Enhancing the thermoelectric performance of free solidified p-type Bi0.5Sb1.5Te3 alloy by manipulating its parent liquid state

In this work, an irreversible temperature induced liquid-liquid structural transition (TI-LLST) during the heating process was suggested by abnormal resistivity behaviors of Bi0.5Sb1.5Te3 melt. Based on this information, by manipulating the parent liquid state in free solidification, series of explorations were carried out on the solidified structures and TE properties of Bi0.5Sb1.5Te3 alloy. We found that, from the melt after TI-LLST, the solidified microstructures are evidently refined with more Te-rich eutectic strips precipitating on matrix boundaries. More significantly, hierarchical crystal defects are obviously increased, with tinier nanoprecipitates, more subgrains and boundaries, and much more densified lattice distortions. Consequently, the thermal conductivity, especially the lattice thermal conductivity, is decreased notably with the power factor increased moderately at high temperature. In addition, the ambipolar excitation temperature is shifted to higher value and the slope of thermal conductivity vs temperature is also declined. All these alterations contribute to a synergistic enhancement of the TE figure of merit (ZT) and the maximum figure shifts to higher temperature, with ZTmax = 0.78 at 442 K. The present work may provide a new hint for innovating preparation methods of bulk TE materials with simple free solidification.