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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Strong effect of scandium source purity on chemical and electronic properties of epitaxial Sc x Al 1–x N/GaN heterostructures

Epitaxial multilayer heterostructures of Sc x Al 1–x N/GaN with Sc contents x = 0.11–0.45 are found to exhibit significant differences in structural quality, chemical impurity levels, and electronic properties depending on the starting Sc source impurity levels. A higher purity source leads to a 2–3 orders of magnitude reduction in the carbon, oxygen, and fluorine unintentional doping densities in MBE-grown Sc x Al 1–x N/GaN multilayers. Electrical measurements of Sc x Al 1–x N/n + GaN single heterostructure barriers show a 5–7 orders of magnitude reduction in the electrical leakage for films grown with a higher purity Sc source at most Sc contents. The measured chemical and electrical properties of epitaxial Sc x Al 1–x N highlight the importance of the starting Sc source material purity for epitaxial device applications that need these highly piezoelectric and/or ferroelectric transition-metal nitride alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(VGa2)2 by Materials Project

Sc(VGa2)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sc is bonded in a distorted square co-planar geometry to twelve Ga atoms. There are four shorter (2.76 Å) and eight longer (3.19 Å) Sc–Ga bond lengths. V is bonded in a 10-coordinate geometry to two equivalent V and eight Ga atoms. Both V–V bond lengths are 2.60 Å. All V–Ga bond lengths are 2.68 Å. There are five inequivalent Ga sites. In the first Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Sc, four equivalent V, and four Ga atoms. There are two shorter (2.60 Å) and two longer (2.76 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Sc, four equivalent V, and four Ga atoms. Both Ga–Ga bond lengths are 2.60 Å. In the third Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Sc, four equivalent V, and four Ga atoms. There are one shorter (2.60 Å) and two longer (2.76 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Sc, four equivalent V, and four Ga atoms. There are two shorter (2.60 Å) and two longer (2.76 Å) Ga–Ga bond lengths. In the fifth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Sc, four equivalent V, and four Ga atoms. Both Ga–Ga bond lengths are 2.76 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(Fe5Si)2 by Materials Project

ScFe10Si2 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Sc is bonded in a 12-coordinate geometry to sixteen Fe and four equivalent Si atoms. There are a spread of Sc–Fe bond distances ranging from 2.87–3.14 Å. All Sc–Si bond lengths are 3.05 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a 8-coordinate geometry to one Sc, eleven Fe, and two equivalent Si atoms. There are a spread of Fe–Fe bond distances ranging from 2.31–2.90 Å. Both Fe–Si bond lengths are 2.59 Å. In the second Fe site, Fe is bonded in a 10-coordinate geometry to one Sc, eleven Fe, and two equivalent Si atoms. There are a spread of Fe–Fe bond distances ranging from 2.45–2.67 Å. Both Fe–Si bond lengths are 2.53 Å. In the third Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent Sc, eight Fe, and two equivalent Si atoms. All Fe–Fe bond lengths are 2.42 Å. Both Fe–Si bond lengths are 2.52 Å. In the fourth Fe site, Fe is bonded to two equivalent Sc, eight Fe, and two equivalent Si atoms to form distorted FeSc2Fe8Si2 cuboctahedra that share corners with four equivalent SiSc2Fe10 cuboctahedra, corners with ten equivalent FeSc2Fe8Si2 cuboctahedra, edges with two equivalent SiSc2Fe10 cuboctahedra, edges with four equivalent FeSc2Fe8Si2 cuboctahedra, faces with four equivalent SiSc2Fe10 cuboctahedra, and faces with six equivalent FeSc2Fe8Si2 cuboctahedra. Both Fe–Fe bond lengths are 2.36 Å. Both Fe–Si bond lengths are 2.37 Å. Si is bonded to two equivalent Sc and ten Fe atoms to form distorted SiSc2Fe10 cuboctahedra that share corners with six equivalent SiSc2Fe10 cuboctahedra, corners with eight equivalent FeSc2Fe8Si2 cuboctahedra, edges with three equivalent SiSc2Fe10 cuboctahedra, edges with four equivalent FeSc2Fe8Si2 cuboctahedra, a faceface with one SiSc2Fe10 cuboctahedra, and faces with eight equivalent FeSc2Fe8Si2 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(SeO5)2 by Materials Project

Sc(SeO4)2O2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of two water molecules and one Sc(SeO4)2 sheet oriented in the (0, 0, 1) direction. In the Sc(SeO4)2 sheet, Sc is bonded to six O atoms to form ScO6 octahedra that share corners with six equivalent SeO4 tetrahedra. There are two shorter (2.09 Å) and four longer (2.12 Å) Sc–O bond lengths. Se is bonded to four O atoms to form SeO4 tetrahedra that share corners with three equivalent ScO6 octahedra. The corner-sharing octahedra tilt angles range from 33–45°. There is two shorter (1.67 Å) and two longer (1.68 Å) Se–O bond length. There are four inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Sc and one Se atom. In the second O site, O is bonded in a distorted bent 150 degrees geometry to one Sc and one Se atom. In the third O site, O is bonded in a single-bond geometry to one Se atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Sc and one Se atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Sputtered ferroelectric aluminum scandium boron nitride (Al 1−x−y B x Sc y N)/ n -GaN heterostructures

This work demonstrates ferroelectric switching in magnetron sputtered Al 1−x−y B x Sc y N/ n -GaN heterostructures. Using high power impulse magnetron sputtering, a silicon doped n -GaN bottom electrode with an electron concentration of 6.0 × 10 19 cm −3 is grown on c-plane sapphire. Al 1−x−y B x Sc y N films are prepared on the GaN surface with Al:B:Sc ratios that produce tensile, lattice matched, or compressive epitaxial strains. X-ray diffraction shows that lattice matched and compressively strained Al 1−x−y B x Sc y N compositions are pseudomorphic, while partial relaxation is observed for tensilely strained Al 1−x−y B x Sc y N/ n -GaN heterostructures. Electrically, the Al 1−x−y B x Sc y N/ n -GaN stacks show robust hysteresis; the P–E loops are fully saturated with both lattice matched and compressively strained Al 1−x−y B x Sc y N compositions exhibiting remanent polarization values of 135 μC/cm 2 . For comparison, Al 1−x−y B x Sc y N films are also prepared on metal organic chemical vapor deposition and single crystal GaN substrates to extend strain and morphology trends to more common substrate types. This report validates that sputter deposition is a feasible technique for fabricating strain-tunable ferroelectric III–N heterostructures with high crystalline fidelity and smooth surface morphologies.

42 ENGINEERING↗
DOE OSTI2020

Materials Data on Sc(FeGe)6 by Materials Project

Sc(FeGe)6 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Sc is bonded to twelve equivalent Fe and eight Ge atoms to form distorted face-sharing ScFe12Ge8 hexagonal bipyramids. All Sc–Fe bond lengths are 3.24 Å. There are two shorter (2.76 Å) and six longer (2.93 Å) Sc–Ge bond lengths. Fe is bonded in a 12-coordinate geometry to two equivalent Sc, four equivalent Fe, and six Ge atoms. All Fe–Fe bond lengths are 2.53 Å. There are a spread of Fe–Ge bond distances ranging from 2.49–2.64 Å. There are three inequivalent Ge sites. In the first Ge site, Ge is bonded in a 6-coordinate geometry to six equivalent Fe atoms. In the second Ge site, Ge is bonded in a 12-coordinate geometry to three equivalent Sc and six equivalent Fe atoms. In the third Ge site, Ge is bonded in a 8-coordinate geometry to one Sc, six equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.56 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(FeSn)6 by Materials Project

Sc(FeSn)6 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Sc is bonded to twelve equivalent Fe and eight Sn atoms to form distorted face-sharing ScFe12Sn8 hexagonal bipyramids. All Sc–Fe bond lengths are 3.47 Å. There are two shorter (2.97 Å) and six longer (3.11 Å) Sc–Sn bond lengths. Fe is bonded in a 12-coordinate geometry to two equivalent Sc, four equivalent Fe, and six Sn atoms. All Fe–Fe bond lengths are 2.69 Å. There are a spread of Fe–Sn bond distances ranging from 2.68–2.80 Å. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a 12-coordinate geometry to three equivalent Sc and six equivalent Fe atoms. In the second Sn site, Sn is bonded in a 6-coordinate geometry to six equivalent Fe atoms. In the third Sn site, Sn is bonded in a 8-coordinate geometry to one Sc, six equivalent Fe, and one Sn atom. The Sn–Sn bond length is 2.97 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Understanding Reproducibility of Sputter‐Deposited Metastable Ferroelectric Wurtzite Al 0.6 Sc 0.4 N Films Using In Situ Optical Emission Spectrometry

High‐Sc Al 1– x Sc x N thin films are of tremendous interest because of their attractive piezoelectric and ferroelectric properties, but overall film quality and reproducibility are widely reported to suffer as x increases. In this study, structural and electrical properties of metastable Al 0.6 Sc 0.4 N films are connected with plasma changes during film growth, identified via glow discharge optical emission spectroscopy (GD‐OES), and linked to the target mode changes. This in situ GD‐OES technique uses changes in the N 2 (I) intensity, correlated with DC bias hysteresis behavior of a Al 0.6 Sc 0.4 target in metallic and poisoned modes, to identify films that subsequently exhibit unacceptable structural and electrical performance. Two representative samples deposited under identical conditions but possessing distinct properties related to phases present in the films are focused on. Films sputtered under a poisoned target mode produce pure wurtzite ferroelectric Al 0.6 Sc 0.4 N with a reversible 80 μC cm −1 polarization and 3.1 MV cm −1 coercive field. When identical chamber settings are used but the process starts in metallic mode, a mixed wurtzite/rocksalt film is deposited which exhibits nanometer‐scale changes to the film microstructure and a nonferroelectric response. These results illustrate the utility of optical emission spectroscopy for tracking target mode fluctuations when fabricating metastable materials such as high‐Sc Al 1– x Sc x N films.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Role of Surface Termination in the Structural and Electronic Properties of Sc$_2$CT$_\textrm{x}$ MXene

Graphene-like layered transition metal carbides, nitrides, or carbonitrides, called MXenes, obey the stoichiometric formula of M n+1 X n T x , where M is an early transition metal such as scandium (Sc), n is a natural number, X is C, N, or CN, and T x is a functional group such as –O, –F, or –OH that passivates the surface of the MXene. The electronic structure of bare Sc 2 C and functionalized Sc 2 CT x MXenes are explored by performing first-principles density functional theory (DFT) calculations. The bare Sc 2 C is metallic, but less stable than its passivated structure. The Sc 2 C MXene has an interlayer 2D electron gas not bound to Sc or C atoms but free to move, making it an electride. DFT calculations show that functionalization can open an energy gap in Sc 2 CT x MXenes. The size and type (direct versus indirect) of the bandgap vary with the functional groups, which provides a means for opening and tuning of the band gap.

DFT↗
DOE OSTI2024

Combining solution-, precipitation- and load-transfer strengthening in a cast Al-Ce-Mn- Sc -Zr alloy

Here, a cast Al-9Ce-0.75Mn-0.18Sc-0.12Zr (wt%) alloy is designed to combine three strengthening phases: (i) micron-scale Al 11 Ce 3 platelets formed during eutectic solidification, (ii) nano-scale L1 2 -Al 3 (Sc,Zr) precipitates formed during aging, and (iii) Mn in solid solution in the α-Al matrix. Microstructural analyses by SEM, TEM, and atom-probe tomography reveal that Mn remains in solid solution in the as-cast alloy, providing solution strengthening with no influence on the eutectic Al-Al 11 Ce 3 microstructure, which provides precipitation- and load-transfer strengthening. During long-term over-aging at 400 °C, Mn-rich precipitates grow at the Al-Al 11 Ce 3 interface, with no effect on the microhardness. However, after short aging at 350 °C, a high number density of fine L1 2 -Al 3 (Sc,Zr) nanoprecipitates form in the Al matrix (with a coarser size at the Al-Al 11 Ce 3 interface), providing precipitation strengthening. The synergistic combination of the three strengthening mechanisms (solution, precipitation, and load transfer) in our Al-Ce-Mn-Sc-Zr alloy results in higher microhardness after aging at 350 and 400 °C, and higher creep resistance at 300 °C, as compared to alloys with two strengthening mechanisms: an Al-10Ce-0.93Mn control alloy (without precipitation strengthening from Sc and Zr), Al-Ce-Sc-Zr (without solution strengthening from Mn), and Al-Mn-Zr-Er (without load-transfer strengthening from Ce). Furthermore, these dual-strengthened alloys are more creep resistant than alloys with a single strengthening mechanism (Al-Ce, Al-Mn, and Al-Sc-Zr), confirming that the three mechanisms can be combined in pairs or all together.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Solute diffusion behavior during heat treatment and its impact in Sc-microalloyed Al-Cu system

Scandium (Sc) is a promising microalloying element that enhances the strength and thermal stability of aluminum (Al) alloys. However, these benefits are not fully realized in aluminum-copper (Al-Cu) systems, and corrosion resistance often declines due to the complex phase evolution and diffusion behavior of Cu and Sc. Here, to clarify this, solute diffusion behavior and Cu-Sc interaction during heat treatment (HT) were investigated using in situ synchrotron-based transmission x-ray microscopy (TXM), wide-angle x-ray scattering (WAXS), and x-ray absorption near-edge structure (XANES) spectroscopy. The results, supported by electron microscopy, reveal strong Cu-Sc bonding that significantly impedes solute diffusion, leading to inhomogeneous solute distribution and non-uniform precipitation. Moreover, the Al-Cu-Sc eutectic phase exhibits high thermal stability, resisting dissolution even near the matrix liquidus. These findings quantitatively elucidate the sluggish diffusion kinetics of Cu and Sc, which can help redesign HT schedules to improve both mechanical properties and corrosion resistance in Sc-microalloyed Al-Cu alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Monolayer Sc 2 CF 2 as a Potential Selective and Sensitive NO 2 Sensor: Insight from First-Principles Calculations

Two-dimensional materials with excellent surface–volume ratios and massive reaction sites recently have been receiving attention for gas sensing. With first-principles calculations, we explored the performance of monolayer Sc 2 CF 2 as a gas sensor. We investigated how molecule adsorption affects its electronic structure and optical properties. It is found that a large charge transfer quantity happens between Sc 2 CF 2 and NO 2 , which results from the fact that the lowest unoccupied molecular orbital (LUMO) of NO 2 is below the valence band maximum (VBM) of Sc 2 CF 2 . Moreover, the MD simulation shows that NO 2 can adsorb on the Sc 2 CF 2 surface stably at room temperature. We explored the effect of biaxial strain on the adsorption energy and charge transfer quantity of each system, and the results show that the biaxial strain can enhance both the adsorption energy and charge transfer quantity of the NO 2 system and thus can improve the sensitivity of Sc 2 CF 2 in detecting the NO 2 molecule. Furthermore, we investigated the adsorption behavior and charge transfer of polar polyatomic molecules at the Sc 2 CF 2 surface with h-BN as a substrate, and the results demonstrate that the h-BN substrate can hardly modify the main results. Our result predicts that Sc 2 CF 2 can be a promising selective and sensitive sensor to detect the NO 2 molecule, and could also give a theoretical guide for other terminated MXenes used for gas sensors or detectors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Tiny Sc Allows the Chains to Rattle: Impact of Lu and Y Doping on the Charge-Density Wave in ScV 6 Sn 6

The kagome metals display an intriguing variety of electronic and magnetic phases arising from the connectivity of atoms on a kagome lattice. A growing number of these materials with vanadium–kagome nets host charge–density waves (CDWs) at low temperatures, including ScV 6 Sn 6 , CsV 3 Sb 5 , and V 3 Sb 2 . Curiously, only the Sc version of the RV 6 Sn 6 materials with a HfFe 6 Ge 6 -type structure hosts a CDW (R = Gd–Lu, Y, Sc). In this study, we investigate the role of rare earth size in CDW formation in the RV 6 Sn 6 compounds. Magnetization measurements on our single crystals of (Sc,Lu)V 6 Sn 6 and (Sc,Y)V 6 Sn 6 establish that the CDW is suppressed by substituting Sc by larger Lu or Y. Single-crystal X-ray diffraction reveals that compressible Sn–Sn bonds accommodate the larger rare earth atoms within loosely packed R–Sn–Sn chains without significantly expanding the lattice. We propose that Sc provides extra room in these chains crucial to CDW formation in ScV 6 Sn 6 . Our rattling chain model explains why both physical pressure and substitution by larger rare earth atoms hinder CDW formation despite opposite impacts on lattice size. Here, we emphasize the cooperative effect of pressure and rare earth size by demonstrating that pressure further suppresses the CDW in a Lu-doped ScV 6 Sn 6 crystal. Our model not only addresses why a CDW only forms in the RV 6 Sn 6 materials with tiny Sc but also advances our understanding of why unusual CDWs form in the kagome metals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electric-field-induced crossover of polarization reversal mechanisms in Al 1–x Sc x N ferroelectrics

Scandium-doped aluminum nitride, Al 1–x Sc x N, represents a new class of displacive ferroelectric materials with high polarization and sharp hysteresis along with high-temperature resilience, facile synthesizability and compatibility with standard CMOS fabrication techniques. The fundamental physics behind the transformation of unswitchable piezoelectric AlN into switchable Al–Sc–N ferroelectrics depends upon important atomic properties such as local structure, dopant distributions and the presence of competing mechanism of polarization switching in the presence of an applied electric-field that have not been understood. We computationally synthesize Al 1–x Sc x N to quantify the inhomogeneity of Sc distribution and phase segregation, and characterize its crystal and electronic structure as a function of Sc-doping. Nudged elastic band calculations of the potential energy surface and quantum molecular dynamics simulations of direct electric-field-driven ferroelectric switching reveal a crossover between two polarization reversal mechanisms—inhomogeneous nucleation-and-growth mechanism originating near Sc-rich regions in the limit of low applied fields and nucleation-limited-switching in the high-field regime. Finally, understanding polarization reversal pathways for these two mechanisms as well as the role of local Sc concentration on activation barriers provides design rules to identify other combinations of dopant elements, such as Zr, Mg etc. to synthesize superior AlN-based ferroelectric materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Materials Data on Sc(Al2Fe)4 by Materials Project

ScFe4Al8 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sc is bonded in a 4-coordinate geometry to eight equivalent Fe and twelve Al atoms. All Sc–Fe bond lengths are 3.29 Å. There are four shorter (2.88 Å) and eight longer (3.12 Å) Sc–Al bond lengths. Fe is bonded in a 12-coordinate geometry to two equivalent Sc, two equivalent Fe, and eight Al atoms. Both Fe–Fe bond lengths are 2.50 Å. There are four shorter (2.50 Å) and four longer (2.59 Å) Fe–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 5-coordinate geometry to one Sc, four equivalent Fe, and five Al atoms. There are a spread of Al–Al bond distances ranging from 2.70–2.83 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent Sc, four equivalent Fe, and six Al atoms. Both Al–Al bond lengths are 2.65 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(P2Rh3)2 by Materials Project

Sc(Rh3P2)2 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. Sc is bonded to six equivalent Rh and six equivalent P atoms to form face-sharing ScP6Rh6 cuboctahedra. All Sc–Rh bond lengths are 2.98 Å. All Sc–P bond lengths are 2.92 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 5-coordinate geometry to five P atoms. There are a spread of Rh–P bond distances ranging from 2.42–2.59 Å. In the second Rh site, Rh is bonded in a 6-coordinate geometry to two equivalent Sc and four P atoms. There are a spread of Rh–P bond distances ranging from 2.28–2.51 Å. There are two inequivalent P sites. In the first P site, P is bonded in a 9-coordinate geometry to nine Rh atoms. In the second P site, P is bonded in a 8-coordinate geometry to two equivalent Sc and six Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(P2Ru3)2 by Materials Project

Sc(Ru3P2)2 crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Sc is bonded to six equivalent Ru and six equivalent P atoms to form face-sharing ScP6Ru6 cuboctahedra. All Sc–Ru bond lengths are 3.00 Å. All Sc–P bond lengths are 2.90 Å. There are two inequivalent Ru sites. In the first Ru site, Ru is bonded in a 6-coordinate geometry to two equivalent Sc and four P atoms. There are two shorter (2.31 Å) and two longer (2.47 Å) Ru–P bond lengths. In the second Ru site, Ru is bonded in a 5-coordinate geometry to five P atoms. There are one shorter (2.44 Å) and four longer (2.49 Å) Ru–P bond lengths. There are two inequivalent P sites. In the first P site, P is bonded in a 8-coordinate geometry to two equivalent Sc and six Ru atoms. In the second P site, P is bonded in a 9-coordinate geometry to nine Ru atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc(Fe2Si)2 by Materials Project

Sc(Fe2Si)2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Sc is bonded in a 6-coordinate geometry to twelve equivalent Fe and six equivalent Si atoms. There are four shorter (3.00 Å) and eight longer (3.13 Å) Sc–Fe bond lengths. There are two shorter (2.75 Å) and four longer (2.83 Å) Sc–Si bond lengths. Fe is bonded in a 3-coordinate geometry to three equivalent Sc and three equivalent Si atoms. There are one shorter (2.31 Å) and two longer (2.35 Å) Fe–Si bond lengths. Si is bonded in a 9-coordinate geometry to three equivalent Sc and six equivalent Fe atoms.

36 MATERIALS SCIENCE↗