Dual-phase competitive behavior in N-type Sn–Bi–Te thermoelectric films achieving high thermoelectric performance

The dual-phase competitive behavior is introduced as an effective strategy to optimize the physical and chemical properties of N-type Bi₂Te₃ thermoelectric (TE) materials. Controllable SnTe-embedded Bi₂Te₃ nanocomposites can be synthesized with the addition of excessive Sn into Bi₂Te₃ by tuning the crystallization behavior under proper thermal heating temperature. Notably, the precipitation temperature of Bi₂Te₃ increases from 473 ​K for Sn_20.9(Bi₂Te₃)_79.1 to 573 ​K for Sn_34.4(Bi₂Te₃)_65.6, expanding the controllable temperature span for the presence of SnTe phase. The second-phase nanoprecipitate SnTe can improve electrical conductivity by competing with the Bi₂Te₃ phase, achieving an increase of four orders of magnitude at the critical temperature of ∼500 ​K. Simultaneously, it increases the interfacial energy filtration effect between nanocrystalline grains, decoupling electrical parameters between conductivity and Seebeck coefficient. Consequently, the high power factor of ∼147 ​μW/mK² at 650 ​K for optimized Sn_26.6(Bi₂Te₃)_73.4 films can be obtained, which is more than twice that of the pure Bi₂Te₃ material. Our work demonstrates a new physical mechanism to unravel the complicated structure-property relationship by dual-phase competitive behavior during phase transition. This study fills the gap in knowledge on the effects of the SnTe phase regarding the Bi₂Te₃ system and provides guidance for the innovative design of high-performing inorganic thermoelectrics.