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9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Angle-Resolved Polarized Raman Study of Layered Cr 2 Se 3

The polarization-resolved Raman spectra of two-dimensional Cr 2 Se 3 synthesized via chemical vapor deposition (CVD) and chemical vapor transport (CVT) techniques were investigated in detail. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). A distinct polarization dependence was observed in the Raman intensity of all the Cr-Cr, Cr-Se, and Se-Se modes in both samples. The observed angle-dependent Raman intensities of each peak could be related to the crystal structure-specific Raman tensor. XRD results of the bulk Cr 2 Se 3 sample synthesized via CVT confirm its trigonal crystal structure, and the Raman peaks can be fitted using the Raman tensors for the A g and E g modes for both the parallel and crossed polarizations. However, for the Cr 2 Se 3 samples directly grown on Si/SiO 2 substrates by CVD, it was necessary to assume the triclinic crystal structure in order to explain the polarized Raman dependence of all the peaks in both parallel and crossed polarization directions. Furthermore, this is the first experimental result suggesting the existence of triclinic Cr 2 Se 3 crystal structure, which has been theoretically predicted in the Materials Project database.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrSe by Materials Project

CrSe is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Cr2+ is bonded to six equivalent Se2- atoms to form a mixture of edge, corner, and face-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles are 48°. All Cr–Se bond lengths are 2.67 Å. Se2- is bonded in a 6-coordinate geometry to six equivalent Cr2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr3Se4 by Materials Project

Cr3Se4 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Cr+2.67+ sites. In the first Cr+2.67+ site, Cr+2.67+ is bonded to six Se2- atoms to form a mixture of corner, edge, and face-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 48–52°. There are two shorter (2.60 Å) and four longer (2.62 Å) Cr–Se bond lengths. In the second Cr+2.67+ site, Cr+2.67+ is bonded to six Se2- atoms to form a mixture of corner, edge, and face-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 48–52°. There are a spread of Cr–Se bond distances ranging from 2.51–2.66 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Cr+2.67+ atoms to form a mixture of distorted corner and edge-sharing SeCr5 trigonal bipyramids. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Cr+2.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr2Se3 by Materials Project

Cr2Se3 is Corundum-like structured and crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are three inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to six equivalent Se2- atoms to form a mixture of edge and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles are 45°. All Cr–Se bond lengths are 2.54 Å. In the second Cr3+ site, Cr3+ is bonded to six equivalent Se2- atoms to form a mixture of face and corner-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 45–50°. All Cr–Se bond lengths are 2.56 Å. In the third Cr3+ site, Cr3+ is bonded to six equivalent Se2- atoms to form a mixture of face, edge, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are three shorter (2.52 Å) and three longer (2.57 Å) Cr–Se bond lengths. Se2- is bonded in a rectangular see-saw-like geometry to four Cr3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrSe by Materials Project

CrSe is Vulcanite structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one CrSe sheet oriented in the (0, 0, 1) direction. Cr2+ is bonded in a 4-coordinate geometry to four equivalent Se2- atoms. All Cr–Se bond lengths are 2.44 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Cr2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr7Se8 by Materials Project

Cr7Se8 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are four inequivalent Cr+2.29+ sites. In the first Cr+2.29+ site, Cr+2.29+ is bonded to six Se2- atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 49–51°. There are two shorter (2.65 Å) and four longer (2.66 Å) Cr–Se bond lengths. In the second Cr+2.29+ site, Cr+2.29+ is bonded to six Se2- atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 47–50°. There are a spread of Cr–Se bond distances ranging from 2.60–2.69 Å. In the third Cr+2.29+ site, Cr+2.29+ is bonded to six Se2- atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 48–51°. There are a spread of Cr–Se bond distances ranging from 2.57–2.71 Å. In the fourth Cr+2.29+ site, Cr+2.29+ is bonded to six Se2- atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 47–51°. There are a spread of Cr–Se bond distances ranging from 2.57–2.75 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Cr+2.29+ atoms to form a mixture of distorted edge and corner-sharing SeCr5 square pyramids. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to six Cr+2.29+ atoms. In the third Se2- site, Se2- is bonded to five Cr+2.29+ atoms to form a mixture of distorted edge and corner-sharing SeCr5 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrSe2 by Materials Project

CrSe2 is trigonal omega-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Cr4+ sites. In the first Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are three shorter (2.50 Å) and three longer (2.52 Å) Cr–Se bond lengths. In the second Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are a spread of Cr–Se bond distances ranging from 2.49–2.51 Å. In the third Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are a spread of Cr–Se bond distances ranging from 2.50–2.52 Å. In the fourth Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are a spread of Cr–Se bond distances ranging from 2.50–2.52 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the third Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the fourth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the fifth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the sixth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the seventh Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the eighth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrSe2 by Materials Project

CrSe2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one CrSe2 sheet oriented in the (0, 0, 1) direction. Cr4+ is bonded to six equivalent Se2- atoms to form edge-sharing CrSe6 octahedra. All Cr–Se bond lengths are 2.50 Å. Se2- is bonded in a distorted T-shaped geometry to three equivalent Cr4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr2Se3 by Materials Project

Cr2Se3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to six Se2- atoms to form a mixture of corner, edge, and face-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 49–52°. There are a spread of Cr–Se bond distances ranging from 2.46–2.65 Å. In the second Cr3+ site, Cr3+ is bonded to six Se2- atoms to form a mixture of corner, edge, and face-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 48–53°. There are a spread of Cr–Se bond distances ranging from 2.46–2.64 Å. In the third Cr3+ site, Cr3+ is bonded to six Se2- atoms to form a mixture of corner and edge-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 47–51°. There are a spread of Cr–Se bond distances ranging from 2.47–2.61 Å. In the fourth Cr3+ site, Cr3+ is bonded to six Se2- atoms to form a mixture of corner, edge, and face-sharing CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 47–53°. There are a spread of Cr–Se bond distances ranging from 2.54–2.63 Å. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Cr3+ atoms. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Cr3+ atoms. In the third Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr3+ atoms. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to four Cr3+ atoms. In the fifth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to four Cr3+ atoms. In the sixth Se2- site, Se2- is bonded to five Cr3+ atoms to form distorted edge-sharing SeCr5 square pyramids.

36 MATERIALS SCIENCE↗