Significantly enhanced thermoelectric figure of merit of n-type Mg3Sb2-based Zintl phase compounds via co-doped of Mg and Sb site

Abstract

N-type Mg3Sb2 thermoelectric material has a complex crystal structure and electronic structure, which is a new thermoelectric material with excellent application prospects. The state density and band structure of Mg24Sb16 and Bi/Se/Pr–Se/Nd–Se doped Mg24Sb16 are first-principles calculated. Se/Pr–Se/Nd–Se doped increases the density of states around the Fermi level. Bi-doped does not impact the band structure because the electronic structure between Sb and Bi are similar. The band gap of Pr–Se/Nd–Se doped becomes narrower, which is more conducive to carrier transport and increases carrier concentration than that of single-doped Se. The experimental results show that Pr and Nd replace Mg to provide more electrons for the system. The carrier concentration of the co-doped sample increases significantly, thus improving the power factor and optimizing the samples' electrical properties. The highest ZT value of the Mg3.2Sb1.5Bi0.49Se0.01 sample is 1.21. Pr–Se/Nd–Se co-doped ZT values are 1.67 and 1.74, respectively, 38% and 43% higher than the Mg3.2Sb1.5Bi0.49Se0.01 sample. Multi-element doped is an effective strategy to improve the thermoelectric properties of materials.