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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Coupled Chemical and Mechanical Control of Phase Stability in Lanthanide-Substituted BiVO 4

Doping is widely used to enhance the photoelectrochemical performance of BiVO 4 , yet solubility limits and polymorphic stability constrain compositional tuning. Here, in this study, the role of trivalent cation substitution (Ln = La, Nd, Dy, Ho, Y) on pressure-induced phase transformations in Bi 1–x Ln x VO 4 (x ≤ 0.5) is described. Powder X-ray and neutron diffraction reveal that increasing Ln content stabilizes the tetragonal zircon-type polymorph under ambient conditions, while applied pressures of up to ∼5 GPa promote conversion to the monoclinic fergusonite-type polymorph. In-situ neutron diffraction on Bi 0.8 La 0.2 VO 4 shows a reversible monoclinic to tetragonal transition near 2–3 GPa with a bulk modulus of 147 GPa. The extent of conversion depends strongly on dopant identity, concentration, and synthetic route, with mixed-phase solid-state samples converting more efficiently than phase-pure coprecipitated materials. These results demonstrate pressure as a viable pathway to access metastable, doped BiVO 4 compositions beyond conventional solubility limits.

Sypkes, Kathryn I. [University of Sydney, NSW (Aus↗
DOE OSTI2019

Tuning phase stability and short-range order through Al doping in ( CoCrFeMn ) 100 - x A l x high-entropy alloys

For ( CoCrFeMn ) 100 - x A l x high-entropy alloys, we report on the phase evolution with increasing Al content ( 0 ≤ x ≤ 20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of ( CoCrFeMn ) 100 - x A l x alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the chemical ordering behavior of arbitrary complex solid-solution alloys—an ideal approach for predictive design of high-entropy alloys. The predictions confirm our present experimental findings and other reported ones.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Phase Stability in Nanocrystals: A Predictive Diagram for Yttria–Zirconia

Predicting the polymorphic stability of nanocrystals entails taking into account the thermodynamic effects from solid–vapor interfaces. With recent advances in microcalorimetry, it is finally possible to obtain reliable surface energy data which allow building of predictive diagrams, such as the usual phase diagrams for bulk crystals, for nanocrystals. Yttria doped zirconia (YZ) is currently utilized in a variety of applications; making it one of the most studied oxide systems to date. However, the polymorphism of nanocrystalline YZ (nYZ) is much less understood as compared to its bulk counterpart, and the stability conditions of cubic, tetragonal, monoclinic, and amorphous polymorphs at the nanoscale is so far only empirically defined. In this work, we present a new predictive nanoscale phase diagram for nYZ using unprecedented data on surface energies and bulk enthalpies acquired by microcalorimetry. The phase diagram shows the stable zirconia polymorph as a function of the composition and size. This is a useful tool and an important and novel advancement to relatively untouched bulk phase diagrams, which holds the key for reliable materials' design.

Drazin, John W.↗
DOE OSTI2015

Influence of valence electron concentration on Laves phases: Structures and phase stability of pseudo-binary MgZn 2-x Pd x

A series of pseudo-binary compounds MgZn 2-x Pd x (0.15 ≤ x ≤ 1.0) were synthesized and structurally characterized to understand the role of valence electron concentration (vec) on the prototype Laves phase MgZn 2 with Pd-substitution. Three distinctive phase regions were observed with respect to Pd content, all exhibiting fundamental Laves phase structures: 0.1 ≤ x ≤ 0.3 (MgNi 2 -type, h P24; MgZn 1.80 Pd 0.20(2) ), 0.4 ≤ x ≤ 0.6 (MgCu 2 -type, cF 24; MgZn 1.59 Pd 0.41(2) ), and 0.62 ≤ x ≤ 0.8 (MgZn 2 -type, hP 12: MgZn 1.37 Pd 0.63(2) ). Refinements from single-crystal X-ray diffraction indicated nearly statistical distributions of Pd and Zn atoms among the majority atom sites in these structures. Interestingly, the MgZn 2 -type structure re-emerges in MgZn 2–x Pd x at x ≈ 0.7 with the refined composition MgZn 1.37(2) Pd 0.63 and a c/a ratio of 1.59 compared to 1.64 for binary MgZn 2 . Electronic structure calculations on a model “MgZn 1.25 Pd 0.75 ” yielded a density of states (DOS) curve showing enhancement of a pseudogap at the Fermi level as a result of electronic stabilization due to the Pd addition. Moreover, integrated crystal orbital Hamilton population values show significant increases of orbital interactions for (Zn,Pd)–(Zn,Pd) atom pairs within the majority atom substructure, i.e., within the Kagomé nets as well as between a Kagomé net and an apical site, from binary MgZn 2 to the ternary “MgZn 1.25 Pd 0.75 ”. Multi-centered bonding is evident from electron localization function plots for “MgZn 1.25 Pd 0.75 ”, an outcome which is in accordance with analysis of other Laves phases.

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

Effect of dose rate on the phase stability of a CrFeNiMn alloy

We report CrFeNi-based multi-principal element alloys (MPEAs) are being considered for nuclear applications because of their potentially superior mechanical properties and irradiation resistance. While the alloys appear stable against phase decomposition during ion irradiation performed at high dose rate, previous electron irradiation and thermal annealing studies suggested that some of them may be susceptible to phase decomposition. Therefore, to clarify the role of dose rate during ion irradiation on phase decomposition, a CrFeNiMn alloy was irradiated using Fe ions at 500 °C with an intermediate dose rate of 10 -4 dpa/s. Transmission electron microscopy and atom probe tomography observations revealed a high number density of NiMn precipitates, cavities, and dislocation loops, which had not previously been observed after ion irradiation at higher dose rates.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing phase stability in CrMoNbV using cluster expansion method, CALPHAD calculations and experiments

High entropy alloys (HEA), a novel class of materials with multiple principal elements, allow us to tune the properties within a wide composition range where the solid-solution phase is stable. However, it is difficult to experimentally determine the boundaries of the single-phase region. In this paper, we calculate the phase diagram of the CrMoNbV quaternary system, as well as its constituent binary and ternary subsystems, using a combination of the cluster expansion method and CALPHAD calculations. We further verify these results by carrying out experiments at two different compositions of the full quaternary system. Furthermore, our work shows how these computational tools can enable efficient discovery and development of new HEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Petalite under pressure: Elastic behavior and phase stability

The lithium aluminosilicate mineral petalite (LiAlSi 4 O 10 ) has been studied using high-pressure single-crystal X-ray diffraction (HP-XRD) up to 5 GPa. Petalite undergoes two pressure-induced first-order phase transitions, never reported in the literature, at ca. 1.5 and 2.5 GPa. The first of these transforms the low-pressure α-phase of petalite (P2/c) to an intermediate β-phase that then fully converts to the high-pressure β-phase at ca. 2.5 GPa. The α→β transition is isomorphic and is associated with a commensurate modulation that triples the unit cell volume. Analysis of the HP-XRD data show that although the fundamental features of the petalite structure are retained through this transition, there are subtle alterations in the internal structure of the silicate double-layers in the β-phase relative to the α-phase. Measurement of the unit cell parameters of petalite as a function of pressure, and fitting of the data with 3rd order Birch-Murnaghan equations of state, has provided revised elastic constants for petalite. The bulk moduli of the α and β-phases are 49(1) and 35(3) GPa, respectively. These values indicate that the compressibility of the- phase of petalite lies between the alkali feldpsars and alkali feldspathoids, whereas the β-phase has a compressibility more comparable with layered silicates. Structure analysis has shown that the compression of the -phase is facilitated by the rigid body movement of the Si 2 O 7 units from which the silicate double-layers are constructed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Phase stability of a eutectic high entropy alloy under extremes of pressures and temperatures

Additively manufactured high-entropy alloys are of interest because of their unique combination of high yield strength and large ductility achieved with far-from-equilibrium crystalline phases and micro/nanostructure morphology. We report on the phase transformation and thermal equation of state of the eutectic high-entropy alloy (EHEA) Al 18 Co 20 Cr 10 Fe 10 Ni 40 W 2 , produced by laser powder-bed fusion (L-PBF). The EHEA was studied in a large-volume Paris–Edinburgh cell using energy-dispersive x-ray diffraction to a pressure of 5.5 GPa and a temperature of 1723 K. Static compression studies in diamond anvil cells using angle-dispersive x-ray diffraction extended the high-pressure structural data to 317 GPa at ambient temperature. The initial dual-phase nanolamellar face-centered cubic (FCC) and body-centered cubic (BCC) structure of Al 18 Co 20 Cr 10 Fe 10 Ni 40 W 2 transforms into a single FCC phase under high pressure, with the BCC-to-FCC phase transformation completing at 9 ± 2 GPa. The FCC phase remained stable up to the highest pressure of 317 GPa. The measured thermal equation of state for the FCC phase of Al 18 Co 20 Cr 10 Fe 10 Ni 40 W 2 is presented up to 5.5 GPa and 1473 K. We observed melting of the EHEA at 1698 ± 25 K at a pressure of 5.5 GPa, and the recrystallized sample shows an increased fraction of the CsCl-type (B2) phase at ambient conditions following release from the high-pressure high-temperature state. The BCC-to-FCC phase transition completion pressure is correlated with the nanolamellae thickness of the BCC layer in this diffusion-less transformation at ambient temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery

Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn 2 O 4 cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn 2 O 4 exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn 2 O 4 with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries.

25 ENERGY STORAGE↗
DOE OSTI2018

Atomistic scale investigation of cation ordering and phase stability in Cs-substituted Ba 1.33 Zn 1.33 Ti 6.67 O 16 , Ba 1.33 Ga 2.66 Ti 5.67 O 16 and Ba 1.33 Al 2.66 Ti 5.33 O 16 hollandite

The titanate-based hollandite structure is proposed as an effective ceramic waste form for Cs-immobilization. In this study, quantum-mechanical calculations were used to quantify the impact of A-site and B-site ordering on the structural stability of hollandite with compositions Ba x Cs y (M z Ti 8-z )O16, where M = Zn 2+ , Ga 3+ , and Al 3+ . The calculated enthalpy of formation agrees with experimental measurements of related hollandite phases from melt solution calorimetry. Ground state geometry optimizations show that, for intermediate compositions (e.g., CsBaGa 6 Ti 18 O 48 ), the presence of both Cs and Ba in the A-site tunnels is not energetically favored. However, the decay heat generated during storage of the Cs-containing waste form may overcome the energetics of Ba and Cs mixing in the tunnel structure of hollandite. The ability of the hollandite structure to accommodate the radioparagenesis of Cs to Ba is critical for long term performance of the waste. For the first time, B-site ordering was observed along the tunnel direction ([001] zone axis) for the Ga-hollandite compositions, as well as the intermediate Al-hollandite composition. These compositionally dependent structural features, and associated formation enthalpies, are of importance to the stability and radiation damage tolerance of ceramic waste forms.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Phase Stability of a Powder Metallurgy Disk Superalloy

Advanced powder metallurgy superalloy disks in aerospace turbine engines now entering service can be exposed to temperatures approaching 700 C, higher than those previously encountered. They also have higher levels of refractory elements, which can increase mechanical properties at these temperatures but can also encourage phase instabilities during service. Microstructural changes including precipitation of topological close pack phase precipitation and coarsening of existing gamma' precipitates can be slow at these temperatures, yet potentially significant for anticipated disk service times exceeding 1,000 h. The ability to quantify and predict such potential phase instabilities and degradation of capabilities is needed to insure structural integrity and air worthiness of propulsion systems over the full life cycle. A prototypical advanced disk superalloy was subjected to high temperature exposures, and then evaluated. Microstructural changes and corresponding changes in mechanical properties were quantified. The results will be compared to predictions of microstructure modeling software.

Gabb, Timothy P.↗
DOE OSTI2024

First Principles Evaluation of Phase Stability in the In-Sn Binary System

Abstract The In-Sn binary alloy system exhibits several unusual features that challenge crystallographic and thermodynamic expectations. We combine first principles total energy calculation with simple thermodynamic modeling to address two key points. First, we evaluate energies along the Bain path to interpret the discontinuous transition between the phases α-In (Pearson type tI2) and β-In 3 Sn (also Pearson type tI2) that are identical in symmetry. Second, we demonstrate that the solid solution phases β-In 3 Sn and γ-InSn 4 (Pearson type hP1) exist at high temperatures only, and they exhibit eutectoid decompositions at low temperatures.

Chemistry↗
DOE OSTI2019

Lattice dynamics and phase stability of rhombohedral antimony under high pressure

The high pressure lattice dynamics of rhombohedral antimony have been studied by a combination of diffuse scattering and inelastic x-ray scattering. The evolution of the phonon behavior as a function of pressure was analyzed by means of two theoretical approaches: density functional perturbation theory and symmetry-based phenomenological phase transition analysis. Here, this paper focuses on the first structural phase transition, SbI-SbIV, and the role of vibrations in leading the transition. The phonon dispersion exhibits complex behavior as one approaches the structural transition, with the branches, corresponding to the two transitions happening at high pressure in the Va elements (A7-to-BCC and A7-to-PC) both showing softening.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Phase stability and microstructures of high entropy alloys ion irradiated to high doses

The microstructures of Al x CoCrFeNi (x = 0.1, 0.75 and 1.5 in molar ratio) high entropy alloys (HEAs) irradiated at room temperature with 3 MeV Au ions at the highest fluence of 105, 91, and 81 displacement per atom, respectively, were studied. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analyses show that the initial microstructures and phase composition of all three alloys are retained after ion irradiation and no phase decomposition is observed. Furthermore, it is demonstrated that the disordered face-centered cubic (FCC) and disordered body-centered cubic (BCC) phases show much less defect cluster formation and structural damage than the NiAl-type ordered B2 phase. This effect is explained by higher entropy of mixing, higher defect formation/migration energies, substantially lower thermal conductivity, and higher atomic level stress in the disordered phases

36 MATERIALS SCIENCE↗
DOE OSTI2020

Phase stability and mechanical properties of wire + arc additively manufactured H13 tool steel at elevated temperatures

Wire + arc additive manufacturing (WAAM) is considered an innovative technology that can change the manufacturing landscape in the near future. WAAM offers the benefits of inexpensive initial system setup and a high deposition rate for fabricating medium- and large-sized parts such as die-casting tools. Here, AISI H13 tool steel, a popular die-casting tool metal, is manufactured by cold metal transfer (CMT)-based WAAM and is then comprehensively analyzed for its microstructural and mechanical properties. Location-dependent phase combinations are observed, which could be explained by nonequilibrium thermal cycles that resulted from the layer-by-layer stacking mechanism used in WAAM. In addition, remelting and reheating of the layers reduces welding anomalies (e.g., pores and voids). The metallurgical characteristics of the H13 strongly correlate with the mechanical properties. The combinations of phases at different locations of the additively manufactured part exhibit a periodic microhardness profile. Martensite, Retained Austenite, Ferrite, and Carbide phases are found in combination at different locations of the part based on the part’s temperature distribution during additive deposition. Moreover, the tensile properties at elevated temperatures (23 °C, 300 °C, and 600 °C) are comparable to those from other WAAM and additive manufacturing (AM) processes. The X-ray diffraction results verify that the microstructural stability of the fabricated parts at high temperatures would allow them to be used in high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Self-assembled complex micelle phase stability in ABA-type triblock copolymers and related core-shell bottlebrushes

We report the synthesis and temperature-dependent morphologies of a series of polylactide--poly (-decalactone)--polylactide (LDL) triblock copolymers with M n = 16.0 – 18.1 kg / mol and volume fractions f L = 0.27 – 0.31 and associated core-shell bottlebrush (csBB) polymers, which derive from enchaining LDL triblocks through a polymerizable midchain functionality. While the LDL triblocks form micellar Frank-Kasper A15 and phases due to the conformational asymmetry of this monomer pair, the csBB morphologies sensitively depend on the backbone degree of polymerization ( N bb ). At low N bb values, micellar Frank-Kasper phases with the brush backbone situated in the matrix domain are stable, albeit with a modest reduction in the mean interfacial curvature evidenced by a to A15 order-to-order transition. However, larger N bb values drive csBBs to form hexagonally packed cylinders phases. This N bb -dependent phase behavior is rationalized in terms of a star-to-bottlebrush transition. At low N bb values, the csBBs are akin to star polymers with pointlike junctions that can support complex micelle packings. As N bb increases, the csBBs adopt cylindrical molecular geometries with extended backbones situated in the matrix domain that prefer hexagonally packed cylinders morphologies. Published by the American Physical Society 2024

Materials Science↗
DOE OSTI2023

Phase Stability, Band Gap Tuning, and Rashba Splitting in Selenium-Alloyed Bournonite: CuPbSb(S 1– x Se x ) 3

Recently, bournonite (CuPbSbS 3 ) has been identified as a potential ferroelectric photovoltaic (PV) material with a 1.3 eV band gap, which falls in an appropriate range for single junction PV devices. Progress in applying bournonite has yielded several studies reporting successful thin-film processing, the most recent of which demonstrated a 2.65% power conversion efficiency for a bournonite-based PV device. In an effort to explore bournonite band gap engineering for PV and other prospective applications (e.g., thermoelectric, spintronic), we here consider the solid-state synthesis of selenium-alloyed bournonite, CuPbSb(S 1-x Se x ) 3 , across the full range of x (0.0 ≤ x ≤ 1.0), and report phase purity for 0.0 ≤ x ≤ 0.5. We characterize the crystal structure and band gap of the samples using X-ray diffraction and diffuse reflectance spectroscopy, determining a band gap decrease for single-phase samples from 1.25 eV at x = 0.0 to 1.06 eV at x = 0.5. Formation energies determined using dispersion corrected hybrid density functional theory (DFT) support experimental findings and are consistent with the stability (instability) of the x = 0.5 (x = 1.0) structure relative to starting materials. The computed band structures show a decreasing trend in the band gap with increasing x, again consistent with experiment, with the states at the conduction (valence) band minima (maxima) being principally derived from Pb (S/Se) states. Spin texture analysis and detailed comparison of spin splitting parameters show that Se-alloying modifies the band gap while maintaining Rashba spin splitting character within the electronic structure. Rashba splitting is most pronounced for the conduction band minimum along the Γ-X path in the Brillouin zone. Energy separation between spin states is maintained at ΔE~0.2 eV for the various Se contents, with σz as the spin direction. Furthermore, a smaller spin splitting occurs along Γ-Z (decreasing value with increasing x), with σ x as the spin direction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗