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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on RbHoS2O9 by Materials Project

RbHoS2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Rb is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of Rb–O bond distances ranging from 3.01–3.28 Å. Ho is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Ho–O bond distances ranging from 2.31–2.44 Å. There are two inequivalent S sites. In the first S site, S is bonded in a tetrahedral geometry to four O atoms. There are a spread of S–O bond distances ranging from 1.48–1.51 Å. In the second S site, S is bonded in a tetrahedral geometry to four O atoms. There are a spread of S–O bond distances ranging from 1.48–1.51 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to one Rb, one Ho, and one S atom. In the second O site, O is bonded in a 2-coordinate geometry to one Rb, one Ho, and one S atom. In the third O site, O is bonded in a distorted bent 150 degrees geometry to one Rb, one Ho, and one S atom. In the fourth O site, O is bonded in a 1-coordinate geometry to one Rb, one Ho, and one S atom. In the fifth O site, O is bonded in a 2-coordinate geometry to one Rb, one Ho, and one S atom. In the sixth O site, O is bonded in a distorted single-bond geometry to one Rb, one Ho, and one S atom. In the seventh O site, O is bonded in a distorted bent 120 degrees geometry to one Rb and one Ho atom. In the eighth O site, O is bonded in a 1-coordinate geometry to one Rb, one Ho, and one S atom. In the ninth O site, O is bonded in a single-bond geometry to one Rb and one S atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoFe4(CuO4)3 by Materials Project

HoFe4(CuO4)3 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Ho3+ is bonded to twelve equivalent O2- atoms to form HoO12 cuboctahedra that share faces with eight equivalent FeO6 octahedra. All Ho–O bond lengths are 2.60 Å. Fe3+ is bonded to six equivalent O2- atoms to form FeO6 octahedra that share corners with six equivalent FeO6 octahedra and faces with two equivalent HoO12 cuboctahedra. The corner-sharing octahedral tilt angles are 45°. All Fe–O bond lengths are 2.02 Å. Cu3+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Cu–O bond lengths are 1.89 Å. O2- is bonded in a 4-coordinate geometry to one Ho3+, two equivalent Fe3+, and one Cu3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nearly Identical but Not Isotypic: Influence of Lanthanide Contraction on Cs 2 NaLn(PS 4 ) 2 (Ln = La–Nd, Sm, and Gd–Ho)

The effect of the lanthanide contraction often results in topological and symmetry changes in compounds with the same compositions as a function of lanthanide cation size. Here we report on the first example of a lanthanide thiophosphate exhibiting a change in the lanthanide cation environment without any topological or symmetry change. A series of new lanthanide thiophosphates with mixed alkali cations was obtained via a flux crystal growth technique using a CsI flux. The obtained compounds Cs 2 NaLn(PS 4 ) 2 (Ln = La–Nd, Sm, Gd–Ho) were grown as large single crystals (~0.1–1 mm 3 ) and characterized using single crystal X-ray diffraction and magnetic susceptibility measurements. Moving across the series, the structural studies revealed a change in the lanthanide coordination environment dependent upon the identity of the lanthanide. Although all compounds in the Cs 2 NaLn(PS 4 ) 2 series crystallize in the same space group and have the same Wyckoff positions of the atoms, a slight size change between Sm 3+ and Gd 3+ causes a subtle change in coordination number from 9 (for Ln = La–Sm) to 8 (for Ln = Gd–Ho), resulting in two distinct but virtually identical structure types. Ab initio calculations were performed, and the observed experimental trend was corroborated computationally. Finally, magnetic measurements performed on the Cs 2 NaLn(PS 4 ) 2 (Ln = Ce, Pr, Nd, Gd, and Tb) compounds revealed paramagnetic behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on HoBiO3 by Materials Project

HoBiO3 is Orthorhombic Perovskite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ho3+ is bonded to six O2- atoms to form corner-sharing HoO6 octahedra. The corner-sharing octahedra tilt angles range from 44–46°. There are two shorter (2.28 Å) and four longer (2.29 Å) Ho–O bond lengths. Bi3+ is bonded in a 3-coordinate geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.20–3.01 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two equivalent Bi3+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and three equivalent Bi3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

An experimental and modeling study on auto-ignition kinetics of ammonia/methanol mixtures at intermediate temperature and high pressure

A rapid compression machine (RCM) has been applied to measure the ignition delay times of NH 3 /CH 3 OH mixtures covering pressures of 20 and 40 bar, equivalence ratios of 0.5, 1.0 and 2.0, and temperatures between 845 and 1100 K. Here the measurements show that the NH 3 /CH 3 OH mixtures become more reactive with increasing methanol addition. Addition of merely 1% (molar basis) of CH 3 OH to NH 3 lowers the ignition temperature around 100 K at 40 bar in comparison to pure NH 3 . The ignition delay is a complex function of fuel mixture and stoichiometry. For the 1% CH 3 OH mixture, the leaner mixtures are more reactive, while the reverse trend is found for mixtures with 5%, 20% and pure CH 3 OH. Analysis of the pressure profiles shows three distinct ignition modes for NH 3/ CH 3 OH mixtures, facilitated by the pre-ignition heat release from NH 3 consumption. A detailed mechanism for ignition of NH 3 /CH 3 OH fuel blends has been developed, capable of reproducing the ignition behavior of mixtures with reasonable accuracy. A subset for amine / methanol interactions was established, with rate constants for the key reaction between NH 2 and CH 3 OH calculated from ab initio theory. A sensitivity analysis indicates that the critical reactions during the auto-ignition process vary with the CH 3 OH mole fraction in the fuel. The ammonia chemistry, namely NH 2 + NO, NH2 + NO 2 and NH 2 + HO 2 , is dominant for the mixture with 1% CH 3 OH, while the reactions related to CH 3 OH and H 2 O 2 are more important for the 20% CH 3 OH mixture. The interaction between ammonia and methanol shows a more prominent effect on auto-ignition for mixtures with 5% CH 3 OH in fuel as compared to those with 1% and 20% CH 3 OH. According to the modeling results, methanol addition is found to enrich the O/H radical pool, consuming ammonia and promoting auto-ignition through different reaction pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Ho(Ni2As)2 by Materials Project

Ho(Ni2As)2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ho is bonded to six equivalent As atoms to form a mixture of distorted corner and edge-sharing HoAs6 octahedra. The corner-sharing octahedral tilt angles are 40°. There are two shorter (2.89 Å) and four longer (2.91 Å) Ho–As bond lengths. Ni is bonded in a 3-coordinate geometry to three equivalent As atoms. All Ni–As bond lengths are 2.40 Å. As is bonded in a 9-coordinate geometry to three equivalent Ho and six equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Impact of wildfires on regional ozone and PM 2.5 : Considering the light absorption of Brown carbon

The influence of wildfire brown carbon (BrC) in moderating the formation of O 3 and fine particulate matter (PM 2.5 ) due to its absorption of ultraviolet (UV) radiation is, for the first time, investigated using a modified community multiscale air quality (CMAQ) model. The wavelength-dependent imaginary refractive index of the organic carbon from wildfires, which are needed by the CMAQ model for its inline photolysis rate calculation, are generated experimentally from wood burning aerosols from a combustion chamber. On high emission days of the Bastrop County Complex fire in Texas in early September 2011, BrC UV absorption reduces the daytime average NO 2 photolysis rate by up to 38% in the core region of the wildfire plume compared to the base scenario that does not consider BrC absorption. Consequently, O 3 production in the smoke plume is suppressed compared to the base scenario due to reduced HO x radical concentrations. Further, in the core region, the predicted O 3 increase due to wildfire reaches as high as 47–123 ppb without considering BrC absorption, the predicted increase of O 3 is 5–15% lower when BrC absorption is considered. Similarly, considering the BrC UV absorption leads to approximately 1% (or ~2–3 µgm -3 ) lower estimation of the wildfire emissions’ impact on total PM 2.5 . This change is small because secondary aerosols, which are the components affected by BrC absorption, only account for a small fraction of the total PM 2.5 in wildfire impacted regions in this study. In addition, our study shows that assumptions about aerosol mixing state (core-shell vs. homogeneous) in the inline photolysis rate calculation would not significantly affect out assessment of the impact of wildfire BrC light absorption on O 3 and PM 2.5 .

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Materials Data on Ho3Si2(SnRh3)3 by Materials Project

Ho3Si2(Rh3Sn)3 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to ten Rh and two equivalent Si atoms. There are a spread of Ho–Rh bond distances ranging from 2.89–3.15 Å. Both Ho–Si bond lengths are 3.00 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 8-coordinate geometry to four equivalent Ho, two equivalent Sn, and two equivalent Si atoms. Both Rh–Sn bond lengths are 2.78 Å. Both Rh–Si bond lengths are 2.42 Å. In the second Rh site, Rh is bonded in a 6-coordinate geometry to two equivalent Ho and four equivalent Sn atoms. All Rh–Sn bond lengths are 2.72 Å. Sn is bonded in a distorted body-centered cubic geometry to eight Rh atoms. Si is bonded in a 9-coordinate geometry to three equivalent Ho and six equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho7(CuTe4)3 by Materials Project

Ho7Cu3Te12 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are seven inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share a cornercorner with one HoTe6 octahedra, corners with three CuTe4 tetrahedra, edges with seven HoTe6 octahedra, and an edgeedge with one CuTe4 tetrahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.05–3.09 Å. In the second Ho3+ site, Ho3+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing HoTe6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.04–3.07 Å. In the third Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share a cornercorner with one HoTe6 octahedra, corners with three CuTe4 tetrahedra, edges with seven HoTe6 octahedra, and edges with two CuTe4 tetrahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.06–3.10 Å. In the fourth Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share a cornercorner with one HoTe6 octahedra, corners with three CuTe4 tetrahedra, edges with seven HoTe6 octahedra, and an edgeedge with one CuTe4 tetrahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.07–3.09 Å. In the fifth Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share a cornercorner with one HoTe6 octahedra, corners with three CuTe4 tetrahedra, edges with seven HoTe6 octahedra, and edges with two CuTe4 tetrahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.06–3.10 Å. In the sixth Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share a cornercorner with one HoTe6 octahedra, corners with three CuTe4 tetrahedra, edges with seven HoTe6 octahedra, and an edgeedge with one CuTe4 tetrahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.06–3.11 Å. In the seventh Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share a cornercorner with one HoTe6 octahedra, corners with three CuTe4 tetrahedra, edges with seven HoTe6 octahedra, and edges with two CuTe4 tetrahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ho–Te bond distances ranging from 3.06–3.10 Å. There are three inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four Te2- atoms to form CuTe4 tetrahedra that share corners with six HoTe6 octahedra, edges with three HoTe6 octahedra, and edges with two CuTe4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–55°. There are a spread of Cu–Te bond distances ranging from 2.59–2.66 Å. In the second Cu1+ site, Cu1+ is bonded to four Te2- atoms to form CuTe4 tetrahedra that share corners with six HoTe6 octahedra, corners with three equivalent CuTe4 tetrahedra, edges with three HoTe6 octahedra, and an edgeedge with one CuTe4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–55°. There are a spread of Cu–Te bond distances ranging from 2.59–2.64 Å. In the third Cu1+ site, Cu1+ is bonded to four Te2- atoms to form CuTe4 tetrahedra that share corners with six HoTe6 octahedra, corners with three equivalent CuTe4 tetrahedra, edges with three HoTe6 octahedra, and an edgeedge with one CuTe4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–55°. There are a spread of Cu–Te bond distances ranging from 2.59–2.64 Å. There are twelve inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to three Ho3+ and two Cu1+ atoms to form distorted TeHo3Cu2 square pyramids that share a cornercorner with one TeHo3Cu3 octahedra, corners with three TeHo3Cu2 square pyramids, edges with two equivalent TeHo3Cu3 octahedra, and edges with two equivalent TeHo3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 92°. In the second Te2- site, Te2- is bonded to three Ho3+ and three Cu1+ atoms to form a mixture of distorted edge and corner-sharing TeHo3Cu3 octahedra. In the third Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the fourth Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the fifth Te2- site, Te2- is bonded to three Ho3+ and two Cu1+ atoms to form distorted TeHo3Cu2 square pyramids that share a cornercorner with one TeHo3Cu3 octahedra, corners with three TeHo3Cu2 square pyramids, edges with two equivalent TeHo3Cu3 octahedra, and edges with two equivalent TeHo3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 91°. In the sixth Te2- site, Te2- is bonded to three Ho3+ and two Cu1+ atoms to form distorted TeHo3Cu2 square pyramids that share corners with four TeHo3Cu2 square pyramids, an edgeedge with one TeHo3Cu3 octahedra, and an edgeedge with one TeHo3Cu2 square pyramid. In the seventh Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the eighth Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the ninth Te2- site, Te2- is bonded to three Ho3+ and two Cu1+ atoms to form distorted TeHo3Cu2 square pyramids that share corners with four TeHo3Cu2 square pyramids, an edgeedge with one TeHo3Cu3 octahedra, and an edgeedge with one TeHo3Cu2 square pyramid. In the tenth Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the eleventh Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the twelfth Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to three Ho3+ and one Cu1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Se3 by Materials Project

Ho2Se3 crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing HoSe6 octahedra. The corner-sharing octahedra tilt angles range from 3–5°. There are a spread of Ho–Se bond distances ranging from 2.85–2.88 Å. In the second Ho3+ site, Ho3+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing HoSe6 octahedra. The corner-sharing octahedral tilt angles are 5°. There are a spread of Ho–Se bond distances ranging from 2.84–2.88 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba4Ho(CuO3)3 by Materials Project

Ba4Ho(CuO3)3 crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. Ba2+ is bonded in a distorted q6 geometry to nine O2- atoms. There are three shorter (2.88 Å) and six longer (2.89 Å) Ba–O bond lengths. Ho3+ is bonded in an octahedral geometry to six equivalent O2- atoms. All Ho–O bond lengths are 2.22 Å. Cu+2.33+ is bonded in a square co-planar geometry to four O2- atoms. There is two shorter (1.85 Å) and two longer (2.04 Å) Cu–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ba2+, one Ho3+, and one Cu+2.33+ atom. In the second O2- site, O2- is bonded to four equivalent Ba2+ and two equivalent Cu+2.33+ atoms to form distorted corner-sharing OBa4Cu2 octahedra. The corner-sharing octahedra tilt angles range from 0–60°.

36 MATERIALS SCIENCE↗
NASA NTRS1999

The Influence of Extremely Large Solar Proton Events in a Changing Stratosphere. Stratospheric Influence of Solar Proton Events

Two periods of extremely large solar proton events (SPEs) occurred in the past thirty years, which forced significant long-term polar stratospheric changes. The August 2-10, 1972 and October 19-27, 1989 SPEs happened in stratospheres that were quite different chemically. The stratospheric chlorine levels were relatively small in 1972 (approximately 1.2 ppbv) and were fairly substantial in 1989 at about (approximately 3 ppbv). Although these SPEs produced both HO(x) and NO(y) constituents in the mesosphere and stratosphere, only the NO(y) constituents had lifetimes long enough to affect ozone for several months to years past the events. Our recently improved two-dimensional chemistry and transport atmospheric model was used to compute the effects of these gigantic SPEs in a changing stratosphere. Significant upper stratospheric ozone depletions > 10% are computed to last for a few months past these SPEs. The long-lived SPE-produced NO(y) constituents were transported to lower levels during winter after these huge SPEs and caused impacts in the middle and lower stratosphere. During periods of high halogen loading these impacts resulted in interference with the chlorine and bromine loss cycles for ozone destruction. The chemical state of the atmosphere, including the stratospheric sulfate aerosol density, substantially affected the predicted stratospheric influence of these extremely large SPEs.

Jackman, Charles H.↗
DOE OSTI2020

Materials Data on Ba2Ho(CuO2)3 by Materials Project

Ba2Ho(CuO2)3 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ba2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.80 Å) and four longer (2.96 Å) Ba–O bond lengths. Ho3+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Ho–O bond lengths are 2.42 Å. There are two inequivalent Cu+1.67+ sites. In the first Cu+1.67+ site, Cu+1.67+ is bonded to five O2- atoms to form distorted corner-sharing CuO5 square pyramids. There are four shorter (1.95 Å) and one longer (2.63 Å) Cu–O bond lengths. In the second Cu+1.67+ site, Cu+1.67+ is bonded in a linear geometry to two equivalent O2- atoms. Both Cu–O bond lengths are 1.81 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to two equivalent Ba2+, two equivalent Ho3+, and two equivalent Cu+1.67+ atoms. In the second O2- site, O2- is bonded in a 6-coordinate geometry to four equivalent Ba2+ and two Cu+1.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Crystal and Magnetic Structures of the Ternary Ho 2 Ni 0.8 Si 1.2 and Ho 2 Ni 0.8 Ge 1.2 Compounds: An Example of Intermetallics Crystallizing with the Zr 2 Ni 1–x P Prototype

We report two new rare-earth (R) ternary intermetallic compounds—Ho 2 Ni 0.8 T 1.2 with T = Si and Ge—that correspond to the R 5 Ni 2 T 3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr 2 Ni 1–x P-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho 2 Ni 0.8 T 1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R 2 Ni 0.8 T 1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr 2 Ni 1–x P structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho 2 Ni 0.8 Si 1.2 and TC = 37 K for Ho 2 Ni 0.8 Ge 1.2 , which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below T C with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ 1 = [0, 0, 0]. Below T N ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ 2 = [κ x , 0, 0] appears to coexist with the first magnetic structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Ho2(WO4)3 by Materials Project

Ho2W3O12 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.29–2.46 Å. There are two inequivalent W6+ sites. In the first W6+ site, W6+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of W–O bond distances ranging from 1.78–2.15 Å. In the second W6+ site, W6+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.80 Å) and two longer (1.85 Å) W–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one W6+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+ and one W6+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one W6+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one W6+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one W6+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Ho3+ and two equivalent W6+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(Ni2P)2 by Materials Project

Ho(Ni2P)2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ho is bonded in a 6-coordinate geometry to six equivalent P atoms. There are two shorter (2.79 Å) and four longer (2.83 Å) Ho–P bond lengths. Ni is bonded in a 3-coordinate geometry to three equivalent P atoms. There are two shorter (2.30 Å) and one longer (2.31 Å) Ni–P bond lengths. P is bonded in a 9-coordinate geometry to three equivalent Ho and six equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2(MoO4)3 by Materials Project

Ho2Mo3O12 crystallizes in the tetragonal P-42_1m 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 2.24–2.43 Å. There are two inequivalent Mo6+ sites. In the first Mo6+ site, Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There is three shorter (1.78 Å) and one longer (1.83 Å) Mo–O bond length. In the second Mo6+ site, Mo6+ is bonded in a tetrahedral geometry to four equivalent O2- atoms. All Mo–O bond lengths are 1.79 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to one Ho3+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one Mo6+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Mo6+ atom. In the fourth O2- site, O2- is bonded in a linear geometry to one Ho3+ and one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Role of Pr-Vacancies and O-Interstitials on the Activity and Stability of (Pr 1−x Ln x ) 2 NiO 4 (Ln = La, Nd, Pm, Sm, Gd, Tb, Dy, and Ho) towards Oxygen Reduction Reactions: A DFT Study

Praseodymium nickelate, Pr 2 NiO 4 (PNO), is a promising electrode to promote oxygen reduction reaction (ORR) in a solid oxide fuel cell, but it exhibits phase transformation during electrochemical operation. The origin of the simultaneous phase transformation and high electrochemical performance remains obscure. We carried out a systematic density functional theory study to elucidate the mechanism for this conjugated phenomenon. Charge, electronic structure, and normal-mode analysis suggest the presence of peroxide. Our study shows that the formation of peroxide (O 2 2– ) is attributed to both oxygen interstitials and Pr vacancies. The peroxide species limits the oxygen ion migration due to the additional energy required to break its O–O bond, which leads to a decrease in ORR activity. Subsequently, we investigate the diffusion paths of Pr-ions while comparing them with those of other Ln 3+ ions (La, Nd, Pm, Sm, Gd, Tb, Dy, and Ho) in PNO. The formation energies for various Ln 3+ cation occupancies are calculated, as well as segregation energies in CeO 2 (111) surfaces. Lastly, criteria for effective Ln 3+ dopants are developed. La, Nd, and Pm are proposed as potential substituents in PNO to obtain a stable structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗