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.
As promising candidates for the progress of low-temperature thermoelectric devices, MgAgSb-based thermoelectric materials have drawn a great deal of attention. However, due to complicated phase changes, high content of impurities and high volatilization of Mg, it is difficult to synthesize pure phase MgAgSb-based thermoelectric materials via conventional methods. Here, MgAgSb alloy was successfully synthesized by a combination of common planetary ball milling and spark plasma sintering. Furthermore, the introduction of Zn improved the purity of alloys, leading to optimization of the electrical transport properties. As a result, the power factor was improved from 1087 μW m−1 K−2 for MgAg0.9Sb0.95 to 1394 μW m−1 K−2 for Mg0.97Zn0.03Ag0.9Sb0.95 at 473 K, and the ZT reached ∼0.7 at 473 K. These results suggest that MgAgSb-based thermoelectric materials have a good thermoelectric application potential and this study can be used as guidance for the synthesis and performance improvement of other thermoelectric materials. Our synthesis route sets forth a new avenue for accelerating commercial applications of MgAgSb-based thermoelectric power generation or refrigeration.
P-type nanostructured α-MgAgSb by virtue of its intrinsically low thermal conductivity and environment friendly characteristics has drawn a great deal of attention for low temperature power generation. In this study, MgAgSb alloys were successfully prepared via ordinary planetary ball milling, followed by a spark plasma sintering process. In addition, we explored the effects of phase composition and micro-pores that can be rationally engineered via simply controlling the spark plasma sintering pressure on the thermoelectric performance of MgAgSb alloys. The results show that the carrier mobility is significantly increased from 55.1 cm2 V−1 s−1 for MgAg0.95Sb0.99 with a sintering pressure of 20 MPa to 87.7 cm2 V−1 s−1 for ones with a sintering pressure of 80 MPa due to the increase of crystallinity and the reduction of pore size, resulting in a high power factor of 2214.0 μW m−1 K−2. Simultaneously, a large number of micro-pores can strengthen the phonon scattering to reduce the lattice thermal conductivity. As a result, a peak ZT ∼1.22 at 473 K and a high average ZT ∼1.11 from 323 K to 573 K were achieved for the sample MgAg0.95Sb0.99, which was synthesized under a sintering pressure of 80 MPa. This work reveals that the thermoelectric performance of MgAgSb alloys can be enhanced via controlling the pore effect, which could provide guidance for the synthesis and optimization performance of other thermoelectric materials.
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