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CuSe crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of six CuSe sheets oriented in the (0, 0, 1) direction. Cu2+ is bonded in a trigonal non-coplanar geometry to three equivalent Se2- atoms. All Cu–Se bond lengths are 2.44 Å. Se2- is bonded in a trigonal non-coplanar geometry to three equivalent Cu2+ atoms.
CuSe is lead oxide structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one CuSe sheet oriented in the (0, 0, 1) direction. Cu2+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.44 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Cu2+ atoms.
CuSe crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of six CuSe sheets oriented in the (0, 0, 1) direction. Cu2+ is bonded in a trigonal non-coplanar geometry to three equivalent Se2- atoms. All Cu–Se bond lengths are 2.44 Å. Se2- is bonded in a trigonal non-coplanar geometry to three equivalent Cu2+ atoms.
CuSe is Covellite structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded in a trigonal planar geometry to three equivalent Se2- atoms. All Cu–Se bond lengths are 2.32 Å. In the second Cu2+ site, Cu2+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with three equivalent SeCu3Se tetrahedra and corners with seven equivalent CuSe4 tetrahedra. There are three shorter (2.42 Å) and one longer (2.49 Å) Cu–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Cu2+ and one Se2- atom to form distorted SeCu3Se tetrahedra that share corners with three equivalent CuSe4 tetrahedra, corners with six equivalent SeCu3Se tetrahedra, and corners with three equivalent SeCu5 trigonal bipyramids. The Se–Se bond length is 2.43 Å. In the second Se2- site, Se2- is bonded to five Cu2+ atoms to form SeCu5 trigonal bipyramids that share corners with six equivalent SeCu3Se tetrahedra and corners with six equivalent SeCu5 trigonal bipyramids.
K(CuSe)2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. K1+ is bonded in a body-centered cubic geometry to eight equivalent Se2- atoms. All K–Se bond lengths are 3.43 Å. Cu+1.50+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.47 Å. Se2- is bonded in a 8-coordinate geometry to four equivalent K1+ and four equivalent Cu+1.50+ atoms.
CuSe is Covellite structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with three equivalent SeCu3Se tetrahedra and corners with seven equivalent CuSe4 tetrahedra. There are a spread of Cu–Se bond distances ranging from 2.41–2.49 Å. In the second Cu2+ site, Cu2+ is bonded in a trigonal planar geometry to three equivalent Se2- atoms. All Cu–Se bond lengths are 2.32 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Cu2+ atoms to form SeCu5 trigonal bipyramids that share corners with six equivalent SeCu3Se tetrahedra and corners with six equivalent SeCu5 trigonal bipyramids. In the second Se2- site, Se2- is bonded to three equivalent Cu2+ and one Se2- atom to form distorted SeCu3Se tetrahedra that share corners with three equivalent CuSe4 tetrahedra, corners with six equivalent SeCu3Se tetrahedra, and corners with three equivalent SeCu5 trigonal bipyramids. The Se–Se bond length is 2.43 Å.
Dy(CuSe)3 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Dy3+ is bonded to six equivalent Se2- atoms to form DySe6 octahedra that share corners with twelve equivalent CuSe4 tetrahedra, edges with three equivalent DySe6 octahedra, and edges with six equivalent CuSe4 tetrahedra. There are three shorter (2.87 Å) and three longer (2.88 Å) Dy–Se bond lengths. Cu1+ is bonded to four equivalent Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent DySe6 octahedra, corners with six equivalent CuSe4 tetrahedra, edges with two equivalent DySe6 octahedra, and edges with three equivalent CuSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 16–60°. There are a spread of Cu–Se bond distances ranging from 2.42–2.52 Å. Se2- is bonded in a 6-coordinate geometry to two equivalent Dy3+ and four equivalent Cu1+ atoms.
CuSeS is Pyrite-derived structured and crystallizes in the cubic P2_13 space group. The structure is three-dimensional. Cu3+ is bonded to three equivalent Se1- and three equivalent S2- atoms to form CuSe3S3 octahedra that share corners with twelve equivalent CuSe3S3 octahedra, corners with three equivalent SeCu3S tetrahedra, and corners with three equivalent SCu3Se tetrahedra. The corner-sharing octahedra tilt angles range from 65–66°. All Cu–Se bond lengths are 2.56 Å. All Cu–S bond lengths are 2.49 Å. Se1- is bonded to three equivalent Cu3+ and one S2- atom to form SeCu3S tetrahedra that share corners with three equivalent CuSe3S3 octahedra, corners with six equivalent SeCu3S tetrahedra, and corners with nine equivalent SCu3Se tetrahedra. The corner-sharing octahedral tilt angles are 76°. The Se–S bond length is 2.22 Å. S2- is bonded to three equivalent Cu3+ and one Se1- atom to form distorted SCu3Se tetrahedra that share corners with three equivalent CuSe3S3 octahedra, corners with six equivalent SCu3Se tetrahedra, and corners with nine equivalent SeCu3S tetrahedra. The corner-sharing octahedral tilt angles are 75°.
Yb(CuSe)3 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Yb3+ is bonded to six equivalent Se2- atoms to form YbSe6 octahedra that share corners with twelve equivalent CuSe4 tetrahedra, edges with three equivalent YbSe6 octahedra, and edges with six equivalent CuSe4 tetrahedra. All Yb–Se bond lengths are 2.91 Å. Cu1+ is bonded to four equivalent Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent YbSe6 octahedra, corners with six equivalent CuSe4 tetrahedra, edges with two equivalent YbSe6 octahedra, and edges with three equivalent CuSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 18–55°. There are a spread of Cu–Se bond distances ranging from 2.43–2.51 Å. Se2- is bonded in a 6-coordinate geometry to two equivalent Yb3+ and four equivalent Cu1+ atoms.
BaCu2Se2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ba2+ is bonded in a body-centered cubic geometry to eight equivalent Se2- atoms. All Ba–Se bond lengths are 3.40 Å. Cu1+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.52 Å. Se2- is bonded in a 8-coordinate geometry to four equivalent Ba2+ and four equivalent Cu1+ atoms.
BaCu2Se2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ba2+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of Ba–Se bond distances ranging from 3.23–3.43 Å. There are two inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four Se2- atoms to form a mixture of corner and edge-sharing CuSe4 tetrahedra. There are a spread of Cu–Se bond distances ranging from 2.50–2.58 Å. In the second Cu1+ site, Cu1+ is bonded to four Se2- atoms to form a mixture of corner and edge-sharing CuSe4 tetrahedra. There are a spread of Cu–Se bond distances ranging from 2.47–2.64 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 7-coordinate geometry to three equivalent Ba2+ and four Cu1+ atoms. In the second Se2- site, Se2- is bonded in a 8-coordinate geometry to four equivalent Ba2+ and four Cu1+ atoms.
BiCuSeO is Parent of FeAs superconductors structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one BiO sheet oriented in the (0, 0, 1) direction and one CuSe sheet oriented in the (0, 0, 1) direction. In the BiO sheet, Bi3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Bi–O bond lengths are 2.35 Å. O2- is bonded to four equivalent Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the CuSe sheet, Cu1+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.52 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms.
EuCuOSe is Parent of FeAs superconductors structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one CuSe sheet oriented in the (0, 0, 1) direction and one EuO sheet oriented in the (0, 0, 1) direction. In the CuSe sheet, Cu1+ is bonded to four equivalent Se2- atoms to form a mixture of corner and edge-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.49 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms. In the EuO sheet, Eu3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Eu–O bond lengths are 2.30 Å. O2- is bonded to four equivalent Eu3+ atoms to form a mixture of corner and edge-sharing OEu4 tetrahedra.
Bi2YO4Cu2Se2 crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two CuSe sheets oriented in the (0, 0, 1) direction and two Y(BiO2)2 sheets oriented in the (0, 0, 1) direction. In each CuSe sheet, Cu+1.50+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.47 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Cu+1.50+ atoms. In each Y(BiO2)2 sheet, Y3+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Y–O bond lengths are 2.40 Å. Bi3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Bi–O bond lengths are 2.25 Å. O2- is bonded to two equivalent Y3+ and two equivalent Bi3+ atoms to form a mixture of edge and corner-sharing OY2Bi2 tetrahedra.
LaCuOSe is Parent of FeAs superconductors structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one CuSe sheet oriented in the (0, 0, 1) direction and one LaO sheet oriented in the (0, 0, 1) direction. In the CuSe sheet, Cu1+ is bonded to four equivalent Se2- atoms to form a mixture of corner and edge-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.52 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms. In the LaO sheet, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All La–O bond lengths are 2.38 Å. O2- is bonded to four equivalent La3+ atoms to form a mixture of corner and edge-sharing OLa4 tetrahedra.
SmCuOSe is Parent of FeAs superconductors structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one CuSe sheet oriented in the (0, 0, 1) direction and one SmO sheet oriented in the (0, 0, 1) direction. In the CuSe sheet, Cu1+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CuSe4 tetrahedra. All Cu–Se bond lengths are 2.52 Å. Se2- is bonded in a 12-coordinate geometry to four equivalent Cu1+ atoms. In the SmO sheet, Sm3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Sm–O bond lengths are 2.31 Å. O2- is bonded to four equivalent Sm3+ atoms to form a mixture of edge and corner-sharing OSm4 tetrahedra.
The entanglement of lattice thermal conductivity, electrical conductivity, and Seebeck coefficient complicates the process of optimizing thermoelectric performance in most thermoelectric materials. Semiconductors with ultralow lattice thermal conductivities and high power factors at the same time are scarce but fundamentally interesting and practically important for energy conversion. In this work, an intrinsic p-type semiconductor TlCuSe that has an intrinsically ultralow thermal conductivity (0.25 W m -1 K -1 ), a high power factor (11.6 μ W cm -1 K -2 ), and a high figure of merit, ZT (1.9) at 643 K is described. The weak chemical bonds, originating from the filled antibonding orbitals p-d* within the edge-sharing CuSe 4 tetrahedra and long Tl-Se bonds in the PbClF-type structure, in conjunction with the large atomic mass of Tl lead to an ultralow sound velocity. Strong anharmonicity, coming from Tl + lone-pair electrons, boosts phonon-phonon scattering rates and further suppresses lattice thermal conductivity. The multiband character of the valence band structure contributing to power factor enhancement benefits from the lone-pair electrons of Tl + as well, which modify the orbital character of the valence bands, and pushes the valence band maximum off the Gamma-point, increasing the band degeneracy. The results provide new insight on the rational design of thermoelectric materials.
This study investigates Ga-doped n-type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu 2 Se alloying. Introducing Cu 2 Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κlat) via weak electron–phonon coupling. Additionally, Cu 2 Te and CuGa(Te/Se) 2 (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n-type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 10 19 cm –3 and ≈1870 S cm –1 to ≈2.26 × 10 19 cm –3 and ≈3029 S cm –1 , respectively. With increasing temperature, the sample exhibits a dynamic change in Cu 2 Te content and the generation of a new phase of CuGa(Te/Se) 2 (cubic phase), strengthening the phonon scattering and obtaining an ultralow k lat . Pb 0.975 Ga 0.025 Te-3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate-temperature device applications.