Incompletely Decomposed In4SnSe4 Leads to High‐Ranged Thermoelectric Performance in n‐Type PbTe

Abstract Additives in thermoelectric materials are conventionally considered as either extrinsic defects or second phases regardless of their dynamic processes. Herein, In 4 SnSe 4 , with inherent low thermal conductivity, is introduced into n‐type PbTe. It is revealed that In 4 SnSe 4 decomposes incompletely at high temperatures, in which around 80% of In 4 SnSe 4 dissolves into InSe and Sn, while 20% forms as nano‐precipitates. Benefiting from the incomplete decomposition, PbTe‐0.1%In 4 SnSe 4 presents superior thermoelectric performance compared to the stepwise and compositionally identical PbTe‐0.4%InSe‐0.1%Sn. The residual In 4 SnSe 4 along with Sn and InSe jointly contribute to the synergetic optimization of carrier mobility and lattice thermal conductivity in PbTe‐0.1%In 4 SnSe 4 . As a result, the room‐temperature dimensionless figure of merit ( ZT ) of ≈0.4 and the ZT ave of ≈0.83 at 300–573 K are obtained, and an experimental maximum thermoelectric conversion efficiency (η) of ≈2.5% (Δ T ≈ 400 K) is obtained, demonstrating significant research progress in n‐type PbTe. This work indicates that the In 4 SnSe 4 incomplete decomposition effectively decouples the electron and phonon transports in n‐type PbTe and the strategy of utilizing the unstable additives is proven feasible. Additionally, more dynamic behaviors of additives are worth expecting and may promote more achievements for other thermoelectric systems.