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Enhancement of Thermoelectric Performance in Na-Doped Pb0.6Sn0.4Te0.95–xSexS0.05 via Breaking the Inversion Symmetry, Band Convergence, and Nanostructuring by Multiple Elements Doping

Ginting, Dianta, Lin, Chan-Chieh, Rathnam, Lydia, Kim, Gareoung, Yun, Jae Hyun, So, Hyeon Seob, Lee, Hosun, Yu, Byung-Kyu, Kim, Sung-Jin, Ahn, Kyunghan, Rhyee, Jong-Soo
ACS applied materials & interfaces 2018 v.10 no.14 pp. 11613-11622
electrical conductivity, energy, materials science, selenium, sodium, sulfur, temperature, thermal conductivity, topology
Topological insulators have attracted much interest in topological states of matter featuring unusual electrical conduction behaviors. It has been recently reported that a topological crystalline insulator could exhibit a high thermoelectric performance by breaking its crystal symmetry via chemical doping. Here, we investigate the multiple effects of Na, Se, and S alloying on thermoelectric properties of a topological crystalline insulator Pb₀.₆Sn₀.₄Te. The Na doping is known to be effective for breaking the crystalline mirror symmetry of Pb₀.₆Sn₀.₄Te. We demonstrate that simultaneous emergence of band convergence by Se alloying and nanostructuring by S doping enhance the power factor and decrease lattice thermal conductivity, respectively. Remarkably, the high power factor of 22.3 μW cm–¹ K–² at 800 K is achieved for Na 1%-doped Pb₀.₆Sn₀.₄Te₀.₉₀Se₀.₀₅S₀.₀₅ mainly due to a relatively high Seebeck coefficient via band convergence by Se alloying as well as the suppression of bipolar conduction at high temperatures by the increase of energy band gap. Furthermore, the lattice thermal conductivity is significantly suppressed by PbS nanoprecipitates without deteriorating the hole carrier mobility, ranging from 0.80 W m–¹ K–¹ for Pb₀.₆Sn₀.₄Te to 0.17 W m–¹ K–¹ at 300 K for Pb₀.₆Sn₀.₄Te₀.₈₅Se₀.₁₀S₀.₀₅. As a result, the synergistically combined effects of breaking the crystalline mirror symmetry of topological crystalline insulator, band convergence, and nanostructuring for Pb₀.₆Sn₀.₄Te₀.₉₅–ₓSeₓS₀.₀₅ (x = 0, 0.05, 0.1, 0.2, and 0.95) give rise to an impressively high ZT of 1.59 at 800 K for x = 0.05. We suggest that the multiple doping in topological crystalline insulators is effective for improving the thermoelectric performance.