Enhanced thermoelectric performance of n-type Mg3.2Sb1.5Bi0.5 by rare-earth elements (Er, Tb, Tm) doping into Mg site

Abstract

The n-type Mg3.2Sb1.5Bi0.5 has emerged as a promising candidate for thermoelectric materials and has attracted significant research interest. However, effective n-type dopants have been predominantly limited to chalcogens. In our work, we found that rare-earth elements (Er, Tb, Tm) are highly effective dopants for n-type Mg3.2Sb1.5Bi0.5. Through a combination of theoretical predictions and experimental validations, we demonstrate that these dopants significantly enhance the carrier concentration, leading to improved thermoelectric performance. Specifically, we employed direct ball milling and spark plasma sintering to introduce rare-earth elements at the Mg sites. Experimental results show that doping rare-earth elements in n-type Mg3.2Sb1.5Bi0.5 has a higher carrier concentration ( ≈ 8.4 × 1019 cm−3), which is higher than that of chalcogen-doped samples ( ≈ 2 × 1019 cm−3). High power factor (S2σ) ≈ 16 μW cm−1K−2 was obtained in rare-earth elements (Er, Tb, Tm) doped samples. Combined with the lowered lattice thermal conductivity due to the introduction of effective phonon scattering centers in Mg3.2−xAxSb1.5Bi0.5 (A= Er, Tb, Tm) sample. Finally, the ZT values of all doped samples reached ≈ 1.44 at 750 K. The highest peak ZT is ≈ 1.65 at 750 K for Mg3.195Er0.005Sb1.5Bi0.5. The rare-earth elements (Er, Tb, Tm) doped n-type Mg3Sb1.5Bi0.5 has comparable thermoelectric performance with the chalcogen-doped n-type Mg3Sb1.5Bi0.5, exhibiting promising potential for practical applications. This present work offers a comprehensive understanding of the effect of cation site doping improves the thermoelectric properties of n-type Mg3Sb2.