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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

High-volume and -adiabat capsule (“HVAC”) ignition: Lowered fuel compression requirements using advanced Hohlraums

Lower-than-expected deuterium–tritium fuel areal densities have been experimentally inferred across a variety of high-convergence, nominally low-adiabat implosion campaigns at the National Ignition Facility (NIF) using cylinder-shaped Hohlraums [Hurricane et al., Phys. Plasmas 26, 052704 (2019)]. A leading candidate explanation is the presence of atomic mix between the fuel and ablator from hydrodynamic instability growth [Clark et al., Phys. Plasmas 26, 050601 (2019)], leading to reduced fuel compressibility and an effectively higher (in-flight) fuel adiabat α. Tolerating a high-α implosion can be obtained with significantly higher capsule absorbed energy Ecap according to the one-dimensional (1-D) ignition-threshold-factor analytic scaling [S. Atzeni and J. Meyer-ter-Vehn, Nucl. Fusion 41, 465 (2001)], ITF∼Ecap·α−1.8. Recent experiments with large Al shells in rugby-shaped Hohlraums have established high laser-capsule coupling efficiencies of ≽ 30% [Ping et al., Nat. Phys. 15, 138 (2019)], enabling a path to Ecap≽ 0.5 MJ at the NIF and increased performance margin M ≡ ITF − 1. The ability to operate at high adiabat with large capsules using nonstandard Hohlraums leads to the predicted onset of a volume-ignition mode, defined as when both the entire fuel is the “hot spot” and inertial confinement is principally provided by the ablator compared with the compressed fuel. Such an ignition mode, normally reserved for high-Z targets, e.g., double shells [Amendt et al., Phys. Plasmas 14, 056312 (2007)], is predicted to lead to lower fuel convergence and less exposure to mix due to the intended high adiabat—but at the expense of ∼3–4 × reduced (1-D) yield compared with conventional central hot-spot ignition designs.

Amendt, Peter (ORCID:0000000174021777)↗
DOE OSTI2020

Materials Data on LiB(HO)4 by Materials Project

LiB(OH)4 crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four equivalent BO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.96–2.05 Å. B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share corners with four equivalent LiO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.51 Å. There are four 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 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.73 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.67 Å) H–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Li1+, one B3+, and one H1+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one Li1+, one B3+, and two H1+ atoms. In the third O2- site, O2- is bonded in a 1-coordinate geometry to one Li1+, one B3+, and two H1+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Li1+, one B3+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NaHoO2 by Materials Project

NaHoO2 is Caswellsilverite-like structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with two equivalent NaO6 octahedra, corners with four HoO6 octahedra, edges with five NaO6 octahedra, and edges with seven HoO6 octahedra. The corner-sharing octahedra tilt angles range from 7–14°. There are a spread of Na–O bond distances ranging from 2.42–2.76 Å. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with two equivalent NaO6 octahedra, corners with four HoO6 octahedra, edges with five NaO6 octahedra, and edges with seven HoO6 octahedra. The corner-sharing octahedra tilt angles range from 1–14°. There are a spread of Na–O bond distances ranging from 2.40–2.74 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six O2- atoms to form HoO6 octahedra that share corners with two equivalent HoO6 octahedra, corners with four NaO6 octahedra, edges with five HoO6 octahedra, and edges with seven NaO6 octahedra. The corner-sharing octahedra tilt angles range from 7–14°. There are a spread of Ho–O bond distances ranging from 2.28–2.32 Å. In the second Ho3+ site, Ho3+ is bonded to six O2- atoms to form HoO6 octahedra that share corners with two equivalent HoO6 octahedra, corners with four NaO6 octahedra, edges with five HoO6 octahedra, and edges with seven NaO6 octahedra. The corner-sharing octahedra tilt angles range from 1–14°. There are a spread of Ho–O bond distances ranging from 2.29–2.31 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to three Na1+ and three Ho3+ atoms to form a mixture of edge and corner-sharing ONa3Ho3 octahedra. The corner-sharing octahedra tilt angles range from 3–13°. In the second O2- site, O2- is bonded to three Na1+ and three Ho3+ atoms to form a mixture of distorted edge and corner-sharing ONa3Ho3 octahedra. The corner-sharing octahedra tilt angles range from 2–13°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg3P2(HO)16 by Materials Project

Mg3P2(HO)16 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of four Mg3P2(HO)16 sheets oriented in the (0, 1, 0) direction. there are three inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four equivalent PO4 tetrahedra and an edgeedge with one MgO6 octahedra. There are four shorter (2.07 Å) and two longer (2.17 Å) Mg–O bond lengths. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four equivalent PO4 tetrahedra and an edgeedge with one MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.03–2.17 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent PO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.05–2.16 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with five MgO6 octahedra. The corner-sharing octahedra tilt angles range from 46–57°. There are a spread of P–O bond distances ranging from 1.55–1.57 Å. There are eight inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.73 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.74 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the fifth H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.64 Å) H–O bond length. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+, one P5+, and one H1+ atom. In the third O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+, one P5+, and two H1+ atoms. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to two Mg2+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+ and two H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Investigation of the effects of ternary deep eutectic solvent composition on pretreatment of sorghum stover

Biomass‐derived deep eutectic solvents (DESs) have been introduced as promising pretreatment and fractionation solvents because of their mild processing conditions, easy synthesis, and green solvent components from biomass. In recent DES studies, solvent‐based third constituents like water, ethanol, and others improve the processibility of typical binary DESs. However, the impacts of these components are not well understood. Here, two solvent‐based constituents, including water and ethylene glycol, were applied to 3,4‐dihydroxybenzoic acid (DHBA)‐based DES system for improving the conversion efficiency of cellulose‐rich fraction and the properties of lignin fraction. Chemical composition, enzymatic digestibility, degree of polymerization of cellulose and physicochemical properties of lignin were used to evaluate the impact of each third constituent on biomass processing. Ternary ChCl‐DHBA DESs exhibited better performances in delignification, fermentable sugar production, and preservation of β‐O‐4 ether linkage in lignin compared with binary ChCl‐DHBA DES.

09 BIOMASS FUELS↗
DOE OSTI2020

Materials Data on CaMgB6(HO)22 by Materials Project

CaMgB6(H9O10)2(H2O)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional and consists of eight water molecules and one CaMgB6(H9O10)2 framework. In the CaMgB6(H9O10)2 framework, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.54 Å. Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four BO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.11–2.13 Å. There are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share a cornercorner with one MgO6 octahedra and a cornercorner with one BO4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. There are a spread of B–O bond distances ranging from 1.45–1.50 Å. In the second B3+ site, B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share a cornercorner with one MgO6 octahedra and a cornercorner with one BO4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. There are a spread of B–O bond distances ranging from 1.45–1.52 Å. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.37 Å) and one longer (1.39 Å) B–O bond length. There are nine 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 0.97 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.62 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+, one B3+, and one H1+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ atoms. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+, one B3+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one B3+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one B3+, and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the eighth O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two H1+ atoms. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+ and two B3+ atoms. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one B3+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho3Se4O12F by Materials Project

Ho3Se4O12F crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Ho3+ is bonded in a 9-coordinate geometry to eight O2- and one F1- atom. There are a spread of Ho–O bond distances ranging from 2.33–2.56 Å. The Ho–F bond length is 2.35 Å. There are two inequivalent Se4+ sites. In the first Se4+ site, Se4+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. All Se–O bond lengths are 1.72 Å. In the second Se4+ site, Se4+ is bonded in a trigonal non-coplanar geometry to three equivalent O2- atoms. All Se–O bond lengths are 1.74 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Se4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Se4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Se4+ atom. F1- is bonded in a distorted trigonal planar geometry to three equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Design and Realization of Ohmic and Schottky Interfaces for Oxide Electronics

Understanding band alignment and charge transfer at complex oxide interfaces is critical to tailoring and utilizing their diverse functionality. Toward this goal, both Ohmic- and Schottky-like charge transfers at oxide/oxide semiconductor/metal interfaces are designed and experimentally validated. A method for predicting band alignment and charge transfer in ABO 3 perovskites is utilized, where previously established rules for simple semiconductors fail. The prototypical systems chosen are the rare class of oxide metals, SrBO 3 with B = V–Ta, when interfaced with the multifaceted semiconducting oxide, SrTiO 3 . For B = Nb and Ta, it is confirmed that a large accumulation of charge occurs in SrTiO 3 due to the higher energy Nb and Ta states relative to Ti. Furthermore, this gives rise to a high mobility metallic interface, which is an ideal epitaxial oxide/oxide Ohmic contact. On the contrary, for B = V, there is no charge transfer into the SrTiO 3 interface, which serves as a highly conductive epitaxial gate metal. Going beyond these specific cases, this work opens the door to integrating the vast phenomena of ABO 3 perovskites into a wide range of practical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Feld-induced modulation of two-dimensional electron gas at LaAlO 3 /SrTiO 3 interface by polar distortion of LaAlO 3

Since the discovery of two-dimensional electron gas at the LaAlO 3 /SrTiO 3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO 3 /SrTiO 3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO 3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO 3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lithium calix[4]arenes: structural studies and use in the ring opening polymerization of cyclic esters

We have structurally characterized a number of lithiated calix[4]arenes, where the bridge in the calix[4]arene is thia (–S–, L S H 4 ), sulfinyl (–SO–, L SO H 4 ), sulfonyl (–SO 2 –, L SO2 H 4 ), dimethyleneoxa (–CH 2 OCH 2 –, L COC H 4 ) or methylene (–CH 2 –, LH 4 ). In the case of L 4S H 4 , interaction with LiO t Bu led to the isolation of the complex [Li 8 (L 4S ) 2 (THF) 4 ]·5THF ( 1 ·5THF), whilst similar interaction of L 4SO H 4 led to the isolation of [Li 6 (L 4SO H) 2 (THF) 2 ]·5(THF) ( 2 ·5THF). Interestingly, the mixed sulfinyl/sulfonyl complexes [Li 8 (calix[4]arene(SO)(SO 2 )(SO 1.68 ) 2 ) 2 (THF) 6 ]·8(THF) ( 3 ·8THF) and [Li 5 Na(L SO/3SO2 H) 2 (THF) 5 ]·7.5(THF) ( 4 ·7.5(THF) have also been characterized. Interaction of LiO t Bu with L SO2 H 4 and L COC H 4 afforded [Li 5 L 4SO2 (OH)(THF) 4 ]·2THF ( 5 ·2THF) and [Li 6 (L COC ) 2 (HO t Bu) 2 ]·0.78THF·1.22hexane ( 6 ·0.78THF·1.22hexane), respectively. In the case of LH 4 , reaction with LiO t Bu in THF afforded a monoclinic polymorph [LH 2 Li 2 (thf)(OH 2 ) 2 ]·3THF ( 7 ·3THF) of a known triclinic form of the complex, whilst reaction of the de-butylated analogue of LH 4 , namely de-BuLH 4 , afforded a polymeric chain structure {[Li 5 (de-BuL)(OH)(NCMe) 3 ]·2MeCN} n ( 8 ·2MeCN). For comparative catalytic studies, the complex [Li 6 (L Pr ) 2 (H 2 O) 2 ]·hexane ( 9 hexane), where L Pr2 H 2 = 1,3-di- n -propyloxycalix[4]areneH 2 , was also prepared. The molecular crystal structures of 1–9 are reported, and their ability to act as catalysts for the ring opening (co-)/polymerization (ROP) of the cyclic esters ε-caprolactone, δ-valerolactone, and rac -lactide has been investigated. In most of the cases, complex 6 outperformed the other systems, allowing for higher conversions and/or greated polymer M n .

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

Crystal and magnetic structure of polar oxide HoCrWO 6

In this study, polar magnetic oxide HoCrWO 6 is synthesized and its crystal structure, magnetic structure, and thermodynamic properties are investigated. HoCrWO 6 forms the polar crystal structure (space group Pna 2 1 (#33)) due to the cation ordering of W 6+ and Cr 3+ . There is an antiferromagnetic transition at T N = 24.5 K along with the magnetic entropy change (~5 J.Kg. –1 K –1 at 70 kOe). Neutron diffraction measurement indicates that both Cr and Ho sublattices are ordered with the moment of 2.32(5)μ B and 8.7(4)μ B at 2 K, respectively. While Cr forms A-type collinear antiferromagnetic (AFM) structure with magnetic moment along the b axis, Ho sublattice orders in a non-coplanar AFM arrangement. A comparison with isostructural DyFeWO 6 and DyCrWO 6 indicates that the magnetic structure of this family of compounds is controlled by the presence or absence of e g electrons in the transition metal sublattice.

42 ENGINEERING↗
DOE OSTI2020

Materials Data on HoC3S3(O2F)9 by Materials Project

HoO9(CF3)3(SO3)3 crystallizes in the hexagonal P6_3/m space group. The structure is zero-dimensional and consists of six fluoroform molecules, six sulfur trioxide molecules, and two HoO9 clusters. In each HoO9 cluster, Ho is bonded in a 9-coordinate geometry to nine O atoms. There are six shorter (2.30 Å) and three longer (2.31 Å) Ho–O bond lengths. There are two inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Ho atom. In the second O site, O is bonded in a single-bond geometry to one Ho atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Spin Wave Excitations in Honeycomb Antiferromagnet MnTiO 3

Using inelastic neutron scattering, we investigate the spin wave excitations on the antiferromagnetic MnTiO 3 (T N = 65 K), which has the stacked honeycomb structure. At T = 2 K, the spin wave energy extends up to 10.7 meV with the zone-center anisotropy gap of 0.8 meV. Whereas the dispersion is also strong along the direction perpendicular to the honeycomb planes, the exchange cancellation causes the magnetic interactions to be effectively anisotropic below TN. Furthermore, while the spin wave spectrum survives at temperatures above TN, we find that the magnetic interactions become more anisotropic within the paramagnetic phase. These results suggest that the magnetic interaction in MnTiO 3 crosses over from being three dimensional to two dimensional above T N .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoSeO3F by Materials Project

HoSeO3F crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to six O2- and two equivalent F1- atoms. There are a spread of Ho–O bond distances ranging from 2.29–2.64 Å. There are one shorter (2.20 Å) and one longer (2.21 Å) Ho–F bond lengths. Se4+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.71–1.78 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Se4+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ho3+ and one Se4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three equivalent Ho3+ and one Se4+ atom. F1- is bonded in a distorted bent 120 degrees geometry to two equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaHoFe4O7 by Materials Project

BaHoFe4O7 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ba2+ is bonded to twelve equivalent O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, edges with twelve equivalent FeO4 tetrahedra, and faces with four equivalent HoO6 octahedra. All Ba–O bond lengths are 3.24 Å. Ho3+ is bonded to six equivalent O2- atoms to form HoO6 octahedra that share corners with twelve equivalent FeO4 tetrahedra and faces with four equivalent BaO12 cuboctahedra. All Ho–O bond lengths are 2.26 Å. Fe+2.25+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three equivalent HoO6 octahedra, corners with six equivalent FeO4 tetrahedra, and edges with three equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 51°. There are three shorter (1.98 Å) and one longer (2.10 Å) Fe–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ba2+, one Ho3+, and two equivalent Fe+2.25+ atoms. In the second O2- site, O2- is bonded in a tetrahedral geometry to four equivalent Fe+2.25+ atoms.

36 MATERIALS SCIENCE↗