Band degeneracy enhanced thermoelectric performance in layered oxyselenides by first-principles calculations

Abstract

Band degeneracy is effective in optimizing the power factors of thermoelectric (TE) materials by enhancing the Seebeck coefficients. In this study, we demonstrate this effect in model systems of layered oxyselenide family by the density functional theory (DFT) combined with semi-classical Boltzmann transport theory. TE transport performance of layered LaCuOSe and BiCuOSe are fully compared. The results show that due to the larger electrical conductivities caused by longer electron relaxation times, the n-type systems show better TE performance than p-type systems for both LaCuOSe and BiCuOSe. Besides, the conduction band degeneracy of LaCuOSe leads to a larger Seebeck coefficient and a higher optimal carrier concentration than n-type BiCuOSe, and thus a higher power factor. The optimal figure of merit (ZT) value of 1.46 for n-type LaCuOSe is 22% larger than that of 1.2 for n-type BiCuOSe. This study highlights the potential of wide band gap material LaCuOSe for highly efficient TE applications, and demonstrates that inducing band degeneracy by cations substitution is an effective way to enhance the TE performance of layered oxyselenides.

High Thermoelectric Performance Achieved in Bulk Selenium with Nanostructural Building Blocks

“…Here we take into account the intrinsic electron scattering of selenium, which with carrier mainly interacts with the longitudinal acoustic phonon. , Under this theory, relaxation time can be estimated by the following formula: where the deformation potential constant E 1 = Δ E /(Δ a / a 0 ), in which Δ E is the variation of band edge position with the lattice dilation of Δ a / a 0 . The energies of band extremum are calculated with respect to the deep core energy level of the Se atom and reasonably assume that its position is not influenced by small lattice deformation. − E and V 0 in the formula of elastic modulus C = ∂ 2 E /[ V 0 ∂(Δ a / a 0 ) 2 ] are total energy and volume, respectively. From Table we see for t-Se, x / y -directional elastic constants are much smaller than that parallel to chain direction, while it is about two times of that along z -direction for r-Se, which are consistent with their structure characters.…”

General strategies to improve thermoelectric performance with an emphasis on tin and germanium chalcogenides as thermoelectric materials

“…A high ZT via the resonant-state formation has already been discussed. The “optimal figure of merit” ( ZT optimal ) depends on “Thermoelectric quality factor” ( B ), where 70,71,74,82 The DOS effective mass can be expressed as, Where, N V -is the band degeneracy, -is the band effective mass and with m 1 , m 2 and m 3 as mass components along three principal axes in a 3D bulk sample. In an isotropic band and Here is called inertial effective mass and expressed by the given relation, 32 So, we can see that large can arise due to either a large number of conducting bands ( N V ) or by flat bands (with high ).…”

“…So, higher or flatter bands are beneficial to improve the Seebeck coefficient. If, the charge transport by acoustic phonon is dominant, then So using isotropic band approximation, we get 70,71,74,82–94 Thus, it can be concluded that heavy band effective mass harms TE performance as it reduces mobility and hence ZT . Pei et al 75 synthesized La- and I-doped PbTe by the melting, quenching, annealing, and hot pressing methods.…”

Exceptional Thermoelectric Properties of Bilayer GeSe: First Principles Calculation

“…Layered material, such as thallium oxygen, bismuth oxygen selenide, and tin chalcogenide, show great promise in thermoelectric applications due to the intrinsic low lattice thermal conductivity with phonon anharmonicity generated by the interaction between adjacent layers [3][4][5][6]. Since the discovery of excellent thermoelectric performance of singlecrystal SnSe [7], the thermoelectric properties of nontoxic, earth-abundant group IV-VI have attracted special attention [8][9][10][11][12].…”