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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Spectroscopic evidence of spin-state excitation in d-electron correlated semiconductor FeSb 2

Iron antimonide (FeSb 2 ) has been investigated for decades due to its puzzling electronic properties. It undergoes the temperature-controlled transition from an insulator to an ill-defined metal, with a cross-over from diamagnetism to paramagnetism. Extensive efforts have been made to uncover the underlying mechanism, but a consensus has yet to be reached. While macroscopic transport and magnetic measurements can be explained by different theoretical proposals, the essential spectroscopic evidence required to distinguish the physical origin is missing. In this paper, through the use of X-ray absorption spectroscopy and atomic multiplet simulations, we have observed the mixed spin states of 3d 6 configuration in FeSb 2 . Furthermore, we reveal that the enhancement of the conductivity, whether induced by temperature or doping, is characterized by populating the high-spin state from the low-spin state. Our work constitutes vital spectroscopic evidence that the electrical/magnetical transition in FeSb 2 is directly associated with the spin-state excitation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Materials Data on Cs(FeSb)2 by Materials Project

Cs(FeSb)2 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Cs1+ is bonded to four equivalent Cs1+ and eight equivalent Sb3- atoms to form a mixture of distorted corner and face-sharing CsCs4Sb8 cuboctahedra. There are two shorter (3.68 Å) and two longer (3.70 Å) Cs–Cs bond lengths. All Cs–Sb bond lengths are 3.87 Å. Fe+2.50+ is bonded in a 4-coordinate geometry to four equivalent Sb3- atoms. All Fe–Sb bond lengths are 2.62 Å. Sb3- is bonded in a 8-coordinate geometry to four equivalent Cs1+ and four equivalent Fe+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSb by Materials Project

FeSb is Tungsten Carbide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Fe3+ is bonded to six equivalent Sb3- atoms to form a mixture of face, edge, and corner-sharing FeSb6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Fe–Sb bond lengths are 2.64 Å. Sb3- is bonded in a 6-coordinate geometry to six equivalent Fe3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSbS by Materials Project

FeSbS crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Fe3+ is bonded to three equivalent Sb1- and three equivalent S2- atoms to form distorted FeSb3S3 octahedra that share corners with eight equivalent FeSb3S3 octahedra, corners with three equivalent SbFe3S tetrahedra, corners with three equivalent SFe3Sb tetrahedra, and edges with two equivalent FeSb3S3 octahedra. The corner-sharing octahedra tilt angles range from 49–63°. There are a spread of Fe–Sb bond distances ranging from 2.55–2.60 Å. There are a spread of Fe–S bond distances ranging from 2.21–2.26 Å. Sb1- is bonded to three equivalent Fe3+ and one S2- atom to form distorted SbFe3S tetrahedra that share corners with three equivalent FeSb3S3 octahedra, corners with four equivalent SbFe3S tetrahedra, corners with nine equivalent SFe3Sb tetrahedra, and an edgeedge with one SbFe3S tetrahedra. The corner-sharing octahedra tilt angles range from 70–77°. The Sb–S bond length is 2.62 Å. S2- is bonded to three equivalent Fe3+ and one Sb1- atom to form distorted SFe3Sb tetrahedra that share corners with three equivalent FeSb3S3 octahedra, corners with four equivalent SFe3Sb tetrahedra, corners with nine equivalent SbFe3S tetrahedra, and an edgeedge with one SFe3Sb tetrahedra. The corner-sharing octahedra tilt angles range from 74–78°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti5(FeSb)4 by Materials Project

Ti5(FeSb)4 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are five inequivalent Ti sites. In the first Ti site, Ti is bonded in a body-centered cubic geometry to four Fe and four Sb atoms. There are one shorter (2.71 Å) and three longer (2.74 Å) Ti–Fe bond lengths. There are three shorter (2.81 Å) and one longer (2.85 Å) Ti–Sb bond lengths. In the second Ti site, Ti is bonded in a body-centered cubic geometry to four Fe and four Sb atoms. There are one shorter (2.64 Å) and three longer (2.78 Å) Ti–Fe bond lengths. There are one shorter (2.63 Å) and three longer (2.70 Å) Ti–Sb bond lengths. In the third Ti site, Ti is bonded in a body-centered cubic geometry to four Fe and four Sb atoms. There are one shorter (2.64 Å) and three longer (2.69 Å) Ti–Fe bond lengths. There are three shorter (2.67 Å) and one longer (2.74 Å) Ti–Sb bond lengths. In the fourth Ti site, Ti is bonded in a body-centered cubic geometry to four Fe and four Sb atoms. There are three shorter (2.72 Å) and one longer (2.79 Å) Ti–Fe bond lengths. There are three shorter (2.70 Å) and one longer (2.71 Å) Ti–Sb bond lengths. In the fifth Ti site, Ti is bonded in a body-centered cubic geometry to four Fe and four Sb atoms. There are one shorter (2.61 Å) and three longer (2.69 Å) Ti–Fe bond lengths. There are one shorter (2.78 Å) and three longer (2.84 Å) Ti–Sb bond lengths. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a 7-coordinate geometry to seven Ti atoms. In the second Fe site, Fe is bonded in a 11-coordinate geometry to five Ti and six Sb atoms. There are three shorter (2.96 Å) and three longer (3.26 Å) Fe–Sb bond lengths. In the third Fe site, Fe is bonded in a 4-coordinate geometry to four Ti and six Sb atoms. There are three shorter (3.06 Å) and three longer (3.18 Å) Fe–Sb bond lengths. In the fourth Fe site, Fe is bonded in a 4-coordinate geometry to four Ti and six Sb atoms. There are three shorter (3.04 Å) and three longer (3.15 Å) Fe–Sb bond lengths. There are four inequivalent Sb sites. In the first Sb site, Sb is bonded in a 5-coordinate geometry to five Ti and three equivalent Fe atoms. In the second Sb site, Sb is bonded to four Ti and six Fe atoms to form a mixture of distorted face and corner-sharing SbTi4Fe6 tetrahedra. In the third Sb site, Sb is bonded in a 10-coordinate geometry to seven Ti and three equivalent Fe atoms. In the fourth Sb site, Sb is bonded to four Ti and six Fe atoms to form a mixture of distorted face and corner-sharing SbTi4Fe6 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSb(P2O7)2 by Materials Project

FeSb(P2O7)2 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 1.97–2.11 Å. Sb5+ is bonded to six O2- atoms to form SbO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Sb–O bond distances ranging from 1.96–1.99 Å. There are four inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one SbO6 octahedra, corners with two equivalent FeO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 29–43°. There are a spread of P–O bond distances ranging from 1.51–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one FeO6 octahedra, corners with two equivalent SbO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 28–35°. There are a spread of P–O bond distances ranging from 1.49–1.58 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one FeO6 octahedra, corners with two equivalent SbO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 39–41°. There are a spread of P–O bond distances ranging from 1.49–1.58 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one SbO6 octahedra, corners with two equivalent FeO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 23–32°. There are a spread of P–O bond distances ranging from 1.50–1.62 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Sb5+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Sb5+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Sb5+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Sb5+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to one Sb5+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the twelfth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Sb5+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optimal carrier concentration for FeSb 2 colossal thermopower

Crystals of FeSb 2 correlated narrow-gap semiconductor host colossal thermopower values. By tuning the impurity level here, we demonstrate that electron-phonon scattering that transfers phonon momentum to electrons is efficient only for certain optimal carrier concentration in the low-mobility band. Phonon drag acting on such states in crystals with high phonon mean free path enhances thermopower to colossal values, whereas for different carrier concentration, dominant thermal transport mechanism is electronic diffusion. This highlights the dual nature of correlated in-gap states that take part in the phonon drag but also reduce phonon mean free path.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb 2

The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB 6 has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb 2 , a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB 6 and YbB 12 may also exist in systems with d instead of f electrons.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSb(ClO)8 by Materials Project

FeCl2(O)4Sb(OCl3)2O2 crystallizes in the triclinic P1 space group. The structure is one-dimensional and consists of one hydrogen peroxide molecule; one FeCl2(O)4 cluster; and one Sb(OCl3)2 ribbon oriented in the (1, 0, 0) direction. In the FeCl2(O)4 cluster, Fe is bonded in a 6-coordinate geometry to four O and two Cl atoms. There are a spread of Fe–O bond distances ranging from 1.83–2.14 Å. There are one shorter (2.28 Å) and one longer (2.29 Å) Fe–Cl bond lengths. There are four inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Fe atom. In the second O site, O is bonded in a 2-coordinate geometry to one Fe and one O atom. The O–O bond length is 1.28 Å. In the third O site, O is bonded in a single-bond geometry to one Fe atom. In the fourth O site, O is bonded in a 2-coordinate geometry to one Fe and one O atom. There are two inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to one Fe atom. In the second Cl site, Cl is bonded in a single-bond geometry to one Fe atom. In the Sb(OCl3)2 ribbon, Sb is bonded in an octahedral geometry to six Cl atoms. There are a spread of Sb–Cl bond distances ranging from 2.36–2.51 Å. There are two inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to one O and two Cl atoms. The O–O bond length is 2.01 Å. There are one shorter (2.41 Å) and one longer (2.50 Å) O–Cl bond lengths. In the second O site, O is bonded in a distorted L-shaped geometry to one O and one Cl atom. The O–Cl bond length is 2.45 Å. There are six inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to one Sb atom. In the second Cl site, Cl is bonded in a single-bond geometry to one Sb atom. In the third Cl site, Cl is bonded in a single-bond geometry to one Sb and one O atom. In the fourth Cl site, Cl is bonded in a single-bond geometry to one Sb and one O atom. In the fifth Cl site, Cl is bonded in a single-bond geometry to one Sb atom. In the sixth Cl site, Cl is bonded in a distorted single-bond geometry to one Sb and one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSb(ClO)8 by Materials Project

FeCl2(O)4SbCl6(O2)2 crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one dichloroiron;tetrahydrate molecule, four water molecules, and one SbCl6 cluster. In the SbCl6 cluster, Sb is bonded in an octahedral geometry to six Cl atoms. There are two shorter (2.36 Å) and four longer (2.44 Å) Sb–Cl bond lengths. There are two inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to one Sb atom. In the second Cl site, Cl is bonded in a single-bond geometry to one Sb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSb(PO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2021

Prediction of unconventional magnetism in doped FeSb 2

Significance For many decades, it has been commonly believed that all electronic states of a collinear antiferromagnet (AF) are spin-degenerate, unless the underlying crystal structure lacks centrosymmetry and has spin–orbit coupling. This has been essentially definitional for antiferromagnetism and is widely used experimentally to distinguish ferromagnets from AFs. Recently, it was demonstrated that a new class of magnets, possessing antiferromagnetic order and without net magnetization but showing a typical ferromagnetic response in many aspects, is possible. We predict that F e S b 2 , which is well known but poorly understood magnetically, is an incipient unconventional magnet of this type and can be pushed to become one by Co or Cr doping. Moreover, the calculated magnetic anisotropy is favorable for exhibiting various anomalous properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Toward High Conversion Efficiency of Thermoelectric Modules through Synergistical Optimization of Layered Materials

Abstract Waste‐heat electricity generation using high‐efficiency solid‐state conversion technology can significantly decrease dependence on fossil fuels. Here, a synergistical optimization of layered half‐Heusler (hH) materials and module to improve thermoelectric conversion efficiency is reported. This is realized by manufacturing multiple thermoelectric materials with major compositional variations and temperature‐gradient‐coupled carrier distribution by one‐step spark plasma sintering. This strategy provides a solution to overcome the intrinsic concomitants of the conventional segmented architecture that only considers the matching of the figure of merit ( zT ) with the temperature gradient. The current design is dedicated to temperature‐gradient‐coupled resistivity and compatibility matching, optimum zT matching, and reducing contact resistance sources. By enhancing the quality factor of the materials by Sb‐vapor‐pressure‐induced annealing, a superior zT of 1.47 at 973 K is achieved for (Nb, Hf)FeSb hH alloys. Along with the low‐temperature high‐ zT hH alloys of (Nb, Ta, Ti, V)FeSb, the single stage layered hH modules are developed with efficiencies of ≈15.2% and ≈13.5% for the single‐leg and unicouple thermoelectric modules, respectively, under Δ T of 670 K. Therefore, this work has a transformative impact on the design and development of next‐generation thermoelectric generators for any thermoelectric material families.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Grain Boundary Phases in NbFeSb Half‐Heusler Alloys: A New Avenue to Tune Transport Properties of Thermoelectric Materials

Abstract Many thermoelectric materials benefit from complex microstructures. Grain boundaries (GBs) in nanocrystalline thermoelectrics cause desirable reduction in the thermal conductivity by scattering phonons, but often lead to unwanted loss in the electrical conductivity by scattering charge carriers. Therefore, modifying GBs to suppress their electrical resistivity plays a pivotal role in the enhancement of thermoelectric performance, zT . In this work, different characteristics of GB phases in Ti‐doped NbFeSb half‐Heusler compounds are revealed using a combination of scanning transmission electron microscopy and atom probe tomography. The GB phases adopt a hexagonal close‐packed lattice, which is structurally distinct from the half‐Heusler grains. Enrichment of Fe is found at GBs in Nb 0.95 Ti 0.05 FeSb, but accumulation of Ti dopants at GBs in Nb 0.80 Ti 0.20 FeSb, correlating to the bad and good electrical conductivity of the respective GBs. Such resistive to conductive GB phase transition opens up new design space to decouple the intertwined electronic and phononic transport in thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Suppression of thermal conductivity and electronic correlations in Fe 1– x Ru x Sb 2 (0 ≤ x ≤ 0.6)

We present simultaneous suppression of FeSb 2 thermal conductivity and electronic correlations in Fe 1– x Ru x Sb 2 (0 ≤ x ≤ 0.6) single crystal alloys. Small energy gap Δ 1 in Kondo-insulator-like semiconductor FeSb 2 associated with impurity in-gap state increases whereas the intrinsic bandgap Δ 2 decreases upon Ru substitution on Fe atomic site. Thermopower is suppressed along with the intrinsic bandgap and with the thermal conductivity. The more delocalized 4 d character of atomic orbital of Ru brings suppression of electronic correlations, but also an increase in impurity density which reduces phonon mean free path and surface scattering length. Our results indicate a range of Ru doping x where nanostructuring could be used to suppress thermal conductivity further, potentially toward the amorphous limit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗