Amorphous Nanodomains Enable High Device-Level Cooling Performance in Crack-Free Hot-Extruded n-Type Bi2Te3 Thermoelectrics

Premature cracking during free hot deformation (FHD) of n-type Bi2Te2.7Se0.3 limits the attainable strain, thereby interrupting dynamic recrystallization (DRX) and capping (0001) basal-texture development. Here, we identify this crack-limited DRX bottleneck through thermomechanical compression and interrupted-deformation evidence, and then eliminate it using hot extrusion (HE), where the inherently triaxial compressive stress state suppresses crack initiation and propagation. Crack-free extrusion enables near-complete DRX and a near-ideal (0001) basal texture, while retaining ∼10 nm amorphous nanodomains, which contribute to reducing lattice thermal conductivity without degrading electrical transport. The optimized alloy is tougher-95.8 MPa in bending and 138.4 MPa in compression (+62%/+48% vs FHD)-and reaches zT ≈ 1.20 at 343 K. Importantly, under strictly identical single-stage micro-TEC assembly and test boundaries (identical p-legs; only n-legs varied), the extruded n-legs increase ΔTmax to an outstanding 75.8 K at Th ≈ 300 K, which is among the highest values reported for Bi2Te3-based TECs under comparable testing conditions. These results establish crack-free hot extrusion as a scalable route to remove the fracture-imposed DRX ceiling in layered brittle thermoelectrics and to translate microstructural gains into device-level cooling performance.