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DOE OSTI2020

Materials Data on TbSn2 by Materials Project

Sn2Tb is Zirconium Disilicide structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Tb is bonded in a 10-coordinate geometry to ten Sn atoms. There are a spread of Tb–Sn bond distances ranging from 3.17–3.47 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 4-coordinate geometry to six equivalent Tb and two equivalent Sn atoms. Both Sn–Sn bond lengths are 3.01 Å. In the second Sn site, Sn is bonded in a 8-coordinate geometry to four equivalent Tb and four equivalent Sn atoms. All Sn–Sn bond lengths are 3.12 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb4Si7 by Materials Project

Tb4Si7 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are four inequivalent Tb3+ sites. In the first Tb3+ site, Tb3+ is bonded in a 8-coordinate geometry to nine Si+1.71- atoms. There are a spread of Tb–Si bond distances ranging from 2.93–3.32 Å. In the second Tb3+ site, Tb3+ is bonded to twelve Si+1.71- atoms to form a mixture of face and edge-sharing TbSi12 cuboctahedra. There are a spread of Tb–Si bond distances ranging from 3.04–3.27 Å. In the third Tb3+ site, Tb3+ is bonded in a 8-coordinate geometry to nine Si+1.71- atoms. There are a spread of Tb–Si bond distances ranging from 2.93–3.31 Å. In the fourth Tb3+ site, Tb3+ is bonded to twelve Si+1.71- atoms to form a mixture of face and edge-sharing TbSi12 cuboctahedra. There are a spread of Tb–Si bond distances ranging from 3.04–3.27 Å. There are seven inequivalent Si+1.71- sites. In the first Si+1.71- site, Si+1.71- is bonded in a 9-coordinate geometry to six Tb3+ and three Si+1.71- atoms. There are a spread of Si–Si bond distances ranging from 2.34–2.40 Å. In the second Si+1.71- site, Si+1.71- is bonded in a 9-coordinate geometry to six Tb3+ and three Si+1.71- atoms. There are one shorter (2.34 Å) and one longer (2.41 Å) Si–Si bond lengths. In the third Si+1.71- site, Si+1.71- is bonded in a 9-coordinate geometry to six Tb3+ and three Si+1.71- atoms. There are one shorter (2.37 Å) and one longer (2.40 Å) Si–Si bond lengths. In the fourth Si+1.71- site, Si+1.71- is bonded in a 8-coordinate geometry to six Tb3+ and two Si+1.71- atoms. In the fifth Si+1.71- site, Si+1.71- is bonded in a 9-coordinate geometry to six Tb3+ and three Si+1.71- atoms. Both Si–Si bond lengths are 2.33 Å. In the sixth Si+1.71- site, Si+1.71- is bonded in a 8-coordinate geometry to six Tb3+ and two Si+1.71- atoms. The Si–Si bond length is 2.47 Å. In the seventh Si+1.71- site, Si+1.71- is bonded in a 9-coordinate geometry to six Tb3+ and three Si+1.71- atoms. The Si–Si bond length is 2.33 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb4Te3N2 by Materials Project

Tb4N2Te3 crystallizes in the orthorhombic Pnna space group. The structure is three-dimensional. there are two inequivalent Tb3+ sites. In the first Tb3+ site, Tb3+ is bonded in a distorted L-shaped geometry to two N3- and four Te2- atoms. There are one shorter (2.25 Å) and one longer (2.28 Å) Tb–N bond lengths. There are a spread of Tb–Te bond distances ranging from 3.09–3.53 Å. In the second Tb3+ site, Tb3+ is bonded in a distorted L-shaped geometry to two N3- and four Te2- atoms. Both Tb–N bond lengths are 2.25 Å. There are a spread of Tb–Te bond distances ranging from 3.09–3.35 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded to four Tb3+ atoms to form edge-sharing NTb4 tetrahedra. In the second N3- site, N3- is bonded to four Tb3+ atoms to form distorted edge-sharing NTb4 tetrahedra. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 6-coordinate geometry to six Tb3+ atoms. In the second Te2- site, Te2- is bonded in a 5-coordinate geometry to five Tb3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbH18(BrO6)3 by Materials Project

Tb(H2O)9(BrO3)3 crystallizes in the hexagonal P6_3mc space group. The structure is zero-dimensional and consists of six hypobromous acid;dihydrate molecules and two Tb(H2O)9 clusters. In each Tb(H2O)9 cluster, Tb3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Tb–O bond distances ranging from 2.42–2.47 Å. There are three 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 0.98 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 one O2- atom. The H–O bond length is 0.98 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a water-like geometry to one Tb3+ and two equivalent H1+ atoms. In the second O2- site, O2- is bonded in a water-like geometry to one Tb3+ and two equivalent H1+ atoms. In the third O2- site, O2- is bonded in a water-like geometry to one Tb3+ and two equivalent H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb4Ga12Fe by Materials Project

Tb4FeGa12 crystallizes in the cubic Im-3m space group. The structure is three-dimensional. Tb is bonded to twelve Ga atoms to form TbGa12 cuboctahedra that share corners with twelve equivalent TbGa12 cuboctahedra, edges with twelve equivalent GaTb4Ga8 cuboctahedra, faces with six equivalent TbGa12 cuboctahedra, faces with six equivalent GaTb4Ga8 cuboctahedra, and faces with two equivalent FeGa6 octahedra. There are six shorter (3.05 Å) and six longer (3.06 Å) Tb–Ga bond lengths. Fe is bonded to six equivalent Ga atoms to form FeGa6 octahedra that share corners with twenty-four equivalent GaTb4Ga8 cuboctahedra and faces with eight equivalent TbGa12 cuboctahedra. All Fe–Ga bond lengths are 2.44 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded to four equivalent Tb and eight Ga atoms to form distorted GaTb4Ga8 cuboctahedra that share corners with four equivalent GaTb4Ga8 cuboctahedra, corners with four equivalent FeGa6 octahedra, edges with eight equivalent TbGa12 cuboctahedra, edges with eight equivalent GaTb4Ga8 cuboctahedra, faces with four equivalent TbGa12 cuboctahedra, and faces with six equivalent GaTb4Ga8 cuboctahedra. The corner-sharing octahedral tilt angles are 49°. There are four shorter (2.85 Å) and four longer (3.05 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 5-coordinate geometry to four equivalent Tb, one Fe, and four equivalent Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbMgIn by Materials Project

MgTbIn crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Mg is bonded in a 4-coordinate geometry to four In atoms. There are two shorter (2.92 Å) and two longer (2.97 Å) Mg–In bond lengths. Tb is bonded in a 5-coordinate geometry to five In atoms. There are four shorter (3.24 Å) and one longer (3.25 Å) Tb–In bond lengths. There are two inequivalent In sites. In the first In site, In is bonded in a 9-coordinate geometry to six equivalent Mg and three equivalent Tb atoms. In the second In site, In is bonded in a 9-coordinate geometry to three equivalent Mg and six equivalent Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbRe2 by Materials Project

TbRe2 is Hexagonal Laves structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Tb is bonded in a 12-coordinate geometry to twelve Re atoms. There are three shorter (3.16 Å) and nine longer (3.19 Å) Tb–Re bond lengths. There are two inequivalent Re sites. In the first Re site, Re is bonded to six equivalent Tb and six equivalent Re atoms to form a mixture of corner, edge, and face-sharing ReTb6Re6 cuboctahedra. All Re–Re bond lengths are 2.74 Å. In the second Re site, Re is bonded to six equivalent Tb and six Re atoms to form a mixture of corner, edge, and face-sharing ReTb6Re6 cuboctahedra. There are two shorter (2.65 Å) and two longer (2.80 Å) Re–Re bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbRu2 by Materials Project

TbRu2 is Hexagonal Laves structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Tb is bonded in a 12-coordinate geometry to twelve Ru atoms. There are a spread of Tb–Ru bond distances ranging from 3.10–3.21 Å. There are two inequivalent Ru sites. In the first Ru site, Ru is bonded to six equivalent Tb and six equivalent Ru atoms to form a mixture of face, edge, and corner-sharing RuTb6Ru6 cuboctahedra. All Ru–Ru bond lengths are 2.74 Å. In the second Ru site, Ru is bonded to six equivalent Tb and six Ru atoms to form a mixture of face, edge, and corner-sharing RuTb6Ru6 cuboctahedra. There are two shorter (2.56 Å) and two longer (2.71 Å) Ru–Ru bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbGa6 by Materials Project

TbGa6 crystallizes in the tetragonal P4/nbm space group. The structure is three-dimensional. Tb is bonded to twelve Ga atoms to form a mixture of distorted edge and face-sharing TbGa12 cuboctahedra. There are four shorter (3.11 Å) and eight longer (3.25 Å) Tb–Ga bond lengths. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a 9-coordinate geometry to four equivalent Tb and five Ga atoms. There are one shorter (2.43 Å) and four longer (2.60 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 4-coordinate geometry to one Tb and three Ga atoms. The Ga–Ga bond length is 2.50 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb2Pr2O5 by Materials Project

Tb2Pr2O5 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Tb is bonded to five O atoms to form TbO5 square pyramids that share corners with five equivalent TbO5 square pyramids and faces with four equivalent PrO12 cuboctahedra. There are one shorter (2.12 Å) and four longer (2.20 Å) Tb–O bond lengths. There are two inequivalent Pr sites. In the first Pr site, Pr is bonded in a body-centered cubic geometry to eight equivalent O atoms. All Pr–O bond lengths are 2.90 Å. In the second Pr site, Pr is bonded to twelve O atoms to form PrO12 cuboctahedra that share corners with four equivalent PrO12 cuboctahedra, faces with four equivalent PrO12 cuboctahedra, and faces with eight equivalent TbO5 square pyramids. There are eight shorter (3.01 Å) and four longer (3.11 Å) Pr–O bond lengths. There are two inequivalent O sites. In the first O site, O is bonded to two equivalent Tb and four Pr atoms to form a mixture of distorted corner, edge, and face-sharing OTb2Pr4 octahedra. The corner-sharing octahedra tilt angles range from 0–65°. In the second O site, O is bonded in a linear geometry to two equivalent Tb and four equivalent Pr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb2MgSe4 by Materials Project

MgTb2Se4 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one TbSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four TbSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four TbSe6 octahedra, and edges with three TbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–53°. There are a spread of Mg–Se bond distances ranging from 2.67–2.96 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one TbSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four TbSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four TbSe6 octahedra, and edges with three TbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Mg–Se bond distances ranging from 2.70–2.87 Å. There are four inequivalent Tb3+ sites. In the first Tb3+ site, Tb3+ is bonded to six Se2- atoms to form TbSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent TbSe6 octahedra, corners with four TbSe7 pentagonal bipyramids, an edgeedge with one TbSe6 octahedra, edges with four MgSe6 octahedra, and edges with three TbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Tb–Se bond distances ranging from 2.83–2.89 Å. In the second Tb3+ site, Tb3+ is bonded to six Se2- atoms to form TbSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent TbSe6 octahedra, corners with four TbSe7 pentagonal bipyramids, an edgeedge with one TbSe6 octahedra, edges with four MgSe6 octahedra, and edges with three TbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–53°. There are a spread of Tb–Se bond distances ranging from 2.82–2.93 Å. In the third Tb3+ site, Tb3+ is bonded to seven Se2- atoms to form distorted TbSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four TbSe6 octahedra, edges with three MgSe6 octahedra, edges with three TbSe6 octahedra, and faces with two equivalent TbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–68°. There are a spread of Tb–Se bond distances ranging from 2.87–3.14 Å. In the fourth Tb3+ site, Tb3+ is bonded to seven Se2- atoms to form distorted TbSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four TbSe6 octahedra, edges with three MgSe6 octahedra, edges with three TbSe6 octahedra, and faces with two equivalent TbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–68°. There are a spread of Tb–Se bond distances ranging from 2.86–3.17 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three Tb3+ atoms to form distorted SeTb3Mg2 trigonal bipyramids that share corners with two equivalent SeTb3Mg2 square pyramids, corners with three equivalent SeTb3Mg tetrahedra, corners with two equivalent SeTb3Mg2 trigonal bipyramids, edges with five SeTb3Mg2 square pyramids, and edges with three SeTb3Mg2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Tb3+ atoms to form distorted SeTb3Mg2 trigonal bipyramids that share corners with six SeTb3Mg2 square pyramids, corners with two equivalent SeTb3Mg tetrahedra, corners with two equivalent SeTb3Mg2 trigonal bipyramids, edges with three SeTb3Mg2 square pyramids, an edgeedge with one SeTb3Mg tetrahedra, and edges with three SeTb3Mg2 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Tb3+ atoms to form a mixture of distorted corner and edge-sharing SeTb3Mg tetrahedra. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Tb3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Tb3+ atoms to form distorted SeTb3Mg2 square pyramids that share a cornercorner with one SeTb3Mg tetrahedra, corners with eight SeTb3Mg2 trigonal bipyramids, edges with four SeTb3Mg2 square pyramids, an edgeedge with one SeTb3Mg tetrahedra, and edges with two SeTb3Mg2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Tb3+ atoms to form distorted SeTb3Mg2 square pyramids that share corners with two equivalent SeTb4Mg square pyramids, a cornercorner with one SeTb3Mg tetrahedra, corners with six SeTb3Mg2 trigonal bipyramids, edges with three SeTb3Mg2 square pyramids, an edgeedge with one SeTb3Mg tetrahedra, and edges with three SeTb3Mg2 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Tb3+ atoms to form distorted SeTb4Mg square pyramids that share corners with two equivalent SeTb3Mg2 square pyramids, corners with two equivalent SeTb3Mg tetrahedra, corners with two equivalent SeTb4Mg trigonal bipyramids, edges with three SeTb3Mg2 square pyramids, an edgeedge with one SeTb3Mg tetrahedra, and edges with five SeTb3Mg2 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Tb3+ atoms to form distorted SeTb4Mg trigonal bipyramids that share corners with eight SeTb3Mg2 square pyramids, corners with three equivalent SeTb3Mg tetrahedra, edges with two SeTb3Mg2 square pyramids, and edges with four SeTb3Mg2 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La3Tb by Materials Project

TbLa3 is Copper-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tb is bonded to twelve La atoms to form TbLa12 cuboctahedra that share corners with four equivalent TbLa12 cuboctahedra, corners with eight equivalent LaLa8Tb4 cuboctahedra, edges with eight equivalent TbLa12 cuboctahedra, edges with sixteen equivalent LaLa8Tb4 cuboctahedra, faces with four equivalent TbLa12 cuboctahedra, and faces with fourteen LaLa8Tb4 cuboctahedra. There are four shorter (3.70 Å) and eight longer (3.72 Å) Tb–La bond lengths. There are two inequivalent La sites. In the first La site, La is bonded to four equivalent Tb and eight La atoms to form LaLa8Tb4 cuboctahedra that share corners with twelve equivalent LaLa8Tb4 cuboctahedra, edges with eight equivalent TbLa12 cuboctahedra, edges with sixteen LaLa8Tb4 cuboctahedra, faces with four equivalent TbLa12 cuboctahedra, and faces with fourteen LaLa8Tb4 cuboctahedra. There are four shorter (3.70 Å) and four longer (3.72 Å) La–La bond lengths. In the second La site, La is bonded to four equivalent Tb and eight equivalent La atoms to form LaLa8Tb4 cuboctahedra that share corners with four equivalent LaLa8Tb4 cuboctahedra, corners with eight equivalent TbLa12 cuboctahedra, edges with twenty-four LaLa8Tb4 cuboctahedra, faces with six equivalent TbLa12 cuboctahedra, and faces with twelve LaLa8Tb4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbMgAu by Materials Project

MgTbAu crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Mg is bonded in a 4-coordinate geometry to four Au atoms. There are two shorter (2.79 Å) and two longer (2.94 Å) Mg–Au bond lengths. Tb is bonded in a 5-coordinate geometry to five Au atoms. There are four shorter (3.09 Å) and one longer (3.14 Å) Tb–Au bond lengths. There are two inequivalent Au sites. In the first Au site, Au is bonded in a 9-coordinate geometry to six equivalent Mg and three equivalent Tb atoms. In the second Au site, Au is bonded in a 9-coordinate geometry to three equivalent Mg and six equivalent Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Short- and medium-range orders in Al90Tb10 glass and their relation to the structures of competing crystalline phases

Molecular dynamics simulations using an interatomic potential developed by artificial neural network deep machine learning are performed to study the local structural order in Al90Tb10 metallic glass. We show that more than 80% of the Tb-centered clusters in Al90Tb10 glass have short-range order (SRO) with their 17 first coordination shell atoms stacked in a ‘3661’ or ‘15551’ sequence. Medium-range order (MRO) in Bergman-type packing extended out to the second and third coordination shells is also clearly observed. Analysis of the network formed by the ‘3661’ and ‘15551’ clusters show that ~82% of such SRO units share their faces or vertexes, while only ~6% of neighboring SRO pairs are interpenetrating. Such a network topology is consistent with the Bergman-type MRO around the Tb-centers. Moreover, crystal structure searches using genetic algorithm and the neural network interatomic potential reveal several low-energy metastable crystalline structures in the composition range close to Al 90 Tb 10 . Some of these crystalline structures have the ‘3661’ SRO while others have the ‘15551’ SRO. While the crystalline structures with the ‘3661’ SRO also exhibit the MRO very similar to that observed in the glass, the ones with the ‘15551’ SRO have very different atomic packing in the second and third shells around the Tb centers from that of the Bergman-type MRO observed in the glassy phase.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Evaluation of mitigation strategies for radioactive fission gases in fluoride-salt-cooled high-temperature reactors

Here, the Fluoride-salt-cooled High-temperature Reactor (FHR) is a promising Generation IV nuclear reactor due to its improved safety design, near atmospheric working pressure, and high electric power conversion efficiency. However, control of radioactive fission gases, such as tritium, is a critical issue in FHRs due to the significantly larger production rate and potentially larger leakage rate of tritium compared to those in Light Water Reactors (LWRs). Therefore, this study proposes two mitigation strategies for tritium in FHRs: Double-Wall Heat eXchanger with a Tritium Carrier (DWHX-TC) option and Single-Wall Heat eXchanger with a Tritium Barrier (SWHX-TB) option. For the DWHX-TC option, two tube surface configurations, i.e., plain and fluted tubes, and four tritium carriers, i.e., helium, FLiBe, FLiNaK, and KF-ZrF 4 , are initially considered, among which the best tube configuration and promising tritium carrier are then selected and used for design optimization of the DWHX. For the SWHX-TB option, two cases, tritium barriers with and without cracks, are investigated in this study. In addition, the two mitigation strategies are evaluated by an in-house, one-dimensional, coupled HEat and MAss Transfer (HEMAT) code developed to predict the leakage rate of tritium in nuclear systems. Our analysis shows that (1) a double-wall configuration using fluted tubes as both the inner and outer tubes is better than other double-wall configurations investigated; (2) helium, as a tritium carrier, is superior to other candidates, including FLiBe, FLiNaK, and KF-ZrF 4 ; (3) the leakage rate of tritium (into the atmosphere) is reduced from 3400 Ci/day, taking the Advanced High-Temperature Reactor (AHTR) as a reference, to 4.0 Ci/day for an optimum design of the DWHX-TC option using helium as the tritium carrier and 1.7 Ci/day for an optimum design of the SWHX-TB option using 30-µm thick silicon carbide (SiC) as the tritium barrier (no cracks); and (4) potential cracks in tritium barriers may significantly deteriorate mass transfer performance of the SWHX-TB option. For example, a cracking rate of 0.1% leads to an increase of 694.1% in the leakage rate under the conditions investigated.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Structurally Frustrated Remeika Phases: Tolerance Factor and Non-Kramers’ Ion Effects

Quantum materials that are found on the verge of structural, magnetic, and electronic instabilities are deep reservoirs for exotic phenomena. Our criteria to study the reported Ln 5 Ru 6 Sn 18 (Ln = Gd, Tb) are guided by the tolerance factor for Remeika phases─a class of intermetallic compounds with the general formula A 3 M 4 X 13 (where A = rare-earth element, M = transition metal, and X = tetrel), which can be viewed as structural analogues of pseudoperovskites (4 × ABX 3 ), with one of the tetrel atoms occupying the A-site. We have grown single crystals, up to 0.5 cm on the largest facet, of Gd 5 Ru 6 Sn 18 (a = 13.8052(12) Å) and Tb 5 Ru 6 Sn 18 (a = 13.7825(9) Å), which we expect to be on the verge of a formation instability. Bulk magnetic, heat capacity, and electrical transport measurements reveal unusual behavior that originates from the trivalent Gd and Tb ions, with deviations from typical metallic behavior and magnetic ordering that is short-range or disrupted in some other way. Furthermore, to better understand these phenomena, single-crystal neutron diffraction is investigated, which reveals short-range correlations among the partially occupied Tb and Sn sublattices, with 3D-ΔPDF analysis supporting direction-dependent local order. Taken together, these measurements show the utility of using tolerance factors in identifying materials that are likely to exhibit complex phenomena and uncover environments where a formation instability may strongly impact emergent bulk magnetic and electronic phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Expanding the Transuranic Metal–Organic Framework Portfolio: The Optical Properties of Americium(III) MOF-76

Reported here is the synthesis, crystal structure, and solid-state characterization of a new americium containing metal–organic framework (MOF), [Am(C 9 H 3 O 6 )(H 2 O)], MOF-76(Am). This material is constructed from Am 3+ metal centers and 1,3,5-tricarboxylic acid (BTC) ligands, forming a porous three-dimensional framework that is isostructural with several known trivalent lanthanide (Ln) analogs (e.g., Ce, Nd, and Sm–Lu). The Am 3+ ions have seven coordinates and assume a distorted, capped trigonal prismatic geometry with C1 symmetry. The Am 3+ –O bonds were studied via infrared spectroscopy and compared to several MOF-76(Ln) analogs, where Ln = Nd 3+ , Eu 3+ , Tb 3+ , and Ho 3+ . The results show that the strength of the ligand carboxylate stretching and bending modes increase with Nd 3+ < Eu 3+ < Am 3+ < Tb 3+ < Ho 3+ , suggesting the metal–oxygen bonds are predominantly ionic. Optical absorbance spectroscopy measurements reveal strong f–f transitions; some exhibit pronounced crystal field splitting. The photoluminescence spectrum contains weak Am 3+ -based emission that is achieved through direct and indirect metal center excitation. The weak emissive behavior is somewhat surprising given that ligand-to-metal resonance energy transfer is efficient in the isoelectronic Eu 3+ (4f 6 ) and related Tb 3+ (4f 8 ) analogs. The optical properties were explored further within a series of heterometallic MOF-76(Tb 1–x Am x ) (x = 0.8, 0.2, and 0.1) samples, and the results reveal enhanced Am 3+ photoluminescence.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Strong Ferromagnetic Exchange Coupling and Single-Molecule Magnetism in MoS 4 3– -Bridged Dilanthanide Complexes

We report the synthesis and characterization of the trinuclear 4d-4f compounds [Co(C 5 Me 5 ) 2 ][(C 5 Me 5 ) 2 Ln(μ-S) 2 Mo(μ-S) 2 Ln(C 5 Me 5 ) 2 ], 1-Ln (Ln = Y, Gd, Tb, Dy), containing the highly polarizable MoS 4 3 - bridging unit. UV-Vis-NIR diffuse reflectance spectra and DFT calculations of 1-Ln reveal a low-energy metal-to-metal charge transfer transition assigned to charge transfer from the singly occupied 4d z 2 orbital of Mo V to the empty 5d orbitals of the lanthanides (4d in the case of 1-Y ), mediated by sulfur-based 3p orbitals. Electron paramagnetic resonance spectra collected for 1-Y in a tetrahydrofuran solution show large 89 Y hyperfine coupling constants of A ⊥ = 23 MHz and A || = 26 MHz, indicating the presence of significant yttrium-localized unpaired electron density. Magnetic susceptibility data support similar electron delocalization and ferromagnetic Ln-Mo exchange for 1-Gd , 1-Tb , and 1-Dy . This ferromagnetic exchange gives rise to an S = 15/2 ground state for 1-Gd and one of the largest magnetic exchange constants involving Gd III observed to date, with J Gd-Mo = +16.1(2) cm -1 . Additional characterization of 1-Tb and 1-Dy by ac magnetic susceptibility measurements reveals that both compounds exhibit slow magnetic relaxation. Although a Raman magnetic relaxation process is dominant for both 1-Tb and 1-Dy , an extracted thermal relaxation barrier of U eff = 68 cm -1 for 1-Dy is the largest yet reported for a complex containing a paramagnetic 4d metal center. Furthermore, these results provide a potentially generalizable route to enhanced n d-4f magnetic exchange, revealing opportunities for the design of new n d-4f single-molecule magnets and bulk magnetic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗