Synthesis Route-Controlled Atomic Ordering Optimizes Thermoelectric Transport in Bi₂SbSe₃

Thermoelectrics have leveraged band and phonon engineering to optimize performance, typically realized through chemical composition control via one-pot doping or alloying. However, for compounds with complex atomic sites, the thermodynamic drive of conventional one-pot synthesis generally favors a thermodynamically preferred atomic occupation, thereby limiting atomic ordering control and obscuring its influence on thermoelectric transport. Herein, we constructed a synthetic pathway for composition-invariant band and phonon engineering via atomic ordering control in one-third Sb-alloyed BiSe (Bi₂SbSe₃), a compound with multiple crystallographically distinct cation sites. Using BiSbSe₃ and Bi powders as precursors, we synthesized more disordered Bi₂SbSe₃ than the one-pot synthesized counterpart, achieved by redistributing Sb atoms between the Bi₂Se₃ quintuple layers and the Bi bilayers in the BiSe structure. Reduced atomic ordering suppresses the higher-lying conduction band contribution, lowering effective mass and enhancing carrier mobility, while simultaneously triggering lattice structure, slowing phonon velocities, and reducing lattice thermal conductivity. Finally, decreased atomic ordering enhances the ZT value of Bi₂SbSe₃ by ∼15% to ∼0.61 at 423 K, with an energy conversion efficiency of ∼4.3% under a temperature difference of ∼323 K. These results reveal that synthesis-controlled atomic ordering is an effective strategy for enhancing thermoelectric performance in structurally complex materials.