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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on V(FeSe2)2 by Materials Project

V(FeSe2)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. V2+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of V–Se bond distances ranging from 2.42–2.77 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Fe–Se bond distances ranging from 2.41–2.88 Å. In the second Fe3+ site, Fe3+ is bonded in a 4-coordinate geometry to four Se2- atoms. There are a spread of Fe–Se bond distances ranging from 2.33–2.43 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to one V2+ and three Fe3+ atoms. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent V2+ and two Fe3+ atoms. In the third Se2- site, Se2- is bonded in a 4-coordinate geometry to one V2+ and three Fe3+ atoms. In the fourth Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent V2+ and two Fe3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V(FeSe2)2 by Materials Project

V(FeSe2)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. V2+ is bonded to six Se2- atoms to form VSe6 octahedra that share corners with twelve equivalent FeSe6 octahedra, edges with two equivalent VSe6 octahedra, and faces with two equivalent FeSe6 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are two shorter (2.53 Å) and four longer (2.54 Å) V–Se bond lengths. Fe3+ is bonded to six Se2- atoms to form distorted FeSe6 octahedra that share corners with six equivalent VSe6 octahedra, edges with six equivalent FeSe6 octahedra, and a faceface with one VSe6 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are a spread of Fe–Se bond distances ranging from 2.41–2.79 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to one V2+ and three equivalent Fe3+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent V2+ and three equivalent Fe3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V(FeSe2)2 by Materials Project

V(FeSe2)2 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. V2+ is bonded to six Se2- atoms to form distorted VSe6 octahedra that share corners with six equivalent FeSe6 octahedra, edges with two equivalent VSe6 octahedra, edges with four equivalent FeSe6 octahedra, and a faceface with one FeSe6 octahedra. The corner-sharing octahedra tilt angles range from 52–57°. There are a spread of V–Se bond distances ranging from 2.39–2.75 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six Se2- atoms to form FeSe6 octahedra that share corners with six equivalent VSe6 octahedra, corners with six equivalent FeSe6 octahedra, edges with two equivalent FeSe6 octahedra, a faceface with one VSe6 octahedra, and a faceface with one FeSe6 octahedra. The corner-sharing octahedra tilt angles range from 51–57°. There are a spread of Fe–Se bond distances ranging from 2.43–2.53 Å. In the second Fe3+ site, Fe3+ is bonded to six Se2- atoms to form distorted FeSe6 octahedra that share corners with six equivalent FeSe6 octahedra, edges with two equivalent FeSe6 octahedra, edges with four equivalent VSe6 octahedra, and a faceface with one FeSe6 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are a spread of Fe–Se bond distances ranging from 2.38–2.70 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to one V2+ and four Fe3+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent V2+ and three Fe3+ atoms. In the third Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent V2+ and two Fe3+ atoms. In the fourth Se2- site, Se2- is bonded in a 4-coordinate geometry to one V2+ and three Fe3+ atoms.

36 MATERIALS SCIENCE↗
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)↗