Nonequilibrium Solidification Kinetics Engineer Rich Microstructures and Strong Texture in p-Type Bi_0.5Sb_1.5Te₃ Ribbons

Melt spinning is widely used to manufacture bismuth telluride-based thermoelectrics, yet the rapid-solidification physics that governs defect formation remains insufficiently resolved. Here, we study p-type Bi_0.5Sb_1.5Te₃ ribbons as a function of wheel speed and identify a kinetic window in which a strong columnar texture coexists with pronounced interfacial lattice distortion. Atomic-scale characterization reveals Te-enriched and Sb-depleted intergranular regions, while geometric phase analysis shows that the associated lattice mismatch is accommodated by dense dislocation arrays confined to low-angle boundaries. These observations are consistent with nonequilibrium solute redistribution during directional solidification, which concentrates off-stoichiometry in the intergranular liquid that solidifies last. Upon consolidation by layered directional sintering, the textured grains preserve high electrical transport, whereas the chemically/structurally complex interfaces suppress lattice thermal conductivity, yielding a peak ZT of 1.54 at 400 K. This work links solidification kinetics to interfacial defect chemistry and thermoelectric performance in rapidly solidified alloys.