High Entropy Semiconductor AgMnGeSbTe4 with Desirable Thermoelectric Performance

A new p-type high entropy semiconductor AgMnGeSbTe₄ with a band gap of ≈0.28 eV is reported as a promising thermoelectric material. AgMnGeSbTe₄ crystallizes in the rock-salt NaCl structure with cations Ag, Mn, Ge, and Sb randomly disordered over the Na site. Thus, a strong lattice distortion forms from the large difference in the atomic radii of Ag, Mn, Ge, and Sb, resulting in a low lattice thermal conductivity of 0.54 W m⁻¹ K⁻¹ at 600 K. In addition, the AgMnGeSbTe₄ exhibits a degenerate semiconductor behavior and a large average power factor of 10.36 µW cm⁻¹ K⁻² in the temperature range of 400–773 K. As a consequence, the AgMnGeSbTe₄ has a peak figure of merit (ZT) of 1.05 at 773 K and a desirable average ZT value of 0.84 in the temperature range of 400–773 K. Moreover, the thermoelectric performance of AgMnGeSbTe₄ can be further enhanced by precipitating of Ag₈GeTe₆, which acts as extra scatting centers for holes with low energy and phonons with medium wavelength. The simultaneous optimization in power factor and lattice thermal conductivity yields a peak ZT of 1.27 at 773 K and an average ZT of 0.92 (400–773 K) in AgMnGeSbTe₄-1 mol% Ag₈GeTe₆.