Multiple Effects Promoting the Thermoelectric Performance of SnTe by Alloying with CuSbTe₂ and CuBiTe₂

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-VI₂ 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 CuPnTe₂ (Pn = Sb, Bi) alloying. Moreover, we found that the alloying with both CuSbTe₂ and CuBiTe₂ can facilitate the valence band convergence of SnTe, but their relative influence is different. Interestingly, compared to CuBiTe₂, alloying with CuSbTe₂ 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)_0.90(CuSbTe₂)_0.10 attains a peak zT of ∼1.26 at 823 K. In contrast, the thermoelectric performance of (SnTe)₁(CuBiTe₂) is restricted by the reduced carrier concentration and diminished band gap, showing only a humble maximum zT value of ∼0.91 at 823 K in the sample with a nominal composition of (SnTe)_0.96(CuBiTe₂)_0.04. These results demonstrate the multiple effects on thermoelectric transport during the formation of complex solid solutions.