Thermoelectric performance of materials with CuCh4 ( Ch= S, Se) tetrahedra: Similarities and differences among their low-dimensional electronic structure from first principles

Abstract

In this study, we perform a comparative theoretical study on the thermoelectric performance of materials with CuCh4 (Ch = S, Se) tetrahedra, including famous thermoelectric materials BiCuSeO and tetrahedrite Cu12Sb4S13, by means of first-principles calculations. By comparing these electronic band structures, we find that many of these materials possess a Cu-t2g band structure consisting of quasi-one-dimensional band dispersions and the isotropic (two-dimensional for layered compounds) band dispersion near the valence-band edge. Therefore, the key factors for the thermoelectric performance are the anisotropy of the former band dispersion and the degeneracy of these two kinds of band dispersions. We also find that a large extension of the chalcogen orbitals often improves their thermoelectric performance by improving these two factors or by going beyond such a basic band structure through a large alternation of its shape. Such a large extension of the chalcogen orbitals might partially originate from the anisotropic Cu-Ch bond geometry of a tetrahedron. Our study reveals interesting similarities and differences of materials with CuCh4, which provides important knowledge for a future search of high-performance thermoelectric materials.

Thermoelectric properties of layered oxyselenides with 3d transition metal ions

“…As the M sites change from Mn to Zn, compared to rigid [Sr 2 MO 2 ] 2+ layers, the [Cu 2 Se 2 ] 2− layers are easily distorted with the change of lattice constant. As shown in Figure 3, the bond angles ( α , β ) of Se–Cu–Se vary with the c / a values, which may cause changes in the band structure and electrical transport properties by affecting hopping amplitudes 66 . In particular, for M = Mn, the structure shows a large quantity of Cu vacancies, so the formula could be written as Sr 2 MnO 2 Cu 1.5 Se 2 .…”

“…As shown in Figure 3, the bond angles (α, β) of Se-Cu-Se vary with the c/a values, which may cause changes in the band structure and electrical transport properties by affecting hopping amplitudes. 66 In particular, for M = Mn, the structure shows a large quantity of Cu vacancies, so the formula could be written as Sr 2 MnO 2 Cu 1.5 Se 2 . 7 The abnormal Mn analogs result from the mixed valence 2.5+ state of Mn.…”

Comparative First-Principles Study of Antiperovskite Oxides and Nitrides as Thermoelectric Material: Multiple Dirac Cones, Low-Dimensional Band Dispersion, and High Valley Degeneracy

“…For more detailed investigation of this kind of band structure, i.e., coexisting low-dimensional bands with anisotropy along different directions, we refer the readers to Ref. 81. We also note that, in real one-dimensional systems, technological applications are not straightforward because they require high orientation of samples, without which the conductivity is easily lost.…”

“…We also note that, in real one-dimensional systems, technological applications are not straightforward because they require high orientation of samples, without which the conductivity is easily lost. Low-dimensionality owing to the anisotropy of the electron wave function realized in rather isotropic crystal structure, like our target materials here, is favorable from this perspective [81][82][83][84] because the conductivity is expected to be kept without very high orientation of samples.…”

Electronic structure of a thermoelectric material: BiCuSO

“…5(c)], indicating the formation of a quasi-one-dimensional electronic structure in real space (Fig. 6), which is favorable for the TE performance [37][38][39][40]. We also notice some contribution from the Bi orbitals at the topmost band along -X and -Z (Fig.…”