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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Hf4CN3 by Materials Project

Hf4CN3 is Caswellsilverite-like structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded to six N atoms to form a mixture of edge and corner-sharing HfN6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. All Hf–N bond lengths are 2.27 Å. In the second Hf site, Hf is bonded to three equivalent C and three equivalent N atoms to form a mixture of edge and corner-sharing HfC3N3 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. All Hf–C bond lengths are 2.27 Å. All Hf–N bond lengths are 2.32 Å. C is bonded to six equivalent Hf atoms to form CHf6 octahedra that share corners with six equivalent NHf6 octahedra, edges with six equivalent CHf6 octahedra, and edges with six equivalent NHf6 octahedra. The corner-sharing octahedral tilt angles are 2°. There are two inequivalent N sites. In the first N site, N is bonded to six Hf atoms to form NHf6 octahedra that share corners with three equivalent CHf6 octahedra, corners with three equivalent NHf6 octahedra, edges with three equivalent CHf6 octahedra, and edges with nine NHf6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the second N site, N is bonded to six equivalent Hf atoms to form a mixture of edge and corner-sharing NHf6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf6CoSb2 by Materials Project

Hf6CoSb2 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 4-coordinate geometry to two equivalent Co and two equivalent Sb atoms. Both Hf–Co bond lengths are 2.58 Å. Both Hf–Sb bond lengths are 3.02 Å. In the second Hf site, Hf is bonded in a 5-coordinate geometry to one Co and four equivalent Sb atoms. The Hf–Co bond length is 3.08 Å. All Hf–Sb bond lengths are 2.97 Å. Co is bonded in a 6-coordinate geometry to nine Hf atoms. Sb is bonded in a 9-coordinate geometry to nine Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf9CoW4 by Materials Project

Hf9W4Co crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 1-coordinate geometry to four W and one Co atom. There are a spread of Hf–W bond distances ranging from 2.94–3.09 Å. The Hf–Co bond length is 2.56 Å. In the second Hf site, Hf is bonded in a 2-coordinate geometry to two equivalent W atoms. Both Hf–W bond lengths are 2.89 Å. There are two inequivalent W sites. In the first W site, W is bonded in a 12-coordinate geometry to eight Hf and four W atoms. There are two shorter (2.71 Å) and two longer (2.93 Å) W–W bond lengths. In the second W site, W is bonded to six equivalent Hf and six equivalent W atoms to form face-sharing WHf6W6 cuboctahedra. Co is bonded in a 6-coordinate geometry to six equivalent Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf2InCu2 by Materials Project

Hf2Cu2In crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 6-coordinate geometry to six equivalent Cu and four equivalent In atoms. There are two shorter (2.69 Å) and four longer (2.80 Å) Hf–Cu bond lengths. All Hf–In bond lengths are 3.21 Å. In the second Hf site, Hf is bonded in a 6-coordinate geometry to six equivalent Cu and four equivalent In atoms. There are four shorter (2.72 Å) and two longer (2.73 Å) Hf–Cu bond lengths. All Hf–In bond lengths are 3.13 Å. Cu is bonded in a 9-coordinate geometry to six Hf, one Cu, and two equivalent In atoms. The Cu–Cu bond length is 2.51 Å. Both Cu–In bond lengths are 2.85 Å. In is bonded in a 12-coordinate geometry to eight Hf and four equivalent Cu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf5Zr5Ga6 by Materials Project

Hf5Zr5Ga6 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 6-coordinate geometry to six Ga atoms. There are a spread of Hf–Ga bond distances ranging from 2.86–2.88 Å. In the second Hf site, Hf is bonded in a 5-coordinate geometry to five Ga atoms. There are a spread of Hf–Ga bond distances ranging from 2.76–3.10 Å. There are three inequivalent Zr sites. In the first Zr site, Zr is bonded in a 5-coordinate geometry to five Ga atoms. There are a spread of Zr–Ga bond distances ranging from 2.77–3.11 Å. In the second Zr site, Zr is bonded in a 5-coordinate geometry to five Ga atoms. There are a spread of Zr–Ga bond distances ranging from 2.76–3.11 Å. In the third Zr site, Zr is bonded in a 5-coordinate geometry to five Ga atoms. There are a spread of Zr–Ga bond distances ranging from 2.76–3.11 Å. There are four inequivalent Ga sites. In the first Ga site, Ga is bonded in a 9-coordinate geometry to five Hf and four Zr atoms. In the second Ga site, Ga is bonded in a 9-coordinate geometry to five Hf and four Zr atoms. In the third Ga site, Ga is bonded in a 9-coordinate geometry to six Hf and three Zr atoms. In the fourth Ga site, Ga is bonded in a 9-coordinate geometry to four equivalent Hf and five Zr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf4C3N by Materials Project

Hf4C3N is Caswellsilverite-like structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded to six C atoms to form a mixture of edge and corner-sharing HfC6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. There are three shorter (2.30 Å) and three longer (2.35 Å) Hf–C bond lengths. In the second Hf site, Hf is bonded to three equivalent C and three equivalent N atoms to form a mixture of edge and corner-sharing HfC3N3 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. All Hf–C bond lengths are 2.26 Å. All Hf–N bond lengths are 2.34 Å. There are two inequivalent C sites. In the first C site, C is bonded to six Hf atoms to form CHf6 octahedra that share corners with three equivalent CHf6 octahedra, corners with three equivalent NHf6 octahedra, edges with three equivalent NHf6 octahedra, and edges with nine CHf6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. In the second C site, C is bonded to six equivalent Hf atoms to form a mixture of edge and corner-sharing CHf6 octahedra. The corner-sharing octahedral tilt angles are 2°. N is bonded to six equivalent Hf atoms to form NHf6 octahedra that share corners with six equivalent CHf6 octahedra, edges with six equivalent CHf6 octahedra, and edges with six equivalent NHf6 octahedra. The corner-sharing octahedral tilt angles are 3°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf2Te3 by Materials Project

Hf2Te3 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are three inequivalent Hf sites. In the first Hf site, Hf is bonded to six equivalent Te atoms to form a mixture of edge and corner-sharing HfTe6 octahedra. The corner-sharing octahedral tilt angles are 51°. All Hf–Te bond lengths are 2.89 Å. In the second Hf site, Hf is bonded to six equivalent Te atoms to form a mixture of face, edge, and corner-sharing HfTe6 octahedra. The corner-sharing octahedral tilt angles are 49°. There are three shorter (2.92 Å) and three longer (2.95 Å) Hf–Te bond lengths. In the third Hf site, Hf is bonded to six equivalent Te atoms to form a mixture of face and corner-sharing HfTe6 octahedra. The corner-sharing octahedra tilt angles range from 49–51°. All Hf–Te bond lengths are 2.90 Å. Te is bonded in a rectangular see-saw-like geometry to four Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2HfO6 by Materials Project

K2HfO6 crystallizes in the orthorhombic Cmme space group. The structure is two-dimensional and consists of two K2HfO6 sheets oriented in the (0, 1, 0) direction. there are two inequivalent K sites. In the first K site, K is bonded in a 10-coordinate geometry to ten O atoms. There are a spread of K–O bond distances ranging from 2.75–3.09 Å. In the second K site, K is bonded in a 10-coordinate geometry to ten O atoms. There are a spread of K–O bond distances ranging from 2.76–3.14 Å. There are two inequivalent Hf sites. In the first Hf site, Hf is bonded to six O atoms to form corner-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are two shorter (2.06 Å) and four longer (2.08 Å) Hf–O bond lengths. In the second Hf site, Hf is bonded to six O atoms to form corner-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are a spread of Hf–O bond distances ranging from 2.01–2.09 Å. There are five inequivalent O sites. In the first O site, O is bonded in a linear geometry to four K and two Hf atoms. In the second O site, O is bonded in a linear geometry to four K and two Hf atoms. In the third O site, O is bonded in a distorted single-bond geometry to four K and one Hf atom. In the fourth O site, O is bonded in a distorted single-bond geometry to four K and one Hf atom. In the fifth O site, O is bonded in a water-like geometry to two K atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf3Th by Materials Project

ThHf3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Th is bonded to twelve Hf atoms to form ThHf12 cuboctahedra that share corners with six equivalent ThHf12 cuboctahedra, corners with twelve equivalent HfHf8Th4 cuboctahedra, edges with eighteen HfHf8Th4 cuboctahedra, faces with eight equivalent ThHf12 cuboctahedra, and faces with twelve HfHf8Th4 cuboctahedra. There are six shorter (3.33 Å) and six longer (3.34 Å) Th–Hf bond lengths. There are two inequivalent Hf sites. In the first Hf site, Hf is bonded to four equivalent Th and eight Hf atoms to form HfHf8Th4 cuboctahedra that share corners with four equivalent ThHf12 cuboctahedra, corners with fourteen HfHf8Th4 cuboctahedra, edges with six equivalent ThHf12 cuboctahedra, edges with twelve HfHf8Th4 cuboctahedra, faces with four equivalent ThHf12 cuboctahedra, and faces with sixteen HfHf8Th4 cuboctahedra. There are a spread of Hf–Hf bond distances ranging from 3.10–3.55 Å. In the second Hf site, Hf is bonded to four equivalent Th and eight equivalent Hf atoms to form HfHf8Th4 cuboctahedra that share corners with four equivalent ThHf12 cuboctahedra, corners with fourteen HfHf8Th4 cuboctahedra, edges with six equivalent ThHf12 cuboctahedra, edges with twelve equivalent HfHf8Th4 cuboctahedra, faces with four equivalent ThHf12 cuboctahedra, and faces with sixteen HfHf8Th4 cuboctahedra.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Observations of stratospheric hydrogen fluoride by halogen occultation experiment (HALOE)

The Halogen Occultation Experiment (HALOE) Hydrogen Fluoride (HF) channel on the Upper Atmospheric Research Satellite (UARS) is providing the first global measurements of stratospheric HF, the dominant flourine reservoir in the atmosphere. This paper describes the latitudinal and seasonal variations of HALOE-observed HF in terms of vertical profiles, altitude/latitude cross sections, and column abundances. The HF global distribution shows a 'tracerlike' structure and its column amount increases with latitude, in agreement with previous aircraft measurements of the HF column amount. A comparison between the HALOE HF column above 20 km and the ATMOS 1985 measurements is used to estimate the annual rate of increase of stratospheric HF. Exponential rates of 4.9-6.6%/yr and linear growth rates of 6-8.6%/yr in 1985 and 4.3-5.5%/yr in 1992-1993 are found. HALOE HF measurements during the 1993 Antarctic spring are briefly described. This species behaves like a conserved tracer and its distribution shows an area of enhanced mixing ratios correlated with the polar vortex that has a clear latitude boundary. Finally, simulated HF distributions by the National Center for Atmospheric Research (NCAR) two-dimensional model are used to compare with HALOE observations of HF. Reasonable agreements in the global structure and the absolute amount of HF are found. The differences between the model and the observed results indicate the need for improving treatment of atmospheric dynamics and fluorine-related chemical parameters in the model simulations.

Luo, M.↗
NASA NTRS2005

High Frequency QRS ECG Accurately Detects Cardiomyopathy

High frequency (HF, 150-250 Hz) analysis over the entire QRS interval of the ECG is more sensitive than conventional ECG for detecting myocardial ischemia. However, the accuracy of HF QRS ECG for detecting cardiomyopathy is unknown. We obtained simultaneous resting conventional and HF QRS 12-lead ECGs in 66 patients with cardiomyopathy (EF = 23.2 plus or minus 6.l%, mean plus or minus SD) and in 66 age- and gender-matched healthy controls using PC-based ECG software recently developed at NASA. The single most accurate ECG parameter for detecting cardiomyopathy was an HF QRS morphological score that takes into consideration the total number and severity of reduced amplitude zones (RAZs) present plus the clustering of RAZs together in contiguous leads. This RAZ score had an area under the receiver operator curve (ROC) of 0.91, and was 88% sensitive, 82% specific and 85% accurate for identifying cardiomyopathy at optimum score cut-off of 140 points. Although conventional ECG parameters such as the QRS and QTc intervals were also significantly longer in patients than controls (P less than 0.001, BBBs excluded), these conventional parameters were less accurate (area under the ROC = 0.77 and 0.77, respectively) than HF QRS morphological parameters for identifying underlying cardiomyopathy. The total amplitude of the HF QRS complexes, as measured by summed root mean square voltages (RMSVs), also differed between patients and controls (33.8 plus or minus 11.5 vs. 41.5 plus or minus 13.6 mV, respectively, P less than 0.003), but this parameter was even less accurate in distinguishing the two groups (area under ROC = 0.67) than the HF QRS morphologic and conventional ECG parameters. Diagnostic accuracy was optimal (86%) when the RAZ score from the HF QRS ECG and the QTc interval from the conventional ECG were used simultaneously with cut-offs of greater than or equal to 40 points and greater than or equal to 445 ms, respectively. In conclusion 12-lead HF QRS ECG employing RAZ scoring is a simple, accurate and inexpensive screening technique for cardiomyopathy. Although HF QRS ECG is highly sensitive for cardiomyopathy, its specificity may be compromised in patients with cardiac pathologies other than cardiomyopathy, such as uncomplicated coronary artery disease or multiple coronary disease risk factors. Further studies are required to determine whether HF QRS might be useful for monitoring cardiomyopathy severity or the efficacy of therapy in a longitudinal fashion.

Schlegel, Todd T.↗
NASA NTRS2012

Rugged, Portable, Real-Time Optical Gaseous Analyzer for Hydrogen Fluoride

Hydrogen fluoride (HF) is a primary evolved combustion product of fluorinated and perfluorinated hydrocarbons. HF is produced during combustion by the presence of impurities and hydrogen- containing polymers including polyimides. This effect is especially dangerous in closed occupied volumes like spacecraft and submarines. In these systems, combinations of perfluorinated hydrocarbons and polyimides are used for insulating wiring. HF is both highly toxic and short-lived in closed environments due to its reactivity. The high reactivity also makes HF sampling problematic. An infrared optical sensor can detect promptly evolving HF with minimal sampling requirements, while providing both high sensitivity and high specificity. A rugged optical path length enhancement architecture enables both high HF sensitivity and rapid environmental sampling with minimal gaseous contact with the low-reactivity sensor surfaces. The inert optical sample cell, combined with infrared semiconductor lasers, is joined with an analog and digital electronic control architecture that allows for ruggedness and compactness. The combination provides both portability and battery operation on a simple camcorder battery for up to eight hours. Optical detection of gaseous HF is confounded by the need for rapid sampling with minimal contact between the sensor and the environmental sample. A sensor is required that must simultaneously provide the required sub-parts-permillion detection limits, but with the high specificity and selectivity expected of optical absorption techniques. It should also be rugged and compact for compatibility with operation onboard spacecraft and submarines. A new optical cell has been developed for which environmental sampling is accomplished by simply traversing the few mm-thick cell walls into an open volume where the measurement is made. A small, low-power fan or vacuum pump may be used to push or pull the gaseous sample into the sample volume for a response time of a few seconds. The optical cell simultaneously provides for an enhanced optical interaction path length between the environmental sample and the infrared laser. Further, the optical cell itself is comprised of inert materials that render it immune to attack by HF. In some cases, the sensor may be configured so that the optoelectronic devices themselves are protected and isolated from HF by the optical cell. The optical sample cell is combined with custom-developed analog and digital control electronics that provide rugged, compact operation on a platform that can run on a camcorder battery. The sensor is inert with respect to acidic gases like HF, while providing the required sensitivity, selectivity, and response time. Certain types of combustion events evolve copious amounts of HF, very little of other gases typically associated with combustion (e.g., carbon monoxide), and very low levels of aerosols and particulates (which confound traditional smoke detectors). The new sensor platform could warn occupants early enough to take the necessary countermeasures.

Pilgrim, Jeffrey↗
DOE OSTI2020

Materials Data on Hf3Rh5 by Materials Project

Hf3Rh5 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 10-coordinate geometry to ten Rh atoms. There are a spread of Hf–Rh bond distances ranging from 2.69–2.99 Å. In the second Hf site, Hf is bonded in a body-centered cubic geometry to eight Rh atoms. There are a spread of Hf–Rh bond distances ranging from 2.66–2.81 Å. There are three inequivalent Rh sites. In the first Rh site, Rh is bonded in a 6-coordinate geometry to six Hf atoms. In the second Rh site, Rh is bonded in a 5-coordinate geometry to five Hf atoms. In the third Rh site, Rh is bonded in a 6-coordinate geometry to six Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf3(NbGe2)2 by Materials Project

Hf3(NbGe2)2 is delta Molybdenum Boride-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 7-coordinate geometry to seven Ge atoms. There are a spread of Hf–Ge bond distances ranging from 2.80–3.01 Å. In the second Hf site, Hf is bonded in a 6-coordinate geometry to six Ge atoms. There are a spread of Hf–Ge bond distances ranging from 2.71–2.83 Å. Nb is bonded in a 6-coordinate geometry to six Ge atoms. There are a spread of Nb–Ge bond distances ranging from 2.59–2.80 Å. There are three inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to four Hf, four equivalent Nb, and one Ge atom. The Ge–Ge bond length is 2.58 Å. In the second Ge site, Ge is bonded in a 9-coordinate geometry to five Hf, three equivalent Nb, and one Ge atom. The Ge–Ge bond length is 2.78 Å. In the third Ge site, Ge is bonded in a 9-coordinate geometry to six Hf, two equivalent Nb, and one Ge atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf5CuSn3 by Materials Project

Hf5CuSn3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 6-coordinate geometry to six equivalent Sn atoms. All Hf–Sn bond lengths are 3.03 Å. In the second Hf site, Hf is bonded to two equivalent Cu and five equivalent Sn atoms to form a mixture of distorted corner, edge, and face-sharing HfCu2Sn5 pentagonal bipyramids. Both Hf–Cu bond lengths are 2.69 Å. There are a spread of Hf–Sn bond distances ranging from 2.94–3.11 Å. Cu is bonded to six equivalent Hf atoms to form face-sharing CuHf6 octahedra. Sn is bonded in a 9-coordinate geometry to nine Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf4NbGe4 by Materials Project

Hf4NbGe4 is delta Molybdenum Boride-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 6-coordinate geometry to six Ge atoms. There are a spread of Hf–Ge bond distances ranging from 2.64–2.82 Å. In the second Hf site, Hf is bonded in a 7-coordinate geometry to seven Ge atoms. There are a spread of Hf–Ge bond distances ranging from 2.79–3.11 Å. Nb is bonded in a 6-coordinate geometry to six Ge atoms. There are a spread of Nb–Ge bond distances ranging from 2.69–2.88 Å. There are three inequivalent Ge sites. In the first Ge site, Ge is bonded in a 8-coordinate geometry to seven Hf and one Nb atom. In the second Ge site, Ge is bonded in a 9-coordinate geometry to six Hf, two equivalent Nb, and one Ge atom. The Ge–Ge bond length is 2.61 Å. In the third Ge site, Ge is bonded in a 9-coordinate geometry to six Hf, two equivalent Nb, and one Ge atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf5CuPb3 by Materials Project

Hf5CuPb3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 6-coordinate geometry to six equivalent Pb atoms. All Hf–Pb bond lengths are 3.07 Å. In the second Hf site, Hf is bonded to two equivalent Cu and five equivalent Pb atoms to form a mixture of distorted corner, edge, and face-sharing HfCu2Pb5 pentagonal bipyramids. Both Hf–Cu bond lengths are 2.68 Å. There are a spread of Hf–Pb bond distances ranging from 2.98–3.15 Å. Cu is bonded to six equivalent Hf atoms to form face-sharing CuHf6 octahedra. Pb is bonded in a 9-coordinate geometry to nine Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf5ZnSb3 by Materials Project

Hf5ZnSb3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded to two equivalent Zn and five equivalent Sb atoms to form a mixture of distorted edge, face, and corner-sharing HfZn2Sb5 pentagonal bipyramids. Both Hf–Zn bond lengths are 2.73 Å. There are a spread of Hf–Sb bond distances ranging from 2.95–3.06 Å. In the second Hf site, Hf is bonded in a 6-coordinate geometry to six equivalent Sb atoms. All Hf–Sb bond lengths are 3.04 Å. Zn is bonded to six equivalent Hf atoms to form distorted face-sharing ZnHf6 octahedra. Sb is bonded in a 9-coordinate geometry to nine Hf atoms.

36 MATERIALS SCIENCE↗