Multiple Effects Promoting the Thermoelectric Performance of SnTe by Alloying with CuSbTe and CuBiTe.

In a SnTe-based thermoelectric material, the naturally high hole concentration caused by cation vacancies and high total thermal conductivity seriously hinder its thermoelectric performance. A recent work shows that alloying SnTe with other compounds from the I-V-VI family (I = Ag, Na; V = Sb, Bi; VI = Te) can be considered an effective strategy to boost the figure of merit efficiently via the synergy of manipulating hole concentration and lowering lattice thermal conductivity. Herein, we present a markedly enhanced thermoelectric performance in p-type SnTe through CuPnTe (Pn = Sb, Bi) alloying. Moreover, we found that the alloying with both CuSbTe and CuBiTe can facilitate the valence band convergence of SnTe, but their relative influence is different. Interestingly, compared to CuBiTe, alloying with CuSbTe increases the carrier concentration of SnTe, which suppresses the bipolar effect. Ultimately, under the positive effect of valence band convergence, increased vacancy concentration, and decreased lattice thermal conductivity, compounds with a nominal composition of (SnTe)(CuSbTe) attains a peak of ∼1.26 at 823 K. In contrast, the thermoelectric performance of (SnTe)(CuBiTe) is restricted by the reduced carrier concentration and diminished band gap, showing only a humble maximum value of ∼0.91 at 823 K in the sample with a nominal composition of (SnTe)(CuBiTe). These results demonstrate the multiple effects on thermoelectric transport during the formation of complex solid solutions.