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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Two-Dimensional Tantalum Carbo-Selenide for Hydrogen Evolution

Herein, we report the synthesis of two-dimensional Ta 2 Se 2 C (2D-Ta 2 Se 2 C) nanosheets using electrochemical lithiation in multilayer Ta 2 Se 2 C followed by sonication in deionized water. Multilayer Ta 2 Se 2 C was obtained via solid-state synthesis of Fe x Ta 2 Se 2 C followed by chemical etching of Fe. 2D-Ta 2 Se 2 C exhibited promising electrocatalytic activity for the hydrogen evolution reaction from water compared to multilayer Ta 2 Se 2 C and 2D-TaSe 2 . 2D-Ta 2 Se 2 C showed an overpotential at 10 mA·cm -2 (η 10 ) of 264 mV, a Tafel slope of 91 mV·dec -1 , and an electrochemically active surface area of 17.61 m ECSA 2 ·g catalyst -1 . The high performance could be attributed to the large surface area of single sheets which hence maximizes the number of exposed catalytic sites and increased density of vacancies, observed with transmission electron microscopy, during synthesis and processing.

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

Selenium infiltrated hierarchical hollow carbon spheres display rapid kinetics and extended cycling as lithium metal battery (LMB) cathodes

Lithium metal–selenium (Li–Se) batteries offer high volumetric energy but are limited in their cycling life and fast charge characteristics. Here a facile approach is demonstrated to synthesize hierarchically porous hollow carbon spheres that host Se (Se@HHCS) and allow for state-of-the-art electrochemical performance in a standard carbonate electrolyte (1 M LiPF 6 in 1:1 EC:DEC). The Se@HHCS electrodes display among the most favorable fast charge and cycling behavior reported. For example, they deliver specific capacities of 442 and 357 mA h g -1 after 1500 and 2000 cycles at 5C and 10C, respectively. At 2C, Se@HHCS delivers 558 mA h g -1 after 500 cycles, with cycling coulombic efficiency of 99.9%. Post-mortem microstructural analysis indicates that the structures remain intact during extended cycling. Per GITT analysis, Se@HHCS possesses significantly higher diffusion coefficients in both lithiation and delithiation processes as compared to the baseline. Furthermore, the superior performance of Se@HHCS is directly linked to its macroscopic and nanoscale pore structure: the hollow carbon sphere morphology as well as the remnant open nanoporosity accommodates the 69% volume expansion of the Li to Li 2 Se transformation, with the nanopores also providing a complementary fast ion diffusion path.

25 ENERGY STORAGE↗
DOE OSTI2023

Nanoscale heterogeneity of arsenic and selenium species in coal fly ash particles: analysis using enhanced spectroscopic imaging and speciation techniques

Coal combustion byproducts are known to be enriched in arsenic (As) and selenium (Se). This enrichment is a concern during the handling, disposal, and reuse of the ash as both elements can be harmful to wildlife and humans if mobilized into water and soils. The leaching potential and bioaccessibility of As and Se in coal fly ash depends on the chemical forms of these elements and their association with the large variety of particles that comprise coal fly ash. The overall goal of this research was to determine nanoscale and microscale solid phase mineral associations and oxidation states of As and Se in fly ash. We utilized nanoscale 2D imaging (30–50 nm spot size) with the Hard X-ray Nanoprobe (HXN) in combination with microprobe X-ray capabilities (~5 μm resolution) to determine the As and Se elemental associations. Speciation of As and Se was also measured at the nano- to microscale with X-ray absorption spectroscopy. The enhanced resolution of HXN showed As and Se as either diffusely located around or comingled with Ca- and Fe-rich particles. The results also showed nanoparticles of Se attached to the surface of fly ash grains. Overall, a comparison of As and Se species across scales highlights the heterogeneity and complexity of chemical associations for these trace elements of concern in coal fly ash.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2023

Targeted synthesis of predicted metastable compounds using modulated elemental reactants

Three metastable compounds predicted to be kinetically stable using an “island” approach were successfully synthesized from designed modulated elemental reactants. Fe0.8V0.2Se2 was synthesized by depositing ultrathin elemental layers in a V|Fe|Se sequence to control the local composition. An alloyed rock salt structured Pb3Mn2Se5 constituent layer, which does not exist as a bulk compound, was synthesized in the heterostructure (Pb3Mn2Se5)0.6VSe2 by depositing a precursor with a V|Se|Pb|Se|Mn|Se|Pb|Se|Mn|Se|Pb|Se sequence of elemental layers that mimicked the compositional profile of the targeted heterostructure. The heterostructure (PbSe)1+δ(FeSe2)2 was prepared by depositing a precursor with a repeating layering sequence of Fe|Pb|Fe|Se, where each sequence contains the number of atoms required to form a single unit cell. In all three systems, the local compositions in the layer sequence kinetically favored the nucleation and growth of the targeted products during the deposition. The diffusion lengths to form the targeted compounds were short, and the diffusion was limited by postdeposition low temperature annealing to favor the growth of the targeted compounds and avoid the decomposition into a mixture of thermodynamically stable compounds.

Lemon, Mellie (ORCID:0000000328705881)↗
DOE OSTI2020

Production and characterization of extracellular cellulases from a native strain of Trichoderma harzianum using wheat straw from the Mexicali valley as the carbon source. Producción y caracterización de celulasas Extracelulares a partir de cepa nativa de Trichoderma harzianum usando como fuente de Carbono paja de trigo del valle de Mexicali

The purpose of this study was to produce cellulase enzyme from a native strain Trichoderma harzianum, isolated from crop soil. Cellulase production was carried out by two different methods of fermentation, submerging and solid state fermentation. Mandels mineral medium was used as a source of nitrogen and ammonium sulfate. Dry and ground wheat straw was used in fermentation as a carbon source. Cellulase activity was determined using the 3,5-dinitrosalicylic acid (DNS) method. The results showed that wheat straw has the potential to be used as a substrate in the production of cellulases. Trichoderma harzianum showed enzymatic activity of 0.125 FPU / ml (filter paper units) and 1. 35 U / ml CMC (carboxymethyl cellulose units) by solid state fermentation (FSS) after 96 hours of fermentation. The optimum pH for the two substrates was determined by testing with citrate buffers (pH 4 to 6), phosphates (pH 6 to 7) and tris-HCL (pH 8 to 9). To determine the optimum temperature the range of 30 ° C to 80 ° C was investigated. Storage tests were performed every seven days over a period of 6 weeks. The optimum activity pH on paper and CMC was found to be 6. The optimum activity temperature is 70 ° C for PF and 80 ° C for CMC. El propósito de este estudio fue producir enzima celulasa a partir de una cepa nativa Trichoderma harzianum, aislada de suelo de cultivo. La producción de celulasa se realizó por dos métodos diferentes de fermentación, sumergida y fermentación en estado sólido. Se utilizó medio mineral Mandels y como fuentes de nitrógeno urea y sulfato de amonio. Se utilizó paja de trigo seca y molida en las fermentaciones como fuente de carbono. La actividad de la celulasa se determinó por medición de azúcares reductores al papel filtro y a la carboximetilcelulosa usando el método del ácido 3,5- dinitrosalicílico (DNS). Los resultados mostraron que la paja de trigo tiene el potencial para usarse como sustrato en la producción de celulasas. Trichoderma harzianum mostró actividad enzimática de 0.125 FPU/ml (unidades de papel filtro) y 1.35 U/ml a la CMC (unidades de carboximetilcelulosa) por fermentación en estado sólido (FSS) después de 96 horas de fermentación. El pH óptimo para los dos sustratos se determinó realizando pruebas con buffers de citratos (pH 4 a 6), de fosfatos (pH 6 a 7) y tris- HCL (pH 8 a 9). Para la determinación de la temperatura óptima se manejó el rango de 30°C a 80°C. Las pruebas de almacenamiento se realizaron cada siete días en un periodo de 6 semanas. Se encontró que el pH óptimo de actividad en papel y CMC es de 6. La temperatura óptima de actividad es de 70°C para PF y de 80°C para CMC.

09 BIOMASS FUELS↗
DOE OSTI2020

Materials Data on K2Ga3CuSe6 by Materials Project

K2CuGa3Se6 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of K–Se bond distances ranging from 3.38–3.74 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of K–Se bond distances ranging from 3.39–3.74 Å. Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with eight GaSe4 tetrahedra. There are two shorter (2.44 Å) and two longer (2.46 Å) Cu–Se bond lengths. There are four inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to four Se2- atoms to form GaSe4 tetrahedra that share corners with two equivalent CuSe4 tetrahedra and corners with four GaSe4 tetrahedra. There are two shorter (2.44 Å) and two longer (2.47 Å) Ga–Se bond lengths. In the second Ga3+ site, Ga3+ is bonded to four Se2- atoms to form GaSe4 tetrahedra that share corners with two equivalent CuSe4 tetrahedra and corners with four GaSe4 tetrahedra. There are a spread of Ga–Se bond distances ranging from 2.43–2.47 Å. In the third Ga3+ site, Ga3+ is bonded to four Se2- atoms to form GaSe4 tetrahedra that share corners with four equivalent CuSe4 tetrahedra and corners with four GaSe4 tetrahedra. There are two shorter (2.44 Å) and two longer (2.46 Å) Ga–Se bond lengths. In the fourth Ga3+ site, Ga3+ is bonded to four Se2- atoms to form GaSe4 tetrahedra that share corners with four equivalent CuSe4 tetrahedra and corners with four GaSe4 tetrahedra. There are two shorter (2.44 Å) and two longer (2.46 Å) Ga–Se bond lengths. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to two K1+, one Cu1+, and two Ga3+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to two K1+, one Cu1+, and two Ga3+ atoms. In the third Se2- site, Se2- is bonded in a 5-coordinate geometry to three K1+ and two Ga3+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to two K1+, one Cu1+, and two Ga3+ atoms. In the fifth Se2- site, Se2- is bonded in a 5-coordinate geometry to three K1+ and two Ga3+ atoms. In the sixth Se2- site, Se2- is bonded in a 3-coordinate geometry to two K1+, one Cu1+, and two Ga3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KPt2Se3 by Materials Project

KPt2Se3 crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three KPt2Se3 sheets oriented in the (0, 0, 1) direction. K1+ is bonded in a 9-coordinate geometry to three equivalent Se+1.67- atoms. All K–Se bond lengths are 3.51 Å. There are two inequivalent Pt2+ sites. In the first Pt2+ site, Pt2+ is bonded in an octahedral geometry to six equivalent Se+1.67- atoms. All Pt–Se bond lengths are 2.55 Å. In the second Pt2+ site, Pt2+ is bonded in a square co-planar geometry to four equivalent Se+1.67- atoms. All Pt–Se bond lengths are 2.48 Å. Se+1.67- is bonded to one K1+ and three Pt2+ atoms to form a mixture of distorted corner and edge-sharing SeKPt3 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbPt2Se3 by Materials Project

RbPt2Se3 crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three RbPt2Se3 sheets oriented in the (0, 0, 1) direction. Rb1+ is bonded in a 9-coordinate geometry to three equivalent Se+1.67- atoms. All Rb–Se bond lengths are 3.66 Å. There are two inequivalent Pt2+ sites. In the first Pt2+ site, Pt2+ is bonded in an octahedral geometry to six equivalent Se+1.67- atoms. All Pt–Se bond lengths are 2.55 Å. In the second Pt2+ site, Pt2+ is bonded in a square co-planar geometry to four equivalent Se+1.67- atoms. All Pt–Se bond lengths are 2.48 Å. Se+1.67- is bonded in a 4-coordinate geometry to one Rb1+ and three Pt2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rb9Fe2Se7 by Materials Project

Rb9Fe2Se7 crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are five inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of Rb–Se bond distances ranging from 3.64–3.70 Å. In the second Rb1+ site, Rb1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are three shorter (3.52 Å) and three longer (3.64 Å) Rb–Se bond lengths. In the third Rb1+ site, Rb1+ is bonded to six Se2- atoms to form distorted RbSe6 octahedra that share corners with three equivalent RbSe5 square pyramids, corners with three equivalent FeSe4 tetrahedra, and faces with three equivalent RbSe5 square pyramids. There are three shorter (3.51 Å) and three longer (3.77 Å) Rb–Se bond lengths. In the fourth Rb1+ site, Rb1+ is bonded in a distorted T-shaped geometry to three equivalent Se2- atoms. All Rb–Se bond lengths are 3.47 Å. In the fifth Rb1+ site, Rb1+ is bonded to five Se2- atoms to form distorted RbSe5 square pyramids that share a cornercorner with one RbSe6 octahedra, corners with six equivalent RbSe5 square pyramids, a cornercorner with one FeSe4 tetrahedra, an edgeedge with one FeSe4 tetrahedra, and a faceface with one RbSe6 octahedra. The corner-sharing octahedral tilt angles are 40°. There are a spread of Rb–Se bond distances ranging from 3.31–3.53 Å. There are two inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded in a trigonal planar geometry to three equivalent Se2- atoms. All Fe–Se bond lengths are 2.37 Å. In the second Fe+2.50+ site, Fe+2.50+ is bonded to four Se2- atoms to form FeSe4 tetrahedra that share corners with three equivalent RbSe6 octahedra, corners with three equivalent RbSe5 square pyramids, and edges with three equivalent RbSe5 square pyramids. The corner-sharing octahedral tilt angles are 44°. There are three shorter (2.45 Å) and one longer (2.50 Å) Fe–Se bond lengths. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 7-coordinate geometry to six Rb1+ and one Fe+2.50+ atom. In the second Se2- site, Se2- is bonded in a 1-coordinate geometry to seven Rb1+ and one Fe+2.50+ atom. In the third Se2- site, Se2- is bonded in a 1-coordinate geometry to six Rb1+ and one Fe+2.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HfSe3 by Materials Project

HfSe3 crystallizes in the monoclinic P2_1/m space group. The structure is two-dimensional and consists of one HfSe3 sheet oriented in the (0, 0, 1) direction. Hf4+ is bonded in a 8-coordinate geometry to eight Se+1.33- atoms. There are a spread of Hf–Se bond distances ranging from 2.73–2.90 Å. There are two inequivalent Se+1.33- sites. In the first Se+1.33- site, Se+1.33- is bonded in a distorted L-shaped geometry to two equivalent Hf4+ atoms. In the second Se+1.33- site, Se+1.33- is bonded to four equivalent Hf4+ atoms to form a mixture of distorted edge and corner-sharing SeHf4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2In3AgSe6 by Materials Project

K2AgIn3Se6 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to seven Se2- atoms to form distorted KSe7 pentagonal bipyramids that share corners with two equivalent KSe7 pentagonal bipyramids, corners with two equivalent AgSe4 tetrahedra, corners with six InSe4 tetrahedra, an edgeedge with one KSe7 pentagonal bipyramid, an edgeedge with one AgSe4 tetrahedra, edges with four InSe4 tetrahedra, and faces with two equivalent KSe7 pentagonal bipyramids. There are a spread of K–Se bond distances ranging from 3.41–3.77 Å. In the second K1+ site, K1+ is bonded to seven Se2- atoms to form distorted KSe7 pentagonal bipyramids that share corners with two equivalent KSe7 pentagonal bipyramids, corners with two equivalent AgSe4 tetrahedra, corners with six InSe4 tetrahedra, an edgeedge with one KSe7 pentagonal bipyramid, an edgeedge with one AgSe4 tetrahedra, edges with four InSe4 tetrahedra, and faces with two equivalent KSe7 pentagonal bipyramids. There are a spread of K–Se bond distances ranging from 3.40–3.77 Å. There are two inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to four Se2- atoms to form AgSe4 tetrahedra that share corners with four equivalent KSe7 pentagonal bipyramids, corners with eight InSe4 tetrahedra, and edges with two equivalent KSe7 pentagonal bipyramids. There are two shorter (2.68 Å) and two longer (2.71 Å) Ag–Se bond lengths. In the second Ag1+ site, Ag1+ is bonded to four Se2- atoms to form AgSe4 tetrahedra that share corners with four equivalent KSe7 pentagonal bipyramids, corners with eight InSe4 tetrahedra, and edges with two equivalent KSe7 pentagonal bipyramids. There are two shorter (2.69 Å) and two longer (2.71 Å) Ag–Se bond lengths. There are three inequivalent In3+ sites. In the first In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with four KSe7 pentagonal bipyramids, corners with two AgSe4 tetrahedra, corners with four InSe4 tetrahedra, and edges with three KSe7 pentagonal bipyramids. There are two shorter (2.63 Å) and two longer (2.64 Å) In–Se bond lengths. In the second In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with four KSe7 pentagonal bipyramids, corners with two AgSe4 tetrahedra, corners with four InSe4 tetrahedra, and edges with three KSe7 pentagonal bipyramids. There are two shorter (2.63 Å) and two longer (2.64 Å) In–Se bond lengths. In the third In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with four KSe7 pentagonal bipyramids, corners with four AgSe4 tetrahedra, corners with four InSe4 tetrahedra, and edges with two KSe7 pentagonal bipyramids. There are two shorter (2.61 Å) and two longer (2.63 Å) In–Se bond lengths. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Ag1+, and two In3+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Ag1+, and two In3+ atoms. In the third Se2- site, Se2- is bonded in a 5-coordinate geometry to three K1+ and two In3+ atoms. In the fourth Se2- site, Se2- is bonded in a 5-coordinate geometry to three K1+ and two In3+ atoms. In the fifth Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Ag1+, and two In3+ atoms. In the sixth Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Ag1+, and two In3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2In3CuSe6 by Materials Project

K2CuIn3Se6 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of K–Se bond distances ranging from 3.36–3.54 Å. In the second K1+ site, K1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of K–Se bond distances ranging from 3.36–3.53 Å. Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with eight InSe4 tetrahedra. There are two shorter (2.46 Å) and two longer (2.48 Å) Cu–Se bond lengths. There are four inequivalent In3+ sites. In the first In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with two equivalent CuSe4 tetrahedra and corners with four InSe4 tetrahedra. All In–Se bond lengths are 2.62 Å. In the second In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with two equivalent CuSe4 tetrahedra and corners with four InSe4 tetrahedra. There are two shorter (2.62 Å) and two longer (2.63 Å) In–Se bond lengths. In the third In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with four equivalent CuSe4 tetrahedra and corners with four InSe4 tetrahedra. There are two shorter (2.63 Å) and two longer (2.65 Å) In–Se bond lengths. In the fourth In3+ site, In3+ is bonded to four Se2- atoms to form InSe4 tetrahedra that share corners with four equivalent CuSe4 tetrahedra and corners with four InSe4 tetrahedra. There are two shorter (2.63 Å) and two longer (2.65 Å) In–Se bond lengths. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Cu1+, and two In3+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Cu1+, and two In3+ atoms. In the third Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to two K1+ and two In3+ atoms. In the fourth Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Cu1+, and two In3+ atoms. In the fifth Se2- site, Se2- is bonded in a 5-coordinate geometry to two K1+, one Cu1+, and two In3+ atoms. In the sixth Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to two K1+ and two In3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K9Fe2Se7 by Materials Project

K9Fe2Se7 crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are five inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to five Se2- atoms to form distorted KSe5 trigonal bipyramids that share a cornercorner with one KSe6 octahedra, a cornercorner with one FeSe4 tetrahedra, corners with six equivalent KSe5 trigonal bipyramids, an edgeedge with one FeSe4 tetrahedra, and a faceface with one KSe6 octahedra. The corner-sharing octahedral tilt angles are 38°. There are a spread of K–Se bond distances ranging from 3.19–3.43 Å. In the second K1+ site, K1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are three shorter (3.36 Å) and three longer (3.53 Å) K–Se bond lengths. In the third K1+ site, K1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of K–Se bond distances ranging from 3.45–3.57 Å. In the fourth K1+ site, K1+ is bonded in a distorted T-shaped geometry to three equivalent Se2- atoms. All K–Se bond lengths are 3.31 Å. In the fifth K1+ site, K1+ is bonded to six Se2- atoms to form distorted KSe6 octahedra that share corners with three equivalent FeSe4 tetrahedra, corners with three equivalent KSe5 trigonal bipyramids, and faces with three equivalent KSe5 trigonal bipyramids. There are three shorter (3.35 Å) and three longer (3.55 Å) K–Se bond lengths. There are two inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded in a trigonal planar geometry to three equivalent Se2- atoms. All Fe–Se bond lengths are 2.36 Å. In the second Fe+2.50+ site, Fe+2.50+ is bonded to four Se2- atoms to form FeSe4 tetrahedra that share corners with three equivalent KSe6 octahedra, corners with three equivalent KSe5 trigonal bipyramids, and edges with three equivalent KSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 45°. There are three shorter (2.43 Å) and one longer (2.49 Å) Fe–Se bond lengths. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 7-coordinate geometry to six K1+ and one Fe+2.50+ atom. In the second Se2- site, Se2- is bonded in a 1-coordinate geometry to seven K1+ and one Fe+2.50+ atom. In the third Se2- site, Se2- is bonded in a 1-coordinate geometry to six K1+ and one Fe+2.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb(SeCl)2 by Materials Project

NbSe2Cl2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one NbSe2Cl2 sheet oriented in the (0, 0, 1) direction. Nb5+ is bonded in a 8-coordinate geometry to four Se+1.50- and four Cl1- atoms. There are two shorter (2.64 Å) and two longer (2.66 Å) Nb–Se bond lengths. There are a spread of Nb–Cl bond distances ranging from 2.61–2.65 Å. There are two inequivalent Se+1.50- sites. In the first Se+1.50- site, Se+1.50- is bonded in a 9-coordinate geometry to two equivalent Nb5+ atoms. In the second Se+1.50- site, Se+1.50- is bonded in a 10-coordinate geometry to two equivalent Nb5+ atoms. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted water-like geometry to two equivalent Nb5+ atoms. In the second Cl1- site, Cl1- is bonded in a distorted water-like geometry to two equivalent Nb5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na4GeSe4 by Materials Project

Na4GeSe4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are five inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six Se2- atoms to form distorted NaSe6 octahedra that share corners with four GeSe4 tetrahedra, corners with two equivalent NaSe4 trigonal pyramids, edges with six NaSe5 square pyramids, an edgeedge with one GeSe4 tetrahedra, and edges with two equivalent NaSe4 trigonal pyramids. There are a spread of Na–Se bond distances ranging from 3.02–3.23 Å. In the second Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 square pyramids that share corners with four equivalent NaSe5 square pyramids, corners with three equivalent GeSe4 tetrahedra, corners with two equivalent NaSe4 trigonal pyramids, edges with two equivalent NaSe6 octahedra, an edgeedge with one GeSe4 tetrahedra, and edges with two equivalent NaSe4 trigonal pyramids. There are three shorter (2.99 Å) and two longer (3.25 Å) Na–Se bond lengths. In the third Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of Na–Se bond distances ranging from 2.93–3.36 Å. In the fourth Na1+ site, Na1+ is bonded to four Se2- atoms to form distorted NaSe4 trigonal pyramids that share a cornercorner with one NaSe6 octahedra, corners with five NaSe5 square pyramids, corners with two equivalent GeSe4 tetrahedra, corners with two equivalent NaSe4 trigonal pyramids, an edgeedge with one NaSe6 octahedra, an edgeedge with one NaSe5 square pyramid, an edgeedge with one GeSe4 tetrahedra, and an edgeedge with one NaSe4 trigonal pyramid. The corner-sharing octahedral tilt angles are 24°. There are a spread of Na–Se bond distances ranging from 2.91–2.97 Å. In the fifth Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 square pyramids that share corners with three NaSe5 square pyramids, a cornercorner with one GeSe4 tetrahedra, corners with four equivalent NaSe4 trigonal pyramids, edges with two equivalent NaSe6 octahedra, an edgeedge with one NaSe5 square pyramid, and edges with two GeSe4 tetrahedra. There are a spread of Na–Se bond distances ranging from 2.94–3.43 Å. There are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to four Se2- atoms to form GeSe4 tetrahedra that share corners with three equivalent NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, and edges with three NaSe5 square pyramids. The corner-sharing octahedra tilt angles range from 9–66°. There are a spread of Ge–Se bond distances ranging from 2.38–2.41 Å. In the second Ge4+ site, Ge4+ is bonded to four Se2- atoms to form GeSe4 tetrahedra that share a cornercorner with one NaSe6 octahedra, corners with three equivalent NaSe5 square pyramids, corners with four equivalent NaSe4 trigonal pyramids, an edgeedge with one NaSe6 octahedra, edges with two equivalent NaSe5 square pyramids, and edges with two equivalent NaSe4 trigonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ge–Se bond distances ranging from 2.38–2.40 Å. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Na1+ and one Ge4+ atom to form distorted SeNa5Ge octahedra that share corners with five SeNa5Ge octahedra, a cornercorner with one SeNa4Ge trigonal bipyramid, and edges with five SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 17–59°. In the second Se2- site, Se2- is bonded in a 8-coordinate geometry to seven Na1+ and one Ge4+ atom. In the third Se2- site, Se2- is bonded to four Na1+ and one Ge4+ atom to form a mixture of distorted edge and corner-sharing SeNa4Ge trigonal bipyramids. The corner-sharing octahedra tilt angles range from 12–81°. In the fourth Se2- site, Se2- is bonded to five Na1+ and one Ge4+ atom to form distorted SeNa5Ge octahedra that share corners with six SeNa5Ge octahedra, corners with two equivalent SeNa4Ge trigonal bipyramids, edges with three SeNa5Ge octahedra, and an edgeedge with one SeNa4Ge trigonal bipyramid. The corner-sharing octahedra tilt angles range from 17–57°. In the fifth Se2- site, Se2- is bonded in a distorted see-saw-like geometry to three Na1+ and one Ge4+ atom. In the sixth Se2- site, Se2- is bonded to five Na1+ and one Ge4+ atom to form SeNa5Ge octahedra that share corners with two equivalent SeNa5Ge octahedra, corners with two equivalent SeNa4Ge trigonal bipyramids, and edges with six SeNa5Ge octahedra. The corner-sharing octahedral tilt angles are 29°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na4Ge2Se5 by Materials Project

Na4Ge2Se5 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are five inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 5–13°. There are a spread of Na–Se bond distances ranging from 3.06–3.21 Å. In the second Na1+ site, Na1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 4–13°. There are a spread of Na–Se bond distances ranging from 3.00–3.27 Å. In the third Na1+ site, Na1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 3–9°. There are a spread of Na–Se bond distances ranging from 3.04–3.21 Å. In the fourth Na1+ site, Na1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 3–4°. There are four shorter (3.12 Å) and two longer (3.16 Å) Na–Se bond lengths. In the fifth Na1+ site, Na1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 3–8°. There are a spread of Na–Se bond distances ranging from 2.96–3.26 Å. There are two inequivalent Ge3+ sites. In the first Ge3+ site, Ge3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are two shorter (2.36 Å) and one longer (2.49 Å) Ge–Se bond lengths. In the second Ge3+ site, Ge3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are two shorter (2.36 Å) and one longer (2.48 Å) Ge–Se bond lengths. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Na1+ and one Ge3+ atom to form a mixture of edge and corner-sharing SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 0–89°. In the second Se2- site, Se2- is bonded to four Na1+ and two Ge3+ atoms to form a mixture of distorted edge and corner-sharing SeNa4Ge2 octahedra. The corner-sharing octahedra tilt angles range from 0–86°. In the third Se2- site, Se2- is bonded to five Na1+ and one Ge3+ atom to form a mixture of edge and corner-sharing SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 0–89°. In the fourth Se2- site, Se2- is bonded to five Na1+ and one Ge3+ atom to form a mixture of edge and corner-sharing SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 0–87°. In the fifth Se2- site, Se2- is bonded to five Na1+ and one Ge3+ atom to form a mixture of distorted edge and corner-sharing SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 0–87°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na4Cd3Se5 by Materials Project

Na4Cd3Se5 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 trigonal bipyramids that share corners with two equivalent NaSe6 octahedra, corners with three equivalent NaSe5 square pyramids, corners with six CdSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, edges with two equivalent CdSe4 tetrahedra, edges with four NaSe5 trigonal bipyramids, and a faceface with one NaSe6 octahedra. The corner-sharing octahedral tilt angles are 58°. There are a spread of Na–Se bond distances ranging from 2.97–3.17 Å. In the second Na1+ site, Na1+ is bonded to six Se2- atoms to form NaSe6 octahedra that share corners with three equivalent NaSe5 square pyramids, corners with five CdSe4 tetrahedra, corners with four NaSe5 trigonal bipyramids, edges with four equivalent NaSe6 octahedra, edges with five CdSe4 tetrahedra, an edgeedge with one NaSe5 trigonal bipyramid, and a faceface with one NaSe5 trigonal bipyramid. There are a spread of Na–Se bond distances ranging from 3.04–3.49 Å. In the third Na1+ site, Na1+ is bonded to five Se2- atoms to form NaSe5 square pyramids that share corners with three equivalent NaSe6 octahedra, corners with four CdSe4 tetrahedra, corners with five NaSe5 trigonal bipyramids, edges with four equivalent NaSe5 square pyramids, and edges with four CdSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 40–53°. There are a spread of Na–Se bond distances ranging from 3.11–3.19 Å. In the fourth Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 trigonal bipyramids that share corners with two equivalent NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, corners with three CdSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, an edgeedge with one NaSe6 octahedra, edges with four CdSe4 tetrahedra, and edges with four NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 33°. There are a spread of Na–Se bond distances ranging from 2.88–3.12 Å. There are three inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to four Se2- atoms to form CdSe4 tetrahedra that share corners with two equivalent NaSe6 octahedra, corners with six CdSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, edges with three equivalent NaSe6 octahedra, and edges with two equivalent NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 13°. There are a spread of Cd–Se bond distances ranging from 2.67–2.77 Å. In the second Cd2+ site, Cd2+ is bonded to four Se2- atoms to form CdSe4 tetrahedra that share corners with two equivalent NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, corners with six CdSe4 tetrahedra, corners with two equivalent NaSe5 trigonal bipyramids, an edgeedge with one NaSe5 square pyramid, and edges with four NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. There are a spread of Cd–Se bond distances ranging from 2.65–2.77 Å. In the third Cd2+ site, Cd2+ is bonded to four Se2- atoms to form CdSe4 tetrahedra that share a cornercorner with one NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, corners with six CdSe4 tetrahedra, corners with three NaSe5 trigonal bipyramids, edges with two equivalent NaSe6 octahedra, and edges with three equivalent NaSe5 square pyramids. The corner-sharing octahedral tilt angles are 9°. There are a spread of Cd–Se bond distances ranging from 2.69–2.71 Å. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 7-coordinate geometry to five Na1+ and two equivalent Cd2+ atoms. In the second Se2- site, Se2- is bonded in a 8-coordinate geometry to six Na1+ and two Cd2+ atoms. In the third Se2- site, Se2- is bonded to three equivalent Na1+ and three Cd2+ atoms to form SeNa3Cd3 octahedra that share a cornercorner with one SeNa3Cd3 octahedra, corners with two equivalent SeNa4Cd2 pentagonal pyramids, and edges with four equivalent SeNa3Cd3 octahedra. The corner-sharing octahedral tilt angles are 70°. In the fourth Se2- site, Se2- is bonded to three Na1+ and three Cd2+ atoms to form SeNa3Cd3 octahedra that share a cornercorner with one SeNa3Cd3 octahedra, corners with four equivalent SeNa4Cd2 pentagonal pyramids, and edges with two equivalent SeNa3Cd3 octahedra. The corner-sharing octahedral tilt angles are 70°. In the fifth Se2- site, Se2- is bonded to four Na1+ and two Cd2+ atoms to form distorted SeNa4Cd2 pentagonal pyramids that share corners with six SeNa3Cd3 octahedra and edges with two equivalent SeNa4Cd2 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 61–74°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3(BiSe)2 by Materials Project

Ni3Bi2Se2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Ni sites. In the first Ni site, Ni is bonded in a distorted linear geometry to four Bi and two equivalent Se atoms. There are two shorter (2.77 Å) and two longer (2.86 Å) Ni–Bi bond lengths. Both Ni–Se bond lengths are 2.31 Å. In the second Ni site, Ni is bonded in a distorted linear geometry to four Bi and two equivalent Se atoms. There are a spread of Ni–Bi bond distances ranging from 2.77–2.90 Å. Both Ni–Se bond lengths are 2.31 Å. In the third Ni site, Ni is bonded in a distorted linear geometry to four Bi and two equivalent Se atoms. There are two shorter (2.80 Å) and two longer (2.85 Å) Ni–Bi bond lengths. Both Ni–Se bond lengths are 2.31 Å. There are two inequivalent Bi sites. In the first Bi site, Bi is bonded in a 6-coordinate geometry to six Ni atoms. In the second Bi site, Bi is bonded in a 6-coordinate geometry to six Ni atoms. Se is bonded in a 3-coordinate geometry to three Ni atoms.

36 MATERIALS SCIENCE↗