and unloading paths of the pressure–strain curve for the material, which serves as compelling evidence for the occurrence of a shock-induced phase transition in the material at relatively low pressures. Furthermore, the release wave speed vs strain data obtained from experiments were used to construct a methodology for modeling the shock and release behavior of SLG. Lastly, this scheme implemented in numerical simulations was able to capture the release behavior of shock compressed SLG, for which a robust and satisfactory model was previously unavailable.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Comprehensive study of the magnetic phase transitions in Tb 3 Co combining thermal, magnetic and neutron diffraction measurements

A comprehensive study of the magnetic phase transitions in Tb 3 Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe 3 C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T 2 ≈ 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the crystallographic c-axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb 3 Co is a competitive magnetocaloric material in this temperature range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Structural and magnetic phase transition in samarium hydrogen system SmH{sub x} (x=1, 2, 3)

We report ab-initio calculations for the structural and magnetic phase transition of SmH{sub x} (x= 1, 2, 3) using the Vienna ab-initio simulation package (VASP). The non-spin polarized (NSP) and spin polarized (SP) calculations are performed for these hydrides at normal and high pressure. It is found that these compounds are stable in ferromagnetic state at normal pressure. The calculated lattice parameters and bulk modulus of these hydrides are in good agreement with the available experimental results. A pressure-induced structural phase transition from cubic to hexagonal phase in SmH and SmH{sub 2} and hexagonal to cubic phase in SmH{sub 3} is predicted. A pressure-induced ferromagnetic to nonmagnetic phase transition is observed in SmH, SmH{sub 2} and SmH{sub 3} at the pressures of 104 GPa, 76 GPa and 81 GPa respectively. Ferromagnetism is quenched in mono, di and tri hydrides at high pressures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

X-ray tracking of structural changes during a subnanosecond solid-solid phase transition in cobalt nanoparticles

This work presents measurements of laser-induced solid-solid phase transitions in Co nanoparticles, using time-resolved wide-angle x-ray scattering with <100-ps time resolution. A comparison of the experimental results with scattering simulations indicates a phase transition from the as-synthesized ε phase into a mixed phase of 2/3 hcp and 1/3 fcc character during the first 100 ps. The measured scattering signal observed at the shortest investigated time delay of 20 ps has less scattering intensity at the dominant fcc/hcp Bragg peak positions compared to the difference signal acquired at 100 ps. This suggests the formation of a partially disordered solid intermediate phase on the sub-100-ps timescale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Gravitational wave signals of electroweak phase transition triggered by dark matter

We study in this work a scenario that the universe undergoes a two step phase transition with the first step happened to the dark matter sector and the second step being the transition between the dark matter and the electroweak vacuums, where the barrier between the two vacuums, that is necessary for a strongly first order electroweak phase transition (EWPT) as required by the electroweak baryogenesis mechanism, arises at the tree-level. We illustrate this idea by working with the standard model (SM) augmented by a scalar singlet dark matter and an extra scalar singlet which mixes with the SM Higgs boson. We study the conditions for such pattern of phase transition to occur and especially for the strongly first order EWPT to take place, as well as its compatibility with the basic requirements of a successful dark matter, such as observed relic density and constraints of direct detections. We further explore the discovery possibility of this pattern EWPT by searching for the gravitational waves generated during this process in spaced based interferometer, by showing a representative benchmark point of the parameter space that the generated gravitational waves fall within the sensitivity of eLISA, DECIGO and BBO.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Cubic to tetragonal phase transition of Tm{sup 3+} doped nanocrystals in oxyfluoride glass ceramics

Tm{sup 3+} ions doped β-PbF{sub 2} nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm{sup 3+} doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an O{sub h} to D{sub 4h} site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm{sup 3+} doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Negative Thermal Expansion, Response to Pressure and Phase Transitions in CaTiF 6

Strong volume negative thermal expansion over a wide temperature range typically only occurs in ReO 3 -type fluorides that retain an ideal cubic structure to very low temperatures, such as ScF 3 , CaZrF 6 , CaHfF 6 , and CaNbF 6 . In this work, CaTiF 6 was examined in an effort to expand this small family of materials. However, it undergoes a cubic ($Fm\overline{3}m$) to rhombohedral ($R\overline3$) transition on cooling to ~120 K, with a minimum volume coefficient of thermal expansion (CTE) close to –42 ppm K –1 at 180 K and a CTE of about –32 ppm K –1 at room temperature. On compression at ambient temperature, the material remains cubic to ~0.25 GPa with K 0 = 29(1) GPa and K' 0 = –50(5). Cubic CaTiF 6 is elastically softer and shows more pronounced pressure induced softening, than both CaZrF 6 and CaNbF 6 . In sharp contrast to both CaZrF 6 and CaNbF 6 , CaTiF 6 undergoes a first-order pressure induced octahedral tilting transition to a rhombohedral phase ($R\overline3$) on compression above 0.25 GPa, which is closely related to that seen in ScF 3 . Just above the transition pressure, this phase is elastically very soft with a bulk modulus of only ~4 GPa as octahedral tilting associated with a reduction in the Ca–F–Ti angles provides a low energy pathway for volume reduction. This volume reduction mechanism leads to highly anisotropic elastic properties, with the rhombohedral phase displaying both a low bulk modulus and negative linear compressibility parallel to the crystallographic c -axis for pressures below ~2.5 GPa. At ~3 GPa, a further phase transition to a poorly ordered phase occurs.

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

[N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4}: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy

The X-ray powder diffraction pattern shows that at room temperature, [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T{sub 1} = 255 K, T{sub 2} = 282 K, T{sub 3} = 302 K, T{sub 4} = 320 K, and T{sub 5} = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10{sup −1}–10{sup 7 }Hz frequency range and 233–363 K temperature intervals. The temperature dependence of the dielectric constant at different temperatures proved that this compound is ferroelectric below 282 K. Besides, [N(CH{sub 3}){sub 3 }H]{sub 2}ZnCl{sub 4} shows classical ferroelectric behaviour near curie temperature. In order to characterize the phase transitions, Raman spectra have been recorded in the temperature range of 233–383 K and the frequency range related to the internal and external vibrations of the cations and anions (90–4000 cm{sup −1}). The temperature dependence of the Raman line shifts ν and the half-width Δν detects all phase transitions and confirms their nature, especially at 282 K that corresponds to the ferroelectric-paraelectric phase transition.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pressure induced phase transition and elastic properties of cerium mono-nitride (CeN)

In the present paper, we have investigated the high-pressure structural phase transition and elastic properties of cerium mono-nitride. We studied theoretically the structural properties of this compound (CeN) by using the improved interaction potential model (IIPM) approach. This compound exhibits first order crystallographic phase transition from NaCl (B{sub 1}) to tetragonal (BCT) phase at 37 GPa. The phase transition pressures and associated volume collapse obtained from present potential model (IIPM) show a good agreement with available theoretical data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Phase transitions of cesium azide at pressures up to 30 GPa studied using in situ Raman spectroscopy

Cesium azide has been studied by Raman spectroscopy at pressures up to ≈30 GPa at room temperature. The sequence of phase transitions to Phase III (at 0.5 GPa), Phase IV (at 4.3 GPa), and Phase V (at ≈19 GPa) has been observed in agreement with recent X-ray diffraction studies. Phase III has been found to adopt a monoclinic C2/m structure with two azide anions in nonequivalent positions, where one set of azide anions appears to be orientationally disordered according to the observed Raman spectra. The transition to Phase IV has been associated with orientational ordering of azide anions, while the transition to Phase V has been shown to proceed with a lowering of crystal symmetry. Moreover, spectroscopic features indicate a possible change of bonding in CsN{sub 3} toward formation of covalent bonds at high pressures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Boosting electrochemical reaction and suppressing phase transition with a high-entropy O3-type layered oxide for sodium-ion batteries

Complex phase transitions induced by interlayer slides in layered cathode materials lead to poor cycling stability and rate capability for sodium-ion batteries. Herein, we design and prepare a new six-component high-entropy oxide (HEO) layered cathode O3–Na(Fe 0.2 Co 0.2 Ni 0.2 Ti 0.2 Sn 0.1 Li 0.1 )O 2 to enable highly reversible electrochemical reaction and phase-transition behavior. The HEO cathode exhibits good cycling performance (capacity retention of ~81% after 100 cycles at 0.5C) and outstanding rate capability (capacity of ~81 mA h g –1 at 2.0C) due to the higher sodium diffusion coefficient (above 5.75 × 10 –11 cm 2 s –1 ) than most reported O3-type cathodes. Moreover, the high-entropy cathode has superior compatibility with the hard carbon anode and delivers a specific capacity of 90.4 mA h g –1 (energy density of ~267.5 W h kg –1 ). Ex situ X-ray diffraction proves that the high-entropy designing effectively suppresses the intermediate phase change to achieve reversible O3–P3 phase evolution, and in turn stabilizes the layered structure. X-ray absorption spectroscopy and Mössbauer spectrum of 57 Fe suggest that Ni 2+ /Ni 3.5+ , Co 3+ /Co 3.5+ , and part of Fe 3+ /Fe 3.5+ redox reaction contribute the charge compensation. Finally, the enhanced performance can be attributed to the disordered distribution of multi-component transition metals in HEO suppressing the ordering of electric charges and sodium vacancies, thereby inhibiting the interlayer slide and phase transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

Microgravity Studies of Liquid-Liquid Phase Transitions in Alumina-Yttria Melts

The scientific objective of this research is to increase the fundamental knowledge base for liquid- phase processing of technologically important oxide materials. The experimental objective is to define conditions and hardware requirements for microgravity flight experiments to test and expand the experimental hypotheses that: 1. Liquid phase transitions can occur in undercooled melts by a diffusionless process. 2. Onset of the liquid phase transition is accompanied by a large change in the temperature dependence of melt viscosity. Experiments on undercooled YAG (Y3A15012)- and rare earth oxide aluminate composition liquids demonstrated a large departure from an Arrhenian temperature dependence of viscosity. Liquid YAG is nearly inviscid at its 2240 K melting point. Glass fibers were pulled from melts undercooled by ca. 600 K indicating that the viscosity is on the order of 100 Pans (1000 Poise) at 1600 K. This value of viscosity is 500 times greater than that obtained by extrapolation of data for temperatures above the melting point of YAG. These results show that the liquids are extremely fragile and that the onset of the highly non-Arrhenian viscosity-temperature relationship occurs at a temperature considerably below the equilibrium melting point of the solid phases. Further results on undercooled alumina-yttria melts containing 23-42 mole % yttrium oxide indicate that a congruent liquid-liquid phase transition occurs in the undercooled liquids. The rates of transition are inconsistent with a diffusion-limited process. This research is directed to investigation of the scientifically interesting phenomena of polyamorphism and fragility in undercooled rare earth oxide aluminum oxide liquids. The results bear on the technologically important problem of producing high value rare earth-based optical materials.

Guynes, Buddy↗
DOE OSTI2022

Phase Transition and Criticality of Methane Confined in Nanopores

For the first time, the phase transition and criticality of methane confined in nanoporous media are measured. The measurement is performed by establishing an experimental setup utilizing a differential scanning calorimeter (DSC) capable of operating under very low temperatures as well as high pressures to detect the capillary phase transition of methane inside nanopores. By performing experiments along isochoric cooling paths, both the capillary condensation and the bulk condensation of methane are detected. Here, the pore critical point (PCP) of nanoconfined methane is also determined and then used to derive the parameters of a previously developed self-consistent equation of state based on the Generalized van der Waals (vdW) partition function. Using this parameter, the equation of state can predict the capillary-condensation curves that agree well with the experimental data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Kibble-Zurek mechanism for nonequilibrium phase transitions in driven systems with quenched disorder

Abstract We show that the Kibble-Zurek mechanism applies to nonequilibrium phase transitions found in driven assemblies of superconducting vortices and colloids moving over quenched disorder where a transition occurs from a plastic disordered flowing state to a moving anisotropic crystal. We measure the density of topological defects as a function of quench rate through the nonequilibrium phase transition, and find that on the ordered side of the transition, the topological defect density ρ d scales as a power law, $${\rho }_{{{{{{{{\rm{d}}}}}}}}}\propto 1/{t}_{{{{{{{{\rm{q}}}}}}}}}^{\beta }$$ ρ d ∝ 1 / t q β , where t q is the quench time duration, consistent with the Kibble-Zurek mechanism. We show that scaling with the same exponent holds for varied strengths of quenched disorder and that the exponents fall in the directed percolation universality class. Our results suggest that the Kibble-Zurek mechanism can be applied to the broader class of systems that exhibit absorbing phase transitions.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Quantum phase transition in solid hydrogen at high pressure

Extensive experimental and theoretical studies have been devoted to determining the high-pressure phase diagram of hydrogen. Here we present evidence of a phase at a higher pressure than phase III and below the pressure of the recently observed phase of metallic hydrogen (495 GPa). This phase was determined from infrared (IR) spectroscopy of hydrogen samples at static pressures above 360 ± 15 GPa in a diamond anvil cell, and has been observed in three separate experiments. Whereas earlier studies found new high-pressure phases that only occurred at elevated temperatures, this phase transition occurs at the lowest temperatures investigated, ~5 K, and the steep phase line indicates that it is a quantum phase transition. This phase is characterized by two distinct IR absorption bands (2950 and 3335 c m –1 at 365 GPa). Above the transition pressure we observe strong darkening of the sample in the visible spectrum as pressure is increased. Observations are compatible with the cmca-12 crystal structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structure, phase transitions, and isotope effects in [(CH3)4N]2PuCl6

The single crystal X-ray diffraction structure of [(CH3)4N]2PuCl6 is presented for the first time, resolving long standing confusion and speculation regarding the structure of this compound in the literature. A temperature dependent study of this compound shows that the structure of [(CH3)4N]2PuCl6 undergoes no fewer than two phase transitions between 100 and 360 K. The phase of [(CH3)4N]2PuCl6 at room temperature is Fd-3c a = 26.012(3) Å. At 360 K, the structure is in space group Fm-3m with a = 13.088(1) Å. The plutonium octahedra and tetramethylammonium cations undergo a rotative displacement and the degree of rotation varies with temperature, giving rise to the phase transition from Fm-3m to Fd-3c as the crystal is cooled. Synthesis and structural studies of the deuterated salt [(CD3)4N]2PuCl6 suggest that there is an isotopic effect associated with this phase transition as revealed by a changing transition temperature in the deuterated versus protonated compound indicating that the donor-acceptor interactions between the tetramethylammonium cations and the hexachloroplutonate anions are driving the phase transformation.

crystallography↗