Abstract
Eco-friendly SnTe based thermoelectric materials are intensively studied recently as candidates to replace PbTe; yet the thermoelectric performance of SnTe is suppressed by its intrinsically high carrier concentration and high thermal conductivity. In this work, we confirm that the Ag and La co-doping can be applied to simultaneously enhance the power factor and reduce the thermal conductivity, contributing to a final promotion of figure of merit. On one hand, the carrier concentration and band offset between valence bands are concurrently reduced, promoting the power factor to a highest value of ∼2436 µW·m−1·K−2 at 873 K. On the other hand, lots of dislocations (∼3.16×107 mm−2) associated with impurity precipitates are generated, resulting in the decline of thermal conductivity to a minimum value of 1.87 W·m−1·K−1 at 873 K. As a result, a substantial thermoelectric performance enhancement up to zT ≈ 1.0 at 873 K is obtained for the sample Sn0.94Ag0.09La0.05Te, which is twice that of the pristine SnTe (zT ≈ 0.49 at 873 K). This strategy of synergistic manipulation of electronic band and microstructures via introducing rare earth elements could be applied to other systems to improve thermoelectric performance.
Highlights
Clean, reliable, and sustainable energy utilization technologies become more and more important [1].Thermoelectric (TE) materials can provide such technologies to directly convert heat into electricity and vice versa [2,3,4,5,6]
In order to reduce κl, many researches focus on introducing point defects [20,21,22], dislocations [23], nano-precipitation [24,25], and grain boundaries [26] to act as the centers of phonon scattering, thereby effectively preventing phonon transport [27]
To suppress the excess inherent Sn vacancies, we adopted the approach of Sn self-compensation at first, which effectively enhances the figure of merit zT
Summary
Reliable, and sustainable energy utilization technologies become more and more important [1].Thermoelectric (TE) materials can provide such technologies to directly convert heat into electricity and vice versa [2,3,4,5,6]. The low energy conversion efficiency of TE materials severely restricts their wide range of commercial applications, which can be governed by a dimensionless figure of merit, zT = (S2σ/κ)T, where S, σ, T, and κ are the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively. In order to obtain a high zT, it is necessary to optimize the power factor (PF = S2σ) and simultaneously reduce κ. Due to the opposite promotion effect of n on S and σ, the strategy of optimizing TE performance by improving the power factor has become extremely significant, including the introduction of resonance levels [15,16], energy filtering [17], band convergence [18], increasing the band gap [19], etc. In order to reduce κl, many researches focus on introducing point defects [20,21,22], dislocations [23], nano-precipitation [24,25], and grain boundaries [26] to act as the centers of phonon scattering, thereby effectively preventing phonon transport [27]
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