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11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Mo 4 FeGa 17.25– x Ge x : Complementary Point Substitutions, Buffering Frameworks, and Merging of the 18-n and Octet Bonding Schemes

We present the discovery of Mo 4 FeGa 17.25–x Ge x (x ∼ 2.1(4), based on determination of Ge content), a complex gallide featuring a variety of point substitution phenomena. Its crystal structure is derived from the Ti 2 Ni type, in which a diamond network of face-sharing octahedra is interpenetrated by a second diamond network of vertex-sharing stella quadrangula. However, while in the ideal Ti 2 Ni type these two frameworks run uninterrupted through the crystal, Mo 4 FeGa 17.25–x Ge x shows three variations. First, the inner tetrahedron of every other stella quadrangula is replaced with a main group atom, creating tetrahedra reminiscent of the Zintl phase NaTl. Next, a selection of Ga 6 octahedra are filled with Fe atoms, in a manner analogous to the stuffed AuCu 3 -type phases. Finally, the refined crystal structure shows that in each unit cell a single Ga2 atom in the octahedral network is substituted with a dumbbell of Ga/Ge atoms. Electronic structure calculations on ordered models of Mo 4 FeGa 17.25–x Ge x reveal a narrow band near the Fermi energy, which is explained in terms of the 18-n and octet bonding schemes using reversed approximation Molecular Orbital analysis. A DFT-chemical pressure analysis connects the tetrahedron/atom and atom/dumbbell substitutions to the relief of atomic packing tensions and highlights soft atomic motions within the octahedral framework and driving forces for atom/dumbbell substitution. The combination of soft vibrational modes, disorder, and a narrow band gap could make this phase of interest for potential thermoelectric properties.

Chemical structure↗
DOE OSTI2022

Magnetic state switching in FeGa microstructures

This work demonstrates that magnetoelectric composite heterostructures can be designed at the length scale of 10µms that can be switched from a magnetized state to a vortex state, effectively switching the magnetization off, using electric field induced strain. This was accomplished using thin film magnetoelectric heterostructures of Fe 81.4 Ga 18.6 on a single crystal (011) [Pb(Mg 1/3 Nb 2/3 )O 3 ] 0.68 -[PbTiO 3 ] 0.32 (PMN-32PT) ferroelectric substrate. Here, the heterostructures were tripped from a multi-domain magnetized state to a flux closure vortex state using voltage induced strain in a piezoelectric substrate. FeGa heterostructures were deposited on a Si-substrate for superconducting quantum interference device magnetometry characterization of the magnetic properties. The magnetoelectric coupling of a FeGa continuous film on PMN-32PT was characterized using a magneto optical Kerr effect magnetometer with bi-axial strain gauges, and magnetic multi-domain heterostructures were imaged using x-ray magnetic circular dichroism—photoemission electron microscopy during the transition to the vortex state. The domain structures were modelled using MuMax 3 , a micromagnetics code, and compared with observations. The results provide considerable insight into designing magnetoelectric heterostructures that can be switched from an ‘on’ state to an ‘off’ state using electric field induced strain.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optical conductivity and vibrational spectra of the narrow-gap semiconductor FeGa 3

Intermetallic narrow-gap semiconductors have been intensively explored due to their large thermoelectric power at low temperatures and a possible role of strong electronic correlations in their unusual thermodynamic and transport properties. Here we study the optical spectra and vibrational properties of FeGa 3 . The optical conductivity indicates that FeGa 3 has a direct band gap of ≈ 0.7 eV, consistent with density functional theory (DFT) calculations. Most importantly, we find a substantial spectral weight also below 0.4 eV, which is the energy of the indirect (charge) gap found in resistivity measurements and ab initio calculations. We find that the spectral weight below the gap decreases with increasing temperature, which indicates that it originates from the impurity states and not from the electronic correlations. Interestingly, we did not find any signatures of the impurity states in vibrational spectra. The infrared and Raman vibrational lines are narrow and weakly temperature dependent. The vibrational frequencies are in excellent agreement with our DFT calculations, implying a modest role of electronic correlations. Narrow Mössbauer spectral lines also indicate high crystallinity of the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Electrical and Magnetic Properties of FeGa 3 with Antisite Disorder

We investigated the electronic and magnetic ground states of the cage compound FeGa 3 under the presence of Fe antisite disorder (namely as Fe 0.258 Ga 0.742 ) by x-ray diffraction (XRD), Mössbauer spectroscopy (MS), magnetization and electrical resistivity. Our results show that approximately 4.5 (5)% Fe antisite occupying one of the two non-equivalent Ga sites changes significantly the electronic and magnetic ground states of the pristine compound. We uncover that Fe 0.258 Ga 0.742 undergoes two magnetic transitions, T 1 ≈ 60 K and T 2 ≈ 15 K, the latter associated with the suppression of semiconducting behavior. We focus our discussion on the role that in-gap impurity states and spin disorder play across semiconducting-metal and paramagnetic-magnetic transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Surface structures of magnetostrictive D0 3 -Fe 3 Ga(0 0 1)

First-principles total energy calculations and scanning tunneling microscopy experiments were performed to study the surface reconstruction of the magnetostrictive Fe 3 Ga alloy. The inverse magnetostrictive behavior was evaluated in the bulk by compressing and stretching its lattice parameter, showing an increase in magnetic moments as strain increases. Surface analysis demonstrates two thermodynamically stable surfaces, the (1 × 1) and (3 × 1). The (1 × 1) is an ideal FeGa terminated surface, whereas the (3 × 1) is also FeGa terminated but it has a first-layer Fe atom substituted by a Ga atom every three unit-cells, forming a row-like surface structure. Tersoff–Hamann scanning tunneling microscopy simulations were obtained and compared with experimental results. We found good agreement between theory and experiment, in which the distance between rows is ~12.3 Å. Theoretical findings suggest that the substrate-induced strain may increase the stability of the (3 × 1) reconstruction. Analysis of the magnetic moments in the reconstructions showed that their behavior is affected by a surface effect, as well as by the inverse magnetostriction of the structure. A good understanding of the FeGa surface reconstructions is an important step towards further improvements in magnetic storage devices and sensors.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ti- and Fe-related charge transition levels in $β$ – Ga 2 O 3

Here, deep-level transient spectroscopy measurements on $β$ – Ga 2 O 3 crystals reveal the presence of three defect signatures labeled $E$ 2a , $E$ 2b , and $E$ 3 with activation energies at around 0.66 eV, 0.73 eV, and 0.95 eV below the conduction band edge. Using secondary ion mass spectrometry, a correlation between the defect concentration associated with $E$ 3 and the Ti concentration present in the samples was found. Particularly, it is found that $E$ 3 is the dominant Ti-related defect in $β$ – Ga 2 O 3 and is associated with a single Ti atom. This finding is further corroborated by hybrid functional calculations that predict Ti substituting on an octahedral Ga site, denoted as Ti GaII , to be a good candidate for $E$ 3 . Moreover, the deep level transient spectroscopy results show that the level previously labeled $E$ 2 and attributed to Fe substituting on a gallium site (FeGa) consists of two overlapping signatures labeled E2a and E2b. We tentatively assign $E$ 2a and $E$ 2b to Fe substituting for Ga on a tetrahedral or an octahedral site, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb(GaFe)6 by Materials Project

Yb(FeGa)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Yb is bonded to twelve Fe and eight Ga atoms to form distorted YbGa8Fe12 hexagonal bipyramids that share corners with eight equivalent YbGa8Fe12 hexagonal bipyramids, faces with twenty-four FeYb2Ga6Fe4 cuboctahedra, and faces with two equivalent YbGa8Fe12 hexagonal bipyramids. There are four shorter (3.27 Å) and eight longer (3.28 Å) Yb–Fe bond lengths. There are a spread of Yb–Ga bond distances ranging from 2.79–2.95 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Yb, four equivalent Fe, and six Ga atoms to form distorted FeYb2Ga6Fe4 cuboctahedra that share corners with fourteen FeYb2Ga6Fe4 cuboctahedra, edges with seven FeYb2Ga6Fe4 cuboctahedra, faces with nine FeYb2Ga6Fe4 cuboctahedra, and faces with four equivalent YbGa8Fe12 hexagonal bipyramids. All Fe–Fe bond lengths are 2.50 Å. There are a spread of Fe–Ga bond distances ranging from 2.56–2.61 Å. In the second Fe site, Fe is bonded to two equivalent Yb, four Fe, and six Ga atoms to form distorted FeYb2Ga6Fe4 cuboctahedra that share corners with fourteen FeYb2Ga6Fe4 cuboctahedra, edges with six FeYb2Ga6Fe4 cuboctahedra, faces with ten FeYb2Ga6Fe4 cuboctahedra, and faces with four equivalent YbGa8Fe12 hexagonal bipyramids. Both Fe–Fe bond lengths are 2.51 Å. There are two shorter (2.54 Å) and four longer (2.59 Å) Fe–Ga bond lengths. There are five inequivalent Ga sites. In the first Ga site, Ga is bonded in a 1-coordinate geometry to one Yb, six Fe, and one Ga atom. The Ga–Yb bond length is 2.79 Å. There are four shorter (2.59 Å) and two longer (2.61 Å) Ga–Fe bond lengths. The Ga–Ga bond length is 2.91 Å. In the second Ga site, Ga is bonded in a 1-coordinate geometry to one Yb, six Fe, and one Ga atom. The Ga–Yb bond length is 2.79 Å. In the third Ga site, Ga is bonded in a 10-coordinate geometry to one Yb, six Fe, and three Ga atoms. There are one shorter (2.76 Å) and two longer (2.87 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Yb, six Fe, and two equivalent Ga atoms. In the fifth Ga site, Ga is bonded in a 1-coordinate geometry to one Yb, six Fe, and one Ga atom. Both Ga–Fe bond lengths are 2.61 Å. The Ga–Ga bond length is 2.91 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(GaFe)6 by Materials Project

Zr(FeGa)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Zr is bonded to twelve Fe and eight Ga atoms to form distorted ZrGa8Fe12 hexagonal bipyramids that share corners with eight equivalent ZrGa8Fe12 hexagonal bipyramids, faces with twenty-four FeZr2Ga6Fe4 cuboctahedra, and faces with two equivalent ZrGa8Fe12 hexagonal bipyramids. There are four shorter (3.24 Å) and eight longer (3.26 Å) Zr–Fe bond lengths. There are two shorter (2.79 Å) and six longer (2.93 Å) Zr–Ga bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Zr, four equivalent Fe, and six Ga atoms to form distorted FeZr2Ga6Fe4 cuboctahedra that share corners with fourteen FeZr2Ga6Fe4 cuboctahedra, edges with seven FeZr2Ga6Fe4 cuboctahedra, faces with nine FeZr2Ga6Fe4 cuboctahedra, and faces with four equivalent ZrGa8Fe12 hexagonal bipyramids. All Fe–Fe bond lengths are 2.49 Å. There are a spread of Fe–Ga bond distances ranging from 2.56–2.61 Å. In the second Fe site, Fe is bonded to two equivalent Zr, four Fe, and six Ga atoms to form distorted FeZr2Ga6Fe4 cuboctahedra that share corners with fourteen FeZr2Ga6Fe4 cuboctahedra, edges with six FeZr2Ga6Fe4 cuboctahedra, faces with ten FeZr2Ga6Fe4 cuboctahedra, and faces with four equivalent ZrGa8Fe12 hexagonal bipyramids. Both Fe–Fe bond lengths are 2.50 Å. There are two shorter (2.54 Å) and four longer (2.58 Å) Fe–Ga bond lengths. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 8-coordinate geometry to one Zr, six Fe, and one Ga atom. The Ga–Ga bond length is 2.88 Å. In the second Ga site, Ga is bonded in a 10-coordinate geometry to one Zr, six Fe, and three Ga atoms. There are one shorter (2.73 Å) and two longer (2.87 Å) Ga–Ga bond lengths. In the third Ga site, Ga is bonded in a 8-coordinate geometry to two equivalent Zr, six Fe, and two equivalent Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GaFe by Materials Project

FeGa crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Fe is bonded to six equivalent Fe and six equivalent Ga atoms to form FeGa6Fe6 cuboctahedra that share corners with eighteen equivalent FeGa6Fe6 cuboctahedra, edges with six equivalent FeGa6Fe6 cuboctahedra, edges with twelve equivalent GaGa6Fe6 cuboctahedra, faces with eight equivalent FeGa6Fe6 cuboctahedra, and faces with twelve equivalent GaGa6Fe6 cuboctahedra. All Fe–Fe bond lengths are 2.75 Å. All Fe–Ga bond lengths are 2.57 Å. Ga is bonded to six equivalent Fe and six equivalent Ga atoms to form GaGa6Fe6 cuboctahedra that share corners with eighteen equivalent GaGa6Fe6 cuboctahedra, edges with six equivalent GaGa6Fe6 cuboctahedra, edges with twelve equivalent FeGa6Fe6 cuboctahedra, faces with eight equivalent GaGa6Fe6 cuboctahedra, and faces with twelve equivalent FeGa6Fe6 cuboctahedra. All Ga–Ga bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GaFe(BiO3)2 by Materials Project

FeGa(BiO3)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. Fe3+ is bonded to five O2- atoms to form distorted FeO5 trigonal bipyramids that share corners with two equivalent FeO5 trigonal bipyramids and corners with two equivalent GaO5 trigonal bipyramids. There are a spread of Fe–O bond distances ranging from 1.90–1.96 Å. Ga3+ is bonded to five O2- atoms to form distorted GaO5 trigonal bipyramids that share corners with two equivalent FeO5 trigonal bipyramids and corners with two equivalent GaO5 trigonal bipyramids. There are a spread of Ga–O bond distances ranging from 1.84–2.01 Å. There are two inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.26–2.79 Å. In the second Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.27–2.80 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to one Ga3+ and three Bi3+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one Fe3+ and three Bi3+ atoms. In the third O2- site, O2- is bonded to two equivalent Ga3+ and two Bi3+ atoms to form distorted corner-sharing OGa2Bi2 tetrahedra. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Fe3+ and two Bi3+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to one Fe3+, one Ga3+, and two equivalent Bi3+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to one Fe3+, one Ga3+, and two equivalent Bi3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nd(GaFe)6 by Materials Project

Nd(FeGa)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Nd is bonded in a 8-coordinate geometry to twelve Fe and eight Ga atoms. There are four shorter (3.28 Å) and eight longer (3.31 Å) Nd–Fe bond lengths. There are a spread of Nd–Ga bond distances ranging from 2.88–3.03 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Nd, four Fe, and six Ga atoms to form a mixture of distorted edge, face, and corner-sharing FeNd2Ga6Fe4 cuboctahedra. There are two shorter (2.52 Å) and two longer (2.53 Å) Fe–Fe bond lengths. There are a spread of Fe–Ga bond distances ranging from 2.54–2.63 Å. In the second Fe site, Fe is bonded to two equivalent Nd, four equivalent Fe, and six Ga atoms to form a mixture of edge, face, and corner-sharing FeNd2Ga6Fe4 cuboctahedra. There are a spread of Fe–Ga bond distances ranging from 2.58–2.67 Å. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 1-coordinate geometry to one Nd, six Fe, and three Ga atoms. There are one shorter (2.84 Å) and two longer (3.04 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 10-coordinate geometry to one Nd, six Fe, and three Ga atoms. There are one shorter (2.67 Å) and two longer (2.87 Å) Ga–Ga bond lengths. In the third Ga site, Ga is bonded in a 12-coordinate geometry to two equivalent Nd, six Fe, and four Ga atoms.

36 MATERIALS SCIENCE↗