Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n-Type V₂VI₃ Alloys Through Progressive Hot Deformation

Here a progressive hot deformation procedure that endows the benchmark n-type V₂VI₃ thermoelectric materials with short range disorder (multiple defects), long range order (crystallinity), and strong texture (nearly orientation order) is reported. Not only it is rare for these structural features to coexist but also these structural features elicit the synergistic compositional–mechanical–thermal effects, i.e., a profound interplay among the counts, magnitude, and temperature of hot deformation in relation to the as formed point defects, dislocations, textures, strain clusters, and distortions. Using progressively larger die sets and relatively low hot deformation temperature, rich multiscale microstructures concurrently with a high level of texture comparable to that of zone melted ingot are obtained. The strong donor-like effect significantly increases the majority carrier concentration, suppressing the detrimental bipolar effect. In addition, the multiscale microstructures yield an ultralow lattice thermal conductivity ≈0.31 W m⁻¹ K⁻¹ at 405 K. A record zT ≈ 1.3 at 450 K are attained in progressively hot deformed n-type Bi_1.95Sb_0.05Te_2.3Se_0.7 through the synergistic effects. These results not only promise a better pairing between n-type and p-type legs in device fabrication but also bring our understanding of n-type V₂VI₃ alloys and hot deformation technique to a new level.