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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Electrochemically-assisted removal of cadmium ions by redox active Cu-based metal-organic framework

An electrochemically-assisted wastewater treatment using Faradaic materials offers a promising technique for the selective removal of hazardous substances. Here, we demonstrate the reversible capture and release of cadmium ions in aqueous solutions, using a redox-active metal-organic framework (MOF) electrode. As-synthesized copper-based MOF (Cu-MOF-74; copper 2,5-dihydroxyterephthalate) is a highly attractive candidate for Faradaic electrosorption due to its large surface area, water stability, and redox-active metal nodes. Our work demonstrates the reversible capture and release of Cd 2+ ions assisted by the electrochemical redox reaction of Cu 2+ /Cu + within the MOF structure. Combined material characterization and electrosorption tests were carried out to determine the operational conditions for maximizing adsorption capacity, energy efficiency, and material stability, thus leading to excellent electrosorption (>100 mg g -1 ) and regeneration efficiency (>90%). This study demonstrates the feasibility of leveraging MOFs containing redox-active metal nodes for the selective separation of toxic cations, and paves the way for promising future applications of these 3-D porous structures for wastewater treatment and environmental remediation.

42 ENGINEERING↗
DOE OSTI2022

Muon spin rotation and relaxation in Pr 1 - x Nd x Os 4 Sb 12 : Superconductivity and magnetism in Pr-rich alloys

The Pr-rich end 0 ≤ x ≤ 0.25 of the alloy series Pr 1-x Nd x ⁢Os 4 ⁢Sb 12 has been studied using muon spin rotation and relaxation. The end compound PrOs 4 ⁢Sb 12 is an unconventional heavy-fermion superconductor, which exhibits a spontaneous magnetic field associated with broken time-reversal symmetry (TRS) in the superconducting phase. Further, no such field is observed in the Nd-doped alloys for x ≥ 0.05, indicating that TRS has been restored. The superfluid density from the vortex-lattice field distribution is insensitive to Nd concentration for x ≲ 0.2, indicating that TRS restoration does not have a strong effect on the superconducting state. No Nd 3+ static magnetism, ordered or disordered, is found down to the lowest temperatures of measurement.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1987

Carbon kinetic isotope effect in the reaction of CH4 with HO

The carbon kinetic isotope effect in the CH4 + HO reaction is measured experimentally and the use of carbon isotope ratios to diagnose atmospheric methane is examined. The chemical, photolysis, and analytical experimental conditions and procedures are described. It is determined that the CH4 + HO reaction has a carbon kinetic isotope effect of 1.010 + or 0.007 for k(12)k(13) (rate constants ratio) at 297 + or - 3 K. This value is compared with the data of Rust and Stevens (1980). Causes for the poor correlation between the data at high methane conversions are discussed. It is supposed that the difference between the k(12) and k(13) values is due to a difference in the activation energy of the two reactions.

Davidson, J. A.↗
NASA NTRSDate not supplied

6 um Pulsed OP-GaAs OPO Laser for Unambiguous Water Ice Detection on the Moon and Other Planetary Bodies

NASA demands a laser transmitter for planetary remote sensing to detect water-ice on the Moon and other planetary bodies. Based on the measurement of the Moon Mineralogy Mapper (M3) instrument, the discovery of water ice on the Moon was acclaimed, but the measurement is disputed because OH- and/or H2O-bearing materials share the absorption line around 3 μm wavelength. Lunar Flashlight, another mission project exploring the surface of Moon which will be launched later this year, enables to map the minerals on dark area of the Moon, but could not resolve the above-mentioned ambiguity. The absorption of 6.08 μm light is uniquely associated with the bending resonance of H2O since there is no comparable vibration in confounding OH-bearing materials. 6.08 μm laser between the atmospheric windows: middle-wave infrared (3-5 μm) and long-wave infrared (8-12 μm) has not been commercially available. Our approach is a Q-switched Ho:YLF laser pumped the orientation-pattern Gallium Arsenide optical parametric oscillator (OP-GaAs OPO) for generating high-energy laser pulses at the wavelength of 6.08 μm. In the current design, a 1.94 μm Tm:fiber is used as the pump source. In the compact design, a 1.94 μm laser diode will replace the Tm:fiber laser as the pump source. We will combine this proposed mid-infrared laser with the latest HgCdTe avalanche photodiode (APD) array to design a lidar for detecting water ice on the Moon and Mars from their respective orbits, enabling novel science and in-situ resource utilization. Our instrument is an enabling technology aboard the Artemis program and others.

mid-infrared laser↗
DOE OSTI2020

Materials Data on Cs6Ho21S34Cl by Materials Project

Cs6Ho21S34Cl crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 1-coordinate geometry to eight S2- and one Cl1- atom. There are a spread of Cs–S bond distances ranging from 3.61–4.16 Å. The Cs–Cl bond length is 3.42 Å. In the second Cs1+ site, Cs1+ is bonded in a 1-coordinate geometry to eight S2- and one Cl1- atom. There are a spread of Cs–S bond distances ranging from 3.61–4.15 Å. The Cs–Cl bond length is 3.42 Å. There are eight inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six S2- atoms to form edge-sharing HoS6 octahedra. There are two shorter (2.72 Å) and four longer (2.73 Å) Ho–S bond lengths. In the second Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedra tilt angles range from 7–9°. There are a spread of Ho–S bond distances ranging from 2.64–2.84 Å. In the third Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedra tilt angles range from 6–9°. There are a spread of Ho–S bond distances ranging from 2.69–2.81 Å. In the fourth Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedra tilt angles range from 6–11°. There are a spread of Ho–S bond distances ranging from 2.71–2.80 Å. In the fifth Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedra tilt angles range from 5–11°. There are a spread of Ho–S bond distances ranging from 2.63–2.92 Å. In the sixth Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedral tilt angles are 5°. There are a spread of Ho–S bond distances ranging from 2.70–2.79 Å. In the seventh Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedral tilt angles are 8°. There are two shorter (2.74 Å) and four longer (2.77 Å) Ho–S bond lengths. In the eighth Ho3+ site, Ho3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing HoS6 octahedra. The corner-sharing octahedral tilt angles are 9°. There are a spread of Ho–S bond distances ranging from 2.67–2.77 Å. There are ten inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three Cs1+ and three Ho3+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Cs1+ and three Ho3+ atoms. In the third S2- site, S2- is bonded to one Cs1+ and four Ho3+ atoms to form distorted SCsHo4 trigonal bipyramids that share a cornercorner with one ClCs6 octahedra, corners with five SCsHo4 trigonal bipyramids, an edgeedge with one SHo5 square pyramid, and edges with four SCsHo4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 52°. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Cs1+ and three Ho3+ atoms. In the fifth S2- site, S2- is bonded to one Cs1+ and four Ho3+ atoms to form distorted SCsHo4 trigonal bipyramids that share a cornercorner with one ClCs6 octahedra, corners with four SCsHo4 trigonal bipyramids, and edges with five SCsHo4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°. In the sixth S2- site, S2- is bonded to one Cs1+ and four Ho3+ atoms to form distorted SCsHo4 trigonal bipyramids that share a cornercorner with one ClCs6 octahedra, a cornercorner with one SHo5 square pyramid, corners with three SCsHo4 trigonal bipyramids, an edgeedge with one SHo5 square pyramid, and edges with five SCsHo4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 52°. In the seventh S2- site, S2- is bonded in a 3-coordinate geometry to three Cs1+ and three Ho3+ atoms. In the eighth S2- site, S2- is bonded to one Cs1+ and four Ho3+ atoms to form distorted SCsHo4 trigonal bipyramids that share a cornercorner with one ClCs6 octahedra, a cornercorner with one SHo5 square pyramid, corners with five SCsHo4 trigonal bipyramids, an edgeedge with one SHo5 square pyramid, and edges with five SCsHo4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 53°. In the ninth S2- site, S2- is bonded to one Cs1+ and four Ho3+ atoms to form distorted SCsHo4 trigonal bipyramids that share a cornercorner with one ClCs6 octahedra, a cornercorner with one SHo5 square pyramid, corners with four SCsHo4 trigonal bipyramids, and edges with five SCsHo4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. In the tenth S2- site, S2- is bonded to five Ho3+ atoms to form SHo5 square pyramids that share corners with six SCsHo4 trigonal bipyramids, an edgeedge with one SHo5 square pyramid, and edges with six SCsHo4 trigonal bipyramids. Cl1- is bonded to six Cs1+ atoms to form ClCs6 octahedra that share corners with twenty SCsHo4 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Cu(SiO3)4 by Materials Project

Ho2Cu(SiO3)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.22–2.77 Å. Cu2+ is bonded in a distorted square co-planar geometry to four O2- atoms. There is two shorter (1.98 Å) and two longer (1.99 Å) Cu–O bond length. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.62–1.67 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+, one Cu2+, and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Si4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Cu2+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and two Si4+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Crystal Growth and Phase Formation of High-Entropy Rare-Earth Aluminum Perovskites

In this work, we demonstrate for the first time the crystal growth of high-entropy rare-earth (RE) aluminum perovskites (REAlO 3 ) using the micro-pulling-down method to inform future exploration of functional crystals. To determine how composition affects phase formation, we formulate equiatomic compositions containing five REs from the following list: Lu, Yb, Tm, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, Pr, Ce, La. To test whether combinations of REs with similar ionic radii may favor a single phase, compositions containing REs with consecutive or nonconsecutive ionic radius values were formulated. Powder and single-crystal X-ray diffraction indicate that crystals containing only REs with similar ionic radii that form orthorhombic single-RE REAlO 3 are a single phase. Crystals containing REs with dissimilar ionic radii or mixtures of REs that form orthorhombic, rhombohedral, and tetragonal single-RE REAlO 3 are a mixture of phases. The elemental distribution in single-phase crystals analyzed via electron probe microanalysis confirms no evidence of preferential incorporation of any of the constituent REs. The distribution and composition of secondary phases were analyzed via scanning electron microscopy and energy dispersive spectroscopy; secondary phases were seen as a small region in the center of the crystals with branching features closer to the outer surface.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoFe3(BO3)4 by Materials Project

HoFe3(BO3)4 is Calcite-derived structured and crystallizes in the trigonal P3_121 space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are four shorter (2.33 Å) and two longer (2.41 Å) Ho–O bond lengths. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form edge-sharing FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.09 Å. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form edge-sharing FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.06 Å. There are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.38 Å) and two longer (1.39 Å) B–O bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. All B–O bond lengths are 1.38 Å. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. All B–O bond lengths are 1.38 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Fe3+ and one B3+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Fe3+ and one B3+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+, one Fe3+, and one B3+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Fe3+ and one B3+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Fe3+, and one B3+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Fe3+ and one B3+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Fe3+, and one B3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KHoCoSi2O7 by Materials Project

KHoCoSi2O7 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of K–O bond distances ranging from 2.63–3.36 Å. Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.14–2.55 Å. There are two inequivalent Co2+ sites. In the first Co2+ site, Co2+ is bonded to four O2- atoms to form CoO4 tetrahedra that share corners with four SiO4 tetrahedra. There is two shorter (1.97 Å) and two longer (1.99 Å) Co–O bond length. In the second Co2+ site, Co2+ is bonded to four O2- atoms to form CoO4 tetrahedra that share corners with four SiO4 tetrahedra. There are two shorter (1.99 Å) and two longer (2.02 Å) Co–O bond lengths. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one SiO4 tetrahedra and corners with two CoO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.61–1.69 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one SiO4 tetrahedra and corners with two CoO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.63–1.68 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to one K1+, one Ho3+, one Co2+, and one Si4+ atom to form distorted corner-sharing OKHoCoSi tetrahedra. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ho3+ and two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one K1+, one Ho3+, one Co2+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+, one Ho3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two equivalent Si4+ atoms. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Ho3+, one Co2+, and one Si4+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+, one Ho3+, one Co2+, and one Si4+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Ho3+, and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Insights on the corrosion thermodynamics of chromium in molten LiF-NaF-KF eutectic salts

The thermodynamic stability of chromium in the Cr 0 , Cr 2+ , and Cr 3+ oxidation states considering various F - ion coordination compounds was investigated in molten LiF–NaF-KF (FLiNaK) eutectic salt. Potential fluoride ion activity (F - and CrF 3 - ) diagrams were constructed to predict the most stable Cr oxidation states as a function of anion activity, solvation state of chromium ions and potential at 600 °C. The Gibbs free energies of these compounds were estimated by utilizing a combined cyclic voltammetry – Nernst theory analysis approach in FLiNaK salt. To verify the constructed diagrams, X-ray diffraction was utilized after exposure of Cr at various applied potentials to determine whether compounds detected in solidified FLiNaK salts agreed with thermodynamic calculations. This work aims to identify key thermodynamic factors that are significant to chromium corrosion for molten salt nuclear reactor applications. The F - stability region spans the entire region where spontaneous corrosion of Cr occurs. Cr may be oxidized to Cr 2+ and Cr 3+ in the presence HF (due to moisture as an impurity) spontaneously except some conditions of p 1/2 H 2 /a HF etc. This situation is not changed qualitatively for various states of solvation between oxidized Cr solute in F - solvent and this aspect is substantially similar for the two cases (pair 1: Cr 0 /CrF 3 - / CrF 6 3- ; pair 2: Cr 0 /CrF 4 2- /CrF 5 2- ) considered in this work.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Influence of Surface and Structural Variations in Donor–Acceptor–Donor Sensitizers on Photoelectrocatalytic Water Splitting

Conjugated organic chromophores composed of linked donor (D) and acceptor (A) moieties have attracted considerable attention for photoelectrochemical applications. In this work, we compare the optoelectronic properties and photoelectrochemical performance of two D–A–D structural isomers with thiophene-X-carboxylic acid (X denotes 3 and 2 positions) derivatives and 2,1,3-benzothiadiazole as the D and A moieties, respectively. 5,5′-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-3-carboxylic acid), BTD1, and 5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-2-carboxylic acid), BTD2, were employed in the study to understand how structural isomers affect surface attachments within chromophore–catalyst assemblies and their influence on charge-transfer dynamics. Crystal structures revealed that varying the position of the −COOH anchoring group causes the molecules to either contort out of a plane (BTD1) or adopt a near-perfect planar conformation (BTD2). BTD1 and BTD2 were co-loaded with either a water oxidation catalyst, [Ru(2,6-bis(1-methylbenzimidazol-2-yl)pyridine)-(4,4′-((HO) 2 OPCH 2 )2-2,2′-bipyridine)(OH 2 )] 2 , RuCt 2+ , or proton reduction catalyst [Ni(P 2 Ph N 2 C 6 H 4 CH 2 PO 3 H 2 ) 2 ] 2+ , NiCt 2+ , on oxide electrodes to facilitate photodriven water splitting reactions. Emission quenching measurements indicate that both BTD1 and BTD2 inject electrons into n-type SnO 2 |TiO 2 electrodes and holes into p-type NiO semiconductors from their respective excited states at high efficiencies >60%. Photocurrent densities of chromophore–catalyst assemblies obtained using linear sweep voltammetry (LSV) show that BTD2-sensitized photoanodes generate significantly more photocurrent than BTD1-sensitized electrodes; however, both exhibit similar performances at the photocathode. Photoelectrocatyltic measurements demonstrate that both BTD1 and BTD2 performed similarly, generating Faradaic efficiencies of 39 and 38% at the anode or 61 and 79% at the cathode. Transient absorption measurements suggest that the differences between the LSV and photoelectrocatalytic measurements result from the differences in quantum yields of the photogenerated redox equivalents, which is also a reflection of the varying metal oxide surface conformation. Our findings suggest that BTD2 should be investigated further in photocathodic studies since it has the structural advantage of being incorporated into diverse types of chromophore–catalyst assemblies.

Chromophores↗
DOE OSTI2020

Materials Data on Na2Ho2B2TeO10 by Materials Project

Na2Ho2B2TeO10 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.33–2.96 Å. Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.20–2.47 Å. B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.36–1.43 Å. Te6+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Te–O bond distances ranging from 1.93–2.01 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Na1+, one Ho3+, and one B3+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+, two equivalent Ho3+, and one Te6+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Na1+, one B3+, and one Te6+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one Na1+, two equivalent Ho3+, and one B3+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Na1+, two equivalent Ho3+, and one Te6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba2Ho2CuPtO8 by Materials Project

Ba2Ho2PtCuO8 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a 12-coordinate geometry to twelve O2- atoms. There are a spread of Ba–O bond distances ranging from 2.87–3.39 Å. In the second Ba2+ site, Ba2+ is bonded in a 11-coordinate geometry to eleven O2- atoms. There are a spread of Ba–O bond distances ranging from 2.66–3.25 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share a cornercorner with one HoO7 pentagonal bipyramid, corners with two equivalent CuO5 square pyramids, edges with five HoO7 pentagonal bipyramids, an edgeedge with one CuO5 square pyramid, and a faceface with one PtO6 octahedra. There are a spread of Ho–O bond distances ranging from 2.29–2.42 Å. In the second Ho3+ site, Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with two equivalent PtO6 octahedra, a cornercorner with one HoO7 pentagonal bipyramid, edges with three equivalent HoO7 pentagonal bipyramids, edges with two equivalent CuO5 square pyramids, and a faceface with one PtO6 octahedra. The corner-sharing octahedral tilt angles are 12°. There are a spread of Ho–O bond distances ranging from 2.25–2.45 Å. Pt5+ is bonded to six O2- atoms to form PtO6 octahedra that share corners with two equivalent HoO7 pentagonal bipyramids, corners with three equivalent CuO5 square pyramids, and faces with two HoO7 pentagonal bipyramids. There are a spread of Pt–O bond distances ranging from 2.04–2.11 Å. Cu1+ is bonded to five O2- atoms to form CuO5 square pyramids that share corners with three equivalent PtO6 octahedra, corners with two equivalent HoO7 pentagonal bipyramids, and edges with three HoO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 5–10°. There are a spread of Cu–O bond distances ranging from 2.00–2.15 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to three Ba2+, one Ho3+, one Pt5+, and one Cu1+ atom to form a mixture of distorted edge, corner, and face-sharing OBa3HoCuPt octahedra. The corner-sharing octahedra tilt angles range from 55–68°. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Ba2+, three Ho3+, and one Cu1+ atom. In the third O2- site, O2- is bonded in a 6-coordinate geometry to four Ba2+, one Pt5+, and one Cu1+ atom. In the fourth O2- site, O2- is bonded to three Ba2+, two Ho3+, and one Pt5+ atom to form a mixture of distorted corner and face-sharing OBa3Ho2Pt octahedra. The corner-sharing octahedra tilt angles range from 2–68°. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to three Ba2+, two Ho3+, and one Pt5+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Growth and characterization of materials for tunable lasers in the near infrared spectral region

During this reporting period, work proceeded in two directions. The first was the development of crystal growth procedures for rare earth doped LiYF4 crystals. The procedures for growth and pre-growth treatment of starting materials for undoped LiYF4 crystals were established and good optical quality materials were grown. A significant amount of time was spent trying to establish the optimum growth parameters for Yb(3+)-doped crystals. Unfortunately, it has proven difficult to obtain large size boules of high optical quality crystals of LiYF4 with doping concentrations of Yb(3+) of several percent. Because of these problems, this research is to be changed to attempt doping with other trivalent rare earth ions such as Ho, Er, and Tm. The second research area was investigating the potential of LiNbO3:Mg,Cr and LiNbO3:Mg,Cr,Yb as possible laser materials. The results are summarized.

Powell, Richard C.↗
NASA NTRS2007

2-.mu.m fiber amplified spontaneous emission (ASE) source

A 2-.mu.m fiber Amplified Spontaneous Emission (ASE) source provides a wide emission bandwidth and improved spectral stability/purity for a given output power. The fiber ASE source is formed from a heavy metal oxide multicomponent glass selected from germanate, tellurite and bismuth oxides and doped with high concentrations, 0.5-15 wt. %, thulium oxides (Tm.sub.2O.sub.3) or 0.1-5 wt% holmium oxides (Ho.sub.2O.sub.3) or mixtures thereof. The high concentration of thulium dopants provide highly efficient pump absorption and high quantum efficiency. Co-doping of Tm and Ho can broaden the ASE spectrum.

Jiang, Shibin↗
DOE OSTI2020

Phylogenetics-based identification and characterization of a superior 2,3-butanediol dehydrogenase for Zymomonas mobilis expression

Abstract Background Zymomonas mobilis has recently been shown to be capable of producing the valuable platform biochemical, 2,3-butanediol (2,3-BDO). Despite this capability, the production of high titers of 2,3-BDO is restricted by several physiological parameters. One such bottleneck involves the conversion of acetoin to 2,3-BDO, a step catalyzed by 2,3-butanediol dehydrogenase (Bdh). Several Bdh enzymes have been successfully expressed in Z. mobilis, although a highly active enzyme is yet to be identified for expression in this host. Here, we report the application of a phylogenetic approach to identify and characterize a superior Bdh, followed by validation of its structural attributes using a mutagenesis approach. Results Of the 11 distinct bdh genes that were expressed in Z. mobilis, crude extracts expressing Serratia marcescens Bdh ( Sm Bdh) were found to have the highest activity (8.89 µmol/min/mg), when compared to other Bdh enzymes (0.34–2.87 µmol/min/mg). The Sm Bdh crystal structure was determined through crystallization with cofactor (NAD + ) and substrate (acetoin) molecules bound in the active site. Active Sm Bdh was shown to be a tetramer with the active site populated by a Gln247 residue contributed by the diagonally opposite subunit. Sm Bdh showed a more extensive supporting hydrogen-bond network in comparison to the other well-studied Bdh enzymes, which enables improved substrate positioning and substrate specificity. This protein also contains a short α6 helix, which provides more efficient entry and exit of molecules from the active site, thereby contributing to enhanced substrate turnover. Extending the α6 helix to mimic the lower activity Enterobacter cloacae ( Ec Bdh) enzyme resulted in reduction of Sm Bdh function to nearly 3% of the total activity. In great contrast, reduction of the corresponding α6 helix of the Ec Bdh to mimic the Sm Bdh structure resulted in ~ 70% increase in its activity. Conclusions This study has demonstrated that Sm Bdh is superior to other Bdhs for expression in Z. mobilis for 2,3-BDO production. Sm Bdh possesses unique structural features that confer biochemical advantage to this protein. While coordinated active site formation is a unique structural characteristic of this tetrameric complex, the smaller α6 helix and extended hydrogen network contribute towards improved activity and substrate promiscuity of the enzyme.

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