Maximized atomic disordering approach boost the thermoelectric performance of Mg2Sn through the self-compensation effect and steric effect

Atomic disordering was an effective strategy to reduce lattice thermal conductivity. In this work, the atomic disordering of Mg_2-δSn_1-xBi_x was maximized by both the charge self-compensation and steric effects. Due to the strong phonon scattering arose from substitutional defects Bi_Sn and self-compensational vacancies V_Mg, an exclusively low lattice thermal conductivity of 1.38 W m⁻¹ K⁻¹ was observed in the Mg_2-δSn_0.8Bi_0.2 sample, corresponding to only 30% of Mg₂Sn, while a 30% less than that of its counterpart Mg_2-δSn_0.8Sb_0.2 (1.97 W m⁻¹ K⁻¹). The EPMA result presents that the Mg_2-δSn_0.8Bi_0.2 has a higher concentration of V_Mg than that of Mg_2-δSn_0.8Sb_0.2, suggesting an apparent steric effect for the formation of V_Mg. Furthermore, the Mg vacancy and its induced lattice shrinkage also result in band convergence. Consequently, a high ZT of 1.14 was obtained at 500 °C in the Mg_2-δSn_0.8Bi_0.2 sample, which is 52% higher than the conventionally doped Mg₂Sn_0.99Bi_0.01, while comparable with the Mg_2-δSn_0.8Sb_0.2. This work provides new insight into tuning thermoelectric transport properties through the atomic disorder strategy.