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All-Scale Hierarchically Structured p-Type PbSe Alloys with High Thermoelectric Performance Enabled by Improved Band Degeneracy
- Tan, Gangjian, Hao, Shiqiang, Cai, Songting, Bailey, Trevor P., Luo, Zhongzhen, Hadar, Ido, Uher, Ctirad, Dravid, Vinayak P., Wolverton, Christopher, Kanatzidis, Mercouri G.
- Journal of the American Chemical Society 2019 v.141 no.10 pp. 4480-4486
- alloys, ambient temperature, cadmium, energy, lead, thermal conductivity
- We show an example of hierarchically designing electronic bands of PbSe toward excellent thermoelectric performance. We find that alloying 15 mol % PbTe into PbSe causes a negligible change in the light and heavy valence band energy offsets (ΔEV) of PbSe around room temperature; however, with rising temperature it makes ΔEV decrease at a significantly higher rate than in PbSe. In other words, the temperature-induced valence band convergence of PbSe is accelerated by alloying with PbTe. On this basis, applying 3 mol % Cd substitution on the Pb sites of PbSe₀.₈₅Te₀.₁₅ decreases ΔEV and enhances the Seebeck coefficient at all temperatures. Excess Cd precipitates out as CdSe₁–yTey, whose valence band aligns with that of the p-type Na-doped PbSe₀.₈₅Te₀.₁₅ matrix. This enables facile charge transport across the matrix/precipitate interfaces and retains the high carrier mobilities. Meanwhile, compared to PbSe the lattice thermal conductivity of PbSe₀.₈₅Te₀.₁₅ is significantly decreased to its amorphous limit of 0.5 W m–¹ K–¹. Consequently, a highest peak ZT of 1.7 at 900 K and a record high average ZT of ∼1 (400–900 K) for a PbSe-based system are achieved in the composition Pb₀.₉₅Na₀.₀₂Cd₀.₀₃Se₀.₈₅Te₀.₁₅, which are ∼70% and ∼50% higher than those of Pb₀.₉₈Na₀.₀₂Se control sample, respectively.