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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Hf(Se2Cl3)2 by Materials Project

Hf(SeCl3)2(Se)2 crystallizes in the tetragonal P4_2/ncm space group. The structure is one-dimensional and consists of eight selen molecules and two Hf(SeCl3)2 ribbons oriented in the (-1, 1, 0) direction. In each Hf(SeCl3)2 ribbon, Hf4+ is bonded in an octahedral geometry to six Cl1- atoms. There are two shorter (2.42 Å) and four longer (2.49 Å) Hf–Cl bond lengths. Se+0.50+ is bonded in a bent 120 degrees geometry to two equivalent Cl1- atoms. Both Se–Cl bond lengths are 2.98 Å. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Hf4+ and one Se+0.50+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Hf4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(TeCl)6 by Materials Project

Hf(TeCl2)3(Te)3 crystallizes in the orthorhombic Pbcm space group. The structure is one-dimensional and consists of twelve telloy molecules and two Hf(TeCl2)3 ribbons oriented in the (0, 0, 1) direction. In each Hf(TeCl2)3 ribbon, Hf4+ is bonded in an octahedral geometry to six Cl1- atoms. There are a spread of Hf–Cl bond distances ranging from 2.42–2.50 Å. There are two inequivalent Te+0.33+ sites. In the first Te+0.33+ site, Te+0.33+ is bonded in a water-like geometry to two equivalent Cl1- atoms. Both Te–Cl bond lengths are 3.15 Å. In the second Te+0.33+ site, Te+0.33+ is bonded in a single-bond geometry to one Cl1- atom. The Te–Cl bond length is 3.11 Å. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Hf4+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Hf4+ atom. In the third Cl1- site, Cl1- is bonded in a distorted water-like geometry to one Hf4+ and one Te+0.33+ atom. In the fourth Cl1- site, Cl1- is bonded in a 1-coordinate geometry to one Hf4+ and one Te+0.33+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(TlSe)4 by Materials Project

Hf(TlSe)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six Se2- atoms to form HfSe6 octahedra that share corners with three TlSe5 square pyramids, edges with two HfSe6 octahedra, and edges with six TlSe5 square pyramids. There are a spread of Hf–Se bond distances ranging from 2.66–2.78 Å. In the second Hf4+ site, Hf4+ is bonded to six Se2- atoms to form HfSe6 octahedra that share corners with four TlSe5 square pyramids, edges with two HfSe6 octahedra, and edges with four TlSe5 square pyramids. There are a spread of Hf–Se bond distances ranging from 2.65–2.79 Å. In the third Hf4+ site, Hf4+ is bonded to six Se2- atoms to form HfSe6 octahedra that share corners with two equivalent TlSe5 square pyramids, edges with two equivalent HfSe6 octahedra, and edges with four TlSe5 square pyramids. There are a spread of Hf–Se bond distances ranging from 2.70–2.74 Å. There are ten inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two equivalent HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and an edgeedge with one TlSe5 square pyramid. The corner-sharing octahedra tilt angles range from 15–18°. There are a spread of Tl–Se bond distances ranging from 3.02–3.49 Å. In the second Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 7–9°. There are a spread of Tl–Se bond distances ranging from 3.08–3.48 Å. In the third Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.01–3.34 Å. In the fourth Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and edges with two TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 10–11°. There are a spread of Tl–Se bond distances ranging from 3.05–3.53 Å. In the fifth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.04–3.46 Å. In the sixth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.02–3.51 Å. In the seventh Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 11–15°. There are a spread of Tl–Se bond distances ranging from 3.03–3.45 Å. In the eighth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.00–3.36 Å. In the ninth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.01–3.50 Å. In the tenth Tl1+ site, Tl1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.05–3.50 Å. There are ten inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the second Se2- site, Se2- is bonded to two equivalent Hf4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHf2Tl4 octahedra. The corner-sharing octahedra tilt angles range from 12–20°. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to two Hf4+ and four Tl1+ atoms. In the fourth Se2- site, Se2- is bonded to two Hf4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHf2Tl4 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifth Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the sixth Se2- site, Se2- is bonded to two Hf4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHf2Tl4 octahedra. The corner-sharing octahedral tilt angles are 12°. In the seventh Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the eighth Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the ninth Se2- site, Se2- is bonded to one Hf4+ and five Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHfTl5 octahedra. The corner-sharing octahedra tilt angles range from 0–20°. In the tenth Se2- site, Se2- is bonded in a 6-coordinate geometry to two Hf4+ and four Tl1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(TlS)4 by Materials Project

Hf(TlS)4 is Orthorhombic Perovskite-like structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six S2- atoms to form HfS6 octahedra that share corners with two TlS5 square pyramids, edges with two HfS6 octahedra, and edges with five TlS5 square pyramids. There are a spread of Hf–S bond distances ranging from 2.52–2.63 Å. In the second Hf4+ site, Hf4+ is bonded to six S2- atoms to form HfS6 octahedra that share corners with three TlS5 square pyramids, edges with two HfS6 octahedra, and edges with three TlS5 square pyramids. There are a spread of Hf–S bond distances ranging from 2.51–2.66 Å. In the third Hf4+ site, Hf4+ is bonded to six S2- atoms to form HfS6 octahedra that share corners with two equivalent TlS5 square pyramids, edges with two equivalent HfS6 octahedra, and edges with two equivalent TlS5 square pyramids. There are two shorter (2.57 Å) and four longer (2.59 Å) Hf–S bond lengths. There are ten inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded to five S2- atoms to form distorted TlS5 square pyramids that share corners with two equivalent HfS6 octahedra, edges with three HfS6 octahedra, and an edgeedge with one TlS5 square pyramid. The corner-sharing octahedra tilt angles range from 15–19°. There are a spread of Tl–S bond distances ranging from 2.88–3.41 Å. In the second Tl1+ site, Tl1+ is bonded to five S2- atoms to form distorted TlS5 square pyramids that share corners with two HfS6 octahedra, corners with two equivalent TlS5 square pyramids, edges with three HfS6 octahedra, and edges with two TlS5 square pyramids. The corner-sharing octahedra tilt angles range from 7–8°. There are a spread of Tl–S bond distances ranging from 2.96–3.45 Å. In the third Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four S2- atoms. There are a spread of Tl–S bond distances ranging from 2.89–3.25 Å. In the fourth Tl1+ site, Tl1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Tl–S bond distances ranging from 2.92–3.50 Å. In the fifth Tl1+ site, Tl1+ is bonded in a 4-coordinate geometry to four S2- atoms. There are a spread of Tl–S bond distances ranging from 2.92–3.46 Å. In the sixth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four S2- atoms. There are a spread of Tl–S bond distances ranging from 2.92–3.49 Å. In the seventh Tl1+ site, Tl1+ is bonded to five S2- atoms to form distorted TlS5 square pyramids that share corners with two HfS6 octahedra, corners with two equivalent TlS5 square pyramids, edges with three HfS6 octahedra, and edges with two TlS5 square pyramids. The corner-sharing octahedra tilt angles range from 12–16°. There are a spread of Tl–S bond distances ranging from 2.88–3.37 Å. In the eighth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four S2- atoms. There are a spread of Tl–S bond distances ranging from 2.89–3.28 Å. In the ninth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four S2- atoms. There are a spread of Tl–S bond distances ranging from 2.89–3.45 Å. In the tenth Tl1+ site, Tl1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Tl–S bond distances ranging from 2.93–3.43 Å. There are ten inequivalent S2- sites. In the first S2- site, S2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the second S2- site, S2- is bonded in a 6-coordinate geometry to two equivalent Hf4+ and four Tl1+ atoms. In the third S2- site, S2- is bonded in a 6-coordinate geometry to two Hf4+ and four Tl1+ atoms. In the fourth S2- site, S2- is bonded to two Hf4+ and four Tl1+ atoms to form distorted corner-sharing SHf2Tl4 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifth S2- site, S2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the sixth S2- site, S2- is bonded in a 6-coordinate geometry to two Hf4+ and four Tl1+ atoms. In the seventh S2- site, S2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the eighth S2- site, S2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the ninth S2- site, S2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the tenth S2- site, S2- is bonded in a 6-coordinate geometry to two Hf4+ and four Tl1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(US)3 by Materials Project

Hf(US)3 crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. U is bonded in a square co-planar geometry to four equivalent S atoms. All U–S bond lengths are 2.64 Å. Hf is bonded to six equivalent S atoms to form corner-sharing HfS6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Hf–S bond lengths are 2.64 Å. S is bonded to four equivalent U and two equivalent Hf atoms to form a mixture of edge and corner-sharing SHf2U4 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High-Pressure Synthesis of Metal–Inorganic Frameworks Hf 4 N 20 •N 2 , WN 8 •N 2 , and Os 5 N 28 •3N 2 with Polymeric Nitrogen Linkers

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one-step synthesis of metal–inorganic frameworks Hf 4 N 20 •N 2 , WN 8 •N 2 , and Os 5 N 28 •3N 2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf 4 N 20 , WN 8 , and Os 5 N 28 ) are built from transition-metal atoms linked either by polymeric polydiazenediyl (polyacetylene-like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high-pressure reaction between Hf and N 2 also leads to a non-centrosymmetric polynitride Hf 2 N 11 that features double-helix catena-poly[tetraz-1-ene-1,4-diyl] nitrogen chains [–N–N–N=N–] ∞ .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High-Pressure Synthesis of Metal–Inorganic Frameworks Hf 4 N 20 ·N 2 , WN 8 ·N 2 , and Os 5 N 28 ·3 N 2 with Polymeric Nitrogen Linkers

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one-step synthesis of metal–inorganic frameworks Hf 4 N 20 ·N 2 , WN 8 ·N 2 , and Os 5 N 28 ·3 N 2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf 4 N 20 , WN 8 , and Os 5 N 28 ) are built from transition-metal atoms linked either by polymeric polydiazenediyl (polyacetylene-like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high-pressure reaction between Hf and N 2 also leads to a non-centrosymmetric polynitride Hf 2 N 11 that features double-helix catena-poly[tetraz-1-ene-1,4-diyl] nitrogen chains [–N–N–N=N–] ∞ .

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

Microstructure, compression properties, and oxidation behavior of Hf-25Ta-5Me alloys (Me is Mo, Nb, W, 0.5Mo + 0.5 W, Cr, or Zr)

Hf–Ta based alloys have recently been investigated as potential candidates for high-temperature structural applications. While most attentions have been given to the properties above ~1200 °C where the alloys are mainly single-phase BCC structures and have excellent oxidation performance due to formation of super-oxides, structural properties at lower temperatures are equally important for applications in which an alloy may experience a range of temperatures. In the present work, microstructure, phase composition, mechanical properties and oxidation behavior of six Hf-25Ta-5Me alloys (Me is Mo (HTM alloy), W (HTW), 0.5Mo + 0.5 W (HTMW), Cr (HTC) or Zr (HTZ), the compositions are in at.%) are reported at temperatures below the eutectoid transformation. The alloys were prepared by arc melting followed by hot isostatic pressing for 3 h at 1400 °C and 207 MPa. All the alloys display coarse grains of partially or fully transformed (by a eutectoid reaction) high-temperature BCC phase. The eutectoid regions consist of fine lamellae of Hf-rich HCP and Ta-rich BCC phases. The ternary alloys containing W or Cr also contained small amounts of a cubic Laves phase. At 25 °C, the HTW alloy was the strongest (yield stress σ y = 1966 MPa) but brittle and HTZ was the weakest (σ y = 1120 MPa) but ductile among the studied alloys. Other alloys showed intermediate behaviors. In general, the room temperature ductility of the alloys increased with decreasing σy. All alloys maintained high strength up to 800 °C, but displayed a noticeable strength decrease at 1000 °C. At 1000 °C, HTMW was the strongest alloy (σ y = 468 MPa) and HTC was the weakest alloy (σ y = 368 MPa). All alloys had excellent deformability at 1000 °C. Oxidation behavior of the alloys was studied at 800 °C and 1000 °C and compared with that of Hf–27Ta binary alloy. Although the ternary additions improved oxidation resistance, overall oxidation performance of the studied alloys at 800 °C and 1000 °C was poor.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Rare earth metals production using alternative feedstock that eliminates HF

This work reports the successful production of rare earth (RE) metal using Na-RE-F. Presently, RE metals are primarily produced using RE-fluoride due to its higher air and moisture stability compared to RE-chloride. However, its preparation requires the use of corrosive and hazardous chemicals, such as hydrofluoric acid (HF) or ammonium bifluoride (NH 4 HF 2 ). The present study demonstrates that Na-RE-F is an alternative salt to the typically used RE-fluoride. The Na-RE-F for this work is produced via a scalable hydrometallurgical approach using three different RE salts as feedstock, including acetate, nitrate, and chloride. HF is neither used nor generated during the salt preparation process. Furthermore, the Na-RE-F powder dries in air (without dry HF), and only water evolves during the drying process. Analyses of the Na-RE-F show that NaF liberates as a flux during the heating process, which lowers the salt reduction temperature to <900 °C, thus minimizing or eliminating the need for additional flux. Calciothermic reduction of the Na-RE-F salt is successfully employed to obtain RE metal. This work represents a safer, greener, and more widely deployable approach for producing the RE metals needed for permanent magnets which support the transition to a cleaner society through the decarbonization of the transportation industry.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Phase diagrams and polarization reversal in nanosized Hf x Zr 1–x O 2–y

To describe the polar properties of nanosized Hf x Zr 1–x O 2–y , we evolve the “effective” Landau–Ginzburg–Devonshire (LGD) model based on the parametrization of the Landau expansion coefficients for polar and antipolar orderings. We have shown that the effective LGD model can predict the influence of screening conditions and size effects on phase diagrams, polarization reversal, and structural properties of nanosized Hf x Zr 1–x O 2–y of various shapes and sizes. To verify the model, we use the available experimental results for Hf x Zr 1–x O 2 thin films and oxygen-deficient HfO2–y nanoparticles prepared under different annealing conditions. X-ray diffraction, which was used to determine the phase composition of the HfO 2–y nanoparticles, revealed the formation of a ferroelectric orthorhombic phase in them. Micro-Raman spectroscopy was used to explore the correlation of lattice dynamics and structural changes that depend on the oxygen vacancy concentration in the HfO 2–y nanoparticles. Since our approach allows us to determine the conditions (shape, sizes, Zr content, and/or oxygen vacancy amount) for which nanosized Hf x Zr 1–x O 2–y are ferroelectric or antiferroelectric, we hope that the obtained results are useful for creation of next generation Si-compatible ferroelectric gate oxide nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ferro-ionic states and domains morphology in Hf x Zr 1–x O 2 nanoparticles

Unique polar properties of nanoscale hafnia-zirconia oxides (Hf x Zr 1–x O 2 ) are of great interest for condensed matter physics, nanophysics, and advanced applications. These properties are connected (at least partially) to the ionic–electronic and electrochemical phenomena at the surface, interfaces, and/or internal grain boundaries. Here, we calculated the phase diagrams, dielectric permittivity, spontaneous polar, and antipolar ordering, as well as the domain structure morphology in Hf x Zr 1–x O 2 nanoparticles covered by ionic–electronic charge originating from surface electrochemical adsorption. We revealed that the ferro-ionic coupling supports the polar long-range order in nanoscale Hf x Zr 1–x O 2 , induces, and/or enlarges the stability region of the labyrinthine domains toward smaller sizes and smaller environmental dielectric constant at low concentrations of the surface ions. The ferro-ionic coupling causes the transition to the single-domain ferro-ionic state at high concentrations of the surface ions. We predict that the labyrinthine domain states, being multiple-degenerated, may significantly affect the emergence of the negative differential capacitance state in the nanograined/nanocrystalline Hf x Zr 1–x O 2 films.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Phase stability in the Hf-N and Zr-N systems

Hf and Zr nitrides are promising compounds for many technologically important areas, including high-temperature structural applications, quantum computing, and solar and optical applications. Here, this article reports on a comprehensive first-principles statistical mechanics study of phase stability in the Hf-N and Zr-N binary systems. A high solubility of nitrogen in the hcp forms of Hf and Zr is predicted. The rocksalt forms of HfN and ZrN can also tolerate a high degree of off-stoichiometry through the introduction of nitrogen and metal vacancies. The Hf-N binary favors a family of stacking faulted parent crystal structures at intermediate nitrogen concentrations that host a unique form of short-range order among nitrogen interstitials and vacancies. These phases can accommodate some degree of configurational entropy and remain ordered to temperatures as high as 1200 K.

Monte Carlo methods↗
DOE OSTI2022

Effects of Hydrogen Bonding on Nuclear Data Development of Liquid Anhydrous HF

Anhydrous Hydrogen Fluoride (HF) at high temperatures and pressures is used to process and manufacture nuclear fuel. As HF is often used directly with uranium, correct neutron thermal scattering cross sections are crucial to criticality safety applications. Classical molecular dynamics (CMD) simulation of the flexible HF system was used to create the thermal scattering law (TSL) and cross sections. The initial 2-site model is used in LAMMPS, and it can not capture the H-bond. To correctly represent the H-bond effects, a second, 3-site model was constructed in GROMACS. The 3-site model handled H-bonds by connecting a massless charge to the molecule. Key model parameters were compared to experimental data to verify the approach and models. To get the normalized VACF, the model was compared using hydrogen and fluorine bond length, density, potential energy, and diffusion coefficient. The phonon DOSs for both models were derived from the normalized VACF. DOSs were used to estimate the TSL ( S ( α, β )) and neutron thermal scattering cross sections for hydrogen in HF. The TSLs were evaluated using the FLASSH code with the Schofield diffusion model. It was observed that the representation of the hydrogen bonding changes the TSL's diffusional contributions. This is represented in the low energy scattering cross section, where intermolecular binding effects shift the cross section.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Materials Data on Hf(BH4)4 by Materials Project

Hf(BH4)4 is alpha Po structured and crystallizes in the cubic P-43m space group. The structure is zero-dimensional and consists of one Hf(BH4)4 cluster. Hf4+ is bonded to twelve equivalent H+0.50+ atoms to form HfH12 cuboctahedra that share faces with four equivalent BH4 tetrahedra. All Hf–H bond lengths are 2.13 Å. B3- is bonded to four H+0.50+ atoms to form BH4 tetrahedra that share a faceface with one HfH12 cuboctahedra. There is one shorter (1.19 Å) and three longer (1.25 Å) B–H bond length. There are two inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Hf4+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(Te2Cl3)2 by Materials Project

Hf(Te2Cl3)2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one Hf(Te2Cl3)2 cluster. Hf4+ is bonded in an octahedral geometry to six Cl1- atoms. There are two shorter (2.43 Å) and four longer (2.49 Å) Hf–Cl bond lengths. There are two inequivalent Te+0.50+ sites. In the first Te+0.50+ site, Te+0.50+ is bonded in a single-bond geometry to one Cl1- atom. The Te–Cl bond length is 3.22 Å. In the second Te+0.50+ site, Te+0.50+ is bonded in a distorted single-bond geometry to one Cl1- atom. The Te–Cl bond length is 3.11 Å. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Hf4+ and one Te+0.50+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Hf4+ atom. In the third Cl1- site, Cl1- is bonded in a distorted water-like geometry to one Hf4+ and one Te+0.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(VH2)2 by Materials Project

HfV2H4 crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional. Hf is bonded in a 8-coordinate geometry to eight equivalent H atoms. All Hf–H bond lengths are 2.04 Å. V is bonded in a distorted rectangular see-saw-like geometry to four equivalent H atoms. There is two shorter (1.80 Å) and two longer (1.83 Å) V–H bond length. H is bonded to two equivalent Hf and two equivalent V atoms to form a mixture of edge and corner-sharing HHf2V2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(SiO)2 by Materials Project

Hf(SiO)2 crystallizes in the tetragonal I4_1/amd space group. The structure is zero-dimensional and consists of eight Hf(SiO)2 clusters. Hf4+ is bonded in a linear geometry to two equivalent O2- atoms. Both Hf–O bond lengths are 2.01 Å. Si is bonded in a single-bond geometry to one O2- atom. The Si–O bond length is 1.64 Å. O2- is bonded in a bent 120 degrees geometry to one Hf4+ and one Si atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Multicarrier Spread Spectrum Communications With Noncontiguous Subcarrier Bands for HF Skywave Links

Existing high-frequency (HF) radio platforms offer robust performance against the volatile HF propagation channel. However, the growing traffic across the band contests the reliability of these systems. While techniques to mitigate the effects of narrowband interference have been thoroughly explored, they are insufficient against wideband interference or when the transmission band is occupied by numerous scattered users. To improve reliability in these congested channel conditions, we propose a filter-bank based multicarrier spread-spectrum waveform with noncontiguous subcarrier bands. Using noncontiguous subcarrier bands enables the system to at once leverage the robustness of a wideband system while retaining the frequency agility of a narrowband system. In this study, we modify a filter-bank transmitter structure to accommodate noncontiguous subcarrier bands and consider several immediate impacts of this change, such as elevated peak-to-average-power ratios (PAPRs). A receiver architecture to process the noncontiguous spread-spectrum signal is also introduced, along with details regarding wideband channel estimation. Finally, we develop efficient transmitter and receiver structures to support practical system implementations. We conclude by comparing the performance of contiguous and noncontiguous systems through both simulation and over-the-air testing. The results show that the noncontiguous system remains robust in typical HF channels while significantly outperforming the contiguous system in congested spectral conditions.

(PAPR↗