Enhancing Mg3(Bi, Sb)2 thermoelectric performance via ZrSb1-x modified grain-boundary

Abstract

Grain boundaries, as critical structural defects in materials, play a pivotal role in thermoelectric research. Mg₃(Bi, Sb)₂-based materials, which are prominent n-type thermoelectric materials, are significantly affected by the second phase at grain boundaries. This study investigates the influence of ZrSb_1-x on the thermoelectric properties of Mg₃(Bi, Sb)₂, with particular focus on its impact on the chemical environment at grain boundaries. The ZrSb₂ exacerbates the loss of Mg, resulting in a transition of the material from n-type to p-type conductivity. In contrast, the ZrSb_3/5 mitigates the formation of Bi-rich precipitate, reduces the interfacial potential barriers, and enhances grain growth. A sample containing 5 % ZrSb_3/5 achieved a room temperature zT of 0.9, and the formation of $<10\overline{1}1>$ twins was observed. Furthermore, a thermoelectric device composed of this material, paired with commercial p-type Bi₂Te₃, demonstrated a maximum temperature difference of 67 K and a peak cooling power density of 1.2 W/cm². The mathematical relationship between the device's COP under any operating condition and its fundamental parameters (Q_c,max, ΔT_max and I_max) was derived.