Large effective mass and ultralow thermal conductivity lead to high thermoelectric performance in the high-entropy semiconductor MnGeAgBiTe4

Abstract

Entropy engineering has emerged as an effective strategy to optimize the lattice and electronic structures of thermoelectric (TE) materials, with significant efforts toward achieving exceptional TE performance. In this study, we carried out entropy engineering on the well-known binary compound MnTe by both the partial Ge substitution of Mn and the mixture of AgBiTe₂ in the form of a solid solution. Such an engineering strategy results in the formation of the high-entropy quintuple semiconductor MnGeAgBiTe₄, stabilizes the single-phase rock-salt structure without the occurrence of impurity, and remarkably improves the TE properties. High-entropy engineering simultaneously enhances the carrier concentration and mobility in MnGeAgBiTe₄ compared with pristine MnTe. Furthermore, the first-principles calculations reveal the multi-peak nature of MnGeAgBiTe₄, in consistence with a high band effective mass of 5.1m_e estimated from the Pisarenko line. Consequently, an excellent power factor of 10.5 μW cm⁻¹ K⁻² and an ultralow lattice thermal conductivity κ_l ∼ 0.34 W m⁻¹ K⁻¹ at temperature T = 773 K are obtained in MnGeAgBiTe₄. These superior electrical and thermal transport properties lead to a maximal ZT of ∼1.09 at T = 773 K and an average ZT of ∼0.90 from 400 K to 773 K.