Mg3(Bi,Sb)2 single crystals towards high thermoelectric performance

Abstract

The rapid growth of the thermoelectric cooler market makes the development of novel room temperature thermoelectric materials of great importance. Ternary n-type Mg₃(Bi,Sb)₂ alloys are promising alternatives to the state-of-the-art Bi₂(Te,Se)₃ alloys but grain boundary resistance is the most important limitation. n-type Mg₃(Bi,Sb)₂ single crystals with negligible grain boundaries are expected to have particularly high zT but have rarely been realized due to the demanding Mg-rich growth conditions required. Here, we report, for the first time, the thermoelectric properties of n-type Mg₃(Bi,Sb)₂ alloyed single crystals grown by a one-step Mg-flux method using sealed tantalum tubes. High weighted mobility ∼140 cm² V⁻¹ s⁻¹ and a high zT of 0.82 at 315 K are achieved in Y-doped Mg₃Bi_1.25Sb_0.75 single crystals. Through both experimental angle-resolved photoemission spectroscopy and theoretical calculations, we denote the origin of the high thermoelectric performance from a point of view of band widening effect and electronegativity, as well as the necessity to form high Bi/Sb ratio ternary Mg₃(Bi,Sb)₂ alloys. The present work paves the way for further development of Mg₃(Bi,Sb)₂ for near room temperature thermoelectric applications.