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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ga(HO)3 by Materials Project

Ga(OH)3 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to six O2- atoms to form corner-sharing GaO6 octahedra. The corner-sharing octahedra tilt angles range from 43–45°. There are a spread of Ga–O bond distances ranging from 2.00–2.05 Å. In the second Ga3+ site, Ga3+ is bonded to six equivalent O2- atoms to form corner-sharing GaO6 octahedra. The corner-sharing octahedral tilt angles are 43°. All Ga–O bond lengths are 2.02 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the second H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.01 Å) and one longer (1.61 Å) H–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Ga3+ and two H1+ atoms. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two Ga3+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2(Ga3Ru)3 by Materials Project

Ho2(RuGa3)3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ho is bonded in a 11-coordinate geometry to eleven Ga atoms. There are a spread of Ho–Ga bond distances ranging from 3.04–3.17 Å. There are two inequivalent Ru sites. In the first Ru site, Ru is bonded in a 8-coordinate geometry to eight Ga atoms. There are a spread of Ru–Ga bond distances ranging from 2.56–2.63 Å. In the second Ru site, Ru is bonded in a 8-coordinate geometry to eight Ga atoms. There are four shorter (2.60 Å) and four longer (2.61 Å) Ru–Ga bond lengths. There are four inequivalent Ga sites. In the first Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Ru, and six Ga atoms. All Ga–Ga bond lengths are 2.75 Å. In the second Ga site, Ga is bonded in a 3-coordinate geometry to three equivalent Ho, three Ru, and five Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.77–2.96 Å. In the third Ga site, Ga is bonded in a 3-coordinate geometry to two equivalent Ho, three Ru, and five Ga atoms. There are one shorter (2.72 Å) and two longer (2.84 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Ru, and six Ga atoms. The Ga–Ga bond length is 2.73 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2(Ga3Rh)3 by Materials Project

Ho2(RhGa3)3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ho is bonded in a 11-coordinate geometry to eleven Ga atoms. There are a spread of Ho–Ga bond distances ranging from 3.02–3.14 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 8-coordinate geometry to eight Ga atoms. There are a spread of Rh–Ga bond distances ranging from 2.58–2.65 Å. In the second Rh site, Rh is bonded in a 8-coordinate geometry to eight Ga atoms. There are a spread of Rh–Ga bond distances ranging from 2.56–2.64 Å. There are four inequivalent Ga sites. In the first Ga site, Ga is bonded in a 2-coordinate geometry to two equivalent Ho, two equivalent Rh, and six Ga atoms. There are four shorter (2.75 Å) and two longer (2.77 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 3-coordinate geometry to three equivalent Ho, three Rh, and five Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.77–2.94 Å. In the third Ga site, Ga is bonded in a 3-coordinate geometry to two equivalent Ho, three Rh, and five Ga atoms. There are one shorter (2.80 Å) and two longer (2.82 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Rh, and six Ga atoms. The Ga–Ga bond length is 2.74 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2(Ga3Ir)3 by Materials Project

Ho2(IrGa3)3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ho is bonded in a 11-coordinate geometry to eleven Ga atoms. There are a spread of Ho–Ga bond distances ranging from 3.01–3.16 Å. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a 8-coordinate geometry to eight Ga atoms. There are a spread of Ir–Ga bond distances ranging from 2.58–2.66 Å. In the second Ir site, Ir is bonded in a 8-coordinate geometry to eight Ga atoms. There are a spread of Ir–Ga bond distances ranging from 2.56–2.65 Å. There are four inequivalent Ga sites. In the first Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Ir, and six Ga atoms. There are four shorter (2.75 Å) and two longer (2.76 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 3-coordinate geometry to three equivalent Ho, three Ir, and five Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.78–2.95 Å. In the third Ga site, Ga is bonded in a 3-coordinate geometry to two equivalent Ho, three Ir, and five Ga atoms. There are one shorter (2.81 Å) and two longer (2.82 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Ir, and six Ga atoms. The Ga–Ga bond length is 2.74 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of controlled disorder on the dipolar spin-ice state of Ho-based pyrochlores

Pyrochlore magnets of the form 𝑅 2 ⁢𝐵 2 ⁢O 7 , in which rare-earth ions on the 𝑅 site form a three-dimensional network of corner-sharing tetrahedra, provide a canonical setting for geometrical frustration. Ho-based pyrochlores host a dipolar spin-ice ground state, characterized by Ising moments constrained by the ice rules and elementary excitations analogous to magnetic monopoles. Here, in this work, we examine how controlled chemical disorder influences this state by introducing site mixing on the nonmagnetic 𝐵 site in two compounds. Ho 2⁢ GaSbO 7 contains only Ga 3+ /Sb 5+ charge disorder, whereas Ho 2 ⁢ScSbO 7 exhibits both charge and substantial size disorder arising from the large ionic-radius mismatch between Sc 3+ and Sb 5+ . Although both materials retain the pyrochlore structure, neutron-scattering measurements reveal a reduced correlation length for the 𝑅/𝐵-site cation ordering and enhanced local structural distortions in Ho 2 ⁢ScSbO 7 . Despite these structural differences, bulk thermodynamic measurements and magnetic diffuse scattering demonstrate that both systems exhibit the defining signatures of a dipolar spin-ice state. Low-energy inelastic neutron spectroscopy further uncovers broad magnetic excitations that develop within the dipolar spin-ice regime, a feature absent in pristine Ho pyrochlores and indicative of disorder-induced splitting of the non-Kramers ground-state doublet. Together, these results show that controlled disorder generates tunable transverse-field-driven quantum fluctuations in Ho-based pyrochlores, although the dipolar spin-ice state is remarkably robust to this disorder.

magnetic anisotropy↗
DOE OSTI2020

Materials Data on HoAlGa by Materials Project

HoAlGa is hexagonal omega structure-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Ho is bonded to six equivalent Ga and six equivalent Al atoms to form a mixture of edge and face-sharing HoAl6Ga6 cuboctahedra. All Ho–Ga bond lengths are 3.12 Å. All Ho–Al bond lengths are 3.12 Å. Ga is bonded in a 3-coordinate geometry to six equivalent Ho and three equivalent Al atoms. All Ga–Al bond lengths are 2.57 Å. Al is bonded in a 3-coordinate geometry to six equivalent Ho and three equivalent Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho8Ga3Co by Materials Project

Ho8CoGa3 crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are four inequivalent Ho sites. In the first Ho site, Ho is bonded to one Co and four equivalent Ga atoms to form distorted HoGa4Co trigonal pyramids that share corners with two equivalent HoGa6 octahedra, corners with three equivalent HoGa3Co tetrahedra, corners with six equivalent HoGa4Co trigonal pyramids, an edgeedge with one HoGa3Co tetrahedra, edges with four equivalent HoGa4Co trigonal pyramids, and faces with two equivalent HoGa6 octahedra. The corner-sharing octahedra tilt angles range from 54–58°. The Ho–Co bond length is 2.81 Å. There are a spread of Ho–Ga bond distances ranging from 2.93–3.74 Å. In the second Ho site, Ho is bonded to one Co and three equivalent Ga atoms to form distorted HoGa3Co tetrahedra that share corners with six equivalent HoGa6 octahedra, corners with nine equivalent HoGa4Co trigonal pyramids, and edges with three equivalent HoGa4Co trigonal pyramids. The corner-sharing octahedra tilt angles range from 16–47°. The Ho–Co bond length is 2.64 Å. All Ho–Ga bond lengths are 3.07 Å. In the third Ho site, Ho is bonded in a 3-coordinate geometry to one Co and four equivalent Ga atoms. The Ho–Co bond length is 2.77 Å. There are two shorter (3.15 Å) and two longer (3.69 Å) Ho–Ga bond lengths. In the fourth Ho site, Ho is bonded to six equivalent Ga atoms to form distorted HoGa6 octahedra that share corners with six equivalent HoGa3Co tetrahedra, corners with six equivalent HoGa4Co trigonal pyramids, faces with two equivalent HoGa6 octahedra, and faces with six equivalent HoGa4Co trigonal pyramids. There are three shorter (3.25 Å) and three longer (3.36 Å) Ho–Ga bond lengths. Co is bonded in a 7-coordinate geometry to seven Ho atoms. Ga is bonded in a 11-coordinate geometry to eleven Ho atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho5Ga3 by Materials Project

Ho5Ga3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 3-coordinate geometry to five equivalent Ga atoms. There are a spread of Ho–Ga bond distances ranging from 3.02–3.54 Å. In the second Ho site, Ho is bonded in a 6-coordinate geometry to six equivalent Ga atoms. All Ho–Ga bond lengths are 3.07 Å. Ga is bonded in a 9-coordinate geometry to nine Ho atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Ga4Fe13C2 by Materials Project

Ho2Fe13Ga4C2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a distorted bent 120 degrees geometry to seven Fe, two equivalent Ga, and two C atoms. There are a spread of Ho–Fe bond distances ranging from 3.12–3.36 Å. There are one shorter (3.12 Å) and one longer (3.50 Å) Ho–Ga bond lengths. There are one shorter (2.46 Å) and one longer (2.49 Å) Ho–C bond lengths. In the second Ho site, Ho is bonded in a distorted bent 120 degrees geometry to eight Fe, one Ga, and two C atoms. There are a spread of Ho–Fe bond distances ranging from 3.09–3.51 Å. The Ho–Ga bond length is 3.17 Å. There are one shorter (2.48 Å) and one longer (2.53 Å) Ho–C bond lengths. There are thirteen inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to five Fe, one Ga, and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.49–2.78 Å. The Fe–Ga bond length is 2.61 Å. The Fe–C bond length is 1.84 Å. In the second Fe site, Fe is bonded in a single-bond geometry to six Fe and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.46–2.78 Å. The Fe–C bond length is 1.86 Å. In the third Fe site, Fe is bonded to two Ho, eight Fe, and two Ga atoms to form distorted FeHo2Ga2Fe8 cuboctahedra that share a cornercorner with one GaHo3GaFe8 cuboctahedra, corners with seven FeHo2Ga3Fe7 cuboctahedra, corners with four CHo2GaFe3 octahedra, edges with three FeHo2Ga3Fe7 cuboctahedra, edges with two CHo2GaFe3 octahedra, faces with two equivalent GaHo3GaFe8 cuboctahedra, and faces with seven FeHo2Ga3Fe7 cuboctahedra. The corner-sharing octahedra tilt angles range from 23–31°. There are a spread of Fe–Fe bond distances ranging from 2.44–2.73 Å. There are one shorter (2.53 Å) and one longer (2.61 Å) Fe–Ga bond lengths. In the fourth Fe site, Fe is bonded in a single-bond geometry to five Fe, one Ga, and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.46–2.77 Å. The Fe–Ga bond length is 2.70 Å. The Fe–C bond length is 1.85 Å. In the fifth Fe site, Fe is bonded to two Ho, seven Fe, and three Ga atoms to form distorted FeHo2Ga3Fe7 cuboctahedra that share a cornercorner with one GaHo3GaFe8 cuboctahedra, corners with seven FeHo2Ga2Fe8 cuboctahedra, corners with four CHo2GaFe3 octahedra, edges with three FeHo2Ga2Fe8 cuboctahedra, edges with two CHo2GaFe3 octahedra, faces with two equivalent GaHo3GaFe8 cuboctahedra, and faces with seven FeHo2Ga2Fe8 cuboctahedra. The corner-sharing octahedra tilt angles range from 23–29°. There are a spread of Fe–Fe bond distances ranging from 2.46–2.75 Å. There are two shorter (2.52 Å) and one longer (2.67 Å) Fe–Ga bond lengths. In the sixth Fe site, Fe is bonded in a single-bond geometry to six Fe and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.47–2.79 Å. The Fe–C bond length is 1.83 Å. In the seventh Fe site, Fe is bonded in a 1-coordinate geometry to one Ho, ten Fe, and three Ga atoms. There are a spread of Fe–Fe bond distances ranging from 2.37–2.72 Å. There are a spread of Fe–Ga bond distances ranging from 2.64–2.68 Å. In the eighth Fe site, Fe is bonded in a 3-coordinate geometry to one Ho, twelve Fe, and one Ga atom. There are a spread of Fe–Fe bond distances ranging from 2.57–2.70 Å. The Fe–Ga bond length is 2.57 Å. In the ninth Fe site, Fe is bonded to two Ho, seven Fe, and three Ga atoms to form distorted FeHo2Ga3Fe7 cuboctahedra that share a cornercorner with one GaHo3GaFe8 cuboctahedra, corners with seven FeHo2Ga2Fe8 cuboctahedra, corners with two equivalent CHo2GaFe3 octahedra, an edgeedge with one GaHo3GaFe8 cuboctahedra, edges with three FeHo2Ga2Fe8 cuboctahedra, a faceface with one GaHo3GaFe8 cuboctahedra, faces with seven FeHo2Ga2Fe8 cuboctahedra, and faces with two equivalent CHo2Ga2Fe2 octahedra. The corner-sharing octahedra tilt angles range from 40–44°. The Fe–Fe bond length is 2.41 Å. There are one shorter (2.47 Å) and two longer (2.50 Å) Fe–Ga bond lengths. In the tenth Fe site, Fe is bonded to two Ho, eight Fe, and two Ga atoms to form distorted FeHo2Ga2Fe8 cuboctahedra that share a cornercorner with one GaHo3GaFe8 cuboctahedra, corners with seven FeHo2Ga2Fe8 cuboctahedra, corners with two equivalent CHo2Ga2Fe2 octahedra, an edgeedge with one GaHo3GaFe8 cuboctahedra, edges with three FeHo2Ga2Fe8 cuboctahedra, a faceface with one GaHo3GaFe8 cuboctahedra, faces with seven FeHo2Ga2Fe8 cuboctahedra, and faces with two equivalent CHo2GaFe3 octahedra. The corner-sharing octahedra tilt angles range from 42–43°. Both Fe–Fe bond lengths are 2.42 Å. There are one shorter (2.45 Å) and one longer (2.47 Å) Fe–Ga bond lengths. In the eleventh Fe site, Fe is bonded to two Ho, seven Fe, and three Ga atoms to form distorted FeHo2Ga3Fe7 cuboctahedra that share corners with three equivalent GaHo3GaFe8 cuboctahedra, corners with eleven FeHo2Ga2Fe8 cuboctahedra, an edgeedge with one FeHo3Ga2Fe7 cuboctahedra, an edgeedge with one GaHo3GaFe8 cuboctahedra, a faceface with one GaHo3GaFe8 cuboctahedra, faces with nine FeHo2Ga2Fe8 cuboctahedra, and faces with four CHo2GaFe3 octahedra. The Fe–Fe bond length is 2.42 Å. There are a spread of Fe–Ga bond distances ranging from 2.47–2.52 Å. In the twelfth Fe site, Fe is bonded to three Ho, seven Fe, and two Ga atoms to form distorted FeHo3Ga2Fe7 cuboctahedra that share corners with two equivalent GaHo3GaFe8 cuboctahedra, corners with nine FeHo2Ga2Fe8 cuboctahedra, corners with four CHo2GaFe3 octahedra, an edgeedge with one GaHo3GaFe8 cuboctahedra, edges with three FeHo2Ga3Fe7 cuboctahedra, a faceface with one GaHo3GaFe8 cuboctahedra, faces with seven FeHo2Ga2Fe8 cuboctahedra, and faces with two CHo2GaFe3 octahedra. The corner-sharing octahedra tilt angles range from 65–69°. There are one shorter (2.54 Å) and one longer (2.56 Å) Fe–Ga bond lengths. In the thirteenth Fe site, Fe is bonded in a single-bond geometry to four Fe, one Ga, and one C atom. The Fe–Ga bond length is 2.54 Å. The Fe–C bond length is 1.86 Å. There are four inequivalent Ga sites. In the first Ga site, Ga is bonded in a single-bond geometry to four Fe, one Ga, and one C atom. The Ga–Ga bond length is 2.64 Å. The Ga–C bond length is 2.08 Å. In the second Ga site, Ga is bonded to three Ho, eight Fe, and one Ga atom to form distorted GaHo3GaFe8 cuboctahedra that share corners with two equivalent GaHo3GaFe8 cuboctahedra, corners with nine FeHo2Ga2Fe8 cuboctahedra, corners with four CHo2GaFe3 octahedra, edges with four FeHo2Ga3Fe7 cuboctahedra, faces with eight FeHo2Ga2Fe8 cuboctahedra, and faces with two CHo2GaFe3 octahedra. The corner-sharing octahedra tilt angles range from 63–67°. In the third Ga site, Ga is bonded in a single-bond geometry to five Fe and one C atom. The Ga–C bond length is 2.16 Å. In the fourth Ga site, Ga is bonded in a single-bond geometry to five Fe and one C atom. The Ga–C bond length is 2.11 Å. There are two inequivalent C sites. In the first C site, C is bonded to two Ho, three Fe, and one Ga atom to form CHo2GaFe3 octahedra that share corners with two equivalent GaHo3GaFe8 cuboctahedra, corners with eight FeHo2Ga2Fe8 cuboctahedra, corners with two equivalent CHo2Ga2Fe2 octahedra, edges with two FeHo2Ga2Fe8 cuboctahedra, a faceface with one GaHo3GaFe8 cuboctahedra, and faces with five FeHo2Ga3Fe7 cuboctahedra. The corner-sharing octahedral tilt angles are 61°. In the second C site, C is bonded to two Ho, two Fe, and two Ga atoms to form CHo2Ga2Fe2 octahedra that share corners with two equivalent GaHo3GaFe8 cuboctahedra, corners with eight FeHo2Ga2Fe8 cuboctahedra, corners with two equivalent CHo2GaFe3 octahedra, edges with two FeHo2Ga2Fe8 cuboctahedra, a faceface with one GaHo3GaFe8 cuboctahedra, and faces with five FeHo2Ga3Fe7 cuboctahedra. The corner-sharing octahedral tilt angles are 61°.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Theoretical branching ratios for the 5I7 to 5I7 levels of Ho(3+) in the garnets A3B2C3O12 (A = Y,La,Lu,Gd; B = Al,Lu,Sc,Ga; C = Al,Ga)

Results are reported from an experimental study investigating triply ionized holmium in 10 garnets using the point-change model to predict theoretical energy levels and temperature-dependent branching ratios for the 5I7 to 5I8 manifolds for temperatures between 50 and 400 K. Plots were made for the largest lines at 300 K. YScAG was plotted twice, once for each set of X-ray data available. Energy levels are predicted based on theoretical crystal-field parameters, and good agreement to experiment is found. It is suggested that the present set of theoretical crystal-field parameters provides good estimates of the energy levels for the other hosts on which there are no experimental optical data. X-ray and index-of-refraction data are used to evaluate the performance of 10 lasers via a quantum mechanical model to predict the position of the energy levels and the temperature-dependent branching rations of the 5I7 to 5I8 levels of holmium. The fractional population inversion required for threshold is also evaluated.

Filer, Elizabeth D.↗
DOE OSTI2020

Materials Data on Ho2(Ga3Co)3 by Materials Project

Ho2(CoGa3)3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ho is bonded in a 11-coordinate geometry to eleven Ga atoms. There are a spread of Ho–Ga bond distances ranging from 2.97–3.03 Å. There are two inequivalent Co sites. In the first Co site, Co is bonded in a 12-coordinate geometry to eight Ga atoms. There are a spread of Co–Ga bond distances ranging from 2.50–2.56 Å. In the second Co site, Co is bonded in a 12-coordinate geometry to eight Ga atoms. There are four shorter (2.52 Å) and four longer (2.55 Å) Co–Ga bond lengths. There are four inequivalent Ga sites. In the first Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Ho, three Co, and five Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.73–2.81 Å. In the second Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, three Co, and five Ga atoms. There are one shorter (2.69 Å) and two longer (2.80 Å) Ga–Ga bond lengths. In the third Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Co, and six Ga atoms. Both Ga–Ga bond lengths are 2.74 Å. In the fourth Ga site, Ga is bonded in a 10-coordinate geometry to two equivalent Ho, two equivalent Co, and six Ga atoms. The Ga–Ga bond length is 2.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Persistent Room-Temperature Photodarkening in Cu-Doped β - Ga 2 O 3

β–Ga 2 O 3 is an ultrawide band gap semiconductor with emerging applications in power electronics. Here, the introduction of acceptor dopants yields semi-insulating substrates necessary for thin-film devices. In the present work, exposure of Cu-doped β–Ga 2 O 3 to UV light > 4 eV is shown to cause large, persistent photo-induced darkening at room temperature. Electron paramagnetic resonance spectroscopy indicates that light exposure converts Cu 2+ to Cu 3+ , a rare oxidation state that is responsible for the optical absorption. The photodarkening is accompanied by the appearance of O–H vibrational modes in the infrared spectrum. Hybrid function calculations show that Cu acceptors can favorably complex with hydrogen donors incorporated as interstitial (Hi) or substitutional (HO) defects. When Cu Ga –HO complexes absorb light, hydrogen is released, contributing to the observed Cu 3+ species and O–H modes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho4GaSbS9 by Materials Project

Ho4GaSbS9 crystallizes in the orthorhombic Aea2 space group. The structure is three-dimensional. there are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Ho–S bond distances ranging from 2.72–2.84 Å. In the second Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Ho–S bond distances ranging from 2.71–2.82 Å. In the third Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Ho–S bond distances ranging from 2.70–3.00 Å. In the fourth Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Ho–S bond distances ranging from 2.69–2.80 Å. Ga3+ is bonded to four S2- atoms to form corner-sharing GaS4 tetrahedra. There are a spread of Ga–S bond distances ranging from 2.29–2.32 Å. Sb3+ is bonded in a rectangular see-saw-like geometry to four S2- atoms. There are a spread of Sb–S bond distances ranging from 2.48–2.85 Å. There are ten inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted water-like geometry to two equivalent Ga3+ atoms. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to two Ho3+ and one Ga3+ atom. In the third S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 trigonal pyramids that share a cornercorner with one SHo3Ga tetrahedra, corners with four SHo4 trigonal pyramids, an edgeedge with one SHo3Ga tetrahedra, and edges with two SHo4 trigonal pyramids. In the fourth S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 trigonal pyramids that share a cornercorner with one SHo3Ga tetrahedra, corners with four SHo4 trigonal pyramids, an edgeedge with one SHo3Ga tetrahedra, and edges with two SHo4 trigonal pyramids. In the fifth S2- site, S2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the sixth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Ho3+ and one Sb3+ atom. In the seventh S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 trigonal pyramids that share a cornercorner with one SHo3Ga tetrahedra, corners with four SHo4 trigonal pyramids, an edgeedge with one SHo3Ga tetrahedra, and edges with two SHo4 trigonal pyramids. In the eighth S2- site, S2- is bonded in a 3-coordinate geometry to one Ho3+ and two equivalent Sb3+ atoms. In the ninth S2- site, S2- is bonded in a 4-coordinate geometry to two Ho3+, one Ga3+, and one Sb3+ atom. In the tenth S2- site, S2- is bonded to three Ho3+ and one Ga3+ atom to form a mixture of distorted edge and corner-sharing SHo3Ga tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Suppressing CO formation in low-temperature methanol steam reforming via Ce-modified CuZnGa layered oxide catalysts

Cu-based layered double hydroxides (LDHs) are widely recognized as effective catalysts for low-temperature methanol steam reforming, yet achieving high hydrogen productivity together with near-complete suppression of CO formation remains challenging. Here, we report the synthesis and evaluation of a series of CuZnGa LDH-derived catalysts and Ce-modified analogues prepared via an aqueous miscible organic method, which enables high metal dispersion and precise structural control. The optimized CuZnGa catalyst exhibits a hydrogen production rate of 16.9 µmol H 2 ·g cat −1 ·s −1 at 180 °C with an H 2 /CO ratio exceeding 3500, outperforming many state-of-the-art low-temperature systems. Importantly, the incorporation of small amounts of Ce further suppresses CO formation while maintaining high hydrogen productivity. Combined spectroscopic characterization and density functional theory calculations reveal that Ce is incorporated into the LDH lattice by substituting Ga 3+ sites up to a critical threshold, beyond which highly dispersed CeO x species are formed. These species provide mobile lattice oxygen that participates in a Mars-van Krevelen-type pathway, selectively oxidizing CO and suppressing the reverse water-gas shift reaction. This study establishes a clear relationship between Ce speciation, oxygen mobility, and catalytic selectivity in LDH-derived systems. The resulting catalysts demonstrate the potential of interface-engineered Cu-based materials for efficient low-temperature hydrogen production with minimal CO contamination.

09 BIOMASS FUELS↗
DOE OSTI2023

Injection mechanisms in a III -nitride light-emitting diode as seen by self-emissive electron microscopy

Here, we report on the investigation of an electrically biased high efficiency green III-nitride light-emitting diode (LED) by electron emission microscopy (EEM) using a low-energy electron microscope (LEEM). The surface of the LED was activated to negative electron affinity via deposition of a submonolayer of Cs. With the illumination column of the LEEM turned off, upon electrical injection of the LED, we directly image the hot electrons generated by eeh Auger-Meitner nonradiative processes that diffuse through the top p-Ga N layer and emit out the surface of the biased LED. By determining the source of emitted electrons using complementary electron emission spectroscopy measurements, EEM allows us to effectively map the carrier density within the LED. Using EEM, we observed nonelectron emitting regions with a density of approximately 3 × 10 8 cm -2 , identified as V-shaped defects (V-defects). This is confirmed through the corresponding dark spots of panchromatic cathodoluminescence measurements of the same sample and by plan-view transmission electron microscopy. The absence of electron emission at the sidewall of the V-defects can be attributed to several factors, including reduced carrier density in the sidewall quantum wells due to carriers traveling fast through the semipolar sidewalls before being injected into the planar quantum wells, the reduced population of hot electrons surviving diffusion through the thicker p-GaN filling in the V-defect before emission onto vacuum, and a smaller Auger-Meitner coefficient for the low In content semipolar sidewall quantum wells. The stronger electron emission observed at the ridges of most V-defects compared to the planar quantum well regions indicates larger local injected carrier densities, confirming that V-defect sidewalls allow for strong lateral carrier injection when compared to the weaker vertical injection away from the V-defect as evidenced by the weaker electron emission intensity away from the V-defects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗