Adaptable sublattice stabilized high-entropy materials with superior thermoelectric performance†
High-entropy engineering is considered one of the most promising strategies in materials science, including the field of thermoelectrics. However, the presence of multiple elements with different atomic sizes and electronegativities in high-entropy materials often results in phase separation instead of the formation of a single phase. Herein, we propose that the adaptable sublattice can effectively stabilize single-phase high-entropy materials. Furthermore, the electrical and thermal transports can be efficiently tuned for much enhanced thermoelectric performance. Taking Mg2−δ(Si, Ge, Sn, Bi) as a case study, the loosely bonded Mg sublattice is featured with large dynamic adaptability or flexibility, enabling it to release the large lattice strains caused by the large atomic size mismatch among Si, Ge, Sn and Bi. The resulting ultralow lattice thermal conductivity of 0.58 W m−1 K−1 at 800 K is not only approaching the amorphous limit but also lower than that of all known Mg2X-based materials. Additionally, the interplay between the substitutional BiSn defects and self-compensational Mg vacancies leads to an optimized carrier concentration and thereby high power factors. A maximum zT value of 1.3 is finally realized at 700 K in Mg2−δSi0.12Ge0.13Sn0.73Bi0.02, which is among the top values of all Mg2X-based materials. This study highlights the role of an adaptable sublattice in stabilizing high-entropy materials and offers a new pathway for exploring high-performance thermoelectric materials.