Homogenizing composition to achieve high-performance Mg3Bi2-type thermoelectrics

Abstract

Introducing compositional fluctuation is an effective strategy for optimizing thermoelectric performance by scattering phonon transport. However, this approach can also impede carrier transport, resulting in an adverse effect, especially in Mg₃Bi₂-type compounds due to sensitive carrier boundary scattering. This study reveals that homogenizing the composition in Mg₃(Bi, Sb)₂ from macro- to nano-scale improves both electrical and thermal transport properties. Suppressed compositional fluctuation enhances weighted mobility, resulting in a remarkable average power factor of 28.2 μW cm⁻¹ K⁻² (300–523 K) among Bi-rich Mg₃(Bi, Sb)₂ compounds. Increased carrier concentration from restrained Mg loss mitigates the typical bipolar thermal conductivity effects at high temperatures. Consequently, a room-temperature zT of 0.78 and peak zT of 1.27 are achieved, with an exceptional average zT of 1.09 within the particularly useful 300–523 K temperature range. A two-pair module of Mg₃(Bi, Sb)₂/MgAgSb shows simultaneously high conversion efficiency of 8.3 % and power density of 0.37 W cm⁻² under 294 K temperature difference, validating their potential for low-grade waste heat harvesting. These intriguing results demonstrate an unconventional strategy for enhancing thermoelectric performance via compositional fluctuation control.