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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

CeO 2 Doping of Hf 0.5 Zr 0.5 O 2 Thin Films for High Endurance Ferroelectric Memories

Ferroelectric switching is demonstrated in CeO 2 -doped Hf 0.5 Zr 0.5 O 2 (HZCO) thin films with application in back-end-of-line compatible embedded memories. At low cerium oxide doping concentrations (2.0–5.6 mol%), the ferroelectric orthorhombic phase is stabilized after annealing at temperatures below 400 °C. HZCO ferroelectrics show reliable switching characteristics beyond 10 11 cycles in TiN/HZCO/TiN capacitors, several orders of magnitude greater than identically processed Hf 0.5 Zr 0.5 O 2 (HZO) capacitors, without sacrificing polarization and retention. Internal photoemission and photoconductivity experiments show that CeO 2 -doping introduces in-gap states in HZCO that are nearly aligned with TiN Fermi level, facilitating electron injection through these states. Furthermore, the enhanced average bulk conduction, which may lead to more uniform thermal dissipation in the HZCO films, delays irreversible degradation via breakdown that leads to device failure after repeated programming cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of HCP/BCC element ratios on the room-temperature tensile properties of Ti-Zr-Hf-Nb-Ta refractory high-entropy alloys

Equiatomic and non-equiatomic Ti-Zr-Hf-Nb-Ta refractory high-entropy alloys (RHEAs) were arc melted, homogenized, cold rolled, and recrystallized to produce single-phase, body-centered cubic (BCC), microstructures with weak texture and equiaxed grains 76–199 μm in size. Here, the non-equiatomic alloys had either a 60:40 or 80:20 atomic ratio of hexagonal close-packed (HCP) elements (Ti + Zr + Hf) to BCC elements (Nb + Ta). Alloy compositions were measured after thermomechanical processing to determine the concentrations of the major (substitutional) and minor (interstitial) elements. We investigated how elastic constants and uniaxial tensile properties were affected by changes in the relative concentrations of the constituent elements at fixed HCP:BCC ratios. Yield strengths ranged from 801 to 922 MPa and ultimate tensile strengths from 815 to 933 MPa. Good agreement is obtained between the experimental yield strengths and those predicted by a strength theory based on edge dislocations indicating that the observed compositional effects are due to their effects on shear modulus and volume misfit. Fracture occurred by dimpled rupture with fracture strains of 19.4%–25.7%, but uniform strains were an order of magnitude lower at 1.1%–3.2%, calling into question the useable ductility (prior to necking) of RHEAs considered to be ductile based on their fracture strain. Contrary to predictions in the literature that HCP elements promote ductility, our present results show that increasing the HCP:BCC ratio decreases both the total strain and the uniform strain. Similar trends were not evident in the yield or ultimate strengths; rather, strengths were affected mainly by shear modulus and volume misfit.

BCC high-entropy alloys↗
DOE OSTI2020

Domain-Matching Epitaxy of Ferroelectric Hf 0.5 Zr 0.5 O 2 (111) on La 2/3 Sr 1/3 MnO 3 (001)

Epitaxial ferroelectric HfO2 films are the most suitable to investigate intrinsic properties of the material and for prototyping emerging devices. Ferroelectric Hf 0.5 Zr 0.5 O 2 (111) films were epitaxially stabilized on La 2/3 Sr 1/3 MnO 3 (001) electrodes. This epitaxy, considering the symmetry dissimilarity and the huge lattice mismatch, is not compatible with conventional mechanisms of epitaxy. In this work, to gain insight into the epitaxy mechanism, scanning transmission electron microscopy characterization of the interface was performed, revealing arrays of dislocations with short periodicities. Additionally, these observed periodicities agree with those expected for domain matching epitaxy, indicating that this unconventional mechanism could be the prevailing factor in the stabilization of ferroelectric Hf0.5Zr0.5O2 with (111) orientation in the epitaxial Hf 0.5 Zr 0.5 O 2 (111)/La 2/3 Sr 1/3 MnO 3 (001)heterostructure.

36 MATERIALS SCIENCE↗
DOE OSTI2026

SCF Framework, HF Stability, and RPA Correlation for Jordan–Wigner-Transformed Spin Hamiltonians on Arbitrary Coupling Topologies

Mapping spins to fermions via the Jordan–Wigner (JW) transformation can render mean-field (Hartree–Fock, HF) descriptions effective for strongly correlated spin systems. As established in recent work, the application of such approaches is not limited by the nonlocal structure of JW strings or by site ordering because string operators can be absorbed into Thouless rotations of a Slater determinant, and the variational optimization of a unitary Lie-algebraic similarity transformation removes any ordering dependence. Leveraging these ideas, we develop a self-consistent field (SCF) scheme that expresses the mean-field energy as a functional of the single-particle density matrix, providing an alternative to gradient-based optimization of Thouless parameters. We derive the analytical orbital Hessian to diagnose HF stability and compute the ground-state correlation energy through the random-phase approximation (RPA). Benchmark results for the XXZ and J 1 –J 2 model on one- and two-dimensional lattices demonstrate that RPA significantly improves mean-field accuracy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Propane Dehydrogenation Catalyzed by Supported Group IV (Ti, Zr, Hf) Organometallics on Silicon Nitride

Mesoporous silicon nitride (Si 3 N 4 ) enables access to chemisorbed group IV organometallics catalysts active for propane dehydrogenation (PDH) compared to the organometallic analogues on mesoporous silica under the same reaction conditions. The series of Si 3 N 4 -supported materials are active catalysts, (Zr > Hf > Ti k f = 290, 232, and 162 mol mol Metal -1 h -1 at 450 °C with 2% C 3 H 8 in Ar, respectively) with selectivity above 95%, demonstrating additional examples of Ti and Hf systems for PDH. However, the underlying mechanism of the improved performance relative to oxide supported homologues is not well-understood. Characterization of thermally treated samples (DRIFTS, XAS and SSNMR) and computational modeling of this catalyst series was utilized to differentiate between potential amido - (C-H activation along the M-N bond) and imido - (C-H activation along the M=N bond) mechanisms. Due to remaining mechanistic ambiguity, a Ga analogue was synthesized and evaluated for PDH activity as an indirect probe to experimentally differentiate pathways. An inversion of the oxide/nitride performance trend is observed for the Ga congener which does not form a Ga=N bond, most consistent with different mechanisms dictating the performance of the group IV/Si 3 N 4 catalysts vs Ga/Si 3 N 4 .

heterolytic cleavage↗
DOE OSTI2021

Ion beam etching dependence of spin-orbit torque memory devices with switching current densities reduced by Hf interlayers

We report on the fabrication of nanoscale, three-terminal in-plane spin–orbit torque switching devices with low switching current densities. Critical parameters in the fabrication process, including the ion beam etching angle and time, were optimized to avoid fabrication defects and improve device yield. Measurements of the magnetic field and current-induced switching behavior of the tunnel junctions demonstrate a sensitivity to the nanopillar aspect ratio, which dictates the nanopillars’ anisotropy and thermal stability. Additionally, we show that the current density required for switching can be reduced and the device thermal stability increased by inserting Hf interlayers into the heterostructure. Micromagnetic simulations are generally consistent with the experimentally observed switching behavior, suggesting an increase in the interfacial perpendicular anisotropy at the CoFeB/MgO interface and the reduction in the Dzyaloshinskii–Moriya interaction at the W/CoFeB interface by the Hf interlayers.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ferroelectricity of wurtzite Al 1−x Hf x N heterovalent alloys

Thin films of aluminum hafnium nitride (Al1−xHfxN) were synthesized via reactive magnetron sputtering for Hf contents up to x = 0.13. X-ray diffraction showed a single c-axis oriented wurtzite phase for all films. Hard x-ray photoelectron spectroscopy demonstrated homogeneous Al:Hf distribution through the thin films and confirmed their insulating character. A collection of complementary tests showed unambiguous polarization inversion, and thus ferroelectricity in multiple samples. Current density vs electric field hysteresis measurements showed distinct ferroelectric switching current peaks, the piezoelectric coefficient d 33,f,meas measured using a double beam laser interferometer (DBLI) showed a reversal in sign with similar magnitude, and anisotropic wet etching confirmed field-induced polarization inversion. This demonstrates the possibility of using tetravalent–and not just trivalent–alloying elements to enable ferroelectricity in AlN-based thin films, highlighting the compositional flexibility of ferroelectricity in wurtzites and greatly expanding the chemistries that can be considered for future devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Efficiency of using nitrogen trifluoride as an oxidiser in a supersonic continuous-wave chemical HF laser

We report the results of an experimental study of possible ways to increase the efficiency of using NF{sub 3} nitrogen trifluoride as an oxidiser in an atomic fluorine generator of a supersonic continuous-wave chemical HF laser with a flat nozzle block corresponding to the nozzle – nozzle reagent mixing scheme. As such ways, we consider increasing the residence time of reagents in the combustion chamber and rising temperature in the chemical reaction zone. Comparison of specific energy characteristics of an HF laser operating with the use of the studied (NF{sub 3}) and ‘basic’ (F{sub 2}) oxidisers shows that the replacement of molecular fluorine with nitrogen trifluoride during the burning with deuterium in the combustion chamber of an atomic fluorine generator with allowance for the proposed measures leads to a reduction in the specific laser energy output by no more than 23 % – 24 % at high burning completeness. (paper)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Thermodynamics of the dipole-octupole pyrochlore magnet Ce 2 Hf 2 O 7 in applied magnetic fields

The recently discovered dipole-octupole pyrochlore magnet Ce 2 Hf 2 O 7 is a promising three-dimensional quantum spin liquid candidate which shows no signs of ordering at low temperature. Here we investigate the thermodynamic response to magnetic fields applied along the global [110] direction using specific heat measurements and fits using numerical methods, and solve the corresponding magnetic structure using neutron diffraction. Specific heat data in moderate fields are reproduced well, however, at high fields the agreement is not satisfactory. We especially observe a two-step release of entropy, a finding that demands a review of both theory and experiment. We address it within the framework of three possible scenarios, including an analysis of the crystal field Hamiltonian not restricted to the two-dimensional single-ion doublet subspace. We conclusively rule out two of these scenarios and find qualitative agreement with a simple model of field misalignment with respect to the crystalline direction. As a result, we discuss the implications of our findings for [111] applied fields and for future experiments on Ce 2 Hf 2 O 7 and its sister compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Decay of a microsecond seniority 3 isomeric state in Hf 155

Excited states in the neutron-deficient nuclide Hf 155 have been investigated in experiments performed at the Accelerator Laboratory of the University of Jyväskylä. The Hf 155 nuclei were produced in fusion-evaporation reactions induced by beams of 295 and 315 MeV Ni 58 ions bombarding an isotopically enriched Pd 102 target and separated using the recoil mass separator MARA. An isomeric state having a half-life of 510(30) ns was discovered and is interpreted as a seniority υ = 3 , ( π h 11 / 2 2 ⊗ ν f 7 / 2 ) 27 / 2 − configuration. The γ -ray transitions emitted in the deexcitation of the isomeric state to the ground state were identified and a level scheme was constructed, from which the excitation energy of the isomer was determined to be 2581.5(10) keV. A B ( E 2 ) value of 0.45(3) W.u. was deduced for the 105.4 keV transition depopulating the isomeric state. The deduced level scheme and B ( E 2 ) value are compared with systematics and shell-model calculations. Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

First-principles investigation of elastic, vibrational, and thermodynamic properties of kagome metals CsM 3 Te 5 (M = Ti, Zr, Hf)

Kagome metals are a unique class of quantum materials characterized by their distinct atomic lattice arrangement, featuring interlocking triangles and expansive hexagonal voids. These lattice structures impart exotic properties, including superconductivity, interaction-driven topological many-body phenomena, and magnetism, among others. The kagome metal CsM 3 ⁢Te 5 (where M = Ti, Zr, or Hf) exhibits both superconductivity and nontrivial topological electronic properties, offering a promising platform for exploring topological superconductivity. This study employs first-principles density functional theory calculations to systematically analyze the elastic, mechanical, vibrational, thermodynamic, and electronic properties of CsM 3 ⁢Te 5 (M = Ti, Zr, Hf). Our calculations reveal that the studied compounds—CsTi 3 ⁢Te 5 , CsZr 3 ⁢Te 5 , and CsHf 3 ⁢Te 5 —are ductile metals with elastic properties akin to the hexagonal Bi and Sb, with average elastic constants, including a bulk modulus of 27 GPa, a shear modulus of 11 GPa, and Young's modulus of 29 GPa. We observe peculiar dispersionless, flat, phonon branches in the vibrational spectra of these metals. Additionally, we thoroughly analyze the symmetries of the zone-center phonon eigenvectors and predict vibrational fingerprints of the Raman- and infrared-active phonon modes. The analysis of thermodynamic properties reveals the Einstein temperature for CsTi 3 ⁢Te 5 , CsZr 3 ⁢Te 5 , and CsHf 3 ⁢Te 5 to be 66, 54, and 53 K, respectively. Our orbital-decomposed electronic structure calculations reveal significant in-plane steric interactions and multiple Dirac band crossings near the Fermi level. We further investigate the role of spin-orbit coupling effect on the studied properties. Furthermore, this theoretical investigation sheds light on the intriguing quantum behavior of kagome metals.

36 MATERIALS SCIENCE↗
DOE OSTI2020

R.Q. Wright’s Hf updates [Slides]

This presentation details R.Q. Wright’s Hf updates. It discusses the stable Hf isotope (174, 176-180), RRR and URR + fast (n, g), and the motivation and deficiencies in the current ENDF/B-VIII.0. It also discusses what new data and/or theory will motivate a new evaluation and/or update and what validation testing has been/will be done.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Investigation of oxygen ion mobility through Zr x Ta 2 O 2x+5 (ZTOx) and Hf 6 Ta 2 O 17 (HTO) at elevated temperatures

Thermal Protection Systems (TPS) allow for technology to withstand high heat, which is especially critical for aerospace applications. As technology advances, better TPS are required to keep up with more extreme operating temperatures. Ultra-High Temperature Ceramics (UHTCs) are of interest because of their high melting points above 3000°C, but they suffer from oxidation when exposed to the atmosphere. A standard remedy to prevent oxidation is the use an oxide coating to shield from oxygen in the atmosphere while still allowing high operating temperatures and thermal cycling. However, standard oxide coatings such as yttria stabilized zirconia (YSZ) have limited operating temperatures before they allow oxygen to diffuse into the substrate material. A recently proposed alternative material has the formula A 6 B 2 O 17 (A: Zr or Hf) (B: Ta or Nb). In this study, determination of the oxygen protection ability of Hf 6 Ta 2 O 17 (HTO), Zr 6 Ta 2 O 17 (ZTO6), and various Zr x Ta 2 O 2x+5 (ZTOx) was determined using Electrochemical Impedance Spectroscopy (EIS). Optimal synthesis and sintering conditions were determined for ZTO6 and several of its ZTO variations. Activation energy for oxygen mobility was also determined. The importance of ball milling was found to be crucial to achieve high sintering density with these ceramics. The sintering study revealed that the ideal temperature of the ZTO variations increased with increased Zr/Ta ratio in the formulation. It was determined that both HTO and the ZTO variations conduct oxygen ions less than current ceramic coatings such as YSZ, with HTO conducting the least, with results confirming the validity of both HTO and ZTO materials as candidates for TPS coatings based on their low oxygen ion conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Synthesis of Hf 0.75 Ta 0.25 B 2 for self-coating TPS

Ultra-high temperature ceramic materials (UHTCs) are important for designing high-performance aerospace vehicles that can withstand repeated exposures to high temperatures. UHTCs mixed with silicides often have well-controlled oxidation due to the formation of protective silicates, which create a regenerative outer protective layer. Borides are known to have high melting points, high hardness and reasonably good oxidation resistance. In this study, Hf 0.75 Ta 0.25 B 2 (HTB) is proposed as a potential alternative to YSZ protective coatings and ZrB 2- SiC composites via the formation of Hf 6 Ta 2 O 17 (HTO) passivation layer. The objective of this paper is to explore the parameter space of HTB synthesis via borocarbothermal (BCTR). Effects on particle size, phase purity, and residual oxygen content were analyzed with parameters of atmosphere composition, reactant grain sizes, and differing reaction pathways. The BCTR of HfO 2 and Ta 2 O 5 were analyzed to predict HTB behavior. It was shown that both one-step and two-step reaction routes can yield HTB, but two-step yields a purer product. Nano B 4 C produced finer HTB and facilitated reaction completion. Using a reducing atmosphere also enhanced reaction completion

36 MATERIALS SCIENCE↗
DOE OSTI2025

Advancements in HF-free bipolar pulsed electropolishing for next-generation superconducting cavities

Hydrofluoric acid (HF)-free bipolar pulsed electropolishing (BPEP) offers an environmentally sustainable alternative to conventional Buffered Chemical Polishing (BCP) and Electropolishing (EP) techniques for superconducting radiofrequency (SRF) cavities. Recent studies at Jefferson Lab have demonstrated that a single-cell 1.3 GHz niobium cavity processed using HF-free BPEP achieved an accelerating gradient Eacc of 35 MV/m with a quality factor Q0 of 1E10 at 2 K, following extensive research and optimization. This talk will highlight the challenges encountered in developing this technique, key insights gained from experimental studies, and ongoing efforts to enhance its capabilities. In particular, we will explore its potential for refining Nb3Sn-coated niobium cavities via vapor diffusion techniques and for electroplating Nb3Sn films onto various cavity substrates, contributing to the advancement of high-performance SRF systems.

Tian, Hui [Thomas Jefferson National Accelerator F↗
DOE OSTI2020

Low-Energy Electron Elastic Total Cross Sections for Ho, Er, Tm, Yb, Lu, and Hf Atoms

The robust Regge-pole methodology wherein is fully embedded the essential electron-electron correlation effects and the vital core polarization interaction has been used to explore negative ion formation in the large lanthanide Ho, Er, Tm, Yb, Lu, and Hf atoms through the electron elastic total cross sections (TCSs) calculations. These TCSs are characterized generally by dramatically sharp resonances manifesting ground, metastable, and excited negative ion formation during the collisions, Ramsauer-Townsend minima, and shape resonances. The novelty and generality of the Regge-pole approach is in the extraction of the negative ion binding energies (BEs) of complex heavy systems from the calculated electron TCSs. The extracted anionic BEs from the ground state TCSs for Ho, Er, Tm, Yb, Lu, and Hf atoms are 3.51 eV, 3.53 eV, 3.36 eV, 3.49 eV, 4.09 eV and 1.68 eV, respectively. The TCSs are presented and the extracted from the ground; metastable and excited anionic states BEs are compared with the available measured and/or calculated electron affinities. We conclude with a remark on the existing inconsistencies in the meaning of the electron affinity among the various measurements and/or calculations in the investigated atoms and make a recommendation to resolve the ambiguity.

Felfli, Zineb↗
DOE OSTI2023

Inhomogeneous Enrichment of Radioactive Nuclei in the Galaxy: Deposition of Live 53 Mn, 60 Fe, 182 Hf, and 244 Pu into Deep-sea Archives. Surfing the Wave?

Abstract While modeling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modeling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution. Using a three-dimensional GCE model, we investigated the evolution of four SLRs: 53 Mn, 60 Fe, 182 Hf, and 244 Pu with the aim of explaining detections of recent (within the last ≈1–20 Myr) deposition of live 53 Mn, 60 Fe, and 244 Pu of extrasolar origin into deep-sea reservoirs. We find that core-collapse supernovae are the dominant propagation mechanism of SLRs in the Galaxy. This results in the simultaneous arrival of these four SLRs on Earth, although they could have been produced in different astrophysical sites, which can explain why live extrasolar 53 Mn, 60 Fe, and 244 Pu are found within the same, or similar, layers of deep-sea sediments. We predict that 182 Hf should also be found in such sediments at similar depths.

79 ASTRONOMY AND ASTROPHYSICS↗