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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Li3AlF6 by Materials Project

Li3AlF6 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are five inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to six F1- atoms to form distorted LiF6 octahedra that share corners with two equivalent AlF6 octahedra, corners with two equivalent LiF4 tetrahedra, corners with two equivalent LiF5 trigonal bipyramids, and edges with two equivalent AlF6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are a spread of Li–F bond distances ranging from 2.01–2.12 Å. In the second Li1+ site, Li1+ is bonded to four F1- atoms to form LiF4 tetrahedra that share a cornercorner with one LiF6 octahedra, corners with four AlF6 octahedra, a cornercorner with one LiF5 trigonal bipyramid, and an edgeedge with one LiF4 tetrahedra. The corner-sharing octahedra tilt angles range from 48–66°. There are a spread of Li–F bond distances ranging from 1.87–1.91 Å. In the third Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six F1- atoms. There are a spread of Li–F bond distances ranging from 1.92–2.49 Å. In the fourth Li1+ site, Li1+ is bonded to five F1- atoms to form distorted LiF5 trigonal bipyramids that share a cornercorner with one LiF6 octahedra, corners with three equivalent AlF6 octahedra, a cornercorner with one LiF4 tetrahedra, an edgeedge with one AlF6 octahedra, and an edgeedge with one LiF5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 46–79°. There are a spread of Li–F bond distances ranging from 1.88–2.23 Å. In the fifth Li1+ site, Li1+ is bonded in a 4-coordinate geometry to six F1- atoms. There are a spread of Li–F bond distances ranging from 1.92–2.56 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share corners with two equivalent LiF4 tetrahedra, edges with two equivalent LiF6 octahedra, and edges with two equivalent LiF5 trigonal bipyramids. There are a spread of Al–F bond distances ranging from 1.81–1.84 Å. In the second Al3+ site, Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share a cornercorner with one LiF6 octahedra, corners with three equivalent LiF4 tetrahedra, and corners with three equivalent LiF5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 46°. There are a spread of Al–F bond distances ranging from 1.82–1.86 Å. There are nine inequivalent F1- sites. In the first F1- site, F1- is bonded in a 4-coordinate geometry to three Li1+ and one Al3+ atom. In the second F1- site, F1- is bonded to three Li1+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing FLi3Al trigonal pyramids. In the third F1- site, F1- is bonded in a 4-coordinate geometry to three Li1+ and one Al3+ atom. In the fourth F1- site, F1- is bonded in a trigonal planar geometry to two Li1+ and one Al3+ atom. In the fifth F1- site, F1- is bonded in a distorted trigonal planar geometry to two Li1+ and one Al3+ atom. In the sixth F1- site, F1- is bonded in a 4-coordinate geometry to three Li1+ and one Al3+ atom. In the seventh F1- site, F1- is bonded to three Li1+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing FLi3Al tetrahedra. In the eighth F1- site, F1- is bonded in a distorted rectangular see-saw-like geometry to three Li1+ and one Al3+ atom. In the ninth F1- site, F1- is bonded in a trigonal planar geometry to two Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li3AlF6 by Materials Project

Li3AlF6 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are three inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six F1- atoms. There are a spread of Li–F bond distances ranging from 1.91–2.44 Å. In the second Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six F1- atoms. There are a spread of Li–F bond distances ranging from 1.90–2.46 Å. In the third Li1+ site, Li1+ is bonded to six F1- atoms to form distorted LiF6 octahedra that share corners with two equivalent LiF6 octahedra, corners with two equivalent AlF6 octahedra, and edges with two equivalent AlF6 octahedra. The corner-sharing octahedra tilt angles range from 49–54°. There are a spread of Li–F bond distances ranging from 1.94–2.24 Å. Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share corners with two equivalent LiF6 octahedra and edges with two equivalent LiF6 octahedra. The corner-sharing octahedra tilt angles range from 52–54°. There are a spread of Al–F bond distances ranging from 1.81–1.86 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a 4-coordinate geometry to three Li1+ and one Al3+ atom. In the second F1- site, F1- is bonded to three Li1+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing FLi3Al trigonal pyramids. In the third F1- site, F1- is bonded to three Li1+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing FLi3Al trigonal pyramids. In the fourth F1- site, F1- is bonded in a trigonal planar geometry to two equivalent Li1+ and one Al3+ atom. In the fifth F1- site, F1- is bonded in a 4-coordinate geometry to three Li1+ and one Al3+ atom. In the sixth F1- site, F1- is bonded in a 5-coordinate geometry to four Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li3AlF6 by Materials Project

Li3AlF6 is (Cubic) Perovskite-like structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to twelve equivalent F1- atoms to form LiF12 cuboctahedra that share corners with twelve equivalent LiF12 cuboctahedra, faces with six equivalent LiF12 cuboctahedra, faces with four equivalent LiF6 octahedra, and faces with four equivalent AlF6 octahedra. All Li–F bond lengths are 2.66 Å. In the second Li1+ site, Li1+ is bonded to six equivalent F1- atoms to form LiF6 octahedra that share corners with six equivalent AlF6 octahedra and faces with eight equivalent LiF12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Li–F bond lengths are 1.95 Å. Al3+ is bonded to six equivalent F1- atoms to form AlF6 octahedra that share corners with six equivalent LiF6 octahedra and faces with eight equivalent LiF12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Al–F bond lengths are 1.81 Å. F1- is bonded in a distorted linear geometry to five Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2024

Optimization of Mission Enabling Broadband Lyman Ultraviolet Series to Infrared Aluminum Lithium Fluoride Reflectors

The Habitable Worlds Observatory (HWO) concept NASA flagship mission aims extend the ultraviolet (UV) observation range and sensitivity capabilities of the Hubble Space Telescope (HST) with respective goals of reaching photons down to 100 nm and containing an ultraviolet multi-object spectrograph with sensitivity improved 30-100 times. Adding the sensitivity capabilities near the Lyman series spectral range of ~100-121.6 nm reduces the reliance of redshift for key diagnostic ion lines such as O VI (103.2 nm), and heavily ionized gases of Ne VIII (77.5 nm) and MgX (62.5 nm). Clean and unoxidized aluminum (Al) reflectors provide optimal efficiency over a broadband down to the extreme ultraviolet (EUV) wavelength of ~83 nm. To prevent oxidation and maintain high spectral efficiency down to ~100 nm, the Al reflector is conventionally overcoated with a thin lithium fluoride (LiF) layer. We investigate the optimization of the deposition of the Al+LiF coating material composition to attain high spectral efficiency broadband reflectors down to 100 nm and enable the scientific goals of HWO. Lithium hexafluoroaluminate (Li3AlF6) is investigated as a different composition form of LiF to overcoat Al. The spectral efficiency and durability of the reflectors is evaluated. We will demonstrate the use of Li3AlF6 as an overcoat to protect aluminum yields ultra-high efficiency at the Hydrogen Lyman-alpha (HLyα, 121.6 nm) line with experimental reflectance values peaking up to 99%.

optical coatings↗
NASA NTRS2024

Optimization of Mission Enabling Broadband Lyman Ultraviolet Series to Infrared Aluminum Lithium Fluoride Reflectors

The Habitable Worlds Observatory (HWO) concept NASA flagship mission aims extend the ultraviolet (UV) observation range and sensitivity capabilities of the Hubble Space Telescope (HST) with respective goals of reaching photons down to 100 nm and containing an ultraviolet multi-object spectrograph with sensitivity improved 30-100 times. Adding the sensitivity capabilities near the Lyman series spectral range of ~100-121.6 nm reduces the reliance of redshift for key diagnostic ion lines such as O VI (103.2 nm), and heavily ionized gases of Ne VIII (77.5 nm) and MgX (62.5 nm). Clean and unoxidized aluminum (Al) reflectors provide optimal efficiency over a broadband down to the extreme ultraviolet (EUV) wavelength of ~83 nm. To prevent oxidation and maintain high spectral efficiency down to ~100 nm, the Al reflector is conventionally overcoated with a thin lithium fluoride (LiF) layer. We investigate the optimization of the deposition of the Al+LiF coating material composition to attain high spectral efficiency broadband reflectors down to 100 nm and enable the scientific goals of HWO. Lithium hexafluoroaluminate (Li3AlF6) is investigated as a different composition form of LiF to overcoat Al. The spectral efficiency and durability of the reflectors is evaluated. We will demonstrate the use of Li3AlF6 as an overcoat to protect aluminum yields ultra-high efficiency at the Hydrogen Lyman-alpha (HLyα, 121.6 nm) line with experimental reflectance values peaking up to 99%.

optical coatings↗