High Thermoelectric Performance and Low Lattice Thermal Conductivity in Lattice-Distorted High-Entropy Semiconductors AgMnSn_1–xPb_xSbTe₄

We investigate the structure and thermoelectric properties of a new high-entropy solid solution system AgMnSni(1-x)Pb(x)SbTe(4) (x = 0, 0.25, 0.5, 0.75, and 1), which crystallizes in the rock-salt NaCl structure with cations Ag, Mn, Sn, Pb, and Sb randomly disordered over the Na site. Our density functional theory calculations indicate that AgMnSn1-xPbxSbTe4 exhibits complex multi-peak valence band structures, whose energy difference is lower than 0.11 eV, leading to effective band convergence and thus high density of states effective mass m* and Seebeck coefficients. As a consequence, AgMnSn0.25Pb0.75SbTe4 has a peak ZT of 1.3 at 773 K and a desirable average ZT value of 0.8 in the temperature range of 400-773 K. In addition, we propose the lattice distortion degree (i.e., delta) as an important indicator of thermoelectric performance for high-entropy materials. Specifically, with the gradual increase in delta, the lattice thermal conductivity decreases monotonically from 0.90 W m(-1) K-1 for AgMnSnSbTe4 (i.e., delta = 0.205) to 0.54 W m(-1) K-1 for AgMnPbSbTe4 (i.e., delta = 0.230) at 300 K. Meanwhile, the generalized material parameter B-x*/B-0* and ZT increase monotonically from 1 and 0.11 for delta = 0.205 to 3.15 and 0.29 for delta = 0.230 at 300 K.