Extraordinary thermoelectric performance in MgAgSb alloy with ultralow thermal conductivity

MgAgSb-based materials are ideal candidates for thermoelectric applications due to several advantages, such as rich elements, low cost and excellent mechanical robustness. Recently, the all-scale hierarchical architecture and strong anharmonicity in bonding are realized as effective strategies to reduce the lattice thermal conductivity greatly. Here, a design of the all-scale hierarchical architectures, in which the phonon is scattered by the high density of grain boundaries, dislocation, stacking faults, twin boundaries and nanopores , and enhancement of Grüneisen parameter have been demonstrated in reducing the lattice thermal conductivity of MgAgSb materials in the whole temperature range, resulting in an ultralow lattice thermal conductivity ∼ 0.45 W m −1 K −1 at 473 K. Furthermore, the carrier concentration and mobility are also optimized by Zn-doping and heat-treating. The simultaneous optimization of electrical and thermal transport properties contributes to a tremendous enhancement of average ZT to about 1.3 in the range from 323 K to 548 K (the maximum ZT is about 1.4 at 423 K) in the sample Mg 0.97 Zn 0.03 Ag 0.9 Sb 0.95 with heat-treating for 10 days. The method we designed not only boosts the thermoelectric application of MgAgSb-based materials but also enables a synergetic strategy for designing thermoelectric materials with high thermoelectric performance.