Extended phase homogeneity and improved out-of-plane charge transfer in Sb and Te co-alloyed n-type BiSe layered compound with extraordinary thermoelectric performance

BiSe is a promising n-type layered thermoelectric compound near room temperature. However, its full potential is not realized because of its overall high electron density and inferior interlayer charge transport. In this study, we demonstrate that these drawbacks are well addressed by a feasible Sb and Te co-alloying approach. Sb, preferably substituting Bi atoms in the Bi2Se3 quintuplet layer, effectively neutralizing excess electrons of BiSe by suppressing positively charged Se vacancies. On the other hand, Te exclusively replaces Se, and promotes interlayer charge transfer by increasing chemical bond covalency. In addition, Te alloying significantly impedes phonon propagation of BiSe by introducing considerable size and mass disorders. More importantly, it is found that co-alloying expands the phase homogeneity of BiSe, which further intensifies the respective functions of Sb and Te alloying. As a consequence, a peak ZT value of 0.6 at 425 K is realized in the sample Bi0.6Sb0.4Se0.6Te0.4, which is 2.5 times that of pristine BiSe. Our work suggests that Sb and Te co-alloyed BiSe is a robust candidate for thermoelectric application near room temperature.