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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Non-Linear Optics at Twist Interfaces in h-BN/SiC Heterostructures

Understanding the emergent electronic structure in twisted atomically thin layers has led to the exciting field of twistronics. However, practical applications of such systems are challenging since the specific angular correlations between the layers must be precisely controlled and the layers have to be single crystalline with uniform atomic ordering. Here, in this work, an alternative, simple, and scalable approach is suggested, where nanocrystalline two-dimensional (2D) film on 3D substrates yields twisted-interface-dependent properties. Ultrawide-bandgap hexagonal boron nitride (h-BN) thin films are directly grown on high in-plane lattice mismatched wide-bandgap silicon carbide (4H-SiC) substrates to explore the twist-dependent structure-property correlations. Concurrently, nanocrystalline h-BN thin film shows strong non-linear second-harmonic generation and ultra-low cross-plane thermal conductivity at room temperature, which are attributed to the twisted domain edges between van der Waals stacked nanocrystals with random in-plane orientations. First-principles calculations based on time-dependent density functional theory manifest strong even-order optical nonlinearity in twisted h-BN layers. This work unveils that directly deposited 2D nanocrystalline thin film on 3D substrates could provide easily accessible twist-interfaces, therefore enabling a simple and scalable approach to utilize the 2D-twistronics integrated in 3D material devices for next-generation nanotechnology.

36 MATERIALS SCIENCE↗
NASA NTRS1979

Fibrous refractory composite insulation

A refractory composite insulating material was prepared from silica fibers and aluminosilicate fibers in a weight ratio ranging from 1:19 to 19:1, and about 0.5 to 30% boron oxide, based on the total fiber weight. The aluminosilicate fiber and boron oxide requirements may be satisfied by using aluminoborosilicate fibers and, in such instances, additional free boron oxide may be incorporated in the mix up to the 30% limit. Small quantities of refractory opacifiers, such as silicon carbide, may be also added. The composites just described are characterized by the absence of a nonfibrous matrix.

Leiser, D. B.↗
DOE OSTI2020

Materials Data on Mg30SiBO32 by Materials Project

Mg30SiO32B is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one boron molecule and one Mg30SiO32 framework. In the Mg30SiO32 framework, there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with two equivalent SiO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 1.99–2.26 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent SiO6 octahedra, corners with four equivalent MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.12 Å) and two longer (2.21 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.11–2.16 Å. In the fourth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.02 Å) and four longer (2.16 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one SiO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 2–10°. There are a spread of Mg–O bond distances ranging from 2.10–2.19 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 2°. There are two shorter (2.12 Å) and four longer (2.15 Å) Mg–O bond lengths. In the seventh Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one SiO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–8°. There are a spread of Mg–O bond distances ranging from 2.11–2.16 Å. In the eighth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–9°. There are a spread of Mg–O bond distances ranging from 2.11–2.16 Å. Si is bonded to six O atoms to form SiO6 octahedra that share corners with six MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.01 Å) and two longer (2.07 Å) Si–O bond lengths. There are nine inequivalent O sites. In the first O site, O is bonded to five Mg and one Si atom to form a mixture of edge and corner-sharing OMg5Si octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the second O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg5Si octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the third O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four equivalent OMg6 octahedra, corners with five OMg5 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedral tilt angles are 4°. In the fourth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OMg5Si octahedra, and edges with three OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 1–4°. In the fifth O site, O is bonded to five Mg and one Si atom to form OMg5Si octahedra that share corners with four OMg5Si octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg5Si octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–5°. In the sixth O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four OMg5Si octahedra, corners with five OMg5 square pyramids, and edges with eight OMg5Si octahedra. The corner-sharing octahedra tilt angles range from 6–10°. In the seventh O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–5°. In the eighth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–5°. There are two shorter (2.13 Å) and two longer (2.15 Å) O–Mg bond lengths. In the ninth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg30BSbO32 by Materials Project

Mg30SbO32B is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one boron molecule and one Mg30SbO32 framework. In the Mg30SbO32 framework, there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with two equivalent SbO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.03–2.18 Å. In the second Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.02 Å) and four longer (2.17 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.12–2.15 Å. In the fourth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent SbO6 octahedra, corners with four equivalent MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.04 Å) and four longer (2.15 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one SbO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–11°. There are a spread of Mg–O bond distances ranging from 2.08–2.23 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–4°. There are two shorter (2.14 Å) and four longer (2.16 Å) Mg–O bond lengths. In the seventh Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 2–8°. There are a spread of Mg–O bond distances ranging from 2.12–2.18 Å. In the eighth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one SbO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–3°. There are a spread of Mg–O bond distances ranging from 2.09–2.21 Å. Sb is bonded to six O atoms to form SbO6 octahedra that share corners with six MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.24 Å) and two longer (2.26 Å) Sb–O bond lengths. There are nine inequivalent O sites. In the first O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four equivalent OMg6 octahedra, corners with five OMg5 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedral tilt angles are 5°. In the second O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. In the third O site, O is bonded to five Mg and one Sb atom to form a mixture of edge and corner-sharing OMg5Sb octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the fourth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OMg6 octahedra, and edges with three OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 2–7°. In the fifth O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four OMg5Sb octahedra, corners with five OMg5 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedral tilt angles are 5°. In the sixth O site, O is bonded to five Mg and one Sb atom to form OMg5Sb octahedra that share corners with four OMg5Sb octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. In the seventh O site, O is bonded to five Mg and one Sb atom to form OMg5Sb octahedra that share corners with four OMg5Sb octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. Both O–Mg bond lengths are 2.20 Å. In the eighth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. In the ninth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six OMg5Sb octahedra and edges with twelve OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg30GaBO32 by Materials Project

Mg30GaO32B is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one boron molecule and one Mg30GaO32 framework. In the Mg30GaO32 framework, there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.03–2.16 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent GaO6 octahedra, corners with four MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.10–2.17 Å. In the third Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.12 Å) and two longer (2.14 Å) Mg–O bond lengths. In the fourth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.12 Å) and four longer (2.14 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one GaO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 2–12°. There are a spread of Mg–O bond distances ranging from 2.10–2.17 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Mg–O bond distances ranging from 2.12–2.14 Å. In the seventh Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–7°. There are a spread of Mg–O bond distances ranging from 2.12–2.15 Å. In the eighth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one GaO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are four shorter (2.13 Å) and two longer (2.14 Å) Mg–O bond lengths. Ga is bonded to six O atoms to form GaO6 octahedra that share corners with four equivalent MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (1.95 Å) and four longer (2.10 Å) Ga–O bond lengths. There are eleven inequivalent O sites. In the first O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four OMg5Ga octahedra, corners with five OMg5 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedra tilt angles range from 2–4°. In the second O site, O is bonded to five Mg and one Ga atom to form OMg5Ga octahedra that share corners with four OMg5Ga octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg5Ga octahedra, and edges with two equivalent OMg4Ga square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the third O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the fourth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. Both O–Mg bond lengths are 2.14 Å. In the fifth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are two shorter (2.13 Å) and two longer (2.14 Å) O–Mg bond lengths. In the sixth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OMg5Ga octahedra, and edges with three OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 1–2°. In the seventh O site, O is bonded to four equivalent Mg and one Ga atom to form OMg4Ga square pyramids that share corners with four equivalent OMg6 octahedra, corners with five OMg4Ga square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedral tilt angles are 8°. In the eighth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg4Ga square pyramids, edges with ten OMg5Ga octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the ninth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the tenth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. The O–Mg bond length is 2.13 Å. In the eleventh O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are three shorter (2.13 Å) and two longer (2.14 Å) O–Mg bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg30TiBO32 by Materials Project

Mg30TiO32B is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one boron molecule and one Mg30TiO32 framework. In the Mg30TiO32 framework, there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with four MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.11 Å) and four longer (2.14 Å) Mg–O bond lengths. In the second Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.03 Å) and four longer (2.15 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.13 Å) and four longer (2.14 Å) Mg–O bond lengths. In the fourth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.13 Å) and two longer (2.14 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one TiO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–12°. There are a spread of Mg–O bond distances ranging from 2.09–2.18 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Mg–O bond distances ranging from 2.13–2.15 Å. In the seventh Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one TiO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are four shorter (2.13 Å) and two longer (2.15 Å) Mg–O bond lengths. In the eighth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–7°. There are a spread of Mg–O bond distances ranging from 2.12–2.15 Å. Ti is bonded to six O atoms to form TiO6 octahedra that share corners with four equivalent MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (1.96 Å) and four longer (2.14 Å) Ti–O bond lengths. There are eleven inequivalent O sites. In the first O site, O is bonded to five Mg and one Ti atom to form OMg5Ti octahedra that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg5Ti octahedra, and edges with two equivalent OMg4Ti square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. In the second O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four OMg5Ti octahedra, corners with five OMg4Ti square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedra tilt angles range from 2–4°. In the third O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. Both O–Mg bond lengths are 2.14 Å. In the fourth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the fifth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are two shorter (2.13 Å) and two longer (2.14 Å) O–Mg bond lengths. In the sixth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.13 Å) and two longer (2.15 Å) O–Mg bond lengths. In the seventh O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OMg5Ti octahedra, and edges with three OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 1–3°. In the eighth O site, O is bonded to four equivalent Mg and one Ti atom to form OMg4Ti square pyramids that share corners with four equivalent OMg6 octahedra, corners with five OMg4Ti square pyramids, and edges with eight OMg5Ti octahedra. The corner-sharing octahedral tilt angles are 7°. In the ninth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg4Ti square pyramids, edges with ten OMg5Ti octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. In the tenth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the eleventh O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. The O–Mg bond length is 2.14 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HfMg30BO32 by Materials Project

Mg30HfO32B is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one boron molecule and one Mg30HfO32 framework. In the Mg30HfO32 framework, there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.01–2.18 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent HfO6 octahedra, corners with four MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.12–2.15 Å. In the third Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.13 Å) and two longer (2.16 Å) Mg–O bond lengths. In the fourth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.14 Å) and four longer (2.15 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one HfO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–10°. There are a spread of Mg–O bond distances ranging from 2.07–2.23 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. There are a spread of Mg–O bond distances ranging from 2.13–2.17 Å. In the seventh Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–8°. There are a spread of Mg–O bond distances ranging from 2.14–2.16 Å. In the eighth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one HfO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. There are a spread of Mg–O bond distances ranging from 2.11–2.19 Å. Hf is bonded to six O atoms to form HfO6 octahedra that share corners with four equivalent MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.04 Å) and four longer (2.16 Å) Hf–O bond lengths. There are eight inequivalent O sites. In the first O site, O is bonded to five Mg atoms to form OMg5 square pyramids that share corners with four OHfMg5 octahedra, corners with five OMg5 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedra tilt angles range from 2–5°. In the second O site, O is bonded to five Mg and one Hf atom to form OHfMg5 octahedra that share corners with four OHfMg5 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OHfMg5 octahedra, and edges with two equivalent OHfMg4 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the third O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the fourth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the fifth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OHfMg5 octahedra, and edges with three OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–5°. In the sixth O site, O is bonded to four equivalent Mg and one Hf atom to form distorted OHfMg4 square pyramids that share corners with four equivalent OMg6 octahedra, corners with five OHfMg4 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedral tilt angles are 8°. In the seventh O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OHfMg4 square pyramids, edges with ten OHfMg5 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the eighth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YMg30BO32 by Materials Project

Mg30YO32B is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one boron molecule and one Mg30YO32 framework. In the Mg30YO32 framework, there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with two equivalent YO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.03–2.18 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent YO6 octahedra, corners with four equivalent MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.07 Å) and four longer (2.15 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded to six O atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.12–2.15 Å. In the fourth Mg site, Mg is bonded to six O atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.02 Å) and four longer (2.17 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one YO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–11°. There are a spread of Mg–O bond distances ranging from 2.08–2.23 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–4°. There are two shorter (2.13 Å) and four longer (2.16 Å) Mg–O bond lengths. In the seventh Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one YO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. There are a spread of Mg–O bond distances ranging from 2.08–2.21 Å. In the eighth Mg site, Mg is bonded to six O atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 2–8°. There are a spread of Mg–O bond distances ranging from 2.12–2.18 Å. Y is bonded to six O atoms to form YO6 octahedra that share corners with six MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.21 Å) and two longer (2.23 Å) Y–O bond lengths. There are eight inequivalent O sites. In the first O site, O is bonded to five Mg and one Y atom to form OYMg5 octahedra that share corners with six OYMg5 octahedra and edges with twelve OMg6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OYMg5 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the third O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four equivalent OMg6 octahedra, corners with five OMg5 square pyramids, and edges with eight OMg6 octahedra. The corner-sharing octahedral tilt angles are 5°. In the fourth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OYMg5 octahedra, and edges with three OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 1–7°. In the fifth O site, O is bonded to five Mg and one Y atom to form OYMg5 octahedra that share corners with four OYMg5 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OYMg5 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the sixth O site, O is bonded to five Mg atoms to form distorted OMg5 square pyramids that share corners with four OYMg5 octahedra, corners with five OMg5 square pyramids, and edges with eight OYMg5 octahedra. The corner-sharing octahedra tilt angles range from 5–6°. In the seventh O site, O is bonded to six Mg atoms to form a mixture of corner and edge-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the eighth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5 square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5 square pyramids. The corner-sharing octahedra tilt angles range from 0–1°.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Ceramic fibers from Si-B-C polymer precursors

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (Si3N4), and silicon borides (SiB4, SiB6) have thermal stability, oxidation resistance, hardness, and varied electrical properties. All these materials can be prepared in a fiber form from a suitable polymer precursor. The above mentioned fibers, when tested over a temperature range from 25 to 1400 C, experience degradation at elevated temperatures. Past work in ceramic materials has shown that the strength of ceramics containing both carbides and borides is sustained at elevated temperatures, with minimum oxidation. The work presented here describes the formation of ceramic fibers containing both elements, boron and silicon, prepared via the polymer precursor route previously reported by the authors, and discusses the fiber mechanical properties that are retained over the temperature range studied.

Riccitiello, S. R.↗
NASA NTRS1999

Continuous method of producing silicon carbide fibers

This invention pertains to a method for production of polycrystalline ceramic fibers from silicon oxycarbide (SiCO) ceramic fibers wherein the method comprises heating an amorphous ceramic fiber containing silicon and carbon in an inert environment comprising a boron oxide and carbon monoxide at a temperature sufficient to convert the amorphous ceramic fiber to a polycrystalline ceramic fiber. By having carbon monoxide present during the heating of the ceramic fiber, it is possible to achieve higher production rates on a continuous process.

Barnard, Thomas Duncan↗
NASA NTRS1981

Infrared absorption spectra of metal carbides, nitrides and sulfides

The infrared absorption spectra of 12 kinds of metal carbides, 11 kinds of nitrides, and 7 kinds of sulfides, a total of 30 materials, were measured and the application of the infrared spectra of these materials to analytical chemistry was discussed. The measurements were done in the frequency (wave length) range of (1400 to 400/cm (7 to 25 mu). The carbides Al4C3, B4C, the nitrides AlN, BN, Si3N4, WB, and the sulfides Al2S3, FeS2, MnS, NiS and PbS were noted to have specific absorptions in the measured region. The sensitivity of Boron nitride was especially good and could be detected at 2 to 3 micrograms in 300 mg of potassium bromide.

Kammori, O.↗
NASA NTRS1986

A metallurgical route to solar-grade silicon

The aim of the process is to produce silicon for crystallization into ingots that can be sliced to wafers for processing into photovoltaic cells. If the potential purity can be realized, the silicon will also be applicable for ribbon pulling techniques where the purification during crystallization is negligible. The process consists of several steps: selection and purification of raw materials, carbothermic reduction of silica, ladle treatment, casting, crushing, leaching, and melting. The leaching step is crucial for high purity, and the obtainable purity is determined by the solidification before leaching. The most difficult specifications to fulfill are the low contents of boron, phosphorus, and carbon. Boron and phosphorus can be excluded from the raw materials, but the carbothermic reduction will unavoidably saturate the silicon with carbon at high temperature. During cooling carbon will precipitate as silicon carbide crystals, which will be harmful in solar cells. The cost of this solar silicon will depend strongly on the scale of production. It is as yet premature to give exact figures, but with a scale of some thousand tons per year, the cost will only be a few times the cost of ordinary metallurgical silicon.

Schei, A.↗
NASA NTRS1984

Sinterability, strength and oxidation of alpha silicon carbide powders

An investigation is made of pressureless sintering of commercially available alpha-SiC powders at temperatures between 1900 and 2150 C for periods of 10 to 240 min under one atmosphere of argon pressure. It is found that alpha-SiC powder containing boron and carbon sintering aids is sinterable at 2150 C for a period of 30 min to a high final density (greater than 96 percent of theoretical). In alpha-SiC powder containing aluminum and carbon sintering aids, the final density achieved is only about 80 percent of theoretical. Determinations are made of room temperature and high temperature (1370 C) flexure strength and oxidation resistance on sintered high density (more than 96 percent of theoretical) alpha-SiC (boron, carbon) material. It is found that both the strength and the resistance to oxidation are equivalent and comparable to those of the sintered alpha-SiC which represents the state of the art.

Dutta, S.↗
DOE OSTI2022

Amorphous 2D Materials – A Novel Platform for Remote Epitaxy and Nanopatterned Epitaxy of III-V Semiconductors with Low Decomposition Temperatures

III-V semiconductor materials such as indium phosphide (InP) offer outstanding photonic properties that outperforms silicon, but the cost of these wafers is extremely expensive. Although reusing original wafers can effectively minimize the cost, current techniques for wafer recycling of these substrates add significant costs in fabrication, nullifying the cost savings by reusing the wafers. Besides, unlike other III-V materials such as gallium arsenide (GaAs), commonly used epitaxial lift-off method for wafer recycling is not well studied for materials like InP due to lack of lattice-matched sacrificial layers, which makes reusing these wafers more difficult. Remote epitaxy and nanopatterned epitaxy are newly discovered methods that enable single-crystal growth of III-V semiconductor thin films and easy exfoliation of these grown films, thus promising for a new cost-effective pathway of reusing wafers. However, previous methods of transferring two-dimensional (2D) materials, which use polymethyl methacrylate (PMMA) or metal stressor layers to transfer 2D materials grown on foreign substrates like copper (Cu) or silicon carbide (SiC), introduce defects and damages on the 2D layer and/or substrates during the transfer process. Remote epitaxial and nanopatterned epitaxial films grown on the damaged 2D layer/substrate suffer from lower crystal quality and imperfect exfoliation, which undermines wafer reusability and device performance. Here we report the MBE growth of amorphous boron nitride (a-BN) on InP wafers at low temperature that enabled improved quality of remote epitaxial and nanopatterned epitaxial films and their perfect exfoliation. We show fully covered a-BN on InP substrates despite their low decomposition temperatures. The surface of a-BN coated InP substrate remains smooth with a RMS roughness of around 3Â. We also demonstrate 100% coverage of single-crystal InP thin films grown on a-BN, with the film's quality significantly improved compared to the case of transferred 2D materials. In addition, the growth and exfoliation were successfully repeated multiple times, proving the feasibility for InP wafer recycling. Through this low temperature MBE growth approach with remote epitaxy and nanopatterned epitaxy, we successfully demonstrate large-scale flexible thin film exfoliation and recycling of InP substrates, which will lead to new opportunities in InP thin film-based photonics and novel heterostructures with significantly reduced cost.

Lu, Kuangye↗
DOE OSTI2022

Amorphous 2D Materials – A Novel Platform for Remote Epitaxy and Nanopatterned Epitaxy of III-V Semiconductors with Low Decomposition Temperatures

III-V semiconductor materials such as indium phosphide (InP) offer outstanding photonic properties that outperforms silicon, but the cost of these wafers is extremely expensive. Although reusing original wafers can effectively minimize the cost, current techniques for wafer recycling of these substrates add significant costs in fabrication, nullifying the cost savings by reusing the wafers. Besides, unlike other III-V materials such as gallium arsenide (GaAs), commonly used epitaxial lift-off method for wafer recycling is not well studied for materials like InP due to lack of lattice-matched sacrificial layers, which makes reusing these wafers more difficult. Remote epitaxy and nanopatterned epitaxy are newly discovered methods that enable single-crystal growth of III-V semiconductor thin films and easy exfoliation of these grown films, thus promising for a new cost-effective pathway of reusing wafers. However, previous methods of transferring two-dimensional (2D) materials, which use polymethyl methacrylate (PMMA) or metal stressor layers to transfer 2D materials grown on foreign substrates like copper (Cu) or silicon carbide (SiC), introduce defects and damages on the 2D layer and/or substrates during the transfer process. Remote epitaxial and nanopatterned epitaxial films grown on the damaged 2D layer/substrate suffer from lower crystal quality and imperfect exfoliation, which undermines wafer reusability and device performance. Here we report the MBE growth of amorphous boron nitride (a-BN) on InP wafers at low temperature that enabled improved quality of remote epitaxial and nanopatterned epitaxial films and their perfect exfoliation. We show fully covered a-BN on InP substrates despite their low decomposition temperatures. The surface of a-BN coated InP substrate remains smooth with a RMS roughness of around 3Å. We also demonstrate 100% coverage of single-crystal InP thin films grown on a-BN, with the film's quality significantly improved compared to the case of transferred 2D materials. In addition, the growth and exfoliation were successfully repeated multiple times, proving the feasibility for InP wafer recycling. Through this low temperature MBE growth approach with remote epitaxy and nanopatterned epitaxy, we successfully demonstrate large-scale flexible thin film exfoliation and recycling of InP substrates, which will lead to new opportunities in InP thin film-based photonics and novel heterostructures with significantly reduced cost.

Lu, Kuangye↗
NASA NTRS1973

Development of a process for producing ribbon shaped filaments

Silicon carbide (SiC) ribbon filaments were produced on a carbon ribbon substrate, about 1500 microns (60 mils) wide and 100 microns (4 mils) thick in lengths up to 2 meters (6 ft), and with tensile strengths up to 142 KN/cm sq (206 Ksi). During the course of the study, ribbon filaments of boron were also produced on the carbon ribbon substrate; the boron ribbon produced was extremely fragile. The tensile strength of the SiC ribbon was limited by large growths or flaws caused by anomalies at the substrate surface; these anomalies were either foreign dirt or substrate imperfections or both. Related work carried out on round 100 micron (4 mils) diameter SiC filaments on a 33 micron (1.3 mil) diameter, very smooth carbon monofilament substrate has shown that tensile strengths as high as 551 KN/cm sq (800 Ksi) are obtainable with the SiC-carbon round substrate combination, and indicates that if the ribbon substrate surface and ribbon deposition process can be improved similar strengths can be realizable. Cost analysis shows that 100 micron x 5-10 micron SiC ribbon can be very low cost reinforcement material.

Debolt, H. E.↗
NASA NTRS2006

SiC Composite Turbine Vanes

Turbine inlet guide vanes have been fabricated from composites of silicon carbide fibers in silicon carbide matrices. A unique design for a cloth made from SiC fibers makes it possible to realize the geometric features necessary to form these vanes in the same airfoil shapes as those of prior metal vanes. The fiber component of each of these vanes was made from SiC-fiber cloth coated with boron nitride. The matrix was formed by chemical-vapor infiltration with SiC, then slurry-casting of SiC, followed by melt infiltration with silicon. These SiC/SiC vanes were found to be capable of withstanding temperatures 400 F (222 C) greater than those that can be withstood by nickel-base-superalloy turbine airfoils now in common use in gas turbine engines. The higher temperature capability of SiC/SiC parts is expected to make it possible to use them with significantly less cooling than is used for metallic parts, thereby enabling engines to operate more efficiently while emitting smaller amounts of NOx and CO. The SiC/SiC composite vanes were fabricated in two different configurations. Each vane of one of the configurations has two internal cavities formed by a web between the suction and the pressure sides of the vane. Each vane of the other configuration has no web (see Figure 1). It is difficult to fabricate components having small radii, like those of the trailing edges of these vanes, by use of stiff stoichiometric SiC fibers currently preferred for SiC/SiC composites. To satisfy the severe geometric and structural requirements for these vanes, the aforementioned unique cloth design, denoted by the term Y-cloth, was conceived (see Figure 2). In the regions away from the trailing edge, the Y-cloth features a fiber architecture that had been well characterized and successfully demonstrated in combustor liners. To form a sharp trailing edge (having a radius of 0.3 mm), the cloth was split into two planes during the weaving process. The fiber tows forming the trailing-edge section were interlocked, thereby enhancing through-thickness strength of the resulting composite material. For vanes of the webless configuration, each made from a layup of six plies of Ycloth, the length of each Y-cloth layer was cut so that the two strips corresponding to the aforementioned two planes would wrap around the perimeter of a graphite vane preform tool with a 10-mm overlap. The overlap was used to join the two strips in a fringe splice. To make the external sixth ply, a standard woven cloth was cut to the required final length and a fringe splice joined the two ends of the cloth at the trailing edge. The cloth was then prepregged. The entire assembly was then placed into an aluminum compaction tool designed to form the outer net shape of the vane. After the prepreg material was allowed to dry, the preform was removed from the aluminum tooling and placed into an external graphite tool before being shipped to a vendor for matrix infiltration. To make the SiC fiber preform for a vane having an internal web, a slightly different initial approach was followed. Each of two sections forming the internal cavities (and ultimately the web) was created by first slipping two concentric layers of a two-dimensional, 2-by-2, 45 - braided tube around a net-shape graphite mandrel. The tubes on both mandrels were prepregged and allowed to dry. The resulting two subassemblies were put together, then four additional plies were wrapped around them in the same fashion as that described above for the six plies of the vaneless configuration. The consolidation of the SiC fiber preforms into SiC/SiC composite parts was performed by commercial vendors using their standard processes. The capability of two of the webless SiC/SiC turbine vanes was demonstrated in tests in a turbine environment. The tests included 50 hours of steady-state operation and 102 two-minute thermal cycles. A surface temperature of 1,320 C was reached during the tests.

Calomino, Anthony M.↗
NASA NTRS1990

Status and applications of diamond and diamond-like materials: An emerging technology

Recent discoveries that make possible the growth of crystalline diamond by chemical vapor deposition offer the potential for a wide variety of new applications. This report takes a broad look at the state of the technology following from these discoveries in relation to other allied materials, such as high-pressure diamond and cubic boron nitride. Most of the potential defense, space, and commercial applications are related to diamond's hardness, but some utilize other aspects such as optical or electronic properties. The growth processes are reviewed, and techniques for characterizing the resulting materials' properties are discussed. Crystalline diamond is emphasized, but other diamond-like materials (silicon carbide, amorphous carbon containing hydrogen) are also examined. Scientific, technical, and economic problem areas that could impede the rapid exploitation of these materials are identified. Recommendations are presented covering broad areas of research and development.

Source record↗