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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Nonlocal thermodynamic equilibrium effects in stratospheric HF by collisional energy transfer from electronically excited O2 and implications for infrared remote sensing

A possible nonlocal thermodynamic equilibrium (non-LTE) effect involving stratospheric HF arising from the direct photochemical excitation of vibrationally excited HF by collisional energy transfer from electronically excited O2 is presented. Although this non-LTE effect is smaller that one associated with the direct solar excitation of both HF(nv = 1) and HF(nv = 2), calculations show that inclusion of the mechanism into retrieval algorithms is necessary if correct daytime upper stratosphere HF profiles are to be inferred in future IR thermal emission measurements.

Kaye, Jack A.↗
NASA NTRS1994

Does human cognition allow Human Factors (HF) certification of advanced aircrew systems?

This paper has examined the requirements of HF specification and certification within advanced or complex aircrew systems. It suggests reasons for current inadequacies in the use of HF in the design process, giving some examples in support, and suggesting an avenue towards the improvement of the HF certification process. The importance of human cognition to the operation and performance of advanced aircrew systems has been stressed. Many of the shortfalls of advanced aircrew systems must be attributed to over automated designs that show little consideration on either the mental limits or the cognitive capabilities of the human system component. Traditional approaches to system design and HF certification are set within an over physicalistic foundation. Also, traditionally it was assumed that physicalistic system functions could be attributed to either the human or the machine on a one to one basis. Moreover, any problems associated with the parallel needs, or promoting human understanding alongside system operation and direction, were generally equated in reality by the natural flexibility and adaptability of human skills. The consideration of the human component of a complex system is seen as being primarily based on manifestations of human behavior to the almost total exclusion of any appreciation of unobservable human mental and cognitive processes. The argument of this paper is that the considered functionality of any complex human-machine system must contain functions that are purely human and purely cognitive. Human-machine system reliability ultimately depends on human reliability and dependability and, therefore, on the form and frequency of cognitive processes that have to be conducted to support system performance. The greater the demand placed by an advanced aircraft system on the human component's basic knowledge processes or cognition, rather than on skill, the more insiduous the effects the human may have on that system. This paper discusses one example of an attempt to devise an improved method of specificaiton and certification with relation to the advanced aircrew system, that of the RN Merlin helicopter. The method is realized to have limitations in practice, these mainly associated with the late production of the system specification in relation to the system development process. The need for a careful appreciation of the capabilities and support needs of human cognition within the design process of a complex man machine system has been argued, especially with relation to the concept of system functionality. Unlike the physicalistic Fitts list, a new classification of system functionality is proposed, namely: (1) equipment - system equipment related; (2) cognitive - human cognition related; and (3) associated - necessary combinatin of equipment and cognitive. This paper has not proposed a method for a fuller consideration of cognition within systems design, but has suggested the need for such a method and indicated an avenue towards its development. Finally, the HF certification of advanced aircrew systems is seen as only being possible in a qualified sense until the important functions of human cognition are considered within the system design process. (This paper contains the opinions of its authors and does not necessarily refledt the standpoint of their respective organizations).

Macleod, Iain S.↗
NASA NTRS1996

Microstructure and Phase Stability of Single Crystal NiAl Alloyed with Hf and Zr

Six near stoichiometric, NiAl single-crystal alloys, with 0.05-1.5 at.% of Hf and Zr additions plus Si impurities, were microstructurally analyzed in the as-cast, homogenized, and aged conditions. Hafnium-rich interdendritic regions, containing the Heusler phase (Ni2AlHf), were found in all the as-cast alloys containing Hf. Homogenization heat treatments partially reduced these interdendritic segregated regions. Transmission electron microscopy (TEM) observations of the as-cast and homogenized microstructures revealed the presence of a high density of fine Hf (or Zr) and Si-rich precipitates. These were identified as G-phase, Nil6X6Si7, or as an orthorhombic NiXSi phase, where X is Hf or Zr. Under these conditions the expected Heusler phase (beta') was almost completely absent. The Si responsible for the formation of the G and NiHfSi phases is the result of molten metal reacting with the Si-containing crucible used during the casting process. Varying the cooling rates after homogenization resulted in the refinement or complete suppression of the G and NiHfSi phases. In some of the alloys studied, long-term aging heat treatments resulted in the formation of Heusler precipitates, which were more stable at the aging temperature and coarsened at the expense of the G-phase. In other alloys, long-term aging resulted in the formation of the NiXSi phase. The stability of the Heusler or NiXSi phases can be traced to the reactive element (Hf or Zr) to silicon ratio. If the ratio is high, then the Heusler phase appears stable after long time aging. If the ratio is low, then the NiHfSi phase appears to be the stable phase.

Locci, I. E.↗
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↗
NASA NTRS1974

The effects of composition on mechanical properties of W-4Re-Hf-C alloys

Studies were made of the effects of alloy composition on the mechanical behavior of as-worked W-4Re-Hf-C alloys containing up to about 0.8 mol % Hfc. Extracted second-phase particles were analyzed and related to alloy composition and creep strength. While strengthening is attributed to HfC particles, the presence of excess hafnium or carbon (above the calculated amounts for stoichiometric HfC) in swaged W-4Re-Hf-C alloys generally causes a reduction of the high-temperature (1930 C) tensile strength; maximum creep strength is, however, indicated for alloys with a slight (about 0.05 to 0.1 at. %) excess of hafnium. Particle strengthening is reduced by WC in solid solution with HfC for allow compositions with an excess of carbon. The low-temperature ductility of worked W-4Re-Hf-C alloys appears to be far more dependent on the amount of excess C or Hf present than on the HfC particle content in the range studies.

Witzke, W. R.↗
NASA NTRS1975

Directionally solidified pseudo-binary eutectics of Ni-Cr-(Hf, Zr)

A pseudo-binary eutectic, in which the intermetallic Ni7Hf2 reinforces the Ni-Cr solid solution phase, was previously predicted in the Ni-Cr-Hf system by a computer analysis. The experimental determination of pseudo binary eutectic compositions and the directional solidification of the Ni-Cr-Hf, Zr, and Ni-Cr-Zr eutectic alloys are discussed. To determine unknown eutectics, chemical analyses were made of material bled from near eutectic ingots during incipient melting. Nominal compositions in weight percent of Ni-18.6Cr-24.0HF, Ni19.6Cr-12.8Zr-2.8Hf, and Ni-19.2Cr-14.8Zr formed aligned pseudo-binary eutectic structures. The melting points were about 1270 C. The reinforcing intermetallic phases were identified as noncubic (Ni,Cr)7Hf2 and (Ni,Cr)7(Hf,Zr)2, and face centered cubic (Ni,Cr)5Zr. The volume fraction of the reinforcing phases were about 0.5.

Kim, Y. G.↗
NASA NTRS1982

Spectroscopic requirements for HALOE: An analysis of the HCl and HF channels

Spectral line parameters that have absorption features within the HCl and HF channels of the Halogen Occultation Experiment (HALOE) were evaluated. Line positions and identification of stratospheric and solar absorption features in both channels are presented based on an analysis of high-resolution, balloon-borne solar occultation spectra. For the relevant HCl and HF lines and for transitions of the interfering species, the accuracy of the following spectral parameters was assessed: line positions, line strengths, lower state energies, air-broadened collisional half-widths, and temperature dependence of the air-broadened half-widths. In addition, since the HALOE instrument and calibration cells are filled with mixtures of HCl in N2 and HF in N2, the self-broadened and N2-broadened HF and HCl half-widths were also considered.

Rinsland, C. P.↗