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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Fe(HO)2 by Materials Project

Fe(OH)2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Fe(OH)2 sheet oriented in the (0, 0, 1) direction. Fe2+ is bonded to six equivalent O2- atoms to form edge-sharing FeO6 octahedra. All Fe–O bond lengths are 2.17 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. O2- is bonded in a distorted single-bond geometry to three equivalent Fe2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe(HO)2 by Materials Project

Fe(OH)2 crystallizes in the monoclinic C2 space group. The structure is two-dimensional and consists of one Fe(OH)2 sheet oriented in the (0, 0, 1) direction. Fe2+ is bonded to six equivalent O2- atoms to form edge-sharing FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.14–2.21 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. O2- is bonded in a distorted single-bond geometry to three equivalent Fe2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Revitalizing Iron Redox by Anion-Insertion-Assisted Ferro- and Ferri-Hydroxides Conversion at Low Alkalinity

Iron hydroxides are desirable alkaline battery electrodes for low cost and environmental beneficence. However, hydrogen evolution on charging and Fe 3 O 4 formation on discharging cause low storage capacity and poor cycling life. Here, we report that green rust (GR) (Fe 2+ 4 Fe 3+ 2 (HO – ) 12 SO 4 ), formed via sulfate insertion, promotes Fe(OH) 2 /FeOOH conversion and shows a discharge capacity of ~211 mAh g –1 in half-cells and Coulombic efficiency of 93% after 300 cycles in full-cells. Theoretical calculations show that Fe(OH) 2 /FeOOH conversion is facilitated by intercalated sulfate anions. Classical molecular dynamics simulations reveal that electrolyte alkalinity strongly impacts the energetics of sulfate solvation, and low alkalinity ensures fast transport of sulfate ions. Anion-insertion-assisted Fe(OH) 2 /FeOOH conversion, also achieved with Cl – ion, paves a pathway toward efficient utilization of Fe-based electrodes for sustainable applications.

25 ENERGY STORAGE↗
DOE OSTI2020

Materials Data on Ho2Fe17C by Materials Project

Ho2Fe17C crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are four inequivalent Ho sites. In the first Ho site, Ho is bonded in a distorted bent 120 degrees geometry to twelve Fe and two equivalent C atoms. There are a spread of Ho–Fe bond distances ranging from 2.96–3.29 Å. Both Ho–C bond lengths are 2.49 Å. In the second Ho site, Ho is bonded in a 2-coordinate geometry to twenty Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.94–3.19 Å. In the third Ho site, Ho is bonded in a distorted bent 120 degrees geometry to ten Fe and two equivalent C atoms. There are a spread of Ho–Fe bond distances ranging from 2.96–3.38 Å. Both Ho–C bond lengths are 2.46 Å. In the fourth Ho site, Ho is bonded in a 12-coordinate geometry to eighteen Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.98–3.32 Å. There are fourteen inequivalent Fe sites. In the first Fe site, Fe is bonded to two Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with ten FeHo2Fe10 cuboctahedra, a cornercorner with one CHo2Fe4 octahedra, edges with four FeHo3Fe9 cuboctahedra, faces with nine FeHo2Fe10 cuboctahedra, and a faceface with one CHo2Fe4 octahedra. The corner-sharing octahedral tilt angles are 40°. There are a spread of Fe–Fe bond distances ranging from 2.44–2.62 Å. In the second Fe site, Fe is bonded to two Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with twelve FeHo2Fe10 cuboctahedra, edges with four FeHo3Fe9 cuboctahedra, faces with eight FeHo2Fe10 cuboctahedra, and faces with two equivalent CHo2Fe4 octahedra. There are a spread of Fe–Fe bond distances ranging from 2.44–2.64 Å. In the third Fe site, Fe is bonded in a single-bond geometry to seven Fe and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.53–2.70 Å. The Fe–C bond length is 1.84 Å. In the fourth Fe site, Fe is bonded in a single-bond geometry to seven Fe and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.40–2.71 Å. The Fe–C bond length is 1.84 Å. In the fifth Fe site, Fe is bonded in a 12-coordinate geometry to two Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.56–2.76 Å. In the sixth Fe site, Fe is bonded in a 12-coordinate geometry to two Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.43–2.78 Å. In the seventh Fe site, Fe is bonded in a 12-coordinate geometry to two Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.43–2.78 Å. In the eighth Fe site, Fe is bonded in a 12-coordinate geometry to two Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.55–2.76 Å. In the ninth Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.37–2.69 Å. In the tenth Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are one shorter (2.40 Å) and three longer (2.66 Å) Fe–Fe bond lengths. In the eleventh Fe site, Fe is bonded in a single-bond geometry to one Ho, seven Fe, and one C atom. There are one shorter (2.48 Å) and one longer (2.50 Å) Fe–Fe bond lengths. The Fe–C bond length is 1.92 Å. In the twelfth Fe site, Fe is bonded to three Ho and nine Fe atoms to form distorted FeHo3Fe9 cuboctahedra that share corners with nine FeHo2Fe10 cuboctahedra, corners with four equivalent CHo2Fe4 octahedra, edges with eight FeHo2Fe10 cuboctahedra, and faces with six FeHo2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 66°. Both Fe–Fe bond lengths are 2.47 Å. In the thirteenth Fe site, Fe is bonded to three Ho and nine Fe atoms to form distorted FeHo3Fe9 cuboctahedra that share corners with eleven FeHo2Fe10 cuboctahedra, a cornercorner with one CHo2Fe4 octahedra, edges with five FeHo2Fe10 cuboctahedra, faces with nine FeHo2Fe10 cuboctahedra, and a faceface with one CHo2Fe4 octahedra. The corner-sharing octahedral tilt angles are 42°. In the fourteenth Fe site, Fe is bonded to three Ho and nine Fe atoms to form distorted FeHo3Fe9 cuboctahedra that share corners with fifteen FeHo2Fe10 cuboctahedra, edges with four FeHo2Fe10 cuboctahedra, faces with eight FeHo2Fe10 cuboctahedra, and faces with two equivalent CHo2Fe4 octahedra. C is bonded to two Ho and four Fe atoms to form CHo2Fe4 octahedra that share corners with eight FeHo2Fe10 cuboctahedra, corners with two equivalent CHo2Fe4 octahedra, and faces with eight FeHo3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetocapacitance effect and magnetoelectric coupling in type-II multiferroic HoFeWO 6

We have investigated the multiferroicity and magnetoelectric (ME) coupling in HoFeWO 6 . With a noncentrosymmetric polar structure (space group Pna2 1 ) at room temperature, this compound shows an onset of electric polarization with an antiferromagnetic ordering at the Néel temperature (T N ) of 17.8 K. The magnetic properties of the polycrystalline samples were studied by DC and AC magnetization and heat capacity measurements. The metamagnetic behavior at low temperatures was found to be directly related to the dielectric properties of the compound. In particular, field-dependent measurements of capacitance show a magnetocapacitance (MC) effect with double-hysteresis loop behavior in direct correspondence with the magnetization. Our x-ray diffraction results show the Pna2 1 structure down to 8 K and suggest the absence of a structural phase transition across T N . Soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism (XMCD) measurements at the Fe L 2,3 and Ho M 4,5 edges revealed the oxidation state of Fe and Ho cations to be 3+. Fe L 2,3 XMCD further shows that Fe 3+ cations are antiferromagnetically ordered in a noncollinear fashion with spins arranged 90° with respect to each other. Our findings show that HoFeWO 6 is a type-II multiferroic exhibiting a MC effect. Furthermore, the observed MC effect and the change in polarization by the magnetic field, as well as their direct correspondence with magnetization, further support the strong ME coupling in this compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Chloride Insertion Enhances the Electrochemical Oxidation of Iron Hydroxide Double-Layer Hydroxide into Oxyhydroxide in Alkaline Iron Batteries

Rechargeable alkaline iron batteries that constitute environmentally benign electrolytes and earth-abundant industrial materials are desirable green solutions for large-scale energy storage. As one of the most abundant metal elements in the earth’s crust, iron (Fe) can satisfy nearly all criteria for low-cost and safe battery electrodes. However, challenges in achieving reversible Fe redox impede their extensive implementation in modern energy supply systems. Here, this study revealed that Cl-anion insertion into Fe(OH) 2 layered double hydroxide (LDH) formed a green rust intermediate phase with the formula [Fe 2 2+ Fe 1 3+ (HO – ) 6 ] + [Cl] – , which assisted a high Fe(OH) 2 /FeOOH conversion reaction (64.7%) and improved cycling stability. This new iron redox chemistry was validated by operando X-ray diffraction, electrochemical testing, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) analysis, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM-EDS) mapping, and molecular dynamics (MD) simulations. Our study provides new insight into designing LDH materials for high-capacity alkaline iron batteries.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-Temperature Reaction Kinetics of the e aq – and HO 2 • Radicals with Iron(II) Ions in Aqueous Solutions

Pulsed electron radiolysis was used to determine the chemical reaction kinetics and Arrhenius parameters for iron(II) reactions in aqueous solutions under irradiation. The second-order Fe 2+ reactions with the hydrated electron (e aq – ) and the perhydroxyl radical (HO 2 • ), arising from water radiolysis, were measured to high temperatures using custom-built flow-through cells with a multichannel optical detection system. The reaction with the HO 2 • radical was found to proceed via the formation of a metal-ion adduct species, Fe 2+ –HO 2 • . Additionally, the adduct’s molar extinction coefficient and its first-order decay rate coefficients are reported.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

EXAFS investigation of the local structure in URu 2-x Fe x Si 2 : Evidence for distortions below 100 K

X-ray absorption measurements at the U L III , Ru K , and Fe K edges are reported for the hidden order (HO) material URu 2 - x Fe x Si 2 ( x = 0 , 0.05, 0.08, 0.10, 0.12, 0.15, and 0.20) as a function of x and temperature T . Furthermore, when Fe is substituted for Ru, the local structure about Fe shrinks slightly and the first neighbor Fe-Si bond length decreases by ≈ 0.05 Å . More importantly excess disorder is observed below 80–100 K (the coherence temperature T * ) in plots of the Debye-Waller factor σ 2 ( σ is the width of the pair distribution function); at low T the data deviate from the usual Einstein or correlated-Debye model plots. This excess disorder is most prominent for the Ru-Si bond, and σ 2 actually increases below 80 K. These results suggest a local orthorhombic distortion with B 1 g -like symmetry that develops below 80–100 K. A model that describes these local distortions is presented, and discussed in terms of other measurements that indicate a breaking of fourfold symmetry at low T . In addition, the square root of the difference between σ 2 ( T ) for the Ru-Si pair and a Debye fit to these data serves as an order parameter for this orthorhombic distortion, in the temperature range below 100 K. This quantity is a length related to a - b , the difference between the a and b lattice constants in the orthorhombic phase, and provides a connection between this distortion and T * . X-ray absorption near edge structure (XANES) measurements also show that there are no changes in the edge positions down to 0.1 eV for any edge as a function of x , for T in the HO regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on Ho3Fe29 by Materials Project

Ho3Fe29 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 12-coordinate geometry to twenty Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.97–3.20 Å. In the second Ho site, Ho is bonded in a 8-coordinate geometry to nineteen Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.98–3.27 Å. There are eleven inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with eighteen FeHo2Fe10 cuboctahedra, edges with eight FeHo3Fe9 cuboctahedra, and faces with fourteen FeHo2Fe10 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.36–2.55 Å. In the second Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form a mixture of distorted face, edge, and corner-sharing FeHo2Fe10 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.35–2.58 Å. In the third Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.37–2.83 Å. In the fourth Fe site, Fe is bonded in a 12-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.54–2.90 Å. In the fifth Fe site, Fe is bonded to two Ho and ten Fe atoms to form a mixture of distorted face, edge, and corner-sharing FeHo2Fe10 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.38–2.65 Å. In the sixth Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.29–2.63 Å. In the seventh Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.38–2.59 Å. In the eighth Fe site, Fe is bonded to two Ho and ten Fe atoms to form a mixture of distorted face, edge, and corner-sharing FeHo2Fe10 cuboctahedra. Both Fe–Fe bond lengths are 2.39 Å. In the ninth Fe site, Fe is bonded to two Ho and ten Fe atoms to form a mixture of face, edge, and corner-sharing FeHo2Fe10 cuboctahedra. Both Fe–Fe bond lengths are 2.42 Å. In the tenth Fe site, Fe is bonded to three Ho and nine Fe atoms to form a mixture of face, edge, and corner-sharing FeHo3Fe9 cuboctahedra. Both Fe–Fe bond lengths are 2.45 Å. In the eleventh Fe site, Fe is bonded to three equivalent Ho and nine Fe atoms to form a mixture of face, edge, and corner-sharing FeHo3Fe9 cuboctahedra. The Fe–Fe bond length is 2.45 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe5Co12 by Materials Project

Ho2Fe5Co12 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 12-coordinate geometry to eighteen Co atoms. There are a spread of Ho–Co bond distances ranging from 2.94–3.22 Å. In the second Ho site, Ho is bonded in a 8-coordinate geometry to eight Fe and twelve Co atoms. There are two shorter (2.89 Å) and six longer (3.15 Å) Ho–Fe bond lengths. There are six shorter (3.02 Å) and six longer (3.09 Å) Ho–Co bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 2-coordinate geometry to one Ho, four Fe, and nine Co atoms. There are one shorter (2.33 Å) and three longer (2.56 Å) Fe–Fe bond lengths. There are three shorter (2.65 Å) and six longer (2.70 Å) Fe–Co bond lengths. In the second Fe site, Fe is bonded to two equivalent Ho, two equivalent Fe, and eight Co atoms to form distorted FeHo2Fe2Co8 cuboctahedra that share corners with four equivalent FeHo2Fe2Co8 cuboctahedra, corners with eighteen CoHo3Fe3Co6 cuboctahedra, edges with ten CoHo3Fe3Co6 cuboctahedra, faces with six equivalent FeHo2Fe2Co8 cuboctahedra, and faces with twelve CoHo2Fe4Co6 cuboctahedra. There are four shorter (2.41 Å) and four longer (2.44 Å) Fe–Co bond lengths. There are two inequivalent Co sites. In the first Co site, Co is bonded to two Ho, four Fe, and six Co atoms to form distorted CoHo2Fe4Co6 cuboctahedra that share corners with four equivalent FeHo2Fe2Co8 cuboctahedra, corners with twenty CoHo2Fe4Co6 cuboctahedra, edges with two equivalent FeHo2Fe2Co8 cuboctahedra, edges with three CoHo3Fe3Co6 cuboctahedra, faces with four equivalent FeHo2Fe2Co8 cuboctahedra, and faces with seventeen CoHo2Fe4Co6 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.35–2.57 Å. In the second Co site, Co is bonded to three Ho, three Fe, and six Co atoms to form distorted CoHo3Fe3Co6 cuboctahedra that share corners with five equivalent FeHo2Fe2Co8 cuboctahedra, corners with eighteen CoHo3Fe3Co6 cuboctahedra, edges with three equivalent FeHo2Fe2Co8 cuboctahedra, edges with seven CoHo3Fe3Co6 cuboctahedra, faces with two equivalent FeHo2Fe2Co8 cuboctahedra, and faces with eighteen CoHo2Fe4Co6 cuboctahedra. Both Co–Co bond lengths are 2.39 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe17C2 by Materials Project

Ho2Fe17C2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ho is bonded in a distorted bent 120 degrees geometry to nine Fe and two equivalent C atoms. There are a spread of Ho–Fe bond distances ranging from 3.05–3.35 Å. Both Ho–C bond lengths are 2.51 Å. There are seven inequivalent Fe sites. In the first Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.40–2.73 Å. In the second Fe site, Fe is bonded to three equivalent Ho and nine Fe atoms to form FeHo3Fe9 cuboctahedra that share corners with nine FeHo3Fe9 cuboctahedra, corners with four equivalent CHo2Fe4 octahedra, edges with four FeHo3Fe9 cuboctahedra, faces with four FeHo3Fe9 cuboctahedra, and faces with two equivalent CHo2Fe4 octahedra. The corner-sharing octahedra tilt angles range from 63–69°. There are a spread of Fe–Fe bond distances ranging from 2.47–2.63 Å. In the third Fe site, Fe is bonded in a single-bond geometry to five Fe and one C atom. There are two shorter (2.47 Å) and one longer (2.56 Å) Fe–Fe bond lengths. The Fe–C bond length is 1.91 Å. In the fourth Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent Ho and ten Fe atoms. There are two shorter (2.43 Å) and two longer (2.46 Å) Fe–Fe bond lengths. In the fifth Fe site, Fe is bonded in a single-bond geometry to six Fe and one C atom. Both Fe–Fe bond lengths are 2.43 Å. The Fe–C bond length is 1.86 Å. In the sixth Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form distorted FeHo2Fe10 cuboctahedra that share corners with ten FeHo3Fe9 cuboctahedra, edges with two equivalent FeHo3Fe9 cuboctahedra, faces with six FeHo3Fe9 cuboctahedra, and faces with four equivalent CHo2Fe4 octahedra. In the seventh Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with six FeHo3Fe9 cuboctahedra, corners with two equivalent CHo2Fe4 octahedra, edges with two equivalent FeHo3Fe9 cuboctahedra, faces with six FeHo3Fe9 cuboctahedra, and faces with two equivalent CHo2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C is bonded to two equivalent Ho and four Fe atoms to form CHo2Fe4 octahedra that share corners with six FeHo3Fe9 cuboctahedra, corners with two equivalent CHo2Fe4 octahedra, and faces with six FeHo2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe17 by Materials Project

Ho2Fe17 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 12-coordinate geometry to eighteen Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.97–3.28 Å. In the second Ho site, Ho is bonded in a 8-coordinate geometry to twenty Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.94–3.20 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.37–2.78 Å. In the second Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with fourteen FeHo2Fe10 cuboctahedra, edges with six equivalent FeHo3Fe9 cuboctahedra, and faces with ten FeHo2Fe10 cuboctahedra. There are four shorter (2.45 Å) and four longer (2.46 Å) Fe–Fe bond lengths. In the third Fe site, Fe is bonded in a 12-coordinate geometry to two Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.46–2.59 Å. In the fourth Fe site, Fe is bonded to three Ho and nine Fe atoms to form a mixture of distorted face, edge, and corner-sharing FeHo3Fe9 cuboctahedra. Both Fe–Fe bond lengths are 2.45 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe17C by Materials Project

Ho2Fe17C crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ho is bonded in a distorted single-bond geometry to fourteen Fe and one C atom. There are a spread of Ho–Fe bond distances ranging from 3.00–3.30 Å. The Ho–C bond length is 2.50 Å. There are seven inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to eight Fe and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.42–2.73 Å. The Fe–C bond length is 1.85 Å. In the second Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent Ho and ten Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.43–2.76 Å. In the third Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.40–2.64 Å. In the fourth Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with eight FeHo2Fe10 cuboctahedra, corners with two equivalent CHo2Fe4 octahedra, edges with four equivalent FeHo3Fe9 cuboctahedra, and faces with eight FeHo2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 44°. All Fe–Fe bond lengths are 2.46 Å. In the fifth Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form distorted FeHo2Fe10 cuboctahedra that share corners with twelve FeHo2Fe10 cuboctahedra, edges with four equivalent FeHo3Fe9 cuboctahedra, faces with eight FeHo2Fe10 cuboctahedra, and faces with two equivalent CHo2Fe4 octahedra. There are two shorter (2.45 Å) and two longer (2.47 Å) Fe–Fe bond lengths. In the sixth Fe site, Fe is bonded to three equivalent Ho and nine Fe atoms to form FeHo3Fe9 cuboctahedra that share corners with twelve FeHo2Fe10 cuboctahedra, corners with two equivalent CHo2Fe4 octahedra, edges with six FeHo2Fe10 cuboctahedra, faces with seven FeHo2Fe10 cuboctahedra, and a faceface with one CHo2Fe4 octahedra. The corner-sharing octahedra tilt angles range from 66–70°. There are one shorter (2.50 Å) and one longer (2.53 Å) Fe–Fe bond lengths. In the seventh Fe site, Fe is bonded in a single-bond geometry to seven Fe and one C atom. The Fe–C bond length is 1.92 Å. C is bonded to two equivalent Ho and four Fe atoms to form CHo2Fe4 octahedra that share corners with ten FeHo2Fe10 cuboctahedra and faces with eight FeHo2Fe10 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermal Stability and Decomposition Products of P-Doped Ferrihydrite

This work aimed to determine the effect of various amounts of P admixtures in synthetic ferrihydrite on its thermal stability, transformation processes, and the properties of the products, at a broad range of temperatures up to 1000 °C. A detailed study was conducted using a series of synthetic ferrihydrites Fe 5 HO 8 ·4H 2 O doped with phosphates at P/Fe molar ratios of 0.2, 0.5, and 1.0. Ferrihydrite was synthesized by a reaction of Fe 2 (SO 4 ) 3 with 1 M KOH at room temperature in the presence of K 2 HPO 4 at pH 8.2. The products of the synthesis and the products of heating were characterized at various stages of transformation by using differential thermal analysis accompanied with X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. Coprecipitation of P with ferrihydrite results in the formation of P-doped 2-line ferrihydrite. A high P content reduces crystallinity. Phosphate significantly inhibits the thermal transformation processes. The temperature of thermal transformation increases from below 550 to 710–750 °C. Formation of intermediate maghemite and Fe-phosphates, is observed. The product of heating up to 1000 °C contains hematite associated with rodolicoite FePO 4 and grattarolaite Fe 3 PO 7 . Higher P content greatly increases the thermal stability and transformation temperature of rodolicoite as well.

thermal transformations↗
DOE OSTI2020

Materials Data on Ho2Fe14C by Materials Project

Ho2Fe14C crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 6-coordinate geometry to sixteen Fe atoms. There are a spread of Ho–Fe bond distances ranging from 2.95–3.23 Å. In the second Ho site, Ho is bonded in a 1-coordinate geometry to sixteen Fe and one C atom. There are a spread of Ho–Fe bond distances ranging from 2.99–3.35 Å. The Ho–C bond length is 2.82 Å. There are six inequivalent Fe sites. In the first Fe site, Fe is bonded to three Ho and nine Fe atoms to form distorted FeHo3Fe9 cuboctahedra that share corners with fourteen FeHo3Fe9 cuboctahedra, edges with three FeHo2Fe10 cuboctahedra, and faces with twelve FeHo3Fe9 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.36–2.74 Å. In the second Fe site, Fe is bonded in a single-bond geometry to two Ho, seven Fe, and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.46–2.73 Å. The Fe–C bond length is 1.98 Å. In the third Fe site, Fe is bonded in a 2-coordinate geometry to two Ho and twelve Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.60–2.78 Å. In the fourth Fe site, Fe is bonded to two Ho and ten Fe atoms to form a mixture of distorted corner, edge, and face-sharing FeHo2Fe10 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.41–2.56 Å. In the fifth Fe site, Fe is bonded to four Ho and eight Fe atoms to form a mixture of distorted corner and face-sharing FeHo4Fe8 cuboctahedra. In the sixth Fe site, Fe is bonded in a water-like geometry to two equivalent Ho, four Fe, and two equivalent C atoms. Both Fe–C bond lengths are 2.02 Å. C is bonded in a 6-coordinate geometry to one Ho and six Fe atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe17H3 by Materials Project

Ho2Fe17H3 crystallizes in the hexagonal P6_3/mmc 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 eight Fe and three equivalent H atoms. There are two shorter (2.89 Å) and six longer (3.20 Å) Ho–Fe bond lengths. All Ho–H bond lengths are 2.50 Å. In the second Ho site, Ho is bonded in a trigonal planar geometry to three equivalent H atoms. All Ho–H bond lengths are 2.44 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with four equivalent FeHo2Fe10 cuboctahedra, corners with two equivalent HHo2Fe4 octahedra, faces with six equivalent FeHo2Fe10 cuboctahedra, and faces with four equivalent HHo2Fe4 octahedra. The corner-sharing octahedral tilt angles are 40°. There are a spread of Fe–Fe bond distances ranging from 2.43–2.61 Å. In the second Fe site, Fe is bonded in a single-bond geometry to four Fe and one H atom. Both Fe–Fe bond lengths are 2.73 Å. The Fe–H bond length is 1.82 Å. In the third Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are one shorter (2.38 Å) and three longer (2.66 Å) Fe–Fe bond lengths. In the fourth Fe site, Fe is bonded in a single-bond geometry to three Fe and one H atom. The Fe–H bond length is 1.90 Å. H is bonded to two Ho and four Fe atoms to form HHo2Fe4 octahedra that share corners with two equivalent FeHo2Fe10 cuboctahedra, corners with four equivalent HHo2Fe4 octahedra, and faces with four equivalent FeHo2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 60°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe17C3 by Materials Project

Ho2Fe17C3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Ho sites. In the first Ho site, Ho is bonded in a trigonal planar geometry to three equivalent C atoms. All Ho–C bond lengths are 2.47 Å. In the second Ho site, Ho is bonded in a distorted trigonal planar geometry to eight Fe and three equivalent C atoms. There are two shorter (2.97 Å) and six longer (3.24 Å) Ho–Fe bond lengths. All Ho–C bond lengths are 2.50 Å. In the third Ho site, Ho is bonded in a distorted trigonal planar geometry to eight Fe and three equivalent C atoms. There are two shorter (2.97 Å) and six longer (3.24 Å) Ho–Fe bond lengths. All Ho–C bond lengths are 2.50 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded to two Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with four equivalent FeHo2Fe10 cuboctahedra, corners with two equivalent CHo2Fe4 octahedra, faces with six equivalent FeHo2Fe10 cuboctahedra, and faces with four equivalent CHo2Fe4 octahedra. The corner-sharing octahedral tilt angles are 40°. There are a spread of Fe–Fe bond distances ranging from 2.47–2.64 Å. In the second Fe site, Fe is bonded in a single-bond geometry to four Fe and one C atom. Both Fe–Fe bond lengths are 2.72 Å. The Fe–C bond length is 1.86 Å. In the third Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are one shorter (2.37 Å) and three longer (2.68 Å) Fe–Fe bond lengths. In the fourth Fe site, Fe is bonded in a single-bond geometry to three Fe and one C atom. The Fe–C bond length is 1.91 Å. C is bonded to two Ho and four Fe atoms to form CHo2Fe4 octahedra that share corners with two equivalent FeHo2Fe10 cuboctahedra, corners with four equivalent CHo2Fe4 octahedra, and faces with four equivalent FeHo2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 60°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Fe17N3 by Materials Project

Ho2Fe17N3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Ho sites. In the first Ho site, Ho is bonded in a distorted trigonal planar geometry to eight Fe and three equivalent N atoms. There are two shorter (3.00 Å) and six longer (3.26 Å) Ho–Fe bond lengths. All Ho–N bond lengths are 2.53 Å. In the second Ho site, Ho is bonded in a distorted trigonal planar geometry to eight Fe and three equivalent N atoms. There are two shorter (3.00 Å) and six longer (3.26 Å) Ho–Fe bond lengths. All Ho–N bond lengths are 2.53 Å. In the third Ho site, Ho is bonded in a trigonal planar geometry to three equivalent N atoms. All Ho–N bond lengths are 2.45 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded to two Ho and ten Fe atoms to form FeHo2Fe10 cuboctahedra that share corners with four equivalent FeHo2Fe10 cuboctahedra, corners with two equivalent NHo2Fe4 octahedra, faces with six equivalent FeHo2Fe10 cuboctahedra, and faces with four equivalent NHo2Fe4 octahedra. The corner-sharing octahedral tilt angles are 40°. There are eight shorter (2.48 Å) and two longer (2.65 Å) Fe–Fe bond lengths. In the second Fe site, Fe is bonded in a single-bond geometry to four Fe and one N atom. Both Fe–Fe bond lengths are 2.72 Å. The Fe–N bond length is 1.88 Å. In the third Fe site, Fe is bonded in a 2-coordinate geometry to one Ho and thirteen Fe atoms. There are one shorter (2.40 Å) and three longer (2.68 Å) Fe–Fe bond lengths. In the fourth Fe site, Fe is bonded in a single-bond geometry to three Fe and one N atom. The Fe–N bond length is 1.92 Å. N is bonded to two Ho and four Fe atoms to form NHo2Fe4 octahedra that share corners with two equivalent FeHo2Fe10 cuboctahedra, corners with four equivalent NHo2Fe4 octahedra, and faces with four equivalent FeHo2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 60°.

36 MATERIALS SCIENCE↗