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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Hf(AlNi4)3 by Materials Project

Hf(Ni4Al)3 is Uranium Silicide-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Hf is bonded to twelve Ni atoms to form HfNi12 cuboctahedra that share corners with four equivalent HfNi12 cuboctahedra, corners with eight equivalent AlNi12 cuboctahedra, edges with twenty-four NiHf2Al2Ni8 cuboctahedra, faces with two equivalent AlNi12 cuboctahedra, faces with four equivalent HfNi12 cuboctahedra, and faces with eight NiHf2Al2Ni8 cuboctahedra. There are four shorter (2.56 Å) and eight longer (2.62 Å) Hf–Ni bond lengths. There are six inequivalent Ni sites. In the first Ni site, Ni is bonded in a distorted square co-planar geometry to four equivalent Hf and eight Ni atoms. All Ni–Ni bond lengths are 2.62 Å. In the second Ni site, Ni is bonded to eight Ni and four equivalent Al atoms to form NiAl4Ni8 cuboctahedra that share corners with eight NiAl4Ni8 cuboctahedra, edges with four equivalent HfNi12 cuboctahedra, edges with four equivalent AlNi12 cuboctahedra, edges with sixteen NiHf2Al2Ni8 cuboctahedra, faces with four equivalent AlNi12 cuboctahedra, and faces with thirteen NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.51 Å. All Ni–Al bond lengths are 2.56 Å. In the third Ni site, Ni is bonded to eight equivalent Ni and four equivalent Al atoms to form NiAl4Ni8 cuboctahedra that share corners with twelve NiAl4Ni8 cuboctahedra, edges with eight equivalent AlNi12 cuboctahedra, edges with sixteen equivalent NiAl4Ni8 cuboctahedra, faces with four equivalent AlNi12 cuboctahedra, and faces with fourteen NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.52 Å. All Ni–Al bond lengths are 2.56 Å. In the fourth Ni site, Ni is bonded to two equivalent Hf, eight Ni, and two equivalent Al atoms to form distorted NiHf2Al2Ni8 cuboctahedra that share corners with twelve NiHf2Al2Ni8 cuboctahedra, edges with four equivalent HfNi12 cuboctahedra, edges with four equivalent AlNi12 cuboctahedra, edges with twelve NiAl4Ni8 cuboctahedra, faces with two equivalent HfNi12 cuboctahedra, faces with two equivalent AlNi12 cuboctahedra, and faces with twelve NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.56 Å. Both Ni–Al bond lengths are 2.51 Å. In the fifth Ni site, Ni is bonded to eight Ni and four Al atoms to form distorted NiAl4Ni8 cuboctahedra that share corners with twelve NiHf2Al2Ni8 cuboctahedra, edges with eight AlNi12 cuboctahedra, edges with sixteen NiAl4Ni8 cuboctahedra, faces with four AlNi12 cuboctahedra, and faces with fourteen NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.56 Å. There are two shorter (2.51 Å) and two longer (2.52 Å) Ni–Al bond lengths. In the sixth Ni site, Ni is bonded to two equivalent Hf, eight Ni, and two equivalent Al atoms to form distorted NiHf2Al2Ni8 cuboctahedra that share corners with twelve NiHf2Al2Ni8 cuboctahedra, edges with four equivalent HfNi12 cuboctahedra, edges with four equivalent AlNi12 cuboctahedra, edges with twelve NiAl4Ni8 cuboctahedra, faces with two equivalent HfNi12 cuboctahedra, faces with two equivalent AlNi12 cuboctahedra, and faces with twelve NiAl4Ni8 cuboctahedra. There are two shorter (2.51 Å) and four longer (2.56 Å) Ni–Ni bond lengths. Both Ni–Al bond lengths are 2.51 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded to twelve Ni atoms to form AlNi12 cuboctahedra that share corners with four equivalent HfNi12 cuboctahedra, corners with eight AlNi12 cuboctahedra, edges with twenty NiHf2Al2Ni8 cuboctahedra, a faceface with one HfNi12 cuboctahedra, faces with five AlNi12 cuboctahedra, and faces with twelve NiAl4Ni8 cuboctahedra. In the second Al site, Al is bonded to twelve Ni atoms to form AlNi12 cuboctahedra that share corners with twelve AlNi12 cuboctahedra, edges with twenty-four NiAl4Ni8 cuboctahedra, faces with six AlNi12 cuboctahedra, and faces with twelve NiAl4Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis of Hf 6 Ta 2 O 17 superstructure via spark plasma sintering for improved oxidation resistance of multi-component ultra-high temperature ceramics

Ultra-high temperature ceramics (UHTCs) have shown aspiration to overcome challenges in the thermal protection system (TPS) by designing new materials referred to as multi-component UHTCs (MC-UHTCs) in the compositional space. MC-UHTCs have shown remarkable improvement in oxidation resistance due to the formation of the Hf6Ta2O17 superstructure during plasma exposure. Herein, the Hf 6 Ta 2 O 17 superstructure is synthesized via a solid-state reaction between HfO 2 and Ta 2 O 5 powder mixtures during spark plasma sintering (SPS). The compositions chosen are 50 vol% of HfO 2 -50 vol% of Ta 2 O 5 (50HO-50TO) and 70 vol% of HfO 2 -30 vol% of Ta 2 O 5 (70HO-30TO). The phase quantification via Rietveld analysis showed Hf 6 Ta 2 O 17 as a principal phase with some residual Ta 2 O 5 phase in both the samples. The high-temperature thermal stability of the samples was evaluated using high-velocity plasma jet exposure for up to 3 min. 50HO-50TO was able to withstand the intense plasma condition, which is attributed to the higher content of the Hf 6 Ta 2 O 17 phase (~84%) and lower strain in the Ta 2 O 5 phase. The augmentation in the Hf 6 Ta 2 O 17 phase to 94.7% (in 50HO-50TO) post plasma exposure has been attributed to the invariant transformation from a liquid state to Hf 6 Ta 2 O 17 at temperatures >2500 °C during testing. The mechanical integrity is elucidated from the insignificant change in the hardness ~13.3 GPa before and 11.2 GPa after plasma exposure of the 50HO-50TO sample. As a result, the Hf 6 Ta 2 O 17 superstructure's thermo-mechanical stability suggests developing novel oxidation-resistant MC-UHTCs in compositional space for reusable space vehicle applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The strong influence of Ti, Zr, Hf solutes and their oxidation on microstructure and performance of Nb 3 Sn superconductors

The strong influence of Ti, Zr, Hf solutes and their oxidation on microstructure and performance of Nb 3 Sn superconductors Over the last few years a new type of Nb 3 Sn superconducting composite based on the internal oxidation approach has emerged and has demonstrated performance significantly superior to conventional Nb 3 Sn. It requires a supply of O and the use of a Nb alloy – Nb-X, where X is a solute element that can be selectively oxidized to form oxide particles within the Nb 3 Sn. Such oxide particles not only refine Nb 3 Sn grain size, but also have the proper size to act as artificial pinning centers (APC) directly restraining fluxon motion, and thus dramatically improve superconducting properties. In this article we show that the size and volume fraction of the oxide particles determine both the levels of grain refinement and the shift in the peak field of the flux pinning force (F p -B) curve. Additionally, we explore the factors influencing these microstructure and properties, which we find include: selection of the solute element X, solute content, O content, and heat treatment. For the selection of X, we searched the periodic table for all promising candidates but focused down on the group-IVB elements (Ti, Zr, Hf) here as the drawability of Nb 3 Sn wires made from Nb-Ti, Nb-Zr, and Nb-Hf alloys has been demonstrated in the past few decades. We found that while internally oxidizing Nb-1.5at.%Ti led to negligible grain refinement and F p -B peak shift, Nb-Zr alloys led to much more dramatic results, and internally oxidizing Nb-Hf alloys led to the strongest grain refinement and F p -B peak shift. For Hf alloying in particular, we compared our internal oxidation method with another method for grain refinement, which uses Hf alloying itself without oxidation, and found that internal oxidation led to much stronger grain refinement and F p -B peak shift. We also found that higher solute content and lower reaction temperature led to stronger grain refinement and F p -B peak shift. We conclude with a discussion of the possible mechanisms for the influence of these factors.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Production and performance of a 172 Hf/ 172 Lu generator

A 172 Hf/ 172 Lu radionuclide generator system to produce 172 Lu for laboratory scale applications in lutetium-based radiochemistry development was established and evaluated. The parent 172 Hf radionuclide was produced through 35.2 MeV proton irradiation of natural lutetium metal foil at the Brookhaven Linac Isotope Producer. Four resins were investigated for 172 Hf separation from bulk Lu target material: LN resin, ZR resin, in-house synthesized hydroxamate, and methyl-substituted hydroxamate resins, all with comparable performance. Separated 172 Hf was consolidated and used to create a ZR resin-based 4.9(3) MBq 172 Hf/ 172 Lu generator which was eluted 49 times over two years with no observed breakthrough of 172 Hf, and an average elution efficiency of 98(1)%. The eluted 172 Lu was used to radiolabel the macrocyclic chelator DOTA with an apparent molar activity of 8(2)x10 2 kBq/nmol.

172Hf/172Lu radionuclide generator↗
DOE OSTI2025

Microstructure of Neutron-Irradiated Al 3 Hf-Al Thermal Neutron Absorber Materials

A thermal neutron-absorbing metal matrix composite (MMC) comprised of Al 3 Hf particles in an aluminum matrix was developed to filter out thermal neutrons and create a fast flux environment for material testing in a mixed-spectrum nuclear reactor. Intermetallic Al 3 Hf particles capture thermal neutrons and are embedded in a highly conductive aluminum matrix that provides conductive cooling of the heat generated due to thermal neutron capture by the hafnium. These Al 3 Hf-Al MMCs were fabricated using powder metallurgy via hot pressing. The specimens were neutron-irradiated to between 1.12 and 5.38 dpa and temperatures ranging from 286 °C to 400 °C. The post-irradiation examination included microstructure characterization using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy. This study reports the microstructural observations of four irradiated samples and one unirradiated control sample. All the samples showed the presence of oxide at the particle–matrix interface. The irradiated specimens revealed needle-like structures that extended from the surface of the Al 3 Hf particles into the Al matrix. An automated segmentation tool was implemented based on a YOLO11 computer vision-based approach to identify dislocation lines and loops in TEM images of the irradiated Al-Al 3 Hf MMCs. This work provides insight into the microstructural stability of Al 3 Hf-Al MMCs under irradiation, supporting their consideration as a novel neutron absorber that enables advanced spectral tailoring.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(MnSn)6 by Materials Project

Hf(MnSn)6 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Hf is bonded to eight Sn atoms to form distorted edge-sharing HfSn8 hexagonal bipyramids. There are two shorter (2.93 Å) and six longer (3.12 Å) Hf–Sn bond lengths. Mn is bonded in a 12-coordinate geometry to six Sn atoms. There are a spread of Mn–Sn bond distances ranging from 2.71–2.79 Å. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a 12-coordinate geometry to three equivalent Hf and six equivalent Mn atoms. In the second Sn site, Sn is bonded in a 6-coordinate geometry to six equivalent Mn atoms. In the third Sn site, Sn is bonded in a 7-coordinate geometry to one Hf and six equivalent Mn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(GaNi4)3 by Materials Project

Hf(Ni4Ga)3 is beta Cu3Ti-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Hf is bonded to twelve Ni atoms to form HfNi12 cuboctahedra that share corners with four equivalent HfNi12 cuboctahedra, corners with eight equivalent GaNi12 cuboctahedra, edges with twenty-four NiHf2Ga2Ni8 cuboctahedra, faces with two equivalent GaNi12 cuboctahedra, faces with four equivalent HfNi12 cuboctahedra, and faces with eight equivalent NiHf2Ga2Ni8 cuboctahedra. There are four shorter (2.57 Å) and eight longer (2.63 Å) Hf–Ni bond lengths. There are five inequivalent Ni sites. In the first Ni site, Ni is bonded in a distorted square co-planar geometry to four equivalent Hf and eight equivalent Ni atoms. All Ni–Ni bond lengths are 2.63 Å. In the second Ni site, Ni is bonded to eight Ni and four equivalent Ga atoms to form NiGa4Ni8 cuboctahedra that share corners with eight NiGa4Ni8 cuboctahedra, edges with four equivalent HfNi12 cuboctahedra, edges with four equivalent GaNi12 cuboctahedra, edges with sixteen NiHf2Ga2Ni8 cuboctahedra, faces with four equivalent GaNi12 cuboctahedra, and faces with thirteen NiGa4Ni8 cuboctahedra. There are four shorter (2.51 Å) and four longer (2.52 Å) Ni–Ni bond lengths. All Ni–Ga bond lengths are 2.57 Å. In the third Ni site, Ni is bonded to eight equivalent Ni and four equivalent Ga atoms to form NiGa4Ni8 cuboctahedra that share corners with twelve NiGa4Ni8 cuboctahedra, edges with eight equivalent GaNi12 cuboctahedra, edges with sixteen equivalent NiGa4Ni8 cuboctahedra, faces with four equivalent GaNi12 cuboctahedra, and faces with fourteen NiGa4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.52 Å. All Ni–Ga bond lengths are 2.57 Å. In the fourth Ni site, Ni is bonded to two equivalent Hf, eight Ni, and two equivalent Ga atoms to form distorted NiHf2Ga2Ni8 cuboctahedra that share corners with twelve NiHf2Ga2Ni8 cuboctahedra, edges with four equivalent HfNi12 cuboctahedra, edges with four equivalent GaNi12 cuboctahedra, edges with twelve NiGa4Ni8 cuboctahedra, faces with two equivalent HfNi12 cuboctahedra, faces with two equivalent GaNi12 cuboctahedra, and faces with twelve NiGa4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.57 Å. Both Ni–Ga bond lengths are 2.52 Å. In the fifth Ni site, Ni is bonded to eight Ni and four Ga atoms to form NiGa4Ni8 cuboctahedra that share corners with twelve NiHf2Ga2Ni8 cuboctahedra, edges with eight GaNi12 cuboctahedra, edges with sixteen NiGa4Ni8 cuboctahedra, faces with four GaNi12 cuboctahedra, and faces with fourteen NiGa4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.57 Å. There are two shorter (2.51 Å) and two longer (2.52 Å) Ni–Ga bond lengths. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded to twelve Ni atoms to form GaNi12 cuboctahedra that share corners with four equivalent HfNi12 cuboctahedra, corners with eight GaNi12 cuboctahedra, edges with twenty NiHf2Ga2Ni8 cuboctahedra, a faceface with one HfNi12 cuboctahedra, faces with five GaNi12 cuboctahedra, and faces with twelve NiGa4Ni8 cuboctahedra. In the second Ga site, Ga is bonded to twelve Ni atoms to form GaNi12 cuboctahedra that share corners with twelve GaNi12 cuboctahedra, edges with twenty-four NiGa4Ni8 cuboctahedra, faces with six GaNi12 cuboctahedra, and faces with twelve NiGa4Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf by Materials Project

Hf is Tungsten structured and crystallizes in the cubic Im-3m space group. The structure is three-dimensional. Hf is bonded in a distorted body-centered cubic geometry to eight equivalent Hf atoms. All Hf–Hf bond lengths are 3.07 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf by Materials Project

Hf is Copper structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Hf is bonded to twelve equivalent Hf atoms to form a mixture of corner, edge, and face-sharing HfHf12 cuboctahedra. All Hf–Hf bond lengths are 3.17 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thermomechanical Properties of Neutron Irradiated Al 3 Hf-Al Thermal Neutron Absorber Materials

A thermal neutron absorber material composed of Al 3 Hf particles in an aluminum matrix is under development for the Advanced Test Reactor. This metal matrix composite was fabricated via hot pressing of high-purity aluminum and micrometer-size Al 3 Hf powders at volume fractions of 20.0, 28.4, and 36.5%. Room temperature tensile and hardness testing of unirradiated specimens revealed a linear relationship between volume fraction and strength, while the tensile data showed a strong decrease in elongation between the 20 and 36.5% volume fraction materials. Tensile tests conducted at 200 °C on unirradiated material revealed similar trends. Evaluations were then conducted on specimens irradiated at 66 to 75 °C to four dose levels ranging from approximately 1 to 4 dpa. Tensile properties exhibited the typical increase in strength and decrease in ductility with dose that are common for metallic materials irradiated at ≤0.4T m . Hardness also increased with neutron dose. The difference in strength between the three different volume fraction materials was roughly constant as the dose increased. Nanoindentation measurements of Al 3 Hf particles in the 28.4 vol% material showed the expected trend of increased hardness with irradiation dose. Transmission electron microscopy revealed oxygen at the interface between the Al 3 Hf particles and aluminum matrix in the irradiated material. Scanning electron microscopy of the exterior surface of tensile tested specimens revealed that deformation of the material occurs via plastic deformation of the Al matrix, cracking of the Al 3 Hf particles, and to a lesser extent, tearing of the matrix away from the particles. The fracture surface of an irradiated 28.4 vol% specimen showed failure by brittle fracture in the particles and ductile tearing of the aluminum matrix with no loss of cohesion between the particles and matrix. The coefficient of thermal expansion decreased upon irradiation, with a maximum change of –6.3% for the annealed irradiated 36.5 vol% specimen.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cs absorption capacity and selectivity of crystalline and amorphous Hf and Zr phosphates

Removal of radioactive Cs from sodium-rich solutions is a technical challenge that goes back to post World War II nuclear waste storage and treatment; and interest in this topic was reinvigorated by the Fukushima-Daiichi nuclear power plant disaster, 10 years ago. Since the 1960's there has been considerable focus on layered Zr phosphates as robust inorganic sorbents for separation of radionuclides such as Cs. Here we present synthesis and characterization, and direct comparison of Cs sorption capacity and selectivity of four related materials: 1) crystalline α-Zr phosphate and α-Hf phosphate, and 2) amorphous analogues of these. Powder X-ray diffraction, thermogravimetry, solid-state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and compositional analysis (inductively coupled plasma optical emission spectroscopy and mass spectroscopy, ICP OES and ICP MS) provided formulae; respectively M(HPO4)2∙1H2O and M(HPO4)2∙4H2O (M = Hf, Zr) for crystalline and amorphous analogues. Maximum Cs loading, competitive Cs-Na selectivity and maximum Cs-Na loading followed by the above characterizations plus 133Cs MAS-NMR spectroscopy revealed that amorphous analogues are considerably better Cs-sorbents (based on maximum Cs-loading and selectivity over Na) than the well-studied crystalline Zr-analogue. Additionally, crystalline α-Hf phosphate is better Cs-sorbent than crystalline α-Zr phosphate. All these studies consistently show that Hf phosphate is less crystallize than Zr phosphate, when obtained under similar or identical synthesis conditions. We attribute this to lower solubility of Hf phosphate compared to Zr phosphate, preventing ‘defect healing’ during the synthesis process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

Abstract In recent years there has been an increasing effort in improving the performance of Nb 3 Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields ( H Irr and H c2 , respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb 3 Sn grains and HfO 2 nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb 3 Sn. H c2 (0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb 3 Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5–4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb 3 Sn closer to the requirements necessary for FCC realization.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Degenerate doping in B-Ga 2 O 3 Single Crystals through Hf-doping

n-type conductivity of β-Ga 2 O 3 grown from the melt is typically achieved using Sn and Si. In this paper, we experimentally and computationally investigate Hf doping of β-Ga 2 O 3 single crystals using UV–vis-NIR absorption and Hall effect measurements and hybrid functional calculations. Unintentionally-doped and Hf-doped samples with a nominal concentration of 0.5at% were grown from the melt using vertical gradient freeze and Czochralski method in mixed Ar + O 2 atmosphere. We demonstrate Hf dopants, predicted to incorporate on the octahedral GaII site as a shallow donor, achieve degenerate doping in β-Ga 2 O 3 with a measured electron concentration ~2 × 10 19 cm -3 , mobility 80–65 cm 2 V -1 s -1 , and resistivity down to 5 mΩ cm in our samples. The concentration of Hf was measured to be 1.3 × 10 19 atoms cm -3 using glow discharge mass spectroscopy on doped samples, confirming Hf to be the cause of n-type conductivity (electron concentration ~2 × 10 19 cm -3 ).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Intrinsic electric quadrupole moment of the K π = 8 - isomeric state in Hf 178

The lifetime of the 9 - state in the rotational band based on the 4.0 s, K π = 8 - , isomeric state ( 178 Hf m 1 ) from the decay of the 31-yr isomer ( 178 Hf m 2 ) was determined to be 99(2) ps by means of the fast-timing technique using two LaBr 3 (Ce) scintillators. The δ (E2/M1) mixing ratios of the ΔI = 1 γ rays depopulating levels in this band were deduced from γ-γ angular correlations by using a 178 Hf m 2 radioactive source located at the center of the Gammasphere HPGe detector array. The new results, together with previous spectroscopic information, provide a different way to extract the intrinsic quadrupole moment of Q 0 = 6.45 (14) eb for the 178 Hf m 1 band. A possible explanation for the reduction of the 178 Hf m 1 nuclear charge radius is presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Effect of thickness and surface composition on the stability of polarization in ferroelectric Hf x Zr 1 - x O 2 thin films

Using density functional theory, we find that tailoring the surface composition provides a route to stabilize the polar phases of the promising ferroelectric material, Hf x Zr 1-x O 2 . First, we show that for pure Hf O 2 , controlling the positively polarized surface to be relatively oxygen rich adequately screens the ferroelectric surface charges and stabilizes the polar orthorhombic phase. We then demonstrate that the ferroelectric polarization, as measured by the structural polar displacements, increases with decreasing thickness, leading to the emergence of a polar rhombohedral-like phase at the ultrathin limit (1.5 unit cells). Our findings extend to the cases of Hf 0.5 Zr 0.5 O 2 and Zr O 2 , both of which have surface energy landscapes similar to that of Hf O 2 . In conclusion, these findings are consistent with and offer insights into the observed absence of a ferroelectric thickness limit in Hf x Zr 1-x O 2 -based thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Examining the Performance of Walsh-DSSS Against FBMC-SS in HF Channels

Abstract—Filter bank multicarrier spread spectrum (FBMCSS) has proven to be a robust and reliable waveform choice for communication over high frequency (HF) skywave links. However, the performance of this waveform has yet to be contextualized against typical robust HF waveforms, such as the Walsh-encoded waveform detailed in the MIL-STD-188-110D, Appendix D document. In this paper, we first outline the advantages of both the Walsh and FBMC-SS waveforms as well as present their developments. Simulation results are then presented for ideal, simulated HF, and HF with interference channel conditions. Lastly, skywave-HF results are presented for these two waveforms both with and without interference.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2021

Pinning Characteristics of Zr and Hf- Added REBCO Coated Conductors Made by Advanced MOCVD in Low-to-High Magnetic Fields

BaMO 3 (M=Zr, Hf) pinning centers introduced in REBa 2 Cu 3 O 7-x (REBCO and RE = rare earth) coated conductors yield superior performance in high magnetic fields. We present the critical current density J c over a temperature range of 4.2-77 K and magnetic fields of 0-14 T (B || c-axis), of 5-15 mol.% Zr- and Hf-added REBCO 4+ μm thick film tapes fabricated by advanced metal organic chemical vapor deposition (A-MOCVD). The morphology of self-assembled BMO nanorods aligned along c-axis is found to be dependent on the Zr/Hf content. We also observe a correlation between the density of RE 2 O 3 in-plane nano-precipitates and the continuity and concentration of BMO nanorods in films of different Ba content. It is found that the (Ba+M)/Cu (M=Zr, Hf) content in REBa 2 Cu 3 O 7-x affects the shape of pinning force density curves over a wide magnetic field range and temperatures below 20 K. Another remarkable observation is the similarity in the critical current properties of Hf and Zr -added REBCO films as function of (Ba+M)/Cu content at intermediate to high range of (Ba+M)/Cu content. As a result, a quantitative analysis of pinning efficiency and correlation with the microstructure of Zr and Hf- added REBCO coated conductors is discussed.

2G high-temperature superconductor (2G-HTS)↗
DOE OSTI2020

Investigation of Various Transformer Topologies for HF Isolation Applications

High-frequency (HF) transformers are an essential part of many power electronic devices. The performance and behavior of HF transformers can greatly affect the efficiency and performance of all systems, particularly, from a parasitic parameter point of view. In this article, HF transformers' parasitic parameters, such as leakage inductances and parasitic capacitances, are analyzed using a novel analytical method, finite element method (FEM), and experimental measurements of different structures and winding arrangements. Also, the magnetic field, electric field, electric displacement field, and electric potential distribution within the transformers are simulated and analyzed. Four different HF transformers with E and U cores with different windings are designed and analyzed. Investigation outcomes help to classify structures according to the trade-off between leakage inductances and series parasitic capacitances. This information can later be used for the optimal selection and design of transformers as a function of their operating frequency for any power rating and voltage level. Moreover, 3-D FEM and experimental results validate the proposed methodology to be used for designing HF transformers in high-voltage/power applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗