Incorporating element doping and quantum dot embedding effects to enhance the thermoelectric properties of higher manganese silicides

Element doping and nano-inclusion embedding are effective approaches to enhance the electrical conductivities and decrease the lattice thermal conductivities of thermoelectric (TE) materials, respectively. However, the intrinsic low electrical thermal conductivities and high electrical properties are severely sacrificed, and the final figure of merit (ZT) is usually restricted. In this study, Ag doping and Pt quantum dot (QD) embedding were synchronously achieved via embedding Ag/Pt alloy QDs into the higher manganese silicides to avoid the conventional single-element doping strategy. The power factor (at 823 K) was enhanced from 1.57 × 10−3 W m−1 K−2 to 1.82 × 10−3 W m−1 K−2 (∼16%) due to the ∼18% increase in carrier concentration that was derived from the Ag doping effect. Simultaneously, the lattice thermal conductivity (at 823 K) decreased from 2.65 W m−1 K−1–1.92 W m−1 K−1 (∼28%) because of the broadband phonon scattering effect that resulted from the residual Pt QDs inclusions. Synthetically, the optimal ZT value increased by ∼52% from 0.42 to 0.64 at 823 K. This study demonstrated that incorporating metastable alloy QDs to obtain element doping and nano-inclusion embedding effects is a novel and feasible means to enhance the ZT value of HMS. This method is also possibly applicable to other alloy QD/TE composites.