Supercompliant Lattice Boosts n-type AgSbTe2 Thermoelectrics

AgSbTe2-based compounds, the most promising near-room-temperature thermoelectric material, so far fail to deliver n-type performance neither theoretically nor experimentally. Its intrinsic electron-killer defects with very low formation energy prevent conventional n-type doping. Herein, the first n-type AgSbTe2 by building a supercompliant lattice, which is extremely soft with an n-type doping efficiency far beyond the Hume-Rothery rule settled phase boundary, is reported. The overdosed supercompliant lattice gives Young's modulus lower than the 2D van der Waals crystals, globally softening the phonons. This results in a minimal sound velocity of 1950 m<middle dot>s(-1), which lies far below all AgSbTe2-based compounds previously reported. The substantially softened phonons lead to a low kappa of 0.27 W<middle dot>m(-1)<middle dot>K-1 that approaches the theoretical minimum. Accordingly, the n-type Ag0.8Na0.3Sb0.6Bi0.4Te2 demonstrates a ZT value of approximate to 0.45 at the near-room-temperature range, which is the highest n-type performance ever reported. This work unlocks the door for AgSbTe2 as an exceptional n-type thermoelectric material.