Engineering Electronic Structure and Lattice Dynamics to Achieve Enhanced Thermoelectric Performance of Mn–Sb Co-Doped GeTe

Abstract

GeTe, as a p-type semiconductor, has been intensively studied in recent years as a promising lead-free midtemperature-range thermoelectric (TE) material. Herein, we report an improved energy conversion efficiency (η) using a two-step TE properties optimization in Mn−Sb co-doped GeTe by engineering electronic structure and lattice dynamics. Mn−Sb co-doping enhances the TE properties of GeTe, as evidenced from both experiments and first-principles-based theoretical calculations. The density functional theory (DFT) calculations indicate that Mn−Sb co-doping improves the band convergence and optimizes the Fermi level position. This in turn helps in enhancing the Seebeck coefficient (α). As a result of the optimized Seebeck coefficient and electrical conductivity (σ), an enhanced power factor (α 2 σ) is obtained for the Mn−Sb co-doped system. Moreover, a significant reduction in the phonon (lattice) thermal conductivity (κ ph ∼ 0.753 W/mK) at 748 K is observed for Ge 0.87 Mn 0.05 Sb 0.08 Te, attributed to the point-defect scattering and reduced phonon group velocity. The synergistic improvement in α and reduction in κ ph result in a maximum figure-of-merit (zT) of 1.67 at 773 K, with an average zT (zT av ) of ∼ 0.9 for Ge 0.87 Mn 0.05 Sb 0.08 Te over a temperature range of 300−773 K, leading to an η of ∼12.7%.

Achieving High Thermoelectric Performance by NaSbTe2 Alloying in GeTe for Simultaneous Suppression of Ge Vacancies and Band Tailoring

“…Beneficial from the suppressed Ge vacancies and carrier scattering, together with the enhanced Seebeck coefficient, a high room‐temperature power factor ≈16.3 μW cm −1 K −1 was obtained in (GeTe) 91 (NaSbTe 2 ) 9 , much higher than that of other reported Sb‐doped GeTe‐based materials (Figure 3f). [ 29,37,53,55–59 ]…”

“…d) Room‐temperature Hall carrier mobility, e) Seebeck coefficient, and f) power factor as a function of Hall carrier concentration for (GeTe) 100‐ m (NaSbTe 2 ) m ( m = 5, 8, 9, 10, 12, and 15) in comparison with other reported data. [ 18,29,30,37,53,55–59 ]…”

“…Temperature-dependent a) electrical conductivity, b) Seebeck coefficient, and c) power factor of (GeTe) 100-m (NaSbTe 2 ) m (m = 0, 5, 8, 9, 10, 12, and 15). d) Room-temperature Hall carrier mobility, e) Seebeck coefficient, and f) power factor as a function of Hall carrier concentration for (GeTe) 100-m (NaSbTe 2 ) m (m = 5, 8, 9, 10, 12, and 15) in comparison with other reported data [18,29,30,37,53,[55][56][57][58][59].…”

Phase Analysis and Thermoelectric Properties of Cu-Rich Tetrahedrite Prepared by Solvothermal Synthesis

“…As the Seebeck coefficient, electrical conductivity, and electronic thermal conductivity are interrelated through the carrier concentration and particularities of the band structure, the development of the highly efficient TE materials requires specific properties (narrow bandgap, multivalley band structure, high mobility, high solubility of dopants, intrinsically low κ lat ) [9][10][11]. Such an unusual combination of properties in one compound was found in the heavily-doped semiconductors, e.g., PbTe [12][13][14], Bi 2 Te 3 [15,16], GeTe [17,18], CoSb 3 [19,20], which are excellent thermoelectric materials. The limiting factors, which restrict their widespread utilization, are the costs of production, environmental friendliness, and efficiency of energy conversion.…”

Feasibility of high performance in p‐type Ge1−xBixTe materials for thermoelectric modules

“…1 Therefore, the improvement of the TE performance in materials based on well-established A V B VI and A IV B VI semiconductors seems to be logical. Today, we have only two groups of TE materials that can be really applied in practice for energy conversion: Bi 2 Te 3 -based materials for the ambient temperature range of 300-600 K and A IV B VI (PbTe, GeTe) semiconductors for the temperature range of 500-800 K. Figure 1 represents the dimensionless TE figure of merit ZT for n-and p-type materials, which are optimal for segmented generator modules over the temperature range of 300-800 K. [6][7][8][9][10][11][12][13][14][15] While Bi 2 Te 3 -based materials remain the champion in the low-temperature region, we should mention that among the new materials, Mg 3 Sb 2 n-type material has also been showing high efficiency. 16,17 For the mid-high temperature range, an effective PbTe TE material has been developed recently by indium doping.…”