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.