Abstract
Mg3 (Sb,Bi)2 alloys have recently been discovered as a competitive alternative to the state-of-the-art n-type Bi2 (Te,Se)3 thermoelectric alloys. Previous theoretical studies predict that single crystals Mg3 (Sb,Bi)2 can exhibit higher thermoelectric performance near room temperature by eliminating grain boundary resistance. However, the intrinsic Mg defect chemistry makes it challenging to grow n-type Mg3 (Sb,Bi)2 single crystals. Here, the first thermoelectric properties of n-type Te-doped Mg3 Sb2 single crystals, synthesized by a combination of Sb-flux method and Mg-vapor annealing, is reported. The electrical conductivity and carrier mobility of single crystals exhibit a metallic behavior with a typical T-1.5 dependence, indicating that phonon scattering dominates the charge carrier transport. The absence of any evidence of ionized impurity scattering in Te-doped Mg3 Sb2 single crystals proves that the thermally activated mobility previously observed in polycrystalline materials is caused by grain boundary resistance. Eliminating this grain boundary resistance in the single crystals results in a large enhancement of the weighted mobility and figure of merit zT by more than 100% near room temperature. This work experimentally demonstrates the accurate understanding of charge-carrier scattering is crucial for developing high-performance thermoelectric materials and indicates that single-crystalline Mg3 (Sb,Bi)2 solid solutions can exhibit higher zT compared to polycrystalline samples.
Highlights
Mg3Sb1.5Bi0.5 with zT of 1.6 at 700 K in 2016,[1] extensive research have been conducted to improve their thermoelectric performance via the engineering of the electronic band structure,[5,12] chemical
The absence of any evidence of ionized impurity scattering in Te-doped Mg3Sb2 single crystals proves that the thermally activated mobility carrier and phonon transport mechanisms have been carried out in parallel to understand the underlying reasons behind the high thermoelectric performance
This work experimentally demonstrates the accurate understanding of charge-carrier scattering is crucial in n-type polycrystalline Mg3Sb2–Mg3Bi2 alloys concerning the charge carrier scattering mechanism near room temperature, namely, the origin of the low-temperature electrical conductivity and carrier mobility that increases with temperature
Summary
Mg3Sb1.5Bi0.5 with zT of 1.6 at 700 K in 2016,[1] extensive research have been conducted to improve their thermoelectric performance via the engineering of the electronic band structure,[5,12] chemical. Eliminating this grain boundary resistance in the single crystals results in a large enhancement of the weighted mobility and figure of merit zT by more than 100% near room temperature.
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