Lithium Doping to Enhance Thermoelectric Performance of MgAgSb with Weak Electron–Phonon Coupling

Abstract

Despite the unfavorable band structure with twofold degeneracy at the valence band maximum, MgAgSb is still an excellent p‐type thermoelectric material for applications near room temperature. The intrinsically weak electron–phonon coupling, reflected by the low deformation potential Edef ≈ 6.3 eV, plays a crucial role in the relatively high power factor of MgAgSb. More importantly, Li is successfully doped into Mg site to tune the carrier concentration, leading to the resistivity reduction by a factor of 3 and a consequent increase in power factor by ≈30% at 300 K. Low lattice thermal conductivity can be simultaneously achieved by all‐scale hierarchical phonon scattering architecture including high density of dislocations and nanoscale stacking faults, nanoinclusions, and multiscale grain boundaries. Collectively, much higher average power factor ≈25 μW cm−1 K−2 with a high average ZT ≈ 1.1 from 300 to 548 K is achieved for 0.01 Li doping, which would result in a high output power density ≈1.56 W cm−2 and leg efficiency ≈9.2% by calculations assuming cold‐side temperature Tc = 323 K, hot‐side temperature Th = 548 K, and leg length = 2 mm.

Higher thermoelectric performance of Zintl phases (Eu 0.5 Yb 0.5 ) 1−x Ca x Mg 2 Bi 2 by band engineering and strain fluctuation

“…Therefore, heavy effective mass, high carrier mobility, and low lattice thermal conductivity are highly desirable for good TE performance. Practically, some strategies and concepts have been proposed to achieve this goal, e.g., band convergence and resonant states for heavier effective mass (11)(12)(13), band alignment and weak electron-phonon and alloy scattering to achieve high carrier mobility (14)(15)(16), and alloying or nanostructuring to enhance phonon scattering (17)(18)(19). The complex Zintl phases, especially Sb-based Zintl compounds, have been demonstrated to be promising TE materials for middleto high-temperature applications.…”

Ag-Mg antisite defect induced high thermoelectric performance of α-MgAgSb

“…Previous experimental work showed that Li doping can significantly increase the ZT value of α-MgAg 0.97 Sb 0.99 39 . After Li doping, the carrier concentration increased from 2.3 × 10 19  cm −3 to 1.4 × 10 20  cm −3 .…”

“…After Li doping, the carrier concentration increased from 2.3 × 10 19  cm −3 to 1.4 × 10 20  cm −3 . The achieved average ZT was 1.1 from 300 to 548 K. The authors noted that Li was substituted onto the Mg sites 39 . It is valuable to explore how the chemical potential affects the doping sites in Li-doped α-MgAgSb.…”

“…Liu et al . found that the average ZT can reach as high as 1.1 from 300 K to 548 K when there is Li doping on Mg sites of MgAg 0.97 Sb 0.99 39 . Thus, under more Mg-rich conditions, Li Ag doping may lead to a larger ZT than for Li substitution on Mg sites.…”

Manipulation of charge transport in thermoelectrics

“…42 The benefit of weak scattering by acoustic phonons (low Ξ) for high mobility and thus zT, has also been observed in MgAgSb. 43 Unfortunately, factors directly affect deformation potential coefficient remain not fully clear, and can be a future direction.…”