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Results for “structural phase transition”

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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Temperature scaling in the quantum-Hall-effect regime in a HgTe quantum well with an inverted energy spectrum

The longitudinal and Hall magnetoresistances of HgTe/HgCdTe heterostructures with an inverted energy spectrum (the HgTe quantum well width is d = 20.3 nm) are measured in the quantum-Hall-effect regime at T = 2–50 K in magnetic fields up to B = 9 T. Analysis of the temperature dependences of conductivity in the transition region between the first and second plateaus of the quantum Hall effect shows the feasibility of the scaling regime for a plateau–plateau quantum phase transition in 2D-structures on the basis of mercury telluride.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Directional effects of antiferromagnetic ordering on the electronic structure in NdSb

The recent discovery of unconventional surface-state pairs, which give rise to Fermi arcs and spin textures, in antiferromagnetically ordered NdBi raised the interest in rare-earth monopnictides. Several scenarios of antiferromagnetic (AFM) order have been suggested to explain the origin of these states with some of them being consistent with the presence of nontrivial topologies. Here, in this paper, we use angle-resolved photoemission spectroscopy (ARPES) and density-functional-theory (DFT) calculations to investigate the electronic structure of NdSb. We found the presence of distinct domains that have different electronic structures at the surface. These domains correspond to different orientations of magnetic moments in the AFM state with respect to the surface. We demonstrated remarkable agreement between DFT calculations and ARPES that capture all essential changes in the band structure caused by the transition to a magnetically ordered state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural evolution in the crystallization of rapid cooling silver melt

The structural evolution in a rapid cooling process of silver melt has been investigated at different scales by adopting several analysis methods. The results testify Ostwald’s rule of stages and Frank conjecture upon icosahedron with many specific details. In particular, the cluster-scale analysis by a recent developed method called LSCA (the Largest Standard Cluster Analysis) clarified the complex structural evolution occurred in crystallization: different kinds of local clusters (such as ico-like (ico is the abbreviation of icosahedron), ico-bcc like (bcc, body-centred cubic), bcc, bcc-like structures) in turn have their maximal numbers as temperature decreases. And in a rather wide temperature range the icosahedral short-range order (ISRO) demonstrates a saturated stage (where the amount of ico-like structures keeps stable) that breeds metastable bcc clusters. As the precursor of crystallization, after reaching the maximal number bcc clusters finally decrease, resulting in the final solid being a mixture mainly composed of fcc/hcp (face-centred cubic and hexagonal-closed packed) clusters and to a less degree, bcc clusters. This detailed geometric picture for crystallization of liquid metal is believed to be useful to improve the fundamental understanding of liquid–solid phase transition. - Highlights: • A comprehensive structural analysis is conducted focusing on crystallization. • The involved atoms in our analysis are more than 90% for all samples concerned. • A series of distinct intermediate states are found in crystallization of silver melt. • A novelty icosahedron-saturated state breeds the metastable bcc state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Predicting hidden bulk phases from surface phases in bilayered Sr 3 Ru 2 O 7

The ability to predict hidden phases under extreme conditions is not only crucial to understanding and manipulating materials but it could also lead to insight into new phenomena and novel routes to synthesize new phases. This is especially true for Ruddlesden-Popper perovskite phases that possess interesting properties ranging from superconductivity and colossal magnetoresistance to photovoltaic and catalytic activities. In particular, the physical properties of the bilayer perovskite Sr 3 Ru 2 O 7 at the surface are intimately tied to the rotation and tilt of the RuO 6 octahedra. In order to take advantage of the extra degree of freedom associated with tilting we have performed first principles hybrid density functional simulations of uniaxial pressure applied along the c-axis of bulk Sr 3 Ru 2 O 7 where we find that the octahedra become tilted, leading to two phase transitions. One is a structural transition at ~1.5 GPa, and the other is from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) insulator at ~21 GPa whose AFM spin configuration is different from the AFM state near the FM ground state.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermal and Magnetic Field Switching in a Two-Step Hysteretic Mn III Spin Crossover Compound Coupled to Symmetry Breakings

In this work, a Mn III spin crossover complex with atypical two-step hysteretic thermal switching at 74 K and 84 K shows rich structural–magnetic interplay and magnetic-field-induced spin state switching below 14 T with an onset below 5 T. The spin states, structures, and the nature of the phase transitions are elucidated via X-ray and magnetization measurements. An unusual intermediate phase containing four individual sites, where 1\4 are in a pure low spin state, is observed. The splitting of equivalent sites in the high temperature phase into four inequivalent sites is due to a structural reorganization involving a primary and a secondary symmetry-breaking order parameter that induces a crystal system change from orthorhombic→monoclinic and a cell doubling. Further cooling leads to a reconstructive phase transition and a monoclinic low-temperature phase with two inequivalent low-spin sites. The coupling between the order parameters is identified in the framework of Landau theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Interplay of electronic, magnetic, and structural properties of GdB 6 from first principles

Gadolinium hexaboride (GdB 6 ) is a well-known field emitter material that has been investigated for more than three decades. We perform a systematical density-functional theory study of GdB 6 by using the generalized-gradient approximation and considering the electron interaction parameter U. The basic structural and electronic properties are carefully revised, as well as a strong U-value dependence in determining the antiferromagnetic (AFM) magnetic structures of Gd 4f electronic states. We found a small U(0 ~ 3 eV) showing the most consistent experimental ground-state properties, which gives rise to a magnetic structure with a ground state of C-AFM and a second stable E-AFM. Moreover, we find the distortion modes of boron octahedron play an important role in the interaction between spin and lattice structures in this system. Furthermore, these results will deepen our understanding of the boron-based correlated rare earth compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

High-pressure phase transition of olivine-type Mg 2 GeO 4 to a metastable forsterite-III type structure and their equations of state

Germanates are often used as structural analogs of planetary silicates. We have explored the high-pressure phase relations in Mg 2 GeO 4 using diamond-anvil cell experiments combined with synchrotron X-ray diffraction and computations based on density functional theory. Upon room temperature compression, forsterite-type Mg 2 GeO 4 remains stable up to 30 GPa. At higher pressures, a phase transition to a forsterite-III type (Cmc2 1 ) structure was observed, which remained stable to the peak pressure of 105 GPa. Using a third-order Birch Murnaghan fit to the experimental data, we obtained V 0 = 305.1(3) Å3, K 0 = 124.6(14) GPa, and $K'_0$ = 3.86 (fixed) for forsterite-type Mg 2 GeO 4 and V 0 = 263.5(15) Å 3 , K 0 = 175(7) GPa, and $K'_0$ = 4.2 (fixed) for the forsterite-III type phase. The forsterite-III type structure was found to be metastable when compared to the stable assemblage of perovskite/post-perovskite + MgO, as observed during laser-heating experiments. Understanding the phase relations and physical properties of metastable phases is crucial for studying the mineralogy of impact sites, understanding metastable wedges in subducting slabs, and interpreting the results of shock compression experiments.

58 GEOSCIENCES↗
DOE OSTI2025

High-Pressure Phase Transition of Metastable Wurtzite-Like CuInSe 2 Nanocrystals

Ternary I–III–VI 2 semiconductors, such as CuInSe 2 , exhibit diverse polymorphs with unique structural characteristics and optoelectronic properties. This study investigates the pressure-induced phase transitions of metastable wurtzite-like CuInSe 2 nanocrystals. Using a combination of synchrotron X-ray diffraction, pair distribution function analysis, and density functional theory calculations, we reveal a transition from cation-ordered wurtzite-like (Pmc2 1 ) to cation-disordered NaCl-like (Fm3̅m) structures at 7.7 GPa. The cation-disordered NaCl-like phase persists upon decompression. Bulk modulus calculations highlight size-dependent deviations from bulk material behavior. These findings deepen our understanding of phase stability in colloidal I–III–VI 2 semiconductor nanocrystals, with implications for tailoring functional materials under extreme conditions.

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

Revealing the Nature of Binary-Phase on Structural Stability of Sodium Layered Oxide Cathodes

The emergence of layered sodium transition metal oxides featuring a multiphase structure presents a promising approach for cathode materials in sodium-ion batteries, showcasing notably improved energy storage capacity. However, the advancement of cathodes with multiphase structures faces obstacles due to the limited understanding of the integrated structural effects. Herein, the integrated structural effects by an in-depth structure-chemistry analysis in the developed layered cathode system Na x Cu 0.1 Co 0.1 Ni 0.25 Mn 0.4 Ti 0.15 O 2 with purposely designed P2/O3 phase integration, are comprehended. The results affirm that integrated phase ratio plays a pivotal role in electrochemical/structural stability, particularly at high voltage and with the incorporation of anionic redox. In contrast to previous reports advocating solely for the enhanced electrochemical performance in biphasic structures, it is demonstrated that an inappropriate composite structure is more destructive than a single-phase design. The in situ X-ray diffraction results, coupled with density functional theory computations further confirm that the biphasic structure with P2:O3 = 4:6 shows suppressed irreversible phase transition at high desodiated states and thus exhibits optimized electrochemical performance. Finally, these fundamental discoveries provide clues to the design of high-performance layered oxide cathodes for next-generation SIBs.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Ab initio study of phase transition of boron nitride between zinc-blende and rhombohedral structures

Boron nitride has polymorphs such as zinc-blende (c-BN), wurtzite (w-BN), rhombohedral (r-BN), and graphite-like (h-BN) forms. We simulate the direct conversion of r-BN to c-BN through electronic excitation. In our calculation, the conversion is made possible by increasing the hole concentration to over 0.06/atom. This conversion should be experimentally possible by hole-doping via an electric double layer transistor (EDLT) or capacitor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Phase transition and energy storage behavior of antiferroelectric PLZT thin films epitaxially deposited on SRO buffered STO single crystal substrates [Phase transition and energy storage behavior of antiferroelectric PLZT thin films epitaxially deposited on SRO buffered STO single crystal substrates]

Thin films of 300-nm-thick (Pb 0.98 , La 0.02 )(Zr 0.95 , Ti 0.05 )O 3 (PLZT) were epitaxially deposited on (100), (110), and (111) SrTiO3 single crystal substrates by pulsed laser deposition. X-ray diffraction line and reciprocal space mapping (RSM) scans were used to determine the crystal structure. Tetragonal ((001) PLZT) and monoclinic MA ((O 1 1 ) and (111) PLZT) structures were found, which influenced the stored energy density. Electric field induced antiferroelectric to ferroelectric (AFE—>FE) phase transitions were found to have a large reversible energy density of up to 30J/cm 3 . With increasing temperature, an AFE to relaxor ferroelectric (AFE—>RFE) transition was found. The RFE phase exhibited lower energy loss, and an improved energy storage efficiency. Here, the results are discussed from the perspective of crystal structure, dielectric phase transitions, and energy storage characteristics.

25 ENERGY STORAGE↗
DOE OSTI2015

Quantitative analysis of the local phase transitions induced by the laser heating

Functional imaging enabled by scanning probe microscopy (SPM) allows investigations of nanoscale material properties under a wide range of external conditions, including temperature. However, a number of shortcomings preclude the use of the most common material heating techniques, thereby limiting precise temperature measurements. Here we discuss an approach to local laser heating on the micron scale and its applicability for SPM. We applied local heating coupled with piezoresponse force microscopy and confocal Raman spectroscopy for nanoscale investigations of a ferroelectric-paraelectric phase transition in the copper indium thiophosphate layered ferroelectric. Bayesian linear unmixing applied to experimental results allowed extraction of the Raman spectra of different material phases and enabled temperature calibration in the heated region. Lastly, the obtained results enable a systematic approach for studying temperature-dependent material functionalities in heretofore unavailable temperature regimes.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unraveling the origin of air-stability in single-crystalline layered oxide positive electrode materials

Single-crystalline Ni-rich layered oxides present compelling advantages over conventional polycrystalline counterparts toward large-scale applications, including enhanced mechanical stability and higher energy density. Nevertheless, the deleterious effects of air exposure, which is inevitable in industrial processing, on their structure and electrochemical performance remain poorly understood. Herein, we reveal that air exposure is more detrimental to the electrochemical performance of single-crystalline layered oxide positive electrodes than polycrystalline counterparts. It is found that air-induced surface structural distortions are primarily responsible for the electrochemical performance decay of single-crystalline samples rather than the generally believed surface residual lithium. Leveraging multiscale diffraction and imaging techniques, we identify an undesirable structural transition to a metastable O1* phase, which introduces substantial lattice defects and localized strain concentrations within the layered structure. These adverse structural evolutions compromise structural integrity and promote crack initiation during electrochemical cycling, ultimately accelerating capacity fade. Our findings provide critical insights into the air-induced degradation mechanisms and emphasize the urgent need for developing effective stabilization strategies to facilitate the commercial implementation of single-crystalline Ni-rich positive electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pressure-driven symmetry transitions in dense H 2 O ice

X-ray diffraction and Raman spectroscopy of H 2 O (ice) structures are measured under static compression in combination with grain normalizing heat treatment via direct laser heating. Here, we report the transition from cubic ice-VII to a structure of tetragonal symmetry, ice-VII t at 5.1 ± 0.5 GPa. This is succeeded by the H-bond symmetrization transition occurring at a pressure of 30.9 ± 3 GPa. Both experimental observations are supported by simulated Raman spectra from density-functional theory quantum calculations. The transition to H-bond symmetrization is evidenced by the reversible emergence of its characteristic Raman mode and a 2.5-fold increase in bulk modulus, implying a significant increase in bonding strength.

58 GEOSCIENCES↗
DOE OSTI2023

Nanolamellar phase transition in an additively manufactured eutectic high-entropy alloy under high pressures

Much is unknown about how phase transitions link to micro-/nano-structures in high-entropy systems, especially under extreme pressure and temperature conditions. This work studies the evolution of dual-phase nanolamellar eutectic high-entropy alloy phases of AlCoCrFeNi 2.1 generated by laser powder-bed fusion (L-PBF) for pressures up to 42 GPa. We compare quasi-hydrostatic high pressure synchrotron x-ray diffraction studies on L-PBF printed cylindrical samples up to 5.5 GPa (large-volume Paris–Edinburgh cell) to those carried out on an L-PBF printed foil in a diamond anvil cell where the pressure reached 42 GPa. Our results show that the initially alternating face-centered cubic (FCC) and body-centered cubic (BCC) nanolamellar structure of AlCoCrFeNi 2.1 transformed into single-phase FCC nanolamellae under high pressure with BCC–FCC phase transformation completion at 21 ± 3 GPa. Our results indicate a diffusionless BCC–FCC transformation in this additively manufactured far-from-equilibrium microstructure and demonstrate that the FCC phase is stable up to very high pressures. The measured equation of state for the FCC phase of AlCoCrFeNi 2.1 is presented up to 42 GPa and shows excellent agreement between the data obtained in large-volume press and diamond anvil cell experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

All-optical seeding of a light-induced phase transition with correlated disorder

Ultrafast manipulation of vibrational coherence is an emergent route to control the structure of solids. However, this strategy can only induce long-range correlations and cannot modify atomic structure locally, which is required in many technologically-relevant phase transitions. Here, we demonstrate that ultrafast lasers can generate incoherent structural fluctuations which are more efficient for material control than coherent vibrations, extending optical control to a wider range of materials. We observe that local, non-equilibrium lattice distortions generated by a weak laser pulse reduce the energy barrier to switch between insulating and metallic states in vanadium dioxide by 6%. In conclusion, seeding inhomogeneous structural-fluctuations presents an alternative, more energy efficient, route for controlling materials that may be applicable to all solids, including those used in data and energy storage devices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Collapsed tetragonal phase transition in LaRu 2 P 2

Here, the structural properties of LaRu 2 P 2 under external pressure have been studied up to 14 GPa, employing high-energy x-ray diffraction in a diamond-anvil pressure cell. At ambient conditions, LaRu 2 P 2 (I4/ mmm ) has a tetragonal structure with a bulk modulus of B = 105(2) GPa and exhibits superconductivity at T c = 4.1 K. With the application of pressure, LaRu 2 P 2 undergoes a phase transition to a collapsed tetragonal (cT) state with a bulk modulus of B = 175(5) GPa. At the transition, the c-lattice parameter exhibits a sharp decrease with a concurrent increase of the a-lattice parameter. The cT phase transition in LaRu 2 P 2 is consistent with a second-order transition, and was found to be temperature dependent, increasing from P = 3.9(3) GPa at 160 K to P = 4.6(3) GPa at 300 K. In total, our data are consistent with the cT transition being near, but slightly above 2 GPa at 5 K where superconductivity is suppressed. Finally, we compare the effect of physical and chemical pressure in the R Ru 2 P 2 ( R = Y, La–Er, Yb) isostructural series of compounds and find them to be analogous.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗