Excellent thermoelectric performance of boron-doped n-type Mg3Sb2-based materials via the manipulation of grain boundary scattering and control of Mg content

Abstract

Thermoelectric devices require thermoelectric materials with high figure-of-merit (ZT) values in the operating temperature range. In recent years, the Zintl phase compound, n-Mg3Sb2, has received much attention owing to its rich chemistry and structural complexity. However, it hardly achieves high ZT values throughout the medium temperature range. Herein, by increasing the sintering temperature as much as possible, we successfully increased the average grain size of the compound by 15 times, and the grain boundary scattering was manipulated to obtain high carrier mobility of up to 180 cm2 V−1 s−1. Simultaneously, we optimized the Mg content for ultralow lattice thermal conductivity. We first doped the Mg3Sb2-based materials with boron for higher sintering temperature, good thermal stability, and higher hardness. The synergistic optimization of electrical and thermal transport resulted in excellent ZT values (0.62 at 300 K, 1.81 at 773 K) and an average ZT of 1.4 (from 300 to 773 K), which are higher than the state-of-the-art values for n-type thermoelectric materials, demonstrating a high potential in device applications.