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

Abstract

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 Sn20.9(Bi2Te3)79.1 to 573 ​K for Sn34.4(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 Sn26.6(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.