Multiscale Defects as Strong Phonon Scatters to Enhance Thermoelectric Performance in Mg₂Sn_{1– x}Sb_x Solid Solutions

Mg₂Sn based solid solutions have attracted much research interest due to their high thermoelectric (TE) performance in the mid-temperature region and abundant constituent elements. Further enhancement of the figure of merit zT lies in the effective reduction of the relatively high lattice thermal conductivity. It has been demonstrated that alloying high content of aliovalent Sb (>10%) in Mg₂Si analogue can induce Mg vacancies and dense dislocations to greatly suppress the lattice thermal conductivity. In this work, the strategy is extended to the Sb alloyed Mg₂Sn to enhance zT. Detailed microstructure investigations reveal the existence of high density of interstitial clusters. By introducing these nanostructures as the additional phonon scattering sources, the theoretical calculation well match the low experimental lattice thermal conductivity. Superior to the Sb alloyed Mg₂Si, relatively high power factor is maintained in the Sb alloyed Mg₂Sn and the maximum zT of 0.9 at 750 K is obtained. With simpler chemical composition though, the Mg₂Sn_{1– x}Sb_x (x > 0.1) has comparable TE performance with the Sb alloyed Mg₂Si_0.4Sn_0.6 solid solutions, exhibiting promising potential for practical applications. The present work offers a comprehensive understanding of the effect of aliovalent alloying and concomitant complex microstructure in reducing thermal conductivity and enhancing zT.